Decrease in vascular resistance in the isolated canine hindlimb after graded doses of alfentanil, fentanyl, and sufentanil

Low-dose fentanyl reduces pain perception, muscle sympathetic nerve activity responses, and blood pressure responses during the cold pressor test

Our knowledge about how low-dose (analgesic) fentanyl affects autonomic cardiovascular regulation is primarily limited to animal experiments. Notably, it is unknown if low-dose fentanyl influences human autonomic cardiovascular responses during painful stimuli in humans. Therefore, we tested the hypothesis that low-dose fentanyl reduces perceived pain and subsequent sympathetic and cardiovascular responses in humans during an experimental noxious stimulus. Twenty-three adults (10 females/13 males; 27 ± 7 yr; 26 ± 3 kg·m^-2, means ± SD) completed this randomized, crossover, placebo-controlled trial during two laboratory visits. During each visit, participants completed a cold pressor test (CPT; hand in ∼0.4°C ice bath for 2 min) before and 5 min after drug/placebo administration (75 μg fentanyl or saline). We compared pain perception (100-mm visual analog scale), muscle sympathetic nerve activity (MSNA; microneurography, 11 paired recordings), and beat-to-beat blood pressure (BP; photoplethysmography) between trials (at both pre- and postdrug/placebo timepoints) using paired, two-tailed t tests. Before drug/placebo administration, perceived pain (P = 0.8287), ΔMSNA burst frequency (P = 0.7587), and Δmean BP (P = 0.8649) during the CPT were not different between trials. After the drug/placebo administration, fentanyl attenuated perceived pain (36 vs. 66 mm, P < 0.0001), ΔMSNA burst frequency (9 vs. 17 bursts/min, P = 0.0054), and Δmean BP (7 vs. 13 mmHg, P = 0.0174) during the CPT compared with placebo. Fentanyl-induced reductions in pain perception and Δmean BP were moderately related (r = 0.40, P = 0.0641). These data provide valuable information regarding how low-dose fentanyl reduces autonomic cardiovascular responses during an experimental painful stimulus.

Evaluation of two different radiotherapy anaesthetic protocols for dogs: a randomized clinical crossover trial

OBJECTIVES

To describe alfentanil-propofol admixture for induction of anaesthesia for canine radiotherapy and compare it to alfentanil-atropine followed by propofol induction in terms of heart rate (HR), mean arterial pressure (MAP), recovery duration and quality.

STUDY DESIGN

Prospective, masked, randomized clinical crossover trial.

ANIMALS

A group of 40 client-owned dogs anaesthetized from October 2017 to June 2018.

METHODS

Dogs were randomly assigned to be administered one of two protocols. For both protocols, IV preanaesthetic medication was given 30 seconds before rapid IV administration of a set volume of induction agent, with further induction agent administered as needed to permit intubation. For protocol ADMIX, the preanaesthetic medication was 0.04 mL kg^-1 0.9% sodium chloride and the induction agent was 0.2 mL kg^-1 propofol-alfentanil admixture. For protocol ATRO, the preanaesthetic medication was 10 μg kg^-1 alfentanil with 12 μg kg^-1 atropine (0.04 mL kg^-1 total volume) and the induction agent was 0.2 mL kg^-1 propofol. Anaesthesia was maintained with sevoflurane. Cardiorespiratory variables, agitation, hypotension, or inadequate depth of anaesthesia requiring supplemental boluses of propofol or increased vaporizer settings were recorded. Time to extubation, sternal recumbency and walking was noted. Videos were recorded for recovery quality scoring. Owner questionnaires gave feedback about recoveries at home. The other protocol was administered for the next radiotherapy session.

RESULTS

The only significantly different variable between protocols was mean HR during anaesthesia, which was lower in ADMIX (p < 0.001). Hypotension was recorded in seven (17.5%) dogs in ATRO and three (7.5%) in ADMIX, with an association (p < 0.005) between ATRO and hypotension. Owners reported animals recovered 'normal' behaviour and appetite by the next morning.

CONCLUSIONS AND CLINICAL RELEVANCE

Both protocols were acceptable for dogs undergoing radiotherapy, with minimal differences in anaesthetic quality, recovery duration and quality. Although MAP did not differ overall, the incidence of hypotension was higher in ATRO.

The effect of aging on the cutaneous microvasculature

Aging is associated with a progressive loss of function in all organs. Under normal conditions the physiologic compensation for age-related deficits is sufficient, but during times of stress the limitations of this reserve become evident. Explanations for this reduction in reserve include the changes in the microcirculation that occur during the normal aging process. The microcirculation is defined as the blood flow through arterioles, capillaries and venules, which are the smallest vessels in the vasculature and are embedded within organs and tissues. Optimal strategies to maintain the microvasculature following surgery and other stressors must use multifactorial approaches. Using skin as the model organ, we will review the anatomical and functional changes in the microcirculation with aging, and some of the available clinical strategies to potentially mitigate the effect of these changes on important clinical outcomes.

Anesthesia, microcirculation, and wound repair in aging

Age-related changes in skin contribute to impaired wound healing after surgical procedures. Changes in skin with age include decline in thickness and composition, a decrease in the number of most cell types, and diminished microcirculation. The microcirculation provides tissue perfusion, fluid homeostasis, and delivery of oxygen and other nutrients. It also controls temperature and the inflammatory response. Surgical incisions cause further disruption of the microvasculature of aged skin. Perioperative management can be modified to minimize insults to aged tissues. Judicious use of fluids, maintenance of normal body temperature, pain control, and increased tissue oxygen tension are examples of adjustable variables that support the microcirculation. Anesthetic agents influence the microcirculation of a combination of effects on cardiac output, arterial pressure, and local microvascular changes. The authors examined the role of anesthetic management in optimizing the microcirculation and potentially improving postoperative wound repair in older persons.

