Envenomation and marine bites — branching viva

Opening (candidate)

This is a brown snake envenomation with venom-induced consumption coagulopathy, and my priorities are to keep the pressure-immobilisation bandage in place, confirm the coagulopathy and its pattern, and give brown snake antivenom intravenously at an initial one-vial dose while arranging paediatric retrieval. The unrecordable INR with a very high D-dimer and a low fibrinogen is a true defibrination from a prothrombin-activating venom. I send the full panel and repeat it, I prepare for an antivenom hypersensitivity reaction, and I explain to the family that the INR will take one to three days to recover because the antivenom stops the cause but the liver must resynthesise the factors. [1] [4]

Branch A — The pressure-immobilisation bandage

Examiner: Describe the correct technique and tell me when you will remove it. [5]

Candidate: The bandage is applied over the bite first and then firmly from the toes up the whole leg — about as tight as a bandage for a sprained ankle, firm enough to obstruct lymphatic and venous flow but not arterial, checking that distal pulses and capillary refill remain — with a splint and the limb kept still, because movement pumps venom along the lymphatics. It is indicated for snake, funnel-web spider, blue-ringed octopus and cone snail envenomation, and it is not indicated for redback spider bites, jellyfish stings, or stingray and stonefish injuries. I leave it in place until envenomation is excluded on repeated blood tests, because removing it prematurely can release a lymphatic bolus of venom and precipitate collapse in a previously well child. [5]

Branch B — The coagulopathy pattern and recovery

Examiner: Why is the INR still unrecordable six hours after you gave the antivenom? [4]

Candidate: Because antivenom does not replace clotting factors — it only neutralises the circulating prothrombin activator and stops further consumption. The brown snake venom switched on the coagulation cascade, consumed the factors and fibrinogen, and generated the very high D-dimer; once the venom is neutralised, the liver must resynthesise the consumed factors and fibrinogen over one to three days, so the INR recovers later. A persistently abnormal INR in an improving child is expected, not a treatment failure, so I do not reflexively repeat large antivenom doses for it. I watch for bleeding, especially intracranial, and let the laboratory trend guide care, treating with blood products only if there is active bleeding. [1] [4]

Branch C — The antivenom reaction

Examiner: He develops urticaria and wheeze ten minutes into the antivenom. Walk me through it. [8]

Candidate: This is an immediate hypersensitivity reaction to the antivenom, which occurs in around five per cent of recipients. I stop the infusion, give intramuscular adrenaline at ten micrograms per kilogram of one in one thousand, oxygen, an intravenous fluid bolus and an antihistamine, and reassess the airway, breathing and circulation. Once he is stable, I weigh the risk and benefit: his coagulopathy is real and the circulating venom still needs neutralising, so I usually recommence the antivenom slowly under observation, with senior and toxinology input, rather than abandoning it. I warn the family about serum sickness in the week after, which presents with fever, arthralgia and rash and is treated with corticosteroids. [1] [8]

Branch D — Spider distinctions

Examiner: Contrast this with a funnel-web spider bite and a redback spider bite. [6]

Candidate: A funnel-web spider bite is a pressure-immobilisation emergency, like a snake bite, because its delta-hexatoxin is a presynaptic neurotoxin that triggers a massive catecholamine release — profuse salivation, sweating, piloerection, hypertension, muscle fasciculation and progressive paralysis with pulmonary oedema. It is treated with funnel-web spider antivenom intravenously, two vials initially and repeated, with atropine or glycopyrrolate for the secretions and ventilatory support; it has caused no deaths since the antivenom was introduced. A redback spider bite is completely different: its alpha-latrotoxin causes severe local and radiating pain with sweating and piloerection but is rarely life-threatening, the first aid is ice and analgesia and not a bandage, and antivenom is reserved for severe refractory cases because the RAVE-II trial showed intravenous redback antivenom was no better than placebo for pain. [6] [7]

Branch E — Retrieval and disposition

Examiner: Retrieval is forty minutes away. How do you package him? [1]

Candidate: I keep the bandage on and the limb splinted and still, secure the airway and breathing if there is any neurotoxic progression, maintain intravenous access in the unaffected limb, and give the antivenom before and during transfer if needed. I hand over the coagulation trend, the antivenom given and any reaction, and the observation plan, and the retrieval team continues the monitoring and the repeat bloods. I admit him to a paediatric unit, or intensive care if he is neurotoxic or bleeding, and I follow up the creatinine and creatine kinase for the renal and myotoxic complications and the family for serum sickness. [1] [5]

Close

Keep the pressure-immobilisation bandage on and the child still, confirm the venom-induced consumption coagulopathy pattern, give brown snake antivenom intravenously at one vial, treat any hypersensitivity reaction with intramuscular adrenaline, and explain that the INR recovers over one to three days as the liver resynthesises factors. Distinguish the funnel-web spider bite, which takes the same bandage and an antivenom, from the redback spider bite, which takes ice and analgesia. Debrief the team, document the sequence, and arrange safe retrieval and follow-up. [1] [8]