Measured context-sensitive half-times of remifentanil and alfentanil

Adverse Events Associated with Sedatives, Analgesics, and Other Drugs That Provide Patient Comfort in the Intensive Care Unit

Since the 2002 publication of multidisciplinary clinical practice guidelines for intensive care unit (ICU) sedation and analgesia, additional information regarding adverse drug events has been reported. Our understanding of the risks associated with these sedative and analgesic agents promises to improve outcomes by helping clinicians identify and respond to therapeutic misadventures sooner. This review focuses on many issues, including the potentially fatal consequences associated with the propofol infusion syndrome, the evolving understanding of propylene glycol intoxication associated with parenteral lorazepam, new data involving high-dose and long-term dexmedetomidine therapy, haloperidol- and methadone-related prolongation of QTc intervals on the electrocardiogram, adverse events associated with atypical antipsychotics, and the potential for nonsteroidal antiinflammatory drugs to interfere with bone healing.

Rémifentanil-midazolam versus sufentanil-midazolam pour la sédation prolongée en réanimation

OBJECTIVE

Remifentanil has a unique metabolic pathway that holds potential benefits for long-term sedation. We compared remifentanil-midazolam to sufentanil-midazolam in 41 critically ill adults requiring mechanical ventilation.

STUDY DESIGN

Randomized double-blind trial.

PATIENTS AND METHODS

Infusion rates were titrated every 4 hours to achieve the desired Ramsay score. Five fold increases in dose requirement was considered as the development of tolerance. Drugs requirement, development of tolerance and weaning time of ventilation were compared.

RESULTS

The study was stopped after an interim analysis. The remifentanil and sufentanil groups were comparable regarding IGS II: 56+/-22 vs 64+/-26, mean+/-SD, ICU length of stay: 26 (8-45) vs 19 (11-34) days, and sedation duration: 6 (4-19) vs 6 (3-16)days, median [interquartile range, IQR]). There was a shorter weaning time in the remifentanil group as compared to sufentanil group: 22 h (12-53) vs 96 (47-142) h, median [IQR], p=0.04). The daily opioid infusion rate needed to be decreased over time only in sufentanil group, p < 0.001. Tolerance occurred in 6 (30%; CI(95), 10 to 40%) remifentanil and no sufentanil patients (P=0.02).

CONCLUSION

Sufentanil infusion needed to be reduced over time and prolonged the weaning time when compared to remifentanil.

Decreased duration of mechanical ventilation when comparing analgesia-based sedation using remifentanil with standard hypnotic-based sedation for up to 10 days in intensive care unit patients: a randomised trial [ISRCTN47583497]

INTRODUCTION

This randomised, open-label, multicentre study compared the safety and efficacy of an analgesia-based sedation regime using remifentanil with a conventional hypnotic-based sedation regime in critically ill patients requiring prolonged mechanical ventilation for up to 10 days.

METHODS

One hundred and five randomised patients received either a remifentanil-based sedation regime (initial dose 6 to 9 microg kg(-1) h(-1) (0.1 to 0.15 microg kg(-1) min(-1)) titrated to response before the addition of midazolam for further sedation (n = 57), or a midazolam-based sedation regime with fentanyl or morphine added for analgesia (n = 48). Patients were sedated to an optimal Sedation-Agitation Scale (SAS) score of 3 or 4 and a pain intensity (PI) score of 1 or 2.

RESULTS

The remifentanil-based sedation regime significantly reduced the duration of mechanical ventilation by more than 2 days (53.5 hours, P = 0.033), and significantly reduced the time from the start of the weaning process to extubation by more than 1 day (26.6 hours, P < 0.001). There was a trend towards shortening the stay in the intensive care unit (ICU) by 1 day. The median time of optimal SAS and PI was the same in both groups. There was a significant difference in the median time to offset of pharmacodynamic effects when discontinuing study medication in patients not extubated at 10 days (remifentanil 0.250 hour, comparator 1.167 hours; P < 0.001). Of the patients treated with remifentanil, 26% did not receive any midazolam during the study. In those patients that did receive midazolam, the use of remifentanil considerably reduced the total dose of midazolam required. Between days 3 and 10 the weighted mean infusion rate of remifentanil remained constant with no evidence of accumulation or of a development of tolerance to remifentanil. There was no difference between the groups in SAS or PI score in the 24 hours after stopping the study medication. Remifentanil was well tolerated.

CONCLUSION

Analgesia-based sedation with remifentanil was well tolerated; it reduces the duration of mechanical ventilation and improves the weaning process compared with standard hypnotic-based sedation regimes in ICU patients requiring long-term ventilation for up to 10 days.

General anesthesia with remifentanil for Cesarean section in a patient with HELLP syndrome

HELLP syndrome is a severe complication of pre-eclampsia characterised by hemolysis, elevated liver enzymes and a low platelet count. It is associated with an increased risk of adverse outcome for both the mother and the fetus. Patients with HELLP syndrome are also at greater risk of pulmonary edema, adult respiratory distress syndrome, abruptio placentae, intracerebral hemorrhage, eclamptic convulsions, disseminated intravascular coagulation, ruptured liver hematomas and acute renal failure. Perinatal mortality is equally high. Before delivery, aggressive obstetric management is directed toward stabilization of the affected organ systems, if possible, and interruption of the pregnancy in the early phase of the accelerated disease progression. Definitive therapy is delivery. Parturients HELLP syndrome often require general anesthesia for Cesarean section delivery. The anesthetic technique is critical for these patients with a high risk of uncontrollable hypertension, bleeding and multiple organ failure. Remifentanil is increasingly used as a very short analgesic agent providing cardiovascular stability in high-risk patients. We report the management of a patient presenting in labor with HELLP syndrome, and describe the successful use of remifentanil as part of the anesthetic technique for her subsequent Cesarean section.

Spontaneous ventilation with remifentanil in children

BACKGROUND

Remifentanil is a short-acting drug that allows us to study the specific respiratory effects of potent opioid analgesics. The purpose of this study is to describe the effects of a remifentanil infusion during spontaneous ventilation in children. Pharmacokinetic studies provide useful information on the time course of opioid blood concentrations; however, they cannot be easily translated into infusion administration guidelines for pediatric clinical practice.

METHODS

A total of 32 children, aged 2-7 years, undergoing restorative dentistry, spontaneously breathing under sevoflurane anesthesia were enrolled in the study. After an initial bolus dose of remifentanil, an infusion was administered in ascending logarithmic increments at 10 min intervals. Increments were discontinued when endtidal carbon dioxide exceeded 9 kPa (70 mmHg), desaturation occurred (SpO2 < 94%) or with the onset of apnea (>5 s). The maximum tolerated dose was determined for each subject. Endtidal carbon dioxide, minute ventilation and respiratory rate were continuously recorded.

RESULTS

The median tolerated dose of remifentanil was 0.127 microg.kg(-1).min(-1) (range: 0.053-0.3 microg.kg(-1).min(-1)). When comparing the last four incremental increases in each subject, 35% change in respiratory rate occurred in the last 10 min period while changes in endtidal carbon dioxide and minute ventilation were gradual and of less magnitude. There was no correlation between age and respiratory rate.

CONCLUSIONS

There is a large variation in the dose of remifentanil tolerated by children while breathing spontaneously under anesthesia. A respiratory rate of <10 b.min(-1) appears to be the best predictor of the maximum tolerated dose.

