A tourniquet is a device that wraps tightly around an arm or leg to stop blood flow and control life-threatening bleeding. It works by applying enough pressure around the entire circumference of a limb to compress the arteries shut, preventing blood from reaching the wound. Tourniquets are used both in emergency situations, where they can save a person’s life in minutes, and in surgical settings, where they give surgeons a bloodless field to work in.
How a Tourniquet Works
Blood travels through arteries under pressure from the heart. A tourniquet squeezes the limb hard enough to overcome that pressure and collapse the arteries completely, cutting off flow below the device. The minimum pressure needed to do this is called the limb occlusion pressure, and it varies from person to person based on blood pressure, limb size, and where the tourniquet is placed. Wider tourniquets can stop blood flow at lower pressures than narrow ones, which is one reason purpose-built devices outperform thin strips of fabric.
Types of Tourniquets
Tourniquets fall into two broad categories: windlass-style devices used in emergencies and pneumatic (air-filled) cuffs used in surgery.
Windlass tourniquets are the standard for emergency bleeding control. They use a strap that wraps around the limb and a rigid rod (the windlass) that you twist to tighten the strap until bleeding stops. The two models most widely recommended by the Committee on Tactical Combat Casualty Care are the Combat Application Tourniquet (CAT) and the Special Operations Forces Tactical Tourniquet (SOFT-T). Both were developed for military use and are now common in civilian first aid kits, school emergency supplies, and law enforcement gear.
Pneumatic tourniquets are inflatable cuffs connected to a pressure gauge, similar in concept to a blood pressure cuff but capable of much higher pressures. These are used in operating rooms during orthopedic and limb surgeries. Surgeons inflate them to a calculated pressure above the patient’s own arterial pressure, with a safety margin added to account for blood pressure fluctuations during the procedure.
Junctional tourniquets are a newer category designed for areas where a standard tourniquet can’t be applied, like the groin or shoulder where a limb meets the torso. Devices like the Junctional Emergency Treatment Tool (JETT) and SAM Junctional Tourniquet press directly over the major artery feeding the limb.
Emergency Use: When and How to Apply One
A tourniquet is appropriate when someone has severe, life-threatening bleeding from an arm or leg that can’t be controlled with direct pressure alone. This includes deep lacerations, gunshot wounds, crush injuries, and traumatic amputations. The national Stop the Bleed campaign, which trains civilians in bleeding control, teaches a straightforward approach to tourniquet placement.
The device should be placed 2 to 3 inches above the source of bleeding, never directly over a joint. If you can’t identify exactly where the bleeding is coming from, or if the situation is chaotic and dangerous, placing the tourniquet “high and tight,” as close to the groin or armpit as possible, is the safest default. The general rule: when in doubt, place it higher. Once positioned, the windlass is twisted until the bleeding stops, then locked in place. The time of application should be noted so medical teams know how long it has been on.
Tourniquet use for less than two hours has proven safe, even in cases where the tourniquet turned out not to be strictly necessary. Beyond two hours, the risk of tissue damage from oxygen deprivation increases significantly. Beyond six hours, the likelihood of needing amputation rises sharply.
Improvised vs. Commercial Tourniquets
In a true emergency without a commercial tourniquet available, people have used belts, strips of clothing, and other materials. Research comparing improvised and commercial options in cadaver testing found that an improvised windlass (a strip of fabric tightened with a stick, essentially replicating the mechanics of a commercial device) was as effective at stopping bleeding as the commercial models. Participants also rated it the easiest to learn and apply.
A standard leather belt could stop bleeding too, but it required someone to hold continuous pressure to maintain it, making it impractical if the injured person needs to be moved or the rescuer needs free hands. The key difference with commercial tourniquets is reliability: they lock in place, maintain pressure on their own, and are designed to be applied quickly under stress. An improvised device is better than nothing, but a purpose-built tourniquet in a readily accessible location is better than scrambling to improvise one.
Surgical Tourniquet Use
In orthopedic surgery, tourniquets create a bloodless surgical field that improves visibility and precision. The cuff is inflated to a pressure calculated from the patient’s own limb occlusion pressure, with a safety margin of 40 to 80 mmHg depending on the patient’s blood pressure. For children, a smaller margin of about 50 mmHg is typically added.
Safe inflation time depends on the limb. For legs, surgeons generally deflate the tourniquet after two hours. For arms, the recommended limit is 90 minutes. If a procedure runs longer, the tourniquet is released for at least 10 minutes to restore blood flow before being reinflated. A total safe window of one to three hours has been described in the surgical literature, though shorter is always preferred.
Risks and Complications
The most significant risk of tourniquet use is nerve injury. The pressure that stops blood flow also compresses the nerves running through the limb. In the upper arm, the radial nerve is most vulnerable, while in the leg, the sciatic nerve is most commonly affected. Mechanical compression appears to cause more nerve damage than the loss of blood flow itself, which is why proper cuff width and pressure matter so much.
Many tourniquet-related nerve injuries go undiagnosed initially because postoperative pain and muscle weakness can mask the symptoms, and many cases resolve quickly on their own. Other possible complications include skin damage under the cuff, muscle injury, and a surge of metabolic byproducts flooding back into the bloodstream when the tourniquet is released (reperfusion injury). In extreme cases, prolonged use can cause muscle breakdown severe enough to affect the kidneys.
These risks are real but manageable, and they are almost always preferable to the alternative. Uncontrolled bleeding from a major limb artery can kill in minutes. Analysis of Vietnam War casualties estimated that roughly 7.4% of soldiers killed in action, about 2,590 people, could have been saved with better prehospital tourniquet use. That finding, reinforced by similar data from later conflicts, drove the U.S. military to make tourniquets standard issue for every deploying service member starting in 2003.
What Happens After a Tourniquet Is Applied
Once a patient with a tourniquet reaches medical care, providers decide whether to convert or replace it. Conversion means removing the tourniquet and switching to wound packing with a pressure bandage. This is attempted when the wound can be controlled by other means, the patient is not in shock, someone can monitor for rebleeding, and the injury is not a complete amputation.
If conversion fails or isn’t appropriate, providers may replace the initial tourniquet with a new one positioned closer to the wound, 2 to 3 inches above the bleeding site. This preserves more of the limb’s tissue and is especially important if amputation becomes necessary later. Every effort is made to convert tourniquets that have been on for less than two hours. Those in place longer than six hours are generally left on because removing them at that point risks releasing dangerous levels of metabolic waste into the bloodstream.
A Brief History
The tourniquet concept dates to at least 1674, when French army surgeon Étienne Morel used a belt looped through a wooden block with a stick twisted as a windlass at the siege of Besançon. In 1718, Parisian surgeon Jean-Louis Petit invented a screw-based version and coined the word “tourniquet” from the French “tourner,” meaning to turn. The elastic bandage tourniquet was introduced in 1873 by German military surgeon Friedrich von Esmarch after the Franco-Prussian War.
Despite centuries of use, tourniquets remained controversial well into the 20th century. During World War I, a British military surgeon called them “an invention of the Evil One,” blaming them for lost limbs. The standard U.S. Army tourniquet issued in World War II was a simple cotton strap without a windlass that later testing showed couldn’t reliably stop arterial bleeding in the thigh. It wasn’t until the early 2000s, when purpose-built devices like the Combat Application Tourniquet were fielded during the wars in Iraq and Afghanistan, that tourniquets became universally accepted as a frontline lifesaving tool. That shift in military medicine has since filtered into civilian emergency response, with tourniquets now a core component of public bleeding-control training programs worldwide.