Physiological Deadspace during Normocapnic Ventilation under Anaesthesia

Abstract

Respiratory physiological deadspace (VDphys) during normocapnic ventilation under anaesthesia was studied in 253 patients scheduled for elective non-thoracic surgery. Subjects were ventilated with SERVO 900B ventilator using CO 2 analyser 930 (Siemens-Elema Sweden) to adjust minute volume sufficient to maintain end-tidal carbon dioxide fraction (F É CO 2) around 5.5kPa with normocapnic confirmation using arterial blood gas analysis. VDphys was calculated using Enghoff's modification of Bohr's equation. VDphys and deadspace to tidal volume ratios (VD/VT) 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 VDphys/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). VDphys showed positive correlation with weight, height and body surface area (BSA) but VDphys/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.

Effects of positive end-expiratory pressure on dead space and its partitions in acute lung injury

“…Differences are partly explained by lower degrees of lung injury in our patients. Our data overlap with observations in anaesthetised, ventilated subjects without primary lung disease [40,41]. The small effect of PEEP on VD phys found in our study is fully explained by the effect on VD aw .…”

“…At a PEEP of 15 cmH 2 O, the average plateau pressure was 36 cmH 2 O (range [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44]. Average PaCO 2 varied between 44.3 and 45.0 mmHg at different PEEP levels ( Table 2).…”

Relationship between physiologic deadspace/tidal volume ratio and gas exchange in infants with acute bronchiolitis on invasive mechanical ventilation*

“…VD/VT values ranging from 0.35 to 0.38 were reported in pediatric perioperative patients (23,30,31). A study in adults reported that VD is proportional to weight, height, and body surface area (36). We would not expect significant variations of VD/VT in the first year of life, since both VD and VT increase with age.…”