Spirometric Predictors for the Exclusion of Severe Hypoxemia in Chronic Obstructive Pulmonary Disease

Abstract

BACKGROUND: Controversy has existed over the need for routine arterial blood gas (ABG) analysis in patients with chronic obstructive pulmonary disease (COPD). Some authors recommend it in all patients with COPD, but others find it unnecessary if the forced expiratory volume in 1 s (FEV₁) is 50% of predicted or greater.OBJECTIVES: To clarify this controversy, and to investigate correlations between severe hypoxemia and multiple spirometric parameters in patients with COPD with FEV₁ 50% of predicted or greater.PATIENTS AND METHODS: In 103 consecutive patients with COPD with FEV₁ 50% of predicted or greater, and without any other cardiopulmonary disorder, the incidence of severe hypoxemia (partial pressure of arterial oxygen less than 60 mmHg) was established by ABG analysis. Positive and negative predictive values (PPVs and NPVs, respectively) for severe hypoxemia for multiple spirometric parameters (FEV₁, FEV₁/forced vital capacity [FVC], peak expiratory flow [PEF], maximal midexpiratory flow rate [FEF_25-75]) were evaluated in a stepwise manner.RESULTS: Twenty-two patients (21%) were found to be severely hypoxemic. In the severely hypoxemic group, the mean values for FEV₁, FEV₁/FVC, PEF and FEF_25-75 were 59.0±8.19%, 53.6±11.3, 50.6±9.3 and 34.4±14.2% of predicted, respectively. The mean values for the same parameters in the other patients were 58.0±4.6%, 52.7±7.8, 51.5±7.5 and 39.1±7.7% of predicted, respectively. Comparing these parameters between the two groups, only the difference in FEF_25-75 was statistically significant (P<0.01). Valid PPVs and NPVs could not be established for any of the parameters at any level, except for the NPV for FEF_25-75 50% of predicted or greater, which was 92%. This threshold value resulted in a false negative finding in less than 5% of the patients with hypoxemia.CONCLUSIONS: The results of the present study showed that one in five patients with COPD with FEV₁ 50% of predicted or greater was severely hypoxemic. In such patients, hypoxemia may be excluded, and ABG analysis may not be needed when the FEF_25-75 is also 50% of predicted or greater. The FEV₁, FEV₁/FVC and PEF parameters failed to predict or exclude severe hypoxemia.