OBJECTIVETo investigate the effects of different reference point on intra-abdominal pressure (IAP) measurement.

METHODSNine critically ill patients with risk of intra-abdominal hypertension (IAH) were studied from July 2008 to June 2010, all of the patients were equipped with abdominal cavity drain and urinary drainage tube. By which IAP was measured using direct and indirect methods respectively. The symphysis pubis, phlebostatic axis and the midaxillary line at the level of the iliac crest were defined as reference points. According to the different reference point, three sets of IAP measurements were obtained in the supine position with each method and kept as IAP(S), IAP(P), IAP(I). Bland-Altman method analysis and Pearson's correlation were performed to evaluate the relationships between results from different reference points with direct and indirect methods. Paired t-test was performed to evaluate the differences among different reference points.

RESULTSSixty measurements of IAP(S), IAP(P) and IAP(I) were obtained. In direct measurement through abdominal cavity drain, IAP(I) (13.8 ± 3.9) mmHg (1 mmHg = 0.133 kPa) was significantly higher than IAP(P) (12.8 ± 3.6) mmHg and IAP(S) (9.1 ± 3.6) mmHg, P < 0.05; while in indirect measurement through urinary drainage tube, IAP(I) (12.7 ± 3.2) mmHg was significantly higher than IAP(P) (11.7 ± 2.9) mmHg and IAP(S) (7.9 ± 3.0) mmHg too, P < 0.05. In either direct or indirect method, IAP(P) was higher than IAP(S), P < 0.05. And good correlations were found among IAP(S), IAP(P) and IAP(I).

CONCLUSIONSIn the supine position, pressure obtained via the bladder could reflect authentic IAP. But selection of reference point has great impact on IAP measurement.