Effects of Metoprolol on Systemic Haemodynamics, Myocardial Performance and the Coronary Circulation During Halothane Anaesthesia

Abstract

The effects of metoprolol 1 mg kg-1 i.v. on the systemic and coronary circulations and on myocardial performance were studied in nine open-chested dogs ventilated with halothane 0.8% in oxygen at normocarbia. In terms of the chronotropic effect, this dose of metoprolol produced a substantial shift to the right of the dose-response curve to isoprenaline; substantial reductions of arterial pressure (10%), cardiac output (21%), aortic blood acceleration (13%), left ventricular dP/dt max (13%) and left ventricular power (25%) were observed. Both preload, represented by left ventricular end diastolic pressure, and afterload, represented by systemic vascular resistance, increased. Left circumflex coronary blood flow and myocardial oxygen consumption decreased by approximately the same amount as peak ventricular power.

INTERACTIONS OF ADRENERGIC BETA-RECEPTOR BLOCKADE (OXPRENOLOL) AND P co 2 IN THE ANAESTHETIZED DOG: INFLUENCE OF INTRINSIC BETA-SYMPATHOMIMETIC ACTIVITY

“…Halothane in oxygen was used to make such comparisons possible. Our own study of the effect of metoprolol (Burt and Foex, 1979) fulfills these requirements and may be used for comparison, since both metoprolol 1 mgkg" 1 and oxprenolol 0.3mgkg~' were used in doses producing an eight-fold shift to the right of the dose-response curve of heart rate to isoprenaline, 90 min after injection of the beta-blockers. At normocarbia, the effects of the cardioselective antagonist metoprolol were significant reductions of heart rate (-20%), arterial pressure (-10%), cardiac output (-21 %) and all indices of myocardial performance (-32% for aortic blood acceleration, -31 % for LV dPjdt max, -14% for LV dP/dr max/IP and -27% for LV peak power).…”

“…Electronically derived signals included LV dP/dr, aortic blood acceleration and stroke volume. Details of the methods and calibrations have been given elsewhere (Bun and Foex, 1979).…”

“…Systemic vascular resistance, left ventricular external work, peak left ventricular power and the rate-pressure product were computed as described previously (Burt and Foex, 1979). Oxygen saturation was calculated using the dissociation curve of Rossing and Cain (1966).…”

Oxprenolol and the Circulation During Anaesthesia in the Dog: Influence of Intrinsic Sympathomimetic Activity

“…The difference between the effects of practolol (Prys- Roberts et al, 1976) and metoprolol (Burt and Foex, 1979) had suggested that intrinsic sympathomimetic activity may be important to minimize the interaction between cardioselective /?-adrenoceptor blockade and anaesthesia. The lack of adverse interaction between oxprenolol and anaesthesia with nitrous oxide supplemented by halothane over a very wide range of doses suggests that partial agonists may be safer to use during anaesthesia than pure ^-adrenoceptor antagonists.…”

Beta-Adrenergic Blockade and Anaesthesia with Reference to Interactions with Anaesthetic Drugs and Techniques

“…No change in myocardial efficiency after propranolol could be demonstrated by McKenna et al 94 or Whitsitt and Lucchesi. 89 Using an open chest canine model, Burt and Foex 95 found that the cardioselective drug metoprolol (which lacks ISA) in a dose of 1.0 mg/kg during halothane anaesthesia decreased cardiac output by 21!1Jo and myocardial oxygen requirement was reduced proportionately. They concluded that while such a reduction in cardiac output during halothane anaesthesia may clinically be unacceptable, the increase in myocardial oxygen consumption caused by practolol (+ ISA) under similar conditions 66 could be dangerous if coronary blood flow was compromised by coronary vascular disease.…”