Dupont critical care lecture: Role of ultrashort-acting β-blockers in the perioperative period

[Perioperative beta-blockers. Part two: therapeutic indications]

PURPOSE

To review the pharmacologic and pathophysiologic information necessary to prescribe beta-blockers (BB) in perioperative medicine.

DATA SOURCE

Manual retrieval and electronic research of the literature using MEDLINE (key-words: anesthesia and beta- blocker; surgery and beta-blocker).

DATA SYNTHESIS

In non cardiac surgery, the beneficial effects of BB have been demonstrated in hypertensive patients since 1979. In 1996, the beneficial effects of atenolol in patients with coronary artery disease (reduction of postoperative myocardial ischemia and overall reduction in two-year mortality) were demonstrated. In coronary surgery, the interest of preoperative BB treatment has been shown since 1983. Administration of BB has been shown to be beneficial in acute myocardial infarction or chronic cardiac failure (except in NYHA class IV patients).

CONCLUSION

BB have been shown to exert a beneficial effect on postoperative outcomes in patients with cardiovascular disease or risk factors, and their more widespread use in perioperative medicine is encouraged.

Role of isradipine and other antihypertensive agents in the treatment of peri- and postoperative hypertension

The traditional therapy of perioperative hypertension is now being challenged by the availability of new agents. Vasodilator therapy should be the first-line choice, although dihydropyridine calcium antagonists, particularly isradipine, appear to be suitable in this setting because of their pharmacological properties. Because of its ultrashort half-life, sodium nitroprusside has to be administered by continuous infusion, even for the treatment of an acute elevation of blood pressure. This is not the case with the new agents that have longer durations of action. A bolus administration is sufficient for the correction of most elevations of arterial pressure that are due to transient adrenergic activation. Continuous infusion is required only in patients who have sustained increases of systemic vascular resistance; these are usually patients who are already hypertensive.

An improved lidocaine infusion protocol for cardiac surgical patients

A new protocol for lidocaine administration was tested to determine whether it would provide higher free and total serum lidocaine concentrations during and after weaning from cardiopulmonary bypass (CPB), without leading to accumulation toxicity, than those resulting from a conventional protocol (1.5 mg/kg loading dose bolus + 2 mg/min infusion rate). Ten elective adult cardiac surgical patients were studied. Ten seconds prior to aortic cross-clamp release (0 min), each patient received a lidocaine bolus (1.5 mg/kg) and simultaneous lidocaine infusion (5 mg/min for 1 hour, followed by 2 mg/min for 23 hours). Weaning occurred 20 to 30 minutes after cross-clamp release. Lidocaine levels were determined from arterial blood samples at 0, 10, 20, 30, and 60 minutes, and at 2, 4, and 24 hours postcross-clamp release. Compared with the conventional protocol, the new protocol showed a significant increase in mean total lidocaine concentration (P less than or equal to 0.02) at 30 and 60 minutes, and a significant increase in mean free lidocaine concentration (P less than or equal to 0.005) at 20, 30, and 60 minutes. No patient had toxic levels at 24 hours. Results of this study suggest that in patients undergoing cardiac surgery, a "5 + 2" mg/min infusion protocol is safe and superior to a conventional protocol in achieving therapeutic serum levels of free and total lidocaine.

Intraoperative use of bolus doses of esmolol to treat tachycardia

A randomized, double-blind, parallel, placebo-controlled study was conducted to determine the safety and efficacy of intravenous (IV) bolus administration of esmolol in treating intraoperative tachycardia in patients undergoing noncardiac general surgery. Forty-eight ASA II-IV patients were randomized into three equal groups to receive either placebo, esmolol 50 mg, or esmolol 100 mg. Premedication (lorazepam) and anesthetic induction techniques (thiopental sodium and succinylcholine) were identical between groups. Approximately 20 minutes after intubation, during isoflurane/N2O/O2 maintenance anesthesia, patients with systolic pressure (SBP) greater than or equal to 110 mmHg were advanced into a 10-minute study drug period if one of two conditions were met: (1) heart rate (HR) was greater than or equal to 95 beats/minute, or (2) an increase in HR of greater than 20% above preinduction baseline occurred. After two consecutive recordings of HR and blood pressure (BP), the study drug (or placebo) was injected. HR was recorded every 30 seconds and BP was recorded every minute during the ensuing 10-minute period. Compared to placebo responses, HR was significantly reduced with both doses of esmolol within 1 minute of bolus injection and remained below placebo levels for 5 minutes after 50 mg of esmolol and for 9.5 minutes after 100 mg of esmolol. There were, however, only minor differences among groups with respect to SBP, diastolic blood pressure (DBP), and mean blood pressure (MBP) changes.

CONCLUSION

Bolus administration of esmolol can produce a rapid reduction of HR with relatively few adverse effects in an unhealthy surgical population.(ABSTRACT TRUNCATED AT 250 WORDS)

[Beta blockers and anesthesia]

Beta-adrenoceptor antagonists (BB) demonstrate a competitive antagonism with endogenous catecholamines. Beta-1 receptor blockade mediates the depressive action on contractility, heart rate and atrio-ventricular conduction. Beta-2 receptor blockade mediates vascular, bronchial and uterine smooth muscle constriction. BB with beta-1 selective and intrinsec sympathomimetic activity do not increase systemic vascular resistance. BB are mostly used to treat ischaemic heart disease, hypertension and arrhythmias. Bradycardia, hypotension and bronchospasm are the main hazards in BB treated patients undergoing anaesthesia. However giving BB with premedication to patients taking usely this treatment allows better perioperative haemodynamic stability and avoids rebound effect. Experimentally, oxprenolol reverses regional dysfunction in ischaemic myocardium under halothane anaesthesia. During and after anaesthesia, intravenous (i.v.) BB must be used with caution to treat hypertension associated with tachycardia. In controlled hypotension, i.v. BB potentialise other agents. In phaechromocytoma surgery, alpha-blocking drugs are essential but additional BB can control tachycardia successfully. In coronary artery bypass surgery, giving BB prior to induction decreases cardiac enzymes serum levels. Esmolol, a new ultra-short-acting BB, would control perioperative tachycardia and hypertension without risk of prolonged cardiac depression.