HEMODYNAMIC-RESPONSES OF HORSES TO ANESTHESIA AND SURGERY, BEFORE ANDAFTER ADMINISTRATION OF A LOW-DOSE OF ENDOTOXIN

Seven horses, which were part of an investigation of the effect of end otoxin administration on vascular reactivity, were anesthetized on two separate occasions for surgical excision of 4-cm sections of palmar d igital artery and vein. On the first occasion, the horses were given a n infusion of 1 L 0.9% NaCl solution intravenously (IV) just before in duction of anesthesia (control); on the second occasion, the horses re ceived an infusion of 1 L 0.9% NaCl containing Escherichia coli endoto xin, 0.1 mu g/kg(endotoxin). On both occasions, anesthesia was induced with xylazine, guaifenesin, and ketamine, and maintained with halotha ne in oxygen. Hemodynamic measurements were made with the horses under anesthesia immediately before beginning surgery (period I), during sk in incision (period 2), during dissection and excision of the vessels (period 3), during skin suturing (period 4), and after completion of s urgery during bandaging (period 5). Hemoglobin concentration and mixed venous oxygen content were greater at all periods in horses that rece ived endotoxin. Otherwise, there were no significant differences in he modynamic parameters between control horses and horses administered en dotoxin before beginning surgery (period I). During surgery and bandag ing, horses administered endotoxin had significantly higher heart rate (periods 3, 4, and 5), cardiac index (periods 3, 3, and 5), and oxyge n delivery (periods 2, 3, 4, and 5) than did control horses, and mean arterial blood pressure (period 2) and systemic vascular resistance (p eriods 2, 3, 4, and 5) were less than in control horses. Compared with period 1, surgical stimulation in control horses was associated with increased mean arterial blood pressure and systemic vascular resistanc e (periods 2, 3, 4, and 5), but cardiac index and oxygen delivery were decreased (periods 3, 4, and 5). In contrast, horses administered end otoxin responded to surgical stimulation with increased mean arterial blood pressure (periods 2, 3, 3, and 5) and vascular resistance (perio ds 4 and 5), as well as a heart rate-induced increase in cardiac index (periods 2, 3, 3, and 5) compared with period 1; oxygen delivery also increased (periods 2, 3, 4, and 5) during surgery in the endotoxin gr oup. This study documents some of the differences in the response to a nesthesia and surgery between normal horses and those that have receiv ed endotoxin. (C) Copyright 1995 by The American College of Veterinary Surgeons