Assessment of cardiac index in anemic patients

Study objectives: During isovolemic hemodilution, healthy individuals maint ain oxygen consumption ((V) over dot o(2)) by identical increases in cardia c index (CI) and oxygen extraction ratio (O2ER). In critically ill patients , the relationship between CI and O2ER may be different. Patients with an a ltered cardiac function may have a decreased CI/O2ER ratio, whereas patient s with sepsis may have an increased CI/O2ER ratio. We hypothesized that the analysis of the CI-O2ER relationship could help us to assess the adequacy of cardiac function in critically ill patients with anemia, Design: Prospective, observational study, Setting: Thirty-one-bed medicosurgical ICU of a university hospital. Patients: Sixty patients equipped with arterial and Swan-Ganz catheters pre senting with anemia, which was defined as a hemoglobin level less than or e qual to 10 g/dL in the absence of active bleeding. Patients were classified into those with compromised cardiac function (group 1; n = 40), and those with normal cardiac function (group 2; n = 20). Measurements and results: In addition to the pertinent clinical data, initi al hemodynamic measurements, including pulmonary artery occlusion pressure (PAOP), CI, and O2ER, were collected in all patients at the onset of anemia . As anticipated, group 1 patients (n = 40) had lower CIs, higher O2ER leve ls, and lower CI/O2ER ratios than group 2 patients. However, there was no s ignificant difference in PAOP values between the groups. The CI/O2ER ratio was < 10 in 27 of 40 group 1 patients but only in 4 of 20 group 2 patients. Of these latter four patients, three were found to be hypovolemic, and one patient with sepsis had severe myocardial depression. There was no statist ically significant difference in PAOP in group 2 patients;vith or without h ypovolemia ([mean +/- SD] 12.3 +/- 2.1 mm Hg) vs 13.7 +/- 4.3 mm Hg; p = 0. 21). In group 1, survivors had a higher CI and CI/O2ER ratio than nonsurviv ors. In group 2, however, such a relationship did not reach statistical sig nificance. Conclusions: The relationship between CI and O2ER level can help interpret the CI in anemic patients. In anemic patients with no cardiac history, a lo w CI/O2ER ratio (< 10) suggests hypovolemia even when CI is not depressed.