Assessing risk factors of respiratory complications following abdominal wall reconstruction.

Abstract

Sir: In a retrospective study by Fischer et al.1 assessing associations of perioperative factors with postoperative respiratory morbidity in patients undergoing abdominal wall reconstruction, they had attempted to control most of the known factors that could affect postoperative respiratory complications, such as age, body mass index, smoking status, American Society of Anesthesiologists physical status, preoperative comorbidities, use of steroids, intraoperative blood loss and transfusion, and others. Furthermore, they used appropriate methods to determine risk factors for postoperative respiratory complications. However, this study is a retrospective analysis with observational designs, which are inevitably subject to uncontrolled and unmeasured confounding. In our view, several important issues of this study were not well addressed. First, the authors did not describe use of opioid drugs or neuromuscular blocking agents during surgery, the duration of postoperative assessment, or methods of postoperative analgesia. Fair evidence suggests that intraoperative short-acting rather than long-acting neuromuscular blocking agents reduce the risk of postoperative respiratory complications.2 It has been shown that the first 24 hours after surgery represent the highest risk of unanticipated respiratory failure because of opioid drugs, whereas postoperative hypoxemia is most common by the third night after major surgery.3 Thus, assessment of postoperative respiratory complications is frequently focused on the early postoperative period of 3 days after surgery. Following abdominal surgery, moreover, pain is recognized as being the most frequent postoperative problem, and inadequate postoperative analgesia may result in splinting, with rapid and shallow breathing. As a result, ensuring adequate analgesia in the postoperative period is of great importance, not only for patient comfort but also for improvement of pulmonary function and a reduction in the risk of respiratory complications.4 Second, in this study, 67.2 percent of patients had at least one defined comorbidity preoperatively. Moreover, the most common comorbid condition was hypertension (53.0 percent), and 9.7 percent of patients suffered from coronary artery disease. Thus, preoperative assessment of cardiac function should be included in the study design. Good-quality evidence identifies preoperative cardiac insufficiency as a significant risk factor for postoperative pulmonary complications.2 To exclude the possible influence of existing lung lesions on the postoperative respiratory outcome, preoperative chest radiography is required, especially for patients with new or unstable cardiopulmonary signs or symptoms and patients at increased risk of postoperative pulmonary complications.2 Finally, ventilator-induced lung injury is a possible confounding factor. It is generally believed that use of large tidal volume or high pressure during general anesthesia may adversely influence postoperative pulmonary complications. In this study, the authors assessed the effects of inspiratory pressure on postoperative respiratory morbidities, and showed that the highest peak intraoperative airway pressure was associated with postoperative respiratory complications. We would like to know whether an identical ventilation strategy, with the same settings of ventilation mode, ventilation rate, and tidal volume, was used in all patients. A randomized clinical trial in patients undergoing elective laparotomy confirms that, compared with standard ventilation strategy, a protective ventilation strategy with lower tidal volumes, positive end-expiratory pressure, and recruitment maneuvers during anesthesia improves postoperative respiratory function and reduces the clinical signs of postoperative pulmonary infection.5 In addition, transfusion-related acute lung injury is a well-known issue. To assess associations of intraoperative transfusions with postoperative respiratory morbidity, transfusion indications during surgery should at least be provided. We believe that addressing the above confounding factors would further clarify the transparency of this retrospective study. DISCLOSURE The authors have no financial interest to declare in relation to the content of this communication. No external funding was received. Fu S. Xue, M.D. Shi Y. Wang, M.D. Xin L. Cui, M.D. Rui P. Li, M.D. Department of Anesthesiology Plastic Surgery Hospital Chinese Academy of Medical Sciences and Peking Union Medical College Beijing, People’s Republic of China