v ^ S ^ r r p ^ 2-19 CONTINUING EDUCATION © 2005 Uppineott Williams & Wilkins, Itic, Hypovolemic Shock An Overview Dorothy M. Kelley, MSN, RN, CEN Resuscitation of major trauma victims suffering from shock remains a challenge for trauma systems and trauma centers. Rapid identification, and ensuring correct, aggressive treatment, are necessary for patient survival. This article discusses shock encountered in trauma victims: hypovolemic, cardiogenic, obstructive, and distributive shock. Emphasis is placed on hypovolemic shock and its sequelae. The critical care nurse plays an important role as part of the team involved in the resuscitation and ongoing care of these patients. Understanding the underlying pathophysiology, recognizing signs and symptoms, and being prepared to effectively respond will further enable the nurse to contribute to positive patient outcomes. Key words: hypovolemia, resuscitation, shock, trauma R ESUSCITATION of major trauma victims suffering from shock remains a challenge for trauma systems and trauma centers. Rapid identification, and ensuring correct, aggressive treatment, are necessary for patient survival. Trauma patients are at risk for several types of shock states: hypovolemic, cardiogenic, obstructive, and distributive. Physiologically, regardless of the type of shock, inadequate tissue perfusion is the result of reduced or poorly distributed blood volume. The body activates compensatory mechanisms in an effort to improve perfusion. Care providers must recognize and intervenerapidlyto support tissue oxygenation and blood flow; otherwise, these compensatory mechanisms will fail, resulting in a cascade of events to include inflammatory response, release of mediators, organ failure, and death.' The critical care nurse plays an important role as part ofthe team involved in the resuscitation and ongoing care of these patients. Understanding the underlying pathophysiology, recognizing signs and symptoms, and being prepared to effectively respond will further enable the nurse to contribute to positive patient outcomes. This article describes these 4 categories of shock states. However, since hypovolemic shock is the most common type of shock encountered in the trauma patient population, the majority of the discussion will be dedicated to its recognition, definition, and treatment. CASE STUDY A 35-year-old male, helmeted motorcycle driver, "T-boned" a taxicab at high speed. He was ejected, landing on pavement 30 ft from his bike. Witnesses accessed the 911 emergency medical response system; paramedics arrived quickly. They found the patient lying unresponsive on the pavement; respirations were agonal; pulse, weak, and thready; BP was unobtainable. They placed the patient in full spinal immobilization, administered oxygen, and supported respirations via a bag, valve, mask (BVM) device. Transport time was less than 2 minutes from the trauma center, so they elected to "scoop and haul." Upon arrival, the trauma team evaluated the patient, using Advanced Trauma Life Support (ATLS) guidelines and reported these findings upon primary survey: Ainway: patent; C spine precautions maintained Breathing: No spontaneous respirations Corresponding author: Dorothy M. Kelley, MSN, RN, CEN, Circulation: Thready femoral pulse rate 56; 11076 Montaubon Way, San Diego, CA 92131 (e-mail: hypotensive with unobtainable blood pressure. kelley. dorothy®scrippshealth. org). Skin, cool pale and dry. From the Scripps Mercy Hospital, San Diego, Calif. Hypovolemic Shock Disability: GCS 3, pupils unequal, slightly reactive. The patient was intubated immediately upon arrival, using rapid sequence intubation (RSI) technique. Breath sounds auscultated after Intubation was diminished, despite validation that the ET tube was correctly placed. The respiratory therapist reported difficulty ventilating the patient. Bilateral needle thoracostomy was performed. A right femoral vein cordis was placed, as well as insertion of 2, large bore, 16-gauge, peripheral intravenous catheters, A clot was sent off for type and cross. Normal saline solutions were administered intravenously; the patient remained hypotensive and bradycardic. On secondary survey the patient was found to have the following: Head: abrasions and scalp laceration with occipital skull fracture Chest: diminished breath sounds; CXR, negative for hemothorax Abdomen: multiple contusions, distended, hypoactive bowel sounds Pelvis: unstable to compression and palpation GU: absent rectal tone (paralytics on board from RSI); meatus WNL; prostate WNL Extremities: dusky, delayed capillary refill, unable to palpate peripheral pulses Back/spine: no obvious step off A foley catheter was inserted. Focused Abdominal Sonogram for Trauma (FAST) was negative. Blood for baseline laboratory studies was sent off, and radiological studies were ordered Laboratory findings: ABG, pH 7.01; PCO2 68; P02 38; BE - 1 3 ; HCO3 11.7%; OzSat 59%; O2 15L/min 100%; INR 1.5. The patient remained hypotensive. Pulse varied widely between a low of 32 and high of 120. After infusion of warmed crystalloid, packed red blood cells and FFP the BP stabilized at 102 systolic. Cardiac monitor demonstrated regular sinus rhythm at 98. The trauma surgeon elected to transport the patient, with the trauma team in attendance, to radiology for CT scan. CT results: Closed head injury with intraparenchymal contusions; C-spine fractures at multiple levels; T-spine fractures; open book pelvic fracture, with intrapelvic blood vessel injuries, multiple lower extremity fractures. matic" shock. Initially, he suffered from obstructive shock as a result of tension pneumothorax. Further investigation revealed that the patient suffered from hypovolemic shock from pelvic fractures and internal injuries. He had also suffered distributive shock secondary to cervical and thoracic cord transection associated with spinal column fractures. His lifethreatening, multisystem injuries proved challenging to sort out. However, hypovolemic shock must always be the primary consideration until ruled out. The case described above demonstrates the complex critical thinking processes required by trauma team members. This patient exhibited classic signs and symptoms of "trau- ROLE OF TRAUMA CENTERS TRIMODAL DEATH PATTERN Researchers have identified 3 major epidemiological events, or trimodal patterns of death from trauma. Immediate deaths, those that occur on scene shortly after injury, account for approximately 50% of deaths due to trauma. These usually result from cataclysmic events resulting in high central nervous system injuries, or devastating injuries such as lacerations to the heart or major blood vessels. Early deaths occur within several hours and are typically the sequelae of acute hemorrhage or traumatic brain injury. Late deaths may occur weeks after injury and are typically the result of infection or multisystem organ failure. The preponderance of data demonstrates that immediate and early deaths account for approximately 80% of traumarelated fatalities, with the majority as a result of rapid exsanguination. There is a preventable death rate associated with a failure to recognize and adequately treat patients at risk for acute hemorrhage. This has been reported as high as 27%. These data suggest that the development and implementation of a strategic approach to provide care for at-risk patients could greatly improve outcomes. Goals are aimed at early recognition, and adequate, timely treatment to reduce the overall death rate.^ Trauma systems have been designed to get the "right patient, to the right resources, in 4 CRITICAL CARE NURSING QUARTERLY/JAMJARY-MARCH the right time frame." Inclusive trauma systems assure the availability of rapid transport, by adequately trained prehospital providers, to centers prepared to receive the critically injured patients. The "right resources" and destinations are typically trauma centers, which are required to demonstrate rigorous physical plant and care provider requirements. The right time frame is sometimes referred to as the "golden hour."' The cornerstone of this approach is the rapid recognition and early evaluation and treatment of severely injured patients.^ This early resuscitation phase has typically taken place in emergency departments; however, the resuscitation phase has now moved beyond the walls of the emergency department and now includes operating room resuscitation and continued aggressive resuscitation in the intensive care unit GCU). Therefore it is imperative that nurses in these arenas be proficient In the recognition, assessment, and care of the severely injured trauma patient.' DEFINITION As described in the literature, there are multiple definitions of shock. In the 1870s, Samuel D. Gross described shock as the "rude unhinging of the machinery of life."