Remifentanil update: clinical science and utility

The anilidopiperidine opioid remifentanil has pharmacodynamic properties similar to all opioids; however, its pharmacokinetic characteristics are unique. Favourable pharmacokinetic properties, minimally altered by extremes of age or renal or hepatic dysfunction, enable easy titration and rapid dissipation of clinical effect of this agent, even after prolonged infusion. Remifentanil is metabolised by esterases that are widespread throughout the plasma, red blood cells, and interstitial tissues, whereas other anilidopiperidine opioids (e.g. fentanyl, alfentanil and sufentanil) depend upon hepatic biotransformation and renal excretion for elimination. Consequently, remifentanil is cleared considerably more rapidly than other anilidopiperidine opioids. In addition, its pKa (the pH at which the drug is 50% ionised) is less than physiological pH; thus, remifentanil circulates primarily in the non-ionised moiety, which quickly penetrates the lipid blood-brain barrier and rapidly equilibrates across the plasma/effect site interface. By virtue of these distinctive pharmacokinetic properties, the context-sensitive half-time (i.e. the time required for the drug's plasma concentration to decrease by 50% after cessation of an infusion) of remifentanil remains consistently short (3.2 minutes), even following an infusion of long duration (> or =8 hours). Remifentanil, a clinically versatile opioid, is useful for intravenous analgesia and sedation in spontaneously breathing patients undergoing painful procedures. Profound analgesia may be achieved with minimal effect on cognitive function. Remifentanil may also provide sedation and analgesia during placement of regional anaesthetic blocks, and in conjunction with topical anaesthesia and airway nerve blocks, it may be useful for blunting reflex responses and facilitating 'awake' fibreoptic intubation. Compared with fentanyl and alfentanil in a day-surgery setting, remifentanil supplementation of general anaesthesia may improve intraoperative haemodynamic control. Both emergence time and the incidence of respiratory depression during post-anaesthetic recovery may be reduced. However, outcomes such as home discharge time, post-emergence adverse effect profile, and patient and provider satisfaction are not significantly improved, and the incidence of intraoperative hypotension and bradycardia is greater. In addition, drug acquisition costs for remifentanil are higher and clinicians may need extra time to familiarise themselves with the drug's unique pharmacokinetics.Ironically, the quick dissipation of opioid analgesic effect following remifentanil discontinuation may be a significant clinical disadvantage. Unless little or no postoperative pain is anticipated, the clinician may wish to treat prospectively using local or regional anaesthesia, non-opioid analgesics, or longer-acting opioid analgesics.

The Use of Ultra-Short-Acting Opioids in Paediatric Anaesthesia

Remifentanil is a synthetic opioid that was developed in the early 1990s and introduced into clinical use in 1996. It is a methyl ester and is metabolised by nonspecific tissue and plasma esterases. Consequently, it is a drug that undergoes rapid elimination and has a reported terminal elimination half-life of between 10 and 35 minutes. Because there is no drug accumulation, the context-sensitive half-time remains constant; thus the pharmacokinetics of the drug do not change regardless of the duration of infusion. The organ-independent elimination of remifentanil, coupled with the fact that its clearance is greater in infants and neonates compared with older age groups, make its pharmacokinetic profile different from any other opioid. In addition, its unique metabolism confers predictability in its clinical use. Like other opioid mu receptor agonists, remifentanil provides dose-dependent analgesia, while the adverse effects of this drug, e.g. respiratory depression, are also thought to be dose related. The incidence of nausea and vomiting appear similar to other opioids. Its rapid and consistent metabolism regardless of duration of infusion has made remifentanil an attractive analgesic/anaesthetic option for paediatric care providers.

Remifentanil

Remifentanil (Ultiva), a fentanyl derivative, is an ultra-short acting, nonspecific esterase-metabolised, selective mu-opioid receptor agonist, with a pharmacodynamic profile typical of opioid analgesic agents. Notably, the esterase linkage in remifentanil results in a unique and favourable pharmacokinetic profile for this class of agent. Adjunctive intravenous remifentanil during general anaesthesia is an effective and generally well tolerated opioid analgesic in a broad spectrum of patients, including adults and paediatric patients, undergoing several types of surgical procedures in both the inpatient and outpatient setting. Remifentanil is efficacious in combination with intravenous or volatile hypnotic agents, with these regimens generally being at least as effective as fentanyl- or alfentanil-containing regimens in terms of attenuation of haemodynamic, autonomic and somatic intraoperative responses, and postoperative recovery parameters. The rapid offset of action and short context-sensitive half-time of remifentanil, irrespective of the duration of the infusion, makes the drug a valuable opioid analgesic option for use during balanced general inhalational or total intravenous anaesthesia (TIVA) where rapid, titratable, intense analgesia of variable duration, and a fast and predictable recovery are required.

[Clinical applications of intravenous anaesthetics pharmacology: the example of hypnotics and opioids]

OBJECTIVE

To review the general principles of pharmacokinetics and pharmacodynamics models by focusing on intravenous anaesthetics (hypnotics and opioids).

DATA SOURCES

Medline references, lectures from the French congress of anaesthesiology and intensive care medicine, abstracts.

DATA SYNTHESIS

Pharmacokinetic and pharmacodynamic modelling allows simple estimation of becoming of anaesthetic drugs in the body, instead of classical pharmacologic approach. However, pharmacokinetic as well as pharmacodynamic parameters are often considered as resulting from complex mathematic approaches and remain then poorly used in practice by physicians. The aim of this article is to simply expose concepts underlying PK-PD models building and to explain significance of the main PK-PD parameters (first-order rate constants, k(e0), T(1/2)k(e0), T(peak), context-sensitive half-time, context-sensitive decrement times). Clinical consequences for using intravenous anaesthetic drugs (hypnotics and opioids) are exposed either during bolus injection or continuous infusion, when injected alone or co-administered.

General anaesthesia using remifentanil for caesarean section in parturients with critical aortic stenosis: a series of four cases

Although heart disease is now the joint leading cause of maternal mortality in the UK, critical aortic stenosis is rarely encountered in parturients. Caesarean section is advisable in these patients to minimise the haemodynamic stress of labour and delivery. The use of an opioid-based general anaesthetic technique also helps to maintain cardiovascular stability. During a two-year period, four women with critical aortic stenosis requiring caesarean section presented to our institution. In all women, a rapid sequence induction of anaesthesia was performed using etomidate 0.1 to 0.2 mg.kg(-1), suxamethonium 1.5 mg.kg(-1) and remifentanil 2 to 4 micrograms.kg(-1). Anaesthesia was then maintained with isoflurane, nitrous oxide and a remifentanil infusion at 0.05 to 0.15 micrograms.kg(-1)min(-1). There was good haemodynamic stability throughout, except for a short period in one patient who became hypotensive after a significant post-partum haemorrhage secondary to uterine atony. All parturients were successfully extubated at the end of surgery and made excellent postoperative recoveries. Neonates were born in good condition with Apgar scores of 10, 9, 6 and 5 at 1 min and 10, 10, 10 and 10 at 5 min. We suggest that remifentanil is an ideal agent for parturients with severe aortic stenosis requiring general anaesthesia for caesarean section. Remifentanil provides cardiovascular stability in conjunction with rapid emergence from anaesthesia in the parturient and minimal side effects in the neonate.

Safety and efficacy of analgesia-based sedation with remifentanil versus standard hypnotic-based regimens in intensive care unit patients with brain injuries: a randomised, controlled trial [ISRCTN50308308]

Introduction

This randomised, open-label, observational, multicentre, parallel group study assessed the safety and efficacy of analgesia-based sedation using remifentanil in the neuro-intensive care unit.

Methods

Patients aged 18–80 years admitted to the intensive care unit within the previous 24 hours, with acute brain injury or after neurosurgery, intubated, expected to require mechanical ventilation for 1–5 days and requiring daily downward titration of sedation for assessment of neurological function were studied. Patients received one of two treatment regimens. Regimen one consisted of analgesia-based sedation, in which remifentanil (initial rate 9 μg kg^-1 h^-1) was titrated before the addition of a hypnotic agent (propofol [0.5 mg kg^-1 h^-1] during days 1–3, midazolam [0.03 mg kg^-1 h^-1] during days 4 and 5) (n = 84). Regimen two consisted of hypnotic-based sedation: hypnotic agent (propofol days 1–3; midazolam days 4 and 5) and fentanyl (n = 37) or morphine (n = 40) according to routine clinical practice. For each regimen, agents were titrated to achieve optimal sedation (Sedation–Agitation Scale score 1–3) and analgesia (Pain Intensity score 1–2).

