Thoracic epidural anesthesia improves functional recovery from myocardial stunning in conscious dogs

High thoracic epidural blockade increases myocardial oxygen availability in coronary surgery patients

BACKGROUND

High thoracic epidural techniques are increasingly being used in patients scheduled for cardiothoracic surgery, including coronary artery bypass grafting. In the present study, we evaluated the acute effects of the epidural blockade on myocardial oxygen availability by means of tissue oxygen pressure monitoring in patients submitted for surgical revascularization.

METHODS

Fifty adult patients were included in a prospective, randomized, double-blind study. After placement of an epidural catheter in thoracic space T1-T2, and under general anesthesia, 5-10 ml of either normal saline or 0.3% ropivacaine was injected through the epidural catheter. Hemodynamic parameters and the intramyocardial oxygen partial pressure were recorded before and 20 min after the epidural injection.

RESULTS

There were no demographic or hemodynamic differences between the groups before intervention. A significant increase in intramyocardial partial oxygen pressure was observed in the ropivacaine group (14.6 mmHg vs. 25.1 mmHg, P < 0.0005).

CONCLUSION

High thoracic epidural blockade with 5-10 ml of 0.3% ropivacaine increases myocardial oxygen availability in coronary diseased patients prior to surgical revascularization without deleterious hemodynamic disturbances.

Xenon Improves Recovery from Myocardial Stunning in Chronically Instrumented Dogs

In this study we tested the hypothesis that inhalational administration of xenon improves recovery from myocardial stunning. Ten dogs were chronically instrumented for measurement of heart rate; left atrial, aortic, and left ventricular pressure; coronary blood-flow velocity; and myocardial wall-thickening fraction. Regional myocardial blood flow was determined with fluorescent microspheres. Catecholamine plasma levels were measured by high-performance liquid chromatography. An occluder around the left anterior descending artery (LAD) allowed the induction of a reversible LAD ischemia. Animals underwent 2 experimental conditions in a randomized crossover fashion on separate days: (a) 10 min of LAD occlusion under fentanyl (25 microg. kg(-1). h(-1)) and midazolam (0.6 mg. kg(-1). h(-1)) (control) and (b) a second ischemic episode under the same basal anesthesia with concomitant inhalational administration of 75 +/- 1 vol% xenon (intervention). Anesthesia was induced 35 min before LAD occlusion and was discontinued after 20 min of reperfusion. Dogs receiving xenon showed a significantly better recovery of wall-thickening fraction up to 12 h after ischemia. The increase in plasma epinephrine during emergence from anesthesia and in the early reperfusion period was significantly attenuated in the xenon group. There were no differences between groups concerning global hemodynamics, blood-flow velocity, or regional myocardial blood flow. In conclusion, inhalational administration of 75 vol% xenon improves recovery from myocardial stunning in chronically instrumented dogs under fentanyl/midazolam anesthesia.

[High thoracic epidural anesthesia in coronary surgery]

INTRODUCTION

High thoracic epidural anesthesia and analgesia are being increasingly used for coronary artery bypass graft surgery. The reasons for this include excellent perioperative pain control with advantage of early tracheal extubation, improved postoperative pulmonary function, and cardiac protection due to sympthatetic blockade.

EFFECTS OF HIGH THORACIC EPIDURAL ANESTHESIA

Cardiac protection is the consequence of decreased heart rate, myocardial contractility and arterial blood pressure, without changes in coronary perfusion pressure. Therefore, high thoracic epidural analgesia beneficially alters major determinants of myocardial oxygen consumption, without jeopardizing coronary perfusion pressure. In addition, decrease of functional residual capacity, may reduce postoperative pulmonary morbidity.

RESULTS OF CLINICAL STUDIES

Patients with high thoracic epidural anesthesia revealed a more favourable perioperative hemodynamic profile, lower incidence of ischemia and better response to perioperative stress.

HIGH THORACIC EPIDURAL ANESTHESIA TECHNIQUE

The epidural catheter should be placed at the Th2/Th3 interspace at least one hour before administration of heparin. After local anesthetic bolus dose, a continuous epidural infusion is recommended.

CONCLUSION

There is strong evidence for beneficial effects of high thoracic epidural anesthesia in patients undergoing surgical myocardial revascularization. However, it is still underutilized in current clinical practice.

Regional anaesthesia in patients at coronary risk for noncardiac and cardiac surgery

This review presents a brief overview about the role of regional anaesthesia in patients at risk for myocardial ischemia and/or infarction after cardiac and noncardiac surgical procedures. It includes pathophysiological insights in the problems of plaque rupture and the possible interactions by the use of regional anaesthesia. Special emphasis is put on the subject of thoracic epidural anaesthesia with newer studies showing improvement in relief of angina and improvement of global systolic and diastolic function in patients with coronary artery disease.

Central neuroaxis blockade and coronary circulation

The coronary circulation is subject to modulation by the autonomic nervous system. Thus, sympathetic stimulation causes coronary vasodilation in healthy humans, whereas stenotic coronary arteries react by vasoconstriction in response to sympathetic stimulation. It is for this reason that experimental studies and clinical evidence revealed beneficial effects of a blockade of cardiac sympathetic drive by thoracic epidural anaesthesia on coronary perfusion and myocardial function in normal and in ischaemic myocardium. In contrast, segmental lumbar epidural anaesthesia leads to a compensatory increase in cardiac sympathetic outflow which may jeopardize myocardial areas dependent on perfusion by stenotic coronary arteries.