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How venom moves through the body

Venom does not enter the bloodstream directly. There are two separate systems involved.

The blood stream (aka the circulatory system) and the lymphatic system. 

The circulatory system moves blood around the body via blood vessels.

Arteries – move blood Away from the heart
Veins – move blood back toward the heart
Capillaries – small networks of thin blood vessels that allow for the exchange of gases and fluids between the tissues and the blood.

If you’ve ever had your blood taken, you know how easy it is to miss a vein…. Snakes do not know where your blood vessels are!  Instead, their fangs typically inject venom into muscle tissue.

Some of the large venom proteins are too big to move from the muscle tissue through the capillary walls and therefore, cannot enter the blood stream.
Instead, they travel via the lymphatic system. Unlike the bloodstream that flows around the body (to and from the heart), the lymph can only travel in one direction… towards the heart. When it reaches collection ducts (that sit near the heart) the lymph re-enters the blood stream.

We want to stop venom getting there!
As soon as it enters the blood stream some venom toxins can affect the clotting mechanisms of the blood. If multiple clots form, they can block blood vessels to the heart, lungs, brain and other vital organs and can result in things like heart attack, stroke or pulmonary embolism – which can be fatal.

The lymphatic system has no pump. So how does it move?

The blood stream has the heart, which mechanically forces the blood to flow around the body. The lymphatic system relies instead on muscle contractions to move the lymph and uses valves to prevent any backflow and keep it moving in one direction. Therefore, if you are bitten by a snake you are encouraged to remain still.

How to Use the Pressure Immobilisation Technique for Snake Bites

Bites and stings can be commonplace in Australia, and while some may be quite painful, others can be life-threatening. By ensuring you are equipped with the knowledge to act quickly and effectively First Aiders can help limit the spread of venom through the lymphatic system where it would otherwise cause major damage to the body’s organs and systems. First aid techniques like the Pressure Immobilisation Technique (PIT) can help mitigate the risks associated with venomous bites and stings. In this article, we will take a closer look at the PIT and how to use it to treat bites from venomous creatures.

For a practical demonstration of how to apply the PIT and some hands-on experience you can enrol in the following first aid courses:

You can head to our website to enrol today.

What is the Pressure Immobilisation Technique (PIT)?

The Pressure Immobilisation Technique (PIT) is a first aid treatment that involves applying a pressure bandage around the bitten or stung limb, which helps to restrict lymphatic flow and prevent venom from spreading. Additionally, a splint can be used to immobilise the limb, further reducing the spread of venom.
This is explored in more detail in our previous article – How venom moves through the body.

Which Venomous Creatures Require Pressure Immbolisation First Aid?

The Pressure Immobilisation Technique is recommended for application to bites and stings from the following creatures:

    • All Australian snakes
    • Funnel web spiders
    • Blue ringed octopus
    • Cone shell

* Not all Australian snakes are venomous. But it can be challenging to identify snakes with certainty, as members of the same species can vary in colour, pattern, and size. Don’t take the risk.

How to Use the Pressure Immobilisation Technique (PIT)

If you suspect that someone has been bitten or stung by a venomous creature, it is important to take the following steps:

    1. Ensure the casualty remains as still as possible to help slow the spread of venom through the body.
    2. Follow DRSABCD (Danger, Response, Send for help, Airway, Breathing, CPR, Defibrillation) and be prepared to perform CPR if necessary.
    3. Apply a broad pressure bandage over the bite site as soon as possible.
      It is recommended to use elastic bandages (10-15cm wide) rather than crepe bandages to form the pressure immobilisation bandage. If neither of these are available, clothing or other materials can be used. The bandage should be firm and tight but not so tight as to cut off circulation.
      * There are specialised snake bite bandages available with pressure indicators to assist you with getting this pressure right.
    4. To further restrict lymphatic flow, apply a second pressure bandage. Start at the fingers or toes (the distal end) of the bitten limb and extend upwards, covering as much of the limb as possible. Mark the bite site with a pen or texta.
    5. Apply a splint to the limb to immobilise joints on either side of the bite and restrict movement as much as possible. The splint can be made from a variety of rigid materials, such as a tree branch or rolled-up newspaper, and can be incorporated under the layers of bandaging. Bites to the arm should be immobilised with a sling rather than a splint. The splint will serve as a physical reminder encouraging the patient not to move the limb.
    6. For bites that are not on a limb and cannot be treated with the Pressure Immobilisation Technique, apply localised pressure. Be mindful not to impede breathing.
    7. Bandages should be applied over existing clothing, as any attempts to remove clothing would require muscle movement and could promote the spread of venom into the bloodstream. Be mindful to remove keys and phones from pockets before bandaging.
    8. If only one bandage is available, we recommend starting just below the bitten area and winding the bandage as far up the limb as possible.
 
The application of the PIT does not replace the need for medical treatment – it merely buys you time until medical help arrives.
It is essential to get medical help as soon as possible.
 
Alicia White
Alicia White

Registered Paramedic - Perth, W.A.