Remifentanil

Effects of hypothermia on drug disposition, metabolism, and response: A focus of hypothermia-mediated alterations on the cytochrome P450 enzyme system

OBJECTIVES

Therapeutic hypothermia has been shown to decrease neurologic damage in patients experiencing out-of-hospital cardiac arrest. In addition to being treated with hypothermia, critically ill patients are treated with an extensive pharmacotherapeutic regimen. The effects of hypothermia on drug disposition increase the probability for unanticipated toxicity, which could limit its putative benefit. This review examines the effects of therapeutic hypothermia on the disposition, metabolism, and response of drugs commonly used in the intensive care unit, with a focus on the cytochrome P450 enzyme system.

DATA SOURCES AND STUDY SELECTION

A MEDLINE/PubMed search from 1965 to June 2006 was conducted using the search terms hypothermia, drug metabolism, P450, critical care, cardiac arrest, traumatic brain injury, and pharmacokinetics.

DATA EXTRACTION AND SYNTHESIS

Twenty-one studies were included in this review. The effects of therapeutic hypothermia on drug disposition include both the effects during cooling and the effects after rewarming on drug metabolism and response. The studies cited in this review demonstrate that the addition of mild to moderate hypothermia decreases the systemic clearance of cytochrome P450 metabolized drugs between approximately 7% and 22% per degree Celsius below 37degreesC during cooling. The addition of hypothermia decreases the potency and efficacy of certain drugs.

CONCLUSIONS

This review provides evidence that the therapeutic index of drugs is narrowed during hypothermia. The magnitude of these alterations indicates that intensivists must be aware of these alterations in order to maximize the therapeutic efficacy of this modality. In addition to increased clinical attention, future research efforts are essential to delineate precise dosing guidelines and mechanisms of the effect of hypothermia on drug disposition and response.

Combination sedoanalgesia with remifentanil and propofol versus remifentanil and midazolam for elective cardioversion after coronary artery bypass grafting

Postoperative atrial fibrillation (AF) occurs in up to 50% of cardiac surgery patients and represents the most common postoperative arrhythmic complication. Elective cardioversion, a short but painful procedure, remains an option for patients who do not convert to sinus rhythm with medical therapy. Combinations of remifentanil (a potent analgesic with a short elimination time) with propofol (a hypnotic agent) or midazolam (a sedative agent) produce a synergistic interaction. This study was undertaken to compare these combinations in terms of effectiveness and pain relief when given as sedoanalgesia for elective cardioversion. In this prospective, randomized trial, 60 adult patients with postoperative AF after coronary artery bypass grafting were given a single dose of propofol 1 mg/kg combined with remifentanil 0.1 microg/kg (group 1), or midazolam 0.05 mg/kg combined with remifentanil 0.1 microg/kg (group 2). Cardiorespiratory parameters were monitored and recorded. Demographic data were similar (P>.05) and sufficient sedoanalgesia and successful cardioversion were achieved in both groups. Hemodynamic parameters revealed no significant differences between groups (P>.05); however, induction time, time to eye opening, recuperation time, and time to full recovery of psychomotor function were faster in group 1 than in group 2 (P<.05). The remifentanil/propofol combination provided sufficient analgesia, satisfactory hemodynamic stability, and mild respiratory depression, along with faster recovery and discharge times from the intensive care unit.

Comparison of remifentanil and fentanyl in anaesthesia for elective cardioversion

This prospective, randomized, double-blind study was designed to compare the recovery characteristics of remifentanil and fentanyl in combination with propofol for direct current cardioversion. Patients undergoing elective cardioversion received either intravenous fentanyl 1 microg/kg (n=33) or remifentanil 0.25 microg/kg (n=30) and propofol was titrated to a Ramsay sedation score of 5 by slow intravenous injection. Heart rate, systolic, diastolic and mean blood pressures decreased significantly following sedation in both groups but did not show a significant difference between the groups. Time to answer a question (306 +/- 83 vs 383 +/- 131s, mean +/- SD, P=0.014) and time to sit up (412 +/- 90 vs 511 +/- 126s, P=0.002) were significantly shorter in the remifentanil group compared to the fentanyl group. Side-effects and patient discomfort were similar for both groups. Remifentanil can be used as a suitable supplement to propofol for direct current cardioversion and may provide a faster recovery profile than fentanyl.

The effect of fentanyl and remifentanil, with or without ketoprofen, on pain after thyroid surgery

BACKGROUND AND OBJECTIVES

This study was designed to quantify the additional postoperative analgesic efficacy of a single dose of ketoprofen in patients undergoing thyroid surgery using two different intraoperative analgesic regimens.

METHODS

One hundred and twenty patients were randomly assigned to one of four groups: intraoperative fentanyl or remifentanil with or without ketoprofen (n = 30 for each group). Intravenous ketoprofen (1.5 mg kg-1) or saline was administered 45 min before the end of surgery. Pain scores, opioid demand and length of stay in the postanaesthesia care unit were assessed in a blinded manner.

