Changes in end‐tidal carbon dioxide tension following sodium bicarbonate administration: Correlation with cardiac output and haemoglobin concentration

An intravenous administration of sodium bicarbonate (NaHCO₃) forms excess CO₂, resulting in an immediate increase in end‐tidal carbon dioxide tension (PetCO₂). We hypothesized that the time until PetCO₂ reached a maximum, and the magnitude of the increase in PetCO₂ are influenced by cardiac output and haemoglobin concentration, respectively. To test this hypothesis, we examined changes in PetCO₂ following an intravenous administration of NaHCO₃, at different levels of cardiac output and haemoglobin concentration. We administered 0.2 mmol · kg⁻¹ of 8.4% NaHCO₃ into the vena cava in 15 anesthetized dogs under mechanical ventilation of 20 breaths per min. Cardiac output was increased by dopamine infusion, and decreased by blood withdrawal under halothane anaesthesia. Haemoglobin concentrations were changed by haemodilution with hydroxyethyl starch. When control measurements were taken, time‐max (the time until the increase in PetCO₂ reached a maximum) was 4 ± 0.2 breaths‐time, and ΔCO₂‐max (the magnitude of the increase in PetCO₂) was 0.90 ± 0.04 kPa (6.6 ± 0.3 mmHg). Cardiac output was inversely correlated with time‐max (r = 0.94, P<0.0001), while it revealed a poor correlation with ΔCO₂‐max. Haemoglobin concentration showed a significant correlation with ΔCO₂‐max (r = 0.736, P<0.005), but not with time‐max. We concluded that the time course and the magnitude of changes in PetCO₂ following intravenous administration of NaHCO₃ reflect changes in cardiac output and haemoglobin concentration, respectively. 1995 Acta Anaesthesiologica Scandinavica Fonden