Lactate Levels as Predictors of the Relationship between Oxygen Delivery and Consumption in ARDS: Materials and Methods (2)


16 Jan 2013

Arterial and mixed venous oxygen tensions were measured using standard automated blood gas instrumentation. Hemoglobin concentrations and oxyhemoglobin saturations were measured spectro-photometrically using an automated spectrophotometric oximeter (CO-oximeter). Blood lactate concentrations were determined on iced arterial blood specimens using spectrophotometric or ampe-rometric enzyme assays.
Measurement errors in cardiac output, Hb concentration, and Hb-oxygen saturation may produce an artifactual correlation between Do2 and Vo2; however, the excellent correlation observed by other investigators between Vo2 assessed by direct measurement techniques and Fick-determined Vo2 suggests that the degree of this artifactual correlation is probably negligible.
Patients were divided into two subsets: (1) those with blood lactate concentrations of 2.4 mmol/L or less; and (2) those with lactate levels greater than 2.4 mmol/L. This threshold value, which is approximately twice the upper normal limit, was selected because it represents the cutoff level that our clinical laboratories use to define clinically relevant blood lactate levels, and because previous investigations have shown that blood lactate concentrations above this threshold are associated with a steep decrease in survival. Clinical studies from Detroit Receiving Hospital have corroborated this association. birth control pills
All values are expressed as the mean ± 1 SEM. Statistical analysis was performed using Student s f-test for paired data for comparisons between initial and final Do2 and Vo2. Students f-test for independent samples was used to compare continuous variables for the normal and increased lactate subsets. Discrete variables were compared using the x2 statistic with Yates’ correction for continuity. Differences were considered to be significant at a level of p<0.05. Power analysis was performed retrospectively according to the methods of Lachin2″ for paired observations. A statistical power (1P) of 0.8 or greater was employed for examining nonsignificant changes.

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