Restricted accessResearch articleFirst published online 2000-9
The effects of Pressure Control versus Volume Control Assisted Ventilation on Patient work of Breathing in Acute Lung Injury and Acute Respiratory Distress Syndrome
BACKGROUND: Patient work of breathing (WOB) during assisted ventilation is reduced when inspiratory flow (V₁) from the ventilator exceeds patient flow demand. Patients in acute respiratory failure often have unstable breathing patterns and their requirements for V₁ may change from breath to breath. Volume control ventilation (VCV) traditionally incorporates a pre-set ventilator V₁ that remains constant even under conditions of changing patient flow demand. In contrast, pressure control ventilation (PCV) incorporates a variable decelerating flow wave form with a high ventilator V₁ as inspiration commences. We compared the effects of flow patterns on assisted WOB during VCV and PCV. METHODS: WOB was measured with a BICORE CP-100 monitor (incorporating a Campbell Diagram) in a prospective, randomized cross-over study of 18 mechanically ventilated adult patients with acute lung injury (ALI) or acute respiratory distress syndrome (ARDS). Tidal volume, inspiratory time, and mean ventilator V₁ were constant in each mode. RESULTS: At comparable levels of respiratory drive and minute ventilation, patient WOB was significantly lower with PCV than with VCV (0.59 ± 0.42 J/L vs 0.70 ± 0.58 J/L, respectively, p < 0.05). Ventilator peak V₁ was significantly higher with PCV than with VCV (103.2 ± 22.8 L/min vs 43.8 L/min, respectively, p < 0.01). CONCLUSIONS: In the setting of ALI and ARDS, PCV significantly reduced patient WOB relative to VCV. The decrease in patient WOB was attributed to the higher ventilator peak V₁ of PCV.
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