Objective: To determine the minimal instillation volume at which an intra-abdominal pressure (IAP) curve can be obtained and to compare this with the IAP measured at 20 ml instilled volume.
Design and setting: Prospective cohort study in the Intensive Care Unit of Ghent University Hospital.
Patients: Twenty-five critically ill sedated and ventilated patients at risk for intra-abdominal hypertension (IAH).
Interventions: IAP was measured transvesically using a custom-designed IAP monitoring set. Measurement was started without any additional instillation of saline and was continued at 1-ml increments up to 10 ml. Finally, IAP was measured with 20 ml instillation volume.
Measurements and results: After each instillation an "oscillation test" was performed. The minimal volume at which the oscillation test was positive was recorded. These values were compared to the IAP obtained using 20 ml saline (IAP20 ml). At 2 ml installed saline volume an oscillation curve could be obtained in all patients. Mean IAP2 ml) was 11.2+/-3.2 mmHg, IAP10 ml) 11.4+/-3.7 mmHg, and IAP20 ml) 11.7+/-3.2 mmHg. In four patients (16%) there was a clinically significant difference of 2 mmHg or more between IAP2 ml and IAP20 ml. The mean difference between IAP20 ml) and IAP2 ml was 0.60+/-0.91 mmHg (95% CI 0.22-0.98).
Conclusions: In this sample of patients at risk for IAH 2 ml saline was sufficient for IAP signal transduction. Higher volumes for transvesical IAP measurement resulted in higher pressure readings in some patients.