The pharmacodynamic effect of a remifentanil bolus on ventilatory control

Development of a Translational Model to Assess the Impact of Opioid Overdose and Naloxone Dosing on Respiratory Depression and Cardiac Arrest

In response to a surge of deaths from synthetic opioid overdoses, there have been increased efforts to distribute naloxone products in community settings. Prior research has assessed the effectiveness of naloxone in the hospital setting; however, it is challenging to assess naloxone dosing regimens in the community/first-responder setting, including reversal of respiratory depression effects of fentanyl and its derivatives (fentanyls). Here, we describe the development and validation of a mechanistic model that combines opioid mu receptor binding kinetics, opioid agonist and antagonist pharmacokinetics, and human respiratory and circulatory physiology, to evaluate naloxone dosing to reverse respiratory depression. Validation supports our model, which can quantitatively predict displacement of opioids by naloxone from opioid mu receptors in vitro, hypoxia-induced cardiac arrest in vivo, and opioid-induced respiratory depression in humans from different fentanyls. After validation, overdose simulations were performed with fentanyl and carfentanil followed by administration of different intramuscular naloxone products. Carfentanil induced more cardiac arrest events and was more difficult to reverse than fentanyl. Opioid receptor binding data indicated that carfentanil has substantially slower dissociation kinetics from the opioid receptor compared to 9 other fentanyls tested, which likely contributes to the difficulty in reversing carfentanil. Administration of the same dose of naloxone intramuscularly from 2 different naloxone products with different formulations resulted in differences in the number of virtual patients experiencing cardiac arrest. This work provides a robust framework to evaluate dosing regimens of opioid receptor antagonists to reverse opioid-induced respiratory depression, including those caused by newly emerging synthetic opioids.

The effect of concentration, reconstitution solution and pH on the stability of a remifentanil hydrochloride and propofol admixture for simultaneous co-infusion

Background

There are scenarios where pre-mixing and infusing analgesic and anaesthetic agents as a single intravenous (IV) solution is highly desirable; however, it is important to ensure the agents are compatible when mixed. As such, the long-term stability of a remifentanil-propofol mixture, and means of improving this, were assessed across a range of remifentanil concentrations, diluents, and time points.

Methods

Remifentanil was reconstituted with ultrapure water, 0.9% saline, 20% saline, or 8.4% sodium bicarbonate solution (the latter two chosen for their pH characteristics, rather than their use in pharmaceutical reconstitution) and then mixed with propofol (1%) or further diluted with water to derive concentrations of 10–50 μg mL^− 1. Remifentanil and propofol concentrations were determined initially and then periodically for up to 24 h using high performance liquid chromatography (HPLC). Mass spectrometry (MS) was used to detect degradation products in solutions containing 30 μg mL^− 1 of remifentanil. Statistical analysis was performed using ANOVA and Student’s t-test, with a significance value of 0.05.

Results

Isolated remifentanil (pH < 4) and propofol (pH 7.35) did not degrade significantly when reconstituted with water or saline solution over 24 h, while remifentanil reconstituted with sodium bicarbonate degraded significantly (P < 0.001, pH 8.65). Mixing with propofol substantially increased the pH of the mixture and resulted in significant remifentanil degradation for all reconstitution solutions used, while propofol remained stable (pH 6.50). The amount of degradation product detected in samples containing isolated remifentanil and a mixture of the drugs was proportional to the remifentanil degradation observed.

Conclusions

Remifentanil stability is affected by both the reconstitution solution used and when mixed with propofol, with pH appearing to be a contributing factor to degradation. If the pH of the solution and concentration of remifentanil are correctly controlled, e.g. through the use of a more acidic diluent, an admixture of remifentanil and propofol may be useful clinically.

Supplementary Information

Supplementary information accompanies this paper at 10.1186/s12871-020-01194-5.

A methodology to explore ventilatory chemosensitivity and opioid-induced respiratory depression risk

Our new and noteworthy methodology allows for exploration of preoperative ventilatory chemosensitivity, measured as the hypercapnic ventilatory response (HCVR), as a risk factor for postoperative opioid-induced respiratory depression (OIRD). This feasible and reliable methodology produced preliminary data that showed highly variable depression of HCVR by remifentanil, predominance of OIRD during light sleep, and potentially negative correlation between OIRD frequency generally and HCVR measurements when measured in the presence of remifentanil. Although the results are preliminary in nature, this novel methodology may guide future studies that can one day lead to effective clinical screening tools.

Non–steady State Modeling of the Ventilatory Depressant Effect of Remifentanil in Awake Patients Experiencing Moderate-to-severe Obstructive Sleep Apnea

Editor’s Perspective

What We Already Know about This Topic

What This Article Tells Us That Is New

Background

Evidence suggests that obstructive sleep apnea promotes postoperative pulmonary complications by enhancing vulnerability to opioid-induced ventilatory depression. We hypothesized that patients with moderate-to-severe obstructive sleep apnea are more sensitive to remifentanil-induced ventilatory depression than controls.

Methods

After institutional approval and written informed consent, patients received a brief remifentanil infusion during continuous monitoring of ventilation. We compared minute ventilation in 30 patients with moderate-to-severe obstructive sleep apnea diagnosed by polysomnography and 20 controls with no to mild obstructive sleep apnea per polysomnography. Effect site concentrations were estimated by a published pharmacologic model. We modeled minute ventilation as a function of effect site concentration and the estimated carbon dioxide. Obstructive sleep apnea status, body mass index, sex, age, use of continuous positive airway pressure, apnea/hypopnea events per hour of sleep, and minimum nocturnal oxygen saturation measured by pulse oximetry in polysomnography were tested as covariates for remifentanil effect site concentration at half-maximal depression of minute ventilation (Ce50) and included in the model if a threshold of 6.63 (P &lt; 0.01) in the reduction of objective function was reached and improved model fit.

Results

Our model described the observed minute ventilation with reasonable accuracy (22% median absolute error). We estimated a remifentanil Ce50 of 2.20 ng · ml–1 (95% CI, 2.09 to 2.33). The estimated value for Ce50 was 2.1 ng · ml–1 (95% CI, 1.9 to 2.3) in patients without obstructive sleep apnea and 2.3 ng · ml–1 (95% CI, 2.2 to 2.5) in patients with obstructive sleep apnea, a statistically nonsignificant difference (P = 0.081). None of the tested covariates demonstrated a significant effect on Ce50. Likelihood profiling with the model including obstructive sleep apnea suggested that the effect of obstructive sleep apnea on remifentanil Ce50 was less than 5%.

