Tourniquet

DefinitionTourniquet Arm

 

Device that encircles a limb to occlude the vascular supply

 

Aim is to provide bloodless field

 

Contra-Indications

 

Local

- poor skin

- PVD

- DVT

- vascular bypass surgery

 

General

- sickle cell anaemia

- Polycythemia Rubra Vera

 

Cuff Design

 

Pressure greatest at centre with parabolic fall off either side

 

Options

- tapered / conical

- non-tapered

 

Arterial Occlusion Pressure

 

1.  Less for conical tourniquets than non conical

- limbs are not cylindrical

- limbs are tapered

- tourniquets should be too

- gives even pressure transmission

 

2.  AOP reduced as tourniquet width increased

- Ratio Cuff Width to Limb Circumference

- < 0.1 : 1 then AOP > 400mmHg

- > 0. 3 : 1 then AOP < SBP

 

Cuff Pressure

 

No clear guidelines

 

Aim just enough to stop arterial flow

 

Suggestions

- UL ~ 250mmHg  (100mgHg over SBP)          

- LL ~ 300 - 350mmHG  (double SBP)

 

Mechanism of Tourniquet Injury

 

Thigh Tourniquet

 

1.  Nerve damage

- mainly secondary to pressure

- causes neuropraxia

- usually no Wallerian degeneration or loss of axoplasmic flow

- nerves very susceptible to excessive pressure (i.e. faulty gauge)

 

2.  Muscle damage

- secondary to ischaemia

- damage maximum under cuff

 

3.  Progressive acidosis in venous blood

- pH drops to 6.9 at 2 hours

- requires 15-20 minutes to return to prior levels

- patient's analgesia requirements will rise at this time

- have reaction to metabolites upon tourniquet release

 

4.  Chemical burns

- cannot allow skin prep to pool under tourniquet

- becomes pressured into skin

- can create a 3o chemical burn

- place wool under to protect skin

- occlusive dressing over tourniquet to prevent pooling

- this complication is impossible to defend

 

Cuff Times

               

Sapega et al JBJS Am 1988

- study in dogs

- limiting time to 1.5 hours minimised muscle ischaemia damage

- tourniquet release for 5 minutes

- permitted an additional 1.5 hours with comparative degree of safety

 

Generally

- tourniquet up for maximum of 2 hours

- release for minimum of 20 minutes