Studies of Anaesthesia in Relation to Hypertension V: Adrenergic Beta-Receptor Blockade

Abstract

The effects of intravenous practolol 0.4 mg/kg were studied in 12 hypertensive patients during halothane/nitrous oxide anaesthesia. Practolol decreased heart rate (HR) and cardiac output (Q) from the elevated levels following atropine administration during anaesthesia, but values of arterial pressure (AP), HR and Q after the combination of atropine and practolol were not significantly different from those during anaesthesia prior to blockade. The effects of a similar anaesthetic sequence were studied in a further 11 treated hypertensive patients given practolol by mouth 1.5 mg/kg/6 hours for at least 48 hours preoperatively in addition to current anti-hypertensive therapy. By comparison with treated hypertensive patients previously studied, those pretreated with practolol had similar AP awake, but higher AP throughout anaesthesia with either spontaneous or artificial ventilation. Cardiac output was higher and systemic vascular resistance was lower both before and during anaesthesia. Both the present groups of patients showed significantly attenuated responses of tachycardia and hypertension following laryngoscopy and intubation compared with previous studies. The incidence of dysrhythmia and e.c.g. evidence of myocardial ischaemia was significantly lower (4%) in beta-blocked patients compared with those who had not received practolol (38%).

Perioperative myocardial ischemia and isolated systolic hypertension in non-cardiac surgery

“…7 Since ISH was recognized as a separate hypertensive entity only in recent years, analysis on ISH as a separate group would not have been conducted in previous perioperative studies. Some ISH patients with SBP [ 160 mmHg (DBP \ 90 mmHg) would have been deemed ''normal'', while others were deemed hypertensive, [8][9][10][11][12][13] thereby diluting the impact of ISH as a risk factor. Patients with ISH and SBP 140 to 160 mmHg (DBP \ 90 mmHg) 14 would often have been included in the normotensive group, further confounding the results.…”

Unexplained preoperative tachycardia: is it an important issue?

“…11 Hypertension and tachycardia are prevented by ß-blockers. 12 The combination of hypertension (caused by alpha-adrenoceptor mediated vasoconstriction) and tachycardia creates the worst possible environment for myocardial well-being: demand is increased at a time the shorter duration of diastole impairs supply. Clearly during surgery and postoperatively, other factors may cause sympathetic overactivity: traction on viscera, pain during recovery, shivering if temperature control has been ineffective, and bladder distension to cite only a few.…”

“…10 La laryngoscopie, la bronchoscopie, l'intubation et l'extubation sont connus pour accroître l'activité sympathique et s'accompagnent souvent d'hypertension et de tachycardie, 11 que l'on peut prévenir par les ß-bloquants. 12 La combinaison d'hypertension (causée par la vasoconstriction à médiation alpha-adrénocep-tive) et de tachycardie crée le pire environnement possible pour le bien-être du myocarde : la demande est accrue au moment où la durée plus courte de la diastole compromet l'apport. Pendant l'intervention chirurgicale, d'autres facteurs peuvent causer une hyperactivité sympathique : la traction sur les viscères, la douleur pendant le réveil, les frissons, si le contrôle de la température a été inefficace, et la distension vésicale pour n'en citer que quelques-uns.…”

Intérêt des bêta-bloquants en médecine périopératoire. Première partie: notions fondamentales

“…6 6 Il n'y aurait pas d'interaction néfaste entre, d'une part BB et d'autre part halothane, isoflurane ou morphiniques en présence de protoxyde d'azote. 67,68,69 L'étude de la fonction régionale myocardique chez le chien a montré que l'oxprénolol prévenait la dysfonction ventriculaire gauche provoquée par l'halothane en présence d'une constriction coronaire. 70 Le rôle joué par l'ASI de l'oxprénolol dans cet effet n'est pas connu.…”