Conclusions

Obstructive sleep apnea status, apnea/hypopnea events per hour of sleep, or minimum nocturnal oxygen saturation measured by pulse oximetry did not influence the sensitivity to remifentanil-induced ventilatory depression in awake patients receiving a remifentanil infusion of 0.2 μg · kg–1 of ideal body weight per minute.

Induction of anaesthesia with remifentanil after bolus midazolam administration in Landrace/Large White swine

OBJECTIVE

To investigate an alternative combination for anaesthesia induction in swine.

STUDY DESIGN

Randomized, 'blinded' experimental study.

ANIMALS

Forty-five Landrace/Large White swine weighing 20.0±1.5 kg.

METHODS

Pulse oximetry, heart rate (HR) and blood pressure were measured after premedication with ketamine, midazolam and atropine as well as after intubation following induction with a fixed dose of 0.2 mg kg^-1 midazolam combined with 1, 2, 3, 4 or 5 μg kg^-1 remifentanil (groups R1, R2, R3, R4 and R5, respectively). Intubation was evaluated using a numerical scoring system assessing jaw relaxation, resistance to the laryngoscope, vocal cord position, vocal cord movement and response to intubation. The time required to intubate and necessity for an additional midazolam dose were recorded. Baseline and post-intubation variables were compared with paired t tests, whereas for differences between the remifentanil groups the Spearman's rank correlation coefficient was estimated. Multivariate regression analysis was performed to disentangle the effect of remifentanil dose and the additional midazolam.

RESULTS

Higher dose of remifentanil was associated with better vocal cord position (p<0.001), better response to intubation (p<0.001), shorter time required for intubation (p=0.030) and less frequent necessity for additional administration of midazolam (p=0.004). In total, 39.5% of the animals required additional midazolam. In groups R1, R4 and R5, there were decreases in HRs (p=0.009, p=0.008 and p=0.032, respectively) between baseline and post-intubation phase; in groups R3 and R4, there were decreases in systolic blood pressure (p=0.040 and p=0.019, respectively). In the multivariate analysis, remifentanil dose was not associated with the observed changes in haemodynamic variables. One animal developed apnoea and four electrocardiographic anomalies; all resolved without pharmaceutical interventions.

CONCLUSIONS AND CLINICAL RELEVANCE

A combination of 0.2 mg kg^-1 midazolam with 4 or 5 μg kg^-1 remifentanil may provide an alternative method of anaesthesia induction for swine.

Remifentanil, ketamine, and propofol in awake nasotracheal fiberoptic intubation in temporomandibular joint ankylosis surgery

BACKGROUND

Nasotracheal intubation of patients with temporomandibular joint (TMJ) ankylosis is a challenge for anesthesiologists. Awake fiberoptic intubation (AFOI) is the safest technique in patients with difficult airway. This study compares 3 different techniques of conscious sedation during AFOI in patients with TMJ ankylosis.

METHODS

This study comprised 54 patients, American Society of Anesthesiologists physical status 1, scheduled for TMJ surgery. The patients were randomly allocated to remifentanil group (n = 18, 0.75 μg/kg over 30 seconds), ketamine group (n = 18, 0.25 mg/kg over 30 seconds), or propofol group (n = 18, 0.5 mg/kg over 30 seconds) for conscious sedation. The main determinants affecting the patient's outcome included intubation time, intubation conditions, and patient discomfort, which were determined by scoring system. In addition, postoperative patient dissatisfaction, hemodynamic stability, and respiratory impairment were measured.

RESULTS

Intubation times were significantly different between groups (P < 0.001), where remifentanil had the shortest time (30.28 seconds). Intubation conditions (scores 0-3) were significantly different between groups (P < 0.001).In this context, remifentanil had score 3 (2-3), which was higher compared with 2 (1-3) for ketamine and 2 (1-2) for propofol. Patient discomfort score was lowest in the remifentanil group. Hemodynamic stability was maintained within groups, and its changes were not significant (P > 0.05). Postoperative patient's dissatisfaction was observed in 2, 3, and 5 patients in remifentanil, ketamine, and propofol groups, respectively. Respiratory impairment (apnea) recorded lowest in the remifentanil group.

CONCLUSIONS

Remifentanil was the best agent for AFOI, because it provided shorter intubation time, better intubation conditions, and least patient's complaint.Iranian registry no.: IRCT 201208061674N4 (www.irct.ir).

Intravenous remifentanil versus epidural ropivacaine with sufentanil for labour analgesia: a retrospective study

Remifentanil with appropriate pharmacological properties seems to be an ideal alternative to epidural analgesia during labour. A retrospective cohort study was undertaken to assess the efficacy and safety of remifentanil intravenous patient-controlled analgesia (IVPCA) compared with epidural analgesia. Medical records of 370 primiparas who received remifentanil IVPCA or epidural analgesia were reviewed. Pain and sedation scores, overall satisfaction, the extent of pain control, maternal side effects and neonatal outcome as primary observational indicators were collected. There was a significant decline of pain scores in both groups. Pain reduction was greater in the epidural group throughout the whole study period (0∼180 min) (P<0.0001), and pain scores in the remifentanil group showed an increasing trend one hour later. The remifentanil group had a lower SpO₂ (P<0.0001) and a higher sedation score (P<0.0001) within 30 min after treatment. The epidural group had a higher overall satisfaction score (3.8±0.4 vs. 3.7±0.6, P = 0.007) and pain relief score (2.9±0.3 vs. 2.8±0.4, P<0.0001) compared with the remifentanil group. There was no significant difference on side effects between the two groups, except that a higher rate of dizziness (1% vs. 21.8%, P<0.0001) was observed during remifentanil analgesia. And logistic regression analysis demonstrated that nausea, vomiting were associated with oxytocin usage and instrumental delivery, and dizziness was associated to the type and duration of analgesia. Neonatal outcomes such as Apgar scores and umbilical-cord blood gas analysis were within the normal range, but umbilical pH and base excess of neonatus in the remifentanil group were significantly lower. Remifentanil IVPCA provides poorer efficacy on labor analgesia than epidural analgesia, with more sedation on parturients and a trend of newborn acidosis. Despite these adverse effects, remifentanil IVPCA can still be an alternative option for labor analgesia under the condition of one-to-one bedside care, continuous monitoring, oxygen supply and preparation for neonatal resuscitation.

