What is the normal intra-abdominal pressure in critically ill children and how should we measure it?

Introduction: The intravesical method has been validated and is considered the gold standard for indirect intra-abdominal pressure (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 erroneous 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 saline 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 according to weights 0-10 kg, >10-20 kg, and >20-50 kg. Descriptive 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 considered elevated in children.