EFFECTS OF EPHEDRINE ON CARDIOVASCULAR FUNCTION AND OXYGEN DELIVERY IN ISOFLURANE-ANESTHETIZED DOGS

The hemodynamic effects of 2 dosages of ephedrine were studied in 6 do gs anesthetized with isoflurane only (end-tidal concentration equivale nt to 1.5 times minimum alveolar concentration). Following instrumenta tion, baseline (time 0) measurements included heart rate (HR), respira tory rate, mean arterial blood pressure (MAP), cardiac output, and blo od gas tensions. Cardiac index (CI), stroke volume (sv), systemic vasc ular resistance (SVR), arterial oxygen content (Ca-O2), and oxygen del ivery and consumption (D-O2 and V-O2, respectively) were calculated. T hree dogs were given ephedrine rv at a dosage of 0.1 mg/kg of body wei ght, and 3 dogs were given ephedrine IV at a dosage of 0.25 mg/kg. Mea surements were recorded at 5, 10, 15, 30, and 60 minutes. Each dog the n received the alternate dosage of ephedrine, and measurements were ag ain recorded at the same intervals. Effects of ephedrine varied with d osage. Neither dosage was associated with significant changes in pH, P a-O2, Pa-CO2, V-O2, or respiratory rate. Ephedrine at a dosage of 0.1 mg/kg caused transient significant increases in MAP, CI, SV, Ca-O2, an d D-O2,significant decreases in HR and SVR, and a late, slight decreas e in Ca-O2. Ephedrine at a dosage of 0.25 mg/kg caused a greater and m ore prolonged increase in MAP, as well as increases in CI, SV, and SVR , and a decrease in HR. The higher dosage of ephedrine also caused a p ronounced increase in hemoglobin concentration and Ca-O2, resulting in a 20 to 35% increase in D-O2 throughout the 60-minute experiment.