^ One hundred years later, in the 1970s, G. T. Shires discussed the severity of shock states as proportional to the depression in the cellular membrane potential. He proposed that shock occurs when the physiologically regulated circulation of blood fails to deliver sufficient oxygen to sustain aerobic metabolism to the cellular mitochondria. Therefore, resuscitation from shock is restoration of adequate oxygen deUvery to mitochondria. Organ failure, as shock sequelae, is proportional to the hypoxic damage to intrinsic cellular function.' As defined by Advanced Trauma life Support (ATLS), shock is the consequence of insufficient tissue perfusion, resulting in inadequate cellular oxygenation and an accumulation of metabolic waste. The consequences of untreated shock are metabolic derangements that result in a vicious cascade to include hy- 2005 pothermia, acidosis, and coagulopathy. If unresolved, shock progresses to an irreversible state, resulting in multisystem organ failure and death.^ Others have further described shock as a basic biochemical inability to properly utilize oxygen and other nutrients, or an inappropriate or ampMed stimulation of cellular signaling cascades.^ SHOCK CLASSIFICATIONS Although there are a variety of definitions and methods of classification,^"^ for the purposes of this discussion, shock is divided into 4 pathophysiologic categories: (1) hypovolemic, (2) obstructive, (3) cardiogenic, and (4) distributive. All the 4 interfere with endorgan cellular metabolism.^-*° HYPOVOLEMIC SHOCK Hypovolemic shock occurs as a result of decreased circulating blood volume, most commonly from acute hemorrhage. It may also be the result of fluid sequestration w^ithin the abdominal viscera or peritoneal cavity. The severity of hypovolemic shock depends not only on the volume deficit loss, the time frame within which the fluid is lost, but also on the age and preinjury health status of the individual. Clinically, hypovolemic shock is classified as mild, moderate, or severe, depending on the whole blood volume loss.'" In mild or compensated shock, less than 20% of blood volume is lost. Vasoconstriction begins and redistribution of blood flow is shunted to critical organs. Moderate shock reflects 20% to 40% of blood volume loss; there is decreased perfusion of organs such as kidneys, spleen, and pancreas. In severe shock, greater than 40% of blood volume is lost; there is decreased perfusion of the brain and heart. Hypovolemic shock produces compensatory physiologic responses in almost all organ systems. 10 Pathophysiology of hypovolemic shock Hypovolemic shock usually means hemorrhagic shock in the trauma patient. The Hypovolemic Shock patient may be bleeding internally or externally, and as a result circulating blood volume is decreased. This volume loss reduces both preload and stroke volume and causes reduced cardiac output. Signs and symptoms of early hypovolemic shock include an altered level of consciousness, sometimes manifested in agitation and restlessness, or any central nervous system depression. Physical assessment may demonstrate nonspecific signs and symptoms such as cool, clammy skin, orthostatic hypotension, mild tachycardia, and vasoconstriction.'' The body is able to sustain blood pressure and tissue perfusion by employing compensatory mechanisms that primarily promote vasoconstriction to support an increase in intravascular volume,^ Late signs of shock include worsening changes in mental status to include coma, hypotension, and marked tachycardia. It is important to know, however, that healthy adults with impending hemorrhagic hypovolemic shock may not become hypotensive untU as much as 30% of their circulating blood volume is lost." VASOCONSTRICTION Vasoconstriction is an early compensatory response mechanism to shock. The initial decrease in blood pressure inhibits the afferent discharge of baroreceptors in the aortic arch and carotid sinus. This stimulates sympathetic nervous system output. The decrease in blood volume inhibits the discharge of stretch receptors in the right atrium and also stimulates afferent discharge from chemoreceptors in the aortic arch and carotid bodies. The resulting increased sympathetic tone causes the release of catecholamines, epinephrine, and norepinephrine, intensifying venous tone, increasing heart rate, myocardial contractility, and subsequently, cardiac output. This compensatory mechanism is an effort to improve perfusion to the vital organs and tissues,^ It is important to understand, however, that not all patients in hypovolemic shock demonstrate tachycardia. Patients who are on /3-blockers are unable to mount a compensatory tachycardia. Patients who have a concomitant spinal cord injury cannot increase heart rate in response to volume loss and hypotension due to inhibition of the sympathetic nervous system," This catecholamine release, causing arteriolar constriction, does not affect all systems to the same degree. The body preserves blood flow to the heart and brain at the expense of the gastrointestinal (GI) tract, the skin, and skeletal muscle. However, if the shock state persists or worsens, myocardial function eventually becomes impaired. The greatest decrease in circulation during vasoconstriction occurs in the visceral and splanchnic circulation. Intestinal perfusion is depressed out of proportion to reduction in cardiac output,'° Blood flow to the kidneys is preserved with a small to moderate hemorrhage; however, the renal vessels will constrict w^ith large blood loss. Eventually there is a decline in glomerular filtration and urine output. The kidneys require high blood flow to maintain cellular metabolism. Sustained hypotension may result in tubular necrosis. Blood flow to the liver is reduced but to a lesser extent than in peripheral tissue. Decreased circulation to the skin is responsible for the coolness associated with hypovolemia,^ PLASMA VOLUME Vasoconstriction causes a shift of fluid between the vascular compartment and the interstitial spaces. Normally, there is little fluid movement between these 2 compartments. In early or compensated shock, there is a reduction in capillary hydrostatic pressure, w^hich allows movement of protein-free fluid from the interstitium to the vascular space, increasing intravascular volume and decreasing interstitial volume. This extracellular fluid mobilization usually occurs over a 6- to 12-hour period. It is not responsible for large volume changes in early phases of hemorrhagic shock, ^ CRITICAL CARE NURSING QUARTERLY/JANUARY-MARCH Decreased renal blood flow activates the renin-angiotensin system, stimulating production of angiotensin I, Angiotensin I is subsequently converted to angiotensin II, a strong vasoconstrictor that promotes aldosterone release from the adrenal cortex. Simultaneously, angiotensin II potentiates the action of adrenocorticotrophic hormone on the adrenal cortex and further promotes epinephrine release from the adrenal medulla, Adrenocorticotrophic hormone is released from the adrenal cortex, increasing renal sodium and water retention, as well as potassium excretion, which support the intravascular volume. Simultaneously, the posterior pituitary releases additional antidiuretic hormone, or vasopressin, which promotes reabsorption of solute-free water in the distal tubules and collecting system of the kidneys. It also further stimulates peripheral vasoconstriction, ^ CATABOLISM During shock states, catecholamine output and glucocorticoid production create a catabolic state. Plasma concentrations of glucagon rise. Together, catecholamines and glucagon promote glycogenolysis and lipolysis. As a result, hyperglycemia, as well as elevated lactate and fatty acid levels, may be observed as the shock state progresses.