SNAKE BITE MANAGEMEMENT
Introduction
· Elapidae – have short, fixed front
fangs. The family includes, kraits, cobras, sea snakes and coral snakes.
PATHOPHYSIOLOGY
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Clinical
features
•
Cobra mostly cause pain and swelling at bite site, worrying feature is
neurological dysfunctions: ophthalmoplegia, ptosis, aphasia, respiratory
paralysis and dysphagia.
Sea/water snakes cause slight local effects
and mainly musculoskeletal findings:, stiffness, paresthesia and myalgia leading
to myoglobinuria and later renal failure. Paralysis can also occur.
•
Note: There may be overlap of clinical features caused by venoms of different
species of snake. For example, some cobras can cause severe local envenoming
(formerly thought to be due to only vipers).
Management
First
aid
•
The aims are to retard absorption of venom, provide basic life support and
prevent further complications.
•
Reassure the victim – anxiety state increases venom absorption.
•
Immobilise bitten limb with splint or sling (retard venom absorption).
•
Apply a firm bandage for elapid bites (delay absorption of neurotoxic venom)
but not for viper bites whose venom cause local necrosis.
•
Leave the wound alone - DO NOT incise, apply ice or other remedies.
•
Tight (arterial) tourniquets are not recommended.
•
Do not attempt to kill the snake. However, if it is killed bring the snake to
the hospital for identification. Do not handle the snake with bare hands as
even a severed head can bite!
•
Transfer the victim quickly to the nearest health facility.
Treatment
at the Hospital
•
Do rapid clinical assessment and resuscitation including Airway, Breathing,
Circulation and level of consciousness. Monitor vital signs (blood pressure,
respiratory rate, pulse rate).
•
Establish IV access; give oxygen and other resuscitations as indicated.
•
History: Inquire part of body bitten, timing, type of snake, history of atopy.
•
Examine
•
Bitten part for fang marks (sometimes invisible), swelling,
tenderness,necrosis.
•
Distal pulses (reduced or absent in compartment syndrome)
•
Patient for bleeding tendencies – tooth sockets, conjunctiva, puncture sites.
•
Patient for neurotoxicity – ptosis, ophthalmoplegia, bulbar and respiratory
paralysis.
•
Patient for muscle tenderness, rigidity (sea snakes).
•
Urine for myoglobinuria.
•
Send blood investigations (full blood count, renal function tests, prothrombin
time /partial thromboplastin time, group and cross matching).
•
Perform a 20-min Whole Blood Clotting Test. Put a few mls of blood in a clean,
dry glass test tube, leave for 20 min, and then tipped once to see if it has
clotted. Unclotted blood suggests hypofibrinogenaemia due to pit viper bite and
rules out an elapid bite.
•
Review immunisation history: give booster antitetanus toxoid injection if
indicated.
•
Venom detection kit is used in some countries to identify species of snake.
However, it is not available in Malaysia.
•
Admit to ward for at least 24 hours (unless snake is definitely non-venomous).
Antivenom
treatment
•
Antivenom is the only specific treatment for envenomation.
•
Give as early as indicated for best result. Effectiveness is time and dose
related. It is most effective within 4 hrs after envenomation and less
effective after 12 hrs although it may reverse coagulopathies after 24 hrs.
Indications
for antivenom
•
Should be given only in the presence of envenomation as evidenced by:
•
Coagulopathy.
•
Neurotoxicity.
•
Hypotension or shock, arrhythmias.
•
Generalised rhabdomyolysis (muscle aches and pains).
•
Acute renal failure.
•
Local envenomation e.g. local swelling more than half of bitten limb, extensive
blistering/bruising, bites on digit, rapid progression of swelling.
•
Helpful laboratory investigations suggesting envenomation include anaemia,
thrombocytopenia, leucocytosis, raised serum enzymes (creatine kinase,
aspartate aminotransferase, alanine aminotransferase), hyperkalaemia, and
myoglobinuria.
Choice
of antivenom
•
If biting species is known, give monospecific (monovalent) antivenom (more
effective and less adverse reactions).
•
If it is not known, clinical manifestations may suggest the species:
•
Local swelling with neurological signs = cobra bites
•
Extensive local swelling + bleeding tendency = Malayan Pit vipers
•
If still uncertain, give polyvalent antivenom.
•
No antivenom is available for Malayan kraits, coral snakes and some species of
green pit vipers. Fortunately, bites by these species are rare and usually
cause only trivial envenoming.
Dosage
and route of administration
•
Amount given is usually empirical. Recommendations from manufacturers are
usually very conservative as they are mainly based on animal studies.
Guide
to initial dosages of important Antivenoms
Species
Antivenom
manufacturer
Initial
dose
Malayan
pit viper Thai Red Cross (Monovalent) 100 mls
Cobra
Twyford
Pharmaceuticals (monovalent)
Serum
Institute of India;
Biological
E. Limited, India(Polyvalent) 50 mls (local) 100 mls (systemic) 50 mls (local)
100
- 150 mls (systemic)
•
Repeat antivenom administration until signs of envenomation resolved.
•
Give through IV route only. Dilute antivenom in any isotonic solution
(5-10ml/kg, bigger children dilute in 500mls of IV solution) and infuse the
whole amount in one hour.
•
Infusion may be discontinued when satisfactory clinical improvement occurs even
if recommended dose has not been completed
•
Do not perform sensitivity test as it poorly predicts anaphylactic reactions.
•
Do not inject locally at the bite site.
