Oxygen extraction ratio: a valid indicator of transfusion need in limited coronary vascular reserve?
We have described whole body oxygen (O2) extraction ratio (ER) as a reliable indicator of transfusion need in acute normovolemic anemia. In normal hearts, myocardial lactate production (-LACT), indicating anaerobic metabolism, does not occur until the ER greater than 50% and Hct less than 10%. It is not known if the ER is valid in the setting of limited coronary vascular reserve. This study assesses the effect of a critical left anterior descending (LAD) coronary stenosis on the compensation to acute blood loss anemia. Adult dogs were anesthetized, paralyzed, and mechanically ventilated. A critical LAD stenosis was created in seven animals (STEN). There were seven controls (CON). Animals underwent isovolemic exchange transfusion with 6% HES until cardiac failure (CF). Catheters were placed in the aorta, pulmonary artery, and anterior interventricular coronary vein. Cardiac failure occurred at Hct = 8.6% +/- 0.4% in the CON and 17.0% +/- 0.5% in the STEN animals. Cardiac output increased in the CON, but not in the STEN animals. Blood flow in the LAD increased in the CON but not the STEN animals. -LACT began in the CON and STEN animals at Hct less than 20% and coincided with an ER greater than 50% in both groups. We conclude that CF occurs at a higher hematocrit with a critical LAD stenosis. The whole body ER greater than 50% remains a valid indicator of myocardial metabolism in anemia in the presence of limited coronary vascular reserve. The ER may be a useful guide to transfusion therapy.
Levy
P S
PS
Department of Surgery, Humana Hospital-Michael Reese, Chicago, IL 60616.
Chavez
R P
RP
Crystal
G J
GJ
Kim
S J
SJ
Eckel
P K
PK
Sehgal
L R
LR
Sehgal
H L
HL
Salem
M R
MR
Gould
S A
SA
D000740:Anemia / Q000097:blood* / Q000150:complications / Q000628:therapy; D000818:Animals; D002303:Cardiac Output, Low / Q000209:etiology; D003326:Coronary Circulation; D003327:Coronary Disease / Q000150:complications / Q000378:metabolism* / Q000503:physiopathology; D004195:Disease Models, Animal; D004285:Dogs; D005069:Evaluation Studies as Topic; D005078:Exchange Transfusion, Whole Blood / Q000592:standards*; D006400:Hematocrit; D006470:Hemorrhage / Q000150:complications*; D007773:Lactates / Q000097:blood; D010101:Oxygen Consumption; D015203:Reproducibility of Results
D007773:Lactates