The pharmacodynamic interaction of propofol and alfentanil during lower abdominal surgery in women

The Contribution of Remifentanil to Middle Latency Auditory Evoked Potentials During Induction of Propofol Anesthesia

There is a debate regarding whether opioids, as a component of general anesthesia, are adequately reflected in the assessment of anesthesia based on derivatives of the electroencephalogram. To test the hypothesis of a possible quantitative contribution of remifentanil on middle latency auditory evoked potentials, we studied its interaction with propofol anesthesia in 45 unpremedicated male patients undergoing elective lower limb orthopedic surgery. They were allocated randomly to three groups. The first two groups received remifentanil either with a high (8 ng mL(-1)) or a low (3 ng mL(-1) target concentration using target-controlled infusion (TCI). The third group received spinal anesthesia instead of remifentanil. Anesthesia was induced by a stepwise increase in propofol concentration using TCI. The auditory evoked potential index (AEPex) and calculated propofol effect site concentrations were determined at loss of consciousness and the reaction to laryngeal mask airway insertion was noted. The propofol infusion was then converted to a closed-loop TCI using an AEPex value of 40 as the target. We found no significant contribution of remifentanil alone on the auditory evoked response, whereas increasing concentrations of remifentanil led to a significant decrease of the calculated propofol effect site concentrations (P = 0.023) necessary for unconsciousness. Prediction probability for AEPex was inversely related to the remifentanil concentration and was best for the control group, which received propofol alone. These results support previous findings of a quantitative interaction between remifentanil and propofol for loss of consciousness but question the specific contribution of remifentanil to auditory evoked potentials.

The performance of a target-controlled infusion of propofol in combination with remifentanil: a clinical investigation with two propofol formulations

Target-controlled infusion (TCI) incorporates the pharmacokinetic variables of an IV drug to facilitate safe and reliable administration. In this clinical study we investigated the performance of propofol TCI in combination with remifentanil. Fifty-four adult patients scheduled for general surgery lasting longer than 1 h received a combined TCI of propofol (Marsh parameter set; propofol randomly either dissolved with long- or middle-/long-chain triglycerides) and remifentanil. Arterial propofol plasma concentrations and hemodynamic and derived electroencephalogram variables were determined at various stages before, during, and after surgery. Measured propofol plasma concentrations exceeded the predicted values by 59%, and 48% when recalculated with the Schnider parameter set. Pharmacokinetic population analysis showed a small central volume of distribution (3.55 L) and reduced clearance (1.31 L/min) for propofol. ASA status and sex were the only variables that had a significant influence on propofol pharmacokinetics. In a second step, a new pharmacokinetic variable set for propofol was determined in the first 27 patients. Post hoc performance analysis of the remaining 27 patients showed improved accuracy using the new variable set. Our results show that when remifentanil and propofol are combined, the Marsh and Schnider parameter sets systematically underestimate propofol plasma concentrations. Presented, in part, at the Annual Meeting of the European Society of Anesthesiologists, Amsterdam, The Netherlands, June 1, 1999, and the Annual Meeting of the American Society of Anesthesiologists, Dallas, Texas, October 12, 1999.

Comparison of propofol with propofol-ketamine combination in pediatric patients undergoing auditory brainstem response testing

OBJECTIVE

The aim of our study was to compare propofol with propofol-ketamine combination for sedation and also to compare related complications in children undergoing auditory brainstem response (ABR) testing.

METHODS

Sixty ASA I-II patients aged between 1 and 13 years of age were sedated for ABR testing. Propofol 1.5mg/kg was used in group P (n=30), and ketamine 0.5 mg/kg+propofol 1.5 mg/kg, i.v., in group PK (n=30). Sedation levels of patients were maintained between scores 3 and 4 according to Ramsey sedation scores; when necessary, half of the starting drug dosage was administered for the maintenance of sedation. Side effects which occurred during or within the first 24h of the procedure were assessed.

RESULTS

Additional dosage was needed for 21 cases in group P and eight cases in group PK (p=0.002). While oxygen desaturation and apnea were not observed in any of the patients in group PK, there were four patients (11.4%) with oxygen desaturation, and six (17.1%) with apnea in group P (p<0.05).

CONCLUSIONS

In pediatric cases where ABR testing was applied, addition of low dose ketamine to propofol avoided the risk of respiratory depression due to propofol and lowered the need for additional dose of propofol. Therefore, the co-administration of propofol and ketamine appears to be a safe and useful technique for ABR testing.

The Effect of Different Isoflurane-Fentanyl Dose Combinations on Early Recovery from Anesthesia and Postoperative Adverse Effects

