Sleep-related breathing disorders
Obesity Hypoventilation Syndrome
In some people with obesity, breathing becomes too shallow to clear carbon dioxide, leading to high CO2 levels by day and serious health risks.
Overview
Obesity hypoventilation syndrome (OHS) occurs when obesity affects breathing so much that the lungs do not remove enough carbon dioxide, even while awake. Carbon dioxide builds up in the blood, oxygen levels may fall, and breathing during sleep is often worse still.
About nine in ten people with OHS also have obstructive sleep apnea, often severe. OHS is frequently missed until someone is admitted to hospital with breathing failure, but it can be identified earlier with a simple blood test.
Untreated OHS increases the risk of heart failure, pulmonary hypertension, hospitalisation and death. Positive airway pressure at night combined with weight loss can improve symptoms and outcomes considerably.
According to the 2019 American Thoracic Society guideline, OHS affects roughly 8% to 20% of people with obesity referred to sleep centres for sleep-disordered breathing.
Common symptoms
- Severe daytime sleepiness
- Shortness of breath
- Morning headaches
- Loud snoring and observed pauses in breathing
- Swelling in the legs and ankles
- Fatigue and low energy
- Bluish lips or skin in severe cases
Causes and risk factors
- Obesity, defined as a BMI of 30 or more, with the risk rising at higher BMI
- Coexisting obstructive sleep apnea
- Reduced breathing drive from the brain
- Extra weight on the chest and abdomen that limits breathing movement
How it is diagnosed
OHS is defined by obesity (BMI of 30 or more), a daytime arterial carbon dioxide level (PaCO2) of 45 mmHg or more on a blood gas test, and the exclusion of other causes of hypoventilation such as lung or neuromuscular disease. A raised bicarbonate level on a routine blood test can be an early clue.
A sleep study is used to identify coexisting sleep apnea and guide treatment, and lung function tests and heart assessments help exclude other causes.
Treatment options
Positive airway pressure
CPAP is often used first when severe obstructive sleep apnea is present, and noninvasive ventilation (bilevel) is used for others or if CPAP is not enough.
Weight loss
Sustained weight loss, sometimes with bariatric surgery or medication, can reverse hypoventilation.
Treating related conditions
Managing heart failure, fluid retention and pulmonary hypertension.
Oxygen
Added only when needed, alongside ventilation, under specialist care.
What you can do yourself
- Use your device every night
- Work with your care team on a weight-loss plan
- Avoid alcohol, sedatives and opioids where possible
- Keep follow-up blood gas and sleep appointments
When to see a doctor
- You have obesity with severe daytime sleepiness and shortness of breath
- Your legs are swelling or you become breathless with less effort
- Family notice confusion, extreme drowsiness or blue lips (seek urgent care)
- A blood test showed a high bicarbonate level
Frequently asked questions
What is the difference between OHS and sleep apnea?
Sleep apnea involves breathing pauses during sleep. OHS means carbon dioxide stays high even while you are awake. Most people with OHS also have obstructive sleep apnea, but OHS needs a daytime blood gas test to diagnose.
Why is it sometimes called Pickwickian syndrome?
The old name comes from a sleepy character in a Charles Dickens novel. Clinicians now use obesity hypoventilation syndrome.
Will CPAP or BiPAP fix it?
Positive airway pressure used consistently often lowers daytime carbon dioxide and improves sleepiness. Which device you need depends on your sleep study and blood gas results, and weight loss remains important.
How serious is OHS?
Untreated OHS raises the risk of heart failure, pulmonary hypertension and hospitalisation for breathing failure. Early diagnosis and treatment improve outcomes.
Sources
This page is general information, not a diagnosis or medical advice. Read our medical disclaimer.