Results

Overall, between-patient variability around the time of neurological assessment was statistically significantly smaller when using remifentanil (remifentanil 0.44 versus fentanyl 0.86 [P = 0.024] versus morphine 0.98 [P = 0.006]. Overall, mean neurological assessment times were significantly shorter when using remifentanil (remifentanil 0.41 hour versus fentanyl 0.71 hour [P = 0.001] versus morphine 0.82 hour [P < 0.001]). Patients receiving the remifentanil-based regimen were extubated significantly faster than those treated with morphine (1.0 hour versus 1.93 hour, P = 0.001) but there was no difference between remifentanil and fentanyl. Remifentanil was effective, well tolerated and provided comparable haemodynamic stability to that of the hypnotic-based regimen. Over three times as many users rated analgesia-based sedation with remifentanil as very good or excellent in facilitating assessment of neurological function compared with the hypnotic-based regimen.

Conclusions

Analgesia-based sedation with remifentanil permitted significantly faster and more predictable awakening for neurological assessment. Analgesia-based sedation with remifentanil was very effective, well tolerated and had a similar adverse event and haemodynamic profile to those of hypnotic-based regimens when used in critically ill neuro-intensive care unit patients for up to 5 days.

Comparison of bolus remifentanil versus bolus fentanyl for induction of anesthesia and tracheal intubation in patients with cardiac disease

OBJECTIVE

Large bolus-dose remifentanil may be advantageous for use during induction of anesthesia because of its short duration of effect. Currently, there are little data on the use of large bolus-dose remifentanil because of reports of severe bradycardia and hypotension. The purpose of this study is to compare the hemodynamic effects of bolus remifentanil versus fentanyl with glycopyrrolate for induction of anesthesia in patients with heart disease.

DESIGN

A randomized, double-blinded study.

SETTING

A tertiary-care academic medical center.

PARTICIPANTS

One hundred patients for coronary artery bypass or valvular surgery.

INTERVENTION

Subjects received either (1) remifentanil, 5 microg/kg, with glycopyrrolate, 0.2 mg, or (2) fentanyl, 20 microg/kg, with 0.2 mg of glycopyrrolate, and both groups also received midazolam, 70 microg/kg, for induction of anesthesia.

MEASUREMENTS AND MAIN RESULTS

Heart rate, mean arterial pressure, systemic vascular resistance, and cardiac output were similar between the 2 groups during induction of anesthesia and tracheal intubation. The incidence of adverse events such as bradycardia (remifentanil 10%, fentanyl 10%), hypotension (remifentanil 16%, fentanyl 10%), and ischemia (remifentanil 0%, fentanyl 2%) were also similar. A greater percentage of patients in the remifentanil group lost consciousness within 1 minute of opioid administration (86% v 66%, p = 0.034).

CONCLUSION

Remifentanil with glycopyrrolate is associated with rapid and predictable clinical anesthetic effect, cardiac stability, and the ability to blunt the hemodynamic responses to tracheal intubation. Bolus remifentanil may be a feasible alternative to bolus fentanyl for induction of anesthesia in patients with heart disease because of its short duration of action and its ability to blunt the hemodynamic responses to tracheal intubation.

La kétamine à dose antihyperalgésique augmente l'index bispectral

We report two cases of sudden increase in Bispectral Index (BIS) after the injection of low-dose ketamine for the prevention of postoperative hyperalgesia. The two patients were anaesthetised with a continuous infusion of remifentanil associated with propofol for one and isoflurane for the other. Changes in BIS occurred while the two patients were in a stable phase of surgery (beginning of parietal closure and suture of an anastomosis) and had a stable target concentration of anaesthetic agents. No others signs of awakening were observed. The BIS value returned progressively to 40-50 despite no increase in target concentration. None of the patients complained of intra-operative recall.

Comparative tolerability of sedative agents in head-injured adults

Sedative agents are widely used in the management of patients with head injury. These drugs can facilitate assisted ventilation and may provide useful reductions in cerebral oxygen demand. However, they may compromise cerebral oxygen delivery via their cardiovascular effects. In addition, individual sedative agents have specific and sometimes serious adverse effects. This review focuses on the different classes of sedative agents used in head injury, with a discussion of their role in the context of clinical pathophysiology. While there is no sedative that has all the desirable characteristics for an agent in this clinical setting, careful titration of dose, combination of agents, and a clear understanding of the pathophysiology and pharmacology of these agents will allow safe sedative administration in head injury.

Pharmacokinetics of remifentanil and its major metabolite, remifentanil acid, in ICU patients with renal impairment †

BACKGROUND

The pharmacokinetics of remifentanil, an opioid analgesic metabolized by non-specific esterases, and its principal metabolite, remifentanil acid (RA), which is excreted via the kidneys, were assessed as part of an open-label safety study in intensive care unit (ICU) patients with varying degrees of renal impairment.

METHODS

Forty adult ICU patients with normal/mildly impaired renal function (creatinine clearance [CL(cr)] 62.9 (sd) 14.5 ml min(-1); n=10) or moderate/severe renal impairment (CL(cr) 14.7 (15.7) ml min(-1); n=30) were included. Remifentanil was infused for up to 72 h, at a starting rate of 6-9 microg kg(-1) h(-1) titrated to achieve a target sedation level, with additional propofol (0.5 mg kg(-1) h(-1)) if required. Intensive arterial sampling was performed for up to 72 h after infusion. Pharmacokinetic parameters obtained by simultaneous modelling of remifentanil and RA data were statistically compared between the two groups.

RESULTS

Remifentanil pharmacokinetics were not significantly affected by renal status. RA clearance in the moderate/severe group was reduced to about 25% that of the normal/mild group (41 (29) vs 176 (49) ml kg(-1) h(-1), P<0.0001). Metabolic ratio, a predictor of the ratio of RA to remifentanil concentrations at steady state, was approximately eight-fold higher in the moderate/severe group relative to the normal/mild group (116 (110) vs 15 (4), P<0.0001). Maximum RA levels approached 700 ng ml(-1) in the moderate/severe group.

CONCLUSIONS

Although RA accumulates in patients with moderate/severe renal impairment, pharmacokinetic modelling predicts that RA concentrations during a 9 microg kg(-1) h(-1) remifentanil infusion for up to 15 days would not exceed those reported in the present study, for which no associated prolongation of mu-opioid effects was observed.

Effect of remifentanil on intracranial pressure and cerebral blood flow velocity in patients with head trauma

BACKGROUND

Remifentanil, an ultra-short-acting opioid, is used as an on-top analgesic in head trauma patients during transient painful procedures, e.g. endotracheal suctioning, physiotherapy, on the intensive care unit. However, previous studies have shown that opioids may increase intracranial pressure and decrease cerebral blood flow.

METHODS

The present study investigates the effect of remifentanil on mean arterial blood pressure, intracranial pressure measured with intraparenchymal or epidural probes, and on cerebral blood flow velocity assessed by transcranial Doppler flowmetry in 20 head trauma patients sedated with propofol and sufentanil. Ventilation was adjusted for a target PaCO2 of 4.7-5.1 kPa. After baseline measurements a bolus of remifentanil (0.5 microg x kg(-1) i.v.) was administrated followed by a continuous infusion of remifentanil (0.25 microg x kg(-1) x min(-1) i.v.) for 20 min.

RESULTS

There was no change in mean arterial blood pressure, intracranial pressure, and cerebral blood flow velocity in response to remifentanil infusion over time. Statistical analysis was performed using the Wilcoxon Signed Rank test.

