Cardiovascular and metabolic response to acute normovolemic anemia - Effects of anesthesia

Background: The maintenance of adequate tissue oxygenation during acute ane mia depends on an increase in both cardiac output and tissue oxygen extract ion. This study tested the hypothesis that anesthesia blunts the cardiac ou tput response associated with acute normovolemic hemodilution. Methods: Forty patients undergoing major abdominal surgery were prospective ly randomized to undergo acute normovolemic hemodilution (ANH) either awake (awake group, n = 20) or with fentanyl-nitrous oxide-isoflurane anesthesia (anesthetized group, n = 20). Radial and pulmonary artery catheters were p laced in all patients. After hemodynamic measurements were taken, patients In the two groups underwent hemodilution to decrease their hemoglobin conce ntration from 13 to 8 g/dl. A total of 1,875 +/- 222 ml (mean +/- SD) of bl ood was collected and simultaneously replaced by the same volume of medium molecular weight hydroxyethylstarch in both groups. Results: In the awake group, ANH resulted in a significant increase in card iac index (from 3.1 +/- 0.5 to 4.8 +/- 1.01 . min(-1) . m(-2)) related to b oth an increase in heart rate and stroke index. Oxygen delivery remained un changed, but oxygen consumption increased significantly, resulting in an in crease in oxygen extraction ratio. In the anesthetized group, ANH. resulted in a significantly smaller increase in cardiac index (from 2.3 +/- 0.5 to 3.1 +/- 0.71 . min(-1) . m(-2)) related solely to an increase in stroke ind ex. Oxygen delivery decreased but oxygen consumption was maintained as oxyg en extraction increased. Conclusions: Anesthesia significantly reduces the cardiac output response a ssociated with ANH. This could be related to the effects of the anesthetic drugs on the autonomic and the cardiovascular systems.