Comparison of intubating conditions between rocuronium with priming and without priming: Randomized and double-blind study

BACKGROUND

Rocuronium produces faster neuromuscular blockade compared with other neuromuscular blocking drugs. It produces comparable intubating conditions to that of succinylcholine, but does not have the short intubation time of the latter. Hence, it may not be preferable for rapid sequence intubation, but rocuronium with priming may produce comparable intubating time and conditions to that of succinylcholine. Rocuronium with priming may be an alternative to succinylcholine in rapid sequence intubation in conditions where succinylcholine is contraindicated. The present study was conducted to compare the intubating conditions and intubation time of rocuronium with and without priming.

METHODS

Sixty patients of ASA physical status I and II, aged between 18 and 60 years, of both sexes, were divided into priming and control groups of 30 each. Patients in the priming group received 0.06 mg/kg of rocuronium and those in the control group received normal saline. All patients received fentanyl 1 μg/kg, followed by thiopentone 5 mg/kg for induction. Intubating dose of rocuronium 0.54 mg/kg in the priming group and 0.6 mg/kg in the control group were administered 3 min after priming. Onset time of intubation was assessed using a Train of Four stimuli, and the intubating conditions were compared by the Cooper scoring system.

RESULTS

The onset time of intubation was 50.67±7.39 s in the priming group and 94.00±11.62 s in the control group, with excellent intubating conditions in both the groups and without any adverse effects.

CONCLUSIONS

Priming with rocuronium provides excellent intubating conditions in less than 60 s with no adverse effects.

Intravenous fentanyl during shoulder arthroscopic surgery in the sitting position after interscalene block increases the incidence of episodes of bradycardia hypotension

Background

Episodes of bradycardia hypotension (BH) or vasovagal syncope have a reported incidence of 13-29% during arthroscopic shoulder surgery in the sitting position after an interscalene block (ISB). This study was designed to investigate whether intravenous fentanyl during shoulder arthroscopy in the sitting position after ISB would increase or worsen the incidence of BH episodes.

Methods

In this prospective study, 20 minutes after being in a sitting position, 160 patients who underwent ISB were randomized to receive saline (S, n = 40), 50 µg of fentanyl (F-50, n = 40), 100 µg of fentanyl (F-100, n = 40) or 30 mg of ketorolac (K-30, n = 40) randomly. We assessed the incidence of BH episodes during the operation and the degree of maximal reduction (Rmax) of blood pressure (BP) and heart rate (HR).

Results

The incidence of BH episodes was 10%, 15%, 27.5% and 5% in the S, F-50, F-100 and K-30 groups, respectively. Mean Rmax of systolic BP in the F-100 group was significantly decreased as compared to the S group (-20.0 ± 4.5 versus -6.3 ± 1.6%, P = 0.004). Similarly, mean Rmax of diastolic BP in the F-100 group was also significantly decreased (P = 0.008) as compared to the S group.

Conclusions

These results suggest that fentanyl can increase the incidence of BH episodes during shoulder arthroscopic surgery in the sitting position after ISB.

Repinotan, a selective 5-HT1A-R-agonist, antagonizes morphine-induced ventilatory depression in anesthetized rats

BACKGROUND

Spontaneous breathing during mechanical ventilation improves arterial oxygenation and cardiovascular function, but is depressed by opioids during critical care. Opioid-induced ventilatory depression was shown to be counteracted in anesthetized rats by serotonin(1A)-receptor (5-HT(1A)-R)-agonist 8-OH-DPAT, which cannot be applied to humans. Repinotan hydrochloride is a selective 5-HT(1A)-R-agonist already investigated in humans, but the effects on ventilation and nociception are unknown. In this study, we sought to establish (a) the effects of repinotan on spontaneous breathing and nociception, and (b) the interaction with the standard opiate morphine.

METHODS

The dose-dependent effects of repinotan, given alone or in combination with morphine, on spontaneous minute ventilation (MV) and nociceptive tail-flick reflex latencies (TFLs) were measured simultaneously in spontaneously breathing anesthetized rats. An additional series with NaCl 0.9% and the 5-HT(1A)-R-antagonist WAY 100 135 served as controls.

RESULTS

(a) Repinotan dose-dependently activated spontaneous breathing (MV, mean [95% confidence interval]; 53% [29%-77%]) of pretreatment level) and suppressed nociception (TLF, 91% maximum possible effect [68%-114%]) with higher doses of repinotan (2-200 μg/kg). On the contrary, nociception was enhanced with a small dose of repinotan (0.2 μg/kg; TFL, -47% maximum possible effect [-95% to 2%]). Effects were prevented by 5-HT(1A)-antagonist WAY 100 135. (B) Morphine-induced depression of ventilation (MV, -72% [-100% to -44%]) was reversed by repinotan (20 μg/kg), which returned spontaneous ventilation to pretreatment levels (MV, 18% [-40% to 77%]). The morphine-induced complete depression of nociception was sustained throughout repinotan and NaCl 0.9% administration. Despite a mild decrease in mean arterial blood pressure, there were no serious cardiovascular side effects from repinotan.

CONCLUSIONS

The 5-HT(1A)-R-agonist repinotan activates spontaneous breathing in anesthetized rats even in morphine-induced ventilatory depression. The potency of 5-HT(1A)-R-agonists to stimulate spontaneous breathing and their antinociceptive effects should be researched further.

