Mechanical ventilation guided by esophageal pressure in acute lung injury

Abstract

Background: Survival of patients with acute lung injury or the acute respiratory distress syndrome (ARDS) has been improved by ventilation with small tidal volumes and the use of positive end-expiratory pressure (PEEP); however, the optimal level of PEEP has been difficult to determine. In this pilot study, we estimated transpulmonary pressure with the use of esophageal balloon catheters. We reasoned that the use of pleural-pressure measurements, despite the technical limitations to the accuracy of such measurements, would enable us to find a PEEP value that could maintain oxygenation while preventing lung injury due to repeated alveolar collapse or overdistention.

Methods: We randomly assigned patients with acute lung injury or ARDS to undergo mechanical ventilation with PEEP adjusted according to measurements of esophageal pressure (the esophageal-pressure-guided group) or according to the Acute Respiratory Distress Syndrome Network standard-of-care recommendations (the control group). The primary end point was improvement in oxygenation. The secondary end points included respiratory-system compliance and patient outcomes.

Results: The study reached its stopping criterion and was terminated after 61 patients had been enrolled. The ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen at 72 hours was 88 mm Hg higher in the esophageal-pressure-guided group than in the control group (95% confidence interval, 78.1 to 98.3; P=0.002). This effect was persistent over the entire follow-up time (at 24, 48, and 72 hours; P=0.001 by repeated-measures analysis of variance). Respiratory-system compliance was also significantly better at 24, 48, and 72 hours in the esophageal-pressure-guided group (P=0.01 by repeated-measures analysis of variance).

Conclusions: As compared with the current standard of care, a ventilator strategy using esophageal pressures to estimate the transpulmonary pressure significantly improves oxygenation and compliance. Multicenter clinical trials are needed to determine whether this approach should be widely adopted. (ClinicalTrials.gov number, NCT00127491.)

Figure 1. Ventilator Settings According to the Protocol

For the intervention group, keep the partial pressure of arterial oxygen (PaO₂) between 55 and 120 mm Hg or keep the oxygen saturation, as measured by pulse oximeter, between 88 and 98% by using the ventilator settings in one column at a time. Set the positive end-expiratory pressure (PEEP) at such a level that transpulmonary pressure during end-expiratory occlusion (P_Lexp) stays between 0 and 10 cm of water, and keep transpulmonary pressure during end-inspiratory occlusion at less than 25 cm of water. For the control group, keep PaO₂ between 55 and 120 mm Hg (or keep oxygen saturation according to pulse oximeter between 88 and 98%) by using the ventilator settings in one column at a time. Set the PEEP and tidal volume at such levels that the airway pressure during end-inspiratory occlusion stays at less than 30 cm of water. In both groups, apply ventilation with either pressure-control ventilation or volume-control ventilation with a ratio of inspiratory time to expiratory time between 1:1 and 1:3 to minimize dys-synchrony between the patient and the ventilator while achieving a tidal volume of 6±2 ml per kilogram of predicted body weight and a respiratory rate of 35 breaths per minute or less. Lung-recruitment maneuvers are permitted to reverse episodic hypoxemia after suctioning or inadvertent airway disconnection, but not on a routine basis.

Figure 2. Respiratory Measurements at Baseline and at 24, 48, and 72 Hours in the Control and Esophageal-Pressure–Guided Groups

Means and standard errors are shown. P values were calculated by repeated-measures analysis of variance. Panel A shows the ratio of the partial pressure of arterial oxygen to the fraction of inspired oxygen (PaO₂:FiO₂), Panel B respiratory-system compliance, Panel C the ratio of dead space to tidal volume, Panel D positive end-expiratory pressure (PEEP), Panel E transpulmonary end-expiratory pressure, Panel F plateau pressure, and Panel G transpulmonary end-inspiratory pressure.