Effects of dexmedetomidine on systemic and coronary hemodynamics in the anesthetized dog.

In addition to central effects, which are the basis of their use in anesthesiology, alpha 2-adrenergic agonists have direct peripheral cardiovascular effects. Dexmedetomidine (DM) has been found to depress cardiac function in dogs, even after autonomic denervation. The present experiments evaluated the effects of DM on coronary flow, myocardial oxygen extraction, and cardiac function in intact, open chest dogs under enflurane anesthesia.

Effect of dexmedetomidine, an alpha 2-adrenergic agonist, in the isolated heart.

Dexmedetomidine (DM) was studied in the isolated dog heart in the form of a Starling heart-lung preparation, (HLP). Hearts were subjected to increased loading by (a) increasing cardiac output, and (b) increasing systemic resistance. Results are depicted by cardiac function curves, prepared by plotting left atrial pressure against either systemic cardiac output or mean arterial pressure.

Hemodynamic effects of dexmedetomidine, an alpha 2-adrenergic agonist, in autonomically denervated dogs.

The hemodynamic effects of the alpha 2-adrenergic agonist, dexmedetomidine (DM), were studied in eight anesthetized, autonomically denervated dogs. Autonomic block decreased mean arterial pressure (MAP) and cardiac index (CI) by approximately 20% to 95 +/- 8 mm Hg and 4.1 +/- 0.

Narcotic reversal in hypercapnic dogs: comparison of naloxone and nalbuphine.

Reversal of opioid effects by naloxone (NX) can lead to significant cardiovascular problems. We have reported previously that hypercapnic dogs develop greater increases in blood pressure and plasma catecholamine (CA) levels than hypocapnic ones when reversed with naloxone. We have also demonstrated differences between NX and nalbuphine (NBPH) in producing excitatory adrenergic responses when administered during normocapnia.

Effect of halothane concentration on tachyphylaxis to sodium nitroprusside.

The relationship between halothane concentration and tachyphylaxis to sodium nitroprusside (SNP) was studied in a rabbit model. Three groups of six rabbits (groups A, B, and C) were anesthetized with halothane at 0.75, 1.

Cardiovascular effects of fentanyl reversal by naloxone at varying arterial carbon dioxide tensions in dogs.

Clinical reports, as well as animal studies, have described cardiovascular and sympathetic stimulation after the administration of naloxone (NX) to reverse opioid-induced respiratory depression. This investigation examines the effect of PaCO2 on hemodynamic and adrenergic responses to NX, by means of 24 experiments carried out in six dogs. Each dog underwent NX reversal of fentanyl (FEN) at three different PaCO2 levels: 20, 35, and 60 mm Hg.

Histamine release by four narcotics: a double-blind study in humans.

Histamine release and hemodynamic changes associated with four narcotics were studied in 60 adults (28 men, 32 women) scheduled for general surgery under balanced anesthesia. Under double-blind conditions, incremental equipotent doses of meperidine, morphine, fentanyl, or sufentanil were administered IV for induction of anesthesia, prior to thiopental, succinylcholine, and intubation. Arterial blood samples were drawn before and 1, 6, and 20 min after narcotic administration.

Reduced narcotic requirement by clonidine with improved hemodynamic and adrenergic stability in patients undergoing coronary bypass surgery.

The authors examined the effect of clonidine, a preferential alpha 2-adrenergic agonist, upon narcotic requirements, hemodynamics, and adrenergic responses during the perioperative period in patients undergoing CABG surgery. Anesthesia was provided by sufentanil supplemented with isoflurane; sodium nitroprusside was given as needed for hemodynamic control. Ten patients received oral clonidine preoperatively at the time of premedication, and again intraoperatively by nasogastric tube.

Effect of clonidine on sympathoadrenal response during sodium nitroprusside hypotension.

Supplementation of the antihypertensive action of the peripheral vasodilator sodium nitroprusside (SNP) with clonidine, a centrally-acting agent, was studied in ten dogs anesthetized with isoflurane to evaluate the efficacy of clonidine for reducing the amount of SNP required during induced hypotension. The dose of SNP required to lower mean arterial blood pressure (MAP) by 40% was determined prior to the administration of intravenous clonidine (control), and after incremental doses of 1, 4, and 15 micrograms/kg. After each dose of clonidine, hypotension was induced with SNP and maintained for 30 min, followed by a 30-min recovery period.

Haemodynamic effects of verapamil administration after large doses of fentanyl in man.

Thirteen patients with good left ventricular function undergoing coronary artery revascularization were studied to determine the cardiovascular effects of verapamil, 75-150 micrograms X kg-1, after a large dose (100 micrograms X kg-1) of fentanyl, with pancuronium for muscle relaxation. The patients were continued on their usual cardiovascular medications until the time of surgery, which included nitrates, beta adrenergic blockers, and nifedipine. Anaesthesia with fentanyl was associated with decreases in mean arterial blood pressure, systemic vascular resistance, left ventricular stroke work index, and circulating catecholamine levels.

Myocardial hemodynamics during induced hypotension: a comparison between sodium nitroprusside and adenosine triphosphate.