We evaluated the effect of different combinations of fentanyl-isoflurane on early recovery from anesthesia in 80 adult patients undergoing laparoscopic cholecystectomy. Anesthesia was induced with fentanyl 2 microg/kg and thiopental 5 mg/kg. Nitrous oxide was not used and patients were randomly assigned to one of four groups: Group 1 (n = 20) received 0.6% end-tidal isoflurane plus fentanyl, Group 2 (n = 20) received 1.2% end-tidal isoflurane plus fentanyl, Group 3 (n = 20) received 1.8% end-tidal isoflurane plus fentanyl, and Group 4 (n = 20) received only isoflurane. In Groups 1, 2 and 3 isoflurane concentration was kept constant and fentanyl was given as necessary to maintain the mean arterial blood pressure within +/- 10% of the minimum mean arterial blood pressure measured in the ward. In Group 4, isoflurane concentration was adjusted to maintain mean arterial blood pressure as above. At the end of skin closure isoflurane was discontinued and the time to spontaneous breathing (TSB), time to extubation (TE) and time to eye opening (TEO) were recorded. In the postanesthesia care unit, the degree of sedation, respiratory rate, Spo(2), emesis, pain, and morphine consumption were evaluated every 15 min for 1 h, and thereafter every 30 min until discharge. Fentanyl requirements were 8.3 +/- 4.5 microg/kg (mean +/- sd) in Group 1, 3.8 +/- 1.3 microg/kg in Group 2, and 3.0 +/- 0.7 microg/kg in Group 3 (P < 0.001), whereas in Group 4 the mean end-tidal concentration of isoflurane was 2.0% +/- 0.4%. Although the mean TSB was <5.5 min in all groups, TE increased from 7.3 +/- 5.1 min in Group 1 to 20.6 +/- 10.7 min in Group 4 (P < 0.001), and TEO increased from 7.4 +/- 5.1 min in Group 1 to 25.8 +/- 9.4 min in Group 4 (P < 0.001). There were no differences among the groups in any of the variables measured in the postanesthesia care unit. This study shows that the combination of a small concentration of isoflurane and a relatively larger dose of fentanyl results in a faster recovery from anesthesia than the inverse combination of doses.

IMPLICATIONS

A fast recovery from anesthesia increases patient safety. This study shows that the combination of a small concentration of isoflurane and a relatively larger dose of fentanyl results in a faster recovery from anesthesia than the inverse combination of doses.

The Effect-Site Concentration of Remifentanil Blunting Cardiovascular Responses to Tracheal Intubation and Skin Incision During Bispectral Index-Guided Propofol Anesthesia

We sought to determine the effect-site concentration of remifentanil blunting sympathetic responses to tracheal intubation and skin incision during bispectral index (BIS)-guided propofol anesthesia. Forty-one ASA physical status I-II patients, aged 20-65 yr and undergoing major abdominal surgery, were randomly assigned to one of two groups: tracheal intubation (group TI, n = 20) or skin incision (group SI, n = 21). All patients received a target-controlled infusion of propofol of 4 microg/mL, which was then adjusted to maintain a BIS value ranging between 40 and 50. The effect-site concentration of remifentanil blocking the sympathetic responses to tracheal intubation and skin incision in 50% of cases (Ce50) was determined using an up-and-down sequential allocation method. The mean (95% confidence interval [CI]) Ce50 of remifentanil was 5.0 ng/mL for TI (95% CI, 4.7-5.4 ng/mL) and 2.1 ng/mL for SI (95% CI, 1.4-2.8 ng/mL). This study shows that effect-site concentrations of remifentanil of 5 ng/mL and 2 ng/mL are effective in blunting sympathetic responses to tracheal intubation and skin incision in 50% of patients when combined with a BIS-guided target controlled infusion of propofol.

A comparison of fentanyl-propofol with a ketamine-propofol combination for sedation during endometrial biopsy

STUDY OBJECTIVE

The purpose of this study was to compare the clinical activities of ketamine and fentanyl when used in combination with propofol for outpatients undergoing endometrial biopsy. The investigated parameters were respiration, sedation, recovery rate, side effects, time to discharge, and patient satisfaction.

DESIGN

Prospective, randomized, double-blind study.

SETTING

University hospital.

PATIENTS

Forty American Society of Anesthesiologists physical status I and II patients (age range 38-61 years) scheduled for elective endometrial biopsy.

INTERVENTIONS

Patients received intravenous bolus doses of either fentanyl 1 microg/kg and propofol 1 mg/kg in (group 1 n = 20) or ketamine 0.5 mg/kg and propofol 1 mg/kg in (group 2 n = 20).

MEASUREMENTS

Heart rate, systolic and diastolic blood pressure, respiratory rate, and peripheral O(2) saturation were monitored in all patients. Depth of sedation was assessed by the Ramsay sedation score. The Aldrete score was used for postoperative recovery evaluation. The time to Aldrete score >/=8, side effects, and time to discharge were recorded.

MAIN RESULTS

Respiratory depression was observed in 5 patients from group 1 and 1 patient from group 2, but the difference was not significant (P > .05). Nausea, vertigo, and visual disturbances were more frequent in group 2 (P < .05). The time to Aldrete score >/=8 was similar in the 2 groups (6.2 +/- 3.5 minutes in group 1 and 7.0 +/- 3.1 minutes in group 2); the time to discharge was significantly longer in group 2 (71.2 +/- 9.7 minutes in group 1 and 115.2 +/- 25.6 minutes in group 2). Frequency of patient satisfaction was 95% in group 1 and 60% in group 2.

CONCLUSIONS

Hemodynamic change and degrees of sedation showed that fentanyl-propofol and ketamine-fentanyl combinations can be used safely in patients undergoing endometrial biopsy. However, with regard to side effects and patient satisfaction, the fentanyl-propofol was superior.

