Chapter 108: Snake Bite

Chapter 108: Snake Bite

POISONS & TOXINS

Introduction • Different geographical region and countries will have different snake species of medical importance. • Snakes of medical importance in Malaysia are either equipped with specialised front fangs or without front fangs. The front-fanged snakes are either in the family Elapidae (cobras, kraits, coral snakes and sea snakes) or Crotalinae (Pit vipers). Pythons and some non-front fanged colubroids may also pose danger to humans. • All front-fanged and a few rear-fanged snakes are equipped with venom. • Snake venoms are made of complex and diverse group of proteins, many with enzymatic activity. Envenoming syndromes are treated with timely administration of the appropriate antivenom in adequate amount • It is important to note that a medically important snake found in one state in Malaysia may not be indigenous in another. Therefore, the requirement for antivenom may differ from hospitals to hospitals in the country. • Early access to experts in the field (Clinical Toxinologist) will assist healthcare providers in snake species identification and optimal management, saving lives and limbs. Note: Assistance/query/consultation for identification and clinical management of snakebite can be obtained from the National Poison Centre Malaysia and the Remote Envenomation Consultation Services (RECS) Malaysia (http://mstoxinology.blogspot.com/p/recs.html). Clinical features of common snakebite envenoming • Local envenoming syndrome by cobra (Naja) species include immediate pain, progressively worsening swelling, blistering and necrosis. Systemic envenoming manifest as acute neurological and cardiac dysfunction including ptosis [an early sign], ophthalmoplegia, dysphagia [drooling of saliva], aphasia, dyspnea, muscle paralysis and arrhythmias. • Krait (Bungarus) species bites may cause minimal local effects and may go unnoticed. Systemic envenoming may be delayed and manifest as sudden onset of rapidly progressive myalgia and muscle paralysis. • Sea snake bites cause minimal local effects. Systemic envenoming may present as generalised myalgia, stiffness, paresis, paralysis and myoglobinuria (dark coloured urine). Rhabdomyolysis may lead to acute renal failure. • Pit viper bite envenoming may cause progressively worsening pain and swelling, haemorrhagic blisters, necrosis, hypovolaemic shock from third space fluid loss and bleeding due to coagulopathy. Note: These clinical features are the manifestations of various toxins in the venom. Toxic venom components can vary even within the same snake species. The age, geographical distribution and prey specificity factors may influence the compositions of venom toxins.

606

MANAGEMENT Prehospital care / First Responder The objectives are to provide basic life support, to reduce the rate of venom absorption and to prevent further complications. Prehospital care interventions include: • Calm the patient down and move to safety. • Remove jewellery on the affected limb and loosen tight-fitting clothing. • Immobilise the affected limb with a splint or sling and reduce movements. Pressure Bandaging and Immobilization (PBI) is to be applied only by a trained first-aider. Indications for PBI include 1) the snake is identified as krait, coral snake or sea snake; 2) if the snake is unidentified, the transport time to the hospital is prolonged (more than an hour). • If venom enters the eye (venom ophthalmia), immediately irrigate with copious amounts of clean water. • Transfer all patients to the nearest healthcare facility with emergency care. Note: Document all symptoms and signs that may manifest prior to arrival to the hospital. Do not interfere with the bitten area by applying tourniquet, doing incisions, sucking, rubbing, vigorous cleaning, applying herbs/chemicals, massage or electrical shocks. Avoid wasting time to search or kill the snake. Take several good quality pictures of the snake at a safe distance e.g. using mobile phone camera. If the snake was killed, bring the it along in a secure container.

