TOURNIQUET PARESIS To reduce the risk of tourniquet-related nerve injuries, base the tourniquet cuff pressure on the measurement of the limb occlusion pressure.

Pneumatic tourniquets are used many thousands of times per day in orthopedic cases, facilitating procedures by reliably establishing a bloodless surgical field with a high level of safety. But now there's a new concept in tourniquet use: personalized tourniquet systems — the lowest limb occlusion pressure needed to occlude blood flow and create a clear, dry surgical field.

These tourniquet systems automatically measure the minimum pressure required to occlude the limb and recommend a cuff pressure to be used during surgery that is personalized for each individual patient. They also have specially designed tourniquet cuffs and limb protection sleeves that can conform to the limb shape of each individual patient. The personalization of the tourniquet lets you use lower cuff pressures and better-fitting tourniquet cuffs to dramatically reduce the incidence of nerve injury.

Nerve injuries from tourniquet use
Despite advances in pneumatic tourniquet technology, tourniquet-related nerve injury is a risk that remains a potentially harmful complication of tourniquet use.

Researchers have shown that in most cases nerve damage is limited to the part of the nerve that is underneath and near the edges of the cuff, and that the underlying cause of tourniquet paralysis is compressive neurapraxia rather than ischemic neuropathy or muscle damage. Compression of the large myelinated fibers underneath the tourniquet cuff results in displacement of the node of Ranvier from its usual position under the Schwann-cell junction. Studies of the distribution of pressure beneath tourniquet cuffs demonstrate high tourniquet inflation pressures in narrow, uncontoured tourniquet cuffs result in high pressure gradients near the cuff edges. This in turn results in higher compressive pressures and higher pressure gradients along the underlying nerves and soft tissues. Consequently, higher levels of tourniquet inflation pressure and higher pressure gradients beneath tourniquet cuffs are associated with a higher risk of nerve-related injury.

What's the LOP?
The optimal surgical tourniquet pressure setting for each patient is based on a measurement known as limb occlusion pressure (LOP). LOP is the minimum pressure required — at a specific time in a specific type of 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.

Until recently, the use of personalized tourniquet settings based on LOP has been limited by how difficult it is to manually measure LOP. Using Doppler ultrasound and a distal blood-flow sensor, surgical staff would detect the presence of arterial pulsations in the limb distal to a tourniquet cuff as an indicator of arterial blood flow past the cuff and into the distal limb. An operator would then slowly increase tourniquet cuff pressure from zero, while monitoring arterial pulsations in the limb distal to the cuff until the pulsations could no longer be detected.

Not only is this method costly and complex, but it's also highly dependent on the sensitivity, precision and noise immunity of the technique for detecting and montoring arterial pulsations, as well as on the caregiver's skill, technique and consistency. A new automatic technique for measuring LOP has been developed in an effort to overcome these limitations. It involves using a tourniquet cuff with a continuous pneumatic passageway surrounding the limb as a dual-purpose patient sensor and pneumatic effector. This circumvents the need for a distal sensor, a limiting factor in prior adoption of LOP measurement.

Advances in tourniquet technology that let you measure LOP automatically have reduced the risk of nerve-related injury in recent years. These advances use distal sensors, placed on the digits, to automatically measure the individual's LOP. While this method reduces the dependency on the operator's skill, technique and consistency, it is still costly and complex. Furthermore, it affects the preparation of the sterile field as well as perioperative time and workflow.

GOLDEN RULE Keep the tourniquet inflation pressure to the minimum effective pressure.

Avoiding Tourniquet Complications

Over-pressurization of the cuff	Associated with a higher probability of compression injuries to blood vessels, nerves, muscles, or skin. May cause pain at the tourniquet cuff site, muscle weakness or extremity paralysis.
Under-pressurization of the cuff	Associated with the leakage of arterial blood distally and anesthetic agent proximally in Bier blocks. May result passive congestion of the limb, shock, and hemorrhagic infiltration of a nerve.

Cuff pressure safety margin
When you measure LOP, an additional pressure margin based on recommendations in published surgical literature is added to the automatically measured LOP to provide a "recommended tourniquet pressure" (RTP) as a guideline to help the surgical staff select the lowest tourniquet pressure that will safely stop arterial blood flow for the duration of a surgical procedure. Such systems let you select the RTP as the tourniquet pressure for that patient or to select another pressure based on the physician's discretion or the protocol at the institution where the surgery is being performed.

The difference in pressure between the measured LOP and the selected tourniquet pressure can be defined as the cuff pressure safety margin, which is ideally selected to be greater than the magnitude of any increase in LOP normally expected during surgery due to changes caused by drugs used for anesthesia, the patient's physiologic response to surgery and other variables.

Setting tourniquet pressure at a "standard" setting results in patients having too high or too low tourniquet pressures, which can increase risk of injuries or bleeding. Setting tourniquet pressure as a function of a patient's pre-op systolic blood pressure is not best practice, as it does not take into account adjustments that must be made due to differing cuff widths, differing degrees of match between cuff shape and limb shape, differing degrees of snugness of cuff application to the limb, and differences in the characteristics of the limb tissue beneath the cuff. Setting tourniquet pressure as a function of LOP inherently takes into account all of these variables.

Personalized tourniquet cuffs
Whether the patient is arthritic or athletic, bariatric or pediatric, always select a personalized tourniquet cuff that matches the limb size and shape, tissue characteristics and size of the patient. Also use personalized limb protection sleeves that minimize soft tissue injuries underneath the cuff on the limb.

Personalized cuffs and sleeves designed to better match patient limb size and shape provide more efficient application of cuff pressure to the limb, letting you use lower and safer tourniquet pressures.

The traditional "straight" tourniquet cuffs are best suited to cylindrical limb shapes. New types of cuffs are "variable contour cuffs" that let you adapt the shape of the tourniquet cuff to any of a wide range of non-cylindrical (tapered, for example) limb shapes. Cylindrical cuffs that are applied onto a tapered limb result in poor fits, requiring the use of higher pressures to occlude the limb.