CONCLUSIONS

These data suggest that remifentanil can be used for on-top analgesia in head trauma patients without adverse effects on cerebrovascular haemodynamics, cerebral perfusion pressure or intracranial pressure.

Use of remifentanil in an infant with surgically repaired Shone's syndrome

We describe the use of remifentanil in an infant with a partially repaired Shone's syndrome who required tendon lengthening because of congenital clubfoot. Remifentanil has unique properties, making it a potentially useful and predictable agent for infants with significant comorbidity.

Using fMRI to quantify the time dependence of remifentanil analgesia in the human brain

To understand and exploit centrally acting drugs requires reliable measures of their time course of action in the human brain. Functional magnetic resonance imaging (fMRI) is able to measure noninvasively, drug-induced changes in task-related brain activity. Here, we have characterized, in a specific region of the brain, the time of onset of action and the half-life of action of a clinically relevant dose of a potent opioid analgesic agent, remifentanil. These times were established from the temporal variation of the amplitude of the blood oxygen level-dependent response in the insular cortex contralateral to a painfully hot thermal stimulus, in volunteers receiving a remifentanil infusion. The insular cortex has repeatedly been reported as activated by noxious thermal stimulation. The times of onset and offset of drug action were each characterized by a half-life for changes in fMRI signal from within the insula. These characteristic times agreed with the observed drug-induced analgesia and previous pharmacokinetic-pharmacodynamic measurements for remifentanil. We have successfully measured, for the first time using fMRI, temporal pharmacological parameters for a CNS-active drug based on its effect on task-related activity in a specific brain region. Comparison of the time course of regional brain activity with pain perception could reveal those regions engaged in drug-induced analgesia.

Strategies to Optimise Propofol-Opioid Anaesthesia

Propofol-opioid combinations are widely used in today's anaesthetic practice. Over the past 20-30 years the pharmacology of these agents has been described in increasingly greater detail. Together with novel intravenous administration devices and improved anaesthetic depth monitoring, this has created a basis for the optimisation of the administration of propofol-opioid anaesthesia. This article describes the current strategies regarding the application of this type of anaesthesia, focusing on three strategic tools: (i) application of pharmacokinetic-pharmacodynamic knowledge of propofol and the opioids, with particular attention to pharmacodynamic interactions between them; (ii) the use of state-of-the-art administration techniques; and (iii) the application of bispectral index monitoring. Together, these techniques have improved the level of control, the flexibility and the safety of anaesthetic practice.

Influence of peroperative opioid on postoperative pain after major abdominal surgery: sufentanil TCI versus remifentanil TCI. A randomized, controlled study

BACKGROUND

Sufentanil and remifentanil are characterized by two different pharmacokinetic profiles. The aim of this study was to compare the effects of sufentanil and remifentanil administered using target-controlled infusion (TCI) on recovery and postoperative analgesia after major abdominal surgery.

METHODS

Thirty adult patients scheduled for open colorectal surgery were included in a prospective, randomized study. Sufentanil TCI (sufentanil group) or remifentanil TCI (remifentanil group) was administered during surgery. In the remifentanil group, 30 min before the anticipated end of surgery, morphine 0.15 mg x kg(-1) was administered i.v. In the sufentanil group, an effect-site concentration of 0.25 ng x ml(-1) was targeted at extubation. In both groups, postoperative pain was controlled by titration of i.v. morphine and then patient-controlled analgesia with morphine.

RESULTS

The extubation time was similar in the two groups (mean (SD) 13 (6) and 14 (6) min in the sufentanil and remifentanil groups respectively). Visual analogue scale scores were significantly greater during the first 2 h after tracheal extubation in the remifentanil group than in the sufentanil group. The time to first analgesic request in the postanaesthesia care unit was significantly longer in the sufentanil group than in the remifentanil group (55 (64) (range 2-240) vs 11 (7) (1-29) min; P<0.001). The cumulative morphine dose for titration was significantly greater in the remifentanil group (P<0.01). The cumulative morphine dose used during titration and patient-controlled analgesia was significantly greater in the remifentanil group 4, 12 and 24 h after extubation (P<0.05).

CONCLUSION

TCI sufentanil (0.25 ng ml(-1) effect-site concentration at extubation) is more effective than the intraoperative combination of remifentanil TCI infusion with morphine bolus (0.15 mg x kg(-1)) for postoperative pain relief after major abdominal surgery and does not compromise extubation and recovery.

Low-dose remifentanil infusion does not impair natural killer cell function in healthy volunteers

BACKGROUND

Mu opioid agonists suppress natural killer (NK) cell activity in animal models. Studies in human volunteers, however, have yielded conflicting results, with morphine suppressing and fentanyl increasing NK cell activity. This study evaluated the effect of a constant 8-h infusion of remifentanil on NK cell number and function in human volunteers.

METHODS

After IRB approval and informed consent was obtained, 10 healthy volunteers underwent an 11 pm to 7 am infusion of saline, and at least 1 week later an infusion of 0.02-0.04 microg x kg(-1) min(-1) remifentanil. Blood was collected at 7 am for measurement of NK cell cytotoxicity using a (51)Cr release assay and measurement of NK cell number using fluorescent flow cytometry.

RESULTS

Median and range of the total NK cell cytotoxicity (KU ml(-1)) was 745.0 (498.3-1483.6) on the control morning and 818.6 (238.5-1454.5) on the morning following the remifentanil infusion. Neither the number of NK cells ml(-1) (2.5 x 10(5) (1.4 x 10(5)-4.2 x 10(5)) vs 2.7 x 10(5) (1.1 x 10(5)-4.4 x 10(5))) nor the cytotoxicity per 1000 NK cells (KU 1000 NK cells(-1)) (3.0 (1.8-5.2) vs 2.9 (0.9-6.7)) changed between the control and remifentanil conditions.

CONCLUSIONS

An 8-h infusion of remifentanil did not affect NK cell activity in normal volunteers. This result differs from previous findings of morphine-induced NK cell activity suppression and fentanyl-induced NK cell activity enhancement in normal volunteers.

Offset of pharmacodynamic effects and safety of remifentanil in intensive care unit patients with various degrees of renal impairment

INTRODUCTION

This open label, multicentre study was conducted to assess the times to offset of the pharmacodynamic effects and the safety of remifentanil in patients with varying degrees of renal impairment requiring intensive care.

METHODS

A total of 40 patients, who were aged 18 years or older and had normal/mildly impaired renal function (estimated creatinine clearance >/= 50 ml/min; n = 10) or moderate/severe renal impairment (estimated creatinine clearance <50 ml/min; n = 30), were entered into the study. Remifentanil was infused for up to 72 hours (initial rate 6-9 microgram/kg per hour), with propofol administered if required, to achieve a target Sedation-Agitation Scale score of 2-4, with no or mild pain.

RESULTS

There was no evidence of increased offset time with increased duration of exposure to remifentanil in either group. The time to offset of the effects of remifentanil (at 8, 24, 48 and 72 hours during scheduled down-titrations of the infusion) were more variable and were statistically significantly longer in the moderate/severe group than in the normal/mild group at 24 hours and 72 hours. These observed differences were not clinically significant (the difference in mean offset at 72 hours was only 16.5 min). Propofol consumption was lower with the remifentanil based technique than with hypnotic based sedative techniques. There were no statistically significant differences between the renal function groups in the incidence of adverse events, and no deaths were attributable to remifentanil use.

CONCLUSION

Remifentanil was well tolerated, and the offset of pharmacodynamic effects was not prolonged either as a result of renal dysfunction or prolonged infusion up to 72 hours.

