The effect of different volumes and temperatures of saline on the bladder pressure measurement in critically ill patients

INTRODUCTION: Intra-abdominal hypertension is common in critically ill patients and is associated with increased severity of organ failure and mortality. The techniques most commonly used to estimate intra-abdominal pressure are measurements of bladder and gastric pressures. The bladder technique requires that the bladder be infused with a certain amount of saline, to ensure that there is a conductive fluid column between the bladder and the transducer. The aim of this study was to evaluate the effect of different volumes and temperatures of infused saline on bladder pressure measurements in comparison with gastric pressure. METHODS: Thirteen mechanically ventilated critically ill patients (11 male; body mass index 25.5 ± 4.6 kg/m(2); arterial oxygen tension/fractional inspired oxygen ratio 225 ± 48 mmHg) were enrolled. Bladder pressure was measured using volumes of saline from 50 to 200 ml at body temperature (35 to 37°C) and room temperature (18 to 20°C). RESULTS: Bladder pressure was no different between 50 ml and 100 ml saline (9.5 ± 3.7 mmHg and 13.7 ± 5.6 mmHg), but it significantly increased with 150 and 200 ml (21.1 ± 10.4 mmHg and 27.1 ± 15.5 mmHg). Infusion of saline at room temperature caused a significantly greater bladder pressure compared with saline at body temperature. The lowest difference between bladder and gastric pressure was obtained with a volume of 50 ml. CONCLUSION: The bladder acts as a passive structure, transmitting intra-abdominal pressure only with saline volumes between 50 ml and 100 ml. Infusion of a saline at room temperature caused a higher bladder pressure, probably because of contraction of the detrusor bladder muscle.