A tourniquet is a device that stops arterial blood flow below its application site when there is life-threatening external bleeding from an arm or leg. A tightly tensioned band produces pressure around the limb; a tightening mechanism and a lock maintain that pressure. During military isolation, a suitable tourniquet enables immediate self-aid when the available means cannot otherwise control the bleeding adequately or the threat requires rapid tourniquet application.
Pressure, blood flow and incomplete occlusion
The band sits between the bleeding site and the trunk. Its pressure passes through the tissues to the blood vessels. To control the bleeding, that pressure must interrupt arterial inflow. The slack in the band must therefore be removed before the tightening mechanism is used.
Insufficient pressure can obstruct venous return while arterial blood continues to enter the limb. Blood accumulates below the tourniquet, tissue pressure rises and dangerous pressure can develop within the muscle compartments. Effectiveness must therefore be checked at the bleeding site and, when the limb remains intact, at the pulse below the tourniquet: bleeding must stop, and a reliably assessed distal pulse must be absent. Pain alone does not show that bleeding has been controlled.
Bleeding that requires a tourniquet
Warning signs include heavy pulsatile or steadily flowing bleeding, a growing pool of blood, and clothing or dressings that keep becoming soaked with blood. Traumatic amputation is another immediate indication. A person who becomes pale, confused or unconscious after substantial bleeding may already be in shock. Waiting for this condition, or for visibly spurting blood, loses time; dangerous bleeding can also flow steadily.
When the situation allows assessment, firm direct pressure can first be used to control a bleeding site. Press a dressing or available clean material directly onto the wound and maintain pressure. Once bleeding is controlled, a pressure dressing can maintain local pressure. For life-threatening arm or leg bleeding that direct pressure does not stop, promptly apply the available suitable tourniquet. A small wound that can be controlled by pressure does not require complete interruption of blood flow to the entire arm or leg.
A limb tourniquet needs a suitable site above the wound. It must not be placed around the neck or trunk. A wound very close to the trunk in the groin or armpit may leave no suitable site; an ordinary arm or leg tourniquet cannot then reach the source of bleeding. For an externally compressible wound, firm pressure directly on the bleeding site remains an action the person can take. Specialist tourniquets for these junctional regions have a different design and application.
Rapid tactical application and deliberate placement
Under immediate enemy threat, US and British tactical procedures provide for rapid application over clothing, clearly above the bleeding site. If the site of life-threatening bleeding cannot be identified quickly, the tourniquet is placed as high as possible on the injured arm or leg: “high and tight”. Do not trap solid objects in pockets under the band. This rapid application aims to limit blood loss and enable movement to cover; a thorough wound examination under fire can expose the person to further injury.
When the wound can be assessed, a newly applied tourniquet sits directly on the skin, approximately 5–7 cm above the bleeding site and away from a joint. The US instruction of 2–3 inches describes approximately the same distance. With several wounds, the band must be above the bleeding site closest to the trunk. An effective tourniquet is not simply loosened and moved for later wound assessment. Deliberate repositioning belongs to a controlled medical procedure that maintains bleeding control throughout the change.
Operation using the C-A-T Gen7 as an example
The C-A-T Gen7 has a self-adhering band with a buckle, a windlass rod, retaining clips and a security strap marked “TIME”. The following steps apply to this model. Buckle routing and locking on other tourniquets may work differently; the actions must match the device actually available.
- For one-handed application, insert the injured arm or leg through the prepared loop in the band. For two-handed application, route the band around the limb and pass the red tip through the buckle slot. Position the device at the site appropriate to the situation.
- Pull the band firmly tight and fasten it back onto itself without covering the windlass clips. With the Gen7, the tips of three fingers must not fit between the band and the limb. If the loop is still that loose, pull it tight again and fasten it. This initial tension prepares the band for full occlusion.
- Twist the windlass rod until the bleeding stops. The amount of rotation depends on the result; a fixed number of turns is not a measure of success.
