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Abstract
BackgroundDuring passive mechanical ventilation, the driving pressure of the respiratory system is an important mediator of ventilator-induced lung injury. Monitoring of driving pressure during assisted ventilation, similar to controlled ventilation, could be a tool to identify patients at risk of ventilator-induced lung injury. The aim of this study was to describe driving pressure over time and to identify whether and when high driving pressure occurs in critically ill patients during assisted ventilation.MethodsSixty-two patients fulfilling criteria for assisted ventilation were prospectively studied. Patients were included when the treating physician selected proportional assist ventilation (PAV+), a mode that estimates respiratory system compliance. In these patients, continuous recordings of all ventilator parameters were obtained for up to 72 h. Driving pressure was calculated as tidal volume-to-respiratory system compliance ratio. The distribution of driving pressure and tidal volume values over time was examined, and periods of sustained high driving pressure (≥ 15 cmH2O) and of stable compliance were identified and analyzed.ResultsThe analysis included 3200 h of ventilation, consisting of 8.8 million samples. For most (95%) of the time, driving pressure was < 15 cmH2O and tidal volume < 11 mL/kg (of ideal body weight). In most patients, high driving pressure was observed for short periods of time (median 2.5 min). Prolonged periods of high driving pressure were observed in five patients (8%). During the 661 periods of stable compliance, high driving pressure combined with a tidal volume ≥ 8 mL/kg was observed only in 11 cases (1.6%) pertaining to four patients. High driving pressure occurred almost exclusively when respiratory system compliance was low, and compliance above 30 mL/cmH2O excluded the presence of high driving pressure with 90% sensitivity and specificity.ConclusionsIn critically ill patients fulfilling criteria for assisted ventilation, and ventilated in PAV+ mode, sustained high driving pressure occurred in a small, yet not negligible number of patients. The presence of sustained high driving pressure was not associated with high tidal volume, but occurred almost exclusively when compliance was below 30 mL/cmH2O.
Highlights
During passive mechanical ventilation, the driving pressure of the respiratory system is an important mediator of ventilator-induced lung injury
Despite the fact that driving pressure of respiratory system (ΔP) represents a global measurement of lung stretch and cannot capture lung inhomogeneity, recent studies have shown that ΔP is a main determinant of ventilator-induced lung injury (VILI), and it is associated with mortality in acute respiratory distress syndrome (ARDS) patients, at ΔP values above 14 cmH2O [1,2,3,4,5,6]
ΔP as a risk factor for VILI has been exclusively studied in patients under controlled mechanical ventilation, the potentially harmful effects of high ΔP are probably present in any mode of ventilation
Summary
The driving pressure of the respiratory system is an important mediator of ventilator-induced lung injury. Monitoring of driving pressure during assisted ventilation, similar to controlled ventilation, could be a tool to identify patients at risk of ventilator-induced lung injury. ΔP as a risk factor for VILI has been exclusively studied in patients under controlled mechanical ventilation, the potentially harmful effects of high ΔP are probably present in any mode of ventilation. As the beneficial effects of spontaneous breathing during mechanical ventilation are well established, it becomes increasingly important to identify patients at risk of selfinflicted lung injury during assisted ventilation [9,10,11]. To identify patients at risk and prevent self-inflicted lung injury, monitoring of ΔP during assisted ventilation might be helpful. Limited information is available on the presence of high ΔP in patients ventilated in assisted modes, mainly because measuring ΔP requires valid estimation of Crs, a complicated task with conventional assisted modes of ventilation such as volume assist and pressure support [14]
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