High-frequency oscillatory ventilation guided by transpulmonary pressure in acute respiratory syndrome: an experimental study in pigs

Abstract

Background: Recent clinical studies have not shown an overall benefit of high-frequency oscillatory ventilation (HFOV), possibly due to injurious or non-individualized HFOV settings. We compared conventional HFOV (HFOV_con) settings with HFOV settings based on mean transpulmonary pressures (P_Lmean) in an animal model of experimental acute respiratory distress syndrome (ARDS).

Methods: ARDS was induced in eight pigs by intrabronchial installation of hydrochloric acid (0.1 N, pH 1.1; 2.5 ml/kg body weight). The animals were initially ventilated in volume-controlled mode with low tidal volumes (6 ml kg^{- 1}) at three positive end-expiratory pressure (PEEP) levels (5, 10, 20 cmH₂O) followed by HFOV_con and then HFOV P_Lmean each at PEEP 10 and 20. The continuous distending pressure (CDP) during HFOV_con was set at mean airway pressure plus 5 cmH₂O. For HFOV P_Lmean it was set at mean P_L plus 5 cmH₂O. Baseline measurements were obtained before and after induction of ARDS under volume controlled ventilation with PEEP 5. The same measurements and computer tomography of the thorax were then performed under all ventilatory regimens at PEEP 10 and 20.

Results: Cardiac output, stroke volume, mean arterial pressure and intrathoracic blood volume index were significantly higher during HFOV P_Lmean than during HFOV_con at PEEP 20. Lung density, total lung volume, and normally and poorly aerated lung areas were significantly greater during HFOV_con, while there was less over-aerated lung tissue in HFOV P_Lmean. The groups did not differ in oxygenation or extravascular lung water index.

Conclusion: HFOV P_Lmean is associated with less hemodynamic compromise and less pulmonary overdistension than HFOV_con. Despite the increase in non-ventilated lung areas, oxygenation improved with both regimens. An individualized approach with HFOV settings based on transpulmonary pressure could be a useful ventilatory strategy in patients with ARDS. Providing alveolar stabilization with HFOV while avoiding harmful distending pressures and pulmonary overdistension might be a key in the context of ventilator-induced lung injury.

Keywords: Aerated lung tissue; HFOV; Hemodynamics; Oxygenation; Transpulmonary pressure; Volume controlled ventilation.

Fig. 1

Experimental procedure. ARDS, acute respiratory distress syndrome; HCL, hydrochloric acid; PEEP, positive end-expiratory pressure; BW, body weight; Paw mean, mean airway pressure; Pes mean, mean esophageal pressure; P_L, transpulmonary pressure; CDP, continuous distending pressure; HFOVcon, conventional high frequency oscillatory ventilation group; HFOV P_L, transpulmonary guided high frequency oscillatory ventilation group. Significant P value (P-Level) <0.05

Fig. 2

Normally aerated, poorly aerated, non-aerated, and over aerated lung tissue at positive end-expiratory pressure (PEEP) 10. Data are presented as median, 25th and 75th quartiles, and minimum and maximum (n = 8). VCV, volume controlled ventilation; HFOV_con, conventional high frequency oscillatory ventilation group; HFOV P_L, mean transpulmonary pressure guided high frequency oscillatory ventilation group. Box plots are numbered from the left to the right side from 1 to 4. Significant P value (P-Level) <0.05

Fig. 3

Normally aerated, poorly aerated, non-aerated and over aerated lung tissue at positive end-expiratory pressure (PEEP) 20. Data are presented as median, 25th and 75th quartiles, and minimum and maximum (n = 8). VCV, volume controlled ventilation; HFOV_con, conventional high frequency oscillatory ventilation group; HFOV P_L, mean transpulmonary pressure guided high frequency oscillatory ventilation group. Box plots are numbered from the left to the right side from 1 to 3. Significant P value (P-Level) <0.05

Fig. 4

Mean Hounsfield units at positive end-expiratory pressure (PEEP) 10 and 20. Data are presented as median, 25th and 75th quartiles, and minimum and maximum (n = 8). VCV, volume controlled ventilation; HFOV_con, conventional high frequency oscillatory ventilation group; HFOV P_L, mean transpulmonary pressure guided high frequency oscillatory ventilation group. Box plots are numbered from the left to the right side from 1 to 3 and 1 to 4. Significant P value (P-Level) <0.05

Fig. 5

Mean arterial pressure, extra vascular lung water index (ELWI), heart rate and stroke volume. Data are presented as median, 25th and 75th quartiles, and minimum and maximum (n = 8). T0, start of the measurement process; ARDS, established acute respiratory distress syndrome; VCV, volume controlled ventilation; HFOV_con, conventional high frequency oscillatory ventilation group; HFOV P_L, mean transpulmonary pressure guided high frequency oscillatory ventilation group. Box plots are counted from the left to the right side from 1 to 8. Significant P value (P-Level) <0.05

Fig. 6

Comparison of the continuous distending airway pressures (CDP) guided by the mean airway pressure (Paw mean) and the mean transpulmonary pressure (P_{L mean}). Data are presented as mean and standard deviation (n = 8). CDP, continuous distending pressure; CDP Paw mean HFOV_con, conventional high frequency oscillatory ventilation group; HFOV P_L, mean transpulmonary pressure guided high frequency oscillatory ventilation group