Direct Fick method

The Fick principle states that oxygen consumption ( Vo2) equals the product of cardiac output and the arteriovenous O 2 content difference. Arterial O2 content is measured from a peripheral arterial blood sample, venous O2 content is measured from pulmonary arterial blood, and Vo2 is derived from minute ventilation and inspired and expired gas analysis (Espersen,ยง,LaL 19.9.5). Reliability decreases when the patient is receiving high inspired O 2 concentrations.

CO2 production (VCO2) can be used instead of Vo2 as cardiac output also equals VCO2 divided by (CvCO2 - CaCO2), where CvCO2 and CaCO2 are mixed venous and arterial CO2 contents respectively. The venoarterial difference can be calculated from measured partial presures, and VCO2 can be accurately measured using computerized dual-beam infrared absorption analysers.

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Sleep Apnea

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