Effect of different doses of dexmedetomidine on lung injury during laparoscopic gallbladder surgery in elderly patients with mild obstructive ventilation dysfunction

Objective To evaluate the effect of different doses of dexmedetomidine on the lung injury during laparoscopic gallbladder surgery in elderly patients with mild obstructive ventilation dysfunction. Methods One hundred and twenty patients of both sexes, aged 65-75 yr, with body mass index of 18.5-23.9 kg/m2, of American Society of Anesthesiologists physical status Ⅱ or Ⅲ, who were diagnosed with mild obstructive ventilation dysfunction during the preoperative pulmonary function test, scheduled for elective laparoscopic gallbladder surgery under general anesthesia, were divided into 4 groups (n = 30 each) using a random number table method: control group (group C) and different doses of dexmedetomidine groups (Dex1, Dex2 and Dex3 groups). In Dex1, Dex2 and Dex3 groups, dexmedetomidine was intravenously infused as a bolus of 1 μg/kg over 10 min, followed by an infusion of 0.2, 0.4 and 0.6 μg·kg-1·h-1 until the end of operation, respectively.The equal volume of normal saline was given instead in group C. Airway peak pressure (Ppeak), mean airway pressure (Pmean), airway plateau pressure (Pplat), and positive end-expiratory pressure were measured immediately before pneumoperitoneum (T1), at the end of pneumoperitoneum (T2), and 10 min after the end of pneumoperitoneum (T3), and driving pressure was calculated.Arterial blood samples were obtained to record PaO2 and PaCO2, and oxygenation index (OI), respiratory index (RI), physiologic dead space fraction (VD/VT) and alveolar-arterial oxygen difference (A-aDO2) were calculated.The extubation time and development of complications such as hypercapnia and hypoxemia within 48 h after operation were recorded. Results Compared with group C, Ppeak, Pmean and driving pressure were significantly decreased, OI was increased, and the RI, VD/VT and A-aDO2 were decreased at T1-3, the intraoperative consumption of norepinephrine and atropine was increased, the extubation time was shortened, and the incidence of hyoxemia was decreased after operation in Dex1, Dex2 and Dex3 groups (P<0.05). Compared with group Dex1, Ppeak, Pmean and driving pressure were significantly decreased, OI was increased, and the RI, VD/VT and A-aDO2 were decreased at T1-3 in Dex2 and Dex3 groups, and the intraoperative consumption of norepinephrine and atropine was increased in group Dex3 (P<0.05). The intraoperative consumption of norepinephrine and atropine was significantly higher in group Dex3 than in group Dex2 (P<0.05). Conclusion The optimal maintenance dose of dexmedetomidine in improving pulmonary function during laparoscopic gallbladder surgery is 0.4 μg·kg-1·h-1 in elderly patients with mild obstructive ventilation dysfunction. Key words: Dexmedetomidine; Laparoscopic surgery; Respiratory function tests; Aged