OSA: Screening and Diagnosis
Obstructive Sleep Apnea (OSA) is a common breathing disorder characterized by partial or complete closure of the upper airway while sleeping. These episodes are usually associated with frequent night time wake ups from hypoxemia and hypercarbia. It is estimated to occur in around 13% of males and 6% of females, however many overweight people go undiagnosed. OSA tends to be higher in the surgical population compared to the general public. It can also be associated with comorbidities such as hypertension, ischemic heart disease, pulmonary hypertension, congestive heart failure, stroke, arrhythmia, and insulin resistance. Upper airway obstruction is likely to happen more frequently and for longer periods of time after receiving anesthesia. Postoperatively, patients with OSA have a higher risk of atelectasis, pneumonia, pulmonary embolism, delirium, atrial fibrillation, and ICU transfers. For these reasons, it is vital to screen for and appropriately manage patients with OSA intra- and postoperatively.
The gold standard for diagnosing OSA is a polysomnography, or a sleep study. During this study, a patient is observed for periods of hypopnea (partial airway obstruction) or apnea (complete airway obstruction) per hour. An episode is added to the total for the hour if it lasts for at least 10 seconds and is accompanied by a desaturation of 3-4% on the pulse oximeter. The Apnea-Hypopnea Index is a score for the average number of obstructive episodes per hour. There are 3 levels of the AHI:
Mild OSA: 5 - 14.9 episodes/hour
Moderate OSA: 15 - 29.9 episodes/hour
Severe OSA: > 30 episodes/hour
Many surgical patients have risk factors for OSA but do not carry the formal diagnosis. For this reason, there are screening tools that can be used to risk stratify patients. The most commonly used one is “STOP-BANG”, an 8-question scoring tool. Each letter of the acronym pertains to a risk factor for OSA:
S - Snoring (do you snore loudly enough to be heard by others?)
T - Tired (do you feel tired during the day? Fall asleep driving?)
O - Observed (has anyone observed you gasping for air or choking while sleeping?)
P - Pressure (do you have high blood pressure?)
B - BMI ( > 35 m/kg2)
A - Age ( > 50 years old)
N - Neck size (males > 17 inch collar; females > 16 inch collar)
G - Gender (male)
A positive answer to each question is given 1 point:
0-2 points: low risk of OSA
3-4 points: medium risk of OSA
5-8 points: high risk of OSA
