Elimination of CO from the body: an experimental study on the rabbit

Rabbits were exposed to gases containing CO with concentrations ranging from 2.0 to 2.9% for 40 sec, 1 min, or 5 min, and the time course of the change in the arterial blood COHb concentration was followed from immediately after the end of exposure up to 180 min. All rabbits survived. Hypercapnia was not observed. The COHb concentration at the end of the 5-min exposure ranged from 68.8-82.0%. The pattern of the elimination of CO was not linear; the decreasing rate of COHb concentration became slower with the lapse of time. The COHb concentration plotted against the post-exposure time on a semi-logarithmic graph showed three phases. In the first 10 min, the rate of decrease was the fastest. The second phase was followed by the third phase at about 90 min after exposure. In the shorter exposure groups too, the initial phase was observed. The initial phase was considered to be a stage in which CO was distributed throughout the body. The appearance of the third phase is probably explained by the contribution of CO produced endogeneously. The existing equations for predicting COHb concentrations failed to explain the initial and third phases.