Level 1 of 6Core
Acute neuromuscular weakness
The core to-do list — diagnose and manage, at a glance
Diagnose— recognise it
- Two questions do most of the work: when was the patient last completely normal, and where did the weakness start and where did it go next? Ascending symmetrically from the feet over hours to days = Guillain–Barré syndrome (GBS — follows infection by 1–6 weeks; Campylobacter jejuni triggers 20–40%); descending from eyes and mouth = botulism, envenoming, diphtheria; fluctuating, worse at day's end = myasthenia; sudden and maximal = stroke; with severe spinal pain, a sensory level and sphincter disturbance = cord compression.
- Measure the forced vital capacity (FVC) at the bedside in mL/kg of actual body weight: normal adult 60–70 mL/kg; 20 mL/kg or less = high risk; 15 mL/kg or less = intubation; a falling FVC demands escalation whatever the absolute value. MIP reaching −30 mmHg also indicates intubation. No spirometer: single-breath count above 25 broadly reassuring, 15–25 a warning, below 15 suggests a badly reduced vital capacity.
- Danger signs at the bedside: inability to lift the head from the pillow; paradoxical abdominal movement or intolerance of lying flat; a weak, breathy or wet cough, pooling saliva, nasal regurgitation, a nasal or wet voice; rising respiratory rate with shallow breaths; arms involved within 24 hours; autonomic instability — swinging BP, unexplained bradycardia, ileus, urinary retention.
- A sensory level, saddle anaesthesia or new sphincter disturbance is a compressive lesion until proven otherwise — pyramidal signs, a markedly asymmetric deficit, a sharp sensory level or early sphincter involvement suggest a focal cord lesion, not GBS.
- Check the capillary glucose within the first minute — hypoglycaemia mimics every neurological presentation — and send potassium, calcium, magnesium and phosphate immediately: the only causes curable within the hour. In hypokalaemic periodic paralysis serum potassium is usually below 3.0 mmol/L during an attack.Not available at your setup — Serum electrolytes.
- Never wait for the saturation to fall or the blood gas to change — both are late: a normal or low PaCO2 in a patient whose vital capacity is falling means the patient is still compensating; when the respiratory muscles fatigue the CO2 rises abruptly and arrest follows quickly.
Manage now— do this, in order
- Sit the patient up and stop oral intake: nil by mouth until swallow has been assessed directly, sitting upright, suction available — aspiration pneumonia is the commonest avoidable complication of bulbar weakness.
- Write a schedule for serial respiratory measurement: hourly for progressing weakness, bulbar involvement or any measurement in the warning band; at least two-hourly for a stable patient in the first day — the trend matters more than any single number. Attach continuous cardiac monitoring and do a 12-lead ECG: dysautonomia and electrolyte disturbance kill through rhythm.
- Correct the metabolic causes at once — glucose, potassium, calcium, magnesium, phosphate. Acute hypokalaemic paralysis: replace potassium slowly — oral potassium chloride 20–40 mmol repeated according to response where swallowing is safe; IV potassium chloride not usually exceeding 10 mmol/hour peripherally. In periodic paralysis replace conservatively — rebound hyperkalaemia is a real hazard.Doctor / Nurse
- Intubate at FVC 15 mL/kg, MIP −30 mmHg, or frank dyspnoea. Never use non-invasive ventilation in bulbar weakness (secretions pool behind the mask, deterioration is masked); NIV may buy time in non-bulbar weakness only, with an agreed intubation plan. Never give suxamethonium to a patient denervated or immobilised for about 72 hours or more — life-threatening hyperkalaemia.Doctor / NurseNot available at your setup — Endotracheal intubation kit, Mechanical ventilator.
- GBS immunotherapy: IVIg 0.4 g/kg IV once daily for 5 consecutive days (total 2 g/kg, same regimen for adults and children) for inability to walk unaided (Hughes grade 3 or worse) or lesser disability with rapid progression or bulbar involvement; or plasma exchange, five exchanges over 1–2 weeks — equivalent efficacy. Never both (no added benefit), and never corticosteroids: prednisone is ineffective and may prolong recovery.Doctor / Nurse
- Myasthenic crisis needs a critical care environment: treat the precipitant (most often infection), stop offending drugs, and give IVIg 2 g/kg over 2–5 days or five plasma exchanges. Pyridostigmine 30–180 mg (average 60 mg) orally four times daily; if the patient cannot swallow, convert rather than omit — oral pyridostigmine 60 mg is approximately equivalent to neostigmine 0.5 mg IM or by slow IV, with cardiac monitoring and atropine available.Doctor / NurseNot available at your setup — ICU / HDU bed.
- Suspected cord compression is treated before imaging is complete: dexamethasone 10 mg IV on clinical suspicion, continued at 4 mg every 6 hours orally until definitive radiotherapy and/or surgical decompression. Image the whole spine urgently by MRI (up to 40% have asymptomatic epidural metastases elsewhere); in cauda equina syndrome catheterise, record the residual volume and arrange urgent decompression — paraplegia established for more than 24–48 hours rarely reverses.Doctor / Nurse
- Supportive care carries at least as much survival benefit as immunotherapy: enoxaparin 40 mg SC once daily (20 mg if creatinine clearance below 30 mL/min) or unfractionated heparin 5000 units SC 12-hourly with compression stockings; atropine 0.5–1 mg IV drawn up (max 3 mg; children 20 micrograms/kg, minimum 100 micrograms) for suction-provoked bradyarrhythmia; paracetamol 1 g 6-hourly with gabapentin 300 mg at night titrated or pregabalin 75 mg twice daily; two-hourly repositioning, eye and mouth care, early enteral nutrition, chest physiotherapy.Doctor / Nurse
Bedside respiratory thresholds (FVC in mL/kg actual body weight)
| Measurement | Meaning |
|---|---|
| FVC 60–70 mL/kg | Normal adult |
| Falling FVC on serial measurement | Intensive monitoring + ventilatory planning, whatever the value |
| FVC 20 mL/kg or less | High risk |
| FVC 15 mL/kg or less | Intubation indicated |
| MIP reaching −30 mmHg | Intubation indicated |
| Single-breath count: above 25 / 15–25 / below 15 | Reassuring / warning / badly reduced VC (surrogate only) |
Refer / escalate
Escalate to critical care immediately for a falling vital capacity whatever the absolute value, FVC 20 mL/kg or less, FVC 15 mL/kg or less, MIP reaching −30 mmHg, bulbar weakness with pooling secretions, autonomic instability or myasthenic crisis; refer urgently for neurosurgical decompression in any patient with a sensory level, saddle anaesthesia, retention of urine or suspected cord compression, having first given dexamethasone 10 mg IV.
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