Decreased preoperative plasma substance P concentration is likely associated with postoperative silent aspiration after esophagectomy

Background Postoperative pneumonia is the most common complication after esophagectomy and is closely associated with swallowing dysfunction and silent aspiration. Silent aspiration in the elderly is associated with decreased secretion of substance P (SP), which controls the swallowing and cough reflexes. The majority of patients with esophageal cancer are elderly. We hypothesized that surgical stress would decrease SP secretion, thereby increasing the risk of postoperative aspiration after esophagectomy, and prospectively investigated. Methods Thirty patients with esophageal cancer scheduled to undergo esophagectomy were enrolled in the study. Plasma and salivary SP concentrations and cough reflex sensitivity were measured before surgery and on postoperative days 2 and 7 to examine the association with postoperative aspiration. Results Postoperative silent aspiration was observed in 6 patients, 4 of whom developed pneumonia. Plasma SP concentration did not change significantly during the perioperative period. Salivary SP concentration and cough reflex sensitivity could not be measured in nearly one-third of patients because of postoperative dry mouth and unwillingness of patients to undergo measurement, respectively; thus, these perioperative changes could not be assessed. Preoperative plasma and salivary SP concentrations had a significant association with postoperative aspiration on univariate analysis and multivariate logistic regression analysis using variables selected by stepwise forward selection identified preoperative plasma SP concentration as the only significant risk factor for postoperative aspiration (p = 0.023). Conclusion Definitive results supporting our hypothesis could not be obtained. However, multivariate analysis suggested that decreased preoperative plasma SP concentration is likely associated with postoperative silent aspiration after esophagectomy.