Level 2 of 6Must-remember

Scorpion sting and arthropod envenomation

Assess, manage and stay safe — enough on its own

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The card — assess, manage, caution

Assessment— look, ask, measure

Take the history in one minute: what stung and when, where on the body, how many stings, what the patient was doing (a bare foot at night, a hand into a dark space, shoes, clothing or bedding not shaken out), whether there was any previous severe reaction to a sting, and whether the patient takes a beta-blocker, which makes anaphylaxis harder to reverse.
Expect pain out of all proportion to the visible injury: onset is immediate, with intense burning or electric pain, a barely visible puncture, little or no swelling, and marked local hyperaesthesia.
Do the tap test: gently tapping over the site reproduces or greatly exaggerates the pain and paraesthesia — a bedside sign of considerable value requiring no equipment.
Ask whether the paraesthesia has spread: pain and paraesthesia travelling proximally, and to sites remote from the sting (the classic history is a sting on the foot with tingling around the mouth), means venom has spread systemically and progression is likely.
Time the illness: systemic envenoming develops over minutes to hours, reaches maximal severity at about 5 hours and subsides within a day or two, but systemic involvement may be delayed by up to 24 hours — a normal first assessment excludes nothing and must be repeated through the first 24 hours.
Look for the autonomic storm, which is biphasic: an early, often brief cholinergic phase (salivation, lacrimation, bronchorrhoea, sweating, vomiting, bradycardia, hypotension) overtaken by a prolonged adrenergic phase (hypertension, tachycardia, mydriasis, hyperglycaemia, cool clammy peripheries), with hypersalivation and drooling, rhinorrhoea, piloerection, abdominal colic, diarrhoea and priapism.
Look for cranial nerve dysfunction: blurred vision, roving or chaotic conjugate eye movements, nystagmus, dysarthria, tongue fasciculation, dysphagia and difficulty handling secretions — the last being the sign that precedes aspiration and airway loss.
Do not call the movements a seizure: restlessness, agitation, muscle twitching, jerking, shaking and opisthotonic-type posturing are frequently mistaken for a fit, but the patient is usually alert during and between them, with no eye deviation, incontinence or post-ictal phase.
Examine the chest and circulation: tachycardia or bradycardia, hypertension (often severe and early) or hypotension, arrhythmia, tachypnoea, and the crackles, frothy pink sputum and hypoxaemia of pulmonary oedema; hyperthermia and metabolic acidosis accompany severe cases.
Check the glucose in any twitching or drowsy child before ascribing the movements to venom — although scorpion envenoming itself characteristically causes hyperglycaemia through catecholamine inhibition of insulin release.
Grade the neuroexcitatory syndrome I–IV: I local pain or paraesthesia at the site only with a positive tap test; II grade I plus pain or paraesthesia remote from the sting site; III either cranial-nerve dysfunction or somatic neuromuscular dysfunction; IV both, with or without cardiovascular instability, pulmonary oedema or arrhythmia.
Grade the threat to life I–III: class I local signs only; class II any systemic manifestation without life-threatening features (vomiting, sweating, agitation, priapism, hyperthermia, hypertension, tachycardia); class III life-threatening features — cardiogenic shock, pulmonary oedema, severe neurological impairment or coma.
Danger signs: stridor, hoarse voice, tongue or lip swelling, or a sting inside the mouth; difficulty handling secretions, drooling with dysphagia, or a weak cough; frothy or pink sputum, crackles, rising respiratory rate, falling SpO2 on air; hypotension, or hypertension with end-organ strain; any arrhythmia or ischaemic ECG change; falling conscious level; cola-coloured urine or oliguria; a sting count in the dozens or hundreds; age under 5 or over 65 with any systemic feature; a previous severe reaction to a sting.
Count the stings: several hundred honeybee stings can kill a non-allergic adult and a child reaches the same toxic dose at far fewer — venom dose is effectively per kilogram, so a sting load trivial in a 70 kg adult may be lethal in a 12 kg child.
Separate anaphylaxis from venom toxicity by the clock and the skin: anaphylaxis begins within 10 minutes in most cases and only rarely after 5 hours, with urticaria, angio-oedema, flushing, stridor, hoarseness, bronchospasm and hypotension, whereas scorpion storm gives hypertension, cranial-nerve signs and a several-hour time course.
A necrotic sting site means the diagnosis is wrong: buthid stings do not cause tissue necrosis, so consider Hemiscorpius lepturus, a recluse spider, a stingray injury — or, most commonly, bacterial infection, particularly MRSA.
Exclude the great mimic: organophosphate or carbamate poisoning gives pinpoint pupils, bronchorrhoea, bradycardia and fasciculation with no puncture wound and a negative tap test — the pupils and the cholinesterase level separate them, and the antidotes are entirely different.
In children expect irritability or inconsolable crying rather than a complaint of pain, prominent and easily missed nystagmus and roving eyes, twitching misread as a febrile convulsion, and sudden respiratory failure — grunting, head bobbing, nasal flaring, a rising respiratory rate in a previously settled child, prolonged capillary refill and drowsiness are pre-terminal.