^ ACID-BASE DISTURBANCES Acid-base disturbances are reflective of the shock state. Measures of anaerobic metabolism include serum bicarbonate, pH, base excess, and lactate. In compensated, or mild to moderate, shock, the most frequently observed acid-base abnormality is respiratory alkalosis. It is important to monitor blood gases on a regular basis. Hypoxic or hypotensive stimulation of the aortic and carotid chemoreceptors, the presence of metabolic acidosis, and painful stimuli activate the respiratory center, causing hyperventilation. As the shock state progresses, anaer- 2005 obic metabolism predominates, stimulating lactate production and subsequent metabolic acidosis. The resultant metabolic acidosis further exacerbates the shock state, decreasing sensitivity to catecholamines and stress hormones, resulting in decreased myocardial contractility, promoting predisposition to cardiac dysrhythmias,^ Lactic acidosis, the physiologic deficit resulting from inadequate perfusion, is reflected in high serum lactate levels. The amount of lactate produced correlates with total oxygen debt, signifying the magnitude of hypoperfusion, the severity of shock, and also adequacy of resuscitation. Serum lactate is considered a sensitive indicator of occult shock and may be useful in patients •with a significant mechanism of injury yet demonstrating vital signs within normal limits. Since the 1960s, several studies have pointed to increased death rates associated with metabolic acidosis, as reflected in arterial pH, lactate, and base deficit clearance,^'^ Base deficit is defined as the amount of base, measured in millimoles, required to titrate 1 L of whole arterial blood to a pH value of 7,40, the sample is completely saturated •with oxygen at 37°C, and has a PCO2 of 40 mm Hg,' Base deficit is used as an index of the severity of shock in the adequacy of resuscitation, measuring global tissue acidosis. Some studies suggest a correlation between base deficit and survival probability, although others refute this,'^''' Arterial blood gases assess acid base, ventilation, and oxygenation status in the injured patient. Hypoxemia contributes to tissue oxygen deficit present in hemorrhagic shock; therefore, measurement of arterial PCO2 helps drive decision making regarding the need for intubation and ventilatory support. Treatments for metabolic acidosis are aimed at correcting the underlying cause: hypoperfusion. Supporting adequate oxygen delivery through volume loading, transfusions, and judicious inotropic support are used to achieve resuscitation goals of normal values in arterial pH, base deficit, lactate, and gastric Hypovolemic Shock MONITORING DURING SHOCK AND RESUSCITATION Frequent assessment and reassessment through continuous monitoring is necessary to identify and correct the causes for circulatory compromise. Cardiac monitoring should be initiated upon arrival and continued throughout the critical care phase to monitor and evaluate abnormalities in rate and rhythm. Persistent tachycardia, despite aggressive resuscitation efforts, may indicate ongoing hemorrhage. Rhythm disturbances may reflect a progressive shock state. Ongoing blood pressure monitoring, pulse oximetry, core body temperature, and urine output are all useful in assessing circulatory status. Urine output reflects renal perfusion and indirectly, overall central perfusion, A urine output of 1 to 2 mL/kg per hour is normal; output of less than 1 mL/kg per hour suggests inadequate resuscitation and poor perfusion,^ Central venous pressure monitoring is typically not initiated during early resuscitation, but may prove useful in patients with prolonged and extensive resuscitation, including massive transfusion. It may be necessary to establish central venous access in patients where adequate peripheral intravenous (TV) access has not been successful. It is also an adjunctive tool to aid in the diagnosis of undefined shock or measurement of volume status in patients with CHF or renal disease.^ Pulmonary artery catheter (PAC) placement may be considered in the critical care unit for patients suffering from undifferentiated shock, and to guide volume replacement for patients with comorbid factors such as congestive heart failure and renal insufficiency. Consideration for a PAC may be useful in guiding resuscitation for patients who are not hypotensive, but exhibit more subtle signs of shock such as cool extremities and elevated lactate levels.''* However, PACs are invasive, time-consuming to insert and maintain, and carry certain risks of morbidity. 1 OBSTRUCTIVE SHOCK Obstructive shock refers to a symptom complex where mechanical obstruction interferes with the ability of the heart to generate adequate cardiac output. Intravascular volume is sufficient and the heart pumping action is adequate. Basically, "blood can't flow where it needs to go." The most frequently described causes of obstructive shock are tension pneumothorax, pericardial tamponade, and pulmonary embolus. Recall our case study. Upon arrival to the trauma center, the patient was intubated. However, the respiratory therapist reported difficulty ventilating the patient, despite the fact that correct endotracheal tube placement was confirmed. The trauma surgeon performed a needle thoracostomy to relieve intrathoracic cavity pressure for a suspected tension pneumothorax. In tension pneumothorax, air accumulates in the intrathoracic cavity, causing compression of the vena cava. As a result, venous return to the heart is compromised, limiting cardiac output. This is a life-threatening situation and must be corrected immediately,^ In pericardial tamponade, fluid accumulates in the pericardial space, elevating Lntrapericardial pressure and impairing ventricular filling. As a result, stroke volume and cardiac output are reduced. As aortic pressure falls, coronary blood flow is reduced during a period of increased myocardial oxygen demand and, as a result, myocardial faUure, shock, and cardiac arrest may follow.'^ CARDIOGENIC SHOCK Cardiogenic shock is defined as the inability of the heart to maintain adequate tissue perfusion secondary to impaired pump function or failure. In the presence of trauma, cardiogenic shock is likely the result of an acute myocardial infarction either from pretraumatic event or from direct myocardial injury, Cardiogenic shock could also result from transection of a coronary vessel or chamber injury after a penetrating ^^ 8 CRITICAL CARE NURSING QUARTERLY/FANUARY-MARCH 2005 DISTRIBUTIVE SHOCK Distributive shock describes abnormalities in vascular resistance, causing maldistribution of blood flow. Some of the more common causes are sepsis, anaphylaxis, and spinal cord injury. From a pathophysiologic standpoint, low vascular resistance increases intravascular capacity. This expanded vascular capacity, in the presence of a normal or low intravascular volume, causes a functional hypovolemia, resulting in inadequate tissue perfusion. Distributive shock is also sometimes termed "warm shock." Spinal cord injury above the level of Tl results in almost unopposed parasympathetic tone. These patients do not vasoconstrict and may not demonstrate the cool clammy skin commonly associated w^ith hemorrhagic shock, Transection of the cervical spinal cord may impair cardiovascular control. Unopposed vagal tone contributes to the bradycardia, loss of arterial tone, and the hypotension witnessed in neurogenic shock.^** Septic shock, resulting from infection, is unusual in the early stages of acute trauma, except in the patient presented w^ith grossly contaminated wounds,'' Septic shock will be discussed with multisystem organ failure, as it is a frequent sequela of hypovolemic shock, DIFFERENTIAL DIAGNOSIS Shock due to hypovolemia may be confused with, or confounded by, shock from other causes. In some instances, there may be more than one type of shock in play. Consider the elderly patient who may have had a myocardial event before his car crash, Cardiogenic shock produces signs and symptoms as those found in hypovolemia with the exception that the neck veins are usually distended. However, remember that vein distention may not occur if there is inadequate circulating fluid volume, Hypotensive patients who sustain high spinal cord injuries may be challenging diagnostically. These patients will exhibit hypotension secondary to peripheral vasodilation. This type of shock may be relatively re- sistant to fluid administration. However, the patient is typically bradycardic because of increased parasympathetic tone and the inhibition of the sympathetic nervous system. The team must consider the possibility of spinal cord injury once hypovolemic shock is excluded, How^ever consider the major trauma patients with multisystem injuries w^ho may be suffering from both hypovolemic shock and spinal cord injury. However, it is imperative to assume that shock in spinal cord injury patients is due to hypovolemia, and not due to neurogenic shock. Only after blood loss is summarily ruled out, the physician should consider the diagnosis of neurogenic Diagnosis is most challenging when more than one cause is present. Another example is the patient who suffers a myocardial contusion from blunt trauma and w^ho also has hypovolemic shock from other injuries. Remember that many trauma patients suffer injuries to more than one system. Drug and alcohol intoxication may also make the diagnosis of hypovolemia troublesome. Serum ethanol elevation causes the skin to be warm, flushed, and dry. Urine is usually dilute. These patients may be hypotensive when supine, with exaggerated changes in postural blood pressures measurements, Hypovolemic shock victims present as cold, clammy, oliguric, and tachyeardic,^'' Treatment priorities Throughout every phase of trauma care, the priorities