Validation of an Automatic Continuous Urine Output (CUO) and Intra-Abdominal Pressure (IAP) Measuring Device

The system which is the subject of the current study comprises two connected parts, the controller and the disposable.The disposable is a special pressure sensing fluid pump connected serially between the catheter and urine bag. The pump is operated by controlled air pressures sent via three tubes from the controller. The pump operates in strokes, with each stroke passing exactly 1ml of fluid from the input port which is connected to the catheter in the patients' bladder, to the output port, which is connected via a long tube to the urine collection container (bag or other). Since each stroke of the pump is known and constant, and the monitor is counting and timing the strokes both current urine production rate, flow rate and cumulative urine volume over any period can be measured. The pump is also unique in that its design allows the controller to measure the fluid pressure at both the input port, as well as in the output port allowing automatic high resolution Intra-Abdominal pressure monitoring in parallel and without interrupting the Urine Output monitoring.

Ongoing pressure monitoring and supporting algorithm remove the need to manually fill and empty the bladder and avoid interrupting urine output monitoring. The method also delivers multiple per-hour IAP measurements and is able to show trends to correlate to patient angle and condition.

Urine pumping eliminates all problems associated with existing systems and methods for measuring urine output. The volume measurement is accurate since it is measured in a "digital" format, by calculating of number of fixed bolus units transferred. Dependent loop and tube related accumulation are avoided since the pump passes a fixed volume of urine, no matter how it is distributed in the drain tube. Similarly, urine composition, temperature, production rate, specific weight are irrelevant to the pumping accuracy, as well as patient/bed motions and vibrations.

The controller operates the pump in a cyclic fashion. First, it measures the urine pressure inside the patients' bladder, as it is expressed as the pressure in the pump input port. A positive pressure of a few mmHg indicates that there is a minimal volume of urine in the bladder (and also indicate IAP). The controller then runs the pump for a single cycle, removing 1cc of urine from the bladder and repeating the pressure measurement and pump operation until the pressure at the input port drops back to zero - indicating an empty bladder, then stops. This process repeats for the duration of use. UO is calculated by the number of cycles and time of each divided by the relevant timeframe, normally cc/h.Providing a continuous fully automated and accurate method to measure IAP could be important in several clinical setups. Current reference methods for IAP measurement are intermittent and cumbersome. They are affected by body position, zero reference, and highly user dependent.

Study design allows a large range of pressure levels assessed simultaneously between the study device and the gold standard.