A comparison of remifentanil parturient-controlled intravenous analgesia with epidural analgesia: a meta-analysis of randomized controlled trials

BACKGROUND

Epidural analgesia is generally accepted as the most effective form of pain relief during labor. Remifentanil patient-controlled IV analgesia (PCIA), which is less invasive than epidural analgesia, may be an attractive alternative. In this meta-analysis, we compared the efficacy and safety of the 2 analgesic techniques for labor pain.

METHODS

Databases of PubMed, EMBASE, and Cochrane Library were searched independently by 2 reviewers to retrieve eligible randomized controlled clinical trials. The primary end points were pain scores at 1 and 2 hours, and the secondary end points were nausea, vomiting, pruritus, and umbilical artery pH values. Mean difference (MD) or risk ratio with 95% confidence intervals (CIs) were calculated for each end point. GRADE profiler was applied to assess the quality of evidence.

RESULTS

Five eligible trials were retrieved and analyzed. We found that parturients with remifentanil PCIA had higher visual analog scale (10-cm scale) pain scores than those who received epidural analgesia at 1 hour (MD = 1.9 cm; 95% CI, 0.5-3.3; I = 94%) and 2 hours (MD = 3.0 cm; 95% CI, 0.7-5.2; I = 89%) after initiation of analgesia. There was no statistical difference between epidural analgesia and remifentanil PCIA in the incidence of nausea, vomiting, pruritus, or umbilical artery pH values. However, the CIs are quite wide and contain clinically significant differences. According to GRADE profiler, most end points had moderate quality except that pain scores at 1 hour were of low quality.

CONCLUSIONS

This meta-analysis suggests that remifentanil PCIA is not superior to epidural analgesia in analgesic efficacy during labor. Given the wide CIs of the pooled results for secondary maternal and neonatal outcomes, definite conclusions cannot be drawn for those outcomes. Further studies are still warranted to validate these conclusions.

Effects of anesthetics, sedatives, and opioids on ventilatory control

This article provides a comprehensive, up to date summary of the effects of volatile, gaseous, and intravenous anesthetics and opioid agonists on ventilatory control. Emphasis is placed on data from human studies. Further mechanistic insights are provided by in vivo and in vitro data from other mammalian species. The focus is on the effects of clinically relevant agonist concentrations and studies using pharmacological, that is, supraclinical agonist concentrations are de-emphasized or excluded.

Fentanyl utility function: a risk-benefit composite of pain relief and breathing responses

INTRODUCTION

Integrating opioid risk and benefit into a single function may give a useful single measure of the opioid's positive and negative effects. An explorative study on the effects of fentanyl on antinociception and respiratory depression was performed to construct fentanyl risk-benefit (utility) functions.

METHODS

Twelve volunteers received a 3.5-μg/kg fentanyl intravenous injection on 2 separate study days. On one occasion, ventilation at a clamped increased carbon dioxide concentration was measured and on another the pain tolerance to electrical stimulation. In both sessions, arterial plasma samples were obtained. The data were analyzed with a population pharmacokinetic-pharmacodynamic model. A simulation study was performed, using the model parameter estimates and their variances, in which simulated subjects received 3.5 μg/kg of fentanyl. The resultant distributions were used to calculate the utility functions, defined as the probability of at least 50% analgesia (an increase in pain tolerance by ≥50%) minus the probability of at least 50% respiratory depression (a reduction in ventilation by ≥50%). Utility functions were constructed in concentration and time domains.

RESULTS

Fentanyl produced significant respiratory depression and analgesia. The pharmacokinetic and pharmacodynamic models adequately described the data. The constructed utility functions were negative at effect-site concentrations of greater than 0.5 ng/ml in the first 90 min after the 3.5 μg/kg bolus infusion.

CONCLUSIONS

Utility functions based on fentanyl's experimental effects on respiration and pain relief were successfully constructed. These functions are useful in multiple effect comparisons among experimental drugs. Further studies are required to assess whether this risk-benefit analysis is valuable in clinical practice.

Intravenous boluses of fentanyl, 1 μg kg⁻¹, and remifentanil, 0.5 μg kg⁻¹, give similar maximum ventilatory depression in awake volunteers

BACKGROUND

The relative respiratory effects of fentanyl and remifentanil, administered as i.v. bolus, have not previously been studied. We determined what remifentanil bolus dose gave the same maximum depression of ventilation as 1 µg kg(-1) of fentanyl.

METHODS

Twelve healthy volunteers rebreathed in a system designed to dampen variations in end-tidal carbon dioxide tension PE'CO2 so that measurements would be obtained at similar levels of CO(2) stimulation. The minute ventilation was measured before (V(preinj)) and after injection (V(nadir)) of fentanyl, 1 µg kg(-1), and remifentanil, 0.25, 0.5, and 1 µg kg(-1). The remifentanil doses were plotted against V(nadir)/V(preinj) in a log-probit diagram to determine what amount gave the same maximum ventilatory depression as the fentanyl dose.

RESULTS

V(nadir) was [median (inter-quartile range)] 51 (38-64)% of V(preinj) after fentanyl, and 70 (61-77), 50 (46-56), and 29 (24-38)%, respectively, after remifentanil. The nadir occurred 5.0 (4.4-7.0) min after fentanyl, and 3.8 (2.7-4.6), 2.9 (2.7-3.2), and 3.0 (2.7-3.2) min after remifentanil injection. PE'CO2 at ventilation nadir was 6.26 (5.98-6.62) kPa after fentanyl, and 6.18 (6.12-6.50), 6.11 (5.91-6.45), and 6.11 (5.93-6.45) kPa after remifentanil 0.25, 0.5, and 1 µg kg(-1), respectively. A remifentanil dose of 0.47 (0.42-0.62) µg kg(-1) was equidepressant to 1 µg kg(-1) of fentanyl. Fifteen minutes after fentanyl injection, the median minute ventilation was 30-40% less than after injection of remifentanil, 0.25 and 0.5 µg kg(-1) (P<0.05).

CONCLUSIONS

Fentanyl, 1 µg kg(-1), and remifentanil, 0.5 µg kg(-1), gave similar maximum ventilatory depression. The onset of and recovery from ventilatory depression were faster with remifentanil.

Timing of intravenous patient-controlled remifentanil bolus during early labour

BACKGROUND

Remifentanil labour analgesia is superior to nitrous oxide but less potent than epidural analgesia. The short onset and offset times of effect suggest that the timing of the bolus in the contraction cycle could have importance. We hypothesised that administering a remifentanil bolus during contraction pause would improve analgesia in early labour.