A cardiovascular monitoring system used in conscious cynomolgus monkeys for regulatory safety pharmacology: Part 2: Pharmacological validation

INTRODUCTION

This project addresses the validation study design of a test system using a telemetered non-human primate model for cardiovascular safety pharmacology evaluation.

METHODS

In addition to non-pharmacological validation including installation and operation qualifications, performance qualification (locomotor activity and cardiovascular evaluations) was completed on free-moving cynomolgus monkeys by quantifying the degree of cardiovascular response measured by the telemetric device to various positive control drugs following their intravenous administration. Remifentanil (0.0005, 0.001, 0.002, 0.004, 0.008 and 0.016 mg/kg) was given to induce bradycardia and hypotension. Medetomidine (0.04 mg/kg) was used to induce an initial phase of hypertension followed by hypotension and bradycardia. Esmolol (0.5, 1.0 and 2.0 mg/kg) was used to induce bradycardia. Dopamine (0.002, 0.008, 0.01, 0.02, 0.03 and 0.05 mg/kg/min) was infused over 30 min to induce an increase in arterial and pulse pressures and tachycardia. Amiodarone (0.4, 0.8 and 1.6 mg/kg/min) was infused over 10 min to induce QT interval prolongation. Potassium chloride (0.08 mEq/kg/min) was infused for periods of less than 30 min to induce electrocardiographic (EKG) changes characteristic of hyperkalemia. Reliability was evaluated over 60 days.

RESULTS

Monitoring with a reference methodology and the telemetry system was important in order to evaluate precision and accuracy of the test system. Positive control drugs produced a wide range of cardiovascular effects with different amplitudes, which were useful in identification of the limits of the test system.

DISCUSSION

Reference monitoring methods and selection of a battery of positive control drugs are important to ensure proper test system validation. Drugs inducing not only QT prolongation but also positive and negative chronotropic effects, positive and negative systemic arterial pressure changes and ECG morphology alterations were useful to identify test system limitations during performance qualification. ECG data processing at significantly elevated heart rates revealed that a trained observer should review all cardiac cycles evaluated by computer.

Microcirculatory alterations induced by sedation in intensive care patients. Effects of midazolam alone and in association with sufentanil

Introduction

Sedation is widely used in intensive care unit (ICU) patients to limit the risk of pulmonary barotrauma and to decrease oxygen needs. However, adverse effects of cc5128sedation have not been fully evaluated; in particular, effects of benzodiazepine and opiates on microcirculation have not been extensively studied. The aim of this study was to evaluate the microcirculatory effects of a sedation protocol commonly prescribed in the ICU.

Methods

Ten non-septic patients under controlled ventilation requiring sedation for therapeutic purposes were enrolled in a prospective observational study conducted in an ICU of a university hospital. Sedation was conducted in two successive steps: first, each patient received midazolam (0.1 mg/kg per hour after a bolus of 0.05 mg/kg, then adapted to reach a Ramsay score of between 3 and 5). Second, after one hour, sufentanil was added (0.1 μg/kg per hour after a bolus of 0.1 μg/kg). Arterial pressure, heart rate, cardiac output determined by transthoracic impedance, transcutaneous oxygen (tcPO₂) and carbon dioxide (tcPCO₂) pressures, and microcirculatory blood flow determined by laser Doppler flowmetry at rest and during a reactive hyperaemia challenge were measured before sedation (NS period), one hour after midazolam infusion (H period), and one hour after midazolam-sufentanil infusion (HS period).

Results

Arterial pressure decreased in both sedation periods, but heart rate, cardiac output, tcPO₂, and tcPCO₂ remained unchanged. In both sedation periods, microcirculatory changes occurred with an increase in cutaneous blood flow at rest (H period: 207 ± 25 perfusion units [PU] and HS period: 205 ± 25 PU versus NS period: 150 ± 22 PU, p < 0.05), decreased response to ischaemia (variation of blood flow to peak: H period: 97 ± 16 PU and HS period: 73 ± 9 PU versus NS period: 141 ± 14 PU, p < 0.05), and attenuation of vasomotion.

Conclusion

Sedation with midazolam or a combination of midazolam and sufentanil induces a deterioration of vasomotion and microvascular response to ischaemia, raising the question of whether this effect may further alter tissue perfusion when already compromised, as in septic patients.

Remifentanil-induced mechanical responses and membrane potential changes in human umbilical arteries

BACKGROUND

The aim of this study was to evaluate the characteristic features of the mechanical responses and membrane potential changes induced by remifentanil in human umbilical arteries (HUAs). The ionic mechanisms underlying the electrophysiological responses were pharmacologically assessed using two K(+) channel blockers.

METHODS

Thirty-eight HUAs were obtained. Contraction-relaxation, membrane potential changes and electrical responses of the HUAs were recorded.

RESULTS

Remifentanil produced concentration-dependent relaxation in both endothelium-intact and endothelium-denuded HUA rings. Remifentanil produced a significantly greater relaxation response in intact than in denuded HUA rings. In endothelium-intact rings, pre-treatment with L-nitroarginine [N(w)-NITRO-(L)-ARGININE (L-NO-ARG)] or indomethacin decreased the degree of remifentanil-induced relaxation. Remifentanil (10(-9)-10(-6) mol/l) produced a transient concentration-dependent membrane hyperpolarization, which was not decreased by pre-treatment with L-NO-ARG or indomethacin. It also produced a small concentration-dependent hyperpolarization in the presence of charybdotoxin or tetraethylammonium.

