CHANGES IN END-TIDAL CARBON-DIOXIDE TENSION FOLLOWING SODIUM-BICARBONATE ADMINISTRATION - CORRELATION WITH CARDIAC-OUTPUT AND HEMOGLOBIN CONCENTRATION

An intravenous administration of sodium bicarbonate (NaHCO3) forms exc ess CO2, resulting in an immediate increase in end-tidal carbon dioxid e tension (PETCO(2)). We hypothesized that the time until PETCO(2) rea ched a maximum. and the magnitude of the increase in PETCO(2) are infl uenced by cardiac output and haemoglobin concentration, respectively. To test this hypothesis, we examined changes in PETCO(2) following an intravenous administration of NaHCO3 at different levels of cardiac ou tput and haemoglobin concentration. We administered 0.2 mmol . kg(-1) of 8.4% NaHCO3 into the vena cava in 15 anesthetized dogs under mechan ical ventilation of 20 breaths per min. Cardiac output was increased b y 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 PETCO(2) reached a maximum) was 4 +/- 0.2 breaths-time; and Delta CO2-max (the magnitude of the increase in PETCO(2)) 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 Delta CO2-max. Haemoglobin concentra tion showed a significant correlation with Delta CO2-max (r = 0.736, P <0.005), but not with time-max. We concluded that the time course and the magnitude of changes id PETCO(2) following intravenous administrat ion of NaHCO3 reflect changes in cardiac output and haemoglobin concen tration, respectively.