Automatic Adaptation of Tourniquet Pressure During Surgery to Improve Patient Safety
Our objective is to determine the feasibility of improving surgical patient safety by automatically adapting the pressure of a pneumatic tourniquet system to the minimum effective pressure needed to reliably stop arterial blood-flow into a patient’s limb while facilitating surgery. That minimum quantity, called ‘limb occlusion pressure’ (LOP), is the minimum pressure required, at a specific time in a specific tourniquet cuff applied to a specific patient’s limb at a specific location, to stop the flow of arterial blood into the limb distal to the cuff. LOP is affected by variables including: limb size, shape and tissue characteristics; physiologic parameters such as blood pressure, heart rate and temperature; and tourniquet cuff shape, width, design, position and application technique.
Some commercial tourniquet systems allow LOP to be automatically estimated preoperatively. However, LOP is known to vary intraoperatively, especially in response to changes in blood pressure and other physiologic variables. Existing systems do not adapt automatically to intraoperative changes in LOP. Adapting pressure to remain at a minimum above LOP is important for patient safety because many studies have shown that higher tourniquet pressures are associated with higher probabilities of patient injuries.
This study investigates the feasibility of an adaptive tourniquet by using a commercial tourniquet instrument to estimate LOP preoperatively, periodically measuring changes in blood pressure and heart rate intraoperatively, incorporating that blood pressure and heart rate data into an algorithm for estimating intraoperative LOP, and finally comparing the algorithmically estimated LOP to actual LOP measured at the end of each surgical procedure.
A total of 45 surgical procedures have been completed following the above protocol. Results indicate that an algorithm can be devised to enable a surgical tourniquet system to adapt automatically to LOP changes related to intraoperative changes in blood pressure.