Patient selection: obese patient
Parameters:
(1) body mass index (BMI) in kg per square meter
(2) symptom level (dyspnea, nocturia, lower extremity edema, excessive daytime sleepiness, fatigue)
|
BMI
|
Symptom Level
|
Probability of OHS
|
|
> 40
|
high
|
high
|
|
> 40
|
mild to moderate
|
moderate
|
|
30-40
|
high
|
moderate
|
|
30-40
|
mild to moderate
|
low
|
If the probability of OHS is high, then a resting arterial blood gas is drawn to measure PaCO2.
If the probability of OH is mild to moderate, then serum bicarbonate is measured. If the serum bicarbonate is >= 27 mmol/L then a resting arterial blood gas is drawn to document hypercapnia.
Criteria for a diagnosis of OHS:
(1) high probability with resting PaCO2 elevated >= 45 mm Hg at sea level
(2) low to moderate probability with serum bicarbonate >= 27 mmol/L and resting PaCO2 >= 45 Hg at sea level
(3) exclusion of other causes for hypoventilation
After OHS is diagnosed then sleep studies are performed to identify obstructive sleep apnea (OSA).
