Changes in lung aeration and respiratory function after open abdominal surgery: A quantitative magnetic resonance imaging study

Abstract

Background: Atelectasis is one of the most common respiratory complications in patients undergoing open abdominal surgery. Peripheral oxygen saturation (SpO 2 ) and forced vital capacity (FVC) are bedside indicators of postoperative respiratory dysfunction. The aim of this study was to describe the changes in lung aeration, using quantitative analysis of magnetic resonance imaging (MRI) and the diagnostic accuracy of SpO 2 and FVC to detect postoperative atelectasis. Methods: Post-hoc analysis of a randomized trial conducted at a University Hospital in Dresden, Germany. Patients undergoing pre-and postoperative lung MRI were included. MRI signal intensity was analyzed quantitatively to define poorly and nonaerated lung compartments. Postoperative atelectasis was defined as nonaerated lung volume above 2% of the total lung volume in the respective MRI investigation.Results: This study included 45 patients, 27 with and 18 patients without postoperative atelectasis. Patients with atelectasis had higher body mass index (p = .024), had more preoperative poorly aerated lung volume (p = .049), a lower preoperative SpO 2 (p = .009), and a lower preoperative FVC (p = .029). The amount of atelectasis correlated with preoperative SpO 2 (Spearman's ρ = À.51, p < .001) and postoperative SpO 2 (ρ = À.60, p < .001), and with preoperative FVC (ρ = À.29, p = .047) and postoperative FVC (ρ = À.40, p = .006). A postoperative SpO 2 ≤ 94% had 74% sensitivity and 78% specificity to detect atelectasis, while postoperative FVC ≤ 50% had 56% sensitivity and 100% specificity to detect atelectasis. Conclusion: SpO 2 and FVC correlated with the amount of postoperative non-aerated lung volume, showing acceptable diagnostic accuracy in bedside detection of postoperative atelectasis.

Nitrous Oxide and Postoperative Pulmonary Complications: Conflicting Evidence

“…When evaluated by magnetic resonance imaging, the incidence of atelectasis in patients recovering from general anesthesia without nitrous oxide for major abdominal surgery is about 60%. 10 In contrast, the reported overall incidence in ENIGMA I and the work of Peyton et al 1 was only about 13%. It is thus apparent that most atelectasis was missed in both trials, which is unsurprising since both were based on clinical diagnoses, usually supplemented by conventional radiographs, which are insensitive to atelectasis.…”