Sneaky Pete
08-03-08, 09:13 PM
Just a little extra info that may be of interest and also may be of assistance in understanding how best to act after a bite. Because this is undoubtedly going to end up a bit long-winded, I thought I would make this a separate post rather than hijack another thread. My apologies to those with medical knowledge who may find this too simplistic; my intent is to provide some useful info for fellow hunters, not to get you through medical school.
The object of a compression bandage in the case of snake bite is not to restrict blood flow, but to restrict the flow of lymph fluid. What fluid?? I'm glad you asked. There is a separate system of vessels throughout the body that carries certain waste products from cells into nodes of specialised tissue that is designed to munch up the bad stuff and break it down into chemicals that the body can get rid of, usually via the kidneys. These lymph vessels carry lymph fluid from all over the body, back to the lymph nodes in your armpits, neck and groin where the bad stuff is dealt with by specialised lymph cells. The name of this system? Funnily enough, it is called the Lymph system. You know when you've got an infection or an illness and you get those swollen lumps (often incorrectly called "glands") in your throat? That is the lymph nodes doing their job of stalling the bacteria etc whilst the lymph cells go into action to fight it. From there, the lymph system continues with larger lymph vessels that end up draining into the 'inferior vena cava', which is a huge vein taking blood directly into the right side of the heart, from where it goes to the lungs to pick up oxygen and then back to the other side of the heart to be pumped around the body.
Whilst the walls of the tiniest blood vessels (capillaries) have holes just big enough to let oxygen molecules and other good stuff move in and out of the blood, the large molecules in snake venom are too big to get through the blood vessel walls, BUT the pores in the walls of lymph vessels are large enough for the bigger molecules to get in (thats how the body differentiates what goes into the blood and what has to travel via the lymph system for cleaning up). SO the venom gets into the lymph system, travels to the lymph nodes which become swollen as they attempt to deal with the toxins, then continues through the lymph system which drains into the inferior vena cava that connects to the heart, where it enters the bloodstream and is pumped around the body where the large molecules block up the kidneys and other toxins do their nasty work.
This is the bit that is significant and why this may be helpful to understand:
1; Lymph vessels are softer than arteries and veins, so a bandage is intended to restrict the lymph flow without (overly) restricting blood flow to the limb. You know how they say to bandage it about as tight as you would for a sprained ankle? Think about it; if your sprained ankle was bandaged up for a week tight enough to restrict the blood flow, your foot would drop off like a lamb's tail. Overly tight bandaging causes pain as the limb is starved of blood flow. Restricting the lymph flow rather than the blod flow is the go.
2; The lymph system, unlike the blood, does not have a heart to pump the fluid around. The thing that causes the lymph fluid to move through the lymph vessels is muscle movement. This is why it is recommended to splint the limb after it has been bandaged. Limb movement must be kept to an absolute minimum to reduce lymph flow. The limb is supposed to be kept low also, so that gravity also helps reduce lymph flow rather than accelerate it.
(The above should also help you understand why the tourniquet went out of favour in snake bite management as the understanding of these things developed).
The reason why these things are done to reduce lymph flow is, of course, not so that we can leave the venom in our arm or leg and hope it will go away, but in order to buy us time whilst we make our way to a hospital that has antivenine.
A question was asked in another post about what is the best thing to do if you're up the bush hunting alone and you get bitten. This is a question I've pondered a bit as one who often spends time in the bush alone, be it hunting or whatever. For what it's worth, in light of the above, my plan would be to first apply a firm roller bandage and splint the limb in accordance with what's taught in the first-aid manuals, and then to slowly, carefully and calmly make my way back to my car with the absolute minimum of movement of the bitten limb; i.e. crawling if I'm bitten on the leg. I don't know whether this will work, but it's about the best plan I can come up with based on a reasonable understanding of the process of envenomation, and the fact that most times the chances of me being found if I sit and wait are fairly slim. If you happen to come across a decomposing body in 3D camo with a bandage and splint on one leg, clutching a 70lb Drenalin and somewhere near a good sambar spot, you'll know my plan didn't work. Oh yeah- another part of my plan is to not get bitten on the bum.
