Comparison of intermittent and continuous intra-abdominal pressure monitoring using an in vitro model

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Intra-abdominal pressure (IAP) is increasingly being considered as an important physiologic parameter to be measured in critically ill patients. Traditional methods of monitoring IAP rely on intermittent IAP (IIAP) measurements using indwelling bladder catheters. Recently, a method of continuous IAP (CIAP) monitoring has been developed using a three-way bladder catheter. This study evaluates the reliability of IIAP and CIAP measurement techniques using an in vitro model. An in vitro model of the abdomen was constructed using a 50 l container with a 100 ml infusion bag at the base to simulate a bladder. A three-way catheter tip was centered within the infusion bag filled with 50 ml saline. To simulate IAP the container was filled with water at 5 cm H(2)O increments from 10 to 25 cm H(2)O. Pressures were recorded by observers from a bedside monitor interfaced with a three-way Foley catheter using alternating intermittent and continuous techniques. Each subject was blinded to the known pressure values. Descriptive statistics and a generalised estimating equation (GEE) was used to describe the relationship of IIAP and CIAP to known pressures. One hundred and thirty-two (132) observations were made by 20 subjects for both IIAP and CIAP estimates. In 45.5% of IIAP measures, the estimate was correct, and it was never more than 1 cm H(2)O different from the actual. Similarly, in 38.6% of CIAP measures, the estimate was correct, and was never more than 2 cm H(2)O from the actual. The GEE regression coefficients comparing known pressures with IIAP and CIAP were 1.007 and 0.976 respectively. The minimum and maximum pressure deviations never exceeded more than 1.3 cm H(2)O from the actual. Intermittent IAP and CIAP are both reliable and reproducible methods to measure IAP in an in vitro model. There exists a direct and significant association between both measurements and the actual value. Neither measure was shown to be superior.