RESULTS

Patients receiving intraoperative fentanyl with saline had significantly lower visual analogue scale pain scores in the postanaesthesia care unit compared with those receiving intraoperative remifentanil with saline (55 +/- 10 mm vs. 80 +/- 18 mm, P < 0.05) and they stayed shorter in the postanaesthesia care unit (86 +/- 24 min vs. 126 +/- 37 min). In conjunction with intraoperative fentanyl, ketoprofen significantly decreased postoperative pain scores (40 +/- 10 mm, P < 0.05 compared with fentanyl alone) and opioid demand (4 of 30 patients vs. 14 of 30 patients compared with fentanyl alone, P < 0.05). Patients receiving intraoperative remifentanil had no additional analgesic benefit with ketoprofen.

CONCLUSION

After thyroid surgery, patients receiving intraoperative fentanyl had lower pain scores and needed less rescue analgesia compared with patients receiving intraoperative remifentanil. The adjunction of ketoprofen further improved analgesia in patients who received intraoperative fentanyl only.

The novel analgesic, F 13640, produces intra- and postoperative analgesia in a rat model of surgical pain

F 13640 is a newly discovered high-efficacy 5-HT(1A) receptor agonist that produces exceptional analgesia in animal models of tonic and chronic, nociceptive and neuropathic pains by novel molecular and neuroadaptive mechanisms. Here we examined the effects of F 13640 and remifentanil (0.63 mg/kg with either compound) when injected i.p. either before or 15 min after rats underwent orthopedic surgery. Surgery consisted of the drilling of a hole in the calcaneus bone and of an incision of the skin, fascia and plantar muscle of one foot. During surgery, the concentration of volatile isoflurane was progressively incremented depending on the animal's response to surgical maneuvers. Other experiments examined the dose-dependent effects of F 13640 (0.04 to 0.63 mg/kg) on surgical pain as well as on the Minimum Alveolar Concentration of isoflurane. Both F 13640 and remifentanil markedly reduced the intra-operative isoflurane requirement. F 13640 also reduced measures of postoperative pain (i.e., paw elevation and flexion). With these postoperative measures, remifentanil produced short-lived analgesia followed by hyperalgesia. F 13640 significantly reduced both surgical pain and the isoflurane Minimum Alveolar Concentration from 0.16 mg/kg onward. F 13640 produced powerful intra- and postoperative analgesia in rats undergoing orthopedic surgery. Unlike the opioid, remifentanil, F 13640 caused no hyperalgesia with ongoing postoperative pain, and should remain effective with protracted postoperative use.

Postoperative Analgesia with Remifentanil in Patients Undergoing Cardiac Surgery

Remifentanil, a short-acting opioid, is commonly used in cardiac anesthesia. In this study we sought to demonstrate the feasibility of pain treatment and to determine the remifentanil dose necessary for adequate analgesia in tracheally extubated patients after cardiac surgery. Thirty patients undergoing elective cardiac surgery were included in this study. After surgery, the intraoperatively administered remifentanil was initially continued at 0.05 microg . kg(-1) . min(-1). Before tracheal extubation, a nonsteroidal antiinflammatory drug was administered and remifentanil was reduced to 0.035 microg . kg(-1) . min(-1). Pain assessment using a visual analog scale (VAS) was performed after tracheal extubation, in 2-min intervals for 10 min, every 10 min until the end of the first hour and every 30 min during the ensuing 5 h. A VAS score > or =30 or a respiratory rate <10 breaths/min was followed by an increase or decrease in the remifentanil dose by 0.005 microg . kg(-1) . min(-1), respectively. For rapid dose adaptation during the first 10 min, remifentanil was increased twice by 0.005 microg. kg(-1) . min(-1) and then 3 times by 0.01 microg . kg(-1) . min(-1). With a mean remifentanil dose of 0.051 microg . kg(-1) . min(-1) VAS decreased to 26 +/- 14 after 30 min. Sufficient analgesia was achieved with remifentanil doses ranging from 0.03 to 0.09 microg. kg(-1) . min(-1). A maximum mean remifentanil dose of 0.057microg. kg(-1) . min(-1) was reached after 4 h. The combination of remifentanil with a nonsteroidal antiinflammatory drug provided adequate analgesia in 73% of patients 30 min after tracheal extubation. Rapid dose titration was necessary during the first 10 min in 50% of patients. Increasing the initial remifentanil dose could shorten the titration period but may be associated with respiratory complications.

The comparative hemodynamic effects of methohexital and remifentanil in electroconvulsive therapy

Remifentanil is a short acting opioid frequently used to supplement general anesthesia for brief procedures. Narcotic agents are known for their ability to blunt autonomic responses to stimuli such as laryngoscopy and intubation and do not alter seizure threshold. We hypothesized that the combination of remifentanil and methohexital for induction would produce favorable suppression of sympathetic response during electroconvulsive therapy (ECT). With Institutional Review Board approval and informed consent, patients were enrolled in a prospective, randomized, double-blind, crossover study of methohexital alone versus remifentanil with an adjuvant of low-dose methohexital. One hundred ten ECT treatments were evaluated and subjects were treated in an alternating fashion with one of two induction protocols: Methohexital alone in an 80-100 mg IV bolus or remifentanil 500 mcg IV bolus combined with methohexital 40 mg IV. Bilateral ECT was performed in standard fashion and systolic blood pressure and heart rate were recorded throughout the procedure. No significant differences were found in baseline hemodynamic values between the two groups. Heart rate was significantly lower in the remifentanil group versus methohexital group at one minute post-induction and just prior to ECT stimulus. Pre-ECT systolic blood pressure was not significantly different between the two groups. Heart rate remained lower in the remifentanil group at all measured timepoints during the treatment and continuously for five minutes after the seizure. Systolic blood pressure was significantly lower at one minute following the end of seizure and five minutes after end of seizure. Remifentanil's short duration of action, favorable side effect profile, potential proconvulsant activity and ability to suppress hemodynamic response make it a potential novel drug for ECT induction.

