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Biomedical subjects

I R Thomson

Publications and source records attributed to I R Thomson.

53 records · Page 3Linked to original sources
PubMed1988

Catecholamine responses to anesthetic induction with fentanyl and sufentanil.

In a randomized study, the authors examined the changes in plasma epinephrine and norepinephrine concentrations associated with induction of anesthesia and surgery in 33 patients with good ventricular function undergoing elective coronary artery surgery. After premedication with morphine and scopolamine, patients received either fentanyl, 100 micrograms/kg (n = 16), or sufentanil, 15 micrograms/kg, (n = 17), intravenously (IV), over 10 minutes to induce anesthesia. Metocurine, 0.42 mg/kg, IV, produced muscle relaxation. Arterial blood for plasma catecholamine determinations was drawn prior to induction, every two minutes throughout induction, one minute following endotracheal intubation, and one minute after sternotomy. Plasma epinephrine concentration was unchanged with either induction agent. Plasma norepinephrine concentration increased significantly after administration of either narcotic, peaked between six and ten minutes into induction, and returned to the preinduction value after intubation. Induction-related changes in arterial pressure and pulmonary capillary wedge pressure were significantly correlated with changes in the logarithm of plasma norepinephrine concentration. Similar degrees of endogenous norepinephrine release appear to accompany induction with equipotent doses of fentanyl and sufentanil in patients premedicated with morphine and scopolamine. Norepinephrine release may influence the hemodynamic response to induction with narcotics.

Anesthesia, Intravenous↗
PubMed1988

Premedication and high-dose fentanyl anesthesia for myocardial revascularization: a comparison of lorazepam versus morphine-scopolamine.

Using a randomized double-blind placebo-controlled experimental protocol, the authors compared two premedication regimens in 42 patients undergoing elective myocardial revascularization. Group L patients (n = 23) received lorazepam 0.06 mg/kg po 90 min preoperatively, while group M patients (n = 19) received morphine 0.1 mg/kg im, plus scopolamine 0.006 mg/kg im 60 min preoperatively. Anesthesia was induced with fentanyl 100 micrograms/kg and atracurium 0.50 mg/kg administered over 10 min. The treatment groups did not differ significantly with respect to the degree of sedation or anxiolysis achieved, or the rapidity of induction with fentanyl. Premedication significantly influenced the hemodynamic response to anesthetic induction. Hemodynamics were stable post-induction in group M, but cardiovascular depression was noted in group L. Control heart rate (HR) was lower in group L. The HR, arterial pressure, and cardiac index were significantly lower, following both induction and intubation, in group L. Following sternotomy hemodynamics were identical in both groups. Serum fentanyl concentration was significantly higher during intubation in group L, probably secondary to the pharmacokinetic consequences of a decreased CI. New electrocardiographic evidence of myocardial ischemia did not occur in either group. Based on their findings with fentanyl-at-racurium, and their review of the literature, the authors speculate that premedication exerts a significant hemodynamic effect during induction with other narcotic-relaxant combinations.

Anesthesia, Intravenous↗
PubMed1987

A randomized double-blind comparison of fentanyl and sufentanil anaesthesia for coronary artery surgery.

Using a randomized double-blind protocol the authors compared two narcotic anaesthetic regimens in 33 patients with good ventricular function undergoing coronary artery surgery. After premedication with morphine and scopolamine, patients received either fentanyl 100 micrograms X kg-1 (n = 16), or sufentanil 15 micrograms X kg-1 (n = 17), intravenously (IV) over 10 min to induce anaesthesia. Metocurine 0.42 mg X kg-1 provided muscle relaxation. No further IV anaesthetic agents were given. The haemodynamic response to induction, intubation, and surgery, differed minimally between agents. The degree of rigidity on induction was identical with both agents, as were the intervals following induction at which patients lost consciousness, regained consciousness, or met criteria for extubation. However, the interval until extubation criteria were met did correlate with the duration of cardiopulmonary bypass. Sufentanil 15 micrograms X kg-1, was clinically indistinguishable from fentanyl 100 micrograms X kg-1, when used as the primary anaesthetic agent for coronary surgery.

Aged↗
PubMed1986

Fentanyl oxygen anaesthesia for abdominal aortic surgery.

Patients who present for abdominal aortic surgery often have significant atherosclerotic disease which may involve the coronary arteries. Haemodynamic responses occurring during fentanyl (100 micrograms X kg-1) oxygen anaesthesia for abdominal aortic surgery were studied in 16 patients. Anaesthesia was induced with fentanyl 100 micrograms X kg-1 with no supplemental doses and metocurine-pancuronium mixture (4:1). In 13 of 16 patients hyperdynamic circulatory responses to surgical stimuli required treatment prior to aortic cross-clamping. Interventions instituted were sodium nitroprusside or nitroglycerin (n = 13), propranolol (n = 4), and diazepam (n = 4). The serum fentanyl concentration at time of response to surgical stimulus was 18.5 +/- 5.6 ng X ml-1 (range 7-27 ng X ml-1; time from induction 71 +/- 49 min, n = 9). Eleven of the 16 patients required treatment for postoperative hypertension. Five of the 16 patients developed myocardial ischaemia, defined as ST segment depression greater than 0.1 mV, at some time during the operative procedure. Unsupplemented fentanyl anaesthesia (100 micrograms X kg-1) was unable to maintain a hypodynamic circulation in patients having abdominal aortic operations.

