A tourniquet is a specialized device designed to apply circumferential pressure to a limb to stop severe, life-threatening external bleeding. Its use is reserved for situations where direct pressure has failed or is impractical, such as in a traumatic amputation or when resources are limited. The primary goal is to prevent exsanguination, which can occur rapidly when a major artery is severed. While the device and technique are important, the single most important factor for an effective tourniquet is achieving a specific physiological result.
Achieving Full Arterial Occlusion
The most important element of an effective tourniquet application is the complete cessation of arterial blood flow to the injured limb. This physiological endpoint is known as full arterial occlusion. If the device is not tight enough to stop the high-pressure arterial flow, the application will fail.
A major danger of improper use is achieving only partial occlusion. In this scenario, the tourniquet compresses the low-pressure veins but fails to compress the deep, high-pressure arteries. This prevents blood from leaving the limb through the veins, while arterial blood continues to pump into the extremity. This effect dramatically increases pressure within the limb, which can exacerbate blood loss and potentially lead to compartment syndrome.
When full arterial occlusion is successfully achieved, the visual and tactile signs are definitive. Bleeding from the wound must stop completely, transforming from a torrent or trickle to absolute stillness. A successful application will also result in the absence of a pulse below the device, confirming that no blood is flowing into the limb distal to the tourniquet. The minimum pressure required to achieve this state is known as the Limb Occlusion Pressure, which is the necessary threshold for effectiveness.
Key Application Techniques
Achieving complete occlusion depends heavily on the proper execution of specific application steps. The tourniquet must be placed high on the limb, about two to three inches above the wound and between the injury and the heart. If the exact location of the bleeding is unclear, the device should be placed as high on the extremity as possible, known as the “high and tight” position. Avoid placing the tourniquet directly over any joint, such as the elbow or knee, as this can hinder compression and cause secondary injury.
After positioning, the strap must be pulled as tightly as possible to remove all slack before engaging the windlass mechanism. The windlass, a twisting rod, is then turned until the bleeding stops completely, regardless of the pain caused to the patient. This twisting action generates the high circumferential pressure necessary to compress the underlying arteries.
Once bleeding is controlled, the windlass must be secured in a clip or locking device to prevent it from unwinding. A final step is to clearly note the time of application on the device or the patient. This time stamp is necessary for medical personnel to monitor the duration of blood flow restriction and manage the risk of complications like nerve or muscle damage.
Selecting the Right Device
The selection of a standardized, commercially available tourniquet is a prerequisite for reliably achieving arterial occlusion. These devices are purpose-built with a wide strap and a robust windlass system designed to generate and maintain the high, consistent pressure required. The use of wider cuffs, for example, achieves the necessary occlusion pressure at a lower overall tension, which can reduce the risk of nerve damage.
Improvised devices, such as those made from cloth and a stick, frequently fail because they cannot generate or sustain adequate pressure. Non-windlass versions have been shown to fail in nearly all tested conditions. The materials used in makeshift options often lack the necessary structural integrity or width to effectively compress the deep arteries, leading to only partial occlusion.
While some improvised options incorporating a windlass can show moderate effectiveness, their success rates remain significantly lower than commercial counterparts. A proper, standardized device is engineered to eliminate variables, ensuring the user can quickly and efficiently achieve full arterial occlusion.