Scorpion Sting in a Child: Autonomic Storm Without Antivenom
A 4-year-old girl from a village near Rustaq is brought 40 minutes after being stung on the dorsum of the right foot by a small pale-yellow scorpion. She has vomited twice and is drenched in sweat. On arrival she is agitated with cold, clammy extremities. Heart rate 168/min, blood pressure 128/86 mmHg (above the 99th centile for age), respiratory rate 40/min, SpO2 92% on room air, temperature 36.4°C. Both pupils are dilated and reactive, there is marked piloerection, and fine crackles are audible to both mid-zones. The foot shows a small puncture with minimal local reaction. Capillary glucose 6.8 mmol/L. Chest radiograph shows bilateral perihilar infiltrates. The hospital stocks prazosin tablets, morphine and oxygen, but has no scorpion antivenom and no paediatric intensive care; the tertiary centre is 90 minutes away by ambulance.
1. Explain what is driving the hypertension, sweating, cold peripheries and lung crackles, and why atropine would be harmful here.
Read the worked answer
The picture is a catecholamine-driven autonomic storm, not anaphylaxis and not septic shock.
Scorpion venoms of local medical importance (including the yellow deathstalker, Leiurus quinquestriatus, and Androctonus species found in Oman) contain neurotoxins that open voltage-gated sodium channels and trigger massive release of acetylcholine and catecholamines from nerve terminals and the adrenal medulla. The result is simultaneous sympathetic and parasympathetic overactivity: sweating, piloerection, dilated pupils, vomiting, hypersalivation, tachycardia and hypertension.
Why the lungs are wet: the surge of catecholamines plus direct venom action produces myocardial injury and dysfunction (toxic myocarditis with stunning, sometimes with a reduced ejection fraction), and increases pulmonary capillary permeability. Cold, clammy peripheries with a high blood pressure are therefore not hypovolaemic shock - they are intense vasoconstriction plus incipient cardiogenic pulmonary oedema. Giving a fluid bolus here can flood the lungs.
Why atropine is harmful: it blocks muscarinic receptors and removes the parasympathetic counterbalance, leaving unopposed alpha- and beta-adrenergic stimulation. That worsens tachycardia, hypertension and pulmonary oedema, may precipitate arrhythmias, and treats none of the underlying mechanism. For the same reason, beta-blockers are avoided acutely - unopposed alpha activity and negative inotropy in an already injured myocardium.
Oxygen, upright positioning, analgesia and alpha-1 blockade are the priorities; invasive monitoring and echocardiography guide later care.
2. Write your drug and fluid plan for this child, including the prazosin dose and how you would adjust it, and state what you are monitoring.
Read the worked answer
Prazosin first, oxygen, minimal fluid.
Prazosin dose: 30 micrograms/kg per dose orally, i.e. 120 micrograms (0.12 mg) for a roughly 15-16 kg 4-year-old. Give it as soon as the diagnosis is recognised, then repeat every 6 hours, and in severe cases re-dose after 3 hours or titrate upward (some protocols use 30 micrograms/kg every 3-6 hours, up to 90 micrograms/kg/day) according to blood pressure, sweating and respiratory status. It is an alpha-1 blocker: it reverses vasoconstriction, off-loads the left ventricle and is the single intervention that most reliably clears venom-induced pulmonary oedema. Expect improvement in 30-60 minutes.
Supportive measures:
- Oxygen to keep SpO2 above 94%, sitting upright, minimal handling.
- Fluids: restrict to maintenance (roughly 50 mL/hour by 4-2-1 for 15 kg) unless there is clear evidence of hypovolaemia. No boluses. If hypotension develops after prazosin, that usually signals myocardial dysfunction rather than hypovolaemia - get an echocardiogram and consider inotropic support (dobutamine) rather than pouring in fluid.
- Morphine for pain, cautiously, with monitoring.
- Treat vomiting with an antiemetic that does not add to the anticholinergic burden.
Monitoring: continuous ECG, blood pressure and saturation, hourly respiratory rate and auscultation, urine output, serial troponin, glucose, and a 12-lead ECG looking for arrhythmias and ischaemic change. Reassess after each prazosin dose.
Avoid: atropine, beta-blockers, and large fluid boluses.
3. Should she be transferred, and if so, when and how? What would make you keep her and intubate locally instead?
Read the worked answer
Yes - transfer after the first dose of prazosin and initial stabilisation, before she deteriorates.
Rationale: severe scorpion envenomation evolves over 6-24 hours. Pulmonary oedema, myocardial dysfunction, arrhythmias and shock can develop after an initial period of apparent stability, and this hospital has no paediatric intensive care and no antivenom. She is already hypoxic at 92% with bilateral infiltrates and a blood pressure above the 99th centile, which places her in the severe category at presentation. Waiting for deterioration means transferring a ventilated child, or not transferring at all.
Sequence:
- Prazosin 120 micrograms orally, oxygen, upright positioning, IV access, morphine for pain.
- Confirm improvement or at least stability of saturation and blood pressure over 30-60 minutes.
- Speak to the paediatric intensive care unit at the tertiary centre, document the conversation, and arrange a monitored ambulance with a clinician able to manage the airway.
- Continue prazosin 6-hourly during transfer, with oxygen and continuous monitoring, and carry emergency drugs for arrhythmia and pulmonary oedema.
Do not wait for antivenom. Antivenom has limited effect once severe systemic envenomation is established, it is not stocked here, and delay is more dangerous than its absence.
Keep and intubate locally if she develops respiratory failure (rising rate, falling saturation despite oxygen, inability to speak or cough), worsening pulmonary oedema, hypotension, or arrhythmia - stabilise the airway and ventilate with PEEP before any transfer, then move as a ventilated patient with a retrieval team.