Reversible CO2 Retention in COPD
Reversible CO2 Retention in COPD
ABSTRACT & COMMENTARY
Synopsis: Hypercapnia in patients admitted with acute exacerbations of COPD may be reversible, and patients in whom this occurs may have a better long-term prognosis.
Source: Costello R, et al. Am J Med 1997;103:239-244.
Costello and associates at university college, Dublin, Ireland, report on a five-year prospective study of arterial blood gas changes and outcomes in 85 patients with chronic obstructive pulmonary disease (COPD), who initially presented in acute respiratory failure. Of the 85 patients, 68 (80%) survived the initial hospitalization, and 17 patients (27%) were alive five years after initial admission.
All 68 initially surviving patients were hypoxemic on admission to the hospital. Patients with initial arterial PCO2 values of less than 50 mmHg (n = 27) were designated Group 1; of the 41 patients with initial PCO2 greater than 50 mmHg, 22 became normocapnic prior to discharge (Group 2.1), and 19 had persistent hypercapnia (Group 2.2) at discharge. Although both Group 2.1 and Group 2.2 patients were initially hypercapnic, both initial and discharge PCO2 values were significantly higher in those in Group 2.2. Age, body mass index, FEV1, and vital capacity were not significantly different among the patients in these three groups, but long-term outcome differed substantially; five-year survival was not significantly different between group 1 and group 2.1 patients (33% and 26%, respectively, P = ns), but was worse in those in Group 2.2 (11%, P < 0.05). Only 24% of Group 2.1 patients developed chronic hypercapnia during five years of follow-up. Costello and colleagues conclude that patients with reversible hypercapnia in the setting of acutely decompensated COPD may represent a distinct prognostic group, in which the clinical outlook is better than for patients with hypercapnia that persists after discharge from the hospital.
COMMENTBY DAVID J. PIERSON, MD
The patients in this study whose acute hypercapnia resolved during hospitalization had a long-term prognosis indistinguishable from patients who did not manifest hypercapnia while acutely decompensated. Subsequent long-term survival in patients with reversible hypercapnia was considerably better than in patients presenting with hypercapnia that did not resolve. Only a few patients with reversible hypercapnia developed irreversible hypercapnia during follow-up, suggesting that the latter is not inevitable in such individuals.
Prevailing assumptions about the natural history of COPD hold that as the disease advances, some patients become "CO2 retainers," have severe hypoxemia, and tend to develop cor pulmonale ("blue bloaters"), while others maintain normocapnia, have less hypoxemia, and do not develop cor pulmonale ("pink puffers"). It is also commonly assumed that becoming hypercapnic represents an irreversible stage in the natural history of COPD, and that an elevated PCO2, even when observed during an acute exacerbation, is unlikely to return to normal. This paper illustrates that the latter assumption may not be correct, at least for some patients.
It is important for clinicians to be aware that the presence of hypercapnia on acute presentation to the hospital does not necessarily mean that it will persist, and to realize that patients in whom acute hypercapnia resolves may have a better outlook for long-term survival than those in whom it persists at the time of hospital discharge. These observations should be duplicated and extended by other investigators, as they may have important implications for management as well as for patient counseling and end-of-life discussions.
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