Using Corrected Body Weight To Set Tide Volume For Mechanical Ventilation During General Anesthesia In Obese Patients

Objective:The study was to investigate the accuracy of using corrected body weight to set tidal volume for mechanical ventilation during general anesthesia in obese patients, comparing with that using ideal body weight or actual body weight.Methods:Sixty ASA I-II obese patients, with a body mass index range of28-44kg/m2, undergoing surgery on extremity, were randomly divided into three groups,20case each group. Only obese patients with normal lung function were enrolled. Upon intubation after induction of general anesthesia, patients received mechanical ventilation. Tidal volume was calculated as8ml/kg based on ideal body weight (IBW group), corrected body weight (ideal body weight plus30%of excess weight, CBW group), or actual body weight (ABW group). Respiratory rate15bpm, I:E1:2were set for all the patients. The ventilating parameters such as Ppeak, Pplat, Raw were recorded. At30min after mechanical ventilating, arterial blood gas analysis was studied. The numbers of patients in each group requiring reset of ventilator parameters due to PaCO2out of normal range (PaCO2>45mmHg or<35mmHg) were compared. After ventilating for1h,3ml arterial blood was obtained and the plasma concentration of IL-6and IL-8was determined by ELISA.Results:The difference of PaO2and oxygenation index (01) of the three groups was not significant (P>0.05). The IBW group was associated with a significant increase in PaCO2comparing to the CBW group(P<0.01). The ABW group was associated with a significant decrease in PaCO2and a significant increase in Ppeak, Pplat, Raw, IL-6, IL-8comparing with CBW group(P<0.01). The numbers of patients required resetting ventilator parameters were16/20in IBW group and19/20in ABW group, with were significantly higher (P<0.01) comparing to that of CBW group (0/20).Conclusions:Using corrected body weight to set tide volume for mechanical ventilation during general anesthesia in obese patients was more accurate than that using ideal body weight or actual body weight when calculating tide volume by8ml/kg, and ventilating at15bpm. This may also attenuate ventilator induced lung injury by avoiding unnecessary large tidal volume ventilation.