The Effect of Epidural Bupivacaine on Induction and Maintenance Doses of Propofol (Evaluated by Bispectral Index) and Maintenance Doses of Fentanyl and Vecuronium

The growing interest in combining local and general anesthesia has led to studies investigating possible interactions between general anesthesia and local anesthetics administered via spinal, epidural, IV, or IM routes. However, no study has evaluated the effect of local anesthetics on all three components of balanced anesthesia, i.e., hypnosis, analgesia, and muscle relaxation. In this prospective, randomized, double-blind study, we investigated the effect of epidural bupivacaine on the dose requirement of propofol (as evaluated by using the bispectral index [BIS]), fentanyl, and vecuronium for general anesthesia. This study consisted of 30 adults, ASA physical status I and II, undergoing Whipple's pancreaticoduodenectomy for periampullary carcinoma lasting >4 h. An epidural catheter was placed between T9-10. Depending on the group allocation, 10 mL of the study drug was administered as a bolus followed by an infusion at 6 mL/h via the epidural catheter. Patients were divided into 2 groups of 15 each. Patients in the control group received epidural normal saline whereas those in the bupivacaine group received epidural bupivacaine 0.1%. Induction of anesthesia was performed with IV fentanyl 2 mug/kg and propofol titrated to achieve BIS between 40-50. Endotracheal intubation was facilitated by the IV administration of vecuronium 0.1 mg/kg and patient's lungs were ventilated with 66% nitrous oxide in oxygen. After intubation, infusion of propofol 1% was titrated to maintain BIS between 40-50. Inadequate analgesia was defined as an increase in systolic blood pressure and/or heart rate by >20% of baseline values in response to surgical stimulus and was treated with bolus fentanyl 0.5 mug/kg. Neuromuscular monitoring was used to assess the need for additional doses of vecuronium. Data were analyzed by using the Student's t-test and P </= 0.05 was considered significant. The requirement of propofol for induction and maintenance of anesthesia in the bupivacaine group was 1.3 +/- 0.3 mg/kg and 2.4 +/- 0.9 mg . kg(-1) . h(-1), respectively, compared with 2.4 +/- 0.6 mg/kg and 4.4 +/- 1.6 mg . kg(-1) . h(-1) observed in the control group (P < 0.05). Significant reduction was also observed in the requirement of vecuronium and fentanyl during maintenance in the bupivacaine group (P < 0.05). We conclude that epidural bupivacaine given before induction of anesthesia reduces the requirement of propofol, fentanyl, and vecuronium during general anesthesia.

Le propofol et l'AIVOC en neuro-anesthésie

Propofol is an intravenous anaesthetic agent, which presents interesting features for its use in neuro-anaesthesia: it is a powerful hypnotic that does not increase the intracranial pressure. The delay of recovery is short even after several hours of continuous infusion. This is essential for a fast neurologic examination. Continuous infusion should be preferred to bolus in order to prevent hypotension and decrease of the cerebral perfusion pressure. Target-controlled infusion models based on effect site concentrations are now available through several softwares. This technique appears especially useful for awake craniotomy and functional neurosurgery. The level of consciousness is easily fixed between deep anaesthesia and light sedation permitting to ask the patient to move following orders. A sedation controlled by the patient himself is even possible.

Anaesthesia for carotid endarterectomy: comparison of hypnotic- and opioid-based techniques †

BACKGROUND

Although the synergistic interaction between hypnotics and opioids for total i.v. anaesthesia has been repeatedly demonstrated, questions about different dose combinations of hypnotics and opioids remain. The optimal combination would be based on maximal synergy, using the lowest dose of both drugs and having the lowest incidence of side-effects.

METHODS

The major goal of this prospective randomized study was to compare two different dose combinations of propofol and remifentanil (both administered by target controlled infusion (TCI)) in respect of haemodynamics during surgery and recovery, and the need for cardiovascular treatment in the recovery room. A secondary goal was to compare pain scores (VAS) and morphine consumption in the recovery room. Anaesthesia was induced in both groups using TCI propofol, adjusted to obtain a bispectral index score (BIS) value between 40 and 60. TCI for remifentanil commenced at an initial effect-site concentration of 0.5 ng ml(-1), and was adjusted according to haemodynamics. Patients were divided into one of two groups during anaesthesia: (i). Group H, hypnotic anaesthesia (n=23), propofol effect-site concentration maintained at 2.4 microg x ml(-1); and (ii). Group O, opioid anaesthesia (n=23), propofol effect-site concentration maintained at 1.2 microg x ml(-1). In both groups, remifentanil effect-site concentration was adjusted according to haemodynamics and changes in BIS value.

RESULTS

In Group O, more episodes of intraoperative hypotension (P<0.02) and hypertension (P<0.01), and fewer episodes of tachycardia were observed. More patients in Group O required nicardipine administration for postoperative hypertension (8 patients in Group H vs 15 patients in Group O, P<0.04). During recovery, morphine titration was necessary in approximately 50% of patients. No significant difference between groups was observed concerning pain scores or requirement for morphine titration.

CONCLUSIONS

Maintenance of anaesthesia predominantly with propofol and a low dose of remifentanil, both administered using TCI, is associated with greater stability in perioperative haemodynamics than anaesthesia predominantly with remifentanil alone. Postoperative pain was identical in both groups of patients who underwent relatively short duration, and relatively painless surgery.

Bispectral index, serum drug concentrations and emergence associated with individually adjusted target-controlled infusions of remifentanil and propofol for laparoscopic surgery

BACKGROUND

Target-controlled infusions (TCI) are used to simplify administration and increase precision of i.v. drugs during general anaesthesia. However, there is a limited relationship between preset targets and measured concentrations of drugs and between measured concentrations and measures of brain function, such as the bispectral index (BIS).

METHODS

We set out to evaluate the performance of TCI devices for propofol (Diprifusor) and remifentanil (Remifusor, prototype), during laparoscopic cholecystectomy in 21 patients. We also checked if there was any correlation between serum concentrations of propofol and BIS during individually adjusted anaesthesia.

