In the present study, we found that patients with severe COPD can undergo CABG without increased mortality risk when compared with patients with normal pulmonary function or with mild to moderate COPD. The postoperative outcome in patients with severe airflow obstruction was similar to those with either normal lung function or mild to moderate COPD with the exception of an increased risk of pulmonary infections, a tendency to postoperative atrial fibrillation and a slightly increased length of hospital stay.
These findings are at variance to those previously reported in some studies (1
). In their study, Grover et al (1
) found that an FEV1
less than 1.25 L was associated with an increased post-CABG mortality (11.7% versus 3.8% in patients with an FEV1
greater than 1.25 L). Although these patients had low FEV1
, the type of spirometric abnormalities (obstructive versus restrictive) was not specified. The same authors also reported that a clinical diagnosis of COPD (irrespectively of the FEV1
value) was associated with an increased postoperative mortality (6.4% versus 4.3%). Kurki et al (5
) found an association between a diagnosis of COPD or any pulmonary disorder with an FEV1
50% or less and postoperative morbidity after CABG. Postoperative morbidity end points included various complications such as neurological events, arrhythmia, pulmonary infections, wound infections, renal failure, cardiogenic shock and even death. Other studies have also associated COPD with an adverse post-CABG outcome (2
). However, in these studies, no spirometric data were reported and the postoperative mortality rate for COPD patients was very high, reaching up to 33.3% in some studies. Conversely, more recent studies (7
) failed to identify mild to moderate COPD as a risk factor of postoperative mortality and morbidity.
In this regard, our study may help in clarifying these discrepant findings. First, all patients had a preoperative spirometry and they were classified based on the degree of airflow obstruction. In addition, patients with reduced FEV1
due to restrictive disorder were excluded. Finally, surgeries were performed in a more recent period than previous studies, with improved anesthesia and surgical techniques and postoperative pulmonary care. This could explain the favourable postoperative outcome of our patients, even in the presence of severe airflow obstruction. Our results are consistent with postoperative mortality rates reported in recent studies (16
Many physiological and biochemical changes could contribute to pulmonary dysfunction after cardiac surgery (19
). Cardiopulmonary bypass use, internal mammary artery grafting and general anesthesia are some factors that can alter lung mechanics and gas exchange, and induce lung injury by stimulating production of various proinflammatory mediators (21
). Some studies identified COPD as a risk factor for prolonged mechanical ventilation (22
) or postoperative pneumonia (23
). In the present study, an increased risk of postoperative pulmonary infections in patients with severe COPD was found. The number of patients necessitating prolonged mechanical ventilation or showing other pulmonary complications was comparable among the three groups. It is important to note that patients in both COPD groups had fewer artery mammary grafts compared to those belonging to the control group, a potential bias in favour of reducing pulmonary complications in COPD (21
). The deleterious effects induced by cardiopulmonary bypass on pulmonary mechanics could be reduced by the use of less invasive heart surgery such as beating heart surgery and minimally invasive direct CABG (24
). Whether increasing use of these novel techniques will further improve postoperative outcome in COPD is unknown.
Patients in the severe COPD group had an important alteration in their pulmonary function, with a mean FEV1 less than 1 L. One potential explanation for the low occurrence of postoperative morbidities in these individuals is that they may have been selected in a more restrictive way during their pre-operative evaluation compared with patients with less pulmonary impairment. The number of comorbid conditions, the Parsonnet score and the American Society of Anesthesiologists class were similar in the three groups suggesting that the health status was similar in patients with severe COPD compared with the other groups. It would have been interesting to study the postoperative outcome of very severe COPD. Twenty-five patients with an FEV1 less than 35% were included in the present study. Postoperative mortality and morbidity was similar compared to patients with an FEV1 between 35% and 50% predicted. It should be noted that no patients had an FEV1 less than 20% or were on long-term oxygen therapy. Thus, we cannot comment on the operative risk in these individuals.
Another interesting finding of our study is the high prevalence of postoperative atrial fibrillation in the three groups, up to 45.6% in severe COPD. This may be due to high prevalence of other well-established risk factors including advanced age (more than 50% of studied population were older than 70 years of age), cardiopulmonary bypass use and beta-blocker withdrawal. Whether factors such as electrolyte imbalance, right atrial manipulation and atrial myocardial ischemia (26
) could have played a role was not evaluated in the present study. There was a trend toward more frequent postoperative atrial fibrillation in patients with severe compared with mild to moderate COPD. Although it did not reach statistical significance, this trend is consistent with studies that identified COPD as a significant risk factor for this specific arrhythmia (26
In the present investigation, the overall rate of postoperative sternal dehiscences (1.2%) and mediastinitis (1.2%) was similar to the reported incidence of these complications (28
). Although COPD has been proposed as a risk factor for these complications (28
), the rate of sternal dehiscences and mediastinitis were not increased in patients with COPD in our study. One possible explanation is that less frequent use of mammary artery grafting in COPD may have promoted sternal healing by reducing the occurrence of sternal ischemia. However, caution is warranted in the interpretation of these findings given the small number of sternal dehiscences (n=4) and mediastinitis (n=4) in our patients.
Because a valid spirometric tracing was a requirement to be included in the study, and because spirometry is not routinely performed preoperatively, patients involved in the present investigation represent only a subset of all patients undergoing a CABG in our institution. Accordingly, there could be a bias toward the selection of more symptomatic patients in whom a greater rate of postoperative complications could also be expected. However, the impact of this potential bias is likely to be small because the postoperative mortality and morbidity in this cohort of patients is similar to what is reported in the cardiac surgery literature (16
). On the other hand, in some patients, the diagnosis of COPD was probably made at the time of the surgery as suggested by the considerable portion of patients with unequivocal spirometric evidence of COPD who did not receive any pharmacological treatment for this condition. This observation is consistent with a previous epidemiological study (30
) and with the notion that COPD is under-recognized and undertreated. These potential selection biases should not detract from the usefulness of the present investigation. In fact, this study represents a real life situation where clinicians are confronted with the results of a spirometry in the preoperative evaluation of a patient undergoing a CABG. Pneumonia and bronchitis were defined according to standard clinical criteria. We acknowledge the limitation of these definitions, particularly in a postoperative context where the differential diagnosis of new lung infiltrates is vast. Only clinical episodes for which clinicians thought that a specific treatment with antibiotics was necessary were taken into account into the analysis. This was done in an attempt to minimize the number of false-positive episodes of respiratory tract infections in this retrospective analysis.
In conclusion, the current study shows that the presence and worsening of airflow obstruction are not associated with greater risk of mortality following CABG surgery in COPD compared with patients with normal spirometric function. Severe COPD patients when compared with mild to moderate COPD patients and patients with normal spirometry had a similar postoperative outcome with the exception of more frequent pulmonary infections, a trend toward more frequent atrial fibrillation and a slightly longer hospital stay. Coronary revascularization surgery appears to be a safe procedure in COPD.