Influence of Body Mass Index and Epidural Anesthesia on Lung Function

I read with interest the report by Severgnini et al.¹  in which they describe that the protective mechanical ventilation improves postoperative pulmonary function in patients undergoing open abdominal surgery with general anesthesia. However, we wish to raise two concerns which may undermine the clinical validity of the authors’ conclusions.

First, the authors state that the exclusion criteria included patients with body mass index greater than 40 kg/m². It means that the inclusion criteria included patients with body mass index 40 kg/m² or less, and obese patients (mildly obese: body mass index 25–30; obese: body mass index >30) were also included in this study. Obesity is a risk factor for perioperative pulmonary complications as the pathophysiological changes induced by obesity may jeopardize respiratory function and contribute to pulmonary morbidity, such as hypoxemia, hypercapnia, and atelectasis.²  In addition, obesity is an important risk factor for perioperative impairment of spirometric measurements in patients undergoing laparotomy.³  There is a significant negative correlation between perioperative spirometric tests and obesity. The reduction in postoperative lung volumes was significantly greater in obese patients than in normal-weight patients. Also, surgery with general anesthesia may reduce lung volumes and this effect may be greater in the obese patients.⁴  So, we think the authors should give the information about the proportion of the obese patients in the two groups.

Second, the authors state that most patients underwent epidural anesthesia at the T8 to T12 level before general anesthesia and received continuous analgesia after surgery. High thoracic perioperative epidural anesthesia was shown to decrease spirometric measurements by blocking intercostal muscle innervation.⁵  Even if low concentrations of local anesthetics are used, the sensory levels of epidural anesthesia extending from approximately T4 to L1 are likely to be accompanied by some degree of muscle paralysis.⁶  It is more likely to block the muscles of the abdominal wall (innervation T6–L1). Even a subtle decrease in abdominal muscle tone will affect dynamic parameters. To avoid the influence of the epidural anesthesia on spirometric measurements, we think it is necessary to perform a pulmonary functional test after the epidural anesthesia. Or else, the authors should give the information about the epidural anesthesia including the dose of the local anesthetics, the direction of the epidural catheter, and the plane of the epidural anesthesia.

The authors declare no competing interests.