RESULTS

The Diprifusor and Remifusor had a median absolute performance error of 60% and 25% respectively. Propofol concentrations were underpredicted by a median of 60%, and remifentanil concentrations were slightly overpredicted by a median of 7%. When anaesthesia was adjusted to keep BIS values between 45 and 60, no correlation existed between measured concentrations of propofol and the corresponding BIS values, although both BIS and serum propofol concentration discriminated well between the awake and asleep states. Emergence was rapid and uneventful in all patients. Female patients had a more rapid emergence than male patients (6.6 and 11.6 min respectively).

CONCLUSIONS

TCI devices for remifentanil and propofol result in large variation in measured serum concentrations. The lack of correlation between BIS and serum concentrations of propofol adds to the debate about whether BIS measures hypnosis as a graded state during surgery. This study confirms that women wake up faster than men, but provides no explanation for this repeatedly shown difference.

Strategies to Optimise Propofol-Opioid Anaesthesia

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

Binary combinations of propofol and barbiturates on human α1 glycine receptors expressed in Xenopus oocytes

To test whether there is a common site of action for intravenous anaesthetics at the glycine receptor, the effects of binary combinations of thiopentone, pentobarbitone, methohexitone, and propofol have been tested on human alpha(1) glycine receptors expressed in Xenopus laevis oocytes using two-electrode voltage-clamp techniques. Thiopentone (5-40 microM), pentobarbitone (25-400 microM) and propofol (2-100 microM) (but not methohexitone), potentiated the glycine-induced (50 microM) current in a dose-dependent manner, with the maximum potentiation observed to be 218%, 400%, and 576%, respectively. In binary combination with thiopentone, pentobarbitone or propofol, methohexitone reduced potentiation compared to that by the individual anesthetics to 190%, 260% and 460%, respectively. Combination of thiopentone and pentobarbitone (50 microM) increased potentiation, compared to that by thiopentone alone. Binary combinations of propofol with either thiopentone or pentobarbitone showed more potentiation, compared to that observed with the individual anesthetics. Our results indicate that thiopentone, pentobarbitone and propofol all act as positive allosteric modulators at the alpha(1) glycine receptor. In contrast, methohexitone has no action alone but acts as a competitive antagonist to thiopentone, pentobarbitone and propofol. We suggest that, on the basis of these results, these four intravenous anaesthetics share a common site of action at the glycine receptor.

Propofol sparing effect of remifentanil using closed-loop anaesthesia

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Target-controlled sedation-analgesia using propofol and remifentanil in women undergoing late termination of pregnancy

Twenty-one women undergoing termination of pregnancy for severe fetal abnormality received remifentanil and propofol using a target-controlled infusion system and were studied prospectively. Target concentrations were initially set at 1 ng.mL(-1) for remifentanil and 0.8 microg.mL(-1) for propofol. Remifentanil concentration was adjusted to obtain visual analog scores <50 mm with preservation of ventilation. Visual analog scores assessed by the patients and physiologic data were recorded every 15 min until delivery. The median duration of administration was 150 min [10th-90th centiles: 42-282 min). Visual analog scores decreased within the first 5 min (P < 0.05) and remained under 50 mm for 91.7% of time. The median rate of infusion of remifentanil was 0.056 microg.kg(-1) min(-1) [10th-90th centiles: 0.037-0.15 ng.mL(-1)]. At delivery, the median target concentration was 2.2 ng.mL(-1) [10th-90th centiles: 1.25-4 ng.mL(-1)] for remifentanil and 0.8 microg.mL(-1) [10th-90th centiles: 0.32-1.12 microg.mL(-1)] for propofol. Remifentanil requirements were statistically correlated to gestational age, parity and duration of labor. No episodes of ventilatory depression, nausea, vomiting or pruritus were noted. Patients scored analgesia as excellent in 12 cases, good in 7 cases and moderate in 2 cases. Further studies are required to determine the place and the best regimen of remifentanil infusion for pain management in labor in those cases when epidural analgesia is contraindicated.

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

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

Propofol-sufentanil anesthesia for thyroid surgery: optimal concentrations for hemodynamic and electroencephalogram stability, and recovery features

Hypnotics and opioids interact synergistically to block responses to surgery and different dose combinations may be used to provide adequate anesthesia. In this study, we sought to determine the optimal concentrations of propofol and sufentanil, given by target-controlled infusions, to ensure hemodynamic stability, adequate hypnosis (assessed by electroencephalogram bispectral index), and fast recovery for a moderately painful operation. Forty-five patients, ASA physical status I or II, undergoing thyroidectomy, were randomly assigned to a sufentanil target concentration (STC) that was maintained throughout surgery (0.1, 0.2, or 0.3 ng/mL). The propofol target concentration was adjusted to keep mean arterial blood pressure within 30% of a reference value, and bispectral index between 40 and 60. Adequate anesthesia was obtained in all groups. Hypertension and clinically dangerous movements were more frequent with the small STC, and hypotension requiring treatment was more frequent with the large STC. Propofol target concentration during surgery decreased significantly with increasing STC (median at thyroid removal 5.0, 4.0, and 2.5 microg/mL, respectively) as well as the propofol consumption (740, 668, 474 mg/h). The 0.3 ng/mL STC significantly delayed the return of spontaneous breathing.

IMPLICATIONS

Given as a target-controlled infusion for thyroid surgery, sufentanil 0.3 ng/mL for intubation and 0.2 ng/mL during surgery, combined with propofol 4 microg/mL (corresponding to a maintenance infusion rate of approximately 7-10 mg. kg(-1). h(-1)), is recommended to ensure both optimal intraoperative stability and fast recovery.

Intraoperative awareness: detected by the structured Brice interview?

