Tolerance to acute isovolemic hemodilution. Effect of anesthetic depth.
BACKGROUND
Acceptance of a lower transfusion trigger in the perioperative period requires study of the effects of anesthetic depth on the tolerance to acute isovolemic anemia. Anesthetic agents with negative effects on the cardiovascular system may exert proportionately greater depressant effects on cardiac output response than on tissue oxygen demand, reducing tolerance to acute isovolemic anemia.


METHODS
In the first study, animals were anesthetized with halothane (n = 14; 23.8 +/- 4.8 kg, mean +/- SD). In a second study, animals were anesthetized with ketamine (n = 14; 24.3 +/- 4.7 kg). In each study, dogs were randomly allocated to receive either low or high concentrations of anesthetic. Oxygen delivery and oxygen consumption were determined from independent measurements during a stepwise isovolemic hemodilution protocol. In each dog, critical oxygen delivery was determined from a plot of oxygen consumption versus oxygen delivery using a least-sum-of-squares technique. Critical hemoglobin (hemoglobin) was determined from a plot of hemoglobin versus oxygen consumption using the same method.


RESULTS
With both agents, the higher anesthetic concentration was associated with decreased oxygen consumption, resulting in a lower critical oxygen delivery. However, critical hemoglobin was significantly higher in the animals receiving the higher anesthetic dosage (1.5 vs. 1.0 minimum alveolar concentration of halothane: 4.1 +/- 1.3 vs. 2.3 +/- 0.5 g/dl, P < 0.05; high- vs. low-dose ketamine: 3.7 +/- 1.4 vs. 2.5 +/- 0.6 g/dl, P < 0.05). This was related to a marked blunting of the cardiac output response to hemodilution in the animals receiving the higher anesthetic dosage.


CONCLUSIONS
Increased anesthetic depth with halothane or ketamine resulted in a decreased tolerance to acute anemia, as reflected by a significant increase in critical hemoglobin concentration.
Van der Linden
Philippe
P
Department of Cardiac Anesthesia, CHU Charleroi, Belgium. philippe.vanderlinden@chu-charleroi.be
De Hert
Stefan
S
Mathieu
Nathalie
N
Degroote
Françoise
F
Schmartz
Denis
D
Zhang
Haibo
H
Vincent
Jean-Louis
JL
D000740:Anemia / Q000503:physiopathology; D000777:Anesthetics / Q000494:pharmacology; D000778:Anesthetics, Dissociative / Q000494:pharmacology; D018685:Anesthetics, Inhalation / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D001810:Blood Volume / Q000502:physiology*; D002302:Cardiac Output / Q000187:drug effects; D004285:Dogs; D004566:Electrodes; D006221:Halothane / Q000494:pharmacology; D006339:Heart Rate / Q000502:physiology; D006438:Hemodilution / Q000009:adverse effects*; D006454:Hemoglobins / Q000378:metabolism; D007649:Ketamine / Q000494:pharmacology; D019344:Lactic Acid / Q000097:blood; D003473:Neuromuscular Nondepolarizing Agents / Q000494:pharmacology; D010100:Oxygen / Q000097:blood; D010197:Pancuronium / Q000494:pharmacology; D013156:Splenectomy; D014655:Vascular Resistance / Q000502:physiology
D000777:Anesthetics; D000778:Anesthetics, Dissociative; D018685:Anesthetics, Inhalation; D006454:Hemoglobins; D003473:Neuromuscular Nondepolarizing Agents; D019344:Lactic Acid; D007649:Ketamine; D010197:Pancuronium; D010100:Oxygen; D006221:Halothane