Remifentanil versus fentanyl for analgesia based sedation to provide patient comfort in the intensive care unit: a randomized, double-blind controlled trial [ISRCTN43755713]

INTRODUCTION

This double-blind, randomized, multicentre study was conducted to compare the efficacy and safety of remifentanil and fentanyl for intensive care unit (ICU) sedation and analgesia.

METHODS

Intubated cardiac, general postsurgical or medical patients (aged >/= 18 years), who were mechanically ventilated for 12-72 hours, received remifentanil (9 microgram/kg per hour; n = 77) or fentanyl (1.5 microgram/kg per hour; n = 75). Initial opioid titration was supplemented with propofol (0.5 mg/kg per hour), if required, to achieve optimal sedation (i.e. a Sedation-Agitation Scale score of 4).

RESULTS

The mean percentages of time in optimal sedation were 88.3% for remifentanil and 89.3% for fentanyl (not significant). Patients with a Sedation-Agitation Scale score of 4 exhibited significantly less between-patient variability in optimal sedation on remifentanil (variance ratio of fentanyl to remifentanil 1.84; P = 0.009). Of patients who received fentanyl 40% required propofol, as compared with 35% of those who received remifentanil (median total doses 683 mg and 378 mg, respectively; P = 0.065). Recovery was rapid (median time to extubation: 1.1 hours for remifentanil and 1.3 hours for fentanyl; not significant). Remifentanil patients who experienced pain did so for significantly longer during extubation (6.5% of the time versus 1.4%; P = 0.013), postextubation (10.2% versus 3.6%; P = 0.001) and post-treatment (13.5% versus 5.1%; P = 0.001), but they exhibited similar haemodynamic stability with no significant differences in adverse event incidence.

CONCLUSION

Analgesia based sedation with remifentanil titrated to response provided effective sedation and rapid extubation without the need for propofol in most patients. Fentanyl was similar, probably because the dosing algorithm demanded frequent monitoring and adjustment, thereby preventing over-sedation. Rapid offset of analgesia with remifentanil resulted in a greater incidence of pain, highlighting the need for proactive pain management when transitioning to longer acting analgesics, which is difficult within a double-blind study but would be quite possible under normal circumstances.

Pharmacokinetics of long-term sufentanil infusion for sedation in ICU patients

OBJECTIVE

To determine the pharmacokinetics of long-term infusion of sufentanil in ICU patients.

DESIGN AND SETTING

Open-label study in a surgical intensive care unit.

PATIENTS

Ten consecutive patients without renal or hepatic failure requiring mechanical ventilation for at least 6 days.

INTERVENTIONS

Patients received sufentanil (initial bolus 0.5 micro g/kg and continuous infusion rate of 0.5 micro g/kg per hour) and midazolam (initial bolus 0.08 mg/kg and continuous infusion 0.05 mg/kg per hour). Sedation was adjusted according to the Ramsay scale (score >3). Blood samples were taken during and up to 72 h after the infusion, and plasma concentrations were measured using a sensitive radioimmunoassay method.

MEASUREMENTS AND RESULTS

Plasma concentration-time profiles of sufentanil and pharmacokinetic parameters such as initial postinfusion half-life (t(1/2alpha)), elimination half-life (t(1/2beta)), total clearance (Cl), volume of distribution (Vdbeta), and time required to obtain a 50% decrease in plasma concentration (tcp(0/2)). The mean duration of sedation was 12+/-7 days. The initial half-life t(1/2alpha) was 1.33+/-1.15 h. The observed prolonged elimination half-life (t(1/2beta)=25.5+/-9.4 h) was related to the large volume of distribution (Vdbeta=22.6+/-9.4 l/kg). The mean total clearance was 13.4+/-7.0 ml/kg per minute. The mean time required to obtain a 50% decrease in plasma concentration was short (tcp(0/2=)4.7+/-3.7 h).

CONCLUSIONS

The pharmacokinetic analysis of sufentanil for ICU sedation revealed increased volume of distribution and elimination half-life. Nevertheless the rapid distribution and elimination processes suggest that the rapid reversibility of sedation with sufentanil is maintained after long duration of infusion. Further studies should be carried out to evaluate the clinical relevance of these results.

Detection of Acute Tolerance to the Analgesic and Nonanalgesic Effects of Remifentanil Infusion in a Rabbit Model

Although acute tolerance to analgesia develops rapidly with remifentanil, it is unknown whether acute tolerance also develops to its nonanalgesic effects. We investigated the analgesic and cardiorespiratory effects of remifentanil during a continuous infusion in a rabbit model. Ten tracheotomized New Zealand White rabbits with arterial and venous accesses were placed on a sling that allowed for reasonably free movement. In spontaneously breathing conscious animals, remifentanil was infused IV at a constant-rate of 0.3 microg kg(-1)x min(-1) for 360 min. Sedative/analgesic and cardiorespiratory variables were assessed repeatedly during remifentanil infusion, including the number of animals behaviorally unresponsive to clamping the forepaw (nonresponders) and subcutaneous electrical stimulation thresholds required to elicit head lift (HLT: pain detection/arousal threshold) and escape movement responses (EMT: pain tolerance threshold). Within 60-120 min of starting the infusion, the number of nonresponders, HLT, EMT, and PaCO(2) increased significantly, whereas blood pressure, heart rate, and respiratory rate decreased. Thereafter, all variables returned towards preinfusion levels despite continuing infusion. These results indicate that during a remifentanil infusion acute tolerance develops for both its analgesic and cardiorespiratory effects.

IMPLICATIONS

Using a new rabbit model, we found that during continuous, constant-rate remifentanil infusion acute tolerance developed within the first few hours, not only to its analgesic but also to its cardiovascular and respiratory effects, albeit in slightly different time courses.

A model to evaluate the pharmacokinetic and pharmacodynamic variables of extended-release products using in vivo tissue microdialysis in humans: bupivacaine-loaded microcapsules

Biodegradable microcapsules produce an ultra-long duration of local anesthesia. We hypothesized that this duration is caused by the sustained-release of bupivacaine from the microcapsules into the surrounding tissue. Previous studies investigated the pharmacokinetics (PKs) of bupivacaine after release from microcapsules and absorption into the systemic circulation. Microdialysis sampling can determine the PKs of any drug at its site of injection. This study was performed to characterize the PKs of bupivacaine and dexamethasone released from microcapsules at a subcutaneous injection site over a 96-h period in volunteers. Bupivacaine concentrations were compared with clinical variables of local anesthetic blockade. This study demonstrates that bupivacaine is released in a sustained manner from microcapsules, that bupivacaine concentrations increase for 24-34 h after microcapsule injection, and that analgesia parallels the tissue bupivacaine concentration obtained by microdialysis. Analgesia was equally rapid in onset with aqueous and microcapsule bupivacaine (P = 0.23). Analgesia was still present at 78% of microcapsule-injected sites after 96 h, significantly longer than for aqueous bupivacaine (P < 0.001). Mild pruritus was the most common side effect, occurring with 56% of the microcapsule injections. Dexamethasone-containing bupivacaine microcapsules are well tolerated and produce a prolonged duration of skin analgesia. Systemic absorption of bupivacaine produces higher peak plasma levels after aqueous injection than after microcapsule injection, despite the injection of a threefold larger load of bupivacaine in the latter.

IMPLICATIONS

Microcapsules loaded with bupivacaine and dexamethasone and administered by subcutaneous injection produce prolonged cutaneous anesthesia and analgesia. Determination of local tissue pharmacokinetic variables of bupivacaine by microdialysis confirms that the prolonged duration of anesthesia is caused by the extended release characteristics of the microcapsules.

[General anaesthesia for Caesarean section in a patient with pulmonary atresia and an intact intraventricular septum]

We report the case of a 22-year-old primigravida patient presenting pulmonary atresia with intact ventricular septum, a rare congenital heart disease. Caesarean delivery was performed at 32 weeks of gestation because of moderate maternal function deterioration and foetal growth restriction. General anaesthesia was used because of the presence of lumbar Harrington rods. The administration of etomidate, celocurine and a continuous perfusion of remifentanil right from induction ensured haemodynamic stability and a rapid emergence and recovery.

