The effects of prone positioning on intraabdominal pressure and cardiovascular and renal function in patients with acute lung injury

To detect any harmful effects of prone positioning on intraabdominal pressu re (IAP) and cardiovascular and renal function, we studied 16 mechanically ventilated patients with acute lung injury randomly in prone and supine pos itions, without minimizing the restriction of the abdomen. Effective renal blood flow index and glomerular filtration rate index were determined by th e paraaminohippurate and inulin clearance techniques. Prone positioning res ulted in an increase in IAP from 12 +/- 4 to 14 +/- 5 mm Hg (P < 0.05), Pao (2)/fraction of inspired oxygen from 220 +/- 91 to 267 +/- 82 mm Hg (P < 0. 05), cardiac index from 4.1 +/- 1.1 to 4.4 +/- 0.7 L/min (P < 0.05), mean a rterial pressure from 77 +/- 10 to 82 +/- II mm Hg (P < 0.01), and oxygen d elivery index from 600 +/- 156 to 648 +/- 95mL . min(-1).m(-2) (P < 0.05). Renal fraction of cardiac output decreased from 19.1% +/- 12.5% to 15.5% +/ -: 8.8% (P < 0.05), and renal vascular resistance index increased from 1176 2 +/- 6554 dynes .s . cm(-5).m(2) to 15078 +/- 10594 dynes .s . cm(-5).m(2) (P < 0.05), whereas effective renal blood now index, glomerular filtration rate index, filtration fraction, urine volume, fractional sodium excretion, and osmolar and free water clearances remained constant during prone posit ioning. Prone positioning, when used in patients with acute lung injury, al though it is associated with a small increase in IAP, contributes to improv ed arterial oxygenation and systemic blood Bow without affecting renal perf usion and function. Apparently, special support to allow free chest and abd ominal movement seems unnecessary when mechanically ventilated, hemodynamic ally stable patients without abdominal hypertension are proned to improve g as exchange.