Alveolar hypoventilation is defined as an elevation in PaCO2 to levels >45 mmHg.
Disorders that have associated alveolar hypoventilation make up what is referred to as the hypoventilation syndrome. These include obesity-hypoventilation syndrome, restrictive thoracic disorders, central sleep apnoea syndromes, and COPD.
Hypoxaemia is often present, especially during sleep, and is associated with hypercapnia.
Symptoms are often non-specific, but almost always include disturbed sleep and impaired daytime function.
Physical examination often reveals signs of cor pulmonale in addition to those associated with the primary disorder.
Diagnosis is usually made by the clinician's awareness that alveolar hypoventilation is often associated with certain medical disorders. Investigations include arterial blood gas analysis, pulmonary function tests, measurement of respiratory muscle strength, and an overnight polysomnogram.
Treatment involves nocturnal ventilation, including the use of invasive ventilation.
Alveolar hypoventilation, defined as an elevation in PaCO2 to levels >45 mmHg, can occur with several disorders: obesity-hypoventilation syndrome, restrictive thoracic disorders, central sleep apnoea syndromes, and COPD. These are referred to as the hypoventilation syndromes. Associated with hypercapnia is the development of hypoxaemia, which adds to the clinical manifestations and morbidity. In addition, during sleep, hypoventilation becomes more profound and can worsen pre-existing hypercapnia and hypoxaemia. In some cases, hypercapnia and hypoxaemia may develop only during sleep, which may be unsuspected based on awake values.
History and exam
Key diagnostic factors
- presence of risk factors
Other diagnostic factors
- male sex
- daytime sleepiness
- morning headache
- impaired cough
- repeated lower respiratory tract infections
- BMI ≥30 kg/m²
- increased pulmonary component of second heart sound (P2)
- lower-extremity oedema
- right-sided third heart sound (S3 gallop)
- left-sided fourth heart sound (S4 gallop)
- body mass index (BMI) ≥30 kg/m²
- restrictive thoracic disorders
- central nervous system disorders
- obstructive airway disease
1st investigations to order
- arterial blood gas
- serum bicarbonate
- pulse oximetry
Investigations to consider
- pulmonary function tests
- respiratory muscle strength
- PHOX2B gene
restrictive thoracic disorders
Samuel Krachman, DO
Professor of Medicine
Division of Pulmonary and Critical Care Medicine
Temple University School of Medicine
SK is an author of a number of references cited in this topic.
Professor Samuel Krachman would like to gratefully acknowledge Dr Gerard Criner, a previous contributor to this topic.
GC declares that he has no competing interests.
Matthew Hind, PhD, MRCP
Royal Brompton Hospital
Honorary Senior Lecturer
National Heart and Lung Institute
Department of Respiratory Medicine
MH declares that he has no competing interests.
Kenneth I. Berger, MD
Associate Professor of Medicine
Physiology and Neuroscience
New York University School of Medicine
KIB declares that he has no competing interests.
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