Comparison of ability of pulse pressure variation to predict fluid responsiveness in prone and supine position: an observational study

We aimed to compare the ability of pulse pressure variation (PPV) to predict fluid responsiveness in prone and supine positions and investigate effect of body mass index (BMI), intraabdominal pressure (IAP) and static respiratory compliance (CS) on PPV. A total of 88 patients undergoing neurosurgery were included. After standardized anesthesia induction, patients' PPV, stroke volume index (SVI), CS and IAP values were recorded in supine (T1) and prone (T2) positions and after fluid loading (T3). Also, PPV change percentage (PPV%) between T2 and T1 times was calculated. Patients whose SVI increased more than 15% after the fluid loading were defined as volume responders. In 10 patients, PPV% was -20%. All of these patients had CST230kg/m(2), and two had IAP(T2)>15mmHg. In 16 patients, PPV% was 20%. In these patients, 10 had CST230kg/m(2), and 12 had IAP(T2)>15mmHg. Thirty-nine patients were volume responder. When all patients were examined for predicting fluid responsiveness, area under curves (AUC) of PPVT2 (0.790, 95%CI 0.690-0.870) was significantly lower than AUC of PPVT1 (0.937, 95%CI 0.878-0.997) with ROC analysis (p=0.002). When patients whose CST2 was 30kg/m(2) were excluded from analysis separately, AUC of PPVT2 became similar to PPVT1. PPV in the prone can predict fluid responsiveness as good as PPV in the supine, only if BMI is 31ml/cmH(2)O