Art & science | poisoning
Effects of snake envenomation: a guide for emergency nurses Stephen McGhee and colleagues explain how practitioners should care for people bitten by snakes, including those not native to the UK, and how to recognise the effects of different forms of venom Correspondence [email protected] Stephen McGhee is a clinical instructor at the University of South Florida College of Nursing, Tampa, Florida, United States
Abstract
John M Clochesy is director of faculty mentorship and assistant dean of the doctoral programme
Only one species of venomous snake, the adder, is indigenous to the UK, but many people keep venomous snakes as pets and others travel to places, such as the United States, where a wider variety of venomous snakes can be found. Emergency nurses should therefore be prepared to treat bite wounds caused by venomous and non-venomous snakes. This article offers an overview of the most common forms of envenomation in the UK and makes recommendations for the clinical care of people who have sustained snake bites.
Constance Visovsky is associate dean of student affairs and community engagement
Keywords Snake bite, adder bite, venom, envenomation
Alan Finnegan is Ministry of Defence professor of nursing and head of the academic department of military nursing at the Royal Centre for Defence Medicine, Birmingham
Both at the University of South Florida College of Nursing, Tampa, Florida, United States Date of submission December 8 2014 Date of acceptance December 16 2014 Peer review This article has been subject to double-blind review and has been checked using antiplagiarism software Author guidelines rcnpublishing.com/r/ en-author-guidelines
SNAKES HAVE a reclusive nature and prefer a rural habitat, and usually bite humans only when they sense they are under threat (Klug et al 2010, Evans and Nelson 2013). Nevertheless, venomous snake bites are associated with significant morbidity and mortality worldwide (World Health Organization (WHO) 2010). There have been 14 fatalities from snake bites in the UK since 1876 and the most recent of them, in 1975, involved a child in Scotland (Reid 1976). However, there were 510 cases of snake bite reported to the National Poisons Information Service between 2004 and 2010. Snakes are not indigenous to Northern Ireland. The European adder, or Vipera berus, is responsible for 52% of snake bites in the UK, with exotic species accounting for 26% and the European grass snake for 4%. The causes of the remaining 18% of snake bites are unidentified (Coulson et al 2013). While life-threatening envenomation is rare in the UK, people who have
been bitten can experience long periods of pain and distress (Warrell 2005). Although the adder is the only venomous snake indigenous to the UK, many pet enthusiasts keep snakes that pose a risk of life-threatening envenomation (Persson 2001). Significant envenomation by any of these snakes is considered a medical emergency requiring anti-venom therapy. Every year around the world there are about five million snake-bite envenomations (Girish and Kemparaju 2011), of which about 125,000 result in death and another 375,000 cause pain, loss of function or both (WHO 2010). Some people, including members of the military, farm workers and children who live in isolated rural areas, are especially at risk of envenomation due to their occupations or geographic locations (Johnson et al 2013). Most snake bites are inflicted on the feet and ankles (WHO 2010), with envenomation often causing neurotoxic and haemotoxic effects accompanied by tissue necrosis (Heiner et al 2013). Members of the British armed forces are often deployed to areas where there is a significant risk of snake bite (Wall 2012), although since 1990 there has been only one published case of non-fatal snake-bite envenomation involving a British soldier (Krysta-Clark et al 2004). Although envenomation has occurred among US forces taking part in combat operations in Afghanistan and Iraq, there are little data about the magnitude of the problem. In a voluntary cross-sectional survey of 390 US military personnel leaving Afghanistan, Shiau et al (2007) found there had been seven incidents of snake bite, and that military personnel there were at greater risk of snake bite than those in Iraq. In a more recent case review conducted in Afghanistan,
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Heiner et al (2013) reported on 17 snake bites involving 15 Afghan nationals and two members of the US military who had been bitten mainly on the fingers, hands, feet, ankles or lower legs. Because these are common locations for snake bites, troops in jungle locations must wear boots and gloves, and should exercise appropriate caution when lifting items from the jungle floor (Kasturiratne et al 2008). Envenomation from snake bites is also an important public health issue in tropical countries. In Sierra Leone, for example, nearly 7,000 people are bitten by snakes every year and almost 500 die due to lack of timely access to anti-venom (Kasturiratne 2008).
Venomous snake species The two types of venomous snakes discussed in this article are the Viperidae and Elapidae. Snakes of the Viperidae family include many of those found in the south-eastern US. They include the copperhead (Agkistrodon contortrix), water moccasin or cottonmouth (A. piscivorus), eastern diamondback (Crotalus adamanteus) and European adder (V. barus) (Evans and Nelson 2013). Snakes of the Elapidae family are also found in north America, as well as Africa, Asia, Australia and South America. They include cobras (genus Naja), the common krait (genus Bungarus), coral snakes (genus Micrurus) and mambas (genus Dendroaspis) (Evans and Nelson 2013). Some of these snakes are pictured in Figure 1.
