Charman L. Cousins

The Effects of Nitrous Oxide on Myocardial Metabolism and Hemodynamics during Fentanyl or Enflurane Anesthesia in Patients with Coronary Disease

Twenty patients about to have coronary artery bypass grafts were studied before and after 15 min of 50% nitrous oxide added to either fentanyl (75 μg/kg) or enflurane (0.5%) anesthesia. Arterial and central pressures and cardiac output were measured, plus coronary sinus blood flow and arterio-coronary sinus differences in oxygen, hemoglobin, and lactate contents. Fentanyl-N2O and enflurane-N2O both decreased systemic resistance, heart rate, cardiac output, and hence arterial pressure. Stroke work decreased significantly with little or no change in wedge pressure: ventricular function was impaired. Coronary flow and myocardial O2 consumption decreased with fentanyl-N2O. Oxygen extraction increased with enflurane-N2O, as did lactate contents of coronary sinus blood. Hemodynamic depression occurred from the combined effects of nitrous oxide and fentanyl or enflurane. The β-blocked myocardia of nonstimulated coronary patients were becoming ischemic globally on 50% oxygen, after significant hypotension. From this and other evidence, we conclude that nitrous oxide may not be benign in patients with coronary arterial disease.

Myocardial metabolism and haemodynamic responses during high-dose fentanyl anaesthesia for coronary patients

Fentanyl (mean dose 109 µg.kg-1) and oxygen were given to ten patients having coronary vein grafts. Serial studies were done before, during and after operation, of central and mean arterial pressures (MAP), cardiac index (CI) and coronary sinus flow (CBF) by thermodilution, myocardial oxygen consumption (MVO2) and lactate extraction (MLE). On induction CI and stroke work index decreased, but heart rate and MAP were unchanged as systemic resistance increased. Mean MAP and heart rate remained at the awake levels. Mean CBF remained unchanged along with stable MAP and coronary resistance. Oxygen content of CS blood increased on induction and remained elevated until the incision; it was above the awake level early postoperatively. MVO2 was low normal when the patients were awake and remained so. Normal MLE continued with a few exceptions. High-dose fentanyl did not uniformly abolish autonomic reflexes. Heavy premedication, complete beta adrenergic blockade and a high initial doses of fentanyl plus its continued infusion, aided in retaining a hypodynamic circulation and myocardial oxygenation.RésuméLefentanyl à dose moyenne de 109 µ.g.kg-1 avec oxygène, a été employé comme agent d’anesthésie chez dix malades opérés pour pontage aorto-coronarien. Les mesures suivantes ont été prises avant, durant et après l’opération: pression artérielle moyenne (MAP), pression dans l’artère pulmonaire (PAP), index cardiaque (CI), flux sanguin du sinus coronaire (CBF), consommation d’oxygène par le myocarde (MVO2) et extraction de lactate. A l’ induction, l’index cardiaque et le travail du ventricule gauche ont diminué mais la fréquence cardiaque et la pression artérielle sont demeurées inchangées de même que la résistance systémique. La pression artérielle moyenne et la fréquence cardiaque sont demeurées au niveau préinduction. Le CBF est demeuré inchangé comme la pression artérielle moyenne et les résistances coronaires. Le contenu en oxygène du sang veineux coronaire a augmenté à l’induction et s’est maintenu élevé jusqu’au moment de l’incision. De même ce contenu était audessus des niveaux de contrôle dans la période postopératoire immédiate. La consommation d’oxygène par le myocarde était basse mais normale à l’état d’éveil et s’est maintenue ainsi. A quelques exceptions près, l’extraction de lactate est demeurée normale. Lefentanyl à hautes doses n’a pas contrôlé les réflexes du système nerveux autonome de façon uniforme. Une prémédication lourde, un blocage bêta-adrénergique adéquat et une dose élevée de fentanyl au départ suivie d’une infusion continue contribuent à garder la circulation dans un état hypodynamique et à assurer /’oxygénation myocardique.

