Determining normal values for intra-abdominal pressure

Background: Intra-abdominal pressure (IAP) measurements can be used for the early detection and management of the abdominal compartment syndrome. IAP values are widely thought to be atmospheric or subatmospheric. However, there are no reports that describe normal IAP values using urinary bladder pressure measurements in patients not suspected of having a raised IAP level. This study sought to determine these normal values to aid our interpretation of IAP measurements in post-surgical patients or patients with suspected increased IAP. Methods: Urinary bladder pressure measurements were carried out in 40 men and 18 women awake medical or non-abdominal surgery inpatients with existing indwelling catheters. Measurements were made in the supine, 30 degrees and 45 degrees sitting positions. Comparisons were carried out to determine the effects on urinary bladder pressure of body position, sex and a suspected diagnosis of benign prostatic hypertrophy. Results: Median values for IAP were higher if measured in a more upright position (P < 0.0001). Median values were supine, 9.5 cmH(2)O (range, 1-18 cmH(2)O); 30 degrees upright, 11.5 cmH(2)O (range, 3-19 cmH(2)O); and at 45 degrees upright, 14.0 cmH(2)O (range, 4-22 cmH(2)O). Measurements recorded were neither atmospheric nor subatmospheric. IAP was higher in men compared with women in the supine and 30 degrees positions (P < 0.05) but not in the 45 degrees position (P = 0.083). There was no significant difference between patients with and without suspected benign prostatic hypertrophy. Conclusions: Normal IAP using urinary bladder pressure in awake patients are above atmospheric pressure. As a patient is moved from the supine into the upright position, IAP measurements increase.