•
Prepare adrenaline, hydrocortisone, antihistamine and resuscitative equipment
and be ready if allergic reactions occur.
•
Pretreatment with adrenaline SC remains controversial. Small controlled studies
in adults have shown it to be effective in reducing risk of reactions.
However,
its effectiveness and appropriate dosing in children have not been evaluated.
There is no strong evidence to support the use of hydrocortisone/antihistamine
as premedications. Consider their use in the patient with history of atopy.
Antivenom
reactions occurs in 20% of patients 3 types of reactions may occur:
•
Early anaphylactic reactions
•
Occur 10-180 minutes after starting antivenom. Symptoms range from itching,
urticaria, nausea, vomiting, and palpitation to severe systemic anaphylaxis:
hypotension, bronchospasm and laryngeal oedema.
Treatment
of anaphylactic reactions:
•
Stop antivenom infusion.
•
Give adrenaline IM (0.01ml/kg of 1 in 1000) and repeat every 5-10mins till
symptoms subside. In case of persistent hypotension, life threatening anaphylaxis, adrenaline can be given IV 0.1mg
of 1:10,000 dilution bolus over 5 mins. If hypotension is refractory to bolus
dose start IV infusion at 1 microgm/kg/min. Close monitoring of heart rate is
required.
•
Give antihistamine, e.g. chlorpheniramine 0.2mg/kg, hydrocortisone 4mg/kg/dose
and IV fluid resuscitation (if hypotensive).
•
Nebulised adrenaline in the presence of stridor or partial obstruction
•
Nebulised salbutamol in the presence of bronchospasm or wheeze
•
If only mild reactions, restart infusion at a slower rate.
•
Pyrogenic reactions – develop 1-2 hours after treatment and are due to
pyrogenic contamination during the manufacturing process. Symptoms include
fever, rigors, vomiting, tachycardia and hypotension. Give treatment as above. Treat
fever with paracetamol and tepid sponging.
•
Late reactions – occur about a week later. It is a serum sickness-like illness
(fever, arthralgia, lymphadenopathy,etc).
Treat
with Chlorpheniramine 0.2mg/kg/day in divided doses for 5 days.
If
severe, give Oral prednisolone (0.7 – 1mg/kg/day) for 5-7 days.
When
to restart the antivenom after a reaction:
•
Once the patient has stabilized, BP under control, manifestations of the
reaction has subsided.
•
In severe reactions restart antivenom under cover of adrenaline infusion. Rate
of antivenom infusion is decreased initially and done under close monitoring in
the ICU. Weigh the need for antivenom versus the potential risk of a severe
anaphylactic reaction.
Anticholinesterases
•
They should always be tried in severe neurotoxic envenoming, especially when no
specific antivenom is available, e.g. bites by Malayan krait and coral snakes.
The drugs have a variable but potentially useful effect.
•
Give test dose of Edrophonium chloride (Tensilon) IV (0.25mg/kg, adult 10mg)
with Atropine sulphate IV (50µg/kg, adult 0.6mg). If patients respond
convincingly, maintain with Neostigmine methylsulphate IV (50-100µg/kg) and
Atropine, four hourly by continuous infusion.
Supportive/ancillary
treatment
•
Clean wound with antiseptics.
•
Give analgesia to relief pain (avoid aspirin). In severe pain, morphine may be
administered with care. Watch closely for respiratory depression.
•
Give antibiotics if the wound looks contaminated or necrosed e.g. IV
Crystalline Penicillin +/- Gentamicin, Amoxicillin/clavulanic acid,
Erythromycin or a third generation Cephalosporin.
•
Respiratory support – respiratory failure may require assisted ventilation.
•
Watch for compartment syndrome – pain, swelling, cold distal limbs and muscle
paresis. Get early orthopaedic/surgical opinion.Patient may require urgent
fasciotomy but consider only after sufficient antivenom has been
given
and correction of coagulation abnormalities with fresh frozen plasma and
platelets before any surgical intervention as bleeding may be uncontrollable.
•
Desloughing of necrotic tissues should be carried out as required.
•
For oliguria and renal failure, e.g. due to sea snake envenomation, measure
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 is rarely required.
Downsides
in management
•
Giving antivenom ‘prophylactically’ to all snakebite victims. Not all
snakebites by venomous snakes will result in envenoming. On average, 30% bites
by cobra, 50% by Malayan pit vipers and 75% by sea snakes DO NOT result in
envenoming. Antivenom is expensive and carries the risk of causing severe
anaphylactic reactions (as it is derived from horse or sheep serum). Hence, it
should be used only in patients in whom the benefits of antivenom are considered
to exceed the risks.
•
Delaying in giving antivenom in district hospitals until victims are
transferred to referral hospitals. Antivenom should be given as soon as it is
indicated to prevent morbidity and mortality. District hospitals should stock
important antivenoms and must be equipped with facilities and staff to provide
safe monitoring and care during the antivenom infusion.
•
Giving polyvalent antivenom for envenoming by all type of snakes. Polyvalent
antivenom does not cover all types of snakes, e.g. Sii polyvalent (imported
from India) is effective in cobra and some kraits envenoming but is not
effective against Malayan pit viper. Refer to manufacturer drug insert for
details.
•
Giving smaller doses of antivenom for children. The dose should be the same as
for adults. Amount given depends on the amount of venom injected rather than
the size of victim.
•
Giving pretreatment with hydrocortisone / antihistamine for snakebite victims.
Snakebites do not cause allergic or anaphylactic reactions. These medications
may be considered in those who are given ANTIVENOM.
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