METHODS

With permission from the ethical committee and the National Authority of Medicines, 50 parturients with uncomplicated singleton pregnancies and informed consent participated in a double blind cross-over study. Intravenous doses of 0.4 μg/kg remifentanil with 1-min infusion times were used during two study periods lasting six to eight contractions. Remifentanil and saline syringes were attached to two patient-controlled devices, one of which administered the bolus immediately after a trigger and the other targeted to start 140 s before the next contraction. The parturients assessed contraction pain, pain relief, sedation and nausea. Oxygen saturation (SaO(2)) pulse and blood pressure were recorded. SaO(2)<95% was the indication for oxygen supplement.

RESULTS

Forty-one parturients were included in the analyses. Because of the period effect, pain and pain relief scores were analysed separately for each of the study periods. The mean pain and pain relief scores were similar during the two different dosing regimens. Side effects, the need for supplemental oxygen, SaO(2) and haemodynamics were similar. In a subgroup with long and regular contractions, however, delayed boluses were associated with lower pain scores.

CONCLUSIONS

Administering a remifentanil bolus during the uterine contraction pause does not improve pain relief.

Group III and IV muscle afferents contribute to ventilatory and cardiovascular response to rhythmic exercise in humans

We investigated the role of somatosensory feedback on cardioventilatory responses to rhythmic exercise in five men. In a double-blind, placebo-controlled design, subjects performed the same leg cycling exercise (50/100/150/325 ± 19 W, 3 min each) under placebo conditions (interspinous saline, L(3)-L(4)) and with lumbar intrathecal fentanyl impairing central projection of spinal opioid receptor-sensitive muscle afferents. Quadriceps strength was similar before and after fentanyl administration. To evaluate whether a cephalad migration of fentanyl affected cardioventilatory control centers in the brain stem, we compared resting ventilatory responses to hypercapnia (HCVR) and cardioventilatory responses to arm vs. leg cycling exercise after each injection. Similar HCVR and minor effects of fentanyl on cardioventilatory responses to arm exercise excluded direct medullary effects of fentanyl. Central command during leg exercise was estimated via quadriceps electromyogram. No differences between conditions were found in resting heart rate (HR), ventilation [minute ventilation (VE)], or mean arterial pressure (MAP). Quadriceps electromyogram, O(2) consumption (VO(2)), and plasma lactate were similar in both conditions at the four steady-state workloads. Compared with placebo, a substantial hypoventilation during fentanyl exercise was indicated by the 8-17% reduction in VE/CO(2) production (VCO(2)) secondary to a reduced breathing frequency, leading to average increases of 4-7 Torr in end-tidal PCO(2) (P < 0.001) and a reduced hemoglobin saturation (-3 ± 1%; P < 0.05) at the heaviest workload (∼90% maximal VO(2)) with fentanyl. HR was reduced 2-8%, MAP 8-13%, and ratings of perceived exertion by 13% during fentanyl vs. placebo exercise (P < 0.05). These findings demonstrate the essential contribution of muscle afferent feedback to the ventilatory, cardiovascular, and perceptual responses to rhythmic exercise in humans, even in the presence of unaltered contributions from other major inputs to cardioventilatory control.

[Intravenous remifentanyl for labor analgesia]

BACKGROUND

Intravenous remifentanil may be the preferred analgesic when regional techniques are contraindicated.

OBJECTIVE

To perform a systematic review on the use of remifentanil for analgesia in labor.

METHODS

We searched MEDLINE (January 1995-August 2007) for studies on obstetric analgesia with remifentanil.

RESULTS

We found 32 references representing the use of remifentanil in 257 women in labor. In most cases, patients reported relief of pain and a high level of satisfaction, with no severe side effects in mothers or neonates. When compared with meperidine and nitrous oxide in clinical trials, remifentanil provided better analgesia with fewer adverse effects.

CONCLUSION

Analgesia with intravenous remifentanil is more effective and safer than other alternatives to regional analgesic techniques in obstetrics. Nevertheless, the optimum system for infusing the drug must b e established and further studies of maternal and fetal safety should be carried out.

Spontaneous respiration during intravenous anesthesia in children

PURPOSE OF REVIEW

Maintaining spontaneous respiration during intravenous anesthesia for investigative and surgical procedures may avoid the need for airway instrumentation and reduce the risk of desaturation. In addition, when performing airway endoscopic procedures in children, maintaining spontaneous respiration while using intravenous anesthesia can reduce the need for endotracheal intubation. This facilitates improved access to the smaller airway, allows assessment of the dynamic function of the airway, and reduces exposure of personnel to inhaled anesthetic agents.

RECENT FINDINGS

Anesthetic hypnotic and analgesic agents are potent dose-dependent depressants of respiration. Infants have historically been considered to be at a higher risk of respiratory depression, especially from opioid analgesics. However, recent evidence suggests that infants and younger children outside the neonatal period are more resistant to the effects of remifentanil, even when combined with propofol. Spontaneous respiration can be maintained at doses adequate to suppress somatic responses to painful procedures. The large inter-individual variation in respiratory depressant effects necessitates individualized dose titration. The drug dose is more linearly related to variation in the respiratory rhythm and respiratory rate than to minute volume or end-tidal carbon dioxide. Apneic episodes are less likely when respiratory depressant drugs are administered slowly, as this allows time for the end-tidal carbon dioxide level to rise to a new apneic threshold. Hypnotic anesthetics and opioid analgesics act synergistically to cause respiratory depression and suppression of the somatic response.

SUMMARY

Spontaneous respiration can be maintained when anesthetizing children using intravenous anesthesia.

Manual versus target-controlled infusion remifentanil administration in spontaneously breathing patients

BACKGROUND

The combination of propofol-remifentanil for procedural deep sedation in spontaneously breathing patients is characterized by the frequent incidence of side effects, especially respiratory depression. These side effects may be due to either the drug combination or the drug delivery technique. Target-controlled infusion (TCI) might optimize drug delivery. In this prospective, randomized, double-blind study in patients undergoing elective colonoscopy, we thus tried to answer two questions: first, if adding remifentanil to propofol surpasses the disadvantages of the combination of these two products, and second, if administration of remifentanil via TCI decreases the incidence of side effects, compared to manually controlled administration.

METHODS

Patients undergoing elective colonoscopy were randomly assigned to receive remifentanil via manually controlled continuous infusion (MCI) (0.125 microg x kg(-1) x min(-1) for 2 min followed by a continuous infusion of 0.05 microg x kg(-1) x min(-1)), TCI remifentanil (1 ng/mL), or placebo (normal saline either as TCI or manual infusion of equivalent rate). All patients received TCI propofol, adjusted to a target concentration level that provided deep sedation in which patients were not responsive to verbal commands, but maintained spontaneous ventilation without assistance.

