Pediatric Critical Care What is the normal intra-abdominal pressure in critically ill children and how should we measure it?* J. Chiaka Ejike, MD, FAAP; Khaled Bahjri, MD, MPH; Mudit Mathur, MD, FAAP I ntra-abdominal pressure (IAP) can easily be monitored at the bedside, and several methods have been used for obtaining this measure- ment. These methods include the direct intraperitoneal method as well as indirect measurements by the intragastric, intra- rectal, venacaval, intrauterine, and intra- vesical methods (1–3). Because of its in- vasiveness and potential for serious com- plications, such as peritonitis and bowel perforation, the direct method of mea- surement is rarely used (4). The intravesical method has been val- idated and is now considered the gold standard for indirect IAP measurements (3, 5–9). This method involves the instil- lation of a predetermined volume of ster- ile saline into the bladder via a urethral catheter and measuring the transduced intra-abdominal pressure after allowing for a period of equilibration. Reported volumes used for measuring IAP by the intravesical technique range from 1 mL/kg in children (6, 10) to 50 –250 mL in adults (3, 9, 11, 12). The World Society on Abdominal Compartment Syndrome (WSACS) recommends using 1 mL/kg for children with a maximum of 25 mL; how- ever, this recommendation is based on very little pediatric data (13, 14). Using inappropriate volumes for IAP measure- ments may give erroneous readings, which could affect clinical intervention (4, 15, 16). The optimal volume for IAP measure- ments using the intravesical technique in children has not been adequately studied, yet. The main purpose of this study was to determine the optimal volume for measuring IAP using the intravesical technique in critically ill children of vary- ing sizes and to determine normal intra- abdominal pressures for this population. Interpretation of measured IAP is challenging because normal IAP in chil- dren is not known. As a result, clinicians currently use definitions of elevated IAP that are extrapolated from adult patient data. Several studies have demonstrated that critically ill patients are at highest risk for developing abdominal compart- ment syndrome (ACS) (17–21). There- fore, we sought to determine normal IAP in critically ill children so that elevated IAP could be better defined. MATERIALS AND METHODS The Institutional Review Board of Loma Linda University Children’s Hospital approved the study protocol. Mechanically ventilated children younger than 18 yrs of age and weighing 50 kg who were admitted to the pediatric intensive care unit (PICU) were eligible for the study. Ninety- six children were enrolled after parental/ guardian consent. Enrollment was performed within the first 24 hrs of PICU admission. All patients received intravenous sedatives with or without chemical neuromuscular blockade in doses determined by the critical care team, who were not involved in the study. *See also p. 2215. From the Department of Pediatrics (JCE, MM), Division of Pediatric Critical Care, Loma Linda Univer- sity, School of Medicine, Loma Linda, California; and the Department of Epidemiology and Biostatistics (KB), Loma Linda University, School of Public Health, Loma Linda, California. Supported, in part, by a grant from WolfeTory Medical Inc. For information regarding this article, E-mail: jejike@ahs.llumc.edu The authors have not disclosed any potential con- flicts of interest. Copyright © 2008 by the Society of Critical Care Medicine and Lippincott Williams & Wilkins DOI: 10.1097/CCM.0b013e31817b8c88 Introduction: The intravesical method has been validated and is considered the gold standard for indirect intra-abdominal pres- sure (IAP) measurements. In adults, a standard volume (25 mL) is instilled into the bladder to measure IAP. However, the optimal volume for accurate IAP measurements in children has not been well studied and using inappropriate volumes could give errone- ous IAP readings. Objective: To determine the normal IAP in critically ill children and the optimal volume for IAP measurement by the intravesical method in this population. Design: Prospective observational study. Setting: Tertiary pediatric intensive care unit. Patients: Ninety-six mechanically ventilated children younger than 18 yrs of age with no clinical evidence of intra-abdominal hypertension. Measurements and Results: Graduated volumes of normal sa- line in increments of 3–50 mL were instilled in the bladder via a urethral catheter. IAP was recorded by using the AbViser device (WolfeTory Medical, Inc., Salt Lake City, UT) with each instillation. A pressure–volume curve was generated for every patient, and the minimum and mean optimal volumes were determined from this curve. Data were analyzed by stratification of patients ac- cording to weights 0 –10 kg, >10 –20 kg, and >20 –50 kg. De- scriptive statistics was used for statistical analysis. Normal IAP for critically ill children was 7  3 and was similar in the different weight groups (p  .745). Although the mean optimal volume to measure accurate IAP was variable in the different weight groups, the minimum optimal volume was 3 mL irrespective of weight. Conclusions: Mean IAP in critically ill children is 7  3 mm Hg. The minimum optimal volume needed to accurately measure IAP by the intravesical method in children is 3 mL. We recommend that 3 mL be the standard instillation volume for IAP measurement by the intravesical method in children. IAP >10 mm Hg should be consid- ered elevated in children. (Crit Care Med 2008; 36:2157–2162) KEY WORDS: accurate; volumes; intra-abdominal pressure; mea- surements; vesical 2157 Crit Care Med 2008 Vol. 36, No. 7