Truth or Myth: Intra-abdominal Pressure Increases in the Lithotomy Position

Is it feasible to measure intra-abdominal pressure using a balloon-tipped rectal catheter? Results of a validation study

The gold standard to measure intra-abdominal pressure (IAP) is intra-vesical measurement via the urinary bladder. However, this technique is restricted in ambulatory settings because of the risk of iatrogenic urinary tract infections. Rectal IAP measurements (IAP_rect) may overcome these limitations, but requires validation. This validation study compares the IAP_rect technique against gold standard intra-vesical IAP measurements (IAP_ves). IAP_rect using an air-filled balloon catheter and IAP_ves using Foley Manometer Low Volume were measured simultaneously in sedated and ventilated patients. Measurements were performed twice in different positions (supine and HOB 45° elevated head of bed) and with an external abdominal pressure belt. Sixteen patients were included. Seven were not eligible for analysis due to unreliable IAP_rect values. IAP_rect was significantly higher than IAP_ves for all body positions (p < 0.01) and the correlation between IAP_ves and IAP_rect was poor and not significant in each position (p ≥ 0.25, R² < 0.6, Lin's CCC < 0.8, bias - 8.1 mmHg and precision of 5.6 mmHg with large limits of agreement between - 19 to 2.9 mmHg, high percentage error 67.3%, and low concordance 86.2%). Repeatability of IAP_rect was not reliable (R = 0.539, p = 0.315). For both techniques, measurements with the external abdominal pressure belt were significantly higher compared to those without (p < 0.03). IAP_rect has important shortcomings making IAP estimation using a rectal catheter unfeasible because the numbers cannot be trusted nor validated.