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Measurement of oxygen consumption after uncomplicated acute myocardial infarction
M Y Rady1, J D Edwards, E P Rivers
1Department of Emergency Medicine, Henry Ford Hospital, Detroit, Mich.
Background:
Oxygen consumption (VO2) has been shown to be decreased after acute myocardial infarction (AMI) complicated by cardiogenic shock.
Study Objective:
To evaluate early measurement of VO2 by indirect calorimetry after an uncomplicated AMI (UAMI).
Study Design:
Prospective nonrandomized case study.
Setting:
Emergency department of a large urban hospital.
Participants And Interventions:
Twenty-six consecutive patients presenting with confirmed UAMI. VO2 was measured by indirect calorimetry (Deletrac, Datex Ins,) which is noninvasive. All patients received buccal or intravenous nitroglycerin and thrombolytic therapy, and none received opiates before VO2 measurement.
Results:
Two groups of patients were identified by subsequent development of cardiogenic shock. Group 1 did not develop cardiogenic shock, and group 2 developed shock within 24 h of admission. Group 1 (n = 22) had a significantly higher VO2 compared to group 2 (n = 4), mean 154(SD 25) vs mean 100(SD 13) ml/min.m2, p < 0.002. Group 1 had a significantly higher increase in basal metabolic rate than group 2, mean 30 percent (SD 11) vs mean 10(SD 15) percent, p < 0.007. There was no significant difference in age, heart rate (HR), shock index (SI), or rate-pressure product (RPP) between groups 1 and 2. All patients in group 2 developed cardiogenic shock despite thrombolytic therapy, and two died within 24 h of admission.
Conclusion:
VO2 is increased in UAMI and represents increased metabolic demands of peripheral tissues and not cardiac oxygen uptake. A reduction in VO2 (< 100 ml/min.m2) after AMI may be an early predictor of subsequent development of cardiogenic shock. Measurement of VO2 in UAMI by indirect calorimetry in the emergency department may be of value to identify patients at high risk and could influence their management.