Introduction

Obesity is not just a choice or lack of willpower, as it can be aided by a multitude of factors. These include genetics, childhood eating habits, addictive junk foods, and poor nutrition education; it is crucial to ascertain ways to control it. This is because obesity can trigger a variety of health conditions, such as cardiovascular diseases, diabetes, etc. Added to the list is a pulmonary sleep disorder that can lead to respiratory failure and other life-threatening complications if not managed. 

Obesity hypoventilation syndrome is a disorder primarily triggered by obesity that can occur simultaneously with obstructive sleep apnea (OSA). The syndrome can be caused by a malfunction in your brain’s capacity to coordinate breathing. This article provides more enthralling and concise information on the causes and symptoms of this condition and how it can be managed.

What is obesity hypoventilation syndrome?

Obesity hypoventilation syndrome (OHS) also called Pickwickian syndrome is a condition characterised by both nocturnal and daytime hypoventilation leading to hypoxemia and hypercapnia.¹ OHS comprises chronic hypoventilation in obese patients accompanied by a breathing-related sleep disorder.. It is an obesity-triggered condition whereby impaired breathing decreases oxygen and increases carbon dioxide levels in your blood. 

Obesity is the accumulation of excess body fat, to the point where it can impair overall health and contribute to the development of medical conditions. A body mass index (BMI) that is greater than or equal to 30 is categorised as obese. However, it is not only the BMI but also the distribution of the body adipose tissue that matters in the causation of this syndrome.²

Although on first impression, the disease appears to be limited to breathing disorders and obesity-associated implications, these effects are merely the tip of the iceberg. This is because OHS presents with a plethora of systemic complications such as respiratory failure, pulmonary hypertension, right heart failure, and neurological and endocrinological manifestations.³ OHS is generally not always considered to be gender-specific. Contrarily, among people referred to the clinic for sleep disorders, OHS was more prevalent in women than men.¹⁰ However, this condition presents in an atypical manner in persons assigned female at birth (AFAB). Generally, the prevalence of OHS is higher in those with morbid obesity (BMI > 40 kg/m²). Approximately, 10–20% of patients suffering from OSA get diagnosed with OHS in the long run.⁴ 

How does it occur?

There are three mechanisms leading to the development of OHS:

• Changes in the respiratory system because of obesity: Excess fat deposits affect respiratory function by impeding the motion of the diaphragm, increasing lower airway resistance and weakness of the respiratory muscles.⁵ This significantly increases the oxygen demand for breathing⁵
• Leptin resistance: Leptin is a protein released by the adipose tissues which regulates appetite and functions as a respiratory stimulant.⁶ Burdened by the enormous workload on the respiratory system, the majority of obese patients develop increased respiratory drive. If not controlled, hypoventilation will develop into rapid eye movement (REM) sleep. The high prevalence of central hypoventilation during REM sleep occurs due to a dysfunction in the leptin axis.⁵ As leptin stimulates ventilation, leptin resistance can lead to deterioration of respiratory control. This persistent slow and shallow breathing leads to a buildup of carbon dioxide and subsequently obesity hypoventilation syndrome
• Breathing abnormalities during sleep: Individuals with OHS predominantly develop OSA owing to the impaired function of the respiratory centres. The key features by which obesity reduces pharyngeal size and increases collapsibility are excessive fat deposition in the upper airways and reduction of lung volume. This predisposes the upper airway to narrowing during sleep⁷

What causes OHS?

The exact cause of OHS has not been well elucidated. However, the triggering risk factors of this condition include the following; 

• Obesity
• Leptin resistance
• Occurrence and severity of obstructive sleep apnea⁸
• Elevated serum bicarbonate level⁸
• Daytime hypoventilation which can be caused by malfunctioning of the respiratory centres, recurrent episodes of nocturnal obstructive apnea⁹

According to the American Society of Anesthesiologists, compared with obese patients without hypercapnia, patients with OHS demonstrate four main clinical features; more severe upper airway obstruction, impaired respiratory workings, dysfunctional central respiratory drive, and increased occurrence of pulmonary hypertension. 

Symptoms of OHS

The common symptoms associated with OHS occur as a result of sleep disordered breathing and lack of oxygen in the blood. These symptoms include; 

• Morning headaches
• Extreme daytime lethargy⁶
• Leg swelling
• Daytime somnolence 
• Depression 
• Loud and frequent snoring during sleep 

What treatment options are available? 

Management and treatment of OHS involves incorporating effective weight loss strategies and breathing-assisted therapies to prevent severe complications. The treatment options include:

• Positive airway pressure therapy (PAP therapy): This includes continuous positive airway pressure (CPAP), bilevel positive airway pressure (BPAP) and Average volume-assured pressure support (AVAPS). These therapies are chosen based on clinical history and physical examination of the patient.¹¹ This is because critically ill OHS patients may have challenges with the administration of PAP via a nasal or oronasal interface. Thus, an alternative would be intubation to receive mechanical ventilation¹¹
• Pulmonary rehabilitation: This consists of dietary modification, adopting an exercise regimen, addressing comorbidities, cessation of smoking, psychiatric evaluation and therapy for anxiety and depression, and management of osteoporosis²
• Tracheostomy 
• Oxygen therapy
• Weight reduction surgery
• Pharmacotherapy 

Respiratory stimulants such as medroxyprogesterone or acetazolamide can also be administered for patients as an adjunctive therapy in the advanced stages of the syndrome. It is noteworthy that these stimulants do not significantly alter the respiratory mechanics.⁶

Diagnosis of OHS

The criteria for diagnosis of OHS include;

• Presence of obesity (with BMI > 30kg ∕m²)
• Daytime hypoventilation is not caused by lung or airway disease, medication, or neurological disorder, and all other causes are ruled out
• Hypercapnia with or without obstructive sleep apnea
• Polysomnography reveals nocturnal hypoventilation 

Additional tests may include lung tests to measure the amount of oxygen and carbon dioxide in your body or how well your lungs are functioning. In addition, a sleep study or polysomnography can be used to test levels of PAP therapy to treat OSA and nocturnal hypoventilation. 

FAQs

What is the life expectancy of people with OHS? 

OHS is a life-threatening medical condition mostly triggered by obesity and associated with breathing difficulties. This condition can lead to premature death in most people due to respiratory failure if measures to lose weight are not implemented. 

What are the complications associated with OHS?

This condition has a gamut of systemic effects which include pulmonary hypertension, respiratory and right heart failure, and cardiovascular, neurological and endocrinological abnormalities. 

Why is it important to know if you have OHS?

It is vital to know if you have OHS because OHS can be treated. If left untreated, OHS can be life-threatening or result in the need to be hospitalised for severe complications. The hypoxemia that occurs as a result of this condition can put a strain on your heart and lead to cardiovascular complications. When treated, your symptoms may be reduced or entirely relieved. Treatment could also improve your quality of life and reduce the chances of further OHS-associated health conditions. 

What is the difference between OHS and OSA? 

The difference between obesity hypoventilation syndrome (OHS) and obstructive sleep apnoea (OSA) is that the former has longer and continuous episodes of both nocturnal and daytime hypoventilation while the latter only has nighttime hypoventilation with or without upper airway obstruction. 

Summary

OHS is a sleep-disordered breathing condition with momentous consequences if left untreated. The major risk factors include obesity, OSA, leptin resistance and daytime hypoventilation. However, not all obese people develop OHS due to an interplay of various factors. The mainstay therapy for the management of OHS is PAP therapy because it improves sleep-disordered breathing, hypercapnia, and hypoxemia thereby reducing the mortality rate. All therapies are palliative till weight loss is achieved by the patient through lifestyle modification.