Diagnostic Accuracy of Pulse Pressure Variation Compared to Thoracic Fluid Content in Mechanically Ventilated Patients after Cardiac Surgery

Background: In clinical area, assessment of body fluid and determination of the intravascular volume after major surgeries such as heart surgery is a significant challenge. The initial purpose of intravascular volume assessment in patients with hemodynamic instability is to determine whether they would benefit from fluid administration or not. Objectives: This study aims to compare pulse pressure variation (PPV) compared to thoracic fluid content in checking out and optimizing fluid volume in mechanically ventilated patients admitted to intensive care unit after cardiac surgery. Methods: In the present study a prospective descriptive-analytic design was used. Thirty mechanically ventilated patients admitted to intensive care units of Rajaie heart center, Tehran, Iran, were recruited in the current study after cardiac surgery based on inclusion criteria. Data collection tools included demographic and clinical data sheets. Hemodynamic parameters such as CVP and pulse pressure were recorded by bedside monitoring. Thoracic fluid content (TFC) was measured by non-invasive continuous cardiac output monitoring (NICCOMO) system. Data were analyzed in SPSS version 15, using statistical tests. Results: The mean values of CVP, before and five minutes after fluid administration were significantly different (10.10±6.01 mmHg and 12.37 ± 6.34 mmHg, respectively, P = 0.015). The mean changes in arterial pulse pressure, before and five minutes after fluid administration were significantly different (16.94 ± 8.32 mmHg and 12.77 ± 4.02 mmHg, respectively, P = 0.005). PPV greater than 13% had sensitivity, specificity and positive predictive value of 40%, 71% and 75% respectively while CVP greater than 5 mmHg had sensitivity, specificity and positive predictive of 13%, 85% and 66% respectively compared with cardiac index as the gold standard for fluid responsiveness. These findings suggest a higher diagnostic power of PPV compared to CVP to assess fluid volume. Conclusions: It seems that in the mechanically ventilated patients after heart surgery, PPV dynamic index is preferred to CVP static index to evaluate and maintain fluid volume.