The Management of Chronic Hypoventilation (3)
Table 2 shows the incidence of various etiologies of chronic hypoventilation seen at an outpatient chest clinic in a large general hospital. As expected, COPD was responsible for chronic hypoventilation in the majority of cases. The next most common single cause was the sleep apnea syndrome, which should be considered in any patient with unexplained chronic hypoventilation. Often associated with obstructive apneic episodes during sleep, it should really be considered a mixed disorder arising from an interplay of central ventilatory and anatomic upper airway abnormalities, usually in obese individuals. Sleep apnea also commonly contributes to chronic hypoventilation in patients with severe COPD or kyphoscoliosis.-
Restrictive chest wall diseases were a common cause of chronic hypoventilation in our series, but restrictive lung disease was a relatively unusual cause. Hypoventilation in patients with interstitial lung disease usually occurs late in their course, often as a preterminal event.
The second largest overall category responsible for chronic hypoventilation among our patients was multifactorial, underscoring the fact that a variety of factors often contribute to chronic hypoventilation. Even when a single primary etiologic factor can be identified, chronic hypoventilation should not be seen as the consequence of a single abnormality in the respiratory system, but rather as the interplay of different factors at a number of levels. Chronic C02 retention may develop in a patient with severe COPD whose respiratory center is insensitive to C02 and who has an increased number of apneic episodes during sleep. Another patient with equally severe COPD who has a high sensitivity to C02 and normal sleep may not retain C02. The possible multifactorial etiology of chronic hypoventilation should be considered in the evaluation of patients in order to maximize therapeutic results.
Table 2— The Etiology of Chronic Hypoventilation in an Outpatient Chest Clinic
|Chest wall deformity|
|Interstitial lung disease||3||4|
|Lung resection for cancer||2||3|