Using High Frequency Jet Ventilation in patients with ARDS Eran Segal, MD Director Department of Anesthesia, Intensive Care and Pain Medicine Assuta Medical Centers Israel Why HFJV? In recent years, the damage incurred by the lungs from mechanical ventilation has received increasing attention. The mechanism of VILI – ventilator induced lung injury is multifactorial, and significant components leading to damage are volutrauma – ventilating with large tidal volumes, atelectrauma – allowing for de-recruitment during the ventilator cycle, in addition to barotrauma, and toxic and humoral effects. It has been demonstrated that patients are still being ventilated with higher than optimal tidal volumes, and that the acceptance of low tidal volumes as a critically important part of ventilating the patient with ARDS, is still not universal. Thus, the concept of rapid, high rate and very low tidal volume as delivered with high frequency ventilation is very attractive as an approach directed at prevention of lung injury due to the mechanical ventilation. It could theoretically be expected that there would be less stress due to recruitment-derecruitment of alveoli, and patient outcome may be improved. What is HFJV? HFJV is one of a group of mechanical ventilation modes which utilize high rates at low tidal volumes. HFV has been classified to a number of modalities: HFPPV, HFJV, HFO. HFPPV is essentially increasing respiratory rates, while decreasing the tidal volumes to the low end of that prescribed for conventional mechanical ventilation. HFO is a technique in which a continuous gas flow at the patients ETT, is “oscillated” that is a positive and negative pressure is applied at the proximal end of the tube, leading to a ventilator mode with very low tidal volumes, very high rates and a unique element which is that in this ventilator mode both inspiration and exhalation are active. HFJV is a mode in which a high speed (jet) stream of gas is delivered at rapid rates – often in the hundreds per minute. The velocity of the gas flow leads to the venture effect with entrainment of ambient gas, or from a circuit with continuous flow to which the jet is connected. This means that the tidal volume delivered is comprised of two components – the jet volume and the entrained volume, which can be equivalent in size. Various conditions, such as the location at which the jet is delivered, the size of the injector, and the pressure differences, may lead to a change in the ratio of the entrained volume size versus the jet volume, therefore the assessment of tidal volume during HFJV can be challenging and the “true” tidal volume is usuallyunknown. In contrast to HFO and similarly to conventional ventilation the expiratory phase of ventilation in HFJV is passive. But due to the high rate and short expiratory time, there is an element of air trapping when ventilating with HFJV, and this is a major component of the improved oxygenation seen with HFJV. HFJV has been shown in experimental models to improve gas exchange in lung failure. Quan et al showed improved lung function in an ARDs model induced by lung lavage in rabbits.[1] Johnson and Lachman used HFJV in a dog model of ARDS, and showed that gas exchange could be well controlled, and that oxygenation could be improved by use of external PEEP and increased VE, and frequency had a significant effect of CO2 removal with the lower rate leading to hypocapnea.[2] Is HFJV of value in patients with ARDS? As mentioned before, using HFJV makes great physiological sense. Unfortunately, data proving this potential are extremely weak if at all. A few studies have shown that patients ventilated with HFJV have an improved oxygenation. However, this has not been translated into a better survival rate. Holzapfel showed that using HFJV could achieve the same gas exchange as conventional ventilation but that the patients ventilated with HFJV were more hemodynamically unstable, thus leading to the conclusion that this may not be an appropriate mode for patients with severe lung injury.[3] Simes described a case of a patient with severe ARDS and bronchopleural fistula [4]in which the use of HFJV was very beneficial. Series of patients ventilated with HFJV are few. In 1987 Hurst et al described the use of HFJV in a group of 45 patients with post-traumatic ARDS. The patients showed improved gas exchange but no impact on survival could be demonstrated. [5] Abel et al showed a reduced mortality from ARDS between 2 time periods. They ascribe this improved outcome to organizational change in ICU care between the two time periods. They do note, however that the use of different ventilatory modes including HFV may have contributed to this improved outcome.[6] Still, the data for effectiveness of HFJV or HFV in general in ARDS is not there. Wunsch and colleagues searched for evidence and found only 2 randomized trials looking at GFV in either children or adults. [7] Although there was a trend towards improved outcome, the bottom line is that there is not enough data at this time to support use of HFV in ARDS. Further studies are needed to either prove or disprove the utility of this interesting and potentially useful modality. 1. 2. 3. 4. 5. 6. 7. Quan, S.F., et al., Comparison of high-frequency jet ventilation with conventional mechanical ventilation in saline-lavaged rabbits. Crit Care Med, 1984. 12(9): p. 759-63. Jonson, B. and B. Lachmann, Setting and monitoring of high-frequency jet ventilation in severe respiratory distress syndrome. Crit Care Med, 1989. 17(10): p. 1020-4. Holzapfel, L., et al., Comparison of high-frequency jet ventilation to conventional ventilation in adults with respiratory distress syndrome. Intensive Care Med, 1987. 13(2): p. 100-5. Simes, D.C., Supplemental jet ventilation in a case of ARDS complicated by bronchopleural fistulae. Crit Care Resusc, 2005. 7(2): p. 111-5. Hurst, J.M., R.D. Branson, and C.B. DeHaven, The role of high-frequency ventilation in post-traumatic respiratory insufficiency. J Trauma, 1987. 27(3): p. 236-42. Abel, S.J., et al., Reduced mortality in association with the acute respiratory distress syndrome (ARDS). Thorax, 1998. 53(4): p. 292-4. Wunsch, H. and J. Mapstone, High-frequency ventilation versus conventional ventilation for the treatment of acute lung injury and acute respiratory distress syndrome: a systematic review and cochrane analysis. Anesth Analg, 2005. 100(6): p. 1765-72.
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