Less postoperative nausea and vomiting after propofol + remifentanil versus propofol + fentanyl anaesthesia during plastic surgery

BACKGROUND

The effect of different opioids on postoperative nausea and vomiting (PONV) has not been conclusively determined yet, thus the aim of this study was to compare the incidence of PONV in propofol-anaesthetized patients receiving either fentanyl or remifentanil as opioid supplement.

METHODS

Sixty ASA physical status I and II patients scheduled for plastic surgery gave their written informed consent for this prospective, randomized, double-blind study. Anaesthesia was induced with propofol, rocuronium and fentanyl (n = 30; 2 microg kg(-1)) or remifentanil (n = 30; 1 microg kg(-1)). After tracheal intubation, anaesthesia was maintained with propofol, oxygen in air and an infusion of the opioid studied, which was modified according to clinical criteria. Baseline postoperative analgesia was achieved with intravenous propacetamol + metamizol. Intravenous morphine was given if visual analogic scale (VAS) for pain was > or = 4 (scale 0-10) and metoclopramide was administered if a patient presented > or = 2 PONV episodes (nausea or vomiting) in less than 30 min. Postoperatively (2, 12 and 24 h), we registered VAS, rescue morphine consumption, number of patients with episodes of PONV and number of patients requiring metoclopramide. P < 0.05 was considered significant.

RESULTS

There were no significant differences between groups in the demographic parameters, ASA physical status, propofol dose, VAS, and rescue morphine requirements. Fourteen patients in the fentanyl group and four in the remifentanil group presented PONV episodes 2-12 h postoperative hours' interval; (P < 0.05). Ten patients in the fentanyl group and four in the remifentanil group presented vomiting episodes in the same period (P < 0.05); and eight patients in the fentanyl group and one in the remifentanil group required metoclopramide; (P < 0.05). The number of postoperative PONV episodes were low, both in the 0-2-h period (n = 2 vs. n = 1, fentanyl and remifentanil, respectively) and in the 12-24-h period (n = 3 vs. n = 1).

CONCLUSION

Propofol + fentanyl anaesthesia resulted in a higher incidence of PONV and requirements of antiemetic drugs in the period between 2 and 12 postoperative hours compared with propofol + remifentanil, in patients undergoing plastic surgery.

Pharmacology and pharmacokinetics of sedatives and analgesics

The agents used for sedation and analgesia during endoscopy have complex pharmacokinetic and pharmacodynamic properties. Knowledge of these characteristics is necessary for determining the proper agent and dose for specific patient needs. Short-acting agents, such as fentanyl, midazolam, and propofol, provide rapid sedation with a short duration of action that allows patients to return to normal functioning rapidly. When designing a dosing regimen with these agents, age and organ (liver, kidney) function of patients and concomitant medications that may interfere with metabolic and elimination pathways must be considered.

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.

An animal model for surgical anesthesia and analgesia: characterization with isoflurane anesthesia and remifentanil analgesia

With a traditional clamp test alone, quantitative evaluation of the level of surgical anesthesia/analgesia is not easy. We have developed a rabbit model that allows for repeated quantification of the varying level of surgical anesthesia/analgesia using both mechanical and electrical stimulation as simulated surgical stimuli. After tracheostomy and intravascular cannulations under isoflurane anesthesia, eight rabbits were placed on a sling that allowed for free movement of the head and extremities. The inspired isoflurane concentration was reduced from 3% to 1.5% and then to 0%. Remifentanil was then infused at 4 graded infusion rates (0.1-0.8 microg. kg(-1) x min(-1)). At each drug dose, analgesic variables were determined including the number of animals behaviorally unresponsive to clamping the forepaw (nonresponders) and threshold voltage of subcutaneous electrical stimulation (2 Hz, 5 Hz, and 50 Hz) required to evoke the head lift (HLT, pain detection/arousal threshold) and escape movement responses (EMT, pain tolerance threshold). With increasing drug doses, HLTs and EMTs at 5 Hz increased dose-dependently and most proportionately to increases in the number of nonresponders, a standard indicator of the anesthetic/analgesic level. Therefore, using the HLT and EMT at 5 Hz combined with a clamp test, this rabbit model allows for quantitative evaluation of the varying level of surgical anesthesia/analgesia.

