A tourniquet is a specialized medical device used to control catastrophic hemorrhage from a limb injury, where rapid, massive blood loss presents an immediate threat to life. When applied correctly, it creates circumferential pressure around an arm or leg, completely stopping the flow of blood to the injured area. This action is a powerful, life-saving intervention employed when direct pressure or elevation is insufficient to stop severe bleeding. The ability of a tourniquet to halt arterial flow has established it as a standard tool in both military and civilian emergency medicine protocols.
Understanding the Functional Requirement
The primary physiological goal of a tourniquet is to occlude arterial blood flow, the high-pressure inflow that causes rapid blood loss. This requires applying sufficient pressure to collapse the thick-walled arteries running through the limb. If the device is applied with insufficient force, it may only collapse the low-pressure veins while failing to stop the arteries. This dangerous scenario, known as venous congestion, allows arterial blood to flow into the limb while preventing blood from returning, potentially increasing blood loss and exacerbating swelling.
Therefore, the device must be tightened to achieve a minimum force known as the Limb Occlusion Pressure (LOP). Any pressure applied beyond this threshold necessary to achieve arterial occlusion is considered excessive and creates unnecessary risk.
Immediate Mechanical Damage to Nerves and Soft Tissue
Applying a tourniquet too tightly creates crushing pressure that immediately risks underlying structures. The most common complication from excessive force is a peripheral nerve injury, classified as a compression injury. This mechanical trauma can lead to conditions like neuropraxia, where the nerve’s ability to conduct signals is temporarily blocked, or the more severe axonotmesis, involving damage to the nerve fibers.
The mechanical force compresses the delicate nerve tissue against the underlying bone; the radial nerve in the arm is particularly susceptible to this damage. This direct crushing can occur within minutes if the pressure is unnecessarily high, often manifesting as numbness, tingling, or weakness in the limb. Excessive pressure also damages soft tissues such as muscle and skin directly beneath the device. This physical trauma can cause muscle contusion and bruising, increasing local swelling and pain.
Long-Term Hazards of Prolonged Ischemia and Reperfusion
When the tourniquet remains on for an extended period, the lack of oxygen and nutrients leads to ischemia, causing cellular damage and death. Muscle tissue is particularly vulnerable to this oxygen deprivation, which can result in necrosis and a condition called rhabdomyolysis. After approximately two hours of total ischemia, the risk of permanent muscle damage and functional loss increases significantly.
The most severe systemic hazard occurs when the tourniquet is eventually removed, leading to reperfusion injury. Reintroducing blood flow washes a sudden load of toxic metabolic byproducts from the limb into the central circulation. These byproducts include high concentrations of lactic acid and potassium, which have built up in the oxygen-starved tissue.
The sudden release of potassium can cause severe cardiac arrhythmias, while lactic acid can lead to a dangerous drop in the body’s overall pH, known as metabolic acidosis. This metabolic crisis can induce systemic shock, organ damage, and even death. The goal is to control bleeding while minimizing the duration of ischemia to prevent the cascade of events associated with reperfusion injury.
Indicators of Correct Application
The proper application of a tourniquet is defined by achieving hemorrhage control with the minimum necessary force. The two primary indicators of correct application are the complete cessation of arterial bleeding from the wound, and the absence of a pulse below the device. A pulse check is performed distally, such as at the wrist or ankle, to confirm that arterial inflow has been successfully stopped.
Once bleeding has ceased and the distal pulse is absent, the tourniquet has achieved its functional requirement. Any subsequent tightening serves only to increase the risk of mechanical damage to nerves and soft tissue without providing additional benefit for hemorrhage control. The ideal application is therefore a balance between life-saving pressure and tissue-sparing restraint.