Work of Breathing During Lung-Protective Ventilation in Patients With Acute Lung Injury and Acute Respiratory Distress Syndrome: A Comparison Between Volume and Pressure-Regulated Breathing Modes

BACKGROUND: Pressure-control ventilation (PCV) and pressure-regulated volume-control (PRVC) ventilation are used during lung-protective ventilation because the high, variable, peak inspiratory flow rate (V˙_I) may reduce patient work of breathing (WOB) more than the fixed V˙_I of volume-control ventilation (VCV). Patient-triggered breaths during PCV and PRVC may result in excessive tidal volume (V_T) delivery unless the inspiratory pressure is reduced, which in turn may decrease the peak V˙_I. We tested whether PCV and PRVC reduce WOB better than VCV with a high, fixed peak V˙_I (75 L/min) while also maintaining a low V_T target.

METHODS: Fourteen nonconsecutive patients with acute lung injury or acute respiratory distress syndrome were studied prospectively, using a random presentation of ventilator modes in a crossover, repeated-measures design. A target V_T of 6.4 ± 0.5 mL/kg was set during VCV and PRVC. During PCV the inspiratory pressure was set to achieve the same V_T. WOB and other variables were measured with a pulmonary mechanics monitor (Bicore CP-100).

RESULTS: There was a nonsignificant trend toward higher WOB (in J/L) during PCV (1.27 ± 0.58 J/L) and PRVC (1.35 ± 0.60 J/L), compared to VCV (1.09 ± 0.59 J/L). While mean V_T was not statistically different between modes, in 40% of patients, V_T markedly exceeded the lung-protective ventilation target during PRVC and PCV.

CONCLUSIONS: During lung-protective ventilation, PCV and PRVC offer no advantage in reducing WOB, compared to VCV with a high flow rate, and in some patients did not allow control of V_T to be as precise.