IMPLICATIONS

We have developed a rabbit model of surgical anesthesia and analgesia using both mechanical and electrical stimulation as simulated surgical stimuli, which allows for repeated, quantitative, and qualitative evaluation of the varying level of surgical anesthesia and analgesia, differentiation between sedative/hypnotic and analgesic components of drug actions, and simultaneous monitoring of all the clinically relevant physiological variables including cardiovascular and respiratory variables.

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.

Remifentanil with morphine transitional analgesia shortens neurological recovery compared to fentanyl for supratentorial craniotomy

PURPOSE

To compare the recovery profiles, efficacy and safety of remifentanil and morphine for transitional analgesia with fentanyl in patients undergoing elective craniotomy for supratentorial mass lesions.

METHODS

Ninety-one patients were enrolled in this prospective, randomized, multicentre study. Anesthesia was induced with thiopental and remifentanil (1.0 micro g x kg(-1) bolus and a 1 micro g x kg(-1) x min(-1) infusion) or fentanyl (1 micro g x kg(-1) bolus and a 1.0 micro g x kg(-1) x min(-1) infusion). The opioid infusion continued until the level of anesthesia was deemed appropriate for intubation. Anesthesia was maintained with N(2)O/O(2), isoflurane 0.5 MAC and remifentanil 0.2 micro g x kg(-1) x min(-1) or fentanyl 0.04 micro g x kg(-1) x min(-1). At bone flap replacement, either morphine 0.08 mg x kg(-1) (remifentanil group) or saline (fentanyl group) was given.

RESULTS

Systolic blood pressure was greater in those receiving fentanyl during induction (145.6 +/-17.5 mmHg vs 128.8 +/-18.3 mmHg; P = 0.006) and intubation (126.9 +/-17.1 vs 110.9 +/-16.5 mmHg; P < 0.001). Median time to tracheal extubation was similar but less variable in the remifentanil group (remifentanil = 8 min: range = 2-44 min; fentanyl = 8 min: range = 1-732 min). The fentanyl patients required a longer time to achieve the first normal neurological score (fentanyl = 38.0 min; remifentanil = 26.0 min; P = 0.035). Both the anesthesiologists and the recovery room nurses rated remifentanil better with respect to level of consciousness. Analgesics were required earlier in patients receiving remifentanil; median time 0.5 vs 1.08 hr, P < 0.001.

CONCLUSIONS

Remifentanil is a suitable alternative to fentanyl in supratentorial craniotomy. Time to preoperative neurological recovery is faster and morphine provides some transitional analgesia without compromising the quality of recovery.

Remifentanil vs alfentanil in the total intravenous anaesthesia for paediatric abdominal surgery

BACKGROUND

Our aim was to investigate whether total intravenous anaesthesia (TIVA) with remifentanil and alfentanil would ensure appropriate analgesia and recovery conditions in anaesthesia for children undergoing abdominal surgery.

METHODS

Sixty children, scheduled for abdominal operations were randomized to receive, in a double-blind manner, either remifentanil (loading dose 1 microg x kg(-1); maintenance infusion, 0.25 microg x kg(-1) min(-1)) or alfentanil (loading dose 50 microg x kg(-1); maintenance infusion, 1 microg x kg(-1) min(-1)) as the analgesic component of TIVA. They were combined with propofol (loading dose, 2 mg x kg(-1); step 1 maintenance infusion, 10 mg x kg(-1) h(-1); step 2 maintenance infusion, 8 mg x kg(-1) h(-1); step 3 maintenance infusion, 6 mg x kg(-1) h(-1)) neuromuscular blockade was with mivacurium. Dose changes of the drugs, the times from cessation of anaesthesia to extubation, verbal responses, recovery of ventilation, orientation, and qualification for discharge from the postanaesthetic care unit (PACU) were recorded.

RESULTS

Demographics, duration of surgery and anaesthesia were similar between the two groups. Times to extubation and stay in the PACU were significantly shorter in the remifentanil group compared with the alfentanil group. Quality of emergence (QE) from anaesthesia scale scores were higher in the remifentanil group compared with the alfentanil group.

CONCLUSIONS

Remifentanil provides a more rapid recovery and adequate postoperative analgesia after TIVA for paediatric abdominal surgery, compared with alfentanil.

Reduction of isoflurane MAC by fentanyl or remifentanil in rats

OBJECTIVE

The main objective of the study was to determine the effects of three different infusion rates of fentanyl and remifentanil on the minimum alveolar concentration (MAC) of isoflurane in the rat. A secondary objective was to assess the cardiovascular and respiratory effects of the two opioid drugs.

ANIMAL POPULATION

Thirty-seven male Wistar rats were randomly allocated to one of six treatment groups.

MATERIAL AND METHODS

For all treatment groups anaesthesia was induced with 5% isoflurane in oxygen using an induction chamber. A 14-gauge catheter was used for endotracheal intubation, and anaesthesia was maintained with isoflurane delivered in oxygen via a T-piece breathing system. A baseline determination of the minimum alveolar concentration of isoflurane (MACISO) was made for each animal. Fentanyl (15, 30, 60 micro g kg-1 hour-1) or remifentanil (60, 120, 240 micro g kg-1 hour-1) were infused intravenously into a previously cannulated tail vein. Thirty minutes after the infusion started, a second MACISO (MACISO+drug) was determined. The carotid artery was cannulated to monitor the arterial pressure and to take samples for arterial gas measurements. Cardiovascular (heart rate and arterial pressure) and respiratory (respiratory rate and presence/absence of apnoea) effects after opioid infusion were also recorded.

