EXPERIENCE WITH HIGH FREQUENCY OSCILLATORY VENTILATION IN THE MANAGEMENT OF ADULT SURGICAL/TRAUMA PATIENTS WITH ARDS

Stuart M. Lowson, MD, Daniel D. Rowley, RRT-NPS, RPFT Linda L. Clarke, RRT, Jeffrey S. Young, MD, Roy Hostetter, RRT Surgical/Trauma ICU, University of Virginia Medical Center Charlottesville, Virginia

INTRODUCTION: After participating in the Multicenter Oscillatory Ventilation for Acute Respiratory Distress Syndrome II (MOAT II) study ¹, we hypothesized that early application of HFOV would improve outcomes in surgical/trauma patients with ARDS. 

METHOD: We identified patients at risk of ALI/ARDS by the following criteria: chest trauma, > 10L of initial volume resuscitation, developing infiltrates on roentgenograms, P/F ratio < 200 mmHg, and airway P_plateau > 30 cm H₂0 despite using low V_ts. Patients were sedated, administered a neuromuscular blocking (NMB) agent, and placed on HFOV (SensorMedics 3100B). F_IO₂ is set equivalent to CMV level, frequency = 3 Hz, I_t= 50%, MAP 5-8 cmH₂O > CMV level, Bias Flow (BF)= 40-50 LPM, and Delta-P (∆P) is set to achieve adequate chest wall “wiggle”. Our goals of HFOV are to obtain an arterial pH ≥ 7.25, S_aO₂ ≥ 90%, and F_IO₂ ≤ 50% at the lowest MAP. Patients are returned to CMV when MAP is < 22 cmH₂O or if HFOV fails to achieve adequate ventilation. 

RESULTS: Of the 17 patients we entered into the MOAT II trial, 6-month mortality was 50% in CMV group -vs- 29% in the HFOV group. We have used HFOV in 65 patients to date. Minor changes in our management strategies include: 1. Earlier initiation of HFOV when P/F ratios fail to improve with conventional lung recruitment strategies. 2. Aggressive use of ∆P, increased I_t%, decreased oscillating frequency, and maximized BF (50-60 LPM) to optimize ventilation. 3. Earlier discontinuation of NMBs and scrupulous titration of sedation to permit patient tolerance of HFOV. Our current 28-day mortality in surgical/trauma patients with ARDS, using the above approach, is 20% (30 day mortality in the ARDS Network trial’s low V_t group was 31%²). 

CONCLUSION: The “open lung” model of ARDS management strongly suggests that HFOV should be an effective technique to use in this patient population. This hypothesis is supported by the results of HFOV in animal models of ARDS, and by our outcome data in both the MOAT II study and surgical/trauma patients with ARDS. Studies by Gattinoni and others suggest that patients with secondary lung injury may respond better to recruitment maneuvers –vs- those patients with primary lung injury.³ This may partly explain why our 6 month mortality rate with HFOV in the Moat II study was less than that of the study population as a whole (47% with HFOV).

 
References

1. Derdak, S, Mehta S, Stewart T, et al. High frequency oscillatory ventilation for  acute respiratory distress syndrome in adults. Am J Resp Crit Care Med  2002;166:801-8.
   
2. The Acute Respiratory Distress Syndrome Network. Ventilation with lower tidal   volumes as compared with traditional tidal volumes for acute lung injury and   the acute respiratory distress syndrome. N Eng J Med 2000;342:1301-8.
   
3. Gattinoni L, Pelosi P, Suter P, et al. Acute respiratory distress syndrome caused  by pulmonary and extrapulmonary disease. Different syndromes? Am J Resp  Crit Care Med 1998;158:3-11.