Am. J. Respir. Crit. Care Med.,
Volume 158, Number 1, July 1998, 188-193
Prognostic Value of Hypercapnia in Patients with
Chronic Respiratory Failure during Long-term
Oxygen Therapy
AKIRA
AIDA,
KENJI
MIYAMOTO,
MASAHARU
NISHIMURA,
MIYOJI
AIBA,
SHIRO
KIRA,
YOSHIKAZU
KAWAKAMI,
and
the Respiratory Failure Research Group in Japan
First Department of Medicine, Hokkaido University, School of Medicine, Sapporo; and Department of Respiratory Medicine,
Juntendo University School of Medicine, Tokyo, Japan
Hypercapnia observed in patients with chronic respiratory failure may not be an ominous sign for
prognosis when they are receiving long-term oxygen therapy (LTOT). In this study, we selected 4,552 patients with chronic obstructive pulmonary disease (COPD) and 3,028 with sequelae of pulmonary
tuberculosis (TBsq) receiving LTOT from 1985 to 1993 throughout Japan and prospectively analyzed their prognoses. The hypercapnic patients (PaCO2
45 mm Hg) had a better prognosis than the normocapnic patients (35
PaCO2 < 45 mm Hg) for TBsq, but no difference was found between the two groups with COPD. Furthermore, Cox's proportional hazards model revealed that in TBsq hypercapnia was an independent factor for favorable prognosis, and that the relative risk for mortality was
0.76 in patients with 45
PaCO2 < 55 mm Hg, 0.64 for those with 55
PaCO2 < 65 mm Hg, and 0.49 for patients with PaCO2
65 mm Hg against normocapnic patients. This favorable effect of hypercapnia in TBsq was particularly apparent in the patients without severe airway obstruction. Even a rise of
5 mm Hg or more in PaCO2 over the initial 6- to 18-mo follow-up period was not associated with poor
prognosis in TBsq, although it was in COPD. From these findings, we conclude that hypercapnia
should not be generally considered an ominous sign for prognosis in those patients who receive
LTOT.