Snake bite

First Aid:
  1. Reassure
    • 70% bites are non venomous
    • 50% venomous bites are dry
  2. Immobilise the limb
    • Done like fractured limb, hard scale to be place at joint and tied on either side
    • If it takes > 30 mins to reach hospital , creep bandage 50-70mm hg pressure to be applied to obstruct lymphatic & venous drainage.
  3. Get to hospital
  4. Tell symptoms to doctor
  5. Don'ts
    • Don't time tight tourniquet → can cause gangrene
    • Don't suck blood
    • Don't use herbs , snake stones.

Scenario 1:

Witnessed snake bite
&
No signs of  envenomation
↓
20 min whole blood clotting test
↓
Repeat half hrly for 3 hours
Then Hourly for 3 hours
Then 6 hrly for 24 hours
↓
20 min WBCT normal & clinically well
Discharge at 24 hours

Scenario 2 - Antihemostatic bite:

Witnessed snake bite 
& 
Signs of envenomation
↓
20 min WBCT + 10 Vials ASV + Supportive care
↓
Repeat 20 min WBCT after 6 hrs
↓
5 - 10 vials ASV if needed
↓
Repeat 20 mins WBCT & ASV if needed
↓
If total of 30 ASV reached & no improvement
↓
Fresh frozen plasma considered

Scenario 3 -Neurotoxic bite:

Signs & symptoms
↓
10 vials of ASV
↓
No response in 1-2 hours
↓
10 vials of ASV
↓
Pt in resp failure, received 20 vials & on ventilator
↓
ASV therapy should be stopped
↓
Anticholinesterase challenge test
↓
Atropine 0.05mg/kg (max 0.6mg) iv f/b neostigmine 0.04mg/kg iv (max 1.5mg)
↓
Repeat neostigmine 0.01mg/kg with atropine every 30mins for 3 doses
↓
  1. If positive response (50% improvement in ptosis)→ cobra postsynaptic bite
    • neostigmine 0.01mg/kg with atropine every 30mins for 2 more doses ( total 5 doses with half hour gaps)
    • then 5 more doses (totalling 10 doses) at 1 hour , 2hr , 6hr, 12hr , 24hr tapering for each dose
  2. If no response after initial 3 doses →assume Krait presynaptic bite
    • Calcium gluconate 1-2ml/kg in dilution slow iv every 6 hrly till neuroparalysis recovers.



Signs of evenomation:
  1. Systemic
    1. Coagulation
      • 20 min WBCT
      • Visible spontaneous systemic bleeding gums
    2. Neurotoxicity
      • Ptosis
      • External ophthalmoplegia
      • Muscle paralysis
      • Inability to lift hand
  2. Local
    • Severe local swelling involving more than half of limb
    • Severe swelling of digits after bite
Dosage:
  • 10 vials...each vial dissolved in 10ml NS / 5% dextrose
  • Total dose is diluted to 10ml /kg  and for neonate 5ml/kg
  • Infused over 1 hour and slower in neonate
Response:
  • Spontaneous systemic bleeding stops within 15 minutes
  • Blood coagulation usually restored in 6 hours
  • Postsynaptic envenoming (cobra) start improving in 30 mins , presynaptic envenoming (Krait) usually takes time to improve.
Special cases:
  • Before surgery - upto 25 vials ASV may be given
  • When arrived late at hospital
    • Coagulopathy + administer ASV
    • Neurotoxic & on ventilator - 8-10 vials ASV to ensure no unbound venom.
ASV adverse effects:
  1. Early anaphylactic reactions
    • 10min - 6hrs post ASV
    • urticaria, irritablity, abdomen pain, tachycardia → hypotension, angioedema , shock.
      • Stop ASV
      • Adrenaline (1:1000) 0.01mg/kg i.m repeated 5-10 mins of symptoms persist
      • Pheniramine maleate 0.5mg/kg IV & Hydrocort 2-5mg/kg IV
      • ASV slowly restarted after clinical stabilization
      • Persistent shock : iv bolus +/- adrenaline infusion
  2. Pyrogenic reactions 
    • Usually 1-2 hr after ASV
      • Paracetamol +/- Tepid sponging
      • Don't stop asv
  3. Late serum sickness like reactions
    • 1-2 days post ASV
    • Fever, vomiting, recurring urticaria, myalgia, arthralgia, lymphadenopathy, nephritis.
      • Prednisolone 0.7mg/kg/day 5-7 days
      • +/- Chlorpheniramine maleate 0.35mg/kg/day.