Pressure infusor devices. Do they generate the pressures indicated?

Three currently available pressure infusor devices, based on three different principles, were tested to see if the pressure reading on the infusor manometer corresponds to the pressure generated in the infusion system. Each device was tested in two ways. First, the pressure generated in the infusion system was measured when the infusor bag pressure was maintained at 300 mmHg while the infusion bag was emptied in aliquots of 50 ml. Second, the pressures in the infusor bag required to maintain a pressure of 300 mmHg were measured as the infusion bag was emptied stepwise. The results reveal surprisingly large discrepancies between the pressure registered on the infusor manometer and the actual pressure generated in the fluid, which are not due to manometer inaccuracy. The degree of discrepancy depends on the amount of fluid that remains in the infusion bag and, when the infusor manometer shows a pressure of 300 mmHg, pressure in the fluid can be as much as 170 mmHg above or 200 mmHg below this value. Furthermore, it was impossible to maintain a pressure of 300 mmHg in the infusion system using one of the devices despite the fact that 100 ml fluid remained. The clinical significance of these findings is discussed.