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Obesity hypoventilation syndrome

Medical Professionals

Professional Reference articles are designed for health professionals to use. They are written by UK doctors and based on research evidence, UK and European Guidelines. You may find one of our health articles more useful.

Synonym: Pickwick syndrome

The classic features of obesity hypoventilation syndrome (OHS) are obesity and daytime hypercapnia.1 The differences between OHS and obstructive sleep apnoea (OSA) are that the former has:2

  • Longer and more continuous episodes of hypoventilation overnight (there may or may not be upper airway obstruction).

  • Daytime hypercapnia.

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Controversy surrounds the pathophysiology. Only a small proportion of people with morbid obesity have the condition, so factors other than obesity must be at work. Some authors believe that the basic problem relates to the way the ventilatory drive reacts to hypoxia and hypercapnia.3 Others consider that fat distribution, hormones and upper airway size are involved.

Upper airway obstruction is certainly known to play a prominent role. It may be associated with rapid eye movement (REM) atonia, increased fat distribution around the neck and upward displacement of the diaphragm by abdominal fat.4 Experiments with mouse models suggest that deficiency of or resistance to leptin (a substance which reduces the surface tension of lung tissue) may be involved, leading to alterations in central respiratory drive and reduced ventilatory responsiveness, permitting development of carbon dioxide retention. Changes in neuromodulators resulting from the effects of hypoxia may further exacerbate the problem by depressing arousal from sleep in the face of abnormal breathing.1

Differentiation has been made between people who have sleep apnoea hypoventilation, and OHS in which hypoventilation is also evident whilst they are awake.5 Most patients with the syndrome also have sleep apnoea but some patients do not, suggesting that it is the obesity per se which is causing chronic hypoventilation.6

Patients may also have concomitant features of asthma or chronic obstructive pulmonary disease (COPD).

How common is obesity hypoventilation syndrome? (Epidemiology)

There are no accurate figures for incidence or prevalence, mainly because the condition has been poorly defined in the past and often confused with OSA. It is estimated that obesity hypoventilation syndrome affects 0.4% of the population.7 Risk factors mirror that for obesity and the condition is more common in females. Tonsillar hypertrophy is an aggravating factor in children. The peak ages of presentation are 5-7 years and adolescence.8 However, increased awareness of the condition means that more and more cases are being diagnosed in adults.

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OHS symptoms9


Symptoms suggestive of the diagnosis may include features of sleep apnoea (witnessed apnoea, snoring enuresis, nightmares, sleepwalking), chronic mouth breathing, daytime sleepiness, hyperactivity in children, morning headaches, decreased exercise tolerance, poor school performance, poor memory and poor concentration.

A drug history should be taken to exclude alcohol excess, sedating antihistamines and central nervous system depressants, all of which can aggravate the condition.

  • The typical patient will be clinically obese, with marked fat deposition around the chin and abdomen. Thoracic kyphosis is often a feature. Leg oedema may be present.

  • The head, ears, nose and throat should be examined to exclude facial dysmorphologies or ENT abnormalities that may cause upper airway obstruction, such as macroglossia, micrognathia, retrognathia or high-arched palate. The tonsils should be examined to exclude hypertrophy and the nasal passages to exclude polyps, cysts or swollen nasal turbinates.

  • Examination of the chest may reveal signs of cor pulmonale (loud second heart sound, displaced cardiac impulse). Acquired pes excavatum may result from overuse of the respiratory muscles overcoming extrathoracic obstruction.


OHS cannot be diagnosed on history and examination alone but requires the demonstration of daytime hypercapnia.

Diagnostic criteria for OHS

  • Body mass index ≥30 kg/m2.

  • Daytime PaCO2 >45 mm Hg.

  • Associated sleep-related breathing disorder (sleep apnoea-hypopnoea syndrome or sleep hypoventilation, or both).

  • Absence of other known causes of hypoventilation.

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Differential diagnosis11

Investigations10 12

  • Arterial blood gases - these are needed to confirm daytime hypercapnia and hypoxaemia.

  • Serum bicarbonate level is a useful tool for excluding OHS in low-risk individuals.13

  • Nocturnal oximetry should be carried out to determine whether sleep apnoea is also present (about one fifth of sleep apnoeic patients will have OHS. Formal polysomnography may be required in borderline cases.

  • CXR - may show chest wall deformities, or signs of cardiomegaly or congestive failure.

  • Echocardiogram - may show right ventricular hypertrophy.

  • ECG - arrhythmias and right bundle branch block have been recorded.

