Fundamentals of Tourniquet Technology

Field tourniquets must be capable of reliably applying enough pressure to occlude arterial bleeding. If a tourniquet applies enough pressure to stop only the venous flow, then the rate of blood loss from an arterial wound will most likely increase. It should be noted that some small blood seepage may continue in the case of traumatic amputation due to medullar blood flow even with a properly tightened tourniquet. 

Graham et al. (1993) measured the occlusion pressure of the proximal leg as a function of cuff width and found the following relationship for the occlusion pressure, Pocc (mmHg), systolic pressure, P, (mmHg), and the diastolic pressure, Pdm, (mmHg)  

The occlusion pressure in the following equation is the surface pressure applied by the tourniquet required to occlude the arterial blood flow. Belt tension required for occlusion, rBocc (pounds), is found by combining the two equations above to be  

The primary cause of nerve and tissue damage in the proximity of the tourniquet is not the absolute pressure but the shear stresses associated with the edges of the tourniquet. Since the wider tourniquet belts reduce the required pressure, they also reduce the shear stresses at the edge of the tourniquet, thus reducing the potential for nerve damage. The primary means to reduce the shear is to use the minimal 

The relationship of occlusion pressure to the ratio of width/circumference for tourniquets is plotted in Fig. 5.7. 

---