of airway, breathing, and circulation are paramount. Problems encountered in these areas must be addressed rapidly and sequentially. Sources of bleeding are continually assessed, Hemodynamic monitoring is performed on a continuous basis and changes reported to the trauma-attending physician.'" FLUID RESUSCITATION In the ICU, fluid resuscitation is carried out in a more controlled fashion than in the acute posttraumatic situation. During initial Hypovolemic Shock resuscitation attempts, IV access is obtained through the use of at least 2 large bore (14-16) gauge or larger catheters. Femoral cordis lines are commonly used in our institution when there are no contraindications for using this site. The small ports on the pulmonary artery and triple-lumen catheters are typically inadequate for rapid fluid resuscitation and should be used only after other large bore catheters are in place, INITIAL FLUID MANAGEMENT The goal of fluid administration in the trauma patient is to replace volume in order to support cardiovascular function by increasing cardiac preload and to maintain adequate peripheral oxygen delivery,'' Rapid fluid resuscitation is considered the cornerstone of therapy by some for the initial management of hypovolemic shock,^ However, there has been controversy over the years regarding the aggressive administration of TV fluids to hypotensive patients with penetrating torso wounds. Research studies from the early 1990s suggest that IV fluids should be delayed until the time of definitive operative intervention, '^' "^ In young patients, volume infusion is typically infused at the maximum rate allowed by the equipment and the size of the cannulated vein until a response is appreciated. In older patients or those with comorbid conditions such as cardiac disease, fluid resuscitation is titrated to response to avoid complications associated with hypervolemia,'° Attempting to reach normotension by the transfusion of resuscitation fluids is not necessarily the goal. Much time can be lost chasing vital signs with fluid resuscitation when, in some injuries, early definitive operative intervention to stop blood loss is required, CYSTALLOIDS VERSUS COLLOIDS Parenteral solutions for the IV resuscitation of hypovolemic shock are classified as crystalloid or colloid, depending on molecular weight. Controversy exists regarding the appropriate choice of resuscitation fluid for the trauma victim with mild to moderate hemorrhage. The focus of this controversy centers primarily on the effect each fluid type has on the lungs. Proponents of colloid therapy argue that maintenance ofthe plasma colloid oncotic pressure (PCOP) is necessary to minimize interstitial edema, particularly Ln the lungs. The concern is that massive crystalloid resuscitation creates an oncotic pressure gradient encouraging movement of fluid from the intravascular space into the pulmonary interstitium. Colloid supporters further propose that since colloids remain primarily in the intravascular space, they are more effective volume expanders, and also are less likely to cause peripheral edema than crystalloids. However, little support is found in the literature to support superior efficacy of one solution over the other.^'^ CRYSTALLOIDS Crystalloid solutions are generally safe and effective for resuscitation of patients in hypovolemic shock. Isotonie human plasma solutions, with sodium as the principal osmotic active particle, are used for resuscitation. They can be administered rapidly through peripheral veins due to their low viscosity. Isotonie fluids have the same osmolality as body fluids; therefore, there are no osmotic forces directing fluids into, or out of, intracellular compartments. During resuscitation, isotonie crystalloids are administered approximately 3 to 4 times the assessed vascular deficit to account for the distribution between the intravascular and extravascular spaces. Crystalloids partition themselves in a manner similar to the body's extracellular w^ater content; 75% extravascular and 25% intravascular The majority of complications associated with the use of crystalloid solutions are either because of undertreatment or because of overtreatment.'^'"'' '^ The use of one specific crystalloid over another is largely a matter of institutional or 10 CRITICAL CARE NURSING QUARTERLY/JANUARY-MARCH provider preference. Normal saline is the only crystalloid that can be mixed with blood and blood products. Patients resuscitated with large amounts of normal saline are at risk for developing hyperchloremic metabolic acidosis because its chloride concentration is higher than that of plasma. Lactated Ringer's solution has the advantage of a more physiologic electrolyte composition. Hypertonic saline solutions are crystalloids that contain sodium in amounts higher than physiologic concentrations. They expand the extracellular space, by creating an osmotic effect that displaces water from the intracellular compartments. Hypertonic saline decreases wound and peripheral edema. There is some research to suggest, however, that hypertonic saline resuscitation may contribute to increased bleeding.^''*'"' Most sources agree that the best way to manage hypovolemic shock in trauma patients is the judicious use of w^armed TV fluids and blood products. Many trauma centers initially infuse 2 to 3 L of lactated ringers or normal saline and then consider blood products if the patient remains symptomatic. While crystalloids are infusing, the blood bank has time to type and cross-match the patient for transfusion of type-specific blood.'°" COLLOIDS Colloids are solutions that have a highermolecular-weight species and create an osmotic effect. Colloids remain in the intravascular space for longer periods than do crystalloids. Smaller quantities are required to restore circulating blood volume. Colloids attract fluid from the extravascular to the intravascular space because of their oncotic pressure. Examples are albumin, hetastarch, dextrans, modified fluid gelatin, and urea bridge gelatin. They are expensive to use and complications have been reported Ln their use. Albumin has been implicated in decreased pulmonary function, depressed myocardial function, decreased serum calcium concentration, and coagulation abnormalities.'" Hetastarch may cause 2005 decreased platelet count and prolongation of the partial thromboplastin time. Several complications have been associated with the use of dextran, to include renal failure, anaphylaxis, and bleeding. Gelatins are associated with anaphylactoid reactions. They also may cause depression of serum fibronectin. Because ofthe high cost and complication rates, there appears to be no clear advantage to using colloid solutions,'*'"' Blood products and component therapy Neither crystalloid or colloid solutions increase oxygen-carrying capacity. Administration of large amounts of fluids can also prove detrimental by diluting hemoglobin levels and contributing to fluid volume overload.'' Blood products are currently the most readily available fluids to increase oxygen-carrying capacity and cardiac preload. However, transfusions carry the risk of various blood-borne pathogens and transfusion reactions. There is considerable debate regarding indications for transfusion. Patients with hemorrhage of up to approximately 20% of their total blood volume can be safely volume replaced with crystalloids in a ratio of 3 mL of crystalloid per milliliter of estimated blood loss. During the infusion of crystalloids, the blood bank has time to perform a type and crossmatch, so that, if needed, type-specific blood is available for transfusion. Most agree that patients with 20% to 40% loss of circulating blood volume, or those demonstrating evidence of hemodynamic instability, and those with blood gas evidence of shock, despite aggressive fluid resuscitation, may benefit from blood transfusions,^'^ BLOOD TYPES AND Rh ISSUES The decision to transfuse should be based on the assessment of ongoing blood loss, the patient's ability to compensate, and the availability of cross-matched blood products. Additional considerations are given to the patient's age and presence of comorbidities,^ Ultimately, type-specific blood products are Hypovolemic Shock preferred, but w^hen a patient arrives in apparent shock or extremis, the universal donor type O, Rh negative, is transfused using a rapid infusor/warmer device. Rh-negative blood may be in short supply; therefore, some hospitals have policies in place that allow Rh-positive Group O, packed red blood cells (PRBCs) to be transfused in men, and women older than childbearing age. The rationale behind this practice is that naturally occurring anti-Rh bodies do not exist, therefore there is no advantage to the use of Rh-negative blood. However, there is some concern that Rh-negative patients may have been sensitized from pregnancy or previous transfusions and could develop a delayed hemolytic transfusion reaction from Rh-positive blood use. This is a rare occurrence; therefore, O-Rh-positive PRBCs are considered the first choice for emergency transfusions, with consideration for the use of O-Rh-negative PRBCs for females with childbearing potential.