Rationalisation of first-aid measures for elapid snakebite. 1979

First-hand knowledge about snakes and snake-bite management: an urgent need

Snake-bite is a well-known but fairly ignored medical problem in India. Lack of precise first aid knowledge for snake-bite is a substantial reason for its severe fatality in human beings. The present study is comprised of a pilot survey that assesses and evaluates the knowledge of people of different occupations (teachers, students, farmers, medical residents, and miscellaneous) about snakes and snake-bite management. The pilot survey was conducted through a well-structured open-ended questionnaire about experiences with snakes and snake-bites and first aid measures for accidental snake-bites. Proper knowledge of snakes and snake-bite management was either diminutive or absent in the majority of the subjects, especially amongst teachers. Even the medical professionals were not well acquainted with knowledge about snakes and snake-bite management. Only 13% knew about ‘big four’, 18% knew ‘dry bite’, and 21% of subjects knew about anti-snake venom (ASV) used in India. 39% of subjects knew about the whereabouts of traditional healer. Only 12% of subjects, mostly medical residents, knew of any bedside test for diagnosis of snake-bite, and 11% of respondents also knew of LD₅₀ of Indian cobra. A well-timed first aid treatment is always decisive in the management of life-threatening snake-bite cases but the present survey has found that most of the study groups had inadequate and little misleading fundamental knowledge comprising regional snakes, first aid measures for accidental snake-bite, and welfare schemes for snake-bite victims. Therefore, the present study proposes to conduct more such appraisals and strengthening of education curricula on snake-bite that would surely inculcate an adequate level of primary skill in ignorant societies.

Two pathways for venom toxin entry consequent to injection of an Australian elapid snake venom

Here we test and refute the hypothesis that venom toxins from an Australian elapid, the Eastern Brown snake (Pseudonaja textilis, PTx), solely require lymphatic transport to enter the circulation. Studies were made using anaesthetised non-recovery rats in which a marker dye (India ink) or highly potent PTx venom was injected into the hind paw. The studies required a means of inhibiting lymphatic function, as achieved by cooling of the test hind limb to low temperatures (~3 °C). Maintained entry of a non-lethal dose (0.15 mg/kg) and respiratory arrest consequent to injection of a lethal dose (1 mg/kg) of PTx venom at these low temperatures indicate that venom including toxin components enter the circulation directly via the vascular system, a process facilitated by, but not dependent on, lymphatic transport. Notably, the venom had a direct effect on vascular permeability markedly increasing this to allow extravasation of plasma albumin (MWt ~60 kDa).

Pharmacological approaches that slow lymphatic flow as a snakebite first aid

Background

This study examines the use of topical pharmacological agents as a snakebite first aid where slowing venom reaching the circulation prevents systemic toxicity. It is based on the fact that toxin molecules in most snake venoms are large molecules and generally first enter and traverse the lymphatic system before accessing the circulation. It follows on from a previous study where it was shown that topical application of a nitric oxide donor slowed lymph flow to a similar extent in humans and rats as well as increased the time to respiratory arrest for subcutaneous injection of an elapid venom (Pseudonaja textilis, Ptx; Eastern brown snake) into the hind feet of anaesthetized rats.

Methodology/Principal Findings

The effects of topical application of the L-type Ca²⁺ channel antagonist nifedipine and the local anesthetic lignocaine in inhibiting lymph flow and protecting against envenomation was examined in an anaesthetized rat model. The agents significantly increased dye-measured lymph transit times by 500% and 390% compared to controls and increased the time to respiratory arrest to foot injection of a lethal dose of Ptx venom by 60% and 40% respectively. The study also examined the effect of Ptx venom dose over the lethal range of 0.4 to 1.5 mg/kg finding a negative linear relationship between increase in venom dose and time to respiratory arrest.

Conclusions/Significance

The findings suggest that a range of agents that inhibit lymphatic flow could potentially be used as an adjunct treatment to pressure bandaging with immobilization (PBI) in snakebite first aid. This is important given that PBI (a snakebite first aid recommended by the Australian National Health and Medical research Council) is often incorrectly applied. The use of a local anesthetic would have the added advantage of reducing pain.

Snakebite remains a major problem worldwide causing death or serious illness in many tens of thousands of victims annually. An approach to reduce the burden of envenoming is to provide optimum first aid procedures. We have previously shown that topical application of a nitric oxide (NO) donor slowed lymph flow to similar extent in humans and rats as well as increased the time to respiratory arrest by ∼50% for subcutaneous injection of eastern brown snake venom into the hind feet of anaesthetized rats. The present study examines the use of several other topical pharmacological agents that aim to slow venom toxins reaching the circulation through the lymphatic system. The study found that the agents examined were similarly effective to that previously found for the NO donor. The fact that one of these is a commonly used topical local anesthetic may be an ideal adjunct first aid, as it provides first aid while reducing pain.

Commentary: pressure bandaging for North American snake bite? No!

This issue of The Journal of Medical Toxicology includes a position statement regarding the use of pressure immobilization for the pre-hospital treatment of North American Crotalinae envenomation. This commentary discusses the background behind the creation of the position statement and explores the issues involved in applying science to real-world public health recommendations and practice.

Pressure bandaging for North American snake bite? No!

This issue of Clinical Toxicology includes a Position Statement regarding the use of pressure immobilization for the pre-hospital treatment of North American Crotalinae envenomation. This Commentary discusses the background behind the creation of the Position Statement and explores the issues involved in applying science to real world public health recommendations and practice.

A pharmacological approach to first aid treatment for snakebite

Snake venom toxins first transit the lymphatic system before entering the bloodstream. Ointment containing a nitric oxide donor, which impedes the intrinsic lymphatic pump, prolonged lymph transit time in rats and humans and also increased rat survival time after injection of venom. This pharmacological approach should give snakebite victims more time to obtain medical care and antivenom treatment.