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1 0 6 O U T P AT I E N T S U R G E R Y M A G A Z I N E O N L I N E | M A R C H 2 0 1 4 and control the depth of penetration of arterial blood beneath a tourniquet cuff. This is a similar objective to the algorithm-driven intraoperative LOP adjustment, only the method used is different. You want an intraoperative estimate of how much pressure is required to occlude blood flow, but rather than looking at measures like blood pressure and heart rate, we're investigat- ing how, through the use of sensor technology, you could focus specifically on the limb itself. The sensor would essentially be able to visualize the artery underneath the cuff. To understand the sensor technology, imagine squeezing a hose with water running through it. In this scenario, the hand squeezing — applying pressure — represents the tourniquet cuff; the hose represents the artery; and the water represents a patient's blood. As you squeeze the hose harder, water is directed away from the central point of where you're squeezing. Squeeze lighter and water moves back toward the center, and may start getting past where you're squeezing. With that image in mind, picture blood flowing underneath a deflated tourniquet cuff. When you inflate the cuff, the greatest pressure is applied at the center of the cuff. That is where the artery will first be pinched and the blood flow will stop. Once you apply more pressure, the point of where the artery is occluded gets pushed back further underneath the cuff. An ultrasound sensor system would be able to visualize underneath the cuff whether the artery is occluded. If it isn't occluded, the sensor will tell the tourniquet to increase pressure. During this process, the sensor contin- ues to visualize underneath the cuff and always knows whether blood is going to pass through the central point of pressure (as can happen when you start releasing your grip on the hose). The sensor would visualize the arterial walls and see that the blood is going to leak through and then, accordingly, adjust tourniquet pressures. The 2 methods we're investigating will hopefully let providers not just set LOP at the beginning of a procedure, but vary it throughout the surgery to T O U R N I Q U E T S OSE_1403_part2_Layout 1 3/5/14 10:54 AM Page 106