RESULTS

Significantly more patients in the placebo group showed movement, cough and hiccup, which transiently interfered with the examination. There were no clinically significant differences in hemodynamic or recovery variables among all groups. Remifentanil administered via TCI resulted in a decrease in propofol requirements. The incidence of hypopnea and apnea was less frequent when remifentanil was administered via TCI compared to MCI (TCI n = 7, MCI n = 16, P < 0.05).

CONCLUSION

The combination of remifentanil and propofol for deep sedation in spontaneously breathing patients, offered better conditions for colonoscopy than propofol used as a single drug. Remifentanil administered via TCI resulted in a decrease in propofol dosing and in a lower incidence in apnea and respiratory depression (TCI n = 7, MCI n = 16, P < 0.05), compared to manually controlled administration of remifentanil.

Remifentanil for postoperative patient-controlled analgesia after laparoscopic-assisted vaginal hysterectomy: dose-finding study

BACKGROUND

This randomized, double-blinded clinical study was designed to compare the efficacy and safety of three regimens of intravenous (IV) patient-controlled analgesia (PCA) with remifentanil for postoperative analgesia after laparoscopic-assisted vaginal hysterectomy during the first 24 postoperative hours.

METHODS

Thirty-four patients were randomly allocated into three groups. The first group received IV remifentanil PCA at a basal rate of 0.02 microgram/kg/min, a bolus of 0.3 microgram/kg, and a lockout time of 15 min. The second group received IV-PCA at a basal rate of 0.025 microgram/kg/min, a bolus of 0.375 microgram/kg, and a lockout time of 15 min. The third group received IV-PCA at a basal rate of 0.03 microgram/kg/min, a bolus of 0.45 microgram/kg, and a lockout time of 15 min. Age, weight, height, and duration of surgery and anesthesia were recorded. Heart rate, systolic and diastolic blood pressure (BP) and oxygen saturation by pulse oxymetry were recorded in the recovery room as a base line after the operation. Heart rate, systolic and diastolic BP, sedation score, visual analogue scale (VAS), and postoperative nausea and vomiting (PONV) scores were recorded at 1 h, 3 h, 6 h, 12 h, and 24 h after the initiation of IV-PCA.

RESULTS

Thirty two patients were evaluated. The VAS in group 1 at 1, 3 and 6 hours after surgery was significantly higher than in other groups (P < 0.05). There were no clinically relevant differences between the groups in PONV, sedation scores, or hemodynamic parameters.

CONCLUSIONS

This study suggests that IV remifentanil PCA with at a basal rate of 0.025 microgramram/kg/min (group 2) provided efficacious analgesia after laparoscopic-assisted vaginal hysterectomy. Special attention must be given to respiratory depression during establishment of PCA with remifentanil.

The use of remifentanil in obstetrics

Remifentanil has been proposed as the most suitable systemic opioid for use in obstetrics. Although the onset and offset are rapid, it cannot achieve maximum effect within the time period of a single uterine contraction. Nevertheless, it provides worthwhile analgesia mainly for the first stage of labor with consistently high maternal satisfaction. Maternal oxygen desaturation limits the dose and suitable monitoring during use is advised. As an adjunct to general anesthesia, it is successful in blunting responses to airway manipulation and providing hemodynamic stability in high-risk women. Neonatal effects when used in labor are minimal, but when combined with general anesthesia neonatal depression is unpredictable and more likely with an infusion dose greater than 0.1 microg/kg/min.

Options for systemic labor analgesia

PURPOSE OF REVIEW

This article reviews the challenging practice of systemic analgesia as an alternative to epidural analgesia for labor pain, and places remifentanil within the context of opioid analgesics suitable for managing for labor pain.

RECENT FINDINGS

Although systemic opioids have long been used for labor analgesia, they have become less popular because of frequent maternal and neonatal side effects. Recently, their efficacy has been questioned. Patient-controlled intravenous analgesia with fentanyl or sufentanil is currently the method of choice for achieving analgesia during early labor, when epidural analgesia is not feasible. Remifentanil has been suggested as the opioid of choice for labor analgesia, having the advantage of easy administration, predictable pharmacokinetics, and improved neonatal outcomes. The position of remifentanil in obstetric analgesia is now better understood, as reflected by the increasing number of reported studies describing its use.

SUMMARY

Remifentanil is now gaining popularity. Remifentanil may be more suitable than other traditional opioids for inducing labor analgesia. Careful monitoring of the parturient and the newborn is recommended, however, to mitigate the potential for maternal and neonatal hypoxemia.

Pharmacological FMRI: measuring opioid effects on the BOLD response to hypercapnia

Opioid binding to the cerebral blood vessels may affect vascular responsiveness and hence confound interpretation of blood oxygen level-dependent (BOLD) responses, which are usually interpreted as neuronal in origin. Opioid binding varies in different brain regions. It is unclear whether opioids alter neurovascular coupling, or whether their effects are purely neuronal. This study used BOLD functional magnetic resonance imaging (FMRI) to investigate the effect of a mu-opioid agonist remifentanil, on cerebrovascular CO(2) reactivity (being one component of neurovascular coupling). Hypercapnic challenges were delivered to human volunteers, while controlling potential opioid-induced respiratory depression. The BOLD signal increase to hypercapnia was compared before and during remifentanil administration. Remifentanil was shown not to have a generalised effect on CO(2) responsiveness in the cerebral vasculature. However, it caused a significant reduction in the positive BOLD response to hypercapnia in the bilateral primary sensorimotor cortices, bilateral extrastriate visual areas, left insula, left caudate nucleus, and left inferior temporal gyrus. We conclude that remifentanil does not modulate cerebrovascular CO(2) reactivity, as we saw no difference in BOLD response to hypercapnia in areas with high opioid receptor densities. We did however see a focal reduction in areas related to motor control and putative task activation, which we conclude to be related to changes in neuronal activity related to the sedative effects of remifentanil. Our method of controlling CO(2) levels effectively mitigated the potential confound of respiratory depression and allowed comparison over a similar range of CO(2) levels. We suggest that similar methodology should be used when investigating other potentially vasoactive compounds with FMRI.

Remifentanil-based sedation to treat noninvasive ventilation failure: a preliminary study

OBJECTIVE

To assess the feasibility and safety of remifentanil-based sedation during noninvasive ventilation (NIV) in patients with NIV failure.