Adenosine triphosphate (ATP) has been reported to be a hypotensive agent similar in effect to sodium nitroprusside (SNP). The purpose of this study was to examine and compare the effects of both SNP and ATP on general coronary hemodynamics, myocardial O2 consumption, and circulating catecholamines. Twelve dogs were anesthetized with 1.

Effects of fentanyl and diazepam in dogs deprived of autonomic tone.

In contrast to reports of the untoward hemodynamic effects of fentanyl and diazepam in intact organisms, we found that neither a bolus of 100 micrograms/kg fentanyl nor the addition of intravenous doses of diazepam, up to and including 1 mg/kg (cumulative dose 2 mg/kg) caused cardiovascular depression in 13 anesthetized dogs after elimination of their sympathetic and parasympathetic tone. There were no significant changes in mean arterial blood pressure, cardiac output, heart rate, peak left ventricular dP/dt, cardiac filling pressures, or systemic vascular resistance. Rapid bolus injection of 3 mg/kg diazepam (cumulative dose 5 mg/kg) caused a significant (P less than 0.

Comparison of morphine, meperidine, fentanyl, and sufentanil in balanced anesthesia: a double-blind study.

A double-blind study comparing four narcotic analgesics of different potencies, meperidine, morphine, fentanyl, and sufentanil, was performed on consenting patients undergoing general or orthopedic surgery under balanced anesthesia. Blood pressure, measured through an indwelling arterial catheter, was recorded continuously, as were ECG and heart rates. The narcotics, made up in equipotent concentrations, were given as indicated by hemodynamic and clinical signs.

Verapamil: placental transfer and effects on maternal and fetal hemodynamics and atrioventricular conduction in the pregnant ewe.

Verapamil may have application in the field of obstetrics for treatment of maternal and fetal tachyarrhythmias. This study was performed to assess the maternal and fetal hemodynamic effects of this drug, as well as to determine its placental transfer and effects on maternal and fetal atrioventricular conduction in the pregnant ewe. Verapamil, 0.

Comparison of cardiovascular responses to verapamil during enflurane, isoflurane, or halothane anesthesia in the dog.

The cardiovascular responses to increasing infusion rates of the slow calcium channel inhibitor, verapamil, were studied in three groups of dogs during either enflurane, isoflurane, or halothane anesthesia. Control hemodynamic values and plasma samples were taken after 2 h of anesthesia with the given agent. Increasing infusion rates of verapamil were given to achieve a range of plasma verapamil levels up to approximately 500 ng X ml-1.

Effects of fentanyl, naloxone, and clonidine on hemodynamics and plasma catecholamine levels in dogs.

A 50-micrograms/kg dose of fentanyl, given intravenously in divided doses to dogs under enflurane-nitrous oxide anesthesia caused sharp decreases in heart rate (HR), arterial blood pressure (AP), left ventricular dP/dt, and plasma levels of catecholamines. Naloxone, 20 micrograms/kg given 65-70 min later, completely and rapidly reversed these changes. Because the cardiovascular effects of fentanyl and naloxone occurred in unparalyzed animals under surgical anesthesia without eliciting any motor responses, it seems unlikely that they can be ascribed to changes in awareness and surgical stimulation, especially pain.

Reduction in halothane anesthetic requirement by clonidine, an alpha-adrenergic agonist.

The effects of clonidine, a potent central alpha-adrenergic agonist, and of tolazoline, an alpha-adrenergic antagonist, on the minimal anesthetic concentration (MAC) of halothane were studied in male mongrel dogs. Control halothane MAC was 0.8 +/- 0.

Lack of correlation of verapamil plasma level with cumulative protective effects against halothane--epinephrine ventricular arrhythmias.

The effect of verapamil, 0.2 mg/kg i.v.

Hypotensive effects of adenosine and adenosine triphosphate compared with sodium nitroprusside.

Hypotensive effects of the intravenous injection of adenine compounds [adenosine triphosphate (ATP), adenosine] were compared with those of sodium nitroprusside (SNP) in rabbits during light, stable halothane anesthesia. ATP and adenosine were almost equipotent in their effects on blood pressure and heart rate. The hypotensive potencies of ATP and adenosine were approximately 1/6 (bolus injection) and 1/40 (continuous infusion) that of SNP, but the adenine compounds had a more rapid onset of action and shorter recovery times than SNP.

Epinephrine-induced arrhythmias and cardiovascular function after verapamil during halothane anesthesia in the dog.

The antiarrhythmic and cardiovascular effects of the slow channel inhibitor, verapamil, were studied during 1.1 MAC halothane anesthesia in the dog. The control epinephrine arrhythmogenic dose to induce ventricular arrhythmias was 2.

Reflex responses to sodium nitroprusside and their control by cryptenamine.

In chloralose-anesthetized dogs the hypotensive and reflex cardiovascular responses to infusions of sodium nitroprusside were studied before and during halothane and enflurane, and before after divided doses of cryptenamine. The latter drug, a mixture of hypotensive veratrum alkaloids, lowers blood pressure reflexly by acting on afferent receptors (baroreceptors). Control infusions of nitroprusside, which caused 10% to 15% decreases im mean arterial blood pressure, markedly increased heart rate, myocardial contractility, cardiac output, rate-pressure product, and left ventricular minute work in spite of decreases in peripheral vascular resistance.