Aged↗
PubMed1986

Pharmacokinetics of fentanyl in patients undergoing abdominal aortic surgery.

The authors determined the pharmacokinetics of fentanyl 100 micrograms X kg-1 iv in patients undergoing elective abdominal aortic surgery. The mean (+/- SD) age of the ten patients was 67.2 +/- 8.7 yr; their mean weight was 78.5 +/- 13.7 kg. Seven patients had aortic aneurysm repair, and the other three patients had aortobifemoral grafts. Serum fentanyl concentrations were determined from samples drawn at increasing intervals over a 24-h period. A three-compartment pharmacokinetic model was fit to the concentration versus time data. Total drug clearance was 9.8 +/- 1.8 ml X min-1 X kg-1. The volume of distribution at steady-state (Vdss) was 5.4 +/- 1.9 X 1 kg-1. Elimination half-time was 8.7 +/- 2.5 h. There were no significant correlations between these pharmacokinetic parameters and patient's age, duration of aortic cross-clamping, duration of surgery, intraoperative blood loss, or volume of iv fluids given intraoperatively. In healthy volunteers or patients undergoing general surgery, other investigators report mean elimination half-times for fentanyl ranging from 1.7 to 4.4 h. The prolonged elimination half-time in patients having abdominal aortic surgery has important clinical implications. In particular, recovery from large doses will take much longer than would have been anticipated from previously published fentanyl pharmacokinetic data.

Aged↗
PubMed1985

Adverse effects of pancuronium during high-dose fentanyl anesthesia for coronary artery bypass grafting.

Using a randomized double-blind protocol, the authors prospectively compared three nondepolarizing muscle relaxants with respect to their influence on hemodynamics and on the electrocardiogram. Thirty-three patients undergoing elective coronary artery bypass grafting (CABG) with high-dose (100 micrograms/kg) fentanyl anesthesia were studied. Patients received 1.5 X ED95 of either pancuronium (n = 12), metocurine (n = 9), or a metocurine-pancuronium combination (4:1 ratio by weight) (n = 12) for muscle relaxation. Heart rate and rate pressure product (RPP) were significantly higher postinduction in the pancuronium group. Myocardial ischemia, indicated by new ECG ST-segment depression occurred significantly more frequently, and exclusively, in the pancuronium group. The authors' data suggest that since pancuronium is associated with tachycardia and an increased incidence of myocardial ischemia, it is best avoided in patients with severe coronary artery disease undergoing CABG with high-dose fentanyl. Either metocurine or the metocurine-pancuronium combination provides greater hemodynamic stability, without precipitating myocardial ischemia, and can be safely and effectively substituted for pancuronium.

Anesthesia↗
PubMed1984

Cardiovascular physiology: venous return.

Cardiac output is not regulated simply by autonomically mediated changes in heart rate and stroke volume. More often, changes in cardiac output predominantly reflect changes in the peripheral circulation which in turn change venous return. Any attempt to analyze circulatory function without considering the peripheral circulation will be incomplete. The principles discussed above can be fruitfully applied to the analysis of many clinically important derangements of circulatory function. This discussion is only intended as an introduction to concepts which have been exhaustively developed and discussed by Guyton et al. A careful review of this source material will reward the interested reader.

Anesthetics↗
PubMed1984

Failure of intravenous nitroglycerin to prevent intraoperative myocardial ischemia during fentanyl-pancuronium anesthesia.

Twenty patients undergoing coronary artery bypass grafting under fentanyl-pancuronium anesthesia were studied. Continuous electrocardiographic (ECG) recording by a Holter Monitor was utilized to determine the incidence of ECG changes of myocardial ischemia during the precardiopulmonary bypass period and to determine the efficacy of an intravenous nitroglycerin (iv NTG) infusion for preventing ischemic ECG changes. Patients in Group 1 (n = 9) received a 0.5 microgram . kg-1 . min-1 iv NTG infusion 20 min prior to induction of anesthesia and throughout the study. Patients in Group 2 (n = 11) received placebo. A randomized double-blind protocol was employed. Anesthesia was induced with fentanyl 3 micrograms . kg-1 . min-1. After fentanyl 25 micrograms/kg and pancuronium 0.1 microgram/kg, the trachea was intubated. After fentanyl 50 micrograms/kg surgery commenced. Prior to induction of anesthesia, iv NTG caused significant decreases in mean arterial pressure and pulmonary capillary wedge pressure, whereas placebo had no effect. However, subsequent to induction of anesthesia, hemodynamics in the two groups were identical. Fifty per cent of patients developed ECG changes of myocardial ischemia during the period from induction of anesthesia to commencement of cardiopulmonary bypass. The incidence of ischemic ECG changes was virtually identical in Group 1 (5/9) and Group 2 (5/11). Ischemic ECG changes were associated with increases in heart rate, mean arterial pressure, and rate pressure product, and decreases in the endocardial viability ratio (DPTI/SPTI). Increases in pulmonary capillary wedge pressure were not associated with myocardial ischemia. Fentanyl-pancuronium anesthesia, as administered in this study, was associated with a high incidence of myocardial ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia↗
PubMed1982