Management— do this, in order

Resuscitation precedes everything, including antivenom, and treat the syndrome in front of you, not the animal you were told about — species identification helps but is not a prerequisite, and reported identifications are frequently wrong.
Reduce venom absorption without harming the limb: a significant proportion of venom travels via the lymphatics, so keep the patient still and immobilise the stung limb with a splint, and apply a pressure pad and dressing over the site with a cold pack.
Use no dangerous first aid: tourniquets, incision, cut and suck, suction devices, local chemicals, electric-shock devices and cautery are ineffective and harmful; if a constricting device is already in place, releasing it may deliver a sudden bolus of venom into the circulation with rapid deterioration or cardiorespiratory collapse, so release it only with monitoring, intravenous access and resuscitation drugs immediately available.
Treat the pain, because pain is not a minor symptom — it drives the catecholamine surge that causes the cardiac complications.
Local anaesthetic usually abolishes local pain outright: lidocaine (lignocaine) 1% without adrenaline infiltrated into the sting site, or as a ring block of a digit, maximum 3 mg/kg in adult and child — never an adrenaline-containing preparation in a digit, ear, nose or penis.Doctor / Nurse
Paracetamol is the first-line systemic analgesic: 1 g orally or IV 6-hourly to a maximum of 4 g/24 h in an adult, 15 mg/kg orally or IV 6-hourly in a child.
Morphine 0.1 mg/kg IV titrated in 2 mg increments (child 0.1 mg/kg IV, titrated) only with continuous pulse oximetry and immediate airway capability, since opiates in a neurotoxic patient precipitate respiratory failure; avoid NSAIDs where rhabdomyolysis, haemolysis, acute kidney injury or coagulopathy is suspected.Doctor / Nurse
A continuous intravenous infusion of midazolam is the specific measure for agitation and involuntary movements and lowers catecholamine drive as well: a cautious loading dose of 0.05 mg/kg IV slowly followed by titrated infusion, with continuous monitoring and the capacity to ventilate.Doctor / NurseNot available at your setup — Mechanical ventilator.
The cardiovascular target is afterload reduction, not diuresis: prazosin 30 micrograms/kg orally, repeated 3-hourly until the peripheries are warm and dry and the haemodynamics settle (many adult regimens begin with 0.5 mg and titrate), the same weight-based dose in children — give it with the patient supine and volume-replete and recheck the blood pressure at 15, 30 and 60 minutes, planning for first-dose hypotension.
Alternatives where prazosin is unavailable or ineffective: nifedipine, hydralazine or sodium nitroprusside, all requiring close, ideally invasive, blood pressure monitoring — and never crushed sublingual nifedipine.Doctor / Nurse
Treat pulmonary oedema as cardiogenic: oxygen, upright positioning, non-invasive or invasive positive-pressure ventilation as required, afterload reduction, and restraint with intravenous fluid once crackles appear; diuretics have a limited role because these patients are not fluid-overloaded, and low cardiac output despite afterload reduction may need inotropic support such as dobutamine, guided where possible by echocardiography.Doctor / Nurse
Dangerous bradyarrhythmia only: atropine 0.6 mg IV repeated to a maximum of 3 mg in an adult, 20 micrograms/kg IV with a minimum single dose of 100 micrograms in a child — given indiscriminately in the adrenergic phase it aggravates tachycardia and hyperthermia.Doctor / Nurse
Antivenom, when the correct species-specific product exists, rapidly reverses cranial-nerve dysfunction and skeletal-muscle hyperexcitability: give it intravenously as a slow undiluted push or an infusion diluted in 0.9% sodium chloride, with adrenaline drawn up at the bedside, observing continuously throughout and for at least one hour afterwards; where no appropriate antivenom exists, supportive care is the treatment and it is effective.Doctor / Nurse
Anaphylaxis to a sting: adrenaline first, before any antihistamine or corticosteroid — 1:1000 intramuscularly into the anterolateral thigh, 500 micrograms (0.5 mL) in an adult, 150 micrograms under 6 years, 300 micrograms at 6–12 years and 500 micrograms over 12 years, repeated every 5 minutes if no improvement.Doctor / Nurse
Complete the anaphylaxis package: lie flat with legs elevated (never allow the patient to stand); oxygen 15 L/min via reservoir mask targeting SpO2 94–98%; crystalloid 500–1000 mL in an adult or 20 mL/kg in a child, repeated as required; then second-line chlorphenamine IV or IM 10 mg in an adult (under 6 months 250 micrograms/kg, 6 months–6 years 2.5 mg, 6–12 years 5 mg, over 12 years 10 mg) and hydrocortisone IV 200 mg in an adult (under 6 months 25 mg, 6 months–6 years 50 mg, 6–12 years 100 mg, over 12 years 200 mg); nebulised salbutamol 5 mg oxygen-driven (2.5 mg under 5 years, 5 mg at 5 years and over) for persistent bronchospasm and nebulised adrenaline 1 mL of 1:1000 in 4 mL of 0.9% saline for upper-airway oedema.Doctor / Nurse
Remove an embedded honeybee stinger immediately, since the detached venom sac continues to pump — scrape it off with a blade, fingernail or card edge, or lift it with forceps, because speed matters far more than technique; then cleanse, disinfect, apply a cold pack and elevate. Wasps, hornets and ants leave no stinger.
Mass envenomation and rhabdomyolysis need high-volume crystalloid from the outset, with catheterisation and a target urine output of 1–2 mL/kg/h (adults typically 1000 mL of 0.9% sodium chloride in the first hour, then titrated; children 20 mL/kg boluses with reassessment), and serial CK, potassium and creatinine.Doctor / Nurse
Check the ECG for hyperkalaemia — peaked T waves, flattened or absent P waves, broad QRS — and if present give calcium gluconate 10%, 10 mL IV over 5–10 minutes (paediatric 0.5 mL/kg, maximum 20 mL) for myocardial protection, then insulin–dextrose and nebulised salbutamol to shift potassium; renal replacement therapy is required for established acute kidney injury with refractory hyperkalaemia, acidosis or fluid overload.Doctor / Nurse