The European adder can be found in most of mainland Britain. Adder bites usually occur between February and October, with the number of bites peaking during the summer months (Warrell 2005), a seasonal pattern that is thought to be associated with the adder’s hibernation periods (Coulson et al 2013). Meanwhile, about 75 different types of non-native snakes are kept as pets in the UK and envenomation from these occurs most often when they are being fed, their cages are being cleaned or their venom milked, or their owners handle them while intoxicated (Warrell 2005, Evans and Nelson 2013). Viperidae inject venom into their victims and leave painful, deep puncture wounds (Ferri 2012), although about 25% of Viperidae bites do not cause envenomation and are termed dry bites (Ashton et al 2011, Evans and Nelson 2013). Viperidae inject a haemotoxic venom, while snakes of the Elapidae family inject a neurotoxic venom that attacks blood and nerve tissue (Juckett and Hancox 2002).
Clinical features The first clinical manifestation of a snake bite is anxiety. Patients, even those who have sustained dry bites, may therefore report anxiety-associated autonomic arousal symptoms, including breathlessness, dizziness, numbness in the fingers, palpitations, sweating, tightness in the chest and tingling (Bates 2001). When practitioners attend to, transfer and treat patients, therefore, they must
Left: the coral snake, a snake of the Elapidae family
iStock
Figure 1 Snakes of the Viperidae and Elapidae families
Clockwise from right: an eastern diamondback, a water moccasin and a European adder, all of the Viperidae family
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Art & science | poisoning acute care offer them reassurance at all times. There follows a checklist of good practice in managing snake bites: ■ Keep calm, ensure you appear and sound confident, and maintain good eye contact with the patient. ■ Place patient in a comfortable sitting position. ■ If the patient is hyperventilating, encourage him or her to take deep and slow breaths, and praise their efforts. If the patient has a dry mouth, give him or her water. ■ If the patient is panicking, explain that this is a normal reaction. ■ Explain what the treatment involves but do not overwhelm the patient with information. Avoid using jargon or clinical terms unless you are sure the patient understands them. ■ Explain that pain does not necessarily mean harm. ■ Be positive about outcomes but keep to the facts. Avoid negative messages and do not speculate. ■ Provide the patient with an opportunity to ask questions and acknowledge his or her concerns. ■ After you have explained the treatment, ask the patient to confirm that he or she understands what has been said. The presenting signs and symptoms of envenomation depend on the variety of snake responsible for the bite. Snakes such as the spitting cobra and South African rinkhals (Hemachatus heamachatus) spit a form of venom that can cause venom ophthalmia if it enters the eyes. Venom ophthalmia can cause painful chemical Table 1 Systemic and localised effects of Viperidae and Elapidae venom Effects of envenomation
Snake family Viperidae
Elapidae
Haemotoxic
Ecchymosis, epistaxis, haematemesis, hypovolemia and shock, serious clotting defects, and persistent bleeding from puncture wounds, venipuncture sites and gums
Not applicable
Neurotoxic
Not applicable
Blurred vision, confusion, fasciculation, flaccid paralysis, headache, heaviness of the eyelids, paresthesia, ptosis, respiratory depression or arrest, renal failure, vomiting
Localised
Lymphatic spread Pain, redness, swelling, tenderness, bullae
(Adapted from Bates 2001)
conjunctivitis, sometimes leading to corneal ulceration and anterior uveitis, with the potential for secondary infection (Warrell 2005). Practitioners in Australia often use the enzyme-linked immunosorbent assay-based rapid snake venom detection kit (SVDK), which involves taking a swab of the patient’s bite area or a urine sample to identify the correct anti-venom to administer. SVDKs are not used in the UK or US, however. A summary of the localised and systemic effects of Viperidae and Elapidae venom is listed in Table 1.
Recommendations Most emergency department (ED) nurses in the UK will lack experience in treating patients who present with snake bite (Bates 2001). When someone with suspected snake bite presents to or contacts the ED, clinicians’ most important task is to identify the type of snake involved. There are recorded cases of envenomation in people handling the dead bodies or severed heads of snakes (Suchard and LoVecchio 1999), so anyone who has been bitten should be discouraged from bringing these to an ED. Instead, they should be asked to take a photograph of the snake (Warrell 2005), ideally by smartphone or digital camera so that the photograph can be shared easily. The National Poisons Information Service has a list of herpetologists who can give expert advice on snake species and the actions of their venom. First aid Initial first aid should involve safe transfer of the patient to hospital as quickly and with as little movement as possible (Gold and Barish 1992). Any delay in administering anti-venom can lead to significant complications or even mortality (Sharma et al 2004, Narvencar 2006). Reassurance must be given at all times when moving or transferring patients and during the treatment process. Rings and other tight-fitting jewellery should be removed from the patient in case of local swelling (Bates 2001), while a splint or sling can be applied to the affected limb area for immobilisation during transfer (Warrell 2005). For some Elapidae species, immediate pressure immobilisation is advocated due to the rapid action of neurotoxic venom (Bates 2001, Warrell 2005, Wall 2012). However, pressure immobilisation is not advocated for a patient bitten by a Viperidae species, such as the adder. Figure 2 shows the British armed forces method of pressure immobilisation adapted from Ministry of Defence (2012) clinical guidelines for operations.