- Lock the rod into a retaining clip. Check the bleeding site and, if there is no traumatic amputation, check the pulse below the tourniquet. Continued bleeding or a persistent distal pulse requires further tightening or a second available tourniquet immediately above and alongside the first. Reassess afterwards.
- Route the free end of the band between the clips and over the rod. Secure the rod and band with the TIME strap and record the application time on it.
The lock prevents the tensioned windlass from unwinding. The TIME strap further secures the rod and band against dislodgement during movement; it does not itself produce the required occlusion pressure. If further tightening is needed, open the TIME strap if it is already closed and move the free band end routed over the rod aside. Hold the tensioned rod firmly, free it from the retaining clip and turn it further in the tightening direction without allowing it to unwind. Then lock it into the clip again, route the band end over the rod again and close the TIME strap. When a second tourniquet is applied, the first remains in place to control bleeding. The additional device also needs a suitable site away from a joint. Effective application may be very painful; do not reduce the tension because of that pain.
Check for bleeding again after movement
Crawling, a change of body position or transport can displace the band and its locking components. Repeatedly check the bleeding site and the device's position, especially after each such movement. Renewed blood flow or dressings becoming soaked again requires immediate correction of bleeding control by further tightening or a second suitable device, if available. A closed hook-and-loop surface alone does not confirm effective occlusion. Other wounds on the same limb may also be bleeding and must be identified when examination becomes possible.
The pulse check adds to this assessment. If a distal pulse cannot be assessed reliably, this does not provide reliable evidence of complete occlusion. Visible continued bleeding still requires immediate further action. At any later medical handover, the bleeding site, placement and effectiveness must be reassessed; restored circulation following treatment for shock can also overwhelm a tourniquet that had previously been sufficient.
Application time and the limits of prolonged self-aid
Record each application time on the relevant device, preferably with a permanent marker, and additionally on a note or casualty card carried with the person. With several devices, make clear which time belongs to which device. Later medical repositioning does not reset the time already spent under occlusion. If no clock is available or the original time is unknown, explicitly pass on that uncertainty at any possible handover.
Below a fully tightened tourniquet, muscles and nerves no longer receive arterial blood. The risk of permanent damage increases with prolonged application. The tourniquet prevents further blood loss from the affected limb but does not replace blood already lost or treat other injuries. A functioning tourniquet is therefore not loosened at fixed intervals or opened experimentally to “briefly restore circulation” to the limb: the original bleeding can restart immediately.
Conversion to wound packing or a pressure dressing requires medical assessment, suitable supplies and a wound that can be closely monitored. In US TCCC, the casualty must not be in shock and the tourniquet must not be controlling bleeding from an amputated limb. Once more than two hours have elapsed, personnel trained at the TCCC All Service Members and Combat Lifesaver levels may attempt conversion only under advanced medical direction. After more than six hours, release additionally requires close monitoring and laboratory capability. This gives an isolated person no scheduled time to open the device independently. If the conditions for a controlled conversion are absent, maintain effective occlusion and continue checking for renewed bleeding.
Access and device condition
A tourniquet carried for self-aid must be reachable with the uninjured hand. Check this beforehand in the equipment actually worn, including while lying down. The available hand must be able to grip the device, pull the band firmly, and turn, hold and lock the windlass. Inadequate grip strength or control can prevent the required occlusion pressure from being achieved. The Gen7 band loop can be prepared for rapid application: pass the tip through the buckle, pull approximately 20 cm of band through and fasten it back onto itself, flatten the loop, place the buckle in its middle and fold the device so the buckle lies at one end. Leave the TIME strap open for access.
Check the band, buckle, windlass, clips and adhering surfaces for damage. Prolonged exposure to heat, sand, freezing temperatures and abrasion can impair function. Store the Gen7 somewhere cool and dry, protected from direct sunlight. Use a separate training device for practice; the device carried for an emergency is intended for a single use. During one-handed self-aid, a jammed band, broken clip or incorrectly prepared loop immediately costs time or prevents locking.