Critical Care Medicine
The normal CO range is 4 to 6 L/min, and the normal cardiac index is 2 to
4 L/min/m2. Determining whether a patients CO is adequate depends on the patients clinical condition and laboratory assessments, such as lactate, mixed venous oxygen saturation (MVO2), and the mixed venous-arterial Pco2 gradient. In patients with hyperdynamic states (eg, sepsis, liver failure), CO is often elevated above the normal range (7-10 L/min); therefore, the CO of 4.0 L/min obtained in the case patient is relatively low. The elevated and rising lactate level (normal, < 2.0 mg/dL) suggests that either the oxygen delivery to the tissues is inadequate to meet oxygen demand and/or that lactate clearance by the newly transplanted liver is decreased. It is commonly assumed that low MVO2 levels indicate inadequate oxygen delivery to the tissues; however, high or even normal MVO2 levels may be found in the presence of inadequate oxygen delivery. In this patient, the MVO2 level and Svo2 are in normal range, but the patient is anemic with a relatively low CO. Because of the patients cirrhosis and liver failure, the MVO2 level is raised to normal due to arteriovenous shunting, and thus MVO2 should not be used to evaluate CO. Mixed venous-arterial Pco2 gradient can be used to evaluate CO as well. In this case, the venous-arterial Pco2 gradient is significantly elevated at 12 mm Hg (normal, < 5-6 mm Hg), suggesting that CO is relatively low. The venous-arterial Pco2 may be elevated in patients with high CO (hyperdynamic) if they are also hypermetabolic (eg, high fever, sepsis, malignant hyperthermia). This patient was afebrile and not hypermetabolic.2,4
- CO is not adequate.
2. Leibowitz AB, Oropello JM. The multicenter pulmonary artery catheter questionnaire-questions, answers and explanations. Progr Anesthesiol 1994;8:275-89.
4. Oropello JM, Manasia A, Hannon E, et al. Continuous fiberoptic arterial and venous blood gas monitoring in hemorrhagic shock. Chest 1996;109:1049-55.
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