Tidal Volume Should Be Individualized to the Patient’s Lung Compliance

I appreciate the well-done review by Gottlieb et al1Gottlieb M. Chesis M. Long B. What is the impact of low tidal volume ventilation for emergency department patients?.Ann Emerg Med. 2023; 81: 162-164Abstract Full Text Full Text PDF PubMed Scopus (1) Google Scholar and would like to make some comments. The low tidal volume strategy for acute respiratory distress syndrome had numerous negative trials for more than a decade before the protocol was changed to compare 6 mL/kg with 12 mL/kg of ideal body weight tidal volume instead of the control group of 10 mL/kg, which was the standard of care at that time.2Walkey A.J. Goligher E.C. Del Sorbo L. et al.Low tidal volume versus non-volume-limited strategies for patients with acute respiratory distress syndrome. A systematic review and meta-analysis.Ann Am Thorac Soc. 2017; 14: S271-S279Crossref PubMed Scopus (69) Google Scholar,3Eichacker P.Q. Gerstenberger E.P. Banks S.M. et al.Meta-analysis of acute lung injury and acute respiratory distress syndrome trials testing low tidal volumes.Am J Respir Crit Care Med. 2002; 166: 1510-1514Crossref PubMed Scopus (353) Google Scholar Indeed, even this trial (ARMA) had data on >2,500 patients who remained on 10-mL/kg tidal volume who had the same survival rate as that of the study group of 6 mL/kg, but these data were not published initially. Editorials at that time questioned the study conclusion because it appeared as if the survival difference in the trial was due to the increase in mortality of increasing the tidal volume higher than 10 mL/kg, causing the plateau pressure to go well above the acceptable value, instead of any benefit from the decrease to 6 mL/kg. Additionally, there was an interaction between group assignment (low tidal volume [VT] or high VT) and respiratory system compliance resulting in mortality outcomes. Raising VT in patients with lower compliance increased mortality (42% versus 29%); in contrast, for patients with higher compliance, raising VT decreased mortality (21% versus 37%) compared with low VT (LVT) (P = .003).4Deans K.J. Minneci P.C. Cui X. et al.Mechanical ventilation in ARDS: one size does not fit all.Crit Care Med. 2005; 33: 1141-1143Crossref PubMed Scopus (99) Google Scholar This interaction was confirmed in a secondary analysis of 1,096 patients enrolled in 5 randomized controlled trials of lower versus higher tidal volume ventilatory strategies in acute respiratory distress syndrome showing that the mortality benefit of the low VT strategy occurs in patients with higher elastance (ie, lower compliance).3Eichacker P.Q. Gerstenberger E.P. Banks S.M. et al.Meta-analysis of acute lung injury and acute respiratory distress syndrome trials testing low tidal volumes.Am J Respir Crit Care Med. 2002; 166: 1510-1514Crossref PubMed Scopus (353) Google Scholar This finding suggests that the method used to set the ventilator should match the patient’s lung pathophysiology (the basis for personalized medicine) instead of a fixed ventilator prescription for a tidal volume not based on any actual determination of the patient’s current lung size (known in acute respiratory distress syndrome as the Baby Lung if indeed there is a quite reduced size of available open lung tissue) or compliance. Driving pressure, the difference between the plateau pressure and positive end-expiratory pressure (PEEP), has been found to be the one parameter most consistently associated with lung injury versus lung protection.3Eichacker P.Q. Gerstenberger E.P. Banks S.M. et al.Meta-analysis of acute lung injury and acute respiratory distress syndrome trials testing low tidal volumes.Am J Respir Crit Care Med. 2002; 166: 1510-1514Crossref PubMed Scopus (353) Google Scholar,5Raschke R.A. Stoffer B. Assar S. et al.The relationship of tidal volume and driving pressure with mortality in hypoxic patients receiving mechanical ventilation.PLoS One. 2021; 16e0255812Crossref PubMed Scopus (4) Google Scholar Lung compliance is defined by the change in volume divided by the change in pressure, which is tidal volume/driving pressure so that if the driving pressure is kept safely low but the tidal volume is normal for adults (8 mL/kg of ideal body weight), then that means the compliance is normal (not low). There is no conclusive evidence that 6 mL/kg is better than any other tidal volume, except 12 mL/kg or higher, if the plateau pressure remains safe (<32 cmH2O) in terms of survival, length of time on mechanical ventilation, or barotrauma.5Raschke R.A. Stoffer B. Assar S. et al.The relationship of tidal volume and driving pressure with mortality in hypoxic patients receiving mechanical ventilation.PLoS One. 2021; 16e0255812Crossref PubMed Scopus (4) Google Scholar,6Tobin M. ARDS: Hidden perils of an overburdened diagnosis.Crit Care. 2022; 26: 392Crossref PubMed Scopus (0) Google Scholar Clinicians should continue to use their judgment with each individual case to determine the best mechanical ventilation prescription for every unique patient because, of course, we would never strongly recommend the exact same fluid and vasoactive prescription for every patient in shock.