John Bussell

Myocardial metabolism and hemodynamic responses to halothane or morphine anesthesia for coronary artery surgery.

Eighteen patients having coronary artery bypass grafts were randomly anesthetized with morphine (1 mg/kg) or halothane and oxygen. Central and peripheral pressures were measured serially, plus cardiac output and total coronary sinus blood flow, both by thermodilution catheters, starting before induction of anesthesia and continuing until completion of sternotomy. No significant differences in hemodynamic responses were seen between the two anesthetic techniques during induction: blood pressure and peripheral vascular resistance decreased significantly, but not cardiac output or coronary flow. Myocardial oxygen consumption decreased significantly with induction as oxygen content of coronary sinus blood increased, indicating preservation of oxygen balance. Heart rate and blood pressure increased after sternotomy in the patients given morphine, with the myocardium producing lactate in two of six patients and with nitroprusside being required in four patients to decrease arterial pressure. Halothane-oxygen anesthesia effectively controlled autonomic responses to sternotomy, although one of 12 patients had myocardial lactate production at that time. Neither rate-pressure product or ST segment changes were useful predictors of the ratio between myocardial oxygen consumption and supply. Myocardial oxygen balance can be maintained in coronary patients before cardiopulmonary bypass if pulse rate and blood pressure are kept at less than awake levels.

Rate-pressure product correlates poorly with myocardial oxygen consumption during anaesthesia in coronary patients.

In 26 patients having coronary grafts, haemodynamics, coronary sinus blood flow and the arterio-coronary, sinus difference of oxygen content were determined, awake and at four intervals during morphine-oxygen or halothane-oxygen anaesthesia. Rate-pressure product (RPP), triple product (TP) and myocardial oxygen consumption (MVO2) were calculated. The correlation of the two indirect indices to MVO2 were tested by repeated measures and regression analyses. No significant correlations were seen at four of five study times, when outlying data points were appropriately excluded. A pitfall of using more than one data point from each patient in the linear regression analysis is pointed out. In addition to the lack of correlation of RPP to MVO2, RPP was an imprecise predictor of myocardial lactate production and of postoperative infarction.RésuméChez 26 malades opérés pour pontage aorto-coronaire, nous avons mesuré le profii hémodynamique, le flux sanguin du sinus eoronaire e: la différence artérioveineuse en oxygène du sang coronaire, Des mesures ont été faites avant l’anesthésie et à quatre reprises durant une anesthésie à la morphine-oxygène ou halothane-oxygène. Le produit fréquence/pression (RPP) le triple produit (TP) et la consommation d’oxygène par le myocarde (MVO2) ont été calculés. La corrélation des deux index indirects de MVO2 a été vérifié par des mesures répétées et par des analyses de courbe de régression. Aucune correlation significative n’a été démontrée à quatre des cinq stations de mesure, lorsque les données aberrantes ont été exclues des calculs. Dans la discussion, nous exposons le danger qu’il y a d’ introduire pour chaque patient plus d’une donnée dans l’analyse de régression.En plus d’être un panvre indicateur de consommation d’oxygène par le myocarde, le RPP était un informateur imprécis quam à la production de lactate par le myocarde et l’incidence de l’infarctus post-opératoire.

Effects of protamine sulfate on myocardial oxygen supply and demand in patients following cardiopulmonary bypass.

The effect of protamine sulfate on myocardial oxygen supply and demand was studied under clinical conditions in nine patients following cardiopulmonary bypass. Before surgery, the patients had severe coronary artery disease with good ventricular function. The patients required no vasoactive drugs, but only blood volume adjustments when weaned off bypass, and were hemodynamically stable at the time of study. The protamine dose of 196 mg (2.5 mg/kg) was infused over 4 ± 1 minutes. Although modest variation in hemodynamic function occurred in individual patients after administration of protamine, there were no significant hemodynamic alterations for the group. No significant alteration in global myocardial metabolism was observed. Protamine caused a small decrease in measured coronary blood flow, resulting in a corresponding reduction in calculated myocardial oxygen consumption as coronary sinus oxygen content remained unaltered. Myocardial lactate extraction showed no significant alteration. It is concluded that protamine sulfate, given at rapid infusion rates in hemodynamically stable patients, is not associated with an adverse alteration in hemodynamics or global myocardial metabolism.

Cardiovascular effects of morphine in patients with coronary arterial disease.

Large doses of morphine sulfate have been reported to cause myocardial lactate production and reduction in coronary blood flow in animals. Similar effects with clinical doses in man would significantly alter the management of cardiac patients. Eleven adult patients with significant coronary arterial disease and normal left ventricular ejection fraction were studied before and 30 minutes after infusion of morphine (0.25 mg/kg IV). Evaluation of myocardial metabolism showed an increase in coronary sinus oxygen content (p < 0.001) and a reduction in myocardial oxygen consumption. Myocardial lactate extraction was not altered. No change in coronary sinus blood flow was seen. It is concluded that infusion of morphine sulfate, 0.25 mg/kg IV, does not produce global myocardial ischemia in patients with coronary artery disease and normal ventricular function.

Dobutamine and cardiac oxygen balance in patients following myocardial revascularization.