607

POISONS & TOXINS

Emergency and Hospital • Triage to resuscitation zone and Perform rapid clinical assessment (Primary survey). • Monitor vital signs and cardiac rhythm, and resuscitate as indicated. • Obtain detailed history of presenting complaint: 1) time of incident 2) location of incident 3) how exactly did the patient get bitten 4) what happened to the snake 5) part of body bitten 6) what was done after bitten 7) pain score progression (PSP) since incident 8) current complaints 9) allergy history (to horse or papaya) and other co-morbidities • Perform close serial examination at fixed time intervals (every hour) for any changes over the bitten area (bite marks and surrounding skin), the rate of proximal progression of the oedema (RPP), PSP, palpable tender lymph nodes draining the area, and distal neurovascular status of the affected limb. Taking serial pictures of the affected area helps.

• Examine for neurological dysfunction (tailored according to child’s age group), bleeding tendencies, and muscle tenderness and rigidity. • Send initial laboratory investigations (full blood count, coagulation profile and Creatine Kinase) and repeat serially every 6 hours for the first 24 hours of incident. Consider other tests as necessary (renal function tests, liver function test, fibrinogen level, D-dimer and urine examination). Review the trends. • If laboratory blood test is not available or delayed and the diagnosis is unidentified snakebite or a pit viper bite, consider performing serial bedside 20-min Whole Blood Clotting Test (20WBCT). Put 2mls of venous blood in a clean and dry glass test tube, leave it standing for 20 min, and then tipped once. Note: Unclotted blood suggests a pit viper bite with systemic envenomation. • Review immunisation status: administer IM anti-tetanus injection if indicated. (Note: Arterial puncture and Intramuscular injections are contraindicated if the coagulation profile is abnormal) • Administer analgesia (avoid NSAIDs in pit viper envenoming) and antivenom as indicated. • Admit to medical ward for close serial observation of the progress and response to therapy (vitals, RPP, PSP, LN and blood tests). If there is no signs and symptoms of envenomation for at least 24hrs or if an expert verifies the snake to be a non-venomous species and asymptomatic, the patient may not require hospitalisation.

POISONS & TOXINS

Antivenom • Antivenom (AV) is the only proven antidote for envenomation. • Not all snakebites, even by snakes equipped with venom, results in envenoming syndrome. • Antivenoms carries a (low) risk of adverse reactions. Therefore, the appropriate antivenom should be used only when it is indicated and administered as early as possible. • Antivenoms appropriate for use in Malaysia are currently imported from Thailand and Australia. The dosage for children is the same as for adults (Table 1) • Adrenaline, steroid and antihistamine should not be given prophylactically unless indicated. • Skin sensitivity test is not necessary as it poorly predicts anaphylactic reactions, may induce hypersensitivity and will cause unnecessary delay in antivenom therapy.

608

Indications for antivenom Systemic envenomation • Coagulopathy. • Neurological abnormalities. • Cardiovascular abnormalities. • Generalised rhabdomyolysis / haemolysis. • Acute kidney injury. • Supporting laboratory results. Local envenomation (with other considerations) • Progressive significant oedema of the bitten area, especially if involving the fingers. • Rapid speed of progression of oedema (trends of RPP) within a few hours. • Palpable tender lymph node draining the affected limb. • Rapidly expanding local necrosis. Note: Helpful laboratory results suggesting envenomation include prolonged PT/APTT, raised INR (>1.2), reducing fibrinogen level, thrombocytopenia, leucocytosis, anaemia, hyperkalaemia, hyponatraemia, myoglobinuria and raised serum enzymes (e.g. Creatine kinase, aminotransferases). Choice of antivenom • If snake species is identified and AV is indicated, consider monovalent/ mono-specific antivenom. • If snake species is unidentified and AV is indicated, consider Neuro Polyvalent or Hemato Polyvalent antivenom.

609

POISONS & TOXINS

Preparation and administration • Prepare adrenaline, hydrocortisone, antihistamines and resuscitative equipment prior to antivenom infusion. • Reconstitute freeze-dried antivenom with the solution supplied or 10ml WFI (water for injection). Gently swirl (never shake) to dissolve the freezedried powder. Further dilute in 5-10ml/kg of hypotonic crystalloid solution for children (250-500ml isotonic crystalloid for adults). • Infuse at a slow rate (1 to 2 ml/min) for 5-10min and if there is no reaction, increase the rate to 5-10mls/min to complete the infusion in less than one hour. • Closely observe patient during and for at least 1 hour after completion of intravenous infusion. Document pain score prior to, during and after the antivenom infusion. Document vital signs and clinical progression (RPP, PSP, LN) every 10-15 min then hourly. • Repeat antivenom administration until satisfactory response or improvement of envenoming signs is observed.

