Venomous SnakebiteVenomous Snakebite

R Johnson MBBS MRCS DTM&H

Five Venomous Snake Five Venomous Snake FamiliesFamilies

Viperidae: N.American pit vipers (rattlesnakes, copperheads, mocassins), Asian pit vipers, African and Asian vipers and adders

Elapidae: cobras, kraits, mambas, coral snakes, Laticauda seasnakes of Tropics, Sub-Tropics

Hydrophidae: seasnakes, Australasian venomous snakes

Colubridae: mostly non-venomous but includes rear-fanged boomslang, vine snakes, mole vipers, Japanese yamakagashi, Asian keelback

Actractaspididae: burrowing asps of Africa

Fang Types

Elapid-mamba

Pit viperRear fanged boomslang

Non-venomous python

Venomous snake behaviourVenomous snake behaviour The majority of bites do not lead to envenomation First bite is often a warning Juvenile snakes more dangerous Few snakes are aggressive; they are more scared of us People to not drop dead in seconds!!!Many bites associated with alcohol or trying to tease or

kill the snake98% of U.S. snakebite due to pit vipers but exotic

envenomations are becoming common as wellCoral snakes seldom bite but can be very dangerous

UK experienceUK experienceOne indigenous venomous snake

– Vipera berus (adder)75-100 bites per year

– Last fatality 1975Estimated 2000 dangerous snake “pets”

– 15-20 bites per yearMost bites on the hand whilst picking up

snake

Pit Viper Fang Apparatus

Diamond Back Rattlesnake—a pit viper

Most dangerous U.S. snake

Pitviper Fangs and Ridges

Arizona Coral Snake

Red touch yellow, kill a fellow; red touch black, fear may lack (in U.S.A.)

Elapid

Red touch

Black

fear may

lack

only works north of Mexico City

Pit VipersPit VipersLarge thick-bodied snakes with triangular

headHeat–sensing pit Elliptical pupils Single row of scales past the anal plateRattle—if a rattlesnake!Venom digests tissue and induces

hemolysis and possible later kidney failure

Pit Viper

N.A. Non-venomous

Two Venom Types: Hemolytic Two Venom Types: Hemolytic (Vipers)and Neurotoxic (Elapids)(Vipers)and Neurotoxic (Elapids)

Most Vipers and Pit vipers have a hemolytic or tissue-destroying digestive type of venom that causes immediate local pain and swelling (exceptions: some Mojave rattlesnakes are neurotoxic)

Most Elapids and Hydrophids (seasnakes) have a neurotoxic venom that produces little if any local symptoms—however cranial nerve palsies and respiratory arrest may follow (exception: spitting cobra bites will destroy tissue )

Pit Viper VenomPit Viper Venom Enzyme cocktail: complex mixture of enzymes and

small molecular weight peptides Purpose is to immobilize and predigest prey, defense

is secondary Constituents: proteolytic enzymes, thrombin,

collaginase, hyaluronidase, phospholipase A+B, crotamine (causes tetany), croactin, convulsin, gyroxin

25% bites are dry + 25% minimal= 50% will be OK Same antivenin used for all U.S. pit vipers:

rattlesnakes, copperheads and cottonmouths

Bothrops Envenomation: Hemolytic/Proteolytic

Symptoms of Viper EnvenomationSymptoms of Viper Envenomation Swelling Pain: searing or

burning Fang marks 1-4 Ecchymoses Vomiting Fasciculations Paresthesias Increased bleeding Blood blisters/blebs

Lymphadenitis Metallic taste Arrhythmias Seizures Shock Coagulopathy (DIC) Thrombocytopenia Tetany Coma Death (usually takes

days)

Measure Compartment Pressures but Never do prophylactic fasciotomy!

Bad outcome often results

Myoglobinuria due to tissue destruction can cause renal shutdown

Check the Urine!!! Viper victims often survive the initial bite only to walk in and later die of renal failure

Fatal Bite in a Toddler from Eastern Diamondback: Charleston, S.C.

Diamondback Rattlesnake Fang Marks

Vein penetration documented

The Culprit: Diamond Back Rattlesnake

First Aid in SnakebiteFirst Aid in Snakebite Calm and reassure victim Remove rings, watches, tight clothes Don’t catch or kill snake--second bite likely Don’t cut fang marks or suck out with mouth May use Sawyer-type venom extractor within 3m

(leave on for 30m) May use constriction band (no tourniquet) Don’t use ice or electric shock TRANSPORT ASAP TO HOSPITAL (phone and car

keys most important emergency equipment) Best not to administer antivenin in field setting!!!!! No role for prophylactic antibiotics!