CONCLUSION

In both endothelium-intact and endothelium-denuded HUAs, remifentanil induces concentration-dependent vasorelaxation and simultaneously releases nitric oxide, prostaglandins and possibly an endothelium-derived hyperpolarizing factor. In addition, it produces hyperpolarization in a dose-dependent manner. Hyperpolarization induced by remifentanil involves the activation of Ca(2+)-dependent and Ca(2+)-independent potassium channels regulated by intracellular Ca(2+).

Alfentanil attenuates phenylephrine-induced contraction in rat aorta

BACKGROUND AND OBJECTIVES

Alfentanil was reported to relax the rat aorta by direct action on the vascular smooth muscle. The aims of this in vitro study were to examine the effect of alfentanil on phenylephrine-induced contractions in the rat aorta and to determine the cellular mechanism associated with this process.

METHODS

Endothelium-denuded aortic rings were suspended in order to record isometric tension. In the rings with or without 10(-6) mol naloxone or 10(-5) mol verapamil, the concentration-response curves for phenylephrine and potassium chloride were generated in the presence or absence of alfentanil (10(-6), 5 x 10(-5), 10(-4) mol). In the rings exposed to a calcium-free isotonic depolarizing solution, the contractile response induced by the addition of calcium was assessed in the presence or absence of alfentanil (5 x 10(-5), 10(-4) mol).

RESULTS

Alfentanil (5 x 10(-5), 10(-4) mol) attenuated (P < 0.05) the phenylephrine-induced contraction in the ring with or without 10(-6) mol naloxone but had no effect on the phenylephrine-induced contraction in the rings pretreated with verapamil. Alfentanil (5 x 10(-5), 10(-4) mol) produced a significant rightward shift (P < 0.01) in the potassium chloride dose-response curve, and attenuated the contractile response (P < 0.001) induced by calcium in the calcium-free isotonic depolarizing solution in a dose-dependent manner.

CONCLUSIONS

A supraclinical dose of alfentanil attenuates the phenylephrine-induced contraction via an inhibitory effect on calcium influx by blocking the l-type calcium channels in the rat aortic vascular smooth muscle.

Vasorelaxant effect of opioid analgesics on the isolated human radial artery

BACKGROUND AND OBJECTIVE

Arterial grafts are prone to vasospasm. Opioid analgesics are commonly used in the perioperative course of cardiac surgical procedures. Therefore, we investigated the direct effects of morphine, meperidine, fentanyl and remifentanil on the human radial artery.

METHODS

Radial artery segments, obtained from 20 patients, were precontracted with phenylephrine. Using the organ bath technique, the endothelium-independent vasodilatation was tested in vitro by addition of cumulative concentrations of morphine, meperidine, fentanyl and remifentanil in separate organ baths, in the presence or absence of naloxone. Indomethacin and NG-nitro-L-arginine methyl ester was added to all organ bath in order to determine the effects of prostaglandins and nitric oxide, respectively.

RESULTS

Morphine (10(-8) - 10(-4) mol L-1), meperidine (10(-10) - 10(-6) mol L-1), fentanyl (10(-10) - 10(-6) mol L-1) and remifentanil (10(-8) - 10(-4) mol L-1) caused a concentration-dependent vasorelaxation in the human being artery rings. The relaxations in the presence of naloxane did not change. The maximal relaxant effects of meperidine and fentanyl were significantly greater than those of morphine and remifentanil (P < 0.05).

CONCLUSIONS

These findings indicate that morphine, meperidine, fentanyl and remifentanil produce concentration-dependent and endothelium-independent relaxations in human being radial artery rings. Meperidine and fentanyl are more potent relaxant agents than morphine and remifentanil in the human being radial artery in vitro.

Vasodilation from Sufentanil in Humans

Sufentanil is a potent opioid that occasionally has been associated with hypotension. The mechanism behind this hypotension is unclear. We hypothesized that sufentanil had a direct effect on vascular smooth muscle to cause vasodilation. Sufentanil was infused into the brachial artery of 10 young, healthy volunteers at rates of 0.083, 0.167, 0.333, and 0.833 microg/min. Forearm blood flow was measured in both the experimental and control arms with venous occlusion plethysmography. The forearm blood flow in the infused arm increased in a dose-dependent fashion from 3.2 to 5.2 mL/min per 100 mL of tissue whereas simultaneous measurements in the control (non-infused) arm did not increase. Heart rate and mean arterial blood pressure were unchanged during the infusions. Furthermore, respiratory rate did not change at any infusion level and sedation did not occur. Thus, the data support that significant systemic "spillover" of sufentanil did not occur. We conclude that sufentanil has a direct, vasodilatory effect on human vascular tissue that is likely independent of a neurogenic or systemic mechanism.

The mechanisms of the direct vascular effects of fentanyl on isolated human saphenous veins in vitro

OBJECTIVE

The purpose of this study was to determine the mechanism of the direct effects of fentanyl on human veins in vitro.

DESIGN

In vitro, prospective with repeated measures.

SETTING

University research laboratory.