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José F Donneys
Figure 2 British armed forces method of pressure immobilisation following snake bite
Clockwise from top left: applying pressure and splint to someone with envenomation to the lower leg Below: pressure immobilisation with a sling in someone with envenomation to the lower arm
Emergency management A patient who is thought to have been bitten by a poisonous snake requires maintenance of airway, breathing and circulation, and should be monitored for at least 24 hours or until a diagnosis of venomous snake bite has been excluded (Bates 2001, Evans and Nelson 2013). If the patient is to be transferred by ambulance, intravenous access must be achieved and a 0.9% sodium chlorine infusion commenced (Pittman 2008). Envenomation symptoms can develop between 30 and 60 minutes after a bite so it is important to monitor the patient’s vital signs, and to obtain a detailed clinical history that includes the type of snake and time of bite (Peterson 2006). A top-to-toe examination should then take place to assess for signs of coagulopathy, and nurses should assess for any puncture-type wounds that have been inflicted by fangs or small teeth. Treatment includes marking the border of swollen and tender areas with a view to skin reassessment every 15 minutes so that extension of the bite can be assessed (Ferri 2012).
Lymphatic obstruction, swelling and blister formation can be ameliorated by immobilisation and extension of the limb with a simple splint (Lavonas et al 2011). Tetanus immunisation will have to be considered because cases of Clostridium tetani infection have been reported following snake bite (Ferri 2012). If the patient has been bitten by a snake of the Viperidae family, anaphylactoid symptoms can be treated early with oral or parenteral H1 blockers (Bates 2001). If the patient is in pain, non-steroidal anti-inflammatory drugs (NSAIDs) should be avoided because of the risk of bleeding and renal dysfunction (Pittman 2008). Instead, the patient should be given paracetamol or opiate-based medication according to local guidelines. The recommended laboratory tests and other assessments are listed in Table 2, page 28.
Erratum – 6/2/15 The copy, left, about the kinds of pain relief that should be administered has been changed from the printed version.
Anti-venom Snake bites do not always result in envenomation so the use of anti-venom is not always indicated (Evans and Nelson 2013). However, its use
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Art & science | poisoning acute care Table 2 Assessments for envenomation after snake bite Types of assessment
Snake family Viperidae
Laboratory tests
Elapidae Full blood count Coagulation
Urea and electrolytes in blood Myoglobin in blood Protein and blood in urine Other assessments
Bleeding from tooth sockets, conjunctivae, nose, skin and gastrointestinal tract
None
following envenomation can prevent mortality and reduce the time patients must spend in hospital (Lavonas et al 2011). The use of anti-venom is indicated when there is all of the following: ■ Incoagulable blood or spontaneous systemic bleeding. ■ Neurotoxicity or myotoxicity. ■ Renal failure. ■ Shock. ■ Sustained fall in blood pressure. The NHS has access to a wide range of anti-venom preparations (Warrell 2005). Some clinicians have been reluctant to use anti-venom following adder envenomation due to the risk of severe allergic reaction (Coulson et al 2013). This is because in the late 1950s a child with mild viper envenomation died as a result of an anaphylactic reaction, and it was assumed thereafter that ‘the bite is less dangerous than the anti-serum’ (McKiddie 1979). The risk of anaphylactic reaction, which usually occurs between ten and 18 minutes after administration, can be mitigated by ensuring adrenaline is available during anti-venom administration (Theakston and Reid 1976, Bates 2001). Today the most commonly used anti-venom in the UK is the Zagreb anti-venom, which is an F(ab’)2 antibody used primarily for viper envenomation. Between 2004 and 2010, 85 patients in the UK required anti-venom. No anaphylactic or anaphylactoid reaction or signs of serum sickness were reported during this period (Coulson et al 2013). For people bitten by the more exotic snakes of the Viperidae family, many of which are popular with snake enthusiasts, Crotalidae Polyvalent Immune Fab (Ovine), or CroFab, is the anti-venom of choice (Pittman 2008). Obtained from sheep serum
following injection of pit viper venom, CroFab is used widely in the US (Evans and Nelson 2013). Most patients given anti-venom show a rapid improvement in hemodynamic status and level of consciousness (Bates 2001). Any bleeding should stop within 30 minutes of administration and coagulation profiles should return to normal within six hours. Supportive care Secondary hypovolemia as a result of haemorrhage and vasodilation should be treated with a transfusion of whole blood and plasma expanders (Bates 2001). Inotropes, such as dopamine, should be administered to support patients with hypotension as a result of increased capillary permeability (Bates 2001, Warrell 2005). In cases of envenomation that has led to neurotoxicity, endotracheal intubation with intermittent positive pressure ventilation may be required (Warrell 2005). Anticholinesterase drugs can be used to improve prognosis in patients with neurotoxic envenomation by reversing the effects of the neurotoxic venom (Watt et al 1986). Elapidae envenomation produces a ‘curare-type effect’ in patients by blocking postsynaptic nicotinic acetylcholine receptors at the neuromuscular junction (Evans and Nelson 2013). These patients appear flaccid and are in severe respiratory depression or arrest. Anticoagulants and corticosteroids should be avoided in all cases of envenomation due to the risks of haemorrhage (Pittman 2008). Antibiotics may be required if there are signs of bacterial infection, but there is no evidence to support administration of prophylactic antibiotics following envenomation (Jorge et al 2004). Fasciotomy, a surgical procedure that relieves pressure on the fascia, can treat loss of circulation to some areas of tissue or muscle and is useful for decompressing raised compartment pressures, signs of which include the ‘five Ps’: pain, pallor, paresthesia, pulselessness and paralysis. Fasciotomy is justified only if there is a compartmental pressure of more than 45mmHg, which can result in ischemic necrosis, but can take place only after normal coagulation has returned (Bates 2001). Care and follow up All patients administered anti-venom will require follow up because they are at risk of developing serum sickness, an allergy-type disease (Pittman 2008). Patients given anti-venom should be advised to look for signs of fever, joint pain and malaise, all of which are typical of serum sickness (Evans and Nelson 2013). Further blood testing that includes coagulation assay should be undertaken a few days after patients’
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initial discharge and they should be reviewed about three weeks later (Lavonas et al 2011). Patients who develop serum sickness should be administered prednisolone orally until the signs and symptoms have resolved (Gold and Barish 1992). During follow-up care, patients should be asked to report any signs of further bleeding and infection (Evans and Nelson 2013), and advised to avoid aspirin, NSAIDs, and all types of contact sports and dental work due to the risk of haemorrhage (Pittman 2008).
