WE would like to thank Dr. Zheng et al., Dr. Xue et al., and Dr. Romagnoli et al. for their interest in our investigation1 and their comments. In their letters, they voiced concerns about the selection of the patients included into the study and the clinical management during the perioperative period.
Dr. Zheng et al. emphasize the body mass index and epidural anesthesia technique as possible confounding factors. In our study, the mean body mass index was 25.9 ± 4.2 kg/m2 and 25.0 ± 4.9 kg/m2 in the standard and protective ventilation groups, respectively (P = 0.47). Thus, we believe that obesity did not affect our results. Epidural anesthesia at the level T8 to T12 might cause a decrease in muscle tone affecting spirometer measurements in postoperative period. In our study, both groups were treated with the same type and regimen of epidural anesthesia, and the infusion rate in epidural space was 4 to 6 ml/h, at low concentration of ropivacaine. The reduced velocity of infusion plays an important role to minimize the dose administered with the less motor blockade. The level of epidural anesthesia was not always checked before the induction of general anesthesia, due to longer onset time of the drug administered. However, all patients were evaluated in the postoperative period, every day, to exclude a too high level of anesthesia and the risk of a motor block of respiratory muscles.
Dr. Xue et al. raise several points of criticism: first perioperative hemoglobin levels, which might be associated with increased perioperative mortality, increased postoperative pneumonia, and increased hospital length of stay; second, serum albumin level which has been shown to be an important predictor of pulmonary complications after major noncardiac surgery; third, the use of nasogastric tube after surgery associated with reduced postoperative pulmonary complications; and fourth the perioperative assessment of patients’ cardiac function in older patients.
The Assess Respiratory Risk in Surgical Patients in Catalonia (ARISCAT) score,2 which predicts the risk of postoperative pulmonary complications, was comparable between the standard and protective ventilation groups, being 38.1 ± 8.6 and 34.8 ± 11.6 (P = 0.22), respectively (table 1). It has been shown that preoperative hemoglobin concentration lower than 10 g/dl was associated with an increased risk of postoperative pulmonary complications. In our study, the preoperative hemoglobin concentration was 13.2 ± 1.4 g/dl in the standard ventilation group and 12.3 ± 1.6 g/dl in the protective ventilation group (P = 0.04), showing no clinical relevant differences between the two groups. We did not collect the serum albumin level. However, laboratory indices of hepatic function were comparable within the two groups in the preoperative and postoperative periods. According to the clinical guidelines in our hospital, all patients undergoing open abdominal surgery, as those included in the current study, have a nasogastric tube for at least 24 h. The mean ages of our patients were 67.0 ± 9.0 and 65.5 ± 11.4 yr in the standard and protective ventilation groups, respectively. We agree with Dr. Xue that in the noncardiac surgery patients aged more than 60 yr, the risk of myocardial injury is increased. In our study, we did not measure serum troponin levels, but we did not observe severe arrhythmias or electrocardiographic alterations and for all patients similar perioperative fluid volume was administered. Overall, we did not report any clinical evidence of increased cardiac-related complications between the two groups. Finally, we agree with Dr. Xue that large-sample, randomized, controlled trials are useful to confirm the role of intraoperative ventilation strategies determining or preventing postoperative pulmonary outcomes. In August 2013, Futier et al.3 published a trial reporting that an intraoperative protective ventilation strategy, with a tidal volume of 6 to 8 ml/kg of predicted body weight, a positive end-expiratory pressure of 6 to 8 cm of water, and recruitment maneuvers repeated every 30 min after tracheal intubation compared to nonprotective ventilation with a tidal volume of 10 to 12 ml/kg of predicted body weight, with no positive end-expiratory pressure and no recruitment maneuvers, improved clinical outcomes and reduced healthcare utilization in the postoperative period in 400 patients at intermediate to high risk of pulmonary complications after major abdominal surgery.
Dr. Romagnoli et al. point out the role of oxygen titration as a component of the lung-protective strategy. We did not target the inspiratory oxygen fraction during surgery. However, all patients were preoxygenated with inspiratory oxygen fraction of 0.8 before tracheal intubation and maintained at 0.4 during the entire anesthesia procedure in both groups.
In conclusion, recent evidence from randomized, controlled trials1,3 and meta-analysis4 suggests that in patients at higher risk of postoperative pulmonary complications undergoing surgery, intraoperative protective mechanical ventilation with lower tidal volume (6–7 ml/kg predicted body weight) and positive end-expiratory pressure (6–10 cm H2O) with recruitment manoeuvres improves outcome and reduces healthcare utilization compared with conventional tidal volume (9–11 ml/kg predicted body weight) without positive end-expiratory pressure and recruitment.
The authors declare no competing interests.