Sleep Hypoventilation

Sleep in chronic respiratory disease: COPD and hypoventilation disorders

COPD and obstructive sleep apnoea (OSA) are highly prevalent and different clinical COPD phenotypes that influence the likelihood of comorbid OSA. The increased lung volumes and low body mass index (BMI) associated with the predominant emphysema phenotype protects against OSA whereas the peripheral oedema and higher BMI often associated with the predominant chronic bronchitis phenotype promote OSA. The diagnosis of OSA in COPD patients requires clinical awareness and screening questionnaires which may help identify patients for overnight study. Management of OSA-COPD overlap patients differs from COPD alone and the survival of overlap patients treated with nocturnal positive airway pressure is superior to those untreated. Sleep-related hypoventilation is common in neuromuscular disease and skeletal disorders because of the effects of normal sleep on ventilation and additional challenges imposed by the underlying disorders. Hypoventilation is first seen during rapid eye movement (REM) sleep before progressing to involve non-REM sleep and wakefulness. Clinical presentation is nonspecific and daytime respiratory function measures poorly predict nocturnal hypoventilation. Monitoring of respiration and carbon dioxide levels during sleep should be incorporated in the evaluation of high-risk patient populations and treatment with noninvasive ventilation improves outcomes.

Obesity hypoventilation syndrome

Obesity hypoventilation syndrome (OHS) is defined as a combination of obesity (body mass index ≥30 kg·m-2), daytime hypercapnia (arterial carbon dioxide tension ≥45 mmHg) and sleep disordered breathing, after ruling out other disorders that may cause alveolar hypoventilation. OHS prevalence has been estimated to be ∼0.4% of the adult population. OHS is typically diagnosed during an episode of acute-on-chronic hypercapnic respiratory failure or when symptoms lead to pulmonary or sleep consultation in stable conditions. The diagnosis is firmly established after arterial blood gases and a sleep study. The presence of daytime hypercapnia is explained by several co-existing mechanisms such as obesity-related changes in the respiratory system, alterations in respiratory drive and breathing abnormalities during sleep. The most frequent comorbidities are metabolic and cardiovascular, mainly heart failure, coronary disease and pulmonary hypertension. Both continuous positive airway pressure (CPAP) and noninvasive ventilation (NIV) improve clinical symptoms, quality of life, gas exchange, and sleep disordered breathing. CPAP is considered the first-line treatment modality for OHS phenotype with concomitant severe obstructive sleep apnoea, whereas NIV is preferred in the minority of OHS patients with hypoventilation during sleep with no or milder forms of obstructive sleep apnoea (approximately <30% of OHS patients). Acute-on-chronic hypercapnic respiratory failure is habitually treated with NIV. Appropriate management of comorbidities including medications and rehabilitation programmes are key issues for improving prognosis.

NIV in amyotrophic lateral sclerosis: The 'when' and 'how' of the matter

Non-invasive ventilation (NIV) has become an essential part of the treatment of amyotrophic lateral sclerosis (ALS) since 2006. NIV very significantly improves survival, quality of life and cognitive performances. The initial NIV settings are simple, but progression of the disease, ventilator dependence and upper airway involvement sometimes make long-term adjustment of NIV more difficult, with a major impact on survival. Unique data concerning the long-term adjustment of NIV in ALS show that correction of leaks, management of obstructive apnoea and adaptation to the patient's degree of ventilator dependence improve the prognosis. Non-ventilatory factors also impact the efficacy of NIV and various solutions have been described and must be applied, including cough assist techniques, control of excess salivation and renutrition. NIV in ALS has been considerably improved as a result of application of all of these measures, avoiding the need for tracheostomy in the very great majority of cases. More advanced use of NIV also requires pulmonologists to master the associated end-of-life palliative care, as well as the modalities of discontinuing ventilation when it becomes unreasonable.

Sleep-Disordered Breathing in Neuromuscular and Chest Wall Diseases

Neuromuscular and chest wall diseases include a diverse group of conditions that share common risk factors for sleep-disordered breathing, including respiratory muscle weakness and/or thoracic restriction. Sleep-disordered breathing results from both the effects of normal sleep on ventilation and the additional challenges imposed by the underlying disorders. Patterns of sleep- disordered breathing vary with the specific diagnosis and stage of disease. Sleep hypoventilation precedes diurnal respiratory failure and may be difficult to recognize clinically because symptoms are nonspecific. Polysomnography has a role in both the diagnosis of sleep-disordered breathing and in the titration of effective noninvasive positive-pressure ventilation.

Obesity hypoventilation syndrome in the critically ill

This article summarizes available data on the obesity hypoventilation syndrome and its pertinence to intensivists, outlines clinical and pathophysiologic aspects of the disease, discusses multidisciplinary treatments, and reviews the available literature on outcomes specific to the critically ill patient.