Summary All snake bites must be assessed by clinical professionals so that the patients concerned receive the correct treatments for the specific snakes that bit them. Photographs taken by smartphone can be useful for identifying the species of snake and increase the likelihood of correct management.
Early assessment and effective first aid reduce the chances of significant envenomation, and triage staff must be aware of the signs and symptoms of haemotoxic and neurotoxic envenomation to provide effective assessment. ED staff should be prepared to initiate measures to reverse hypovolemia, bleeding and respiratory sequelae associated with venomous snake bites. Further studies of patients with venomous and non-venomous snake bites are needed to advance clinical care and develop best practice for assessment, thereby increasing patients’ chances of survival.
Find out more A list of herpetologists in the UK, who can give expert advice on snake species and the actions of venoms, is available at www.npis.org
Online archive For related information, visit our online archive and search using the keywords
Conflict of interest None declared Acknowledgements The author would like to thank Defence Medical Services medical director Brigadier Timothy Hodgetts for giving security clearance and permission to reproduce the British armed forces pressure immobilisation technique, and University of South Florida multimedia assistant José F Donneys for taking the photographs
References Ashton J, Baker SN, Weant KA (2011) When snakes bite: the management of North American Crotalinae snake envenomation. Advanced Emergency Nursing Journal. 33, 1, 15-22. Bates N (2001) Venomous snake bites. Emergency Nurse. 9, 6, 28-33. Coulson J, Cooper G, Krishna C et al (2013) Snakebite enquiries to the UK National Poisons Information Service: 2004-2010. Clinical Toxicology. 49, 3, 229-229. Evans D, Nelson L (2013) Treating venomous snakebites in the United States: a guide for nurse practitioners. Nurse Practitioner. 38, 7, 13-22. Ferri F (2012) Ferri’s Clinical Advisor. Elsevier Mosby, Philadeliphia PA.
Johnson C, Rimmer J, Mount G et al (2013) Challenges of managing snakebite envenomation in deployed setting. Journal of the Royal Army Medical Corps. 159, 4, 307-311.
Lavonas E, Kokko J, Schaeffer T (2011) Short-term outcomes after Fab anti-venom therapy for severe crotaline snakebite. Annals of Emergency Medicine. 57, 2, 128-137.
Jorge M, Malaque C, Ribeiro L et al (2004) Failure of chloramphenicol to reduce the frequency of abscess formation as a complication of envenomation by Bothrops snakes in Brazil: a double-blind randomized controlled trial. Transactions of the Royal Society of Tropical Medicine and Hygiene. 98, 9, 529-534.
Matsen FA (1980) Compartmental syndromes. Hospital Practice. 15, 2, 113-117.
Juckett G, Hancox J (2002) Venomous snakebites in the United States: management review and update. American Family Physician. 66, 1, 30-30.
Girish K, Kemparaju K (2011) Overlooked issues of snakebite management: time for a strategic approach. Current Topics in Medicinal Chemistry. 11, 20, 2494-2508.
Kasturiratne A, Wickremasinghe AR, de Silva N et al (2008) The global burden of snakebite: a literature analysis and modelling based on regional estimates of envenoming and deaths. PLoSMedicine. tinyurl.com/n8u87ga (Last accessed: January 12 2015.)
Gold BS, Barish RA (1992) Venomous snakebites: current concepts in diagnosis, treatment and management. Emergency Medical Clinics of North America. 10, 2, 249-267.
Klug EP, Jackerel SL, With KA (2010) Linking snake habitat use to nest predation risk in grassland birds: the dangers of shrub cover. Oecoligia. 162, 2, 803-813.
