Invited Commentary

Abstract

Pulmonary complications are a major source of morbidity and mortality after cardiac surgery and have a significantly prolonged intensive care unit (ICU) and hospital stay [1Reddy L.C. Grayson A.D. Griffiths E.M. Pullan M.D. Rashid A. Logistic risk model for prolonged ventilation after adult cardiac surgery.Ann Thorac Surg. 2007; 84: 528-536Abstract Full Text Full Text PDF PubMed Scopus (60) Google Scholar]. Risk factors for pulmonary complications include advanced age, reduced preoperative pulmonary function, current smoking, postoperative pain, poor cough, effusions, abdominal distention, left internal mammary artery harvest with pleural entry, and most importantly poor cardiac function. The use of cardiopulmonary bypass (CPB) is believed to reduce postoperative lung function by apnea and atelectasis during the bypass run, by an increase in interstitial water, and by inflammatory mediators and microemboli damage to the alveolar membrane. In a large cohort study, the use of cardiopulmonary bypass was an independent risk factor for postoperative intubation beyond 48 hours [1Reddy L.C. Grayson A.D. Griffiths E.M. Pullan M.D. Rashid A. Logistic risk model for prolonged ventilation after adult cardiac surgery.Ann Thorac Surg. 2007; 84: 528-536Abstract Full Text Full Text PDF PubMed Scopus (60) Google Scholar]. In a small prospective, randomized study of on-pump coronary artery bypass (ONCAB) and off-pump coronary artery bypass (OPCAB), it was found that the OPCAB group had improved gas exchange and had earlier extubation when compared with ONCAB [2Staton G.W. Williams W.H. Mahoney E.M. et al.Pulmonary outcomes of off-pump vs on-pump coronary artery bypass surgery in a randomized trial.Chest. 2005; 123: 892-901Crossref Scopus (87) Google Scholar]. Therefore, should we try to avoid CPB, especially in those patients with reduced pulmonary function when performing bypass surgery? The large retrospective study by Kerendi and colleagues [3Kerendi F. Halkos M.E. Puskas J.D. et al.Impact of off-pump coronary artery bypass graft surgery on postoperative pulmonary complications in patients with chronic lung disease.Ann Thorac Surg. 2011; 91: 8-15Abstract Full Text Full Text PDF PubMed Scopus (12) Google Scholar] tries to analyze the difference between OPCAB and ONCAB vis a vis pulmonary complications in patients classified preoperatively as having no, mild, moderate, or severe lung disease. They are to be commended for demonstrating the relationship between the risk of pulmonary complications, early mortality, and long-term mortality to the severity of preoperative lung disease. This is important information and may help in our preoperative decision-making process. They also applied robust statistical applications to achieve their conclusion that OPCAB reduced the incidence of pulmonary complications in all patients as compared with ONCAB; although true, this statement requires clarification and should be nuanced. The greatest impact of OPCAB in reducing prolonged ventilation, ventilator time, pneumonia, ARDS, sepsis, in hospital mortality, and 30-day mortality was among those patients without preoperative lung disease. In those with lung disease, only a reduction in prolonged ventilation and ventilation times was noted. When comparing OPCAB with ONCAB within each category of lung disease, there was no significant difference in primary endpoints among groups. One would have believed that if OPCAB reduces pulmonary complications in a group without lung disease, presumably by avoiding cardiopulmonary bypass, then this effect should be even more pronounced and concordant in a group of patients with lung disease. Unfortunately, this does not seem to be the case. It is known that a sternotomy, in addition to causing pain and discomfort, will provoke a reduction in lung volumes and impair rib-cage expansion and coordination [4Locke T.J. Griffiths T.L. Mould H. Gibson G.J. Rib cage mechanics after median sternotomy.Thorax. 1990; 45: 465-468Crossref PubMed Scopus (90) Google Scholar, 5Braun S.R. Birnbaum M.L. Choprs P.S. Pre and postoperative pulmonary function abnormalities in coronary artery revascularization surgery.Chest. 1978; 73: 316-320Crossref PubMed Scopus (108) Google Scholar]. During OPCAB, the sternum may be aggressively retracted and stretched. It is believed that OPCAB decreases lung compliance due to increase lung fluid and rotation of the heart during circumflex grafting [3Kerendi F. Halkos M.E. Puskas J.D. et al.Impact of off-pump coronary artery bypass graft surgery on postoperative pulmonary complications in patients with chronic lung disease.Ann Thorac Surg. 2011; 91: 8-15Abstract Full Text Full Text PDF PubMed Scopus (12) Google Scholar]. Is it possible that these mechanisms, and others yet identified, are as important in the development of pulmonary complications as the use of cardiopulmonary bypass among patients with pre-existing lung disease? Perhaps the noted reduction in pulmonary complications among those patients without lung disease undergoing OPCAB is more of a reflection of different anesthetic and ICU management and faster extubation rather than avoidance of cardiopulmonary bypass. At the present time, I believe that we are unable to conclude that OPCAB should be performed preferentially among patients with preoperative lung disease. Impact of Off-Pump Coronary Artery Bypass Graft Surgery on Postoperative Pulmonary Complications in Patients With Chronic Lung DiseaseThe Annals of Thoracic SurgeryVol. 91Issue 1PreviewOff-pump coronary artery bypass graft surgery (OPCAB) has proven to be beneficial in many high-risk subgroups. This study aims to determine whether OPCAB lowers the incidence of pulmonary complications among patients with chronic lung disease (CLD) when compared with on-pump coronary artery bypass graft surgery (ONCAB). Full-Text PDF