^ Some sources recommend that the number of transfusions of type O be limited to 4 units, after which type-specific blood should be available in most institutions receiving trauma patients. However, when necessary, type O blood may be continued until the patient stabilizes or type specific is Type-specific blood is ABO and Rh compatible and is available within less than 15 minutes in most institutions. Type-specific blood has been shown to be safe and effective during emergency resuscitations. 18 MASSIVE TRANSEUSION Trauma practitioners are frequently faced with situations that require decision making to weigh the risks and benefits of massive transfusions. When the decision is made to proceed, there are technological considerations that affect infusion rates. Large bore catheters, as well as high-volume IV tubing, allow for the fastest blood administration. Pressure bags and/or mechanical rapid transfusion devices further increase flow rates. Remember that normal saline is the only fluid additive 11 that can be used in conjunction with blood product transfusion, Lactated Ringer's solution w^ill cause precipitation of blood w^ithin BLOOD COMPONENT THERAPIES At this writing, component therapy remains the current standard for blood transfusion. It refers to the utilization of the components of whole blood to include RBCs, fresh frozen plasma (FFP), platelets, and cryoprecipitate. One unit of whole blood contains 200 mL of red blood cells and 250 mL of plasma, which contains coagulation factors. Component therapy has several advantages over whole blood, and evidence suggests that the PRBCs and component therapy are as effective as whole-blood transfusion without the disadvantages. PRBCs and components are more readily available and are less expensive and easier to store than whole blood. Volume expansion can be accomplished w^ith a combination of crystalloids and PRBCs, Another advantage of component therapy over whole blood is that infusions can be tailored specifically to the needs of the individual patient. Furthermore, PRBCs increase oxygencarrying capacity more efficiently than whole blood. The disadvantage of whole blood is that platelets are not w^ell preserved, and clotting factors decrease rapidly at blood storage temperatures. For these reasons, PRBC infusion with component therapies are considered the methods of choice for increasing red blood cell mass and oxygen-carrying capacity in hemorrhagic shock,^ COMPUCATIONS OF TRANSFUSIONS Blood-borne pathogens Improved screening has significantly decreased the incidence of blood-borne pathogens or transfusion-transmitted diseases (TTDs),-^ However, they still contribute to the incidence of late death from transfusion. Increased awareness and concerns related to TTDs, especially HIV infection, have 12 CRITICAL CARE NURSING QUARTERLY/JANUARY-MARCH prompted caution and reconsideration of blood transfusion indications. Hepatitis B is the most common infectious complication. Before testing for hepatitis C, non-A non-B hepatitis was the most frequent infectious complication,'^ Transfusion reactions Transfusion reactions are categorized into hemolytic and nonhemolytic types. Major hemolytic transfusion reactions occur as a result of the interaction of antibodies in the plasma of the recipient with antigens present in the red cells of the donor. It is important to stress that the majority of hemolytic reactions are due to clerical error in the identification of blood samples or in the administration of properly cross-matched blood to the wrong patient. During high-stress situations of massive transfusion administration, meticulous attention must be paid to the processes surrounding blood banking and blood product administration to avoid this preventable complication,'^ Nonhemolytic transfusion reactions are more common and related to reactions to leukocytes or proteins in the donor blood. These may be mitigated by premedication with antipyretics and antihistamines. Typical reactions may be mild, consisting of rash or nuld bronchoconstriction. More rare are severe responses such as subglottic edema, severe bronchoconstriction, and anaphylaxis with cardiovascular collapse,'^ Platelet and coagulation factors Along with the previously mentioned concerns for blood-borne pathogens and transfusion reactions, there are several other complications related to blood product transfusions, with higher complications rates associated with massive transfusion therapy, often considered 10 U or more. Massive transfusion of blood products and concurrent infusion of large volumes of crystalloid cause certain hematologic and physiologic consequences. Not only do coagulation factors and platelet numbers and function diminish during RBC 2005 storage, the massive blood and fluid administration further dilutes the number of circulating platelets. This dilutional thrombocytopenia causes clotting abnormalities. It is important to assure that there is appropriate and timely administration of platelets and FFP to prevent this complication. Treatment should be based on clinical evidence of impaired hemostasis, by following prothrombin time, partial thromboplastin time, and platelet count. While circulating platelet counts of 20,000 per mm^ or fewer may be adequate in nonbleeding patients, platelet transfusion is appropriate for patients with evidence of ongoing microvascular bleeding with levels of 100,000 per mm' (see references 4 and 19), Massive transfusion therapy can contribute to significant electrolyte and acid-base disturbances. Among these are hypocalcemia, hyperkalemia, and hypokalemia, Hypocalcemia occurs during massive transfusion, because each unit of PRBCs contains citrate, which binds to ionized calcium in the blood. Large citrate doses may be toxic and can precipitate hypocalcemia. Clinical signs of hypocalcemia include prolongation of the QT segments on ECG, skeletal muscle tremors, and perioral tingling. Calcium levels should be closely monitored during massive transfusion therapy. Citrate also may contribute to hypomagnesemia. Because of this relationship, treatment of hypocalcemia and hypomagnesemia includes concomitant use of calcium chloride and magnesium chloride in massive transfusion, based on measured serum levels; empiric treatment is not Banked blood contains significantly elevated potassium levels because of cell lysis that occurs during the collection and storage of blood, Hyperkalemia, however, is rare during massive transfusion, because packed cells quickly reestablish their ionic pumping mechanism and potassium is rapidly absorbed. In actuality, hypokalemia occurs more frequently secondary to transient metabolic alkalosis occurring during massive transfusion, which causes potassium to move into the ^'^ Hypovolem ic Shock Acid-base disorders are commonly associated with large volume transfusions. Even though banked blood is acidic because of its citrate content, metabolic acidosis is not typically a result ofthe transfusions, but is related to underlying hypovolemic shock. Treatment should concentrate on improving tissue perfusion and oxygenation as well as an ongoing search for underlying sources of hemorrhage. Sodium bicarbonate administration is not recommended and has several detrimental side effects. In rare circumstances, a trauma patient may have metabolic acidosis due to a cause other than hypovolemia, such as comorbid factors to include diabetic ketoacidosis, carbon monoxide (CO) poisoning, drug, or toxic ingestion,^ 13 HYPOTHERMIA fusions, and exposure of body cavities during surgery.' Gentilello classifies hypothermia in trauma patients into 3 risk categories based on core body temperature. Mild hypothermia (34°C36°C) accelerates oxygen consumption in an at-risk patient population. Moderate hypothermia (32°C-34°C) further slows physiologic functions. Severe hypothermia (<32°C) is considered a life-threatening emergency.