Clinical applications

The measurement of blood lactate levels can serve as an indicator of the presence of impaired tissue oxygenation, once other possible causes have been ruled out. Many experimental and clinical studies have found raised lactate levels in circulatory failure which correlate well with the severity of the shock state. Raised levels have also been associated with the oxygen uptake/supply dependency phenomenon. Hyperlactatemia has been linked with increased mortality, and falling levels have been shown to indicate a better prognosis.

The measurement of blood lactate levels from a simple blood test using automated analyzers is straightforward and readily available, and repeated sequential levels are easily obtained. The enzymatic conversion of lactate to pyruvate is an oxygen-utilizing reaction. The extraction of oxygen from the sample can be detected by a sensitive oxygen fuel cell sensor and is directly proportional to the sample lactate concentration. A whole-blood sample can be collected in a heparin fluoride tube to prevent coagulation and glycolysis. Nitrite can be used in the sample tube to convert hemoglobin to the met-form, thus avoiding uptake of oxygen during the enzyme reaction. The enzymatic method is specific for the L-isomer and therefore will not detect D-lactate (e.g. in short-bowel syndrome). Levels are identical in the central venous blood, the pulmonary artery, and the arterial blood.

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Sleep Apnea

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