RESULTS

Fentanyl (15, 30, 60 micro g kg-1 hour-1) and remifentanil (60, 120, 240 micro g kg-1 hour-1) similarly reduced isoflurane MAC in a dose-dependent fashion: by 10% at lower doses, 25% at medium doses and by 60% at higher doses of both the drugs. Both opioids reduced the respiratory rate in a similar way for all doses tested. No episodes of apnoea were recorded in the remifentanil groups, while administration of fentanyl resulted in apnoea in three animals (one at each dose level). The effects on the cardiovascular system were similar with both drugs.

CONCLUSIONS

We conclude that the intraoperative use of remifentanil in the rat reduces the MAC of isoflurane, and that this anaesthetic sparing effect is dose-dependent and similar to that produced by fentanyl at the doses tested.

CLINICAL RELEVANCE

The use of remifentanil during inhalant anaesthesia in the rat can be considered an intravenous alternative to fentanyl, providing similar reduction in isoflurane requirements. Due to its rapid offset, it is recommended that alternative pain relief be instituted before it is discontinued.

Genetic toxicology of remifentanil, an opiate analgesic

Compounds that interact with opioid receptors are commonly used as analgesics. Opioid agonists vary in their potency and pharmacokinetic properties as well as in their affinity for distinct opioid receptors. The fentanyl opiate analogues are an important group of analgesics that interact with the mu opioid receptor. Remifentanil (GI87084) is a particularly interesting member of this group of opioids because its action is especially short in duration. This report examines the genetic toxicology of remifentanil. Remifentanil was not genotoxic in an Ames test, an in vitro chromosome aberration assay in Chinese hamster ovary cells, an in vivo micronucleus assay in rat erythrocytes, or an in vivo/in vitro unscheduled DNA synthesis assay in rat hepatocytes. In the in vitro L5178Y tk(+/-) mouse lymphoma assay, remifentanil produced a genotoxic response at dose levels >or=308 microg/mL only in the presence of rat liver S9 metabolic activation; primarily tiny and small mutant colonies were produced. This pattern of activity in a battery of genetic toxicology assays is not unique to remifentanil, but has also been observed for other pharmaceuticals, including the opioid fentanyl. A weight-of-evidence analysis, taking into consideration genotoxic mechanisms, in vivo results, and the conditions of clinical use, suggests remifentanil does not pose a genotoxic risk to patients.

Conscious analgesia/sedation with remifentanil and propofol versus total intravenous anesthesia with fentanyl, midazolam, and propofol for outpatient colonoscopy

BACKGROUND

This study tested the hypothesis that, for colonoscopy, analgesia/sedation with remifentanil and propofol might be more effective compared with anesthesia by intravenous administration of midazolam, fentanyl, and propofol.

METHODS

In a prospective, randomized trial, 100 adult patients received either conscious analgesia/sedation (Sedation group) or total intravenous anesthesia (TIVA group). Analgesia/sedation was achieved by infusion of remifentanil (0.20 to 0.25 microg/kg/min) and propofol in titrated doses. TIVA was induced by intravenous administration of fentanyl (2 microg/kg), midazolam (0.05 mg/kg) and propofol (dosage titrated). Cardiorespiratory parameters and bispectral index were monitored and recorded. The quality of the analgesia was assessed with a Numerical Pain Rating Scale (NRS); recovery level and return of psychomotor efficiency were evaluated with, respectively, the Aldrete scale and a Modified Post Anesthesia Discharge Scoring (MPADS) system.

RESULTS

Both groups of 50 patients were comparable with respect to demographic data, initial parameters, and duration of colonoscopy. All patients in the TIVA group found the colonoscopy painless (NRS score 0). In the Sedation group, the average pain intensity score was 0.4 (0.8). There was a marked difference between the Sedation and TIVA groups with respect to the time from the end of the procedure until the maximum MPADS score was reached: respectively, -6.9 (4.0) versus 25.7 (8.4) minutes (p < 0.001). In the TIVA group, changes in mean arterial pressure and heart rate and signs of respiratory depression were significant (p < 0.05).

CONCLUSIONS

Combined administration of remifentanil and propofol for colonoscopy provides sufficient analgesia, satisfactory hemodynamic stability, minor respiratory depression, and rapid recovery, and allows patients to be discharged approximately 15 minutes after the procedure.

Remifentanil produces vasorelaxation in isolated rat thoracic aorta strips

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

End-stage renal failure reduces central clearance and prolongs the elimination half life of remifentanil

PURPOSE

To evaluate the pharmacokinetics of remifentanil in 13 end-stage renal failure patients compared to matched control patients with normal renal function.

