- OHS is a breathing disorder associated with obesity, defined by three criteria: obesity (BMI >30), daytime high CO₂ levels, and sleep disordered breathing
- It is less well-known than sleep apnoea — but can be more dangerous, as low O₂ and high CO₂ place significant strain on the heart and blood vessels
- Many patients with OHS also have Obstructive Sleep Apnoea (OSA)
- Short-term treatment includes ventilation support (CPAP or non-invasive ventilation); the most effective long-term treatment is significant weight loss
- MedSurg Weight Loss can arrange a referral to a Respiratory Physician and support you through a weight loss programme to manage or reverse OHS
What Is Obesity Hypoventilation Syndrome?
Most people are familiar with Obstructive Sleep Apnoea (OSA) as a breathing condition linked to overweight and obesity — but a lesser-known and potentially more serious condition is Obesity Hypoventilation Syndrome (OHS). Many patients with OHS also have OSA, experiencing both conditions simultaneously.
OHS occurs when excess body weight impairs the ability to breathe adequately, leading to a dangerous imbalance in blood gases. To understand why this matters, it helps to first understand what normal gas exchange looks like — and how OHS disrupts it.
In OHS, ventilation is impaired — the body cannot breathe in enough oxygen or breathe out enough carbon dioxide. The resulting low O₂ and high CO₂ levels in the blood place enormous strain on the heart and blood vessels, and can be life-threatening if not recognised and treated.
How Is OHS Defined?
A diagnosis of OHS requires all three of the following criteria to be present:
Symptoms of OHS
OHS symptoms often overlap with those of Obstructive Sleep Apnoea, which is one reason it can be missed or misdiagnosed. Common symptoms include:
How Is OHS Treated?
Treatment for OHS has two components: short-term management of blood gas imbalance, and long-term definitive treatment through weight loss.
In the short term, the priority is correcting the O₂ and CO₂ imbalance. This is achieved through Continuous Positive Airway Pressure (CPAP) or non-invasive ventilation (NIV/BiPAP) devices that support breathing — particularly during sleep. These are effective at managing symptoms and reducing the dangerous blood gas imbalance, but do not address the underlying cause.
Weight loss is the most effective long-term treatment for OHS and the only intervention that can reverse the condition. Reducing body weight decreases the mechanical load on the chest wall and diaphragm, restores normal breathing mechanics, and improves blood gas levels — often dramatically. Weight loss can be achieved through dietary change, medical management, psychological support, or bariatric surgery, depending on individual circumstances.
If OHS is suspected, assessment by a Respiratory and Sleep Physician is essential for formal diagnosis (including arterial blood gas testing and sleep studies) and initiation of ventilation support. MedSurg Weight Loss can arrange a referral to an affiliated Respiratory Physician.
At MedSurg Weight Loss, we assess and manage the full range of obesity-related health conditions — including OHS. If we suspect you may have OHS, we can arrange a review with our affiliated Respiratory Physician and support you to achieve the weight loss that is the cornerstone of definitive management. No referral is necessary. Book an appointment or explore our Medical Weight Loss service.
Medical disclaimer: This article is for general educational purposes only. OHS is a serious medical condition requiring formal diagnosis and specialist management. If you are experiencing symptoms of OHS or sleep disordered breathing, please consult your doctor promptly for assessment and referral.