BACKGROUND

Awareness is a rare complication in general anesthesia, but its consequences are stressful. Efforts must be undertaken to prevent, diagnose, and, if occurring, treat it. The incidence of awareness is higher following anesthesia involving the use of muscle relaxants. As a part of a quality assurance program at our short-stay surgery all patients exposed to general anesthesia are routinely subjected to a Brice interview, which aims to evaluate our standard anesthetic technique regarding awareness.

METHODS

The Brice interview was used prospectively in 5216 patients given a propofol/opioid anesthetic for day-case or short-stay surgery. Neuromuscular blocks were used only for surgical needs, not routinely. All patients were interviewed on discharge from the recovery room. A second interview, according to Brice, was undertaken by telephone 3-7 days later in the case of a notable intraoperative event, or otherwise after postoperative patient complaints. All patients were also interviewed by telephone 1-2 days postoperatively.

RESULTS

None of the patient interviews indicated awareness. This was also the case in five non-relaxed patients who had an incident of light anesthesia with eye opening and gross motor response without forewarning. Neuromuscular blockade was used in 7% of patients.

DISCUSSION

We were unable to detect intraoperative awareness. The anesthetic regimen, including minimal use of muscle relaxants, might be beneficial for awareness prevention. Alternatively, the diagnostic power, the timing of the Brice interview, or the number of interviews performed may be questioned.

Propofol and remifentanil pharmacodynamic interaction during orthopedic surgical procedures as measured by effects on bispectral index

STUDY OBJECTIVE

To identify and quantify the interaction between propofol and remifentanil during surgical procedures with a bispectral index (BIS) of 50 that was chosen as a continuous surrogate measure for "adequate depth" of anesthesia.

DESIGN

Prospective, open-label study.

SETTING

Department of orthopedics of a university hospital.

PATIENTS

20 patients undergoing orthopedic surgery.

INTERVENTIONS

Anesthesia was induced and maintained with propofol and remifentanil, both administered by target-controlled infusion (TCI). Initial target concentrations of propofol (1.5-8 microg/mL) and remifentanil (2-15 ng/mL) were chosen and alternated in order to maintain the BIS between 45 and 55. If constant target concentrations had been maintained for 20 minutes and the BIS did not depart from the desired range, blood samples were taken to determine propofol concentrations, and the BIS value was recorded. Isobolographic interaction models were fitted to the infusion rates of remifentanil and propofol, predicted target concentrations of both drugs, and measured propofol concentrations versus predicted remifentanil concentrations.

MAIN RESULTS

The isobole for the interaction of propofol and remifentanil in the concentration range investigated (propofol 1.5-8 microg/mL and remifentanil 1-30 ng/mL) is a concave up hyperbola ((0.15. C(prop))(3.13). C(rem) = 1) with C(prop) = propofol plasma concentration [microg/mL] and C(rem) = remifentanil blood concentration [ng/mL]). Use of predicted (=TCI target) concentrations or the respective infusion rates did not alter the general shape of the interaction isobole.

CONCLUSIONS

The interaction between propofol and remifentanil for maintenance of a BIS value between 45 and 55 during surgery is synergistic. This finding applies regardless of whether measured concentrations (for propofol), predicted concentrations of the infusion device, or infusion rates are used as model input. Notably, the interaction isobole of the (clinically readily available) infusion rates provides a useful dosing recommendation for the coadministration of propofol and remifentanil during maintenance of anesthesia.

Effects of fentanyl, alfentanil, remifentanil and sufentanil on loss of consciousness and bispectral index during propofol induction of anaesthesia

The bispectral index (BIS) and a sedation score were used to determine and compare the effect of propofol in the presence of fentanyl, alfentanil, remifentanil and sufentanil. Seventy-five non-premedicated patients were assigned randomly into five groups (15 in each) to receive fentanyl, alfentanil, remifentanil, sufentanil or placebo. Opioids were administered using a target-con-trolled infusion device, to obtain the following predicted effect-site concentrations: fentanyl, 1.5 ng ml(-1); alfentanil, 100 ng ml(-1); remifentanil, 6 ng ml(-1); and sufentanil, 0.2 ng ml(-1). After this, a target-controlled infusion of propofol (Diprifusor) was started to increase concentration gradually, to achieve predicted effect-site concentrations of 1, 2, and 4 microg ml(-1). At baseline and at each successive target effect-site concentration of propofol, the BIS, sedation score and haemodynamic variables were recorded. At the moment of loss of consciousness (LOC), the BIS and the effect-site concentration of propofol were noted. The relationship between propofol effect-site concentration and BIS was preserved with or without opioids. In the presence of an opioid, LOC occurred at a lower effect-site concentration of propofol and at a higher BIS50 (i.e. the BIS value associated with 50% probability of LOC), compared with placebo. Although clinically the hypnotic effect of propofol is enhanced by analgesic concentrations of mu-agonist opioids, the BIS does not show this increased hypnotic effect.

Recovery from propofol anaesthesia supplemented with remifentanil

We have examined the effects on recovery end-points of supplementation of a propofol-based anaesthetic with remifentanil. After induction of anaesthesia with propofol and remifentanil 1.0 microg kg(-1), 15 patients each were randomly allocated to target plasma propofol concentrations of 2, 3, 4 or 5 microg ml(-1) for maintenance of anaesthesia. Remifentanil was administered by infusion for supplementation in doses required for maintenance of adequate anaesthesia. All patients received 50% nitrous oxide in oxygen and ventilation was controlled. The total amount of drugs used and times to different recovery end-points were recorded. Cognitive function was also assessed using a Mini-Mental State questionnaire. The median dose of remifentanil for maintenance of adequate anaesthesia (excluding the initial bolus dose) in the four groups was 0.21, 0.15, 0.11 and 0.13 microg kg(-1) min(-1) respectively (P=0.0026). The median times to eye opening and orientation were shortest in the 2 microg ml(-1) group [6.0 and 6.5 min, 8.5 and 10.8 min, 13.4 and 15.8 min, and 14.2 and 19.5 min respectively in the propofol 2, 3, 4, and 5 microg ml(-1) groups respectively (P<0.001)]. The times to discharge from the recovery ward and the Mini-Mental State scores were not significantly different.

