Pulse pressure variability during hemorrhage and reinfusion in piglets: effects of age and tidal volume

The dynamic change in arterial pulse pressure during mechanical ventilation (PPV) predicts fluid responsiveness in adults but may not be applicable to pediatric patients. We compared PPV during hemorrhage and reinfusion in immature vs mature piglets at two clinically relevant tidal volumes (VT).

Following Institutional Animal Care Committee approval, we measured hemodynamics and PPV in two groups of piglets, 10-15 kg (immature, n = 9) and 25-30 kg (mature, n = 10), under stable intravenous anesthesia at VT = 8 and 10 mL·kg(-1). Measurements were taken at baseline, with blood withdrawal in 5 mL·kg(-1) steps up to 30 mL·kg(-1), and during stepwise reinfusion. For each age group and VT, we constructed receiver operating characteristic (ROC) curves to determine the threshold value that was predictive of fluid responsiveness.

Pulse pressure variability was significantly lower in immature vs mature pigs and at VT 8 vs VT 10 at every measurement period. The difference in PPV induced by changing VT was less in immature animals. Significant areas under the ROC curve were obtained in immature pigs at both VTs but in mature animals at VT 10 alone. A PPV threshold was calculated to be 8.2% at VT 8 and 10.9% at VT 10 in immature animals vs 15.9% at VT 10 in mature animals, but sensitivity and specificity were only 0.7.

Pulse pressure variability values are lower and less sensitive to VT in immature vs mature pigs. Adult PPV thresholds do not apply to pediatric patients, and a single PPV value representing fluid responsiveness should not be assumed.