Right Ventricular Function during High-Frequency Oscillatory Ventilation, Use of Noninvasive Positive Pressure Ventilation for Acute Lung Injury, and Dexmedetomidine Use for Sedation during Mechanical Ventilation

Abstract

High-frequency oscillatory ventilation (HFOV) is often used in severe acute respiratory distress syndrome (ARDS), defined as a PaO2/FiO2 ratio of< 100 mmHg. It applies lower tidal volumes with high respiratory frequency and occasionally higher mean airway pressures (mPaw) to achieve oxygenation goals. Although no mortality benefit has been shown, HFOV often results in improved oxygenation (2). The authors hypothesized that higher mPaw during HFOV would negatively affect right ventricular (RV) function in patients with ARDS. Sixteen patients with ARDS with direct lung injury were subjected to a 6-hour period of conventional mechanical ventilation (CMV) with low tidal volume and then switched to HFOV. Three 1-hour periods of HFOV using incremental mPaw of 15, 110, and 115 cm H2O added to mPaw recorded during CMV were administered in randomized order. The mPaw was 18 6 3 cm H2O during CMV and increased progressively up to 336 3 cm H2O on HFOV115. The numbers of patients with RV dysfunction, defined as the ratio of RV end-diastolic area (RVEDA) to left ventricular end diastolic area (LVEDA) . 0.6, on CMV, HFOV15, HFOV110, and HFOV115 were 9 (P , 0.05 vs. HFOV110 and 115), 8, 12, and 15 of 16, respectively. Among these patients, the corresponding numbers with RV failure, defined as RVEDA/LVEDA . 0.9, a subset of dysfunction, were 4 (P , 0.05 versus HFOV115), 4, 6, and 9 of 16. The cardiac index decreased significantly at HFOV115. This is the first study to specifically evaluate RV function during HFOV in ARDS.More than half of the subjects had RV dysfunction at baseline, which significantly worsenedwith increasing mPaw during HFOV. A limitation of the study is that high mPaw onHFOV is usually required over long periods. The acute effects of increased mPaw on RV function may differ with time. The study was performed in a population of patients with ARDS that had a higher incidence of RV dysfunction than has been previously described (3). Whether mPaw-induced RV dysfunction affects patient outcomes should be explored in future studies. Clinicians should be aware that high mPaw during HFOV may precipitate RV failure.