^' There are a number of adverse clinical effects related to hypothermia. These are cardiac dysrhythmias, reduction in cardiac output, increasing systemic vascular resistance, increased lactic acid production, and coagulopathic bleeding. Hypothermia has a deleterious effect on the oxyhemoglobin dissociation curve, shifting it to the left, w^hich impairs oxygen delivery and worsens the shock Hypothermia is a serious consequence of massive blood product transfusion. Progressive core hypothermia with persistent metaboUc acidosis is the precursor of severe and ongoing coagulopathy states,^ There are complex pathophysiologic interactions at play that contribute to impaired coagulation. Mikhail refers to the physiologic limits of the body in response to hypovolemic shock as "the trauma triad of death"; hypothermia, acidosis, and coagulopathy' Hypothermia has been strongly implicated in the development of acidosis and is frequently demonstrated as a consequence of severe injury and routinely prescribed resuscitation efforts,'"^ Studies suggest that as many as two thirds of all trauma patients arrive at emergency departments with hypothermia, regardless of geographic locale,'^*' Many trauma patients develop hypothermia at some point in their treatment and this is poorly tolerated. Hypothermia occurs in trauma patients with minimal cold stress secondary to inadequate tissue oxygenation and perfusion, preventing the body from generating enough heat to maintain normothermia,^' Predisposing factors are age, injury severity, impaired thermogenesis, elevated serum alcohol levels, fluid resuscitation, blood product trans- Many research studies have directly linked the presence of hypothermia in trauma patients with high mortality rates.'^"^' The primary goal is to identify those patients at risk and to intervene in this cycle of hypothermia, acidosis, and coagulopathy' Core temperature should be monitored continuously. At our institution we use a foley catheter with a thermal measuring device that provides continuous core temperature measurement. Efforts to prevent hypothermia should be employed such as using a high-volume fluid warmer during massive transfusion therapy. Based on these findings, the surgical approach to the care of the severely injured trauma patient has changed over time. Early on, the goal of trauma surgeons was to provide definitive operative intervention by performing a traditional exploratory laparotomy, where all injuries were identified and repaired. Patients would spend long periods of time in the operating room, receiving fluids, blood products, and with open peritoneum, resulting in core thermal temperature loss. Predictable evaporative heat loss with an open peritoneum, despite state-ofthe-art resuscitation procedures, is 4,6°C per hour,^^ Patients w^ould leave the operating room cold and coagulopathic. Currently the 14 CRITICAL CARE NURSING QUARTERLY/JANLIARY-MARCH goal in trauma operative resuscitation is to perform "damage control" or staged laparotomy. This initial procedure is abbreviated and intended to control hemorrhage and contamination, pack the abdomen, perform temporary closure of the abdominal wall, and move the patient quickly to the ICU for further stabilization and rewarming procedures. Stopping or abbreviating the initial procedure allows the trauma team to correct coagulopathy, maximize oxygen delivery, and reverse acidosis and hypothermia. Following stabilization in the ICU, the patient can return to the operating room for a more controlled completion ofthe surgical procedure,^ Again, the goal is to prevent the triad of hypothermia, acidosis, and coagulopathy, because of the high mortality associated with this syndrome,' As we compress the time frames through which we move our patients tow^ard definitive operative intervention, it is imperative that critical care nurses understand their role in intervening in this pathogenesis. Rewarming techniques The selection of rewarming techniques is based on how severely hypothermia is affecting the patient. Stable patients who are mildly hypothermic, and without life-threatening injuries, are typically treated with passive external rewarming techniques. Passive rewarming techniques involve removing wet clothing, increasing ambient room temperature, decreasing airflow^ and insulating the patient, and allowing his or her metabolic heat to increase body temperature. Active external rewarming techniques include warm fluid circulating, convection air, "space blankets," and radiant heat lamps. Head covering is important, as 50% of radiant heat loss occurs from the scalp. These strategies are typically more effective in preventing hypothermia than in treating it. It should not be the sole source of rewarming for patients exhibiting an adverse response to hypothermia, as results are not immediately effective. 2005 Active core rewarming techniques include the administration of warmed humidified air, heated body cavity lavage to include peritoneum and pleura, and warmed IV fluid infusion and blood transfusions. Patients requiring large boluses of fluid for resuscitation as well as blood products can receive a substantial amount of heat through warm IV fluids, Extracorporeal circulatory rewarming techniques, such as cardiopulmonary bypass, venovenous, or arteriovenous, are the most efficient rew^arming methods. However, they require large bore vessel cannulation, especially trained technician and dedication to the duty. Therefore, these procedures are typically restricted to a few tertiary centers.^' Coagulopathy Coagulopathy, or hypocoagulability after major trauma, is common in severely injured patients and recognized as a major cause of early death. There are many contributing factors, and the pathophysiologic relationships are complex. Little progress has been made in correcting this phenomenon once it develops. Virtually all normal physiologic clotting mechanisms are severely deranged in the cold, acidotic, bleeding trauma patient. The clotting cascade, governed by a series of temperature sensitive reactions, is inhibited during episodes of hypothermia. Clotting abnormalities are exacerbated when core body temperature falls below 34°C, Platelet function is also affected by lo^w body temperatures. Treatment for hypovolemia includes infusion of cystalloids and blood products, Coagulopathy becomes clinically important during massive transfusion therapy. Coagulation factors are rapidly depleted. During shock, hepatic function is impaired, impacting the ability ofthe liver to rapidly mobilize additional coagulation factors. Prothrombin time and partial thromboplastin time should be carefully monitored. Transfusion of FFP and platelets should be administered on the basis of the results of coagulation profiles."* Hypovolemic Shock BLOOD SUBSTITUTES Despite advances in detecting TTDs, concerns StiU remain regarding the risk of transmitting hepatitis and human immunodeficiency virus (HIV) during transfusion therapy. There are reports of PRBC count shortages every year, and storage of red blood cells has finite limitations. As a result, there is a great deal of interest in the development of blood substitutes as an alternative choice in the treatment of hypovolemic shock. Unlike blood, hemoglobin substitutes require no cross-match, have a long shelf life, and reportedly carry no risk of blood-borne viral pathogens. Additionally, since they have a lower viscosity than blood, flow through small capillaries may be enhanced, which potentiates peripheral oxygen delivery,'*''^' Preclinical studies showed hemoglobin substitutes to be as effective as blood and more effective than standard colloid or crystalloid solutions for resuscitation from hemorrhagic and septic shock. The hope was to provide an immediate on-site replacement for traumatic blood loss, prevent tissue ischemia and organ failure, and provide effective hemodynamic support for septic-shock-induced hypotension.^'••^'* Recent research supports the concept that postinjury multiple organ failure is related to inflammatory response. Biologic mediators present in stored blood have been implicated in early postinjury hyperinflammatory syndrome and multiple organ failure through priming of circulating neutrophils. Some newer hemoglobin-based substitutes are free of priming agents and may provide an alternative to transfusing PRBCs in the early postinjury phase,^^•^'*'^^ Humanpolymerized hemoglobin (PoIyHeme®) is a universally compatible, pathogen-free, readily available, oxygen-carrying blood substitute being developed for use in case of urgent blood loss. Recent study shows that this compound increases survival in patients with lifethreatening red blood cell levels by maintaining hemoglobin levels in the absence of red cell transfusion,'^' The Food and Drug Admin- 15 istration has approved transfusion of up to 10 consecutive units of polytteme for acute bleeding. Stage 3 clinical trials are currently in process in several trauma centers, SHOCK SEQUELAE Systemic inflammatory response syndrome Systemic inflammatory response syndrome (SIRS) describes the pathophysiologic response to a cascade of events precipitated by shock. Usually after trauma, a controlled inflammatory response occurs, which is designed to heal wounds and w^ard off infection. However, continuous stimulation or severe infection may result in a sustained inflammation (SIRS), The result is an imbalance of cellular oxygen supply and demand, which results in oxygen extraction deficit. This inflammatory response may occur without any source of bacterial infection.