Cardiac Output in the Conscious and Anaesthetised Horse

Abstract

SUMMARY Cardiac output in the horse was measured before and at predetermined times during 2‐hour periods of thiopentone‐halothane and thiopentone‐diethyl ether anaesthesia. Left ventricular stroke volume was decreased to a similar extent during anaesthesia with each volatile agent, but a greater reduction in cardiac output occurred during halothane anaesthesia. This finding reflected the differing effects of halothane and ether on heart rate, a slight bradycardia occurring with the former agent while ether produced a small degree of tachycardia. The latter effect was attributed to enhanced sympathoadrenal activity. Changes in cardiac output and stroke volume were considered in relation to other factors, including arterial blood pH and tensions of oxygen and carbon dioxide. Positive correlations between some of these variables and cardiac function were established. With both volatile agents the reductions in stroke volume and cardiac output were related to the duration of anaesthesia, being greatest during the early stages. Possible reasons for the tendency of stroke volume and cardiac output to return towards control levels are discussed. RÉSUMÉ On a mesuré le débit cardiaque chez des chevaux avant puis sous anesthésie durant deux heures, à des moments déterminés: on utilisait soit le thiopentone puis l'halothane soit le thiopentone puis le diéthyl ether. La puissance du ventricule gauche parut diminuer dans les mêmes proportions quelle que soit la méthode mais le débit cardiaque fut réduit dans de plus grandes proportions en utilisant l'halothane. Cette constatation illustre les effets different de l'halothane et de l'éther sur le rythme cardiaque, l'halothane produisant une légère bradycardie, l'éther provoquant une légère tachycardie, par excitation supposée du systeme sympathique. Avec les deux agents volatiles furent constatés une réduction de la puissance et du débit cardiaques en relation avec la durée de l'anesthésie, les réductions étant plus importantes à la phase initiate. Les mécanismes responsables d'une régulation ultèrieure sont discutés. ZUSAMMENFASSUNG Das cardiale Auswurfvolumen wurde bestimmt vor und zu bestimmten Zeiten während einer zweistündigen Narkose mit Thiopenton‐Halothan, beziehungsweise Thiopenton‐Diaethylaether. Das Schlagvolumen des linken Ventrikels verringerte sich während der Narkose, wobei die Halothannarkose das Volumen deutlicher herabsetzte. Dieser Befund stimmt mit den abweich‐enden Wirkungen von Halothan und Aether auf das Herz überein, indem Halothan eine leichte Bradycardie, Aether eine leichte Tachycardie hervorruft. Dieser Effekt wird einer stärkeren sympathoadrenalen Aktivität zugeschrieben. Die Veränderungen im Schlag‐ und Auswurfvolumen wurden in Beziehung gesetzt zu andern Faktoren, einschliesslich arterielles pH, O2‐ und CO2‐Spannungen. Es konnten zwischen einigen dieser Variablen und der Herzfunktion positive Korrelationen errechnet werden. Bei beiden Gasarten war die Senkung von Schlag‐ und Auswurfvolumen abhàngig von der Narkosedauer, am deutlichsten während der...

Use of lithium dilution and pulse contour analysis cardiac output determination in anaesthetized horses: a clinical evaluation

“…Cardiac output determination by t TDCO or by dye dilution during halothane, or isoflurane anaesthesia has obtained cardiac indices between 20 and 85 mL kg −1 minute −1 (Hillidge & Lees 1975; Steffey & Howland 1980; Steffey et al. 1993; Mizuno et al.…”

Adrenocortical and metabolic responses to dobutamine infusion during halothane anaesthesia in ponies

“…It is well recognised that anaesthesia with halothane and other volatile agents causes marked hypotension in horses ( Hillidge & Lees, 1975; Steffey & Howland, 1978; Steffey & Howland, 1980). The association between intra operative hypotension and post operative myopathy is now well established ( Lindsay et al ., 1980 ; Grandy et al ., 1987 ) and it has become common practice to use inotropes during anaesthesia in this species to prevent serious hypotension ( Muir, 1991).…”

Pharmacokinetics and toxic effects of lithium chloride after intravenous administration in conscious horses

“…Historically, cardiac output measurements in horses have been performed by use of dye dilution or thermodilution. [6][7][8] More recently, transesophageal Doppler echocardiography has been used in anesthetized horses. 9 Dye dilution is expensive and cumbersome, and the equipment required for transesophageal Doppler echocardiography is specialized and expensive.…”