high altitude can worsen CSA

In patients with untreated OSA, sojourn to a high altitude can significantly worsen sleep-disordered breathing. The exacerbation of sleep-disordered breathing is driven primarily by development of central sleep apnea, not worsening of OSA. Hypobaric hypoxia at altitudes >6,666.67 ft (>2,000 m) induces periodic breathing with central apnea. Breathing instability is related to hypoxic stimulation of ventilation, resulting in a reduced CO2 reserve—that is, eupneic PCO2 close to the apneic threshold promoting a central apnea at a minor rise in ventilation (hypoxia => breath more => lower pCO2). Enhanced chemosensitivity causes a ventilatory overshoot, leading to a vicious cycle of periodic breathing with central apneas. In a Swiss study of patients with OSA, the mean apnea-hypopnea index (AHI) increased from 51 to 89 events per hour after 2 days at a high altitude of 8,633.33 ft (2,590 m). The obstructive AHI did not change significantly, but the central apnea index increased from two to 29 events per hour. During altitude sojourns, combined treatment with acetazolamide and auto-CPAP, compared with auto-CPAP alone, resulted in improvement in nocturnal Spo2, better control of sleep apnea, and reduced insomnia. In this study, acetazolamide was initiated on arrival at the high-altitude destination and was prescribed as 250 mg every morning and 500 mg every evening, prior to meals.

In the current case, a more detailed download of the patient's auto-CPAP device revealed that the estimated AHI of 25 events per hour while at high altitude consisted of an obstructive AHI of 2 and a central apnea index of 23 events per hour. The reason this patient's auto-CPAP device did not increase the delivered pressure while at high altitude is because the device is not designed to increase CPAP pressure in response to central apneas. Therefore, preemptively increasing the range of the auto-CPAP device will not solve the patient's problem. Switching to a bilevel positive airway pressure (PAP) device will not solve the problem because, in fact, bilevel PAP therapy will lead to larger tidal volume delivery and will further decrease the PaCO2, thereby increasing respiratory instability and worsening of central apneas. Moreover, it is not practical to switch the device to bilevel PAP because insurance providers will not cover the cost. The download reveals that the amount of large leak is minimal. Switching from a nasal mask to an oronasal mask is unnecessary; in some patients, it can increase discomfort and even worsen OSA by pushing the chin and the tongue backward, inducing upper airway obstruction.1

Footnotes

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