^ Overwhelming SIRS occurs with persistent stimulation disrupting anaerobic cellular cycles. Disruption in the process of cellular metabolism promotes a cascade of events including promotion of adhesion of molecules, catecholamines, chemotaxis, and a coagulation cascade. There is an accompanying decrease in vascular resistance resulting in profound increased cardiac index, designed to promote oxygen delivery and cellular oxygen uptake. This hypermetabolic demand, coupled with acute deficit in oxygen extraction and metabolic failure, is precursors of multiple organ dysfunction syndrome MODS Historically, infection has been considered the cause of SIRS and MODS. Typical sources of infection are IV catheters placed in the prehospital environment or emergency department. Also implicated are urethral catheters and endotracheal tubes. Decreased gastric acid allows for increased numbers of bacteria to survive and multiply, theoretically, allowing translocation of bacteria in the 16 CRITICAL CARE NURSING QUARTERLY^ANUARY-MARCH distal bowel, theoretically resulting in high pneumonia rates,^^ Studies show that approximately 60% of trauma patients will have clinical signs of sepsis without an apparent bacterial source. Sepsis, and the ensuing multiple organ failure, remains a leading cause of death in the surgical ICU, despite significant advances made regarding the management of trauma victims.^^ Sepsis is characterized by increased oxygen consumption, and increased cardiac index w^ith decreased vascular resistance. These are indicators of the hyperdynamic cardiovascular state associated with sepsis,' The process of an uncontrolled inflammatory response with a progression to MODS is recognized as a defect in cellular signaling. Recall the previous discussion of trimodal death patterns following major traumatic injury. Late deaths may occur 5 to 4 weeks after the initial shock episode. Inadequate early resuscitation has been implicated in the cascade of acidosis, hypothermia, and coagulopathy. This triad leads to multisystem organ failure and death. Lee and others describe the initial response to shock and development of SIRS, followed by progressive organ failure. This continuum is initiated and perpetuated by inflammation and inflammatory mediators.^^ These topics are complex, requiring indepth discussion and, as such, are beyond the scope of this overview article, How^ever, it is important for the critical care nurse to explore ongoing research regarding cytokines, complement activation, and lipid mediators. Studies are currently adding to the body of knowledge regarding inflammatory response and multisystem organ failure after hypovolemic shock. As compensatory mechanisms continue to fail, tissue ischemia results from hypoperfusion as blood flow is shunted away from tissues with high metabolic demands, either from microvascular injury or from inflammatory response. Organ system failures commonly seen are pulmonary, hepatic, and renal failure. When 3 or more systems are affected. 2005 the mortality rate climbs as high as 80% to End points of resuscitation At what point does one determine that resuscitation is complete? Many researchers use the same clinical, physiologic, or laboratory studies to identify subtle hypoperfusion and to determine when adequate or normal perfusion resumes following resuscitation. Typical end points are blood pressure, heart rate, and urine output,'"^ However, recent studies suggest tissue hypoperfusion can persist despite normal vital signs. Cardiac and pulmonary function can be monitored fairly accurately in the ICU with current technology. By contrast, tissue perfusion, which represents circulatory function ofthe peripheral tissues, is measured indirectly by a variety of subjective symptoms, such as vital signs, pulse rate and quality, skin temperature, color, and moistness as well as mental status. These assessments are routinely used to infer circulatory status and tissue perfusion, but they are not direct quantitative measurements of tissue perfusion, ^^ The challenge is to identify those patients at risk for hypoperfusion; it may be present despite normal cardiac indices,^'* Other modes of assessment, to include gastric tonometry, transcutaneous oxygen, and CO2 measurements, are currently being utilized as early warning signs of tissue hypoxia and hemodynamic shock in critically ill patients.'" If we go back and review the defmition of shock as the consequence of insufficient tissue perfusion, resulting in inadequate cellular oxygenation, what parameters do w^e choose to measure cellular oxygenation and tissue perfusion? In patients with inadequate tissue perfusion, oxygen delivery is insufficient for the generation of adenosine triphosphate. Without adenosine triphosphate, the body cannot sustain normal cellular function. Anaerobic metabolism and tissue acidosis are results, CO2 levels increase in the splanchnic or gut circulation. Successful resuscitation from shock is measured by a limitation of oxygen debt and tissue acidosis Hypovolemic Shock with the return of aerobic Clinicians rely upon both global and organspecific parameters to measure end products of inotropic metabolism to determine if complete resuscitation has been achieved. Basically, global indexes measure overall degree of hypoperfusion, based on a number of readily available data sets. Some of these include the following. Oxygen delivery index Oxygen delivery index (DO2D (normal value 500-600 mL/min/m^) is determined by CO (carbon monoxide), hemoglobin saturation, and the ability of the lungs to load oxygen onto the hemoglobin molecule. In severe hemorrhagic shock, there is a decrease in circulating hemoglobin, which influences this component of oxygen delivery. Cardiac output is affected by several clinical conditions related to trauma, to include acute myocardial infarction, hypovolemia, septic shock, neurogenic shock, cardiac contusion, and pericardial tamponade. Pulmonary function relative to oxygen delivery is affected by the presence of pneumothorax, hemothorax, flail chest, pulmonary contusion, loss of effective airway, inadequate mechanical ventilation, and other sequelae of trauma, to include pneumonia, atelectasis, excessive secretions, and patient positioning. In a severely injured patient, it is common to exhibit abnormal DO2I values based on any, or all, of these clinical factors. The oxygen consumption index value (normal value, 125 mL/min/m^) may measure 4 or 5 times the norm in a critically injured patient. Some causes of increased VO2I include pain, agitation, posturing, fever, increased w^ork of breathing, and tachycardia. Mixed venous oxygen saturation Continuous mixed venous oxygen saturation (SVO2) monitoring reflects how much oxygen was consumed by the tissues. Patients 17 requiring aggressive resuscitation will demonstrate abnormally low values because of either inadequate oxygen delivery or excessive oxygen demand by the tissues. Normal values for SVO2 are between 65% and 80%; when values fall below 50%, anaerobic metabolism is present, A low VO2 tells us that the patient is underresuscitated, or still in shock, but it is nonspecific as to the cause. This technology requires invasive monitoring via a PA catheter, which is associated with significant morbidity to include improper catheter placement, pneumothorax, infection, and equipment malfunction,^^ Arteriovenous carbon dioxide gradient The gradient between arterial and mixed venous PACO2 levels reflects the degree and duration of hypoperfusion and is an excellent barometer of the degree of hypovolemic shock. Normally, CO2 is cleared Ln the pulmonary circulation, but in profound shock there is a decrease in cardiac output and poor pulmonary blood flow, resulting in an accumulation of PACO2 in the tissues, A gap greater than 11 mm Hg suggests severe compromise. While arteriovenous carbon dioxide gradient (AVPACO2) provides a general assessment regarding the effectiveness of resuscitation efforts, it does not provide specific organic information,^'^ There have been recent technological advances that may provide more information regarding organ-specific or regional resuscitation effectiveness. These are tonometry, capnometry, and near-infrared spectroscopy. We will discuss their use in measuring specific intracellular tissue response to resuscitation. Gastric tonometry Gastric tonometry assesses gastric mucosal pH as a marker of the adequacy of resuscitation, evaluating perfusion at the splanchnic bed. The GI tract is very sensitive to any decrease in circulating volume and may significantly compromise gut perfusion. This 18 CRITICAL CARE NURSING QUARTERLY/JANUARY-MARCH technique involves the use of a nasogastric tube with a saline-filled, gas-permeable silicone balloon at the tip to measure CO2 emitted from the gastric cells, PACO2 is then converted to a pH value. A pH value less than 7,35 suggests anaerobic metabolism, a potentially negative predictor of adequate splanchnic perfusion, raising the patient's risk for MODS and sepsis. Studies however are not conclusive, yet there are indications that gastric tonometry warrants consideration as a useful assessment tool in measuring gastric tissue perfusion.