Myocardial metabolism and haemodynamic responses with enflurane anaesthesia for coronary artery surgery

Ten patients were studied before, during and after enflurane anaesthesia for coronary vein grafting. All had good ventricular function and nine were receiving effective beta blockade. Cardiac output and vascular pressures were measured, plus coronary sinus blood flow (CBF), myocardial oxygen consumption (MVO2) and lactate extraction (MLE). Enflurane induction (10 minutes, mean 1.72 per cent end tidal) reduced blood pressure (MAP), due to decreased cardiac index (CI), with no change in heart rate or systemic resistance. Intubation returned MAP and CI to control level but the heart rate increased. Subsequently, enflurane kept MAP, CI and stroke work below the awake level. CBF decreased on induction, rose again on intubation and remained normal before bypass. MVO2 fell on induction from an increase in CS oxygen content, which remained elevated. Normal MLE continued in every patient. There was no evidence of myocardial ischaemia in patients on beta blockade, when haemodynamics were maintained at or below those of the sedated, awake state.RésuméDix malades opérés pour pontage aorto-coronarien sous anesthésie à l’enflurane ont été étudiés. Tous avaient une fonction ventriculaire normale et neuf sur dix étaient sous médication bêta-bloquame adéquate. Les mesures suivantes ont été prises avant, durant et pendant l’anesthésie à l’enflurane: le débit cardiaque, les pressions vasculaires, le flux sanguin du sinus coronaire (CBF), la consommation d’oxygène myocardique (MVO2) et l’extraction de lactate (MLE). L’induction de l’anesthésie à l’enflurane s’étendant sur une période de dix minutes à une concentration moyenne de fin d’expiration de 1.72 pour cent a diminué la tension artérielle (MAP) par diminution de l’index cardiaque (CI) sans provoquer de changement dans la fréquence cardiaque ou les résistances périphériques. L’intubation a ramené la MAP et le Cl au niveau contrôle et a aussi accéléré la fréquence cardiaque. Par la suite, l’enflurane a maintenu la MAP, le Cl et le travail du ventricule gauche en-dessous des niveaux mesurés à l’état d’éveil. Le flux coronarien a diminué à l’induction, s’est élevé de nouveau à l’intubation pour se maintenir normal jusqu’à la circulation extracorporelle. La MVO2 a elle aussi chuté à l’Induction comme en témoigne l’élévation du contenu en oxygène du sang du sinus coronarien, contenu qui est demeuré élevé. L’extraction de lactate est demeurée normale chez tous les malades. On n’a donc pas observé d’ischémie myocardique chez les patients adéquatement traités aux bêta-bloquants lorsque les fadeurs hémodynamiques ont été maintenus au niveau mesuré à l’état d’éveil chez les patients prémédiqués; de même, on n’a pas observé d’ischémie myocardique lorsque ces facteurs hémodynamiques ont été réduits en bas des niveaux préopératoires.

Indirect measurement of infarct size. Correlative variability of enzyme, radionuclear angiographic, and body-surface-map variables in 34 patients during the acute phase of first myocardial infarction.

To gain a correlative perspective of indirect indications of the size of a myocardial infarct, we measured several body-surface electrocardiographic variables and several enzyme and radionuclear angiographic indicators of an infarcts size in 34 patients during the acute phase of first infarction. We found that bivariate correlations ranged widely, from an r value of 0.05 to an r value of 0.92, but were significantly (p less than 0.001) higher when variables from the same technique were correlated (mean r, 0.60 +/- 0.27), as opposed to correlations of variables from different techniques (mean r, 0.27 +/- 0.18). Trivariate comparisons among techniques produced significantly (p less than 0.001) higher r values, but the highest, an r value of 0.76 (total wall motion abnormality score; peak lactic dehydrogenase level; ST-segment integral maximum), indicated that even in this best case, only about 60 percent of the variation of one variable was dependent on or due to the two other variables. These data demonstrate that multiple indirect quantitative indicators of myocardial injury can vary widely in their correlations within the same population of infarcts, and much remains unknown in their relationships during the acute phase. Caution should be exercised, therefore, in their clinical application to predict an infarcts size in individual patients with acute myocardial infarction.

