Comparison of perioperative spirometric data following spinal or general anaesthesia in normal-weight and overweight gynaecological patients

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Abstract
There is limited data comparing the impact of spinal anaesthesia (SA) and general anaesthesia (GA) on perioperative lung function. Here we assessed the differences of these two anaesthetic techniques on perioperative lung volumes in normal-weight (BMI < 25) and overweight (BMI 25-30) patients using spirometry. We prospectively studied 84 consenting patients having operations in the vaginal region receiving either GA (n = 41) or SA (n = 43). Both groups (GA and SA) were further divided into two subgroups each (normal-weight vs. overweight). We measured vital capacity (VC), forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), midexpiratory (MEF25-75) and peak expiratory flow rates (PEFR) at the preoperative assessment (baseline), after premedication, after effective SA, and 20 min, 1 h, 2 h and 3 h after the operation (last measurement after patient mobilization). Premedication was associated with a small but significant decrease in lung volumes in direct correlation with BMI (-5%). Spinal anaesthesia resulted in a significant reduction in lung volumes in overweight as opposed to normal-weight patients. Postoperatively, lung volumes were significantly more reduced following GA than SA as indicated by differences in mean VC (SD) of -12 (6)% vs. -6 (5)% 20 min after the end of the operation in the normal-weight and -18 (5)% vs. -10 (5)% in the overweight patients. There was a significant impact of BMI on postoperative respiratory function, which was significantly more important in the GA group than in the SA group, and recovery of lung volumes was more rapid in the normal-weight patients than in the overweight patients, particularly in the SA group. In gynaecological patients undergoing vaginal surgery, the impact of anaesthesia on postoperative lung function as assessed by spirometry was significantly less after SA than GA, particularly in overweight patients.