Improved ventilation efficiency due to continuous gas flow compared to decelerating gas flow in mechanical ventilation - results of a porcine trial.

Background In pressure-controlled ventilation (PCV) a decelerating gas flow pattern occurs during inspiration and expiration. In contrast, flow-controlled ventilation (FCV) guarantees a continuous gas flow throughout the entire ventilation cycle where the inspiration and expiration phases are simply performed by a change of gas flow direction. Aim of this trial was to highlight the effects of different flow patterns on respiratory variables and gas exchange. Methods Anesthetized pigs were ventilated with either FCV or PCV for one hour and thereafter for 30 minutes each in a cross-over comparison. Both ventilation modes were set with a peak pressure of 15 cmH2 O, positive end-expiratory pressure of 5 cmH2 O, a respiratory rate of 20 /min and a fraction of inspired oxygen at 0.3. All respiratory variables were collected every 15 minutes. Results Tidal volume and respiratory minute volume were significantly lower in FCV (n=5) compared to PCV (n=5) animals (4.6 versus 6.6, MD -2.0 (95% CI -2.6 to -1.4) ml/kg; p<0.001 and 7.3 versus 9.5, MD -2.2 (95% CI -3.3 to -1.0) l/min; p=0.006). Notwithstanding these differences, CO2 -removal as well as oxygenation was not inferior in FCV compared to PCV. Conclusion Mechanical ventilation with identical ventilator settings resulted in lower tidal volumes and consecutive minute volume in FCV compared to PCV. This finding can be explained physically by the continuous gas flow pattern in FCV which necessitates a lower alveolar pressure amplitude. Interestingly, gas exchange was comparable in both groups, which is suggestive of improved ventilation efficiency at a continuous gas flow pattern.