Clinical InvestigationsIndirect Measurement of Infarct Size: Correlative Variability of Enzyme, Radionuclear Angiographic, and Body-Surface-Map Variables in 34 Patients during the Acute Phase of First Myocardial Infarction

To gain a correlative perspective of indirect indications of the size of a myocardial infarct, we measured several body-surface electrocardiographic variables and several enzyme and radionuclear angiographic indicators of an infarcts size in 34 patients during the acute phase of first infarction. We found that bivariate correlations ranged widely, from an r value of 0.05 to an r value of 0.92, but were significantly (p less than 0.001) higher when variables from the same technique were correlated (mean r, 0.60 +/- 0.27), as opposed to correlations of variables from different techniques (mean r, 0.27 +/- 0.18). Trivariate comparisons among techniques produced significantly (p less than 0.001) higher r values, but the highest, an r value of 0.76 (total wall motion abnormality score; peak lactic dehydrogenase level; ST-segment integral maximum), indicated that even in this best case, only about 60 percent of the variation of one variable was dependent on or due to the two other variables. These data demonstrate that multiple indirect quantitative indicators of myocardial injury can vary widely in their correlations within the same population of infarcts, and much remains unknown in their relationships during the acute phase. Caution should be exercised, therefore, in their clinical application to predict an infarcts size in individual patients with acute myocardial infarction.

Principles of enzymology.

1. Setting up an enzyme test requires careful consideration of assay temperature and pH, buffer composition, substrate concentration, and linearity of the relationship between enzyme concentration and measured activity. 2. Use of a standard method of measurement (the international unit) is advocated.

Comparison of serum sodium and chloride results for Flame IV-Auto Analyzer II, SMAC, Ektachem 400, and Nova 4 clinical analyzer systems.

We determined serum Na+ and Cl- results using Technicons Flame IV-Auto Analyzer II (FLIV/AAII) system and Kodaks Ektachem 400 clinical analyzer. Our objective was to determine whether Na+ and Cl- results from these analyzers were sufficiently similar to report to clinicians without reference to the system used for the determination. Method precision of the two systems for Na+ results was comparable; whereas Ektachem 400 Cl- results were more imprecise than those determined using the FLIV/AAII, Ektachem Na+ results showed lower correlation with the FLIV/AAII (r = 0.890) and Cl- results were more highly correlated (r = 0.960). When Kodaks newly developed equi-transferant electrolyte reference fluid (ETRF) was used with generation 4 Na+ slides and generation 1 Cl- slides the largest difference observed was 7.0 mmol/L for both Na+ and Cl- results. Using Kodak calibrators and the manufacturers operational conditions for the Ektachem 400, we observed that a considerable number of sample results for both Na+ and Cl- did not agree within 3.0 mmol/L of the FLIV/AAII values. To corroborate our finding, we also analyzed serum Na+ and Cl- using a Technicon Sequential Multiple Analyzer + Computer (SMAC) system and a Nova 4 + 4 Clinical Analyzer (Nova). We conclude that flame emission systems and direct ion specific electrode systems do not yield comparable Na+ and Cl- results even when total protein and triglyceride concentrations of the samples are within reference ranges.(ABSTRACT TRUNCATED AT 250 WORDS)

Continuous-flow enzymic determination of serum total and high density lipoprotein cholesterol using microlitre sample volumes

We determine serum total cholesterol and high-density lipoprotein cholesterol (HDL-C) using a modified Technicon Auto Analyzer II-BMC enzymic system. The method uses 25 microL of sample (serum or supernate) for cholesterol determinations. Pooled serum which was calibrated indirectly against CDCs Abell-Kendall method was used for standardization. Accuracy and precision for total cholesterol determinations are comparable to those obtained using a modified Technicon AAII method. Coefficients of variation for the determination of HDL-C prepared by heparin/Mn++ precipitation are 6.4% and 4.6% at concentration levels of 0.70 mmol/L and 0.94 mmol/L respectively. The interchangeable use of deionized-distilled water and 0.15 mol/L NaCl solution for dilution of samples analyzed by the micro method is shown to produce significantly different cholesterol estimates. The reduced reagent volumes significantly lower the cost of cholesterol determinations. The system is simple, inexpensive and yields reliable cholesterol and HDL-C results.