Dobutamine is frequently used in the early postoperative period following myocardial revascularization to improve cardiac output. Seven postoperative adult patients with low output syndrome were studied before and during intravenous dobutamine (mean ± SD: 5.1 ± 2.5 μg/kg/min) infusion. The metabolic effects were evaluated and related to hemodynamic changes. Cardiac index increased 40% (p < 0.05) with an increase in heart rate (p < 0.05) and decreases in systemic vascular resistance and right atrial pressure (p < 0.05). No significant changes occurred in arterial or pulmonary capillary wedge pressures or in stroke volume index. Dobutamine produced a 29% increase in myocardial oxygen consumption which, in these revascularized patients, was accompanied by a 35% increase in coronary blood flow. No significant alteration was observed in coronary sinus oxygen content or in global myocardial lactate extraction. Thus, despite the increased metabolic cost of dobutamine, global myocardial ischemia was not observed.

Intravenous nitroglycerin and myocardial metabolism during anesthesia in patients undergoing myocardial revascularization.

Although intravenous nitroglycerin has been used to control the hypertensive response during sternotomy in patients undergoing myocardial revascularization, the effects of the drug on myocardial oxygen supply and demand have not been described in this clinical setting. Eight adult patients with good ventricular function (ejection fraction >50%), who were anesthetized for coronary artery bypass, were studied before and after administration of intravenous nitroglycerin (mean dose 12 μg/kg in 6 minutes). Evaluation of myocardial metabolism showed an increase in coronary sinus oxygen content (p < 0.05) and a reduction in myocardial oxygen consumption (p < 0.05), Although mean myocardial lactate extraction and coronary sinus blood flow were not significantly altered in the group as a whole, variations in individual patient responses were observed and are discussed. These direct observations of global myocardial metabolism observed in this study group are similar to the conclusions reached by other investigators using indirect indices of myocardial oxygen supply and demand.

Effects of calcium on the coronary and systemic circulation in patients after coronary surgery

Nine patients were studied three hours after aorto-coronary bypass. Before anaesthesia a radial arterial cannula was inserted and a thermodilution catheter placed into the pulmonary artery by fluoroscopy. A special thermodilution catheter was manipulated into the coronary sinus. Haemodynamic measurements were made plus cardiac output and coronary sinus blood flow. Content of oxygen and lactate in arterial and coronary sinus blood was determined. Series of measurements were done before and after 1 gm of CaCl2 given intravenously over 15 minutes. Calcium increased cardiac index and arterial pressure but not systemic vascular resistance. Total coronary sinus blood flow did not change, nor did myocardial oxygen consumption or coronary sinus oxygen content. Content of lactate in arterial and coronary sinus blood was unaltered and lactate extraction by the heart continued, in eight of nine patients. The improved haemodynamics were accomplished without inordinate risk to global ventricular energy metabolism.RésuméLe but de ce travail était de vérifier si les effets circulatoires bénéfiques du chlorure de calcium étaient obtenus au prix d’une augmentation de la consommation myocardique d’oxygène supérieure aux apports. A cette fin, neuf patients venant de subir un pontage aorto-coronarien ont été étudiés trois heures après leur arrivée aux soins intensifs.Avant l’induction de l’anesthésie, nous leur avions installé sous anesthésie locale une canule dans l’artère radiale et deux cathéters à thermodilution: le premier dans l’artère pulmonaire pour la mesure du débit cardiaque et le second placé sous fluoroscopie dans le sinus coronaire pour la mesure du débit sanguin dans le sinus coronaire (équivalent au débit de l’artère coronaire gauche).Les mesures suivantes ont été effectuées avant et après l’administration par voie intraveineuse, en quinze minutes, d’un gramme de chlorure de calcium: données hémodynamiques, débit cardiaque et débit du sinus coronaire, contenu en oxygène et en lactate du sang artériel et du sang prélevé dans le sinus coronaire.L’administration de chlorure de calcium élève le débit cardiaque et la pression artérielle, mais non la résistance vasculaire périphérique. Le débit du sinus coronaire ne s’est pas modifié, ni la consommation d’oxygène myocardique, ni le contenu en oxygène du sinus coronaire. Le taux des lactates dans le sang artériel et dans celui du sinus coronaire ne s’est pas modifié et l’extraction des lactates par le myocarde s’est continuée chez huit des neuf patients. Les effets bénéfiques sur la circulation se sont donc accomplis sans inconvénient pour l’équilibre énergétique du myocarde.

Effects of digoxin on myocardial oxygen supply and demand in patients following coronary artery bypass surgery.

Although digoxin is used frequently in patients in the prophylaxis of postoperative supraventricular tachyarrhythmias, the effects of the drug on myocardial oxygen supply and demand after coronary bypass have not been described. Seven adult patients with good ventricular function who underwent myocardial revascularization were studied before and three hours after digoxin (0.5 mg, iv). There were no significant changes observed in any measured systemic hemodynamic variable. Evaluation of global myocardial metabolism showed an increase in myocardial oxygen consumption (P < 0.05) which was compensated satisfactorily, as no significant alteration was noted in the coronary sinus oxygen content, or in the lactate gradient across the myocardium.Since the authors studied the effects of only one dose of digoxin, the effects of full digitalization in these patients remains to be defined.