Restrictive lung disease is another category of pulmonary disorders that may require nocturnal PAP therapy. Lung restriction is most commonly seen in obesity, kypho-scoliosis, neuromuscular disease, interstitial lung disease, and pregnancy. PAP therapy should be used unequivocally in these patients if they have coexisting OSA. However, in the absence of OSA, PAP therapy must be considered on a case-by-case manner, depending upon the disease process being considered.
Obese patients without OSA but with obesity hypoventilation syndrome (OHS) may benefit from nocturnal PAP therapy; CPAP, BPAP, or volume cycled NIPPV. BPAP or volume cycled NIPPV allow for increased ventilatory assistance compared to PAP therapy with CPAP. Initiation of PAP therapy should be performed in an attended setting as these patients may, at times, be medically unstable, and/or require supplemental oxygen in addition to positive pressure therapy; however, oxygen therapy alone is insufficient in these patients. NIPPV has been shown to improve long-term outcomes in patients with OHS (76).
Patients with kyphoscoliosis should be considered for PAP therapy in the absence of OSA if there are complaints of daytime sleepiness or sleep disruption and/or evidence of hypoventilation, Cheyne-Stokes respirations, or central apneas, all of which may be seen in these patients (77,78). Again, initiation of PAP therapy should be performed in a supervised setting due to the likelihood of the need to titrate supplemental oxygen in addition to NIPPV as well as the possibility of acute respiratory failure developing in these patients. Acute respiratory failure due to PAP therapy may occur in these patients with its initiation due to the increased work of breathing, which may result from an increased functional residual capacity coupled with extreme chest wall stiffness. Once evidence of hypoventilation is observed, BPAP or volume cycled NIPPV will be required to adequately ventilate these patients at night and may stave off invasive ventilation for some time (79-81).
Patients with progressive neuromuscular disorders will manifest the beginnings of chronic respiratory failure with nocturnal hypoventilation. In these cases, NIPPV should appropriately be started at night with a formal, supervised titration. Stable neuromuscular disorders with partial ventilatory function, including the sequelae of poliomyelitis, tuberculosis, Duchenne muscular dystrophy (DMD), or high-level spinal cord injuries, may successfully be ventilated at night, which may, in turn improve clinical and physiologic daytime function and may, like patients with respiratory failure due to kyphoscoliosis, stave off continuous NIPPV and/or invasive ventilation (82,83).
Interstitial lung disease (ILD) is a broad group of restrictive pulmonary disorders of more than 100 different etiologies. Patients with ILD often manifest disordered sleep due to difficulties with nocturnal breathing, especially in patients with baseline SaO2 < 90% (84). Additionally, nocturnal hypoxemia is fairly common in this group of patients and is likely due to episodic or persistent hypoventilation relative to waking ventilation, and may be more severe in REM sleep (85). PAP therapy is only indicated in patients with coexisting OSA and although no definitive clinical trials have validated its use, nocturnal oxygen in appropriate individuals is likely the treatment of choice (86).
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