Respiratory dead space under anaesthesia in patients with mitral stenosis

Physiological deadspace (VDphys) and arterial to end-tidal carbon dioxide tension difference [P(a-E)CO2] were calculated under anaesthesia in 27 patients with mitral stenosis planned for close mitral commissurotomy and in 15 healthy individuals for elective non-thoracic surgical procedures. A square wave inspiratory flow pattern and an end-inspiratory pause (25% and 10% of cycle time respectively) were given with a SERVO 900B ventilator used at respiratory rate of approximately 16 per min. An infra-red CO2 analyser was used to measure CO2 production and end-tidal CO2 concentration. Measurements were made prior to the start of the surgery after a minimum of 10 min of stable ventilation to avoid the effect of surgery. Patients with multiple stenosis had significantly higher VDphys (4.28 +/- 1.02 ml kg-1 as compared to 2.10 +/- 0.52 ml kg-1 in controls, P less than 0.001), higher P(a-E)CO2 [0.43 +/- 0.51 kPa as compared to -0.02 +/- 0.23 kPa, P less than 0.01] and lower respiratory system compliance (Crs). Péco2 was positively correlated with PaCO2 in both groups (P less than 0.01). PaO2 was lower in mitral stenosis patients and P(A-a)O2 negatively correlated to Crs (P less than 0.01).