Obstructive Sleep Apnoea

Link: 152-Obstructive-Sleep-Apnoea-and-anaesthesia1.pdf

Incidence

4% in men, 2% in women. Underdiagnosed condition. Found in 40% obese females and 50% obese males.

Risk factors

Obesity; age >50; male gender, neck circumference >40cm, nasal/pharyngeal/laryngeal obstruction; craniofacial abnormalities; neuromuscular disorders; alcohol; sedative use; smoking.

Pre-Operative Screening

STOP-BANG model: high risk of OSA if 3 or more criteria present.

• Do you Snore loudly
• Do you feel Tired during the daytime almost every day?
• Has anyone Observed that you stop breathing during sleep?
• Do you have a history of high blood Pressure, with or without treatment?
• Body mass index >35
• Age >50
• Neck circumference >40cm
• Male Gender

Gold standard: overnight sleep study (polysomnography).

Pathophysiology

Collapse of pharyngeal airways due to relaxation of pharyngeal dilator muscles. Increased adipose tissue causes further airway narrowing in the obese. This leads to airway obstruction and desaturation.

Inspiratory efforts increase as arterial deoxygenation progresses causing large intrathoracic negative pressure swings and leading to partial arousal from sleep and sudden airway opening. Hyperventilation follows for a short period until sleep deepens and obstruction recurs, repeating the cycle.

Intermittent hypoxia, and hypercarbia causing oxidative stress, systemic inflammation, and polycythaemia can result.

Anaesthetic Considerations

Increased peri-operative morbidity and mortality.

Danger: Post operative impairment of respiratory drive and hypoxic arousal mechanisms by the sedative action of drugs.

Avoid sedative pre-meds.

Avoid long acting opioids and benzodiazepines intra-operatively.

May have difficult airway either to intubate or to maintain on bag-mask ventilation due to obstruction. Plan accordingly.

Extubate sitting up wide awake and fully reversed. Consider rocuronium/suggamadex use.

Patients should bring their CPAP apparatus to hospital.

Consider HDU/ICU environment depending on severity of OSA and type of operation. All patients should receive post operative oxygen and continuous pulse oximetry. Monitoring should continue for at least 7 hours after the last hypoxaemic episode.

Treatment

CPAP: Nasal continuous positive airway pressure at night time is proven to decrease symptoms and potentially long term sequelae.

UPPP (Uvulopalatopharyngoplasy) surgery: The efficacy of this is controversial and it may render nasal CPAP less effective in the long term.

Medical consequences

Systemic hypertension; pulmonary hypertension (due to pulmonary arteriolar remodelling due to hypoxia); cardiac rhythm disturbances; sudden death. Right ventricular failure is uncommon and more likely if there is coexisting LVF or COPD.