Physiological Deadspace during Normocapnic Ventilation under Anaesthesia

Abstract

Respiratory physiological deadspace (V_Dphys) during normocapnic ventilation under anaesthesia was studied in 253 patients scheduled for elective non-thoracic surgery. Subjects were ventilated with SERVO 900B ventilator using CO₂ analyser 930 (Siemens-Elema Sweden) to adjust minute volume sufficient to maintain end-tidal carbon dioxide fraction (F_Έ CO₂) around 5.5kPa with normocapnic confirmation using arterial blood gas analysis. V_Dphys was calculated using Enghoff's modification of Bohr's equation. V_Dphys and deadspace to tidal volume ratios (V_D/V_T) in male patients were 142.6±28.4 ml and 0.37±0.068 respectively and were significantly higher than that in females (119.4±35.6 ml and 0.36±0.067). Males had significantly higher V_Dphys/mass (2.5±0.68 ml.kg) compared with females (2.2±0.54 ml/kg, P<0.001) but significantly lower body mass index (BMI) (20.67±3.2 in males and 22.47±4.1 in females, P<0.001). V_Dphys showed positive correlation with weight, height and body surface area (BSA) but V_Dphys/kg showed negative correlation with BMI. Multiple regression analysis produced a best fit equation for V_Dphys=9.7+64.3 2BSA+13.51S where S=1 for females and 2 for males.

Keywords

VENTILATION: deadspace normocapnia anaesthesia

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