DESIGN AND SETTING

Prospective clinical investigation in a 16-bed intensive care unit of a university hospital in France.

PATIENTS

Thirteen patients in NIV failure due to discomfort and/or refusal to continue this ventilatory support: 10 with acute respiratory failure and 3 with acute hypercapnic respiratory failure.

INTERVENTION

Patients were administered methylene blue and were sedated (Ramsay scale 2-3) by a continuous perfusion of remifentanil during NIV. Cardiorespiratory and ventilatory parameters, blood gas analysis, and adverse events were prospectively recorded.

MEASUREMENTS AND RESULTS

The 13 patients received a total of 125 NIV sessions, totaling 1200 h, of NIV under remifentanil-based sedation (mean remifentanil dose 0.1+/-0.03 microg/kg per minute). Three patients also required propofol. PaO2/FIO2 ratio increased from 134+/-69 to 187+/-43 mmHg after 1 h. In patients with acute respiratory failure respiratory rate decreased from 34+/-12 per minute before remifentanil to 25+/-4 per minute after 1h. In the three patients with acute hypercapnic respiratory failure PaCO2 decreased from 69+/-7 to 42+/-5 mmHg. Four patients required endotracheal intubation without aspiration pneumonia. Twelve of the 13 patients left the ICU.

CONCLUSION

This pilot study shows that remifentanil-based sedation is safe and effective in the treatment of NIV failure due to low tolerance.

Remifentanil or sufentanil for coronary surgery

BACKGROUND AND OBJECTIVE

High-dose opioid anaesthesia contributes to decreasing metabolic and hormonal stress responses in patients undergoing cardiac surgery. However, the increase in context-sensitive half-life of opioids given as a high-dose regimen can affect postoperative respiratory recovery. In contrast, remifentanil can be given in high doses without prolonging context-sensitive half-life due to its rapid metabolism. Therefore, we performed a prospective, randomized trial to compare anaesthesia consisting of propofol/remifentanil or propofol/sufentanil with regard to postoperative respiratory function and outcome.

METHODS

Patients undergoing coronary artery bypass grafting were randomized to a propofol/remifentanil (0.5-1.0 microg kg(-1) min(-1)) or propofol/sufentanil (30-40 ng kg(-1) min(-1)) based anaesthetic. Carbon dioxide response, forced expiratory volume in one second, vital capacity, and functional residual capacity were measured 1 day prior to the operation, 1 h before extubation, 1, 24 and 72 h after extubation. In addition, the incidence of atelectasis, pulmonary infiltrates, intensive care unit and postoperative length of stay were compared. Patients and physicians were blinded to the treatment group.

RESULTS

Twenty-five patients in each treatment group completed the study. There was no difference between patients of the treatment groups regarding demographics, risk- or pain scores. In all patients, carbon dioxide response, forced expiratory volume in one second, vital capacity and functional residual capacity were decreased postoperatively compared to baseline. Patients randomized to remifentanil had less depression of carbon dioxide response, less atelectasis and shorter postoperative length of stay (12 d vs. 10 d) than after sufentanil (P < 0.05).

CONCLUSIONS

Intraoperative use of high-dose remifentanil for coronary artery bypass grafting may be associated with improved recovery of pulmonary function and shorter postoperative hospital length of stay than sufentanil.

Evaluation of propofol and remifentanil for intravenous sedation for reducing shoulder dislocations in the emergency department

OBJECTIVES

To assess the combination of propofol and remifentanil for sedation to reduce shoulder dislocations in an ED.

METHODS

Eleven patients with anterior glenohumeral dislocation were given propofol 0.5 mg/kg and remifentanil 0.5 microg/kg iv over 90 seconds and then further doses of 0.25 mg/kg and 0.25 microg/kg, respectively, if needed. Another practitioner attempted reduction using the Milch technique.

RESULTS

Reduction was achieved in all patients within four minutes of giving sedation (range 0.3-4; mean 1.6). Seven required one attempt at shoulder reduction, three required two attempts, and one required three attempts. Mean time to recovery of alert status was three minutes (range 1-6). The mean pain score during the reduction was 1.7 out of 10 (range 0-5). Nine patients had full recall, one had partial recall, and one had no recall at all. Eight patients were "very satisfied" with the sedation and three were "satisfied". There were no respiratory or haemodynamic complications that required treatment.

CONCLUSIONS

Propofol and remifentanil provide excellent sedation and analgesia for the reduction of anterior glenohumeral dislocation, enabling rapid recovery.

Acute opioid effects on human brain as revealed by functional magnetic resonance imaging

Functional magnetic resonance imaging has been widely used to study brain activation induced either by specific sensory stimulation or motor or cognitive task performance. We demonstrate that functional magnetic resonance imaging can provide information of brain regions involved in opioid-induced central nervous system effects. The reproducibility of the responses in the predefined regions of interest was confirmed by repeated boluses of ultra-short acting mu-opioid receptor agonist remifentanil and saline. We report spatially and temporally detailed information after remifentanil administration. Areas rich in mu-opioid receptors showed strong activations, whereas primary somatosensory cortex that has the lowest density of mu-opioid receptors showed negligible activation. The cingulate, orbitofrontal, posterior parietal and insular cortices, and amygdala showed activation, which was temporally closely related to most subjective sensations that were strongest at 80 to 90 s after drug administration. These areas belong to a circuitry that modulates the affective experience of sensory stimuli.

Remifentanil

Remifentanil (Ultiva), a 4-anilidopiperidine derivative of fentanyl, is an ultra-short-acting micro-opioid receptor agonist indicated to provide analgesia and sedation in mechanically ventilated intensive care unit (ICU) patients.Analgesia-based sedation with remifentanil is a useful option for mechanically ventilated patients in the ICU setting. Its unique properties (e.g. organ-independent metabolism, lack of accumulation, rapid offset of action) set it apart from other opioid agents. Remifentanil is at least as effective as comparator opioids such as fentanyl, morphine and sufentanil in providing pain relief and sedation in mechanically ventilated ICU patients. Moreover, it allows fast and predictable extubation, as well as being associated with a shorter duration of mechanical ventilation and quicker ICU discharge than comparators in some studies. In addition, remifentanil is generally well tolerated in this patient population. Thus, remifentanil is a welcome addition to the currently available pharmacological agents employed in the management of mechanically ventilated ICU patients.