  • Pulmonary function tests:

    • Flow volume loop - expiratory volume as measured by spirometry is plotted in a continuous curve against flow rate - may show a 'sawtooth' pattern associated with upper airway obstruction.14

    • Forced vital capacity and expiratory reserve volume may be reduced and airways resistance increased.

  • Overnight polysomnography may confirm hypoventilation, hypoxia and hypercapnia during sleep, especially in children and adolescents.

  • FBC and TFTs should be performed to exclude anaemia and myxoedema.

Obesity hypoventilation syndrome treatment and management10

  • A return to normal body weight is the mainstay of treatment. Unfortunately, although they may lose weight initially, many patients are non-adherent with dietary restriction in the long term. They are furthermore restricted from increasing their physical activity due to pulmonary symptoms. Bariatric surgery may be required in severe cases.

  • Continuous positive airways pressure (CPAP) is more helpful in OSA, whereas patients with OHS usually need assisted ventilation which may need to be supplemented by oxygen.

  • The inability of these patients to increase their ventilatory capacity should be borne in mind during their management (eg, when they are subjected to hospital procedures which may lead to hypercapnia).15

  • Treat any concomitant OSA, asthma or COPD as appropriate.



Prognosis is improved by early recognition, weight loss and CPAP. There is also evidence that hospital resource usage is reduced. Evidence that quality of life is improved did not reach statistical significance.

Further reading and references

  1. Piper AJ, Grunstein RR; Current perspectives on the obesity hypoventilation syndrome. Curr Opin Pulm Med. 2007 Nov;13(6):490-6.
  2. Rapoport DM; Obesity hypoventilation syndrome: more than just severe sleep apnea. Sleep Med Rev. 2011 Apr;15(2):77-8. Epub 2011 Feb 3.
  3. Mokhlesi B, Kryger MH, Grunstein RR; Assessment and management of patients with obesity hypoventilation syndrome. Proc Am Thorac Soc. 2008 Feb 15;5(2):218-25.
  4. Al Dabal L, Bahammam AS; Obesity hypoventilation syndrome. Ann Thorac Med. 2009 Apr;4(2):41-9. doi: 10.4103/1817-1737.49411.
  5. Pack AI; Advances in sleep-disordered breathing. Am J Respir Crit Care Med. 2006 Jan 1;173(1):7-15. Epub 2005 Nov 10.
  6. Poulain M, Doucet M, Major GC, et al; The effect of obesity on chronic respiratory diseases: pathophysiology and therapeutic strategies. CMAJ. 2006 Apr 25;174(9):1293-9.
  7. Masa JF, Pepin JL, Borel JC, et al; Obesity hypoventilation syndrome. Eur Respir Rev. 2019 Mar 14;28(151). pii: 28/151/180097. doi: 10.1183/16000617.0097-2018. Print 2019 Mar 31.
  8. Fiorino EK, Brooks LJ; Obesity and respiratory diseases in childhood. Clin Chest Med. 2009 Sep;30(3):601-8, x. doi: 10.1016/j.ccm.2009.05.010.
  9. Iftikhar IH, Roland J; Obesity Hypoventilation Syndrome. Clin Chest Med. 2018 Jun;39(2):427-436. doi: 10.1016/j.ccm.2018.01.006.
  10. Obstructive sleep apnoea/hypopnoea syndrome and obesity hypoventilation syndrome in over 16s; NICE guidance (August 2021)
  11. Olson AL, Zwillich C; The obesity hypoventilation syndrome. Am J Med. 2005 Sep;118(9):948-56.
  12. 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 Aug 1;200(3):e6-e24. doi: 10.1164/rccm.201905-1071ST.
  13. Shah NM, Shrimanker S, Kaltsakas G; Defining obesity hypoventilation syndrome. Breathe (Sheff). 2021 Sep;17(3):210089. doi: 10.1183/20734735.0089-2021.
  14. Tests of pulmonary function; Anaesthesia UK
  15. Nelson JA, Loredo JS, Acosta JA; The Obesity-Hypoventilation Syndrome and Respiratory Failure in the Acute Trauma Patient. J Emerg Med. 2008 Aug 30.
  16. Al Otair HA, Elshaer F, Elgishy A, et al; Left ventricular diastolic dysfunction in patients with obesity hypoventilation syndrome. J Thorac Dis. 2018 Oct;10(10):5747-5754. doi: 10.21037/jtd.2018.09.74.
  17. Alawami M, Mustafa A, Whyte K, et al; Echocardiographic and electrocardiographic findings in patients with obesity hypoventilation syndrome. Intern Med J. 2015 Jan;45(1):68-73. doi: 10.1111/imj.12620.

Article history

The information on this page is written and peer reviewed by qualified clinicians.

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