Antivenom reactions Early hypersensitivity reactions are mostly rate dependent anaphylactoid reaction. Symptoms range from itching, urticaria, nausea, vomiting, palpitation, bronchospasm, laryngeal oedema to hypertensive shock. In the event of antivenom reaction: • Stop antivenom infusion. • Give adrenaline IM 0.01 mg/kg of 1:1,000 (1 mg/mL) solution, into upper lateral thigh and repeat 5 to 10 minutes if not improved (max of 0.5 mg total dose). If IM injection is contraindicated, give slow IV boluses of 0.01 mg/kg of 1:10,000 (0.1mg/mL) solution every 2 min (max of 0.3 mg total dose). If not improving start IV infusion at 0.05-1 mcg/kg/min titrated to response. • Give boluses of IV 0.9% saline at 20 mL/kg as required. • Give slow IV antihistamine and steroid (e.g. chlorpheniramine maleate 0.2mg/kg), hydrocortisone 4mg/kg/dose). • Give nebulised adrenaline in the presence of stridor or partial obstruction. • Give nebulised salbutamol in the presence of bronchospasm or wheeze • Once the patient is hemodynamically stabilised and the signs and symptoms subsided, the antivenom infusion should be restarted at a slower rate with very close vigilance for further reactions. Pyrogenic reactions usually develop 1-2 hours after treatment and is believed due to pyrogenic contamination during the manufacturing process. Symptoms include fever, rigors, vomiting, tachycardia and hypotension. In the event of such reaction, provide treatment as above and treat fever with paracetamol and tepid sponging. Late reactions (serum sickness) may occur between 1 to 12 days (mean 1 week) with symptoms of fever, arthralgia, lymphadenopathy, etc. Treatment of serum sickness: • Give chlorpheniramine maleate 0.25mg/kg/day in divided doses for 5 days. • If fails to respond in 24hrs, give oral prednisolone (0.7mg/kg/day) for 5 days.

POISONS & TOXINS

Anticholinesterases • Should be considered in severe neurotoxic envenoming when antivenom is inadequate or unavailable. • Give test dose of either IV Edrophonium chloride (Tensilon) 0.25mg/kg (max 10mg) or IV Neostigmine 0.05-0.07mg/kg (max 0.5-2.5mg), with IV Atropine sulphate 50μg/kg (max 0.6mg). • If patient convincingly responds, maintain with IV Neostigmine methylsulphate (50-100μg/kg) and Atropine, 4 hourly by continuous infusion.

610

Supportive treatment • Provide respiratory support/assisted ventilation in those with clinical signs of respiratory compromise/paresis. • Give analgesia to relief pain (avoid aspirin/NSAIDs). In severe pain, IV tramadol may be given. Pain relief will normally be seen following optimal antivenom therapy. • Give broad-spectrum antibiotics if the wound appears contaminated with devitalised tissues or necrosis has developed. • Correction of coagulation abnormalities with fresh frozen plasma and platelets is strictly per case-by-case basis. • Renal failure requires measurement of daily urine output, serum creatinine, urea and electrolytes. If urine output fails to increase after rehydration and diuretics (e.g. frusemide), start renal dose of dopamine (2.5μg/kg/minute IV infusion) and place on strict fluid balance. Dialysis may be required in severe cases of envenoming with renal complications. • Clean and dress wound. Debridement of necrotic tissues should be carefully carried out as needed and should not be mistaken with the debridement for necrotising fasciitis. • Observe for the unlikely event of compartment syndrome (pain, swelling, cold distal limbs and muscle paresis). Orthopaedic opinion regarding surgical intervention must be supported with significantly raised (>40mmHg) intracompartmental measurements using Stryker or Wick catheters. • Give optimal amount of appropriate antivenom prior to any urgent surgical intervention.

