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Poisoning monographs

General background

Teaching outlines

Topic structure


Summary points:

STEP 1: Initial assessments, resuscitation and management

ABC (Airway, Breathing and Circulation)
Respiratory rate
Tidal volume
Ability to count for one breath( if a respirometer is not available )
Neck muscle power

Clinical situations which need urgent resuscitation
Respiratory muscle paralysis producing poor respiratory effort
Cardiovascular collapse and profound hypotension.
Comatose or semi comatose state and aspiration of vomitus
Profound bleeding ( haemoptisis, haematemesis )
Cardiac arrhythmias
Intubation and Ambu ventilation (in impending respiratory paralysis)
Establish an intravenous line
Cardiac monitoring
Inotropics and anti-arrhythmic treatment
Left lateral position to prevent aspiration
Transfer with a doctor (if decided to transfer from a peripheral hospital)

STEP 2: Look for evidence of envenoming (to decide antivenom treatment)

Neurotoxicity – double vision, ptosis, ophthalmoplegia, altered consciousness )
Haematotoxicity- positiveWBCT20, haematuria, haematamesis, haemolysis
Local effects – fang marks, pain, swelling, discolouration
Nephrotoxicity – oliguria, rising blood urea and creatinine
Cardiac effects – chest pain, hypotension, ECG
Myotoxicity – muscle pain
Abdominal pain, vomiting (in krait bite)

How to do WBCT20 test
Take a small clean glass test tube
Place a 2ml of freshly sampled venous blood
Tip the tube once to achieve surface contact
Leave undisturbed for 20 min at room temperature
Observe at 5min intervals for clot formation
If blood is unclotted and runs out at 20 min, the patient has positive test or
hypofibrinogenaemia as a result of consumption coagulopathy.

If there is any doubt, repeat the test with a control (healthy person).

It is important that the vessel used should be a cleaned glass test tube and small bottles shouldn’t be used as it may give false positive results.

This test should be repeated at 1h, 2h, 6h and 12hour after admission for detection of the earliest sign of envenoming. This is important only in Russell’s viper bite.

Indications for antivenom
Bleeding and clotting disorder ( Positive WBCT20, spontaneous bleeding)
Intravascular haemolysis(dark urine – dipstick test for haemoglobinuria)
Neutotoxic signs
Cardiovascular manifestations: hypotension, arrhythmia, abnormal ECG
Nephrotoxicity: oliguria, rising blood urea
Rhabdomyolysis( muscle pain, hyperkalaemia, myoglobinuria)
Local swelling( consider extent, rapid extension and degree of tissue damage)
All proven Russell’s viper bite (even before development of signs of envenoming. Fang marks and identification of offending snake are important).

STEP 3: Identify the offending snake (dead specimen, matches with preserved specimens, clinical evidence, circumstantial evidence)

Study the physical features of deadly venomous snakes responsible for the bite.

Seek advice from experts ( SLMA committee on snake bite, Tel: 011 2693324 or from the nearest Medical Faculty)

STEP 4: Antivenom ( Indian polyvalent antivenom made against cobra, Russell’s viper, common krait and saw scaled viper).

Administer of the earliest evidence of envenoming
Not effective in hump-nosed viper bites
Give to all proven Russell’s viper bites if the fang marks and local swelling are present without waiting for evidence of systemic envenoming
Administer initial dose 10 vials,20 vials or 30vials depending on the severity of envenoming. Infusion should be started slowly at the beginning in order to detect allergic reactions and be completed in one hour.
Same dosage should be given to children, but volume of infusion can be decided to suite the body weight.
Repeat WBCT20 six(6) hourly in Russell’s viper bite to decide the second dose.

STEP 5: Prevention of antivenom reactions

Start a parallel infusion of hydrocortisone( 500 – 1000mg ) in 300ml of
normal saline 5 min before antivenom infusion and continue for 30 min
thereafter. May give hydrocortisone bolus(400mg) to begin with.
Give chlorpheniramine 10 mg iv bolus 5min after starting antivenom
Adrenaline sc(exclude contraindications)-0.25ml(1:1000) could be used
as prophylaxis, but carries a high risk of complications.

Step 6: Management of allergic reactions to antivenom

Stop antivenom infusion temporary until the reactions are treated.

Severity of reactions could vary from mild to severe. Mild reactions include itching, urticaria, rigor with normal blood pressure. But hypotension occurs in moderate to severe reactions.

Mild reactions: chlorpheniramine 10mg iv bolus
Moderate reactions: Adrenaline(1:1000 )0.5ml sc and chlorpheniramine
10mg iv bolus
Severe reactions: Adrenaline(1:1000 )0.5ml im and chlorpheniramine
10mg iv bolus

Continue antivenom thereafter irrespective of reactions for 1h
Incidence of reactions comes down for 2nd of 3rd dose of antivenom

STEP 7: Supportive management

Paracetamol for pain , avoid NSAIDs such as aspirin
Fluids – avoid oral fluids for 24 hours in envenomed patients, however, adequate intravenous hydration is needed to prevent pre-renal failure.
Avoid – potassium containing foods
Oxygen via mask SOS
Antibiotics – unnecessary ( for local swelling )
Reassurance – allow a family member to stay with patient

STEP 8: Further monitoring ( to detect complications, assess recovery, treatments)

Urine output (normal 40-50ml/ hour )
Colour of the urine (haematuria, haemoglobinuria, myoglobinuria)
Fluid input ( avoid both over hydration and dehydration, in acute renal failure give fluid amount equal to insensible loss + urine output )
Respiration (respiratory rate / half hourly)
Tidal volume or one breath count (to detect respiratory paralysis)
Cyanosis ( blood gases if available ) to detect respiratory problems
Pulse- BP
Level of consciousness (LOC)
Bleeding and clotting time monitoring (WBCT20). Antivenom should be repeated until WBCT20 become normal for 24hours

Step 9: Anticipation and detection of complications ( important parameters)

Respiratory paralysis – tidal volume, respiratory rate, neck muscle power, hypoxia
Severe coagulopathy(DIC) – Persistently positive WBCT20, bleeding from venepuncture sites, low platelet count, FDP
Hyperkalaemia – serum electrolytes, ECG ( tall peak T wave, wide QRS)
Acute renal failure – oliguria, blood urea, serum creatinine
Shock – hypotension, tachycardia, cold peripheries
ARDS – blood gases ( hypoxaemia,hypercapnoea), Chest X- ray
Severe local effects – pain, discolouration, necrosis, fever
Compartment syndrome – loss of sensation in the digits, ischaemia, gangrene, pain and swelling.

STEP 10: Management of complications

Respiratory paralysis – Ambu ventilation, assisted ventilation
DIC – High dose antivenom, management of multiple organ damage, FFP, platelets
Hyperkalaemia – 10% calcium gluconate 10ml iv, Insulin/dextrose,
1.26% NaHCO3 iv 50-100 ml, dialysis.
Acute renal failure – conservative management, dialysis
Shock- dopamine/ dobutamine
ARDS – IPPV with PEEP, Oxygen 80 –100%
Severe local effects – surgical debridement, antibiotics, skin graft

Compartment syndrome – fasciotomy after haemostasis

Step 11: Management of long term sequels and rehabilitation

Contractures - physiotherapy
Neuropathy - reversible

Problem shooting during transfer and management

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