Diagnostic Approach and Management

The serious and potentially life-threatening disturbances in ventilation and gas exchange that may develop during sleep in patients with COPD raise the question of what investigations are appropriate in these patients (58). It is widely accepted that sleep studies are not routinely indicated in patients with COPD associated with respiratory failure. Although awake oxygen saturation is the best predictor of sleep desaturation in COPD, the degree of airflow obstruction also independently predicts sleep desaturation. Overnight oximetry should be considered in most COPD patients, irrespectively of whether they have symptoms of sleep disruption, to identify significant overnight desaturation that may be associated with reduced survival. Nocturnal oximetry is also mandatory in order to titrate the oxygen flow adequately

FIGURE 2 Correlation between mean SaO2 and total numbers of sleep stage changes (r = -0.54; p < 0.05). Source: Modified from Ref. 57.

FIGURE 2 Correlation between mean SaO2 and total numbers of sleep stage changes (r = -0.54; p < 0.05). Source: Modified from Ref. 57.

in patients who are eligible for long-term oxygen therapy (59). However, when performing overnight pulse oximetry, especially at home, it must be appreciated that patients with COPD considerable night-to-night variability in nocturnal desaturation so that only one recording may be insufficient for an accurate assessment (60).

Sleep studies are generally performed when there is a clinical suspicion of associated OSA or manifestations of hypoxemia not explained by the awake PaO2 level or in the presence of daytime hypoxemia not adequately explained by the level of airflow obstruction.

The first step in the management of sleep-disordered breathing in COPD patients is optimal treatment of the underlying disease. Conventional O2 therapy (both night-time and daytime) is the first-line treatment of nocturnal hypoxemia in COPD patients with stable respiratory failure (PaO2 < 55-60 mmHg). However, COPD patients may have nocturnal desaturation even in the presence of only mild-to-moderate daytime hypoxemia (PaO2 > 60 mmHg), thus not fulfilling the usual criteria for conventional oxygen therapy (40). According to the already mentioned results of Fletcher et al. (19) this group of patients usually receives oxygen therapy only during the night. However, the impact of nocturnal oxygen therapy in such patients is still debated since conflicting results are available both regarding the hypothesis that isolated sleep-related hypoxemia could favor the development of pulmonary hypertension or reduce the survival rate (61).

Noninvasive mechanical ventilation (NIMV) has been increasingly used as a treatment of chronic hypercapnic respiratory failure. Its use in patients affected by COPD is still controversial, while most of the studies performed in patients with restrictive thoracic disorders, and in particular in those with neuromuscular disorders, suggested that the symptoms of chronic hypoventilation were alleviated in the short-term, and in two small studies survival was prolonged (62-66). Indeed, a Cochrane review published in 2001 stated that "long-term mechanical ventilation should be offered as a therapeutic option to patients with chronic respiratory failure due to neuromuscular diseases" (67).

NIMV probably produces improvements in daytime blood gases through a number of mechanisms, including resting of the respiratory muscles, and a resetting of the respiratory drive. It was hypothesized that the nocturnal use of NIMV might prevent episodes of sleep-disordered breathing, reduce associated arousals, and improve the quality of sleep. In addition, NIMV during sleep would ameliorate nocturnal hypoventilation, leading to a downward resetting of the respiratory center's sensitivity to carbon dioxide. As a consequence, daytime gas exchange would improve, and the improved sleep quality would have a favorable impact on daytime function and quality of life. Elliot et al. (68) evaluated eight patients with severe COPD, six of whom had a reduction in daytime PaO2 when treated with nocturnal nasal ventilation using a portable volume ventilator for six months. These patients had improved sleep quality and there was a significant correlation between the drop in PaCO2 and the ventilatory response to CO2, suggesting an increase in respiratory drive (69). In a controlled three-month crossover trial, Meecham-Jones (65) studied 18 patients receiving nasal bilevel positive airway pressure ventilation. Patients receiving NIMV had significant reductions in daytime PaCO2, and the frequent oxygen desaturations and episodes of hypoventilation that occurred during control nights were ameliorated by NIMV. The authors concluded that NIMV improved sleep quality and nocturnal gas exchange, and that these benefits enhanced quality of life. Most of the papers published in the literature on the long-term efficacy of NIMV in patients with chronic hypercapnic respiratory failure do not have the effect of NIMV on sleep quality or the pattern of breathing during sleep (70). When the decision to initiate long-term NIMV is made, the ventilatory parameters to use during night-time are mainly decided according to the patient's tolerance when they are awake and records of diurnal arterial blood gases. However, the scenario during sleep may change considerably. Teschler et al. (71) studied the effect of mouth leak, very common on NIMV while asleep, on effectiveness of nasal bilevel ventila-tory assistance and on sleep architecture. These investigators found that when the mouth was taped closed during nocturnal NIMV there was a significant reduction of transcutaneous carbon dioxide and a significant improvement of sleep quality as demonstrated by a reduction in arousal index and an increase in the amount of REM sleep. Finally, the effect of NIMV on sleep quality and improvement of gas exchange is also dependent on patient/ventilator interaction. Indeed, stable patients receiving nocturnal NIMV for chronic sleep hypoventilation or chronic hypercapnic respiratory failure may have a poor nocturnal gas exchange and disturbed sleep when the patient/ ventilator interaction is not optimal, as was demonstrated by the presence of ineffective inspiratory efforts (72,73). Sleep quality and gas exchange improved after adjusting the ventilatory parameter according to a more physiological setting (Fig. 3).

At the moment, long-term oxygen therapy is the first-line treatment of COPD patients who are hypoxemic during the night but NIMV may become more important in the future. More studies are necessary to understand the true effect of NIMV on sleep quality and control of breathing during sleep. Until the mechanisms to explain the benefit of NIMV in COPD patients are better known, the indications, ideal ventilator settings, and expected response will remain unclear. The decision to start home NIMV during sleep should be individually defined on the basis of clinical and physiological response to a preliminary trial (74).

Sleeping Sanctuary

Sleeping Sanctuary

Salvation For The Sleep Deprived The Ultimate Guide To Sleeping, Napping, Resting And  Restoring Your Energy. Of the many things that we do just instinctively and do not give much  of a thought to, sleep is probably the most prominent one. Most of us sleep only because we have to. We sleep because we cannot stay awake all 24 hours in the day.

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