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Cardiovascular Dynamics After Large Doses of Fentanyl and Fentanyl Plus N₂O in the Dog

WEN-SHIN LIU, MD^*, ARUN V. BIDWAI, MD, THEODORE H. STANLEY, MD, and JESUS ISERN-AMARAL, M.D.

*Fellow in Anesthesiology and Artificial Organs. Department of Anesthesiology and Division of Artificial Organs, University of Utah College of Medicine, Salt Lake City, Utah 84132. Staff Anesthesiologist, Holy Cross Hospital; Clinical Instructor in Anesthesiology, University of Utah. Department of Anesthesiology and Division of Artificial Organs, University of Utah College of Medicine, Salt Lake City, Utah 84132. Associate Professor of Anesthesiology and Assistant Research Professor of Surgery. Department of Anesthesiology and Division of Artificial Organs, University of Utah College of Medicine, Salt Lake City, Utah 84132. Fellow in Anesthesiology and Artificial Organs. Department of Anesthesiology and Division of Artificial Organs, University of Utah College of Medicine, Salt Lake City, Utah 84132.

Abstract

The effects of large doses of fentanyl (0.05 to 2 mg/kg) and fentanyl plus N₂O on cardiovascular dynamics were determined in 10 unpremedicated dogs breathing 100% O₂. Using computer analysis of the central aortic pulse-pressure curve, stroke volume (SV), cardiac output, heart rate (HR), peripheral vascular resistance (PVR), and systolic, diastolic, and mean arterial blood pressures (BP) were determined while fentanyl was being given at a rate of 0.3 to 0.44 mg/min. Fentanyl caused a dose-related decrease in HR, which was significant at 0.05 mg/kg. Cardiac output, PVR, and systolic, diastolic, and mean arterial BP were also decreased and SV increased. The latter changes became significant at 0.1 mg/kg for diastolic BP; 0.15 mg/kg for cardiac output and mean BP; 0.25 mg/kg for SV and systolic BP; and at 1.25 mg/kg for peripheral vascular resistance. Addition of N₂O after fentanyl did not significantly change any parameter, although SV, cardiac output, and HR were usually increased and PVR decreased.

These data demonstrate that, while large doses of fentanyl or fentanyl plus N₂O do alter cardiovascular dynamics in dogs, the changes appear to be less profound than these produced by equianalgesic doses of morphine. Our findings suggest that large doses of fentanyl-O₂ may be an attractive alternative to morphine-O₂ anesthesia in critically ill patients.