INTERVENTIONS

Dose-response curves were obtained for cumulative doses of fentanyl (10(-9)-10(-5) mol/L) on saphenous vein strips precontracted with (10(-6) mol/L) 5-hydroxytryptamine incubated with either naloxone (10(-4) mol/L), Nomega-nitroL-arginine-methyl ester (L-NAME) (10(-4) mol/L), indomethacin (10(-5) mol/L), glibenclamide (10(-4) mol/L), tetraethylammonium (10(-4) mol/L), or ouabain (10(-5) mol/L). Vein strips were also exposed to a Ca++-free solution and 0.1 mmol/L of ethylene glycol-bis-(b-aminoethylether) N,N'-tetraacetic acid; 5-hydroxytryptamine (10(-6) mol/L) was added to the bath before cumulative Ca++ (10(-4)-10(-2) mol/L). The same procedure was repeated in the presence of fentanyl (10(-6) , 3 x 10(-6) , or 10(-5) mol/L) (p < 0.05 = significant).

MEASUREMENTS AND MAIN RESULTS

Preincubation of vein strips with naloxone, L-NAME, or indomethacin did not influence the relaxant responses to fentanyl (p > 0.05). Tetraethylammonium, glibenclamide, and ouabain reduced the relaxation response to fentanyl (p < 0.05). A stepwise increase in tension was recorded with cumulative doses of Ca++ (p < 0.05).

CONCLUSIONS

The present results show that fentanyl causes vasodilatation via both endothelium- and opioid receptor-independent mechanisms in the human saphenous vein. The relaxant effects of fentanyl are probably via activation of K+ channel and Na+K+-adenosine trisphosphatase and inhibition of Ca++ channel.

Cardiorespiratory effects of epidural administration of morphine and fentanyl in dogs anesthetized with sevoflurane

OBJECTIVE

To determine the cardiorespiratory effects of epidural administration of morphine alone and in combination with fentanyl in dogs anesthetized with sevoflurane.

DESIGN

Prospective study.

ANIMALS

6 dogs.

PROCEDURE

Dogs were anesthetized with sevoflurane and allowed to breathe spontaneously. After a stable plane of anesthesia was achieved, morphine (0.1 mg/kg [0.045 mg/lb]) or a combination of morphine and fentanyl (10 microg/kg [4.5 microg/lb]) was administered through an epidural catheter, the tip of which was positioned at the level of L6 or L7. Cardiorespiratory variables were measured for 90 minutes.

RESULTS

Epidural administration of morphine alone did not cause any significant changes in cardiorespiratory measurements. However, epidural administration of morphine and fentanyl induced significant decreases in diastolic and mean arterial blood pressures and total peripheral resistance. Stroke volume was unchanged, PaCO2 was significantly increased, and arterial pH and base excess were significantly decreased. Heart rate was significantly lower after epidural administration of morphine and fentanyl than after administration of morphine alone. None of the dogs had any evidence of urine retention, vomiting, or pruritus after recovery from anesthesia.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that epidural administration of morphine at a dose of 0.1 mg/kg in combination with fentanyl at a dose of 10 microg/kg can cause cardiorespiratory depression in dogs anesthetized with sevoflurane.

Effects of General Anesthetics on Regulation of the Peripheral Vasculature

The heart is a passively filling pump in a circulatory system that is connected in series with distensible blood vessels. Therefore, systemic blood pressure and tissue perfusion depend upon adequate peripheral vascular tone as well as myocardial function. Likewise, pharmacologic agents that alter circulatory stability can affect one or both of these components. The generalized depressor effects of general anesthetics have been well known clinically for over 50 years. Moreover, there are many similarities in basic cellular regulatory mechanisms among the different tissue types, and general anesthetics are well known to distribute freely among the perfusion-rich tissues (eg, central nervous system, cardiovascular system, and renal system). Therefore, it is likely that the hemodynamic depression resulting from the systemic administration of anesthetics results from actions on regulatory mechanisms of the peripheral vasculature as well as on the heart. The peripheral vasculature is regulated by extrinsic neural, endothelial, and humoral mechanisms, which interact with each other as well as with intrinsic membrane and intracellular systems within the vascular smooth muscle cell. Different general anesthetics have been found to act on specific mechanisms at each of these levels. However, the large number and complexity of these known mechanisms, as well as the many anesthetic agents, has made it extremely difficult to determine which are significant in terms of the meaningful mechanisms that are responsible for anesthetic action, major side effects, or both. Current knowledge about the effects of general anesthetics on both the extrinsic intrinsic regulatory mechanisms of peripheral vascular control is reviewed.

The in vitro effects of remifentanil and fentanyl on isolated human right atria and saphenous veins

OBJECTIVE

To determine the myocardial and vascular effects of remifentanil and fentanyl in human atria and saphenous veins.

DESIGN

In vitro, prospective with repeated measures.

SETTING

University research laboratory.

INTERVENTIONS

The direct effects of remifentanil and fentanyl on the electrical stimulation-induced contraction of nonfailing human atrium and saphenous veins contracted with 5-hydroxytryptamine were studied.

MEASUREMENTS AND MAIN RESULTS

In human atrial trabeculae, cumulative (10(-9)-10(-5) mol/L) added remifentanil had no effect on contractile force, compared with untreated muscles (p > 0.05). The force of contraction was significantly less than control values with concentrations of fentanyl ranging from 10(-8) to 10(-5) mol/L (p < 0.05). At the highest concentration (10(-5) mol/L), the inhibition by fentanyl of the electrical stimulation-induced contraction was 40.6% +/- 6.32%. In human saphenous vein strips preconstricted with 5-hydroxytryptamine, remifentanil (10(-8)-10(-5) mol/L) and fentanyl (10(-8)-10(-5) mol/L) produced "concentration-dependent" relaxation when compared with the control contraction value (p < 0.05). The IC(50) was similar with remifentanil and fentanyl and the E(max) of fentanyl was significantly higher than remifentanil (p < 0.05). The venodilatory effects of remifentanil and fentanyl were similar on veins with or without endothelium (p > 0.05).