Heiner JD, Bebarta VS, Varney SM et al (2013) Clinical effects and anti-venom use for snake bite victims treated at three US hospitals in Afghanistan. Wilderness and Environmental Medicine. 24, 4, 412-416.
Krysta-Clark J, Lewis S, Waterworth T (2004) Management of a snake bite in the field. Journal of the Royal Army Medical Corps. 150, 97-98.
McKiddie MT (1979) Treatment of adder bites. British Medical Journal. 2, 6194, 865-866. Ministry of Defence (2012) Clinical Guidelines for Operations. The Stationery Office, London. Narvencar K (2006) Correlation between timing ASV administration and complications in snake bites. Journal of Associated Physicians India. 54, 717-719. Persson H (2001) Envenoming by European vipers: anti-venom treatment: influence on morbidity. Przeglad Lekarski. 58, 4, 223-225. Peterson ME (2006) Snake bite: coral snakes. Clinical Techniques in Small Animal Practice. 21, 4, 183-186. Pittman HJ (2008) Rattlesnake bite. Nursing. 38, 4, 72. Reid J (1976) Treatment of adder bite. The Lancet. 2, 7978, 185-186. Sharma S, Chappuis F, Jha N et al (2004) Impact of snake bites and determinants of fatal outcome in South Eastern Napal. American Journal of Tropical Medicine Hygiene. 71, 2, 234-238.
Shiau DT, Saunders JW, Putnam SD et al (2007) Self-reported incidence of snake, spider and scorpion encounters among deployed US military in Iraq and Afghanistan. Military Medicine. 172, 10, 1099-1102. Suchard JR, LoVecchio F (1999) Envenomation by rattlesnake thought to be dead. New England Journal of Medicine. 340, 24, 1930. Theakston RD, Reid HA (1976) Effectiveness of Zagreb anti-venom against envenoming by adder. Vipera berus. The Lancet. 2, 7977, 121-123. Wall C (2012) British military snake-bite guidelines: pressure immobilisation. Journal of the Royal Army Medical Corps. 158, 3, 194-198. Warrell DA (2005) Treatment of bites by adders and exotic venomous snakes. British Medical Journal. 331, 7527, 1244-1247. Watt G, Theakston R, Hayes C et al (1986) Positive response to edrophonium in patients with neurotoxic envenoming by cobras: a placebo controlled study. New England Journal of Medicine. 315, 23, 1444-1448. World Health Organization (2010) Guidelines for the Management of Snake Bites in the South-East Asia Region. WHO, Geneva.
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Effects of snake envenomation: a guide for emergency nurses Stephen McGhee and colleagues explain how practitioners should care for people bitten by snakes, including those not native to the UK, and how to recognise the effects of different forms of venom Correspondence [email protected] Stephen McGhee is a clinical instructor at the University of South Florida College of Nursing, Tampa, Florida, United States
Abstract
John M Clochesy is director of faculty mentorship and assistant dean of the doctoral programme
Only one species of venomous snake, the adder, is indigenous to the UK, but many people keep venomous snakes as pets and others travel to places, such as the United States, where a wider variety of venomous snakes can be found. Emergency nurses should therefore be prepared to treat bite wounds caused by venomous and non-venomous snakes. This article offers an overview of the most common forms of envenomation in the UK and makes recommendations for the clinical care of people who have sustained snake bites.
Constance Visovsky is associate dean of student affairs and community engagement
Keywords Snake bite, adder bite, venom, envenomation
Alan Finnegan is Ministry of Defence professor of nursing and head of the academic department of military nursing at the Royal Centre for Defence Medicine, Birmingham
Both at the University of South Florida College of Nursing, Tampa, Florida, United States Date of submission December 8 2014 Date of acceptance December 16 2014 Peer review This article has been subject to double-blind review and has been checked using antiplagiarism software Author guidelines rcnpublishing.com/r/ en-author-guidelines
SNAKES HAVE a reclusive nature and prefer a rural habitat, and usually bite humans only when they sense they are under threat (Klug et al 2010, Evans and Nelson 2013). Nevertheless, venomous snake bites are associated with significant morbidity and mortality worldwide (World Health Organization (WHO) 2010). There have been 14 fatalities from snake bites in the UK since 1876 and the most recent of them, in 1975, involved a child in Scotland (Reid 1976). However, there were 510 cases of snake bite reported to the National Poisons Information Service between 2004 and 2010. Snakes are not indigenous to Northern Ireland. The European adder, or Vipera berus, is responsible for 52% of snake bites in the UK, with exotic species accounting for 26% and the European grass snake for 4%. The causes of the remaining 18% of snake bites are unidentified (Coulson et al 2013). While life-threatening envenomation is rare in the UK, people who have
been bitten can experience long periods of pain and distress (Warrell 2005). Although the adder is the only venomous snake indigenous to the UK, many pet enthusiasts keep snakes that pose a risk of life-threatening envenomation (Persson 2001). Significant envenomation by any of these snakes is considered a medical emergency requiring anti-venom therapy. Every year around the world there are about five million snake-bite envenomations (Girish and Kemparaju 2011), of which about 125,000 result in death and another 375,000 cause pain, loss of function or both (WHO 2010). Some people, including members of the military, farm workers and children who live in isolated rural areas, are especially at risk of envenomation due to their occupations or geographic locations (Johnson et al 2013). Most snake bites are inflicted on the feet and ankles (WHO 2010), with envenomation often causing neurotoxic and haemotoxic effects accompanied by tissue necrosis (Heiner et al 2013). Members of the British armed forces are often deployed to areas where there is a significant risk of snake bite (Wall 2012), although since 1990 there has been only one published case of non-fatal snake-bite envenomation involving a British soldier (Krysta-Clark et al 2004). Although envenomation has occurred among US forces taking part in combat operations in Afghanistan and Iraq, there are little data about the magnitude of the problem. In a voluntary cross-sectional survey of 390 US military personnel leaving Afghanistan, Shiau et al (2007) found there had been seven incidents of snake bite, and that military personnel there were at greater risk of snake bite than those in Iraq. In a more recent case review conducted in Afghanistan,