METHODS

Remifentanil was infused for 20 min at a rate of 0.1 microg x kg(-1) x min(-1). Serial arterial blood samples (3 mL) were drawn at the start of infusion (zero), five, ten, 15, 20, 22.5, 25, 27.5, 30, 35, 40, 45, 50, 55 and 60 min. Blood samples were immediately preserved with citric acid and chilled on ice. High performance liquid chromatography-tandem mass spectrometry concentration assay was performed using GI 95779B internal standard.

RESULTS

A two-compartment pharmacokinetic model provided an adequate fit for individual patient data. There was no difference in the mean +/- SD distribution half life (t1/2) between the renal failure group (1.65 +/- 0.7 min) and the control group (1.58 +/- 0.54 min). There was a significant difference in the central clearance (Cl(c)) and elimination half life (t1/2) ss) between the renal failure group (28 +/- 7 mL x kg(-1) x min(-1) and 18.86 +/- 2.06 min, respectively) and the control group (46.3 +/- 13.8 mL x kg(-1) x min(-1) and 16.35 +/- 2.99 min, respectively). Remifentanil blood concentrations were significantly higher in the renal failure group than in the control group.

CONCLUSION

We have demonstrated a significant reduction in the Cl(c) and a prolongation of t1/2 ss of remifentanil in end-stage renal failure patients. While statistically significant, these variations in the pharmacokinetics of remifentanil were clinically modest and may be explained by a reduced volume of distribution in the period following hemodialysis.

Remifentanil-sevoflurane anaesthesia for laparoscopic cholecystectomy: comparison of three dose regimens

The objective of this study was to determine a dosing regimen for remifentanil-sevoflurane anaesthesia that achieves an optimal balance between quality of anaesthesia and time to recovery. Patients undergoing elective laparoscopic cholecystectomy were randomly allocated to receive 0.4, 0.8 or 1.2 MAC (minimal alveolar concentration) of sevoflurane combined with remifentanil as required to maintain stable anaesthesia. For induction of anaesthesia, the remifentanil dose was 25 microg x kg(-1) x h(-1) and the mean propofol dose which was required to obtain loss of consciousness was 1.59 mg x kg(-1). During the maintenance phase, the mean remifentanil dose was 16.0, 14.1 and 13.0 microg x kg(-1) x h(-1) for the 0.4, 0.8 and 1.2 MAC groups, respectively. The mean sevoflurane maintenance dose was 0.91, 1.24 and 2.1% end-tidal for the 0.4, 0.8 and 1.2 MAC groups, respectively. The incidence of somatic responses was significantly higher in the 0.4 MAC sevoflurane group. Recovery times were significantly faster in the 0.4 compared to the 0.8 and 1.2 MAC groups and in the 0.8 compared to the 1.2 MAC group. The combination of 14 microg x kg(-1) x h(-1) remifentanil and 1.24% end-tidal sevoflurane achieved the optimal balance between the quality, and recovery from anaesthesia.

The pharmacokinetics of remifentanil in patients undergoing coronary artery bypass grafting with cardiopulmonary bypass

Remifentanil is a potent opioid with a short duration of action. It has the potential for large-dose opioid anesthesia without an obligatory prolonged period of mechanical ventilation. However, because of high clearance and rapid tissue distribution, cardiopulmonary bypass (CPB) may influence its pharmacokinetics and alter drug requirements. We administered remifentanil by continuous infusion to 68 patients having coronary artery bypass graft surgery during CPB with hypothermia to describe the effects of these interventions on its pharmacokinetics. Remifentanil concentrations were measured before, during, and after CPB. Disposition was best described by a two-compartment model. The volume of distribution increased by 86% with institution of CPB and remained increased after CPB. Elimination clearance decreased by 6.37% for each degree Celsius decrease from 37 degrees C.

IMPLICATIONS

Remifentanil concentrations decrease with the institution of cardiopulmonary bypass because of an increase in the volume of distribution. The decrease in elimination clearance with hypothermia results in increased total remifentanil concentrations during cardiopulmonary bypass if the infusion rate is not altered. More constant blood remifentanil levels may be obtained by reducing remifentanil infusion rate by 30% for each 5 degrees C decrease in temperature.

The effects of remifentanil on epileptiform discharges during intraoperative electrocorticography in patients undergoing epilepsy surgery

PURPOSE

High-dose i.v. opioids (e.g., alfentanil, 50 microg/kg bolus) are known to increase the intraoperative reading of epileptiform activity during epilepsy surgery (ES), thereby facilitating localization of the epileptogenic zone (i.e., the site of ictal onset and initial seizure propagation). However, this phenomenon has not been studied with remifentanil (i.e., a novel ultra-short acting opioid). The purpose of the present study was to evaluate the effect of remifentanil on electrocorticography (ECoG) during ES.

METHODS

After Institutional Review Board approval, 25 adult patients undergoing elective ECoG-guided anterior temporal corticectomy were enrolled. At the time of ECoG, anesthesia consisted of inhaled isoflurane < or =0.1% (end-tidal) in 50% N2O, and i.v. fentanyl, 2 microg/kg/h and vecuronium. Patients were maintained at normocapnia and normoxia during ECoG. After acquisition of baseline ECoG, bolus remifentanil, 2.5 microg/kg i.v., was administered. The number of epileptiform spikes occurring 5 min before and after this bolus were compared by using a one-sided sign test; p values < or =0.05 were considered statistically significant.

