Envenomation and marine bites — formative SAQs

SAQ 1 — Snake bite first aid, coagulopathy and antivenom (10 marks)

A 6-year-old boy is brought to a rural emergency department thirty minutes after a suspected brown snake bite to the calf while walking in long grass. A pressure-immobilisation bandage was applied at the scene. He is anxious but alert, with a pulse of one hundred and ten, a blood pressure of one hundred and five over sixty, and a tender regional lymph node. His initial coagulation profile shows an unrecordable INR, a D-dimer greater than twenty, and a fibrinogen of zero point six grams per litre. [1] [4]

Questions

1. Describe your immediate management of the pressure-immobilisation bandage, the blood tests, and the first antivenom dose. (5 marks) [1] [5]
2. Explain the laboratory pattern, why the INR will remain abnormal for some hours after antivenom, and how you would manage an antivenom hypersensitivity reaction. (5 marks) [4] [8]

Model answer

Immediate management (5). I confirm that the pressure-immobilisation bandage is correctly applied — firm, from the toes up the whole leg, with a splint, and the child kept still — and I leave it in place until envenomation is excluded, because removing it prematurely can release a lymphatic bolus of venom. I run an airway, breathing and circulation assessment, give oxygen and attach monitoring, establish intravenous access in the unaffected limb, and send a coagulation profile, creatine kinase, electrolytes and urea, full blood count, group and hold, and urinalysis, repeating the coagulation and creatine kinase at set intervals. Where the laboratory is delayed I perform a twenty-minute whole blood clotting test — unclotted blood after twenty minutes confirms a coagulopathy. Because this child has an unrecordable INR with a very high D-dimer and a low fibrinogen, he has venom-induced consumption coagulopathy and I give brown snake antivenom intravenously as an initial one-vial dose, observing him for a hypersensitivity reaction, with resuscitation equipment ready and paediatric retrieval arranged. [1] [5]

Coagulopathy pattern, recovery and reactions (5). The laboratory pattern is a true defibrination: the brown snake venom is a prothrombin activator that switches on the coagulation cascade, consumes clotting factors and fibrinogen, and generates fibrin degradation products, producing an unrecordable INR with a very high D-dimer and a low fibrinogen. The INR stays abnormal for one to three days after antivenom because the antivenom only neutralises the circulating venom and stops further consumption — the liver must then resynthesise the consumed factors, so a persistently abnormal INR in an improving child is expected and is not a treatment failure. An antivenom hypersensitivity reaction occurs in around five per cent of recipients; I stop the infusion, treat it as anaphylaxis with intramuscular adrenaline at ten micrograms per kilogram of one in one thousand together with oxygen, fluids and an antihistamine, and then make a measured decision about whether to continue the antivenom, because the underlying envenomation still needs neutralising. I warn the family about serum sickness in the week after and follow up the creatinine and the creatine kinase for renal injury. [4] [8]

SAQ 2 — Tropical marine sting syndrome (10 marks)

A 4-year-old girl is brought to a north Queensland emergency department twenty minutes after wading at a beach in the stinger season. She has severe, immediate pain at the sting site and angry whip-like, cross-hatched skin lesions across both legs. She is distressed and tachycardic. Half an hour later a second child, a 10-year-old boy who reported only a minor sting to the arm while snorkelling, presents with severe generalised back and chest pain, profuse sweating, vomiting and a blood pressure of one hundred and fifty over ninety. [9] [10]

Questions

1. Describe the first aid and hospital management of the first child, including the role of antivenom. (5 marks) [9] [11]
2. Identify the syndrome in the second child, and outline his analgesia, cardiovascular monitoring and the principle behind his first aid. (5 marks) [10] [11]

Model answer

Box jellyfish management (5). The first child has a box jellyfish (Chironex fleckeri) sting — the immediate agonising pain, the characteristic whip-like cross-hatched skin lesions, and the tropical setting make this the most venomous marine sting, capable of killing a small child within minutes. I remove her from the water, call for senior help, attach monitoring and establish intravenous access, and I douse the adherent tentacles with vinegar (four to six per cent acetic acid) for at least thirty seconds to deactivate the undischarged nematocysts, then carefully lift the tentacles off — I do not rub the area and I never use fresh water, which triggers further nematocyst discharge. I give opioid analgesia for the severe pain and watch for cardiorespiratory collapse, because the venom is cardiotoxic. If she develops collapse, hypotension, pulmonary oedema or arrhythmia, I give box jellyfish antivenom intravenously, with magnesium considered for the failing heart, and I continue high-quality cardiopulmonary resuscitation because recovery is possible. The Cochrane review supports hot water for many jellyfish stings, but for the box jellyfish vinegar is the correct first aid. [9] [11]

Irukandji syndrome (5). The second child has the Irukandji syndrome — a delayed catecholamine presentation twenty to forty minutes after a trivial carybdeid sting, with severe generalised muscle, back and chest pain, profuse sweating, vomiting, hypertension and a feeling of doom. I admit him for opioid analgesia for the severe pain, control the catecholamine surge with magnesium, glyceryl trinitrate or an alpha-blocker for the hypertension, and institute cardiac monitoring with a troponin and an electrocardiogram, because the severe end of the syndrome brings a troponin rise, pulmonary oedema and cardiac dysfunction that may need intensive care. There is no specific antivenom, and supportive care over one to two days is usually sufficient. The principle behind his first aid is the same as for the box jellyfish — the venom is from a carybdeid jellyfish whose nematocysts keep discharging, so the sting site is doused with vinegar for at least thirty seconds; a bluebottle sting, by contrast, is treated with hot water at about forty-five degrees for up to twenty minutes, and this distinction is examinable. [10] [11]