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Heiner et al (2013) reported on 17 snake bites involving 15 Afghan nationals and two members of the US military who had been bitten mainly on the fingers, hands, feet, ankles or lower legs. Because these are common locations for snake bites, troops in jungle locations must wear boots and gloves, and should exercise appropriate caution when lifting items from the jungle floor (Kasturiratne et al 2008). Envenomation from snake bites is also an important public health issue in tropical countries. In Sierra Leone, for example, nearly 7,000 people are bitten by snakes every year and almost 500 die due to lack of timely access to anti-venom (Kasturiratne 2008).
Venomous snake species The two types of venomous snakes discussed in this article are the Viperidae and Elapidae. Snakes of the Viperidae family include many of those found in the south-eastern US. They include the copperhead (Agkistrodon contortrix), water moccasin or cottonmouth (A. piscivorus), eastern diamondback (Crotalus adamanteus) and European adder (V. barus) (Evans and Nelson 2013). Snakes of the Elapidae family are also found in north America, as well as Africa, Asia, Australia and South America. They include cobras (genus Naja), the common krait (genus Bungarus), coral snakes (genus Micrurus) and mambas (genus Dendroaspis) (Evans and Nelson 2013). Some of these snakes are pictured in Figure 1.
The European adder can be found in most of mainland Britain. Adder bites usually occur between February and October, with the number of bites peaking during the summer months (Warrell 2005), a seasonal pattern that is thought to be associated with the adder’s hibernation periods (Coulson et al 2013). Meanwhile, about 75 different types of non-native snakes are kept as pets in the UK and envenomation from these occurs most often when they are being fed, their cages are being cleaned or their venom milked, or their owners handle them while intoxicated (Warrell 2005, Evans and Nelson 2013). Viperidae inject venom into their victims and leave painful, deep puncture wounds (Ferri 2012), although about 25% of Viperidae bites do not cause envenomation and are termed dry bites (Ashton et al 2011, Evans and Nelson 2013). Viperidae inject a haemotoxic venom, while snakes of the Elapidae family inject a neurotoxic venom that attacks blood and nerve tissue (Juckett and Hancox 2002).
Clinical features The first clinical manifestation of a snake bite is anxiety. Patients, even those who have sustained dry bites, may therefore report anxiety-associated autonomic arousal symptoms, including breathlessness, dizziness, numbness in the fingers, palpitations, sweating, tightness in the chest and tingling (Bates 2001). When practitioners attend to, transfer and treat patients, therefore, they must
Left: the coral snake, a snake of the Elapidae family
iStock
Figure 1 Snakes of the Viperidae and Elapidae families
Clockwise from right: an eastern diamondback, a water moccasin and a European adder, all of the Viperidae family
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Art & science | poisoning acute care offer them reassurance at all times. There follows a checklist of good practice in managing snake bites: ■ Keep calm, ensure you appear and sound confident, and maintain good eye contact with the patient. ■ Place patient in a comfortable sitting position. ■ If the patient is hyperventilating, encourage him or her to take deep and slow breaths, and praise their efforts. If the patient has a dry mouth, give him or her water. ■ If the patient is panicking, explain that this is a normal reaction. ■ Explain what the treatment involves but do not overwhelm the patient with information. Avoid using jargon or clinical terms unless you are sure the patient understands them. ■ Explain that pain does not necessarily mean harm. ■ Be positive about outcomes but keep to the facts. Avoid negative messages and do not speculate. ■ Provide the patient with an opportunity to ask questions and acknowledge his or her concerns. ■ After you have explained the treatment, ask the patient to confirm that he or she understands what has been said. The presenting signs and symptoms of envenomation depend on the variety of snake responsible for the bite. Snakes such as the spitting cobra and South African rinkhals (Hemachatus heamachatus) spit a form of venom that can cause venom ophthalmia if it enters the eyes. Venom ophthalmia can cause painful chemical Table 1 Systemic and localised effects of Viperidae and Elapidae venom Effects of envenomation
Snake family Viperidae
Elapidae
Haemotoxic
Ecchymosis, epistaxis, haematemesis, hypovolemia and shock, serious clotting defects, and persistent bleeding from puncture wounds, venipuncture sites and gums
Not applicable
Neurotoxic
Not applicable
Blurred vision, confusion, fasciculation, flaccid paralysis, headache, heaviness of the eyelids, paresthesia, ptosis, respiratory depression or arrest, renal failure, vomiting
Localised
Lymphatic spread Pain, redness, swelling, tenderness, bullae
(Adapted from Bates 2001)
conjunctivitis, sometimes leading to corneal ulceration and anterior uveitis, with the potential for secondary infection (Warrell 2005). Practitioners in Australia often use the enzyme-linked immunosorbent assay-based rapid snake venom detection kit (SVDK), which involves taking a swab of the patient’s bite area or a urine sample to identify the correct anti-venom to administer. SVDKs are not used in the UK or US, however. A summary of the localised and systemic effects of Viperidae and Elapidae venom is listed in Table 1.