Remifentanil as a Single Drug for Extracorporeal Shock Wave Lithotripsy: A Comparison of Infusion Doses in Terms of Analgesic Potency and Side Effects

This randomized, double-blind study was designed to evaluate analgesic effectiveness and side effects of two remifentanil infusion rates in patients undergoing extracorporeal shock wave lithotripsy (ESWL) for renal stones. We included 200 patients who were administered remifentanil either 0.05 microg x kg(-1) x min(-1) (n = 100) or 0.1 microg x kg(-1) x min(-1) (n = 100) plus demand bolus of 10 microg of remifentanil via a patient-controlled analgesia (PCA) device. No other sedating drugs were given. The frequencies of PCA demands and deliveries were recorded. Arterial blood pressure, oxygen saturation, and respiratory rate were recorded throughout the procedure; postoperative nausea and vomiting (PONV), dizziness, itching, agitation, and respiratory depression were measured posttreatment. Visual analog scale (VAS) scores were taken preoperatively, directly postoperatively, and 30 min after finishing the procedure. There were no statistically significant differences in the frequency of PCA demands and delivered boluses or among perioperative VAS scores. The extent of PONV and frequency of dizziness and itching immediately after and dizziness 30 min after the end of treatment were significantly reduced in the smaller dose group. We conclude that a remifentanil regimen of 0.05 microg x kg(-1) x min(-1) plus 10 microg demands is superior to 0.1 microg x kg(-1) x min(-1) plus demands, as there was no difference in the VAS scores recorded between groups and it has a less frequent incidence of side effects in patients receiving ESWL.

IMPLICATIONS

Remifentanil is an appropriate analgesic choice for patients undergoing extracorporeal shock wave lithotripsy (ESWL) therapy, as it has both fast onset and offset times. We studied remifentanil as a sole drug for ESWL and have shown that an infusion rate of 0.05 microg x kg-1 x min-1 plus patient-controlled analgesia demands of 10 microg provides adequate analgesia and has significantly less side effects than a dose of 0.1 microg x kg-1 x min-1 plus 10 microg demands.

The safety of remifentanil by bolus injection

Remifentanil is the newest of the fentanyl family of short-acting phenylpiperidine derivatives to be released into clinical practice. Remifentanil is a pure agonist at the mu opioid receptor with relatively little binding at the kappa, sigma or delta receptors. This is precisely the same profile as the other opioids currently popular in anaesthetic practice (fentanyl, alfentanil, sufentanil) and it offers the same advantages (profound analgesia, sedation, attenuation of the stress response). This has led to widespread use of remifentanil as an adjunct to general anaesthesia in a variety of clinical settings. The unique pharmacology of remifentanil, in particular its rapid offset, has more recently attracted clinicians and investigators to the use of remifentanil by bolus injection, especially for procedures requiring a brief, intense, opioid effect. The clinical effects of remifentanil, both therapeutic and adverse, are consistent with that of the other fentanyl congeners. However, the pharmacokinetic profile of remifentanil, that is, its rapid effect site equilibration, has also revealed a significant potential for therapeutic misadventure. The untoward effects of remifentanil, given by continuous infusion, are well-described in the literature. They are predictable and easily managed by experienced clinicians. This review will concentrate on the adverse effects of remifentanil given by bolus injection, either alone or in the context of a background infusion.

Remifentanil for Fetal Immobilization and Maternal Sedation During Fetoscopic Surgery: A Randomized, Double-Blind Comparison with Diazepam

Obstetric endoscopy procedures are routinely performed at our institution to treat selected complications of monochorionic twin gestation. We perform these procedures under combined spinal epidural anesthesia plus maternal sedation. In the absence of general anesthesia, fetal immobilization is not achieved. We hypothesized that remifentanil would induce adequate maternal sedation and provide fetal immobilization, which is equal or superior to that induced by diazepam. Fifty-four second trimester pregnant women were included in this randomized, double-blind trial. After combined spinal epidural anesthesia, maternal sedation was initiated using either incremental doses of diazepam or a continuous infusion of remifentanil. Maternal sedation, hemodynamics, side effects, and fetal hemodynamics and immobilization were evaluated before, during, and for 60 min after surgery. Remifentanil produced adequate maternal sedation with mild but clinically irrelevant respiratory depression (respiratory rate 13 +/- 4 breaths/min and Pco(2) 38.6 +/- 4 mm Hg at 40 min of surgery), whereas diazepam resulted in a more pronounced maternal sedation but no respiratory depression (respiratory rate 18 +/- 3 breaths/min and Pco(2) 32.7 +/- 3 mm Hg at 40 min of surgery). Compared with diazepam, fetal immobilization with remifentanil occurred faster and was more pronounced, resulting in improved surgical conditions; the number of gross body and limb movements was 12 +/- 4 (diazepam) versus 2 +/- 1 (remifentanil) at 40 min of surgery. Because of this, the mean (range) duration of surgery was significantly shorter in the remifentanil-treated patients, 60 (54-71) min versus 80 (60-90) min in the diazepam group. We conclude that remifentanil produces improved fetal immobilization with good maternal sedation and only minimal effects on maternal respiration.

Comparison of remifentanil and nitrous oxide in labour analgesia

BACKGROUND

We compared the efficacy and side-effects of remifentanil with those of nitrous oxide during the first stage of labour.

METHODS

Twenty parturients participated in a randomized, double-blind, cross-over study. Intravenous remifentanil in 0.4 microg kg(-1) PCA doses with 1-min infusion and lock-out times and intermittent inhaled 50% nitrous oxide were compared during 20-min study periods with a 20-min wash-out sequence after each period. The parturients assessed the intensity of contraction pain (verbal numerical score 0-10), pain relief (score 0-4) and side-effects every 10 min. Noninvasive blood pressure, heart rate (HR), oxyhaemoglobin saturation (SaO2), end-tidal carbon dioxide, fractions of inhaled and exhaled oxygen and nitrous oxide and foetal heart rate (FHR) were recorded. Hypoxaemia and bradycardia were defined as SaO2<90% and HR<50, respectively.

RESULTS

Fifteen parturients completed the study. There was no period effect or treatment-period interaction. The median decrease in pain score for remifentanil was 1.5 and that for nitrous oxide 0.5 (P=0.01). The parturients gave better pain relief scores with remifentanil than with nitrous oxide (median 2.5 vs. 0.5, respectively, P<0.001). Sedation was reported more often, and SaO2 was slightly lower during remifentanil administration. No episodes of hypoxaemia occurred. There was no difference in maternal blood pressure and HR or the incidence of abnormal FHR during remifentanil compared to nitrous oxide. Most parturients preferred remifentanil to nitrous oxide (14 vs. 1, P<0.001).

