Patients with chronic obstructive pulmonary disease who have worse lung function and prior history of acidotic hypercapnic respiratory failure (AHRF) are more likely to develop hypercapnia, defined as excessive carbon dioxide (CO2) in the bloodstream, a new study has found.
Respiratory failure is defined as significant hypoxia — low levels of oxygen — with or without hypercapnia.
Chronic obstructive pulmonary disease (COPD) patients can experience both hypoxia and hypercapnia. The identification of patients who may become hypercapnic or develop AHRF is important so that they can avoid hospital admission and be treated in a timely manner with noninvasive ventilation at home.
“AHRF is a well-defined complication of COPD, and noninvasive ventilation (NIV) is an effective treatment in such patients,” the researchers wrote.
To identify patients predisposed to hypercapnia, these researchers, in Birmingham, U.K., analyzed two groups of patients. The first group included 1,224 patients — 637 patients with COPD and 587 patients with alpha-1 antitrypsin deficiency (AATD), a genetic disorder that may cause COPD.
Hypercapnia was 15 times more common in patients with COPD than in those with AATD, the team found.
Given the differences in traits between patients with COPD (those with more homogeneous disease) and patients with AATD (those with a broader range of disease severity), the researchers decided to focus on patients with COPD.
Of the 637 COPD patients analyzed, 314 (49.3%) had a prior history of AHRF, 233 (36.6%) had hypercapnia, and 126 (19.8%) were current smokers. After adjusting for multiple other potential prognostic factors, hypercapnia was found to be independently associated with a lower forced expiratory volume in one second (FEV1) — a measure of lung function — and current use of long-term oxygen therapy.
The risk of hypercapnia was doubled per 1 kilopascal (kPa) decrease in partial pressure of oxygen in blood — a measure of how well oxygen is able to move from the lungs to the blood, which is often altered in COPD — and was nearly 10 times higher in current smokers.
In addition, the researchers found that patients with increasing partial pressure of carbon dioxide in blood — a measure of how well carbon dioxide is able to move out of the body — were 1.65 times more likely to die.
“With the advent of home NIV as a treatment proven to reduce mortality and hospital admissions in COPD, it is possible that prognosis will continue to improve, but only if these high-risk patients are identified early for treatment,” the researchers wrote.
A second group of patients underwent detailed sleep studies. This group included 160 patients with COPD, 44 (28%) of whom were found to have sleep disordered breathing (abnormal breathing during sleep), 94 (59%) had never had AHRF, and 66 (41%) had previously required noninvasive ventilation for AHRF.
Obstructive sleep apnea was more common in patients with a prior history of AHRF than in those who had never had AHRF.
As in the first group, patients with a lower FEV1, meaning they had worse lung function, were also more likely to develop hypercapnia.
Overall, the data showed that “lower FEV1 and prior AHRF are the main associations of stable-state hypercapnia in COPD, which carries a poor prognosis, particularly if it worsens over time in the stable state,” the researchers concluded.
“Whilst sleep disordered breathing does occur and is clinically important, conducting a sleep study is likely only to be valuable in patients who are persistently hypercapnic in the stable state,” the team added.
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