Recommendations Most emergency department (ED) nurses in the UK will lack experience in treating patients who present with snake bite (Bates 2001). When someone with suspected snake bite presents to or contacts the ED, clinicians’ most important task is to identify the type of snake involved. There are recorded cases of envenomation in people handling the dead bodies or severed heads of snakes (Suchard and LoVecchio 1999), so anyone who has been bitten should be discouraged from bringing these to an ED. Instead, they should be asked to take a photograph of the snake (Warrell 2005), ideally by smartphone or digital camera so that the photograph can be shared easily. The National Poisons Information Service has a list of herpetologists who can give expert advice on snake species and the actions of their venom. First aid Initial first aid should involve safe transfer of the patient to hospital as quickly and with as little movement as possible (Gold and Barish 1992). Any delay in administering anti-venom can lead to significant complications or even mortality (Sharma et al 2004, Narvencar 2006). Reassurance must be given at all times when moving or transferring patients and during the treatment process. Rings and other tight-fitting jewellery should be removed from the patient in case of local swelling (Bates 2001), while a splint or sling can be applied to the affected limb area for immobilisation during transfer (Warrell 2005). For some Elapidae species, immediate pressure immobilisation is advocated due to the rapid action of neurotoxic venom (Bates 2001, Warrell 2005, Wall 2012). However, pressure immobilisation is not advocated for a patient bitten by a Viperidae species, such as the adder. Figure 2 shows the British armed forces method of pressure immobilisation adapted from Ministry of Defence (2012) clinical guidelines for operations.
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José F Donneys
Figure 2 British armed forces method of pressure immobilisation following snake bite
Clockwise from top left: applying pressure and splint to someone with envenomation to the lower leg Below: pressure immobilisation with a sling in someone with envenomation to the lower arm
Emergency management A patient who is thought to have been bitten by a poisonous snake requires maintenance of airway, breathing and circulation, and should be monitored for at least 24 hours or until a diagnosis of venomous snake bite has been excluded (Bates 2001, Evans and Nelson 2013). If the patient is to be transferred by ambulance, intravenous access must be achieved and a 0.9% sodium chlorine infusion commenced (Pittman 2008). Envenomation symptoms can develop between 30 and 60 minutes after a bite so it is important to monitor the patient’s vital signs, and to obtain a detailed clinical history that includes the type of snake and time of bite (Peterson 2006). A top-to-toe examination should then take place to assess for signs of coagulopathy, and nurses should assess for any puncture-type wounds that have been inflicted by fangs or small teeth. Treatment includes marking the border of swollen and tender areas with a view to skin reassessment every 15 minutes so that extension of the bite can be assessed (Ferri 2012).
Lymphatic obstruction, swelling and blister formation can be ameliorated by immobilisation and extension of the limb with a simple splint (Lavonas et al 2011). Tetanus immunisation will have to be considered because cases of Clostridium tetani infection have been reported following snake bite (Ferri 2012). If the patient has been bitten by a snake of the Viperidae family, anaphylactoid symptoms can be treated early with oral or parenteral H1 blockers (Bates 2001). If the patient is in pain, non-steroidal anti-inflammatory drugs (NSAIDs) should be avoided because of the risk of bleeding and renal dysfunction (Pittman 2008). Instead, the patient should be given paracetamol or opiate-based medication according to local guidelines. The recommended laboratory tests and other assessments are listed in Table 2, page 28.
Erratum – 6/2/15 The copy, left, about the kinds of pain relief that should be administered has been changed from the printed version.