POISONS & TOXINS

611

612

Guide to dosages of appropriate antivenom for Malaysia Species the AV is raised from Manufacturer: Antivenom First Dose ml/vial Monocle cobra, Naja kaouthia QSMI Thai Red Cross: Cobra Antivenin 100mls/10 vials Subsequent dose 1-2 hr King Cobra, Ophiophagus hannah QSMI Thai Red Cross: King Cobra Antivenin Malayan krait, Bungarus candidus QSMI Thai Red Cross: Malayan Krait Antivenin 50mls/5 vials Subsequent dose 1-2 hr Banded krait, Bungarus fasciatus QSMI Thai Red Cross: Banded Krait Antivenin Malayan pit viper, Calloselasma Rhodostoma QSMI Thai Red Cross: Malayan Pit Viper 30mls/3 vials Subsequent dose 6 hr Green pit viper, Cryptelytrops Albolabris QSMI Thai Red Cross: Green Pit Viper Antivenin Malayan pit viper, Calloselasma rhodostoma, QSMI Thai Red Cross: Hemato Polyvalent Snake An30mls/3 vials Green pit viper, Cryptelytrops Albolabris, tivenom Subsequent dose 6 hr Thai Russell’s Viper, Daboia siamensis Monocled Cobra, Naja kaouthia, QSMI Thai Red Cross: Neuro Polyvalent Snake An50-100mls/ 5-10 vials King Cobra Ophiophagus hannah, tivenom Subsequent dose 1-2 hr Banded Krait Bungarus fasciatus, Malayan Krait, Bungarus candidus. Beaked sea snake, Seqirus, Australia: Sea snake Polyvalent Antivenom 10-30mls/1-3 vials Hydrophis (Enhydrina) schistosus. Subsequent dose 1-2 hr Note: • Subsequent doses are indicated according to the clinical signs and symptoms. • The doses are based on animal studies and manufacturer’s recommendations. • Monocle cobra, Naja kaouthia antivenom has good cross neutrality with the Equatorial spitting cobra, Naja sumatrana venom. • Green pit viper antivenom has good cross neutralization with venom from other green pit vipers belonging to the Trimeresurus complex group. • Beaked sea snake, Hydrophis schistosus antivenom has good cross neutralization with many other sea snake venom.

POISONS & TOXINS

Measuring Rate of Proximal Progression (RPP) of the oedema 1. A more informative parameter for reviewing progressive painful swelling 2. First: Determine the border of the micropore to be used to mark the proximal margin of the oedema, e.g. distal border to distal border of the micropore markers (Figure 1). 3. Second: Palpate for the most proximal margin of the swelling and apply a small strip of micropore tape to the most proximal margin of the oedema. 4. Label the current time and date on the micropoer tape. 5. Determine a fixed interval to review the progression, e.g. every 1-2 hours. 6. Measure the distance between two micropore tape borders over the fixed time interval (Figure 2). 7. The RRP for that interval will be documented in cm/hr.

Figure 1 (above).

POISONS & TOXINS

Figure 2 (above).

613

614

Time am/pm

GCS 3-15

PR bpm

BP mmHg

RR bpm

SpO2 %

PSP 0-10

Serial Clinical Progress Observation Chart at fixed regular time intervals

PSP= pain score progression, RPP = rate of proximal progression, LN = enlarged tender lymph node

Date d/m

POISONS & TOXINS

RPP cm/hr

LN Yes/No

Date

POISONS & TOXINS

615

20WBCT

WBC

Hb

Platelets

PT

APTT

INR

Serial Blood Results (evey 4-6 hours for first 24 hours or after Antivenom administratrion)

Time

CK