Mon22November1200AM 12

A 56-year old man has undergone formal sleep studies for suspected obstructive sleep apnoea (OSA). During a five-hour period of sleep there were 50 apnoea events.

Which one of the following grades of severity corresponds to this patient's Apnoea Hypopnoea Index (AHI)?

(Please select 1 option)

Severe OSA Incorrect answer selected

Profound OSA

Normal

Moderate OSA

Mild OSA This is the correct answer

Explanation

OSA is defined as a cessation of airflow for more than 10 seconds despite continuing ventilatory effort, 5 or more times per hour of sleep and a decrease of more than 4% in SaO2.

Patients can be screened for the likelihood of OSA using the Epworth and STOP-BANG scoring systems.

In the surgical population, a STOP-Bang score of 5-8 identified patients with high probability of moderate/severe OSA.

The Gold Standard for investigating a patient with suspected OSA is a sleep study (polysomnography) where the following are measured:

EEG

EOG

Airflow sensors

ETCO2

Oesophageal pressure

Chest and abdominal movement

Submental EMG

Pulse oximetry

ECG

The severity of ASA can be derived from the Apnoea Hypopnoea Index (AHI).

Apnoea is defined as a cessation of airflow for at least 10 seconds.

Hypopnoea is defined as a reduction in airflow of at least 30% for at least 10 seconds and associated with a decrease in oxygen saturation.

AHI=number of apnoea events / number of hours of sleep

Normal AHI <5

Mild OSA AHI 5-14

Moderate OSA AHI 15-30

Severe OSA AHI >30

However, these studies are time-consuming, labour intensive and expensive.

Overnight pulse oximetry is a more practical alternative and provides satisfactory diagnostic performance in detecting severe OSA patients. From the overnight measurements, an oxyhaemoglobin desaturation index (ODI) is derived as a measure of the severity of OSA.

Answer Statistics

1

50%

2

9%

3

2%

4

22%

5

20%

Times answered: 297