CONCLUSIONS

Remifentanil has no direct effect on the contraction of myocardium. Fentanyl inhibits the electrical stimulation-induced contraction in human right atrial muscles in vitro. Remifentanil and fentanyl produce "concentration-dependent" relaxation in human saphenous vein strips independent from the endothelium.

Sympathetic and vascular consequences from remifentanil in humans

We explored the possible mechanisms of hypotension during the administration of sedation-analgesia doses of remifentanil in young (ASA physical status I) volunteers (n = 24). Cardiorespiratory and sympathetic variables were collected at baseline and at plasma concentrations of remifentanil (2 and 4 ng/mL). Monitoring included electrocardiogram, heart rate (HR), direct blood pressure, muscle sympathetic nerve activity, and forearm blood flow (FBF). A cold pressor test (1-min hand immersion in ice water) quantified analgesia effectiveness (visual analog scale, 0-100). Visual analog scale to the cold pressor test (62 at baseline) decreased to 27 and 18 during remifentanil infusions. Respiratory rate decreased and end-tidal carbon dioxide (ETCO(2)) increased with increasing doses of remifentanil; HR, direct blood pressure, muscle sympathetic nerve activity, SpO(2) remained unchanged, but FBF increased compared with placebo. In a second study (n = 7), timed respiration was used to maintain ETCO(2) during remifentanil, but FBF still increased. In a third study (n = 11), direct effects of remifentanil on vascular tone were determined with progressive infusions from 1 to 100 micro g/h into the brachial artery; FBF increased significantly from 3.5 to 4.3 mL/min per 100 mL of tissue (approximately 13%-18% increase). Sedative doses of remifentanil resulted in analgesia but no changes in neurocirculatory end-points except FBF. Direct effects of remifentanil on regional vascular tone may play a role in promoting hypotension.

IMPLICATIONS

Remifentanil occasionally has been associated with hypotension, the mechanism of which is unclear. This study found that remifentanil directly causes the forearm arterial vasculature to dilate.

The dose-dependent effects of fentanyl on rat skeletal muscle microcirculation in vivo

Determining the effects of analgesia on the microcirculation is difficult because the surgery needed to allow in vivo observation often requires anesthesia. In this study, we used the dorsal microcirculatory chamber (DMC) to determine the effects of large (LF) and small (SF) dose IV fentanyl on the microcirculation compared with a conscious control. Male Wistar rats (130 g, n = 5) were implanted with the DMC to enclose a single layer of striated muscle. Animals were allowed 3 wk to recover from surgery and then, over the following 2 wk (1 infusion/wk) using intravital microscopy, the microcirculation was viewed in conscious animals (t = 0-30 min), followed by an induction bolus dose (t = 40-45 min), then a "step-up" maintenance infusion of one of the following, LF (40-90 microg x kg(-1) x h(-1)), SF (10-60 microg x kg(-1) x h(-1)), or saline (5-10 microg x kg(-1) x h(-1)) (t = 45-105 min). Small arterioles (<30 micro m) dilated (23.6% +/- 7.1%) after induction with LF, but constricted (-21.3% +/- 7.1%) with SF (P < 0.05). During maintenance, constriction increased with increasing dose of LF (-21.9% +/- 4.0%) and SF (-16.7% +/- 9.1%) (t = 105 min, P < 0.05). Similar patterns were observed in all arterioles (10-120 microm) and venules (15-250 microm). We conclude that the DMC provides an excellent technique for observing microcirculatory responses to fentanyl, and in rat skeletal muscle in vivo, an i.v. infusion of fentanyl produces significant constriction of arterioles.

Remifentanil produces vasorelaxation in isolated rat thoracic aorta strips

BACKGROUND

Remifentanil can cause transient instability in hemodynamic variables. However this change may not be solely the result of autonomic or central nervous system inhibition or of centrally mediated vagal stimulation. In this study, the aim was to examine the direct effects of remifentanil on isolated thoracic aorta strips in vitro.

METHODS

Forty-five Wistar rat thoracic aorta rings were isolated, and contraction-relaxation responses were recorded.

RESULTS

In aortic rings precontracted with phenylephrine or potassium chloride, remifentanil produced concentration-dependent relaxation in both endothelium-intact and denuded rings (P<0.001). Remifentanil induced significantly greater relaxation in intact rings than in those denuded of endothelium, regardless of whether they were precontracted with phenylephrine hydrochloride or KCl (P<0.001). When the endothelium was present, remifentanil produced greater relaxation in KCl-contracted rings than in PE-contracted rings at lower concentrations (10-9 and 10-8), and similar relaxation at higher concentrations (10-7 and 10-6). However, when the endothelium was removed, relaxation was similar in both solutions, at all concentrations (10-9 to 10-6). In intact rings, pretreatment with L-NO-ARG or indomethacin reduced the degree of remifentanil-induced relaxation. In Ca+ +/- free media, calcium-dependent KCl contractions were inhibited in a dose-dependent manner by remifentanil (P<0.001).

CONCLUSION

Remifentanil vasodilates by an endothelium-dependent mechanism, involving prostacyclin and nitric oxide released from the endothelium. Its endothelium-independent vasodilation probably occurs via the suppression of voltage-sensitive Ca++ channels.

Influence of opioids on the vascular tone of isolated porcine coronary artery segments

BACKGROUND

It was the aim of this study to elucidate the influence of opioids on coronary vascular tone using the model of isolated porcine coronary artery segments.

