Relationships between ventilatory impairment, sleep hypoventilation and type 2 respiratory failure

The Role of Obstructive Sleep Apnea in Hypercapnic Respiratory Failure Identified in Critical Care, Inpatient, and Outpatient Settings

An emerging body of literature describes the prevalence and consequences of hypercapnic respiratory failure. While device qualifications, documentation practices, and previously performed clinical studies often encourage conceptualizing patients as having a single "cause" of hypercapnia, many patients encountered in practice have several contributing conditions. Physiologic and epidemiologic data suggest that sleep-disordered breathing-particularly obstructive sleep apnea (OSA)-often contributes to the development of hypercapnia. In this review, the authors summarize the frequency of contributing conditions to hypercapnic respiratory failure among patients identified in critical care, emergency, and inpatient settings with an aim toward understanding the contribution of OSA to the development of hypercapnia.

Impact of Desaturation Patterns versus Apnea-Hypopnea Index in the Development of Cardiovascular Comorbidities in Obstructive Sleep Apnea Patients

Various phenotypes of obstructive sleep apnea (OSA) have been recently described and are poorly assessed by the commonly used polysomnographic indices, such as the apnea-hypopnea index and oxygen desaturation index. Nocturnal hypoxemia is the hallmark of OSA and new quantitative markers, as hypoxic burden or desaturation severity, have been shown to be associated with cardiovascular (CV) mortality. The purpose of this overview is to review the endophenotypical and clinical characteristics of OSA, the current metrics, and to analyze different measurements of hypoxemia in OSA to predict the cardiovascular impact (eg hypoxic burden). Potential interest of multidimensional models to classify OSA, such as BAVENO classification, is also discussed, with the goal of focusing on specific endophenotypes that are likely to develop CV comorbidities, in order to guide clinicians to more aggressive management of OSA in these individuals.

Diaphragm dysfunction: A comprehensive review from diagnosis to management

Although the diaphragm represents a critical component of the respiratory pump, the clinical presentations of diaphragm dysfunction are often non-specific and can be mistaken for other more common causes of dyspnoea. While acute bilateral diaphragm dysfunction typically presents dramatically, progressive diaphragm dysfunction associated with neuromuscular disorders and unilateral hemidiaphragm dysfunction may be identified incidentally or by recognising subtle associated symptoms. Diaphragm dysfunction should be considered in individuals with unexplained dyspnoea, restrictive respiratory function tests or abnormal diaphragm position on plain chest imaging. A higher index of suspicion should occur for individuals with profound orthopnoea, those who have undergone procedures in proximity to the phrenic nerve(s) or those with co-morbid conditions that are associated with diaphragm dysfunction, particularly neuromuscular disorders. A systematic approach to the evaluation of diaphragm function using non-invasive diagnostic techniques such as respiratory function testing and diaphragm imaging can often confirm a diagnosis. Neurophysiological assessment may confirm diaphragm dysfunction and assist in identifying an underlying cause. Identifying those with or at risk of respiratory failure can allow institution of respiratory support, while specific cases may also benefit from surgical plication or phrenic nerve pacing techniques. This article is protected by copyright. All rights reserved.

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.

Patterns of use, survival and prognostic factors in patients receiving home mechanical ventilation in Western Australia: A single centre historical cohort study

Home mechanical ventilation (HMV) is used in a wide range of disorders associated with chronic hypoventilation. We describe the patterns of use, survival and predictors of death in Western Australia. We identified 240 consecutive patients (60% male; mean age 58 years and body mass index 31 kg m^-2) referred for HMV between 2005 and 2010. The patients were grouped into four categories: motor neurone disorders (MND; 39%), pulmonary disease (PULM; 25%, mainly chronic obstructive pulmonary disease), non-MND neuromuscular and chest wall disorders (NMCW; 21%) and the obesity hypoventilation syndrome (OHS; 15%). On average, the patients had moderate ventilatory impairment (forced vital capacity: 51%predicted), sleep apnoea (apnoea-hypopnea index: 25 events h^-1), sleep-related hypoventilation (transcutaneous carbon dioxide rise of 20 mmHg) and daytime hypercarbia (PCO₂: 54 mmHg). Median durations of survival from HMV initiation were 1.0, 4.2, 9.9 and >11.5 years for MND, PULM, NMCW and OHS, respectively. Independent predictors of death varied between primary indications for HMV; the predictors included (a) age in all groups except for MND (hazard ratios (HRs) 1.03-1.10); (b) cardiovascular disease (HR: 2.35, 95% confidence interval (CI): 1.08-5.10) in MND; (c) obesity (HR: 0.28, 95% CI: 0.13-0.62) and oxygen therapy (HR: 0.33, 95% CI: 0.14-0.79) in PULM; and (d) forced expiratory volume in 1 s (%predicted; HR: 0.93, 95% CI: 0.88-1.00) in OHS.

Chronic hypoventilation syndromes and sleep-related hypoventilation

Chronic hypoventilation affects patients with disorders on any level of the respiratory system. The generation of respiratory impulses can be impaired in congenital disorders, such as central congenital alveolar hypoventilation, in alterations of the brain stem or complex diseases like obesity hypoventilation. The translation of the impulses via spinal cord and nerves to the respiratory muscles can be impaired in neurological diseases. Thoraco-skeletal or muscular diseases may inhibit the execution of the impulses. All hypoventilation disorders are characterized by a reduction of the minute ventilation with an increase of daytime hypercapnia. As sleep reduces minute ventilation substantially in healthy persons and much more pronounced in patients with underlying thoraco-pulmonary diseases, hypoventilation manifests firstly during sleep. Therefore, sleep related hypoventilation may be an early stage of chronic hypoventilation disorders. After treatment of any prevailing underlying disease, symptomatic therapy with non-invasive ventilation (NIV) is required. The adaptation of the treatment should be performed under close medical supervision. Pressure support algorithms have become most frequently used. The most recent devices automatically apply pressure support and vary inspiratory and expiratory pressures and breathing frequency in order to stabilize upper airways, normalize ventilation, achieve best synchronicity between patient and device and aim at optimizing patients' adherence.