REPTILIAN-KMAN
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New method of first aid for snakebite ? News in Science (ABC Science)
Snakebite victims who apply an ointment to slow down the movement of venom in the body could prolong their survival by up to one and a half times, say Australian researchers.
Snake venom is often made of large toxic molecules that cannot directly enter the bloodstream. Instead, they are dispersed by the lymphatic vessels that run parallel to blood vessels and enter the bloodstream through veins near the heart.
Associate Professor Dirk van Helden of the University of Newcastle describes the lymphatic system as being like "a vacuum cleaner that takes big molecules into circulation."
He and his colleagues were initially looking for ways to improve lymphatic flow when they realised that some snake venoms contain substances that ensure this 'vacuum cleaner' does not become blocked, thus allowing the venom to succeed in its deadly mission.
"Lymph flow is mainly influenced by pumping - like millions of little hearts in series. This is due to smooth muscle contractions in the vessel wall and movement resulting from external compression," he says.
The substances in the snake venom indirectly prevent the release of nitric oxide (NO) that impedes these muscle contractions. This led van Helden to hypothesise that treatment with a topical solution that releases NO, such as one containing glycerol trinitrate (nitroglycerin), will delay the venom's action.
Their results are published today in Nature Medicine.
NO time to wait
To test the treatment, fifteen human volunteers were injected on the top of the foot, with a traceable non-toxic substance that is physically similar to snake venom.
The researchers used a special camera to measure how long it took for the mock venom to travel from the foot to the groin. Then, on a separate occasion, they repeated the experiment with the addition of a 5 centimetre patch of glycerol-nitrate-containing ointment next to the injection site. This was applied within a minute of the injection.
"Transit time to the groin was three-fold greater when we applied the ointment," says van Helden.
The team then used the same methodology to examine the effect of slowing down lymph flow in anaesthetised rats whose hind limbs had been injected with venom from the Eastern brown snake (Pseudonaja textilis).
Transit time of the venom was similarly delayed.
"This doesn't, however, mean you will survive three times longer because the relationship between changes in lymphatic transport time and delays in different venom-induced effects are complex," says van Helden.
But, the rodent experiments did show that respiratory arrest was delayed one and a half times. "This [approach] should give snakebite victims more time to obtain medical care and antivenom treatment," write the researchers.
The results did not seem to be affected by the concentration of a NO-releasing active ingredient nor by a more extensive application over the whole of the rat's foot and leg.
Co-author Professor Geoffrey Isbister says there are approximately 3000 humans with suspected snakebites each year in Australia. "There may be more, but it's always difficult to estimate. [Of these, there are] about 100 to 200 severe envenomings and one to four deaths," he says.
Watch this space
Associate Professor Julian White of the Women's and Children's Hospital in Adelaide believes this new approach may be a useful adjunct to existing treatments, which include immobilisation and pressure bandages. He says that it needs further evaluation and validation before it can be recommended.
"The problem with all first aid treatments is that it is very hard to properly test to see whether the treatments work in real cases ... and with snakebites you don't have lots of patients presenting in a controlled setting," says White.
"[But] looking for new methods to make things better is a very worthwhile enterprise ... from my point of view, as a clinical toxicologist, I'd be saying to people watch this space keenly
Snakebite victims who apply an ointment to slow down the movement of venom in the body could prolong their survival by up to one and a half times, say Australian researchers.
Snake venom is often made of large toxic molecules that cannot directly enter the bloodstream. Instead, they are dispersed by the lymphatic vessels that run parallel to blood vessels and enter the bloodstream through veins near the heart.
Associate Professor Dirk van Helden of the University of Newcastle describes the lymphatic system as being like "a vacuum cleaner that takes big molecules into circulation."
He and his colleagues were initially looking for ways to improve lymphatic flow when they realised that some snake venoms contain substances that ensure this 'vacuum cleaner' does not become blocked, thus allowing the venom to succeed in its deadly mission.
"Lymph flow is mainly influenced by pumping - like millions of little hearts in series. This is due to smooth muscle contractions in the vessel wall and movement resulting from external compression," he says.
The substances in the snake venom indirectly prevent the release of nitric oxide (NO) that impedes these muscle contractions. This led van Helden to hypothesise that treatment with a topical solution that releases NO, such as one containing glycerol trinitrate (nitroglycerin), will delay the venom's action.
Their results are published today in Nature Medicine.
NO time to wait
To test the treatment, fifteen human volunteers were injected on the top of the foot, with a traceable non-toxic substance that is physically similar to snake venom.
The researchers used a special camera to measure how long it took for the mock venom to travel from the foot to the groin. Then, on a separate occasion, they repeated the experiment with the addition of a 5 centimetre patch of glycerol-nitrate-containing ointment next to the injection site. This was applied within a minute of the injection.
"Transit time to the groin was three-fold greater when we applied the ointment," says van Helden.
The team then used the same methodology to examine the effect of slowing down lymph flow in anaesthetised rats whose hind limbs had been injected with venom from the Eastern brown snake (Pseudonaja textilis).
Transit time of the venom was similarly delayed.
"This doesn't, however, mean you will survive three times longer because the relationship between changes in lymphatic transport time and delays in different venom-induced effects are complex," says van Helden.
But, the rodent experiments did show that respiratory arrest was delayed one and a half times. "This [approach] should give snakebite victims more time to obtain medical care and antivenom treatment," write the researchers.
The results did not seem to be affected by the concentration of a NO-releasing active ingredient nor by a more extensive application over the whole of the rat's foot and leg.
Co-author Professor Geoffrey Isbister says there are approximately 3000 humans with suspected snakebites each year in Australia. "There may be more, but it's always difficult to estimate. [Of these, there are] about 100 to 200 severe envenomings and one to four deaths," he says.
Watch this space
Associate Professor Julian White of the Women's and Children's Hospital in Adelaide believes this new approach may be a useful adjunct to existing treatments, which include immobilisation and pressure bandages. He says that it needs further evaluation and validation before it can be recommended.
"The problem with all first aid treatments is that it is very hard to properly test to see whether the treatments work in real cases ... and with snakebites you don't have lots of patients presenting in a controlled setting," says White.
"[But] looking for new methods to make things better is a very worthwhile enterprise ... from my point of view, as a clinical toxicologist, I'd be saying to people watch this space keenly