^^ Subiinguai capnometry Recent research involving both animal and human subjects suggests that measurement of the proximal GI tract using sublingual PACO2 strongly correlates with decreases in distal gut blood flow and increases in lactic acid during shock states. Since it is a relatively simple, noninvasive procedure, it has potential as an early triage resuscitation tool,'^'^ A microelectrode CO2 probe is placed under the tongue, providing continuous information regarding tissue perfusion ofthe proximal GI tract. Continued research is necessary, but early indicators are promising. Near-infrared spectroscopy Near-infrared spectroscopy is another technology on the horizon that may show promise as a guide to end points of resuscitation. Minimally invasive, it measures intracellular oxygen levels, quantifies intracellular function, and identifies other conditions that may affect intracellular metabolism,^^ It assesses the absorption of infrared light by saturated hemoglobin molecules and cytochromea,a^. It works by passing light waves via probes through muscle tissue. The device displays levels of saturated hemoglobin and cytochrome-a,a3 to alert providers to organspecific hypoxia or to indicate successful resuscitation efforts through the reappearance of reflected red light. It holds promise 2005 in predicting patients at risk for multisystem organ failure early in the course of resuscitation. Both global parameter management such as SVO2, lactate, and base deficit are helpful in determining decompensation or improvement in resuscitation states. Care providers should not be lulled into a false sense of security, when vital signs and basic hemodynamic parameters fall within normal limits during resuscitation. New technologies measuring regional tissue perfusion may be an adjunct tool in this assessment process. 29 SUMMARY Shock is a complex physiologic state, resulting in extreme dysfunction of cellular biochemistry, resulting inadequate tissue perfusion, and cellular death, Hypovolemic shock is most commonly seen in major trauma patients, although the major trauma victim is additionally at risk for cardiogenic, obstructive, and distributive shock. Differential diagnoses can be complex. Resuscitation from shock is restoration of adequate tissue perfusion. Early identification and aggressive treatment is necessary to prevent or mitigate the effects of shock states, SIRS and MODS, Current therapies are not without controversy. Ongoing research is aimed at further understanding the complex biochemical and physiologic responses to shock, to guide further development of appropriate treatment methodologies. The critical care nurse remains a key member of the trauma team as resuscitation measures are continued into the critical care environment. It is imperative that the critical care nurse understand the trauma patient's complex physiologic response to injury, be familiar with methods to monitor for key indicators of shock states, and respond as a team member to provide timely and aggressive treatment to achieve positive patient outcomes. Hypovolemic Shock 19 REFERENCES 1, Mower-Wade D, Bartley M, Chiari-Allwein J. Shock: do you know how to respond? Nursing. 2000;30(10):34-40, 2, Stern SA, Bobek EM, Resuscitation: management of shock. In: Ferrera PC, Colucciello SA, Marx JA, et al,, eds. Trauma Management: An Emergency Medicine Approach. St Louis: Mosby; 2001:75102, 3, Bell RM, Krontz BE. Initial assessment. In: Mattox KL, Feliciano DV, Moore EE, eds, Traunia. 4th ed. New York: McGraw-HiU; 2000, 4, Scalea TM, Boswell SA. Initial management of traumatic shock. In: McQuillen K, Von KA, Rueden KT, Nartsock RL, Flynn MB, Whalen E, eds. Trauma Nursing: From Resuscitation Through Rehabilitation. 3rd ed. Philadelphia: WB Saunders; 2002:201221, 5, Mikhail J, The trauma triad of death. AACN Clin Issues. 1999;10(l):85-94. 6, Cairns CB. Rude unhinging of the machinery of life: metabolic approaches to hemorrhagic shock. Curr Opin CritCare. 2OOl;7(6):437-443, 7, Muliins RJ. Management of shock. In: Mattox KL, Feliciano DV, Moore EE, eds. Trauma, 4th ed. New York: McGraw-Hill; 2000:195-229. 8, Advanced Trauma Ufe Support Course for Doctors {Instructor Course Manual). Shock. 6th ed. Chicago: American College of Surgeons; 1997. 9, Vary TV, McLean B, Von Reuden KT. Shock and multiple organ dysfunction syndrome. In: McQuillen K, Von KA, Rueden KT, Nartsock RL, Flynn MB, Wlialen E. eds. Trauma Nursing: From Resuscitation Through Rehabilitation. 3rd ed. Philadelphia: WB Saunders; 2002:173-200. 10. Bongard FS. Shock and resuscitation. In: Bongard FS, Sue DS, eds. Current Critical Care Diagnosis and Treatment. 2nd ed. New York: Lange Medical Books/McGraw-Hill; 242-267; 2002. 11. Cohen S. Shock. In: Cohen S, ed. Trauma Nursing Secrets. PhUadelphia: Hanley and Belfus; 2003:109114, 12. Davis JW, Shackford SR, Holbrook TL. Base deficit as a sensitive indicator of compensated shock in tissue oxygen utilization. Surg Gyencol Obstet. 1991;173:473-476. 13. Husein FA, Martin MJ, MuUinex PS, Steele SR, Elliot DC. Serum lactate and base deficit as predictors of mortality and morbidity. Am f Surg 2003;185(5): 484-491, 14. Kaplan LJ, Me Partland K, Santora TA, Trooskin SZ. Start with a subjective assessment of skin temperature to identify hypoperfusion in intensive care unit patients./ Trauma. 2001;50(4):620-628. 15. Bickell WH, Wall MJ, Pepe PE, et al. Immediate versus delayed fluid resuscitation for hypotensive patients with penetrating torso injuries. A' FnglJ Med. 1994;331:1105-1109, 16. Trunkey DD. Prehospital fluid resuscitation. In: Trunkey DD, Lewis FR Jr, eds. Current Therapy of Trauma. 4th ed. Chicago: Mosby; 1999:129-130. 17. Schierhout G, Roberts I, Alderson P, Bunn F, Colloids versus crystalloids for fluid resuscitation in critically ill patients, Cochran Database SystRev. 1999;3. 18. Moore EE, Mattox KL, Feliciano DV Transfusion, autotransfusion, and blood substitutes. In: Moore EE, Mattox KL, Feliciano DV, eds. Trauma Manual. New York: McGraw-Hill; 2003:84-90, 19. Rotundo MF, Reilly PM. Bleeding and coagulation complications. In: Mattox KL, Feliciano Dy Moore EE, eds. Trauma. 4th ed. New York, McGraw-Hill; 2000:1267-1285. 20. Luna GK, Maier Ry Pavlin EG, Anardi D, Copass MK, Oreskovich MR. Incidence and effect of hypothermia in seriously injured patients, / Trauma. 1987; 27:1014-1018, 21. Gentilello L. Hypothermia in trauma. In: Trunkey DD, Lewis FR, eds. Current Therapy of Trauma. 4th ed. Baltimore: Mosby; 1999:325-328, 22. BurchJM, DentonJR, Noble RD. Physiologic rationale for abbreviated laparotomy. Surg Clin North Am. 1997;77:779-782. 23. Gould SA, Moore EE, Hoyt DB, et al. The first randomized trial of human polymerized hemoglobin as a blood substitute in acute trauma and emergent surgery.yy4;M Coll Surg. 2OO2;445-455. 24. Johnson JL, Moore EE, Offner PJ, et al. Resuscitation with a blood substitute abrogates pathologic postinjury neutrophil cytotoxic function./ Trauma. 2001;50(3):449-456. 25. Biffl WL, Moore EE, Haenel JB. Hemoglobin solutions for trauma resuscitation. In: Trunkey DD, Lewis FR, eds. Current Therapy of Trauma. 4th ed. Baltimore: Mosby; 1999:329-333. 26. Wilson RF, Tyburski JG, Janning SW. Sepsis in trauma. In: Wilson RF, ed. Handbook of Trauma: Pitfalls and Pearls. Philadelphia: Lippincott, Williams & Wilkins; 1999:596-625. 27. Jarrar D, Chaudry IH, Wang P Organ dysfunction following hemorrhage and sepsis: mechanisms and therapeutic approaches. Int f Mol Med. 1999;4(6):575-583. 28. Lee CC, Marill KA, Carter WA, Crupi RS. A current concept of trauma-induced multiorgan failure. Ann FmergMed. 2001;38(2):170-176. 29. Schulman C. End points of resuscitation: choosing the right parameters to monitor. Dimens Crit Care Nurs. 2OO2;21(1):2-I4. 30. Tatevossian R, Wo C, Velhamos G, Demetriades D, Shoemaker W, Transcutaneous oxygen in CO2 as early warning of tissue hypoxia and bemodynamic shock and critically ill emergency patients, Crit Care Med. 2000;28(7):2248-2253, 31. Mikhail J, Massive transfusion in trauma: process and outcomes,/ Trauma Nurs. 2OO4;l l(2):55-60.
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