Introduction: Tonometer determined Phi has been shown to be a valuable tool in POCVS to predict early complications in adults. This has not yet been demonstrated in pediatric patients. Our goal was to determine the usefulness of Phi in comparison with other parameters (PRISM, arterial pH and arterial lactic content), as independent variables, in predicting adverse effects during POCVS which required extracorporeal circulation.Methods: 57 patients (mean age 4.1 ± 3.5 years) were prospectively studied. Phi was determined within the first two hours and again twelve hours after admission to PICU, after cardiovascular surgery. Dependent variables (adverse reaction or complications to predict) were: 1) multiple organ failure 2) infection 3) hemodynamic unstability (Hemodynamic Clinical Score >2)(1), 4) Magnitude of Therapeutic Resources Employed (MTRE)(2). Predicted importance of independent variables was determined by multiple logistic regression analysis and as Odds Ratio (OR). Confidence interval (CI) at 95% was obtained by SD of β coefficient. Results: Twenty four patients presented one or more post operative complications. Of all the co-variants observed, PRISM was the only one to show significant predictive value for the following independent variables: Infections (p<0.032, OR=1,27, CI=1.03-1.57) and MTRE(p<0.035, OR=1.61, CI=1.05-2.49). No complications due to tonometer placement were observed. Conclusions: 1. We were not able to determine the predictive value of Phi for adverse events in pediatrics POCVS. 2. Of the other variables studied, PRISM was the only one to show some predictive value.