Influence of intra-abdominal pressure on the specificity of pulse pressure variations to predict fluid responsiveness.

BACKGROUND: The positive predictive value of pulse pressure variations (Delta PP) to discriminate patients who should respond to volume expansion (VE) may be altered in mechanically ventilated patients. Our goal was to determine whether intra-abdominal pressure (IAP) measurements could discriminate patients with true-positive Delta PP values versus patients with false-positive Delta PP values. METHODS: We designed a prospective pathophysiologic study in a mixed intensive care unit of a university hospital. Sixteen mechanically ventilated patients with hypotension (SAP, <90 mm Hg) and with Delta PP of 13% or more were included. Cardiac output was assessed using Doppler echocardiography before and after VE; IAP was measured using the bladder pressure method. Patients were classified into two groups according to their response to a standardized VE (500 mL of NaCl 0.9%): responders (>= 15% increase in cardiac output) and nonresponders. RESULTS: Nine patients (57%) were responders, and seven patients (43%) were nonresponders. Before VE, IAP was statistically higher in nonresponders (15 [11-22] mm Hg vs. 9 [6.5-11] mm Hg; p = 0.008). The area under the curve of the receiver operating characteristic curve was 0.9 +/- 0.08. In patients with Delta PP of 13% or more, an IAP cutoff value of 10.5 mm Hg discriminated between responders and nonresponders with a sensitivity of 100% (59-100%) and a specificity of 78% (40-97%). CONCLUSION: An increase in IAP of more than 10.5 mm Hg can decrease the positive predictive value of Delta PP. Hence, in patients prone to present abnormal IAP values, IAP should be measured before performing VE directed by the Delta PP marker. (J Trauma Acute Care Surg. 2015; 78: 994-999. Copyright (C) 2015 Wolters Kluwer Health, Inc. All rights reserved.)