We investigated the variability of arterial, mixed venous and peripher
al venous oxygen saturation readings in three co-oximeters in regular
use on two Intensive Care Units. Over a 2-week period, 96 readings wer
e obtained from each of the following machines; two AVL 912 co-oxylite
co-oximeters (Machines A and B, Biomedical Instruments, Graz, Austral
ia) and one lL-282 (Machine C, Instrumentation Laboratories, Lexington
, MA, USA). The coefficient of variation bl the arterial oxygen satura
tions was extremely small on all three machines (< 0.43%). The coeffic
ient of variation in the mixed venous samples, however, ranged from 1.
96 to 4.61 % on machine A, and from 2.73 to 4.71% on machine B, but on
ly from 0.17 to 1.47% on machine C. The variation in mixed venous satu
rations obtained from a single blood sample repeatedly analysed on mac
hines A and B was large enough to influence clinical management.