The effect of different reference transducer positions on intra-abdominal pressure measurement: a multicenter analysis

Objective: To investigate the effect of different reference transducer positions on intra-abdominal pressure (IAP) measurement. Three reference levels were studied: the symphysis pubis; the phlebostatic axis; and the midaxillary line at the level of the iliac crest. Design: Prospective cohort study. Setting: The intensive care units of participating hospitals Patients and participants: One hundred thirty-two critically ill patients at risk for intra-abdominal hypertension (IAH). Interventions: In each patient, three sets of IAP measurements were obtained in the supine position, using the different reference levels. The IAP measurements obtained at the different reference levels were compared using a paired t-test and Bland-Altman statistics were calculated. Measurements and results: IAP_phlebostatic (9.9 ± 4.67 mmHg) and IAP_pubis (8.4 ± 4.60 mmHg) were significantly lower that IAP_midax (12.2 ± 4.66 mmHg; p < 0.0001 for both comparisons). The bias between the IAP_midax and IAP_pubis was 3.8 mmHg (95% CI 3.5-4.1) and 2.3 mmHg (95% CI 1.9-2.6) between the IAP _midax and the IAP_phlebostatic. The precision was 3.03 and 3.40, respectively. Conclusions: In the supine position, IAP_midax is higher than both IAP_phlebostatic and IAP_pubis, differences found to be clinically significant; therefore, the symphysis pubis or phlebostatic axis reference lines are not interchangeable with the midaxillary level.