Obesity Hypoventilation Syndrome (2019 ATS)
Applies the 2019 ATS definition of obesity hypoventilation syndrome: BMI 30 or more, sleep-disordered breathing, an awake resting PaCO2 of 45 mmHg or more at sea level, and exclusion of other causes.
Open the calculator → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- Body mass index, kg/m2
- 38
- Sleep-disordered breathing
- Yes
- Awake resting PaCO2, mmHg
- 50
- Other causes of hypoventilation excluded
- Yes
Result: Obesity hypoventilation syndrome criteria met
The tool opens with these values already filled in. Replace them with your own.
What the result means
- All four
- Body mass index 30 or more; sleep-disordered breathing; an awake resting PaCO2 of 45 mmHg or more at sea level; and exclusion of other causes of hypoventilation.
- Awake, resting, sea level
- Oximetry does not answer this question and altitude changes it. The carbon dioxide tension must come from an awake resting arterial sample.
- Screening rule
- In LOW-to-moderate probability patients, a serum bicarbonate under 27 mmol/L removes the need for an arterial blood gas. At or above 27, measure the PaCO2.
- Its population
- The guideline puts low-to-moderate at under 20 percent probability and illustrates it with a body mass index of 30 to 40. Outside that, a low bicarbonate rules nothing out.
- Why that matters
- Borrowing the threshold into a high-probability patient skips the arterial gas in exactly the person most likely to be retaining carbon dioxide.
- Not a diagnosis
- Bicarbonate cannot establish or exclude the syndrome in either direction. A raised value is a reason to measure the carbon dioxide, not a substitute for measuring it.
What you enter
- Body mass index, kg/m2
- Sleep-disordered breathing
- Awake resting PaCO2, mmHg
- Other causes of hypoventilation excluded
- Serum bicarbonate, mmol/L
- High pretest probability
How this is calculated
Mokhlesi B, Masa JF, Brozek JL, et al. Evaluation and Management of Obesity Hypoventilation Syndrome. An Official American Thoracic Society Clinical Practice Guideline. Am J Respir Crit Care Med. 2019;200(3):e6-e24. Read the source ↗
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.