Cyanide in blood, plasma, and urine of dogs after administration of K14CN was determined with the
isotope dilution technique. The addition of large amounts of inactive KCN as soon as possible to a sample to be analyzed inhibited the decrease of the original
cyanide concentration. After administration of several lethal doses of
cyanide into the stomach or by slow
intravenous infusion a concentration of about 40 micron
cyanide in plasma was found at the moment of respiratory arrest. Since 60% of the
cyanide in plasma was bound to
proteins the concentration of free
cyanide which stopped respiration was about 16 micron. Quick formation of
ferrihemoglobin by i.v. injection of
4-dimethylaminophenol after plasma
cyanide had risen to or above 40 micron decreased the
cyanide concentration in plasma and restored respiration, while
cyanide was accumulated in red cells by formation of
ferrihemoglobin cyanide. Equilibrium constants calculated for the reaction between
ferrihemoglobin and
cyanide in vivo indicated that the reaction approached equilibrium in a few minutes. Up to 60% of the radioactive
cyanide absorbed was found as non-
cyanide radioactivity in the urine.