Caution— what harms

Anti-snake venom does not neutralise scorpion venom: polyvalent ASV exposes the patient to anaphylaxis and serum sickness with no possible benefit.
Do not treat the ECG as an acute coronary syndrome: ST elevation or depression, T-wave inversion, long QT and ectopy reflect catecholamine myocardial injury, not coronary occlusion, are common in class II–III envenoming and are usually reversible — thrombolysis has no role and is hazardous.
Do not pour fluid into pulmonary oedema: it is partly cardiogenic and partly permeability-related, it is not volume overload, and more fluid makes it worse — shock with a poorly contracting ventricle needs inotropic support guided by echocardiography, not further fluid.
Never give crushed sublingual nifedipine, and plan for first-dose hypotension with prazosin by giving it supine and volume-replete with blood pressure checks at 15, 30 and 60 minutes.
Do not give atropine indiscriminately: reserve it for haemodynamically significant bradyarrhythmia, since in the adrenergic phase it aggravates tachycardia and hyperthermia — and remember that atropine reverses organophosphate poisoning but worsens scorpion storm, so the two must be told apart before it is given.
Opiates and sedation in a neurotoxic patient precipitate respiratory failure: use morphine only with continuous pulse oximetry and immediate airway capability, and sedate with midazolam only with continuous monitoring and the capacity to ventilate.
Never use a tourniquet, incision, cut and suck, a suction device, local chemicals, an electric-shock device or cautery — and be careful undoing one already applied, because release can deliver a bolus of venom and precipitate collapse.
Neutrophil leucocytosis is usual and reflects the catecholamine surge, not infection — do not start antibiotics for leucocytosis alone, and remember that a large local reaction spreading 10 cm or more over 1–2 days is hypersensitivity, not cellulitis.
Withhold intramuscular tetanus toxoid until any coagulopathy is reversed, since coagulopathy contraindicates intramuscular injection and intramuscular injection into a coagulopathic patient causes haematoma.Not available at your setup — Coagulation (PT/INR).
Never give an antihistamine or a corticosteroid before adrenaline in anaphylaxis, and never give an undiluted intravenous adrenaline bolus, which is itself lethal — intravenous adrenaline belongs to a monitored setting with pump-controlled titration.
Do not be reassured by a benign-looking sting site: the appearance of the sting site is not the grade of the disease, buthid stings do not necrose, and a necrotic site means a different diagnosis.
Do not treat scorpion myoclonus as epilepsy — the patient is alert during the movements, with no eye deviation, incontinence or post-ictal state — but always check the glucose, since hypoglycaemia must be excluded in any twitching child.
Do not believe an isolated hyperkalaemia result without checking the ECG, and expect the recognised trajectory of a falling potassium early (catecholamine-driven intracellular shift) and a rising one later with rhabdomyolysis and renal failure.
Do not wait for a test to confirm envenomation: there is no bedside test for venom, no laboratory can confirm it quickly enough to be useful, and treatment must never be delayed waiting for one.
Grade III–IV or class III disease in a child under 5 is a respiratory-arrest risk from the moment it is recognised — these children need continuous airway observation, not intermittent observations.

Refer / escalate

Refer or transfer urgently any patient with airway compromise or a sting inside the mouth, difficulty handling secretions, pulmonary oedema or rising oxygen requirement, hypotension or hypertension with end-organ strain, arrhythmia or ischaemic ECG change, falling conscious level, cola-coloured urine or oliguria, dozens or hundreds of stings, grade III–IV or class III disease, any systemic feature in a child under 5 or an adult over 65, or anaphylaxis unresponsive to repeated intramuscular adrenaline — and move them to a facility with ventilation, invasive monitoring, echocardiography, the correct species-specific antivenom and renal replacement therapy before those needs arise.

The card — assess, manage, caution

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