Comparison of alfentanil, fentanyl and sufentanil for total intravenous anaesthesia with propofol in patients undergoing coronary artery bypass surgery

We have studied the pharmacokinetics and pharmacodynamics of alfentanil, fentanyl and sufentanil together with propofol in patients undergoing coronary artery bypass graft surgery (CABG). Sixty patients (age 40-73 yr, 56 male) were assigned randomly to receive alfentanil, fentanyl or sufentanil and propofol. Plasma concentrations of these drugs and times for the plasma concentration to decrease by 50% (t50) and 80% (t80) after cessation of the infusion were determined. Times were recorded to awakening and tracheal extubation. Total dose and plasma concentrations of propofol were similar in all groups. Mean total doses of alfentanil, fentanyl and sufentanil were 443, 45 and 4.4 micrograms kg-1, respectively. Time to awakening did not differ significantly. In patients receiving fentanyl, the trachea was extubated on average 2 h later than in those receiving sufentanil and 3 h later than in those receiving alfentanil (P < 0.05). The t80 of fentanyl was longer (P < 0.05) than that of alfentanil or sufentanil, and there was a linear correlation between the t80 of the opioid and the time to tracheal extubation (r = 0.51; P < 0.01). However, the t50 values for these opioids were similar and did not correlate with recovery time. In conclusion, patients undergoing CABG and who were anaesthetized with fentanyl and propofol needed mechanical ventilatory support for a significantly longer time than those receiving alfentanil or sufentanil and propofol. On the basis of the interindividual variation observed, the time to tracheal extubation was most predictable in patients receiving alfentanil and most variable in patients receiving fentanyl, a finding which may be important if the patients are transferred to a step-down unit on the evening of the operation.

The effects of plasma fentanyl concentrations on propofol requirement, emergence from anesthesia, and postoperative analgesia in propofol-nitrous oxide anesthesia

To determine the effects of plasma fentanyl concentrations on intraoperative propofol requirements, emergence from anesthesia, and relief of postoperative pain, we studied 60 ASA physical status I and II patients undergoing spine fusion. The patients were randomly assigned to four study groups according to the expected intraoperative plasma fentanyl concentrations. Group I received an infusion of saline, and Groups II, III, and IV received fentanyl infusions to maintain the blood levels at 1.5, 3.0, and 4.5 ng/mL, respectively. An infusion rate of propofol was adjusted to keep the mean arterial pressure within 15% of the control value. Inspired nitrous oxide concentrations were maintained at 67%. The following were investigated in each group: 1) an average propofol infusion rate, 2) time to spontaneous eye opening and recovery of orientation (name, date, and place), and 3) total dose of fentanyl used for 24 h after admission to the postanesthetic care unit. Average propofol infusion rates were 10.1 +/- 2.5 (mean +/- SD), 7.5 +/- 1.2, 5.7 +/- 1.1, and 4.9 +/- 1.2 mg. kg(-1). h(-1), in Groups I, II, III, and IV, respectively. Groups receiving fentanyl infusion had significantly smaller infusion rates of propofol (P < 0.01) than the group receiving saline. Among the three fentanyl infusion groups, Group II (P < 0.01) had more than Groups III and IV. The time to spontaneous eye opening and the recovery of orientation were directly related to plasma fentanyl concentrations. The plasma fentanyl levels between Groups III and IV were the same. The total amount of IV patient-controlled analgesia fentanyl during postoperative 24 h increased significantly when the order of plasma fentanyl concentrations was reversed, 913.1 +/- 58.4, 553.4 +/- 129, 222.7 +/- 73.4, and 135.1 +/- 69.5 microg in Groups I, II, III, and IV, respectively. These results suggest that the addition of fentanyl infusions had ceiling effects that reduce the intraoperative propofol requirements according to the plasma fentanyl concentrations. The ceiling effect was demonstrated in the recovery of consciousness but not in the fentanyl requirements for postoperative analgesia.

IMPLICATIONS

The addition of fentanyl, a potent opioid, reduced the intraoperative requirement of propofol, an IV anesthetic, in the order of the plasma fentanyl concentrations. The ceiling effects of fentanyl were demonstrated in the reduction of propofol requirements and recovery of consciousness but not in the fentanyl requirements for postoperative analgesia.

