Blood oxygen saturation measured in the presence of a mixture of cyclopropane, Sulfur hexafluoride, and ethane

Abstract

Some anesthetic gases interfere with the determination of blood O₂ values. We evaluated, for its potential for such interference, a gas mixture containing (v/v) ˜70% ethane, 20% sulfur hexafluoride, and 10% cyclopropane, as is currently used in trace amounts to determine ventilation-perfusion () ratios. Normal human blood samples were first tonometered with control gas mixtures containing (v/v): (1) 20.9% O₂, 0.04% CO₂; (2) 16.0% O₂, 4.0% CO₂; and (3) 9.9% O₂, 7.8% CO₂. A large quantity (20.9%) of the mixture was blended experimentally into the control mixture and the tonometry repeated. The entire experiment was then repeated substituting pure N₂ for the mixture as a dilution control. O₂ values were determined by three methods: (1) a polarographic electrode, ABL-300 (ABL); (2) a spectrophotometric method, Co-Oximeter (COOX); and (3) a galvanic cell, Lex-O₂-Con (LEX). The gas mixture lowered significantly all measured LEX values by 2.5–3.6 saturation percent (sat%), but showed no effect, dilution or otherwise, on the O₂ values determined by the COOX and ABL methods. The N₂ dilution lowered the LEX values by an average of only 0.9 sat%; the ABL and the COOX were ≈0.6 sat% lower. We therefore suggest that, if any of these O₂ measurement methods are used in the presence of the mixture, baseline O₂ values should be determined both before and after injection of the mixture into the bloodstream, prior to performing other experimental manipulations. The difference between the two values, if any, can then be used to interpret subsequent results.