ADJUSTABLE PRESSURE Investigators hope to soon develop a tourniquet that lets you vary limb occlusion pressure (LOP) throughout the surgery to account for the changes that occur during a case.

In the past few years, a number of new devices have raised the bar on tourniquet safety, and investigators aren't stopping there: New developments may transform the technology even further, hopefully letting providers not just set limb occlusion pressure (LOP) at the beginning of a procedure, but have the means to vary it throughout the surgery to account for the changes that occur during a case. Read on to learn about new tourniquet technology available today and technology you can hopefully look forward to seeing over the next few years.

1. Integrated cuff testing. You'll find this feature in some of today's most modern tourniquet systems. It lets you test cuffs, tubing and connectors for potentially hazardous leakage. By pressing a single button in the system, the cuff will inflate by itself and perform a test to see if there is there a leak. The system will find even a pinhole leak that's not easy for the naked to eye detect. This technology can be used during surgery as well as before and after procedures to let you know whether the cuff is working or will work properly. While a slow leak itself isn't likely to harm patients, it can indicate a more serious potential failure of the cuff, which would cause blood to suddenly enter the surgical field and create challenges for the operative team.

2. Alarms to detect cuff depressurization failure. It's extremely important for a cuff to depressurize entirely when deflation is intended. But this doesn't always happen. The surgical staff may think the cuff is completely deflated, but if depressurization fails, it will likely remain inflated for an extended — and unnecessary — period of time.

If the cuff is at a pressure below the limb occlusion pressure (LOP) — essentially the minimum required pressure to occlude blood flow into the limb — there will be arterial occlusion but not venous occlusion. This results in blood being pumped into the limb, but since there's still pressure left in the cuff, no blood can get pumped out of the limb. As a result, there could be limb engorgement. To ensure cuff depressurization, some tourniquet instruments now include an alarm that sounds when the technology detects failure, informing staff of the need to investigate and remove the cuff.

3. Limb protection. Studies have shown that without proper limb protection, high pressures, high-pressure gradients and shear forces applied to skin and soft tissues underneath a tourniquet cuff can lead to skin and soft tissue injuries. It's not uncommon to use cast padding or stockinette as protection, and while these are effective, studies have revealed that the limb protection sleeves that have been developed to specifically match to the limb and tourniquet cuff size provide more effective protection. Furthermore, there is evidence that the greatest safety is achieved through the use of limb protection sleeves consisting of 2-layer material specifically matched to the limb and cuff size.

LIMB OCCLUSION PRESSURE Some tourniquet systems can deliver the minimum amount of tourniquet pressure for each patient.

4. Personalized tourniquets. A recent introduction of personalized tourniquet cuffs has also resulted in safer and more effective tourniquet use. Personalized cuffs are designed to better match patient limb size and shape. This delivers a more efficient application of cuff pressure to the limb, letting you use lower and safer tourniquet pressures. Personalization of tourniquets is critical for addressing the needs of different patient populations. For example, there are pediatric populations and bariatric populations, and there are patients with tapered limbs and patients with cylindrical limbs. The 2 aspects focused on here speak to the different sizes of patients and different shape of their limbs.

When you're looking at size, there are innovations in pediatric and bariatric cuffs that will let you meet the needs of younger and older patients with smaller and larger limb sizes. That's one aspect of personalization.

The other aspect speaks to the shape of limbs. Historically, cuffs have been mostly cylindrical. These had to be fit onto a tapered limb, which didn't result in as good of a fit, requiring the use of higher pressures to occlude the limb.

Now available are variable contour cuffs that let you adjust and fit limbs that are different shapes. These allow for a better-fitting cuff, meaning you can apply lower and safer tourniquet pressures because the pressure is more efficiently transferred to the limb — it's going right to the limb because the cuff is conformed to the limb.

Another advancement relating to personalization concerns the use of LOP. Historically, surgeons requested a specific tourniquet pressure based on their experience and clinical guidelines. For example, they may request 300mmHg for a leg procedure and 250mmHg for an arm procedure. But some advanced surgical tourniquet systems include means to measure LOP automatically before surgery, letting you determine individualized, optimal (minimum) tourniquet pressure settings for the procedure.

Studies have shown that higher tourniquet pressures are associated with higher probabilities of tourniquet-related injuries. The ability to determine LOP and use that as the basis for tourniquet pressure rather than using an estimate, will help reduce the likelihood of injuries.

5. Intraoperative LOP. While personalized tourniquets help determine LOP before surgery, what they can't take into account are the changes to LOP that occur throughout a procedure. What happens is at the start of a surgery, a patient is anesthetized, then during the surgery the blood pressure varies. There are also different physiological parameters that vary due to the anesthetic and pain incurred when the surgeon is working on a limb.

As a result, the LOP will vary in the sense that, in some instances, if blood pressure is higher, more blood will be trying to pump through the tourniquet, while in other instances, if the blood pressure is lower, there will be less blood trying to pump through the tourniquet. In short: The minimum pressure required to occlude the blood flow changes throughout the surgery.

To address this change, we're investigating an algorithm that looks at all of the measures that affect the LOP, including blood pressure and heart rate, and trying to develop technology that will use that algorithm to determine an updated estimate of LOP throughout the surgery, then adjust the tourniquet pressure accordingly.

The LOP helped us get lower tourniquet pressures than what a surgeon would normally use. The next step to improve it further would be to do what we're doing with LOP at the beginning of the surgery, but be able to carry this throughout the surgery by continuously knowing exactly how much pressure is needed to occlude blood flow and develop technology that automatically adjusts the tourniquet pressure.

6. Sensor-adjusted LOP. We're also investigating the development of a system that incorporates sensors at the tourniquet cuff to measure 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 investigating 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 continues 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 account for the changes that occur throughout a case. The indirect method looks at physiological parameters such as blood pressure and heart rate data and uses an algorithm to predict LOP. The direct method entails sticking a sensor right at the cuff to see if there's occlusion. If it's not occluded, the technology increases the pressure. Once the pressure is high enough, the sensor can tell that it's occluded and there's no need to look at the other physiological measures. The end goal is the same for both: maintain LOP throughout the procedure to ensure the safest care possible for patients.