CONCLUSIONS

This study suggests that IVPCA remifentanil provides better labour analgesia than intermittently inhaled nitrous oxide.

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.

Remifentanil used to supplement propofol does not improve quality of sedation during spontaneous respiration

STUDY OBJECTIVE

To evaluate whether the use of remifentanil to supplement propofol during spontaneous respiration confers any benefits in terms of quality of sedation and recovery, or in terms of reduction in propofol requirements.

DESIGN

Prospective, randomized, double-blind study.

SETTING

University hospital.

PATIENTS

50 ambulatory adult ASA physical status I and II patients scheduled for total colonoscopy.

INTERVENTIONS

Patients were randomized to receive either propofol alone or propofol plus remifentanil 0.1 microg/kg/min, while independently maintaining spontaneous respiration.

MEASUREMENTS

Cardiovascular and respiratory variables were measured before induction and at 1-minute intervals thereafter. Recovery from anesthesia was assessed using simple verbal commands and the Steward Post Recovery Score. Patient satisfaction was measured with a visual analog scale. Computer simulation was used to calculate the effect-site concentrations of propofol and remifentanil.

MAIN RESULTS

The depressant effects on blood pressure and respiratory function were significantly higher when propofol and remifentanil were combined. Although the addition of remifentanil resulted in a decrease of propofol usage, recovery of anesthesia was faster and patient satisfaction was higher when using propofol alone.

CONCLUSIONS

The addition of remifentanil to propofol during spontaneous ventilation offered no benefits compared with the use of propofol alone.

Remifentanil by bolus injection: a safety, pharmacokinetic, pharmacodynamic, and age effect investigation in human volunteers

BACKGROUND

Although remifentanil's short-acting pharmacokinetic profile makes it well suited for procedures during which a brief period of intense analgesia is required, setting up an infusion pump for brief procedures is inconvenient. The clinical pharmacology of remifentanil administered by bolus injection, a more convenient alternative, has not been explored in detail. The primary aim of this study was to examine the safety of single bolus doses of remifentanil in conscious, healthy, adult volunteers breathing room air. Secondary aims included the evaluation of remifentanil pharmacokinetics and analgesic effects after bolus injection and a comparison of these issues in younger vs older adults.

METHODS

Using a randomized, double-blind, placebo-controlled, dose-escalation, crossover study design, 64 subjects (16 over 60 years old) received remifentanil or placebo by bolus injection in a fixed unit dose separated by a 1 h washout period. Respiratory effects were assessed using a respiratory intervention scale. Analgesic effects were assessed using pressure algometry. A population pharmacokinetic model was constructed using non-linear, mixed-effects modelling techniques based on arterial blood samples. Computer simulations were performed to illustrate the clinical application of the pharmacokinetic model.

RESULTS

Dose-related increases in both respiratory and analgesic effects were observed. In general, the respiratory depression observed was mild and easily treated with requests to breathe or the administration of oxygen, although the older cohort (and some younger subjects) experienced more substantial respiratory depression at lower doses. The pharmacokinetics of bolus-dose remifentanil were adequately described by a two-compartment model. The pharmacokinetic simulations illustrated the potential utility of bolus-dose remifentanil.

CONCLUSIONS

Bolus injection could potentially be a safe and effective means of administering remifentanil in clinical situations requiring a brief period of intense analgesia. Because some subjects, both old and young, experienced significant respiratory depression even at low doses, careful monitoring of respiratory function is essential.

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.

Awake nasotracheal fiberoptic intubation: patient comfort, intubating conditions, and hemodynamic stability during conscious sedation with remifentanil

Awake nasotracheal fiberoptic intubation requires an anesthetic management that provides sufficient patient comfort, adequate intubating conditions, and stable hemodynamics. Short-acting and easily titratable analgesics are excellent choices for this maneuver. In this study, our aim was to determine an appropriate dosage regimen of remifentanil for awake nasotracheal fiberoptic intubation. For that reason, we compared two different dosage regimens. Twenty-four patients were randomly assigned to receive remifentanil 0.75 micro g/kg in bolus, followed by a continuous infusion of 0.075 micro g x kg(-1) x min(-1) (Group L), or remifentanil 1.5 micro g/kg in bolus, followed by a continuous infusion of 0.15 micro g x kg(-1) x min(-1) (Group H). All patients were premedicated with midazolam 0.05 mg/kg IV and glycopyrrolate 0.2 mg IV. Both dosage regimens ensured patient comfort and sedation. Discomfort did not differ between groups. Patients in Group H were sedated more profoundly. Hemodynamic stability was maintained with both remifentanil doses. Intubating conditions were adequate in all patients and comparable between the groups. The large dosage regimen did not result in any additional benefit compared with the small dosage. For awake nasotracheal fiberoptic intubation, we therefore recommend remifentanil 0.75 micro g/kg in bolus followed by continuous infusion of 0.075 micro g x kg(-1) x min(-1), supplemented with midazolam 0.05 mg/kg.

Choice of opioid supplementation for day-case rigid bronchoscopy:a randomized placebo-controlled comparison of a bolus of remifentanil and alfentanil

OBJECTIVE

To compare the efficacy of different bolus doses of remifentanil, alfentanil, and saline at controlling the hemodynamic responses to day-case rigid bronchoscopy under general anesthesia.

DESIGN

Prospective, randomized, double-blind, placebo-controlled study.

SETTING

Tertiary referral cardiothoracic hospital, single center.

PARTICIPANTS

Eighty consenting adults scheduled for elective day-case rigid bronchoscopy under general anesthesia.

INTERVENTIONS

Patients were randomized to receive a bolus of 10 micro g/kg of alfentanil, 1 micro g/kg of remifentanil, 2 micro g/kg of remifentanil or saline. After this, anesthesia was induced and maintained with a target-controlled propofol infusion (TCI) and succinylcholine was used for muscle relaxation. Heart rate and noninvasive arterial pressure were measured at 1-minute intervals throughout.

MEASUREMENTS AND MAIN RESULTS

Patients' characteristics were similar in all 4 groups. There were no differences in time to return of spontaneous ventilation, wake-up times, or use of rescue vasopressors, and no patients complained of postoperative nausea. Remifentanil provided greater hemodynamic stability than alfentanil and a bolus of remifentanil of 2 micro g/kg significantly attenuated the rise in heart rate and was the most effective in preventing a rise in blood pressure.

CONCLUSIONS

A bolus of 2 micro g/kg of remifentanil successfully attenuated the hemodynamic response to rigid bronchoscopy without delaying recovery.