Anti-venom Snake bites do not always result in envenomation so the use of anti-venom is not always indicated (Evans and Nelson 2013). However, its use
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Art & science | poisoning acute care Table 2 Assessments for envenomation after snake bite Types of assessment
Snake family Viperidae
Laboratory tests
Elapidae Full blood count Coagulation
Urea and electrolytes in blood Myoglobin in blood Protein and blood in urine Other assessments
Bleeding from tooth sockets, conjunctivae, nose, skin and gastrointestinal tract
None
following envenomation can prevent mortality and reduce the time patients must spend in hospital (Lavonas et al 2011). The use of anti-venom is indicated when there is all of the following: ■ Incoagulable blood or spontaneous systemic bleeding. ■ Neurotoxicity or myotoxicity. ■ Renal failure. ■ Shock. ■ Sustained fall in blood pressure. The NHS has access to a wide range of anti-venom preparations (Warrell 2005). Some clinicians have been reluctant to use anti-venom following adder envenomation due to the risk of severe allergic reaction (Coulson et al 2013). This is because in the late 1950s a child with mild viper envenomation died as a result of an anaphylactic reaction, and it was assumed thereafter that ‘the bite is less dangerous than the anti-serum’ (McKiddie 1979). The risk of anaphylactic reaction, which usually occurs between ten and 18 minutes after administration, can be mitigated by ensuring adrenaline is available during anti-venom administration (Theakston and Reid 1976, Bates 2001). Today the most commonly used anti-venom in the UK is the Zagreb anti-venom, which is an F(ab’)2 antibody used primarily for viper envenomation. Between 2004 and 2010, 85 patients in the UK required anti-venom. No anaphylactic or anaphylactoid reaction or signs of serum sickness were reported during this period (Coulson et al 2013). For people bitten by the more exotic snakes of the Viperidae family, many of which are popular with snake enthusiasts, Crotalidae Polyvalent Immune Fab (Ovine), or CroFab, is the anti-venom of choice (Pittman 2008). Obtained from sheep serum
following injection of pit viper venom, CroFab is used widely in the US (Evans and Nelson 2013). Most patients given anti-venom show a rapid improvement in hemodynamic status and level of consciousness (Bates 2001). Any bleeding should stop within 30 minutes of administration and coagulation profiles should return to normal within six hours. Supportive care Secondary hypovolemia as a result of haemorrhage and vasodilation should be treated with a transfusion of whole blood and plasma expanders (Bates 2001). Inotropes, such as dopamine, should be administered to support patients with hypotension as a result of increased capillary permeability (Bates 2001, Warrell 2005). In cases of envenomation that has led to neurotoxicity, endotracheal intubation with intermittent positive pressure ventilation may be required (Warrell 2005). Anticholinesterase drugs can be used to improve prognosis in patients with neurotoxic envenomation by reversing the effects of the neurotoxic venom (Watt et al 1986). Elapidae envenomation produces a ‘curare-type effect’ in patients by blocking postsynaptic nicotinic acetylcholine receptors at the neuromuscular junction (Evans and Nelson 2013). These patients appear flaccid and are in severe respiratory depression or arrest. Anticoagulants and corticosteroids should be avoided in all cases of envenomation due to the risks of haemorrhage (Pittman 2008). Antibiotics may be required if there are signs of bacterial infection, but there is no evidence to support administration of prophylactic antibiotics following envenomation (Jorge et al 2004). Fasciotomy, a surgical procedure that relieves pressure on the fascia, can treat loss of circulation to some areas of tissue or muscle and is useful for decompressing raised compartment pressures, signs of which include the ‘five Ps’: pain, pallor, paresthesia, pulselessness and paralysis. Fasciotomy is justified only if there is a compartmental pressure of more than 45mmHg, which can result in ischemic necrosis, but can take place only after normal coagulation has returned (Bates 2001). Care and follow up All patients administered anti-venom will require follow up because they are at risk of developing serum sickness, an allergy-type disease (Pittman 2008). Patients given anti-venom should be advised to look for signs of fever, joint pain and malaise, all of which are typical of serum sickness (Evans and Nelson 2013). Further blood testing that includes coagulation assay should be undertaken a few days after patients’
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initial discharge and they should be reviewed about three weeks later (Lavonas et al 2011). Patients who develop serum sickness should be administered prednisolone orally until the signs and symptoms have resolved (Gold and Barish 1992). During follow-up care, patients should be asked to report any signs of further bleeding and infection (Evans and Nelson 2013), and advised to avoid aspirin, NSAIDs, and all types of contact sports and dental work due to the risk of haemorrhage (Pittman 2008).
Summary All snake bites must be assessed by clinical professionals so that the patients concerned receive the correct treatments for the specific snakes that bit them. Photographs taken by smartphone can be useful for identifying the species of snake and increase the likelihood of correct management.
Early assessment and effective first aid reduce the chances of significant envenomation, and triage staff must be aware of the signs and symptoms of haemotoxic and neurotoxic envenomation to provide effective assessment. ED staff should be prepared to initiate measures to reverse hypovolemia, bleeding and respiratory sequelae associated with venomous snake bites. Further studies of patients with venomous and non-venomous snake bites are needed to advance clinical care and develop best practice for assessment, thereby increasing patients’ chances of survival.
Find out more A list of herpetologists in the UK, who can give expert advice on snake species and the actions of venoms, is available at www.npis.org
Online archive For related information, visit our online archive and search using the keywords
Conflict of interest None declared Acknowledgements The author would like to thank Defence Medical Services medical director Brigadier Timothy Hodgetts for giving security clearance and permission to reproduce the British armed forces pressure immobilisation technique, and University of South Florida multimedia assistant José F Donneys for taking the photographs
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