关键词: 急性呼吸窘迫综合征, 呼气末正压, 慢吐气, 复张容积, 分层电阻抗成像

Abstract: Objective To explore the feasibility of positive end-expiratory pressure (PEEP) selection based on prolonged expiration combined with ventilator monitoring in the model of acute respiratory distress syndrome (ARDS). Methods ARDS model was established by alveolar instillation of hydrochloric acid. Decremental PEEP trial was performed by prolonged expiration maneuver. A prolonged expiration (6-9 seconds) maneuver was performed while abruptly decreasing PEEP from a high to a low level for one breath (from 20 cmH₂O to 0 cmH₂O in decremental steps of 5 cmH₂O). Because inspiratory tidal volume (VT) was unchanged, the difference in expiratory VT values between the expired VT displayed immediately after decreasing PEEP and the breath before changing PEEP was referred to as the total change in lung volume from high to low PEEP. Meanwhile, the predicted change in lung volume was estimated by the product of respiratory system compliance at low PEEP and the change in pressure. The difference of total change of lung volume and predicted value was taken as an estimate of derecruited volume or recruitment volume (Vrec). The PEEP with the largest Vrec may be the appropriate PEEP interval. This PEEP was verified by electrical impedance tomography (EIT) based on the overdistension and collapse. Optimal PEEP level was set based on the appropriate PEEP interval, hemodynamics, and other indicators. Results The PEEP interval with the largest Vrec by prolonged expiration was 5-10 cmH₂O. According to EIT, the optimal PEEP level was also in the interval of 5-10 cmH₂O with appropriate overdistension and collapse. When PEEP was in 15-20 cmH₂O, intravenous norepinephrine was used to maintain mean arterial pressure (MAP) above 65 mmHg, and driving pressure was large to cause the ventilator-associated lung injury. It was unreasonable for physiological PEEP when PEEP was under 5 cmH₂O. Conclusion It is feasible to select PEEP using prolonged expiration combined with ventilator monitoring. The PEEP with the largest Vrec assessed by prolonged expiration may be the appropriate PEEP interval. Then, the optimal PEEP level may be further confirmed with hemodynamics and other parameters.

Key words: acute respiratory distress syndrome, positive end-expiratory pressure, prolonged expiration, recruitment volume, electrical impedance tomography