A U G U S T 2 0 1 5 O U T P A T I E N TS U R G E R Y. N E T 5 9
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 under-
lying 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 pres-
sure gradients near the cuff edges. This in turn results in higher compressive
pressures and higher pressure gradients along the underlying nerves and soft tis-
sues. Consequently, higher levels of tourniquet inflation pressure and higher pres-
sure 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 ultra-
sound 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.