Opioid-Induced Chest Wall Rigidity

Opioid induced chest wall rigidity is a sudden rise in thoracic, abdominal and laryngeal muscle tone after a potent opioid, which makes ventilation by mask or tube difficult or impossible. It is also called "wooden chest" syndrome.

Epidemiology. It follows rapid injection of fentanyl, sufentanil, alfentanil or remifentanil. Reported rates range from under 5% with ordinary doses to over 50% with large, fast boluses and no muscle relaxant. Onset is usually within 1 to 3 minutes, often just as consciousness is lost.

Risk factors. Fast injection (under 30 seconds), high dose (fentanyl over 5 microgram/kg, or over 150 microgram given quickly), no premedication, nitrous oxide, older age, neonates, critical care infusions and alfentanil or remifentanil bolus.

Pathophysiology.

Mu opioid receptor activation in the locus coeruleus and basal ganglia alters dopamine, noradrenaline, GABA and glutamate signalling, which raises tone in intercostal, abdominal and diaphragmatic muscle.

Closure of the glottis and vocal cords adds airway obstruction, and the effect is dose and speed dependent.

Inability to inflate the lungs by bag and mask, a stiff chest with high airway pressure, flat or absent capnography trace, desaturation, tachycardia or bradycardia, and a rigid abdomen. The patient may be conscious and distressed if paralysis has not been given.

Red flags.

• Saturation under 90% despite 100% oxygen.
• Bradycardia, especially in children.
• No capnography trace after a confirmed airway.

Clinical, after opioid injection. Check circuit, mask seal and tube position first.

Differential diagnosis.

• Laryngospasm.
• Bronchospasm.
• Airway obstruction by tongue or tube kink.
• Anaphylaxis.
• Tension pneumothorax.
• Equipment fault.
• Malignant hyperthermia rigidity.

Stop the opioid, give 100% oxygen, and use a two person jaw thrust with an oral airway. Pressure ventilation often overcomes rigidity but gives gastric insufflation. Muscle relaxation is the definitive step.

• Rocuronium: 0.6 to 1.2 mg/kg IV as a single dose; maximum 1.2 mg/kg; monitor train-of-four, ventilation and oxygenation; dose on ideal body weight in obesity, and expect longer action in hepatic impairment and older adults; sugammadex available for reversal.
• Succinylcholine: 1 mg/kg IV as a single dose; maximum 1.5 mg/kg; monitor ECG, potassium risk and heart rate; avoid in burns, denervation, myopathy, hyperkalaemia and malignant hyperthermia susceptibility; give atropine first in children.
• Naloxone (when no relaxant is available): 40 to 100 microgram IV every 2 to 3 minutes until rigidity eases; maximum 400 microgram before reconsidering the diagnosis; monitor respiratory rate, pain and blood pressure; reverses analgesia and can cause hypertension and pulmonary oedema; use small increments in cardiovascular disease and opioid dependence.

Prevention. Inject potent opioids slowly over at least 60 seconds, use the lowest effective dose, give the neuromuscular blocker with or soon after induction, and consider midazolam 1 to 2 mg IV before the opioid.

Monitoring. Continuous capnography, saturation, airway pressure and heart rate until muscle tone and ventilation are normal.

Referral and escalation. Call senior anaesthetic help if ventilation cannot be restored within 1 to 2 minutes.

Special groups. Neonates and infants are susceptible even at low doses. Older adults need slower injection and lower dose.