Pressure immobilisation first aid for venomous bites and stings was developed in Australia in the 1970s by Professor Struan Sutherland, who was head of immunology research at the Commonwealth Serum Laboratories (CSL).
Venom is spread via the lymph system, so applying a bandage (as tightly as you would strap a sprained ankle) slows the movement of venom from the bite site through the lymphatic system and into the blood circulation. Immobilisation of the limb — with a splint, e.g. a piece of wood/timber — also slows lymphatic drainage. Pressure immobilisation bandaging may also inactivate some types of venom by trapping the venom in the tissues.
This gives the bitten person more time to reach hospital and medical care, although obviously the situation is still a grave emergency.
Research with snake venom has shown that very little venom reaches the bloodstream if firm pressure is applied over the bitten area and the limb is immobilised. Pressure immobilisation first aid is currently recommended for most life-threatening venomous bites and stings in which the venom travels by the lymph system, for example, funnel-web spider bites, snake bites and blue ringed octopus and cone snail envenomations.
Applying the pressure immobilisation technique (PIT)
The pressure immobilisation technique (PIT) involves bandaging the limb that has been bitten and keeping it still using a splint or sling. To apply the pressure immobilisation technique:
- Apply a broad pressure bandage (preferably an elasticised bandage, 10-15 cm wide) to the bite area.
- If you don’t have any elasticised bandages, use crepe bandages. Other material (such as clothing) can be used if there are no bandages available.
- The bandage should be tight enough that you can’t comfortably get a finger underneath the bandage.
- Apply a second pressure bandage to the entire affected limb, starting at the fingers or toes and moving upwards. The bandage should be applied over the person’s clothes.
- If you have only one bandage, simply apply that bandage starting at the fingers or toes and bandage up the limb, including the bite site.
- A splint should also be applied – incorporate the splint under the bandage layers to keep the limb still. The joints on either side of the bite should be immobilised by the splint. For bites on the legs, one leg can be splinted to the other by strapping them together. Arms should be placed in a sling.
- If you are by yourself, use the PIT if possible. If you need to move to call for help, apply local pressure.