The influence of different ventilatory modes on the intensity of pulse pressure variation
© BioMed Central Ltd 2007
Published: 19 June 2007
Pulse pressure variation (PPV) has been recommended to evaluate the cardiac responsiveness to fluid infusion in mechanically ventilated patients with sepsis shock or following cardiac surgery. The recommendation is that PPV measurements must be performed during the volume-controlled ventilatory mode (VC) and not with the pressure control mode (PC).
To test the hypothesis that the PC should not cause an important change on PPV when compared with the VC during mechanical ventilation.
A prospective, nonrandomized, observational and comparative study that compares effects on PPV of the VC with another three PC ventilatory settings applied in sedated and mechanically ventilated critically ill patients with an arterial catheter in place. Initial/control setting (S1): VC with tidal volume (Vt) = 10 ml/kg; setting 2 (S2): PC with the peak pressure (Pp) obtained in S1; setting 3 (S3): PC with the Pp set in the plateau pressure level obtained in S1; setting 4 (S4): PC with pressure values determined with the Vt set at 10 ml/kg. All settings included PEEP of 5 cmH2O and a respiratory rate of 15 rpm. The mean arterial pressure and PPV obtained in each ventilatory set are compared with each other using the paired Student t test.
Thirty-four patients were evaluated. The Pp was significantly lower in S3 and S4 (P < 0.001). The Vt was significantly greater in S2 (P < 0.001) with a parallel PPV increment at this time (S2) (P < 0.001). We found strong clinical concordance between S1 and S4 (accuracy = 98.1%, kappa = 0.93, P < 0.001). Significant but weaker concordance was found between S1 and S2 (accuracy = 91.2%, kappa = 0.80, P < 0.001) and between S1 and S3 (accuracy = 94.1%, kappa = 0.86, P < 0.001).
The pressure-controlled mode should not cause important changes or significant clinical misinterpretation on PPV when compared with the volume-controlled mode during mechanical ventilation. These findings are especially evident when the pressure-controlled mode with the Vt limited at 10 ml/kg (S4 set) is used, demonstrated by the best accuracy on reproducing the PPV obtained during the volume-controlled mode.