Elapid First Aid: Compression/Immobilization

Snake Bite InvestigationsSnake Bite Investigations

FBC with platelets Urinalysis ABG PT/PTT/fibrinogen

(repeat w/in 12h) U&E/ creatinine Liver function tests Glucose

ECG Type and Cross Creatinine kinase

Polyvalent AntiveninPolyvalent AntiveninAntivenin (Crotalidae) polyvalent: rattlesnake,

copperhead, cottonmouth Horse serum antibodies to venom; sheep (ovine)

antivenin should be safer Dangerous—give only under controlled situations where

anaphalaxis can be managed Expect serum sickness later; treat with prednisolone If necessary, use enough (5+ vials for grade I, 5-15 for grade

II, 15-20+ for grade III) Dose not reduced for children! Expensive: £200/vial

Antivenin AdministrationAntivenin Administration Best w/in 4h but effective for at least 24h and

possibly up to 72h with coagulopathy Only give IV with physician in attendance and

adrenaline and antihistamines available at bedside If antivenin to be given, first skin test with horse

serum kit unless pt in extremis. If (+) give only if true threat to life/limb and then pre-medicate with hydrocortisone IV and chlorphenaramine IV

If negative, still consider pre-medication w/ chlorphenaramine IV and Cimetidine 300 mg IV

Antivenin AdministrationAntivenin Administration Reconstitute by injecting 10ml sterile water diluent to each

vial and swirling (takes time) Always get informed consent from pt or family if possible Reconstituted antivenin vials are added to 500 ml NS or

D5W then trial dose of 5-10 ml given over 5 minutes; epinephrine(1:1000) .3cc should be taped to IV bag just in case

If no reaction, adjust rate to give up to 10 vials in 1st hour w/ additional infusions every 2h until sign/sx resolving; common error: too little, too late

Fasciotomy rarely required with proper care

Serum SicknessSerum SicknessExpect 1-4 weeks after antivenin

administration whatever the doseSx: itching, urticarial rash, fever, arthralgiasRx: oral prednisolone therapy 60-80 mg

with taper every 4 daysMany physicians anticipate serum sickness

and discharge on steroids rather than waiting for it to develop

CroFabCroFab® Antivenin® Antivenin

Purified sheep antigen-binding fragmentCompared to equine IgG antivenom

– More effective– Fewer and less severe adverse effects– No anaphylaxis reported to date

Currently approved only for rattlesnake bitesCost $4600 to $14,000 (4 to 18 vials)

Contacts for helpContacts for help Arizona Poison Control; 1-602-626-6016 Good current source of information on exotic

antivenin availability Herpetologists available for consultation Royal Veterinary College, London Tel: +44 (0)20

7468 5000 Liverpool School of Tropical Medicine +44(0)151

705 3100 Nearest zoo will keep antivenins for the snakes in its

collection

Neurotoxic EnvenomationsNeurotoxic Envenomations Elapids and Hydrophids—venom attacks nervous

system and kills by respiratory arrest (hard to reverse) Some snake venoms (e.g. cobra) are intermediate and

are also hemotoxic causing severe local reactions like pit vipers

Minimal local reaction for most elapids (don’t wait for swelling to use antivenin!)

Rapid onset of neurologic symptoms: ptosis, respiratory paralysis, death

Fist Aid: immobilization and compression dressing Swab wound for venom antigen ID (Australia) Antivenin administration very soon

Ptosis due to krait bite (neurotoxic)

Coral Snake (Coral Snake (MicrurusMicrurus) Bites) Bites

Elapid: bites rare since snake is secretive/shy Local symptoms absent—systemic neurologic

symptoms will develop first and will be difficult to reverse

Treat likely eastern coral bites with Micrurus antivenin immediately—bite is unimpressive

3-5 vials if no signs or symptoms 6-10+ vials if systemic symptoms exist

Red touch yellow, kill a fellow; red touch black, fear may lack

Spitting Cobra of Africa

Non-Poisonous Snakes can also kill

Large Constrictors can kill: never wrap a constrictor around your neck!

Snakebite PreventionSnakebite Prevention

Wear protective clothing and boots Avoid drugs and alcohol with snakes Watch where you step and place your hands Avoid tall brush and undergrowth Leave snakes alone, don’t pick up dead snake or

even a snake head (reflex bites) Don’t keep venomous snakes as pets Don’t walk after dark—if you do, use a flashlight

“Ha! Ain’t a rattler, Jake. You got one of them maraca players down your bag—and he’s probably more scared than you.”

Spider Bites/ scorpion stingsSpider Bites/ scorpion stings

No native spiders of importanceOccasional pet spider bitesMost only mildly venomousTreat like bee stingLocal measures; ice packs, analgesia and

topical anaesthetic agents