Postoperative Residual Neuromuscular Blockade

Postoperative residual neuromuscular blockade is persistent paralysis after surgery, defined by a train-of-four ratio under 0.9 measured at the adductor pollicis on arrival in recovery or later.

Epidemiology. It affects about 30% to 60% of patients given intermediate acting relaxants without quantitative monitoring or sugammadex. Rates fall to under 5% with objective monitoring and appropriate reversal.

Risk factors. No quantitative monitor, reliance on clinical tests, inadequate reversal dose or timing, high or repeated relaxant doses, hypothermia, acidosis, hypokalaemia, hypocalcaemia, hypermagnesaemia, renal or hepatic impairment, older age, volatile agents, and drugs that potentiate block (aminoglycosides, clindamycin, polymyxins, antiarrhythmics, magnesium).

Complications. Upper airway collapse, hypoventilation, hypoxaemia, aspiration, atelectasis, pneumonia and reintubation. Patients also report distressing weakness and diplopia.

Pathophysiology.

Residual receptor occupancy impairs pharyngeal and respiratory muscle function before limb strength recovers. Upper airway muscles and hypoxic ventilatory drive are impaired at ratios under 0.9.

Weakness, inability to lift the head for 5 seconds or sustain a grip, diplopia, ptosis, difficulty swallowing or speaking, shallow rapid breathing, upper airway obstruction, desaturation and a sense of suffocation while awake.

Red flags.

• Airway obstruction or hypoventilation.
• Falling saturation.
• Distressed patient who cannot signal.
• Aspiration.

Use quantitative train-of-four monitoring (acceleromyography) on the adductor pollicis. A ratio of 0.9 or more confirms recovery. Clinical tests are insensitive. Check temperature, potassium, magnesium, calcium, pH and drug interactions.

Differential diagnosis.

• Opioid or sedative excess.
• Residual volatile agent.
• Myasthenia or Lambert-Eaton syndrome.
• Electrolyte disturbance.
• Stroke.
• Critical illness neuromyopathy.

Support the airway and ventilation until recovery. Sedate the patient if conscious and paralysed. Reverse by depth of block.

• Sugammadex (rocuronium or vecuronium): 2 mg/kg IV if the train-of-four count is 2 or more; 4 mg/kg if post-tetanic count is 1 to 2 with no response to train-of-four; 16 mg/kg for immediate reversal after rocuronium 1.2 mg/kg; single dose; maximum 16 mg/kg; confirm ratio 0.9 or more; monitor for bradycardia and hypersensitivity; avoid if creatinine clearance is under 30 mL/min; counsel on reduced hormonal contraceptive efficacy for 7 days.
• Neostigmine (only when train-of-four count is 4): 50 microgram/kg IV given with glycopyrronium 10 microgram/kg (or atropine 20 microgram/kg); single dose; maximum 5 mg; monitor ratio, heart rate, secretions and bronchospasm; effect is prolonged in renal impairment; avoid in mechanical bowel or urinary obstruction and use caution in asthma.

Neostigmine has a ceiling effect and is ineffective in deep block. Correct temperature, acid base balance and electrolytes. Stop interacting drugs.

Prevention. Monitor quantitatively in every patient given a relaxant, use the lowest effective dose, and confirm a ratio of 0.9 or more before extubation.

Monitoring. Train-of-four every 5 to 15 minutes, saturation, respiratory rate and end tidal carbon dioxide until recovery is sustained for 30 minutes.

Referral and escalation. Senior anaesthetic help for prolonged block beyond 60 minutes or suspected enzyme deficiency.

Special groups. In renal impairment sugammadex complex clearance is delayed, so avoid if creatinine clearance is under 30 mL/min and use support until recovery. Older adults and obese patients need monitoring and dosing on ideal body weight.