Propofol sparing effect of remifentanil using closed-loop anaesthesia

BACKGROUND

General anaesthesia is a balance between hypnosis and analgesia. We investigated whether an increase in remifentanil blood concentration would reduce the amount of propofol required to maintain a comparable level of anaesthesia in 60 patients undergoing ambulatory surgery.

METHODS

Patients were allocated randomly to receive remifentanil to a target blood concentration of 2 ng ml(-1) (low), 4 ng ml(-1) (medium), or 8 ng ml(-1) (high), administered by target-controlled infusion (TCI). After equilibration, propofol TCI was commenced in closed-loop control, with auditory evoked potentials (AEPex) as the input signal, aiming for an AEPex of 35. This was to ensure a comparable and unbiased level of anaesthesia in all patients.

RESULTS

We found a dose-dependent decrease in propofol requirements with increasing remifentanil concentrations. The mean (95% CI) propofol target blood concentration during adequate anaesthesia was 4.96 (3.85-6.01) micro g ml(-1) in the low, 3.46 (2.96-3.96) micro g ml(-1) in the medium, and 3.01 (2.20-3.38) micro g ml(-1) in the high group. There was no significant difference when recovery end points were achieved between the groups. Cardiovascular changes were moderate, but most pronounced in the high concentration group, with a decrease in heart rate of 21% compared with baseline. The mean calculated effect site propofol concentration at loss of consciousness was 2.08 (1.85-2.32) micro g ml(-1), and at recovery of consciousness was 1.85 (1.68-2.00) micro g ml(-1).

CONCLUSIONS

This study confirms a synergistic interaction between remifentanil and propofol during surgery, whereas the contribution of remifentanil in the absence of stimulation seems limited. In addition, our results suggest that the propofol effect site concentration provides a guide to the value at which the patient recovers consciousness.

Efficacy and safety of remifentanil in coronary artery bypass graft surgery: a randomized, double-blind dose comparison study

OBJECTIVES

To compare the efficacy and safety of 3 doses of remifentanil as part of a total intravenous anesthesia technique with low-dose propofol in patients undergoing coronary artery bypass graft (CABG) surgery.

DESIGN

Multicenter, multinational, double-blind, randomized, dose comparison study.

SETTING

Nine hospitals in 5 countries.

PARTICIPANTS

One hundred forty-one patients undergoing first-time elective CABG surgery.

INTERVENTIONS

Patients were premedicated with a short-acting oral benzodiazepine up to 2 h before surgery and randomized to receive continuous infusions of remifentanil 1.0 microg/kg/min (n = 45), 1.5 microg/kg/min (n = 44), or 2.0 microg/kg/min (n = 43), in combination with propofol 3 mg/kg/h. Nine patients received remifentanil 1.0 microg/kg/min on an open-label basis. Three different induction sequences (IS) were used. In IS 1 (n = 31), induction was started with remifentanil infusion followed 5 minutes later by propofol 0.5 mg/kg bolus and infusion at 3 mg/kg/h. Further bolus doses of propofol (10 mg) were given if loss of consciousness (LOC) was not attained after 5 minutes; pancuronium, 0.04 to 0.1 mg/kg, was administered at LOC. In IS 2 (n = 68), a priming dose of pancuronium, 0.015 mg/kg, was administered just before starting remifentanil. In IS 3 (n = 42), bolus doses of propofol, 10 mg every 10 seconds, were given until LOC, followed by pancuronium, 0.04 to 0.1 mg/kg, and the remifentanil and propofol infusions were started.

MEASUREMENTS AND MAIN RESULTS

There were no significant differences among the remifentanil dose groups with regard to the primary outcome measure, responses to sternotomy/sternal spread/maximal sternal spread. Responses to these stimuli were recorded in 11%, 11%, and 14% of patients in the remifentanil 1.0, 1.5, and 2.0 microg/kg/min dose groups, respectively. Similarly, there were no significant differences in the responses to other surgical stimuli. There was a high incidence of muscle rigidity when remifentanil was used to induce anesthesia.

CONCLUSIONS

All 3 remifentanil dose regimens provided profound suppression of responses to surgical stimuli in the majority of patients. There was no apparent advantage in starting the remifentanil infusion rate above 1.0 microg/kg/min. Remifentanil is not suitable for use as a sole induction agent.

Target-controlled infusion for remifentanil in vascular patients improves hemodynamics and decreases remifentanil requirement

Remifentanil is a potent ultra-short-acting opioid, which permits rapid emergence. However, remifentanil is expensive and may have detrimental effects on hemodynamics in case of overdose. Target-controlled infusion (TCI) permits adapting infusion to pharmacokinetic models. In this prospective randomized study, we compared intra- and postoperative hemodynamics, remifentanil requirement during anesthesia, and postoperative morphine requirement in patients scheduled for carotid surgery, and receiving either continuous IV weight-adjusted infusion of remifentanil (RIVA) or TCI for remifentanil (TCIR). Forty-six patients were enrolled in this study: all were anesthetized by using TCI for propofol. Twenty-three received RIVA (0.5 micro g. kg(-1) x min(-1)) for the induction of anesthesia and endotracheal intubation, with the infusion rate decreased to 0.25 micro g x kg(-1) x min(-1) after intubation, then adapted by step of 0.05 micro g x kg(-1) x min(-1) according to hemodynamics. Twenty-three patients received TCIR (Minto model, Rugloop), with an effect-site concentration at 4 ng/mL during induction, then adapted by step of 1 ng/mL according to hemodynamics. All patients received atracurium and a 50% mixture of N(2)O/O(2). Hemodynamic variables were recorded each minute. The number and duration of hemodynamic events were collected, and total doses of anesthetics (remifentanil and propofol) and vasoactive drugs were noted in both groups of patients. Data were analyzed by using unpaired t-tests. RIVA was significantly associated with more frequent episodes of intraoperative hypotension (16 versus 6, P < 0.001) and more frequent episodes of postoperative hypertension and/or tachycardia requiring more frequent administration of beta-adrenergic blockers (16 vs 10, P < 0.04) in comparison with TCIR. The need for morphine titration was not significantly different between groups. TCIR led to a significantly smaller requirement of remifentanil (700 +/- 290 versus 1390 +/- 555 micro g, P < 0.001) without difference in propofol requirement. This prospective randomized study demonstrated that, during carotid endarterectomy, in comparison with patients receiving remifentanil using continuous RIVA, TCI results in less hypotensive episodes during the induction of anesthesia, in fewer episodes of tachycardia and/or hypertension and a smaller beta-adrenergic blocker requirement during recovery, and a decrease in remifentanil requirement. Recommendations to prefer TCI for remifentanil administration during carotid endarterectomy may be justified.

IMPLICATIONS

Remifentanil for intraoperative analgesia in carotid artery surgery is associated with a better stability in perioperative hemodynamics when administered in target-controlled infusion compared with continuous weight-adjusted infusion. This may be related to a smaller requirement of this drug when using target-controlled infusion, as well as a smooth mode of administration.

A comparison of the remifentanil and fentanyl adverse effect profile in a multicenter phase IV study

STUDY OBJECTIVE

To compare the frequency of adverse effects of remifentanil and fentanyl in a large and diverse patient population.

DESIGN

Prospective, randomized, open-label study.

SETTING

Multicenter study including academic and community hospitals.

PATIENTS

2,438 adult patients (1,496 outpatients and 942 inpatients) scheduled for elective surgical procedures under general endotracheal anesthesia of at least 30-minute duration.