Pete
The object of a compression bandage in the case of snake bite is not to restrict blood flow, but to restrict the flow of lymph fluid. What fluid?? I'm glad you asked. There is a separate system of vessels throughout the body that carries certain waste products from cells into nodes of specialised tissue that is designed to munch up the bad stuff and break it down into chemicals that the body can get rid of, usually via the kidneys. These lymph vessels carry lymph fluid from all over the body, back to the lymph nodes in your armpits, neck and groin where the bad stuff is dealt with by specialised lymph cells. The name of this system? Funnily enough, it is called the Lymph system. You know when you've got an infection or an illness and you get those swollen lumps (often incorrectly called "glands") in your throat? That is the lymph nodes doing their job of stalling the bacteria etc whilst the lymph cells go into action to fight it. From there, the lymph system continues with larger lymph vessels that end up draining into the 'inferior vena cava', which is a huge vein taking blood directly into the right side of the heart, from where it goes to the lungs to pick up oxygen and then back to the other side of the heart to be pumped around the body.
Whilst the walls of the tiniest blood vessels (capillaries) have holes just big enough to let oxygen molecules and other good stuff move in and out of the blood, the large molecules in snake venom are too big to get through the blood vessel walls, BUT the pores in the walls of lymph vessels are large enough for the bigger molecules to get in (thats how the body differentiates what goes into the blood and what has to travel via the lymph system for cleaning up). SO the venom gets into the lymph system, travels to the lymph nodes which become swollen as they attempt to deal with the toxins, then continues through the lymph system which drains into the inferior vena cava that connects to the heart, where it enters the bloodstream and is pumped around the body where the large molecules block up the kidneys and other toxins do their nasty work.
This is the bit that is significant and why this may be helpful to understand:
1; Lymph vessels are softer than arteries and veins, so a bandage is intended to restrict the lymph flow without (overly) restricting blood flow to the limb. You know how they say to bandage it about as tight as you would for a sprained ankle? Think about it; if your sprained ankle was bandaged up for a week tight enough to restrict the blood flow, your foot would drop off like a lamb's tail. Overly tight bandaging causes pain as the limb is starved of blood flow. Restricting the lymph flow rather than the blod flow is the go.
2; The lymph system, unlike the blood, does not have a heart to pump the fluid around. The thing that causes the lymph fluid to move through the lymph vessels is muscle movement. This is why it is recommended to splint the limb after it has been bandaged. Limb movement must be kept to an absolute minimum to reduce lymph flow. The limb is supposed to be kept low also, so that gravity also helps reduce lymph flow rather than accelerate it.
(The above should also help you understand why the tourniquet went out of favour in snake bite management as the understanding of these things developed).
The reason why these things are done to reduce lymph flow is, of course, not so that we can leave the venom in our arm or leg and hope it will go away, but in order to buy us time whilst we make our way to a hospital that has antivenine.
A question was asked in another post about what is the best thing to do if you're up the bush hunting alone and you get bitten. This is a question I've pondered a bit as one who often spends time in the bush alone, be it hunting or whatever. For what it's worth, in light of the above, my plan would be to first apply a firm roller bandage and splint the limb in accordance with what's taught in the first-aid manuals, and then to slowly, carefully and calmly make my way back to my car with the absolute minimum of movement of the bitten limb; i.e. crawling if I'm bitten on the leg. I don't know whether this will work, but it's about the best plan I can come up with based on a reasonable understanding of the process of envenomation, and the fact that most times the chances of me being found if I sit and wait are fairly slim. If you happen to come across a decomposing body in 3D camo with a bandage and splint on one leg, clutching a 70lb Drenalin and somewhere near a good sambar spot, you'll know my plan didn't work. Oh yeah- another part of my plan is to not get bitten on the bum.
Pete