Oxygen consumption in adult patients during cardiac catheterization

Abstract

The determination of cardiac output by the Fick principle requires the quantitation of the arterio-venous oxygen (O₂) content difference across the pulmonary bed and the O₂ consumption. Since a correct measurement of O₂ consumption may be difficult, an assumed value is sometimes substituted into this equation. Despite this practice, there is no appropriate reference standard for O₂ consumption applicable to the adult catheterization laboratory. Therefore, we determined O₂ consumption in 108 patients (69 men and 39 women, mean age, 49 years) at the time of catheterization by multiplying the arteriovenous O₂ content difference by the indicator dilution cardiac output, thereby eliminating errors related to the collection and analysis of a timed collection of expired air. O₂ consumption index (O₂ consumption/m² of body surface area) averaged 126 ± 26 ml/min/m² (mean±SD), but there was wide variability (65–250 ml/min/m²). O₂ consumption was not affected by patient age or sex but was lower in those who were mildly sedated before catheterization (sedated, 121±22 ml/min/m²; nonsedated, 132±28 ml/min/m²; p = 0.023). Thus, O₂ consumption varies greatly among adults at the time of cardiac catheterization, so that any attempt at estimating this variable is fraught with major potential error.