Preoperative Pulmonary Function and Mortality After Cardiac Surgery
Preoperative Pulmonary Function and Mortality After Cardiac Surgery
Background The aim of the study was to examine the relationship between preoperative pulmonary function and outcomes after cardiac surgery.
Methods We performed preoperative pulmonary function tests (PFTs) in 1,169 patients undergoing cardiac surgery at the Minneapolis Veterans Affairs Medical Center. Airway obstruction was defined as forced expiratory volume in 1 minute (FEV1) to forced vital capacity ratio <0.7.
Results Of the 1,169 patients, 483 (41%) had a prior history of chronic obstructive pulmonary disease (COPD). However, 178 patients with a history of COPD had no airway obstruction on PFT. Conversely, 186 patients without a COPD history had airway obstruction on PFT. Thus, PFT results helped reclassify the COPD status of 364 patients (31%). Operative mortality was 2% in patients with no or mild airway obstruction versus 6.7% in those with moderate or severe obstruction (ie, FEV1 to forced vital capacity ratio <0.7 and FEV1 <80% predicted). Postoperative mortality was higher (odds ratio 3.2, 95% CI 1.6–6.2, P = .001) in patients with moderate or severe airway obstruction and in patients with diffusing capacity of the lung for carbon monoxide <50% of predicted (odds ratio 4.9, 95% CI 2.3–10.8, P = .0001). Notably, mortality risk was 10× higher (95% CI 3.4–27.2, P = .0001) in patients with moderate or severe airway obstruction and diffusing capacity of the lung for carbon monoxide <50% of predicted.
Conclusions These data show that PFT before cardiac surgery reclassifies the COPD status of a substantial number of patients and provides important prognostic information that the current risk estimate models do not capture.
A clinical history of chronic obstructive pulmonary disease (COPD) is present in 4% to 27% of patients undergoing cardiac surgery and conveys a higher risk of postoperative pulmonary and infectious complications and death. Accordingly, a history of COPD is one of the clinical variables included in the risk stratification of patients undergoing cardiac surgery. On the other hand, most of the current risk estimation models for cardiac surgery do not include pulmonary function test (PFT) results in their algorithms. This may lead to 2 potential problems. First, in clinical practice, COPD is often diagnosed on an empirical basis without a PFT, raising the possibility of misdiagnosis of this disease and misclassification error when this variable is used in risk stratification. Indeed, there is accumulating evidence in nonsurgical settings that a substantial number of patients with a previous diagnosis of COPD do not have an abnormal spirometry. Among patients undergoing cardiac surgery, such misclassification of COPD status, whether wrongly labeling patients with normal pulmonary function with COPD or vice versa, may alter the surgical risk estimate significantly. Second, a history of COPD alone, even when correctly diagnosed, does not provide any quantitative information on the severity of this disease. It is plausible that the perioperative risk is different in patients with mild versus severe COPD. Preoperative PFTs could avert both of these potential problems. However, PFTs are not routinely performed before cardiac surgery; and there are very few data on the relation between preoperative PFT results and outcomes after cardiac surgery. Furthermore, despite the paucity of supporting data, certain PFT parameters are commonly used in making clinical decisions about the candidacy of patients for cardiac surgery. The objective of this investigation was to fill these gaps in knowledge. Specifically, we aimed to correlate a clinical history of COPD with the results of PFT and examine the relation between the preoperative pulmonary function and outcomes in a large cohort of patients undergoing cardiac surgery.
Abstract and Introduction
Abstract
Background The aim of the study was to examine the relationship between preoperative pulmonary function and outcomes after cardiac surgery.
Methods We performed preoperative pulmonary function tests (PFTs) in 1,169 patients undergoing cardiac surgery at the Minneapolis Veterans Affairs Medical Center. Airway obstruction was defined as forced expiratory volume in 1 minute (FEV1) to forced vital capacity ratio <0.7.
Results Of the 1,169 patients, 483 (41%) had a prior history of chronic obstructive pulmonary disease (COPD). However, 178 patients with a history of COPD had no airway obstruction on PFT. Conversely, 186 patients without a COPD history had airway obstruction on PFT. Thus, PFT results helped reclassify the COPD status of 364 patients (31%). Operative mortality was 2% in patients with no or mild airway obstruction versus 6.7% in those with moderate or severe obstruction (ie, FEV1 to forced vital capacity ratio <0.7 and FEV1 <80% predicted). Postoperative mortality was higher (odds ratio 3.2, 95% CI 1.6–6.2, P = .001) in patients with moderate or severe airway obstruction and in patients with diffusing capacity of the lung for carbon monoxide <50% of predicted (odds ratio 4.9, 95% CI 2.3–10.8, P = .0001). Notably, mortality risk was 10× higher (95% CI 3.4–27.2, P = .0001) in patients with moderate or severe airway obstruction and diffusing capacity of the lung for carbon monoxide <50% of predicted.
Conclusions These data show that PFT before cardiac surgery reclassifies the COPD status of a substantial number of patients and provides important prognostic information that the current risk estimate models do not capture.
Introduction
A clinical history of chronic obstructive pulmonary disease (COPD) is present in 4% to 27% of patients undergoing cardiac surgery and conveys a higher risk of postoperative pulmonary and infectious complications and death. Accordingly, a history of COPD is one of the clinical variables included in the risk stratification of patients undergoing cardiac surgery. On the other hand, most of the current risk estimation models for cardiac surgery do not include pulmonary function test (PFT) results in their algorithms. This may lead to 2 potential problems. First, in clinical practice, COPD is often diagnosed on an empirical basis without a PFT, raising the possibility of misdiagnosis of this disease and misclassification error when this variable is used in risk stratification. Indeed, there is accumulating evidence in nonsurgical settings that a substantial number of patients with a previous diagnosis of COPD do not have an abnormal spirometry. Among patients undergoing cardiac surgery, such misclassification of COPD status, whether wrongly labeling patients with normal pulmonary function with COPD or vice versa, may alter the surgical risk estimate significantly. Second, a history of COPD alone, even when correctly diagnosed, does not provide any quantitative information on the severity of this disease. It is plausible that the perioperative risk is different in patients with mild versus severe COPD. Preoperative PFTs could avert both of these potential problems. However, PFTs are not routinely performed before cardiac surgery; and there are very few data on the relation between preoperative PFT results and outcomes after cardiac surgery. Furthermore, despite the paucity of supporting data, certain PFT parameters are commonly used in making clinical decisions about the candidacy of patients for cardiac surgery. The objective of this investigation was to fill these gaps in knowledge. Specifically, we aimed to correlate a clinical history of COPD with the results of PFT and examine the relation between the preoperative pulmonary function and outcomes in a large cohort of patients undergoing cardiac surgery.