RESULTS

When compared with baseline ECoG, bolus i.v. remifentanil significantly increased the frequency of single spikes or repetitive spike bursts in the epileptogenic zone while suppressing activity in surrounding normal brain.

CONCLUSIONS

During ES, remifentanil enhanced epileptiform activity during intraoperative ECoG. Such observations facilitate localization of the epileptogenic zone while minimizing resection of nonepileptogenic eloquent brain tissue. Although not specifically evaluated in this study, we speculate that remifentanil's short elimination half-life will facilitate neurologic function testing immediately after ES. Should this be the case, we envision remifentanil has the potential to supplant other opioids (e.g., alfentanil) during ECoG-guided ES.

Anesthesia for airway surgery

Surgery of the upper airway requires diagnostic or therapeutic manipulation of the respiratory tree despite ongoing ventilation. Whether internal or external access to the conducting airway is required, anesthesiologist and surgeon, who must work together closely, share the airway. The anesthetic technique is influenced by the chosen mode of ventilation.

Gene therapy with vascular endothelial growth factor for inoperable coronary artery disease: anesthetic management and results

Gene transfer for therapeutic angiogenesis represents a novel treatment for medically intractable angina in patients judged not amenable to further conventional revascularization. We describe the anesthetic management of 30 patients with class 3 or 4 angina, enrolled in a Phase 1 clinical trial to assess the safety and bioactivity of direct myocardial gene transfer of naked DNA-encoding vascular endothelial growth factor (phVEGF(165)), as sole therapy for refractory angina. The phVEGF(165) was injected directly into the myocardium through a mini-thoracotomy. All patients had major clinical predictors for adverse perioperative cardiac complications. Fast-track anesthetic management with remifentanil and desflurane, multimodal analgesia, and aggressive hemodynamic control with nitroglycerin and esmolol were used. All patients tolerated anesthesia and surgery without problems. No perioperative myocardial infarction, hemodynamic instability, or ventricular failure occurred. VEGF injections caused no clinically significant changes in cardiovascular function. Mean hospital stay was 3.8 days. There was one late death (5 months postoperative). Twenty-nine of 30 patients experienced reduced angina (56.2 +/- 4.1 episodes/week preoperatively versus 3.8 +/- 1.6 postoperatively, P < 0.0001) and reduced sublingual nitroglycerin consumption (60.1 +/- 4.4 tablets/week preoperatively versus 2.9 +/- 1.1 postoperatively, P < 0.0001).

IMPLICATIONS

Previously revascularized patients now judged "inoperable," continue to present with chronic, recurrent angina. Our study describes the anesthetic considerations and management of such patients treated with a novel approach by using gene therapy to stimulate angiogenesis and improve perfusion to ischemic myocardium.

Effect of remifentanil compared with fentanyl on intraocular pressure after succinylcholine and tracheal intubation

Rapid sequence induction using succinylcholine is associated with an increase in intraocular pressure (IOP). This may lead to loss of ocular contents in open globe injuries. No method has previously been shown to prevent this increase in IOP. We investigated whether remifentanil, an ultra-short-acting opioid, could attenuate this increase in IOP during rapid sequence induction of anaesthesia. Forty-five patients were randomized blindly to receive remifentanil 1 microgram kg-1, fentanyl 2 micrograms kg-1 or placebo 1 min before thiopental, succinylcholine and tracheal intubation. IOP and haemodynamic variables were measured before, 1 min after the test solution, 30 s after thiopental, 30 s after succinylcholine, immediately after intubation and then every 3 min for 9 min. Remifentanil obtunded the increase in IOP after succinylcholine and intubation, so it could be suitable for use in open globe injuries.

Low-dose remifentanil increases regional cerebral blood flow and regional cerebral blood volume, but decreases regional mean transit time and regional cerebrovascular resistance in volunteers

We have used contrast media-enhanced perfusion magnetic resonance imaging MRI to measure regional cerebral blood flow (rCBF), regional cerebral blood volume (rCBV), regional mean transit time (rMTT) and regional cerebrovascular resistance (rCVR) in volunteers at baseline and during infusion of remifentanil (0.1 microgram kg-1 min-1). Remifentanil increased rCBF and rCBV in white and grey matter (striatal, thalamic, occipital, parietal, frontal) regions, with a parallel decrease in rMTT in those regions with the exception of occipital grey matter. rCVR was decreased in all regions studied. The relative increase in rCBF was greater than that in rCBV. Cerebral haemodynamics were increased significantly in areas less rich in mu-opioid receptors with a tendency towards more pronounced increases in rCBF and rCBV in pain-processing areas. Furthermore, interhemispheric differences in rCBF, rCBV and rMTT found prior to drug administration were almost eliminated during infusion of remifentanil. We conclude that, apart from direct and indirect cerebrovascular effects of remifentanil, these findings are consistent with cerebral excitement and/or disinhibition.

