Feasibility of Setting the Tidal Volume Based on End-Expiratory Lung Volume: A Pilot Clinical Study.

OBJECTIVES

To assess the feasibility of setting the tidal volume (TV) as 25% of the actual aerated lung volume (rather than on ideal body weight) in patients with Acute Respiratory Distress Syndrome (ARDS).

DESIGN

Physiologic prospective single-center pilot study.

SETTING

Medical ICU specialized in the care of patients with ARDS.

PATIENTS: Patients with moderate-severe ARDS deeply sedated or paralyzed, undergoing controlled mechanical ventilation with a ventilator able to measure the end-expiratory lung volume (EELV) with a washin, washout technique.

INTERVENTIONS: Three-phase study (baseline, strain-selected TV setting, ventilation with strain-selected TV for 24 hr). The TV was calculated as 25% of the measured EELV minus the static strain due to the applied positive end-expiratory pressure.

MEASUREMENTS AND MAIN

RESULTS

Gas exchanges and respiratory mechanics were measured and compared in each phase. In addition, during the TV setting phase, driving pressure (DP) and lung strain (TV/EELV) were measured at different TVs to assess the correlation between the two measurements. The maintenance of the set strain-selected TV for 24 hours was safe and feasible in 76% of the patients enrolled. Three patients dropped out from the study because of the need to set a respiratory rate higher than 35 breaths per minute to avoid respiratory acidosis. The DP of the respiratory system was a satisfactory surrogate for strain in this population.

CONCLUSIONS

In our population of 17 patients with moderate to severe ARDS, setting TV based on the actual lung size was feasible. DP was a reliable surrogate of strain in these patients, and DP less than or equal to 8 cm H2O corresponded to a strain less than 0.25.