A comparison of remifentanil and alfentanil for use with propofol in patients undergoing minimally invasive coronary artery bypass surgery

Most patients undergoing minimally invasive direct coronary artery bypass surgery can be awakened and tracheally extubated in the operating room. We have compared two techniques of total IV anesthesia in this patient population: 30 patients (aged 44 to 74 yr; 24 male) premedicated with temazepam were randomly assigned to receive either remifentanil-propofol or alfentanil-propofol. Anesthesia was induced with remifentanil 2 microg/kg or with alfentanil 40 microg/kg, with propofol, and maintained with remifentanil at 0.25 or 0.5 microg x kg(-1) x min(-1) or alfentanil at 0.5 or 1 microg x kg(-1) x min(-1). The stable maintenance infusion rate of propofol was adjusted for age. Times to awakening and tracheal extubation were recorded. Postoperatively, IV morphine provided by patient-controlled analgesia was used for 48 h. Times to awakening and tracheal extubation (mean +/- SD) were shorter (P < 0. 01) in patients receiving remifentanil, and interpatient variations in times to awakening and tracheal extubation smaller (awakening 25 +/- 7 vs 74 +/- 32 min, and extubation 27 +/- 7 vs 77 +/- 32 min). Analysis of variance revealed that postoperative consumption of morphine was dependent on both the intraoperative opioid and the time elapsed after surgery (P < 0.05): patient-controlled analgesia morphine use during the first 3 h after awakening was more in patients receiving remifentanil (P < 0.01).

IMPLICATIONS

Recovery of patients undergoing Minimally Invasive Direct Coronary Artery Bypass Surgery is significantly shorter and more predictable after total IV anesthesia with remifentanil-propofol than with alfentanil-propofol, which may be important if the goal is that patients will be awakened and tracheally extubated in the operating room.

Target-controlled infusion systems: role in anaesthesia and analgesia

Drug delivery by target-controlled infusion (TCI) allows automatic adjustments of the infusion rate of a drug to maintain a desired target concentration. Since drug effect is more closely related to blood concentration than to infusion rate, drug delivery via TCI is capable of creating stable blood concentrations of intravenous anaesthetics and analgesics. In this article the concept and history of TCI are described. The rational administration of TCI requires an appropriate pharmacokinetic data set and knowledge of the concentration-effect relationship; therefore, general pharmacokinetic and pharmacodynamic aspects of intravenous anaesthetics and analgesics are also addressed. Intraoperative investigations have demonstrated that TCI drug delivery allows rapid titration to a desired effect. The use of TCI for postoperative analgesia is still experimental, but TCI can, in part, overcome the disadvantages associated with continuous infusions and patient-controlled analgesia regimens in the postoperative period. Although TCI is capable of creating stable blood concentrations, when the target concentration is changed the resulting effect correlates better with a theoretical effect site concentration. The efficacy of TCI systems that can perform effect-site steering are still to be explored.

Target-controlled remifentanil in combination with propofol for spontaneously breathing day-case patients

Remifentanil is a new potent opioid with a very short duration of action irrespective of duration of infusion. It may have a role in day-case anaesthesia as part of a balanced total intravenous anaesthetic technique with propofol. We examined the respiratory depressant effects of remifentanil in 20 patients undergoing day-case anaesthesia. The target plasma concentration of remifentanil was varied while maintaining a constant target-controlled infusion of 4.5 microg x ml-1 propofol. In only 12 patients was satisfactory spontaneous respiration maintained. In these patients the median remifentanil target concentration was 1.6 ng x ml-1 and was achieved with a median infusion rate of 0.05 microg x kg-1 x min-1. The range of target concentrations associated with satisfactory spontaneous respiration was wide and varied over a 4.7-fold range from 0.6 to 2.8 ng x ml-1.

Interaction modeling of propofol and sufentanil on loss of consciousness

STUDY OBJECTIVES

To examine the possible pharmacodynamic interaction of propofol and sufentanil with respect to the induction of loss of consciousness.

DESIGN

Prospective, randomized, double-blinded study.

SETTING

University hospital.

PATIENTS

30 female, ASA physical status I and II patients undergoing elective gynecologic surgery.

INTERVENTIONS

Patients were allocated randomly to receive an individual combination of propofol (1, 2, 3, 4, 5, or 6 micrograms/ml) and sufentanil (0.1, 0.2, 0.3, 0.5, or 1.0 ng/ml) target blood concentrations using target-controlled infusions.

MEASUREMENTS AND MAIN RESULTS

Study endpoint was loss of consciousness, which was tested by response to verbal commands and classified as responder or nonresponder, as assessed by the anesthetist, who was blinded to the drugs' target blood concentrations. Nonlinear association (interaction) of both drugs was accomplished with logistic regression analysis using the maximum likelihood method, based principally on the hypothesis of interaction: In [p/(1-p)] = beta 0 + beta 1 x Cprop + beta 2 x Csuf + beta 3 x Cprop x Csuf with a p-value < 0.05 for coefficient estimates considered significant. In the logistic regression model, sufentanil and propofol showed no supra-additive interaction regarding loss of consciousness (p = 0.5916).

CONCLUSIONS

Our results give no evidence of additional hypnotic properties of sufentanil compared to the other fentanyl congeners, although logistic regression may be of limited value in modeling interaction of hypnotic-analgesic combinations.

The effect of the interaction of propofol and alfentanil on recall, loss of consciousness, and the Bispectral Index

The Bispectral Index (BIS) correlates well with the level of consciousness with single anesthetic drugs. We studied the effect of the interaction of propofol with alfentanil on propofol concentration and BIS associated with 50% probability of loss of consciousness and lack of recall (Cp50 and BIS50, respectively). We studied 40 consenting volunteers at two institutions who were randomly assigned to receive stepped increases of propofol (10 subjects at each site), propofol plus alfentanil 50 ng/mL (10 subjects at Emory site), or propofol plus alfentanil 100 ng/mL (10 subjects at Duke site) by using a target-controlled infusion device. Measures of sedation, BIS, deltaBIS (absolute change of BIS after a painful stimulus), memory, and drug concentration were obtained at each target drug concentration. The relation among BIS, measured drug concentration, sedation score, and presence or absence of recall was determined by linear and logistic regression for different drug regimens, and the prediction probability (Pk) was calculated. The addition of alfentanil in increasing doses did not significantly affect the BIS50 and propofol Cp50 values for loss of consciousness and lack of recall. DeltaBIS was significantly decreased by both an increase in the concentration of propofol and the presence of alfentanil. The Pk for BIS was >0.93 with all drug regimens, better than those of the target and measured propofol concentrations. We conclude that BIS correlated well with the hypnotic component of anesthesia independent of the presence of an opioid. Moreover, the level of consciousness, and, therefore, the BIS index, is affected by a painful stimulus, and this response is ablated either by opioids or increasing propofol concentration.