METHODS

We studied the effects of fentanyl (0.01, 0.1, 1.0 microg ml(-1)), alfentanil (0.1, 1.0, 10 microg ml(-1)), and sufentanil (0.01, 0.1, 1.0 microg ml(-1)) on the contractile response to three vasoconstrictors, acetylcholine, histamine and serotonin.

RESULTS

Fentanyl (0.1, 1.0 microg x ml(-1)) dose-dependently attenuated the contractile response to acetylcholine, but not to histamine and serotonin. There were no differences in fentanyl's vasorelaxing potency between rings with intact and denuded endothelium. Alfentanil and sufentanil did not exert any significant influence on any of the vasoconstrictors tested.

CONCLUSION

It is concluded that, in isolated porcine coronary artery rings, fentanyl at high concentrations has an attenuating effect on acetylcholine-induced contractions, which is independent of endothelial function, whereas alfentanil and sufentanil do not influence coronary vascular tone.

Sufentanil, fentanyl, and alfentanil in head trauma patients: a study on cerebral hemodynamics

OBJECTIVES

To determine the effects of bolus injection and infusion of sufentanil, alfentanil, and fentanyl on cerebral hemodynamics and electroencephalogram activity in patients with increased intracranial pressure (ICP) after severe head trauma.

DESIGN

Randomized, unblended, crossover study.

SETTING

Intensive care unit and trauma center in a university hospital.

PATIENTS

Six patients with head trauma and ICP monitoring, sedated at the time of the study with propofol infusion and full neuromuscular blockade.

INTERVENTIONS

Following a randomized order, in an unblended and crossover fashion, the level of sedation was deepened with a 6-min injection of either sufentanil (1 microg/kg), alfentanil (100 microg/kg), or fentanyl (10 microg/kg) followed by an infusion of 0.005, 0.7, and 0.075 microg/kg/min, respectively, for 1 hr. The three opioids were given to each patient at 24-hr intervals.

MEASUREMENTS AND MAIN RESULTS

Mean arterial pressure (MAP), ICP, cerebral perfusion pressure (CPP), and jugular vein bulb oxygen saturation (Svjo2) were continuously measured and recorded at 1-min intervals throughout the 60-min study period. Sufentanil, fentanyl, and alfentanil infusions were associated with a significant but transient increase in ICP (9+/-2 mm Hg [SD], 8+/-2 mm Hg, and 5.5+/-1 mm Hg, respectively; p<.05). The increase in ICP peaked at 5, 6, and 3 mins, respectively, then gradually decreased and returned to baseline values after 15 mins. This result was accompanied by a significant decrease in MAP (21+/-2 mm Hg, 24+/-2 mm Hg, and 26+/-2 mm Hg, respectively; p<.05) and, thus, in CPP (30+/-3 mm Hg, 31+/-3 mm Hg, and 34+/-3 mm Hg, respectively; p<.05). After 5 mins, MAP and CPP gradually increased, although they remained significantly decreased throughout the study period. No changes in lactate-oxygen index, used as an ischemia index, were observed. Changes in electroencephalogram tracings were characterized by a switch from a fast to a decreased activity, together with an improvement in the background activity.

CONCLUSION

The results of the present study show that alfentanil, sufentanil, and fentanyl produce similar transient increases in ICP when administered by bolus injection in patients with increased ICP. No evidence of cerebral ischemia was observed in the study patients.

Cardiac function in patients with treated hypertension during aortic aneurysm repair

OBJECTIVES

To investigate the impact of arterial hypertension on cardiac function during aortic cross-clamping and declamping.

DESIGN

Prospective study.

SETTING

University hospital.

PARTICIPANTS

Twenty treated hypertensive males with slight left ventricular hypertrophy and 10 normotensive controls undergoing elective repair of an abdominal aortic aneurysm.

INTERVENTIONS

Using transesophageal echocardiography, the mitral inflow profile was evaluated during aortic cross-clamping and declamping.

MEASUREMENTS AND MAIN RESULTS

During the clamping period, the ratio of peak atrial to peak early filling velocity (PA/PE) was significantly higher in the hypertensive patients. One minute after aortic cross-clamping, mean arterial pressure (MAP) and pulmonary artery occlusion pressure significantly increased in the hypertensive patients, whereas they did not change in the normotensive group. Cardiac index and heart rate significantly decreased after cross-clamping, and increased after clamp release in both groups. PA/PE significantly dropped in both groups after aortic declamping, and returned to baseline values thereafter. MAP also decreased significantly in both groups after clamp release, but the fall of MAP tended to be more pronounced in the hypertensive patients.

CONCLUSIONS

In the treated hypertensive patients, more pronounced hemodynamic and echocardiographic responses to aortic cross-clamping probably mirror the altered diastolic left ventricular function in these patients. With respect to intraoperative management, however, the treated hypertensive patients did not react grossly differently from the normotensive controls.

Phosphatidylinositol responses are involved in the vascular effects of thiamylal and fentanyl

Although thiobarbiturates potentiate, and fentanyl attenuates peripheral vasoconstriction, the intracellular mechanism involved in this phenomenon is not clear. Because smooth muscle contraction induced by alpha 1-adrenoceptor agonists is mediated by the phosphatidylinositol (PI) response, this study was carried out to clarify if thiamylal and fentanyl affect the norepinephrine-induced PI response in rat aortic slices. Rat aortic slices were incubated in Krebs-Henseleit solution containing 5 mM LiCl, [3H]myo-inositol, and varying concentrations of thiamylal or fentanyl. The Pl response was stimulated by 0.9 microM (ED50) norepinephrine (NE). The [3H]inositol monophosphate (IP1) was separated from [3H]myo-inositol by column chromatography and counted with a liquid scintillation counter. The basal IP1 accumulation was not affected by thiamylal and fentanyl. Norepinephrine-induced IP1 accumulation was potentiated by thiamylal at concentrations of 10 microM and 100 microM. Norepinephrine-induced IP1 accumulation was attenuated by 1 microM and 10 microM fentanyl. The results suggest that thiamylal stimulates the NE-induced PI response, which potentiates the vasoconstriction, and fentanyl attenuates NE-induced PI response, which would attenuate the vasoconstriction.

