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 apnea syndromes, and COPD.
Hypoxemia is often present, especially during sleep, and is associated with hypercapnia.
Symptoms are often nonspecific, but almost always include disturbed sleep and impaired daytime function.
Physical exam 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 apnea syndromes, and COPD. These are referred to as the hypoventilation syndromes. Associated with hypercapnia is the development of hypoxemia, which adds to the clinical manifestations and morbidity. In addition, during sleep, hypoventilation becomes more profound and can worsen pre-existing hypercapnia and hypoxemia. In some cases, hypercapnia and hypoxemia may develop only during sleep, which may be unsuspected based on awake values. 
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 monograph.
Professor Samuel Krachman would like to gratefully acknowledge Dr Gerard Criner, a previous contributor to this monograph. GC declares that he has no competing interests.
Royal Brompton Hospital
Honorary Senior Lecturer
National Heart and Lung Institute
Department of Respiratory Medicine
MH declares that he has no competing interests.
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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