INTERVENTIONS

Patients were randomly assigned to receive either intravenous (IV) remifentanil (n = 1,229) 0.5 microg/kg/min for induction and tracheal intubation followed by an infusion rate of 0.25 microg/kg/min or fentanyl (n = 1,209) administered according to the anesthesiologist's usual practice. Anesthesia was maintained with propofol and/or isoflurane (with or without nitrous oxide) titrated according to protocol. Transition analgesia with either morphine or fentanyl was administered in the remifentanil and, at the anesthesiologist's discretion, in the fentanyl group.

MEASUREMENTS

The overall nonspecific and specific (i.e., opioid-related) adverse effects were recorded.

MAIN RESULTS

Remifentanil was associated with more intraoperative hypotension than fentanyl (p < 0.05). All four cases (0.3%) of muscle rigidity occurred in the remifentanil-treated outpatients. There were no significant differences between the two drugs with respect to other adverse events (i.e., episodes of hypertension, bradycardia, respiratory depression, and apnea).

CONCLUSIONS

In the doses used, both remifentanil and fentanyl have a similar frequency of adverse effects except for the higher frequency of hypotension associated with the use of remifentanil.

Narcotrend, bispectral index, and classical electroencephalogram variables during emergence from propofol/remifentanil anesthesia

The aim of this study was to investigate modern and classical electroencephalographic (EEG) variables in response to remifentanil and propofol infusions. We hypothesized that modern EEG variables may indicate the effects of propofol but not of remifentanil. Twenty-five patients were included in the study after the end of elective spine surgery without any surgical stimulation. Baseline values were defined with remifentanil 0.3 microg. kg(-1). min(-1) and target-controlled infusion of propofol 3.0 microg/mL. EEG changes were evaluated 1, 3, 5, 7, and 9 min after the stop of remifentanil infusion, followed by a step-by-step reduction (0.2 microg/mL) every 3 min of target-controlled infusion propofol. Narcotrend (NT; classifying EEG stages from awake to deep anesthesia), bispectral index (BIS), EEG spectral frequency bands (%), 50% (Median) and 95% percentiles (spectral edge frequency), mean arterial blood pressure, heart rate, and oxygen saturation were detected at every time point. The end of remifentanil application resulted in significant increases in %alpha, spectral edge frequency, mean arterial blood pressure, and %theta and decreases in %delta (P < 0.05). NT, BIS, Median, heart rate, and oxygen saturation were unchanged. Decreases in propofol concentration were associated with statistically significant increases in NT and BIS (P < 0.05). Thus, the sedative-hypnotic component of propofol could be estimated by modern EEG variables (NT and BIS), whereas the analgesic component provided by remifentanil was not indicated. However, during conditions without surgical stimulation, neither NT nor BIS provided an adequate assessment of the depth of anesthesia when a remifentanil infusion was used.

IMPLICATIONS

We investigated modern and classical electroencephalographic (EEG) variables during emergence from propofol/remifentanil anesthesia. Modern EEG variables indicate changes of infusion in propofol, but not in remifentanil. Thus, modern EEG variables did not provide an adequate assessment of depth of anesthesia when remifentanil was used.

Context-sensitive half-times: what are they and how valuable are they in anaesthesiology?

The context-sensitive half-time is the time required for blood or plasma concentrations of a drug to decrease by 50% after discontinuation of drug administration. The context-sensitive half-time often cannot be predicted by the elimination half-life (a measure of the time needed for actual drug metabolism or elimination) since it also depends on drug distribution. The context-sensitive half-time is a function of the duration of drug administration and may only be estimated by computer simulation. It is more relevant than other isolated pharmacokinetic parameters to understanding the kinetics of drug concentrations. However, understanding the kinetics of drug effect requires concomitant consideration of pharmacodynamics.

Remifentanil compared with sufentanil during extra-corporeal shock wave lithotripsy with spontaneous ventilation: a double-blind, randomized study

BACKGROUND

The pharmacokinetic properties of remifentanil may allow a rapid analgesic action during painful procedures and short lasting postoperative respiratory depression.

METHODS

We carried out a randomized, blind, study in 60 patients to compare remifentanil (continuous i.v. infusion starting at 0.025 micro g kg(-1) min(-1)) and sufentanil (i.v. doses of 0.15 micro g kg(-1)) during extra-corporeal shock wave lithotripsy (ESWL). Pain was assessed using a numerical pain scale (0-100), and pain relief was defined as a score < or =30. Respiratory depression was defined as a ventilatory frequency less than10 breaths min(-1) on two occasions or a peripheral oxygen saturation < or =92%, or administration of naloxone.

RESULTS

The quality of analgesia was similar in both groups, during and after ESWL. During ESWL, there was no significant difference in respiratory depression in the remifentanil and sufentanil groups (53 vs 73%, NS). The percentage of satisfied patients (73 vs 83%, NS) and satisfied surgeons (97 vs 100%, NS) did not significantly differ between groups. After the procedure patients given remifentanil had less respiratory depression (20 vs 53%, P<0.05) and less nausea and vomiting (3 vs 20%, P<0.05).

CONCLUSION

A continuous i.v. infusion of remifentanil provided comparable analgesia and caused less respiratory depression and nausea and vomiting than i.v. boluses of sufentanil in patients undergoing extra-corporeal shock wave lithotripsy.

The effect of remifentanil or fentanyl on postoperative vomiting and pain in children undergoing strabismus surgery

Postoperative vomiting (POV) after strabismus surgery in children results in discomfort and prolonged hospital stays. Opioids increase the incidence of POV. Remifentanil has a context-sensitive half-life of 3 to 4 min, and how this short half-life influences POV in those patients is unknown. We conducted a prospective, double-blinded study in 81 ASA status I or II children from 2 to 12 yr of age undergoing elective strabismus surgery under general anesthesia. Patients were randomized to receive either remifentanil (bolus 1 microg/kg; infusion 0.1-0.2 microg x kg(-1) x min(-1)) or fentanyl (2 microg/kg, and 1 microg/kg every 45 min). POV episodes were recorded for 25 h. Pain scores were obtained by using an objective pain scale for 60 min during recovery. The number of patients who experienced POV did not differ significantly between groups (49% vs 48%). However, in the Remifentanil group, POV episodes were significantly less frequent (0.95 vs 2.2 episodes). In contrast, fentanyl was associated with lower pain scores during the first 30 min of recovery. We conclude that children undergoing strabismus surgery under balanced anesthesia with remifentanil, compared with fentanyl, showed less frequent POV. However, early postoperative analgesia was better with fentanyl.

IMPLICATIONS

Opioids increase the incidence of postoperative vomiting (POV). Remifentanil is characterized by the shortest half-life of all opioids used in anesthetic practice. Therefore, we studied the effect of remifentanil on POV compared with the longer-acting opioid fentanyl in children undergoing strabismus surgery.

Comparison of hemodynamics, recovery profile, and early postoperative pain control and costs of remifentanil versus alfentanil-based total intravenous anesthesia (TIVA)

STUDY OBJECTIVE

To compare hemodynamics, recovery profiles, early postoperative pain control and costs of total intravenous anesthesia (TIVA) with propofol and remifentanil and propofol and alfentanil.

DESIGN

Randomized, double-blind study.

SETTING

University hospital.

PATIENTS

40 ASA physical status I and II adult patients scheduled for lumbar discectomy.

INTERVENTIONS

Patients were randomly assigned to receive either remifentanil-propofol or alfentanil-propofol. Anesthesia was induced with remifentanil 1 microg kg(-1) or alfentanil 20 microg kg(-1) with propofol 2 mg kg(-1), and maintained with infusions of propofol 150 to 100 microg kg(-1)min(-1) and either remifentanil 0.1 microg kg(-1) min(-1) or alfentanil 0.5 microg kg(-1) min(-1).

