title: Electrocardiographic ST-segment changes during acute, severe isovolemic hemodilution in humans.
abstract: BACKGROUND
  Controversy exists regarding the lowest blood hemoglobin concentration that can be safely tolerated. The authors studied healthy resting humans to test the hypothesis that acute isovolemic reduction of blood hemoglobin concentration to 5 g/dl would produce an imbalance in myocardial oxygen supply and demand, resulting in myocardial ischemia.
  
  
  METHODS
  Fifty-five conscious healthy human volunteers were studied. Isovolemic removal of aliquots of blood reduced blood hemoglobin concentration from 12.8 +/- 1.2 to 5.2 +/- 0.5 g/dl (mean +/- SD). Removed blood was replaced simultaneously with intravenous fluids to maintain constant isovolemia. Hemodynamics and arterial oxygen content (Cao2) were measured before and after removal of each aliquot of blood. Electrocardiographic (ECG) changes were monitored continuously using a Holter ECG recorder for detection of myocardial ischemia.
  
  
  RESULTS
  During hemodilution, transient, reversible ST-segment depression developed in three subjects as seen on the electrocardiogram during hemodilution. These changes occurred at hemoglobin concentrations of 5-7 g/dl while the subjects were asymptomatic. Two of three subjects with ECG changes had significantly higher heart rates than those without ECG changes at the same hemoglobin concentrations. When evaluating the entire study period, the subjects who had ECG ST-segment changes had significantly higher maximum heart rates than those without ECG changes, despite having similar baseline values.
  
  
  CONCLUSIONS
  With acute reduction of hemoglobin concentration to 5 g/dl, ECG ST-segment changes developed in 3 of 55 healthy conscious adults and were suggestive of, but not conclusive for, myocardial ischemia. The higher heart rates that developed during hemodilution may have contributed to the development of an imbalance between myocardial supply and demand resulting in ECG evidence of myocardial ischemia. However, these ECG changes appear to be benign because they were reversible and not accompanied by symptoms.
authors.affiliation: Department of Anesthesia, University of California, San Francisco, USA.jmleung@itsa.ucsf.edu
authors.forename: J M
authors.initials: JM
authors.lastname: Leung
authors.forename: R B
authors.initials: RB
authors.lastname: Weiskopf
authors.forename: J
authors.initials: J
authors.lastname: Feiner
authors.forename: H W
authors.initials: HW
authors.lastname: Hopf
authors.forename: S
authors.initials: S
authors.lastname: Kelley
authors.forename: M
authors.initials: M
authors.lastname: Viele
authors.forename: J
authors.initials: J
authors.lastname: Lieberman
authors.forename: J
authors.initials: J
authors.lastname: Watson
authors.forename: M
authors.initials: M
authors.lastname: Noorani
authors.forename: D
authors.initials: D
authors.lastname: Pastor
authors.forename: H
authors.initials: H
authors.lastname: Yeap
authors.forename: R
authors.initials: R
authors.lastname: Ho
authors.forename: P
authors.initials: P
authors.lastname: Toy
mesh_terms: D000328:Adult; D000740:Anemia / Q000097:blood / Q000209:etiology / Q000503:physiopathology; D001794:Blood Pressure / Q000502:physiology; D001810:Blood Volume / Q000502:physiology; D015716:Electrocardiography, Ambulatory; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006438:Hemodilution / Q000009:adverse effects* / Q000379:methods; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D008297:Male; D009206:Myocardium / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism
chemical_list: D006454:Hemoglobins; D010100:Oxygen