Direct effects of fentanyl on canine coronary artery rings

The potent opioid fentanyl, is commonly used as a general anesthetic for coronary artery bypass surgery. Experiments were designed to determine the direct effects of fentanyl on unstimulated coronary artery tissue. Isolated, endothelium denuded canine epicardial rings were suspended in physiologic tissue baths. Changes in tension were measured as the concentration of fentanyl was increased. Fentanyl caused increases in ring tension at concentrations of 10(-6)M-10(-4)M, then caused a decrease in tension at 10(-3) M. Calcium channel blockade by 10(-7)M nifedipine abolished all increases in contractile responses to fentanyl and prevented the relaxation in tension produced by fentanyl. The fentanyl dose-response curve was unchanged by opioid receptor blockade with 10(-6)M naloxone and by alpha and beta adrenoceptor blockade produced by 10(-6)M prazosin and 10(-6)M propranolol. Muscarinic blockade with 10(-6)M atropine and cyclooxygenase inhibition by 10(-6)M indomethacin attenuated the constrictor response to fentanyl. The opioids alfentanil, sufentanil, morphine, and naloxone all produced a dose-response similar to fentanyl that varied only in amplitude. These findings indicate that increasing concentration of the anesthetic opioid fentanyl can cause biphasic changes in basal canine epicardial coronary artery ring tension. These responses are calcium dependent and may be characteristics of other opioid agonists and antagonists.

Efficacy of epidurally administered sufentanil versus bupivacaine during thoracic surgery. A randomised placebo-controlled double-blind study

The efficacy of thoracic epidural sufentanil 50 micrograms was compared with bupivacaine 0.5% with adrenaline 5 micrograms.ml-1 (dose 40 mg) or saline, in 30 patients (n = 10 in each group) undergoing lateral thoracotomy. Sufentanil, bupivacaine or saline was administered epidurally after induction of anaesthesia with sufentanil 1 microgram.kg-1 and thiopentone 2-5 mg.kg-1. Anaesthesia was maintained with nitrous oxide 66% and halothane 0.3%. Supplementary sufentanil 25 micrograms was given whenever the systolic arterial blood pressure increased more than 15 mmHg above the pre-operative value, whenever heart rate exceeded 90 beat.min-1 in the absence of hypovolaemia, or when other autonomic or somatic signs occurred. Fewer patients in the epidural sufentanil (n = 4, p < 0.005) and bupivacaine (n = 1, p < 0.001) groups required supplementary sufentanil compared to the placebo group, in which all patients needed supplementary sufentanil, but there was no statistical difference between the sufentanil and bupivacaine groups. One or more hypotensive episodes occurred in five patients in the sufentanil group, in all patients in the bupivacaine group and in no patient in the placebo group, and the differences were significant (p < 0.02).

Fentanyl-prilocaine mixture for intravenous regional anaesthesia in patients undergoing surgery

The effect of the addition of 0.1 mg or 0.2 mg fentanyl to 40 ml 0.5% prilocaine in intravenous regional anaesthesia of the arm was investigated in 37 patients in a randomised, double-blind study. The characteristics of the sensory and motor block were studied. There was no difference in the speed of onset of analgesia in the groups (mean latency approximately 4 min in each group). However, significantly more patients in the fentanyl 0.2 mg group (7/12) had complete anaesthesia at 15 min than in the fentanyl 0.1 mg group (1/13) and the control group (2/12) (p less than 0.05). There were no differences in the incidence of tourniquet pain immediately before cuff deflation (tourniquet time 45-87 min). After cuff deflation, in those patients who complained of wound pain within 30 min, on average the pain appeared later in the fentanyl 0.2 mg group (six patients, mean 14.3 min) than in the control group (eight patients, mean 9.4 min) (ns). In the fentanyl groups, the incidence of central nervous system side effects was greater than in the control group (fentanyl 0.1 mg 7/13 patients, fentanyl 0.2 mg 6/12 patients, control 1/12 patients) (p less than 0.05). The plasma concentrations of prilocaine after cuff deflation were higher, in a dose-dependent fashion, in the fentanyl groups than in the control group, but the concentrations of prilocaine and fentanyl did not correlate with the symptoms. Postoperative nausea occurred only in the patients who had received fentanyl.

Effects of sodium pentothal and sufentanil on serotonin induced constriction of canine coronary artery rings without endothelium

1. The individual and combined effects of sufentanil and sodium pentothal on canine coronary artery vasomotor responses to 5-HT were studied in an isolated vascular ring preparation. 2. Clinical concentrations of sufentanil have little effect on basal coronary tension or constriction induced by either 5-HT or sodium pentothal individually, until very high doses greater than 0.26 microM are reached. 3. Sodium pentothal causes coronary constriction at clinical concentrations and this effect is additive and possibly potentiated when combined with 5-HT. 4. Sufentanil inhibits coronary constriction induced by the combination of sodium pentothal and 5-HT.