To evaluate the effect of body mass index (BMI) on tidal volume with controlled mechanical ventilation during general anesthesia.

Ninety patients with ASA (American Society of Anesthesiologists) gradeⅠ orⅡ, 20-60years old and scheduled for elective surgery under general anesthesia, were selected in the study and divided into 3 groups , light weight group(L group, BMI<18.5kg/m², 28 cases), normal weight group(N group, 18.5kg/m²≤BMI<23kg/m², 32 cases), and overweight or obesity group(H group, BMI≥23kg/m² , 30 cases). Partial pressure of end-tidal carbon dioxide (PETCO₂) were maintained between 35-45 mmHg by adjusting tidal volume after indubation , the parameters including mean arterial pressure (MAP), heart rate(HR), pulse oxygen saturation(SpO₂), partial pressure of end-tidal carbon dioxide (PETCO₂), inspiratory tidal volume(VTi), expiratory tidal volume(VTe), peak inspiratory pressure(Ppeak) were recorded 5, 10, 15, 20, 30 and 60 minutes after adjusting tidal volume.

There were no statistical differences in MAP, HR, and SpO₂ in the three groups. Compared with N and L group, VTi and VTe were significantly lower in group H (P<0.05). Ppeak was higher in group H (P<0.05). Compared with L group, VTi and VTe were significantly lower in group N (P<0.05). Ppeak was higher in group N (P<0.05). Compared with N and L group, PETCO₂ was lower in group H (P<0.05). There were no statistical differences between N and L group.

Patients of light weight require more tidal volume, and patients of overweight or obesity require less tidal volume than patients of normal weight. BMI is an important factor for setting up tidal volume with controlled mechanical ventilation during general anesthesi.