Postoperative pain management in patients undergoing major surgery after remifentanil vs. fentanyl anesthesia. Multicentre Investigator Group

PURPOSE

To determine if morphine sulphate was an effective transition analgesic in patients receiving a remifentanil-based anesthetic regimen.

METHODS

Open-label remifentanil or fentanyl was administered to 210 randomized patients undergoing inpatient surgery. Isoflurane and nitrous oxide was administered to all patients. Thirty minutes before the end of surgery, patients receiving remifentanil were randomized to receive morphine 0.15 mg x kg(-1) (R/M15 group) or 0.20 mg x kg(-1) (R/M20 group). Following extubation and prior to patient-controlled analgesia (PCA) initiation, 2 mg boluses of morphine were administered for moderate/severe pain. Efficacy endpoints were total morphine used in the post anesthesia care unit (PACU) and 24 and 48 hr postoperatively; postoperative pain; time to first morphine bolus; time to first PCA administration; and time to recovery endpoints.

RESULTS

Mean total morphine used in PACU was not different among groups (15.5 mg, 16.5 mg and 13.3 mg in R/M 15, R/M20 and F groups, respectively). Mean total 24 hr morphine use (58.1 mg, 56.93 mg and 53.6 mg in R/M15, R/M20 and F groups) and mean total morphine used at 48 hr were not different (69.8 mg, 64.7 mg and 62.1 mg in R/M15, R/M20 and F/I groups). Groups were similar with respect to pain severity ratings at all postoperative times. Patients in the fentanyl arm experienced faster times to some recovery endpoints than patients receiving either remifentanil regimen.

CONCLUSION

Morphine sulphate regimens of 0.15 or 0.20 mg x kg(-1) administered 30 min before the end of surgery are equally effective transition regimens for inpatient procedures.

Conscious sedation with remifentanil during painful medical procedures

Remifentanil, a recently introduced ultra-short acting opioid, was used as a component of a conscious sedation technique in 30 patients for 40 painful medical procedures. In 31 of these procedures, remifentanil provided sufficient analgesia. However, 25 of those 31 patients developed apnea that required constant verbal stimulation at doses equal to or less than the dose required for analgesia. Ten of these apneic patients developed hypoxemia (oxyhemoglobin saturation less than 90%). Nine patients required abandonment of remifentanil and addition of either ketamine or propofol to achieve an analgesic state without respiratory depression. Although discharge times with remifentanil were considerably shorter, most patients, parents, and practitioners were not satisfied with the technique because of the prolonged time to reach an analgesic state, and their fear of persistent apnea. Therefore, remifentanil is generally not a useful agent as part of a conscious sedation technique during brief painful procedures. Although discharge times are rapid, it is accompanied by a high incidence of life-threatening respiratory depression at subtherapeutic levels.

Remifentanil and propofol for sedation in children and young adolescents undergoing diagnostic flexible bronchoscopy

Flexible fibreoptic bronchoscopy (FOB) has become a useful diagnostic and therapeutic procedure in children. We investigated 26 patients (3-14 years) for FOB using a new sedation strategy. All patients received oral premedication and inhalation of topical anaesthetic. Sedation for bronchoscopy was achieved with a continuous infusion of remifentanil and intermittent boluses of propofol. Propofol injection was repeated if sedation was inadequate. Sedation could be successfully performed in all children without adverse effects. Endtidal CO2 concentration and arterial oxygen saturation remained stable throughout the study. All children were awake 5+/-1.3 min after stopping remifentanil infusion. Sedation with remifentanil/propofol is a new sedation strategy for diagnostic flexible paediatric bronchoscopy in children with spontaneous ventilation.

Cost comparison between three different general anaesthetic techniques for elective arthroscopy of the knee

INTRODUCTION

We compared three anaesthetic techniques for elective knee arthroscopy with special reference to cost-effectiveness.

METHOD

Seventy-five ASA I-II patients having elective arthroscopy of the knee joint were randomised to receive an anaesthetic technique based on propofol, fentanyl for induction followed by sevoflurane in oxygen:nitrous oxide (1:2 l/min) for maintenance of one of two intravenous techniques: propofol alfentanil or propofol-remifentanil infusions in combination with oxygen in air.

RESULTS

All patients had an uncomplicated course. No differences were seen with regard to emergence, postoperative pain or emesis or time to discharge. The anaesthetic technique based on sevoflurane was associated with the lowest cost US$ 14.7 as compared to US$ 18 for the propfol/alfentanil and US$ 19.9 for the propofol/remifentanil technique, including both cost for wastage as well as premedication and other fixed drug costs. Looking only at the anaesthetic drugs consumed, the cost per minute was US$ 0.56 for sevoflurane/nitrous oxide as compared to US$ 0.68 and 0.63 per minute for the propofol/alfentanil and proprofol/remifentanil, respectively. When the cost for wastage was taken into account, the difference in mean anaesthetic drug cost was more pronounced: the sevoflurane anaesthetic technique US$ 0.58, the propofol/alfentanil US$ 0.74 and the propofol/remifentanil US$ 0.84 per minute respectively.

CONCLUSION

From a cost-minimisation point of view, anaesthesia based on sevoflurane in oxygen:nitrous oxide is the technique of choice.