IMPLICATIONS

In volunteers, the sedation and changes in memory function produced by propofol correlated well with changes in the Bispectral Index. This relationship was not altered by the addition of an analgesic (alfentanil). However, in moderately sedated patients who received a painful stimulus, the Bispectral Index increased, but this response was blocked by the analgesic or increasing propofol concentrations.

[Target-controlled intravenous anesthesia]

Target-controlled infusion (TCI) is a new delivery system for i.v. anaesthetic agents with which the anaesthetist targets a plasma drug concentration to achieve a predetermined effect. With this system, the tedious task of calculating the amount of administered drug required to achieve the target concentration is left in charge of a microprocessor which commands the infusion device. TCI has long been used only by a few research teams, but this year a much wider field opens to this delivery system through marketing of Diprifusor, a TCI system specifically designed for administration of propofol in everyday practice. This article describes the rationale for administering i.v. agents through TCI delivery systems, the pharmacokinetic basis of TCI, the regulations and a broad overview of clinical applications, both recent and yet to come.

Propofol and alfentanil total intravenous anaesthesia: a comparison of techniques for major thoracic surgery

BACKGROUND

Previous work has highlighted the disadvantages of propofol as a sole agent for total intravenous anaesthesia (TIVA). This randomised study investigated three combinations of propofol and alfentanil as TIVA for major thoracic surgery.

METHODS

In 73 patients undergoing elective thoracic surgery, anaesthesia was conducted either with sodium thiopentone induction and inhalational maintenance (incorporating isoflurane) or with TIVA using propofol with alfentanil (by infusion at one of two rates or in incremental doses). Vital signs and recovery characteristics were recorded.

RESULTS

There were no significant differences in heart rate or blood pressure between groups during either induction or maintenance. Depth of anaesthesia was controlled satisfactorily in all groups. Recovery characteristics were similar between treatment groups, although there was a trend towards earlier orientation in the group which received the highest infusion rate of alfentanil.

CONCLUSION

Continuous infusions of propofol and alfentanil provide safe and reliable TIVA for major thoracic surgery. TIVA was found to be a satisfactory technique in more elderly patients than previously described. The higher of the two alfentanil infusion rates may result in a better combination of propofol and alfentanil with respect to recovery times than the lower.

Influence of analgesic supplementation on the target propofol concentrations for anaesthesia with 'Diprifusor' TCI

Forty healthy patients undergoing orthopaedic surgery were randomly allocated to receive an initial blood propofol target concentration of either 4 micrograms.ml-1 or 6 micrograms.ml-1 for induction of anaesthesia with a 'Diprifusor' target controlled infusion system for propofol, and analgesic supplementation with either nitrous oxide 67% in oxygen or alfentanil 15-20 micrograms.kg-1.h-1. Anaesthesia was induced within 3 min in 80% and 95% of patients with propofol target concentrations of 4 micrograms.ml-1 and 6 micrograms.ml-1, respectively. The frequency of discomfort on infusion was similar for both target concentrations. During maintenance, supplementary doses of alfentanil were required to provide adequate surgical conditions in approximately half of the patients receiving nitrous oxide. There was no statistically significant difference between the target concentration [mean (SD)] of propofol for total intravenous anaesthesia [5.1 (2.0) micrograms.ml-1] compared with a technique using nitrous oxide [4.6 (1.2) micrograms.ml-1] supplemented as needed with small doses of alfentanil.

Propofol concentration required for endotracheal intubation with a laryngoscope or fiberscope and its interaction with fentanyl

The administration of fentanyl with propofol reduces the blood concentration of propofol required to achieve adequate anesthesia for tracheal intubation. However, different intubation procedures have variable intensities of noxious stimulation and may require different levels of anesthesia. The goal of this study was to determine the propofol blood concentration at which 50% of patients did not respond to stimulation (Cp50) for laryngoscopy, intubation with a laryngoscope, insertion of a slotted oral-pharyngeal airway (Ovassapian airway), and intubation with a fiberscope when administered in conjunction with fentanyl. Patients undergoing elective surgery were given varying amounts of propofol or propofol with fentanyl, and their responses to the four procedures listed above were assessed. These experiments demonstrated that the propofol concentration required for intubation with a laryngoscope was similar to that for intubation with a fiberscope, and that the required level was reduced by fentanyl. Hemodynamic responses to intubation were lower with a fiberscope than with a laryngoscope. We conclude that almost the same concentrations of propofol or fentanyl are necessary for suppressing both of the somatic responses to tracheal intubation with a fiberscope or a laryngoscope. Hemodynamic responses were attenuated more during intubation with a fiberscope.

IMPLICATIONS

The propofol blood concentrations at which 50% of patients did not respond to stimulation for laryngoscopy, tracheal intubation with a laryngoscope, and tracheal intubation with a fiberscope were 10.9, 19.6, and 19.9 microg/mL, respectively. These were reduced by fentanyl. Hemodynamic responses to intubation were less with a fiberscope than with a laryngoscope.