MEASUREMENTS

Hemodynamic parameters (heart rate and mean arterial pressure), times to awakening, and tracheal extubation were recorded. In the postanesthesia care unit, pain level, frequency of analgesic demand, frequency of postoperative nausea and vomiting (PONV), partial oxygen saturation (SpO2), and respiratory rates were noted. Drug dosages and costs of each technique were determined.

MAIN RESULTS

The mean arterial pressure significantly decreased compared to baseline values 1 minute after induction (p < 0.05) in both groups, and it significantly decreased at 5, 15, and 30 minutes perioperatively in the remifentanil group compared to the alfentanil group (p < 0.05). Time of extubation, spontaneous eye opening, and response to verbal command were similar in both groups. Visual analog scale pain scores at 30 minutes and 60 minutes were significantly lower in the alfentanil group than remifentanil group (p < 0.05). At 15, 30, and 60 minutes after terminating the operation oxygen saturation and respiratory rate were significantly higher (p < 0.05) and analgesics were required sooner in the remifentanil group than the alfentanil group (p < 0.05). The frequency of PONV was similar in both groups. The remifentanil-propofol anesthesia was found to be slightly more expensive as compared to the alfentanil based TIVA (33.41 +/- 4.53 vs. 29.97 +/- 4.1 USD) (p < 0.05).

CONCLUSIONS

Both remifentanil and alfentanil provided a reasonably rapid and reliable recovery. The remifentanil-based TIVA was associated with high intraoperative cost and early postoperative pain, but it allowed a more rapid respiratory recovery.

The absence of acute tolerance during remifentanil infusion in volunteers

The development of acute opioid tolerance in humans remains controversial. We tested the hypothesis that continuous remifentanil infusion leads to rapid development of opioid tolerance. Twenty healthy male volunteers were enrolled onto a randomized, placebo-controlled, double-blinded, cross-over design study to receive a 3 h continuous infusion of remifentanil (0.08 microg x kg(-1) x min(-1)) or saline. Test procedures included determination of pain perception thresholds and pain tolerance thresholds to heat and cold and neuroselective sine wave constant current at 5 Hz and 250 Hz. Test procedures were performed at baseline and then repeated at 25, 55, 85, 115, and 160 min (heat/cold) and at 35, 65, 95, 125, and 170 min (electrical current) during infusion. No significant decrease of the pain threshold devolutions between 55 and 180 min after the start of infusion of remifentanil could be detected. In conclusion, no development of acute opioid tolerance was observed during constant remifentanil infusion of 3 h in volunteers.

IMPLICATIONS

The opioid remifentanil was applied to 20 volunteers at a constant concentration for 3 h while pain thresholds to temperature and current were repeatedly assessed. Our aim was to study whether thresholds decrease over time because of the rapid development of opioid tolerance. No development of rapid opioid tolerance was observed.

Remifentanil infusion for cardiac catheterization in children with congenital heart disease

BACKGROUND

Cardiac catheterization of children with congenital heart disease is increasingly being performed under general anesthesia. Haemodynamic stability during anesthesia and fast and adequate recovery after the procedure is crucial in these patients. We performed a pilot study to evaluate hemodynamic stability when using remifentanil for anesthesia during cardiac catheterization. We also evaluated extubation times and recovery characteristics.

METHODS

In a randomized, prospective, double-blind study 30 children (aged 1.5-20 months) received a continuous infusion of either 0.2 (group 0.2) or 0.3 microg/kg/min remifentanil (group 0.3) as part of a balanced anesthesia with 0.6 MAC sevoflurane. Heart rate, noninvasive arterial blood pressure, end tidal CO2 and pulse oxymetry were monitored throughout the procedure. Extubation times were noted, and recovery from anesthesia was evaluated using Aldrete scores.

RESULTS

: Haemodynamic response to intubation was well blunted in both groups. No significant changes in hemodynamic variables were noted from induction of anesthesia until 10 min after intubation. From then on there was a decrease in HR and systolic arterial pressure, which remained significant throughout the procedure in both groups. Extubation times were similar in both groups: 7.3 min (2,1) in group 0.2 vs. 6.6 min (2,1) in group 0.3 (NS). The number of patients with an Aldrete score of nine or more was 14 (group 0.2) vs. 15 (group 0.3), 10 min after extubation (NS).

CONCLUSION

Both dose regimens of remifentanil provided stable hemodynamic conditions during anesthesia for cardiac catheterization of children with congenital heart disease and allowed for rapid and adequate recovery.

Remifentanil provides hemodynamic stability and faster awakening time in transsphenoidal surgery

In this prospective study, we evaluated the effects of remifentanil in ASA I-II patients undergoing transsphenoidal surgery. After the induction of anesthesia, patients were randomly allocated to the Isoflurane (n = 22, 60% nitrous oxide, isoflurane up to 2% end-tidal) or Remifentanil group (n = 21, 60% nitrous oxide, 0.5% end-tidal isoflurane, remifentanil up to 2 microg x kg(-1) x min(-1)). If mean arterial pressure (MAP) increased >80 mm Hg during maximal dosage of isoflurane or remifentanil, labetalol was administered. At the end of anesthesia, extubation and awakening times, respiratory rate, SpO(2), MAP, heart rate, and adverse effects were recorded. Hemodynamics and bleeding (minimal, mild, moderate, severe) were not different between groups. Bleeding grade increased with MAP >80 mm Hg (P < 0.001). Labetalol was administered to 20 patients in the Isoflurane group, and 10 patients in the Remifentanil group (P < 0.01). The dose of labetalol was larger in the Isoflurane group (1.0 +/- 0.6 versus 0.5 +/- 0.7 mg/kg, P < 0.05). Time to extubation did not differ, whereas time to follow commands was shorter in Remifentanil patients (16 +/- 8 versus 10 +/- 2 min, P < 0.01). No adverse effects occurred in the early postoperative period.

IMPLICATIONS

In patients undergoing transsphenoidal surgery, balanced anesthesia with remifentanil (0.22 +/- 0.17 microg x kg(-1) x min(-1)) provides faster awakening time, as compared with large-dose volatile-based anesthesia, without the risk of postoperative opioid respiratory depression.

Concurrent ketamine and alfentanil administration: pharmacokinetic considerations

BACKGROUND

A ketamine-alfentanil combination has been suggested for total i.v. anaesthesia. We determined the pharmacokinetics of ketamine and alfentanil, alone and together, in three groups of adult male rats, to assess any pharmacokinetic interaction.

METHODS

Group 1 animals were infused with i.v. ketamine for 5 min; in group 2, constant low plasma concentrations of alfentanil were maintained by computer-controlled infusion; in group 3, the treatments were combined. Serial plasma and terminal tissue concentrations were measured by high performance liquid chromatography or gas chromatography-mass spectrometry.

RESULTS

In the presence of alfentanil, the mean plasma ketamine concentration-time area under the curve (AUC) value was significantly lower (by 13%, P<0.05), while clearance (CIT) and volume of distribution (Vss) were significantly higher (by 16 and 28%, respectively, both P<0.05). Tissue:plasma distribution coefficients for ketamine in the presence of alfentanil were significantly higher in forebrain (by 128%, P<0.005), hindbrain (by 207%, P<0.01), gut (by 254%, P<0.005), and fat (by 344%, P<0.0001). Mean AUC values for alfentanil did not differ significantly in the presence of ketamine, but alfentanil tissue concentrations were significantly lower in forebrain (by 77%, P<0.0001), hindbrain (by 28%, P<0.01), heart (by 33%, P<0.01), lung (30%, P<0.05), and gut (by 21%, P<0.05). Corresponding tissue:plasma distribution coefficients were significantly lower for forebrain (by 69%, P<0.0001) alone.

CONCLUSIONS

The finding that the distribution of ketamine into the brain was increased by low plasma concentrations of alfentanil could have important clinical applications for pain management.