Hemodynamic effects of intravenous nitroglycerin: importance of the delivery system.

Twenty patients about to undergo elective coronary artery bypass grafting entered a randomized double-blind trial comparing the hemodynamic effects of intravenous nitroglycerin (IV NTG) (0.5 micrograms/kg/min) (n = 9) versus placebo (n = 11). After a 20-min infusion period mean arterial pressure, mean pulmonary arterial pressure, pulmonary capillary wedge pressure, central venous pressure, stroke index, and left ventricular stroke work index were significantly decreased by NTG. Cardiac index was unchanged despite a marked reduction of filling pressures, indicating improved ventricular function. The endocardial viability ratio (DPTI/SPTI) was improved by NTG, suggesting a favorable alteration of myocardial oxygen balance. Three additional patients received a larger dose of NTG, (0.1 micrograms/kg/min). The hemodynamic effects were similar to, but more profound than, those noted at 0.5 micrograms/kg/min. The effects of IV NTG described here are compatible with a predominant venodilator effect of NTG and occurred at a dose previously reported to cause little or no hemodynamic change in a similar group of patients. We attribute the apparent increased potency of IV/NTG observed in our study to the use of an infusion system that does not absorb NTG. Previous investigators have used infusion systems containing polyvinyl chloride (PVC) plastic, a substance that avidly adsorbs NTG. The resultant decrease in the administered dose of NTG renders dose-response data invalid when PVC-containing systems are used to deliver NTG.

Blood Pressure↗
PubMedDate not supplied

Dobutamine-atropine stress echocardiography in elderly patients unable to perform an exercise test. Hemodynamic characteristics, safety, and prognostic value.

OBJECTIVE: To establish the hemodynamic effects, safety, and prognostic value of dobutamine-atropine stress echocardiography in patients 70 years of age or older. DESIGN AND SETTING: Observational study at a university hospital. PATIENTS: One hundred seventy-nine patients (mean age, 75 years; range, 70 to 90 years) referred for chest pain (n = 73) or preoperative risk assessment for major vascular noncardiac surgery (n = 106). MEASUREMENTS: All patients underwent clinical evaluation and dobutamine-atropine stress test. RESULTS: One hundred seventy-nine stress tests were performed. Test end points were the target heart rate (85% of theoretical maximum heart rate), reached in 165 tests (92%); inadequate echo images, two tests (1%); and side effects, 12 tests (7%). Side effects that caused a premature end of the test were severe chest pain (n = 5 [2.8%]), electrocardiographic changes (n = 1 [0.6%]), hypotension (n = 2 [1.1%]), chills (n = 2 [1.1%]), and cardiac arrhythmias (paroxysmal atrial fibrillation) (n = 2 [1.1%]). New wall motion abnormalities as a marker of myocardial ischemia occurred in 50 tests (28%). No death or myocardial infarction occurred during the test. Perioperative events occurred in 12 patients (four cardiac deaths, three myocardial infarctions, and five episodes of unstable angina). During 16 +/- 6 months (mean +/- SD) of follow-up of 166 patients, 22 cardiac events occurred (eight cardiac deaths, four myocardial infarctions, and 10 episodes of unstable angina pectoris). By multivariate regression analysis, only perioperative cardiac events (odds ratio, 51; 95% confidence interval, 5.8 to 454) and late cardiac events (odds ratio, 5.2; 95% confidence interval, 2.0 to 14) were correlated with new wall motion abnormalities during stress. CONCLUSION: Dobutamine-atropine stress echocardiography is a feasible and safe test for assessing elderly patients with suspected and/or proven coronary artery disease, providing useful prognostic information for perioperative and late cardiac risk with relatively few side effects.

Aged↗
PubMedDate not supplied

Multiplane transesophageal echocardiography: latest evolution in an imaging revolution.

Multiplane imaging with a rotating phased-array transducer from within the esophagus represents the latest development in transesophageal cardiac ultrasound. Transverse, longitudinal, and all possible intermediate oblique planes are easily obtained from the same transducer with minimal probe manipulation. Three-dimensional conceptualization of complex structures and pathologic conditions is facilitated. The major advantages are a simplified examination procedure and much less patient discomfort than monoplane and biplane probe imaging.

Adult↗