FEV1/FVC lower limit of normal aids surgery risk stratification in COPD

By Lucy Piper, Senior MedwireNews Reporter

Researchers say that using the lower limit of normal (LLN) of the forced expiration volume in 1 second (FEV1)/forced vital capacity (FVC) ratio improves risk stratification in patients with chronic obstructive pulmonary disease (COPD) undergoing thoracic surgery.

Using this classification the team identified an “in-between” group of patients with obstructive impairment whose FEV1/FVC ratio was below the 0.70 fixed ratio, in accordance with The Global Initiative for Chronic Obstructive Lung Disease (GOLD) definition of COPD, but above the lower fifth percentile of an age-matched healthy reference group, thereby failing to meet the American Thoracic Society (ATS)/European Respiratory Society (ERS) criteria for COPD diagnosis.

This in-between group of 124 patients had better postoperative outcomes than a group of 178 COPD patients whose FEV1/FVC ratio was both below 0.7 and the LLN.

The COPD patients had a significant threefold increase in the crude risk of needing prolonged oxygen therapy after surgery compared with in-between patients and a 1.5-fold increase in prolonged hospital stay. After adjusting for age, gender, body mass index, smoking history and operation time, however, only the risk of prolonged oxygen therapy remained significantly increased, at an odds ratio of 3.068.

“This classification provides us with a measure of confidence, for example, in proposing thoracic surgery for the in-between group of patients as opposed to those in the COPD group”, say researcher Naozumi Hashimoto (Nagoya University Graduate School of Medicine, Japan) and colleagues.

The in-between patients had significantly better post-surgery outcomes than 399 individuals without COPD, but adjusted relative risks showed no significant difference.

The researchers note in Respiratory Investigation that the in-between and COPD groups had comparable pre-surgery characteristics in terms of proportion of men and older patients. The only exceptions were a higher incidence of smoking history among COPD patients and an increased prevalence of ischaemic heart disease, although the researchers say the latter did not appear to be related to the development of adverse postoperative outcomes.

The findings suggest that the in-between group has common demographical characteristics with the COPD group, but might retain pulmonary function similar to that of non-COPD individuals, Hashimoto and team note.

“Thus, the criterion of LLN […] was needed to more exactly identify at-risk patients among the subjects with obstructive impairment”, they conclude.

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