Lower extremity tourniquet deflation: Physiologic effects
Advanced, Clinical Subspecialties
Deflation of a lower extremity tourniquet causes multiple physiologic effects based on return of blood from the ischemic limb back into systemic circulation as well as the return of blood flow back into the ischemic limb.
CVP and MAP will decrease rapidly after tourniquet deflation, and can remain lowered for approximately 15 minutes as systemic blood flow returns to the ischemic limb. Afterload will also decrease due to a post-ischemic reactive hyperemia. In cases with bilateral LE tourniquets the hemodynamic effects will be even larger. Hemodynamic effects are treated with volume and vasopressor administration.
Blood in the ischemic limb is hypercarbic, and return of this blood into systemic circulation leads to increased PaCO2/EtCO2. In patients breathing spontaneously, this will lead to compensatory increased minute ventilation. In mechanically ventilated patients, EtCO2 will remain elevated unless ventilator changes are made to increase minute ventilation. Peak elevation in EtCO2 occurs around 1 minute post tourniquet deflation, and lasts for approximately 10-13 minutes. Prolonged tourniquet inflation times will lead to higher elevations in EtCO2 post-deflation.
Increased EtCO2 leads to increased cerebral blood flow that may lead to injury in patients with elevated ICP. Maintenance of normocapnia through hyperventilation can prevent these increases.
Tourniquet deflation leads to ischemic hypothermic blood returning to systemic circulation, decreasing core body temperature.
Blood contained in the ischemic limb contains increased levels of lactic acid, CO2, and potassium. Tourniquet deflation releases these into circulation, leading to transient lactic acidemia, hypercarbia, acidosis, and hyperkalemia. The metabolic effects can be mitigated by administration of sodium bicarbonate, calcium chloride, and hyperventilation. These effects should return to baseline within 30 minutes after tourniquet deflation.
tPA levels increase in the ischemic limb with inflation of the tourniquet, which leads to increased levels of antithrombin III and thrombomodulin-phospholipase C. With deflation, these factors lead to a brief systemic thrombolysis. This thrombolytic activity can lead to post-deflation bleeding.