Study objectives: During isovolemic hemodilution,
healthy individuals maintain oxygen consumption
(V̇o2) by identical increases in cardiac
index (CI) and oxygen extraction ratio (O2ER). In
critically ill patients, the relationship between CI and
O2ER may be different. Patients with an altered cardiac
function may have a decreased CI/O2ER ratio, whereas
patients 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.
Prospective, observational study.
Thirty-one-bed medicosurgical ICU of a university hospital.
Patients: Sixty patients equipped with arterial and
Swan-Ganz catheters presenting with anemia, which was defined as a
hemoglobin level ≤ 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, initial 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 levels, and lower CI/O2ER ratios
than group 2 patients. However, there was no significant 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 statistically significant difference in PAOP
in group 2 patients with or without hypovolemia ([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
nonsurvivors. In group 2, however, such a relationship did not reach
relationship between CI and O2ER level can help interpret
the CI in anemic patients. In anemic patients with no cardiac history,
a low CI/O2ER ratio (< 10) suggests hypovolemia even when
CI is not depressed.