Propofol sparing effect of remifentanil using closed-loop anaesthesia

Effect of remifentanil on three effect-site concentrations of propofol and their relationship during electroencephalography at loss of response, at maximum alpha power, and at onset of burst suppression: a prospective randomized trial

PURPOSE

The effect-site concentration (Ce) at loss of response (Ce-LOR) to propofol closely correlates both with Ce as electroencephalographic alpha power becomes highest (Ce-alpha) and with Ce at onset of burst suppression (BS) (Ce-OBS), when no opioids are administered. Co-administration of opioids dose-dependently decreases Ce-LOR. We investigated the influence of remifentanil on the relationship between these three Ces.

METHODS

After receiving approval from our local ethical committee, with written informed consent, we enrolled 90 participants (ASA-PS I or II) who were scheduled for elective surgery. Participants were randomly assigned to three groups: constant remifentanil Ce 0 ng/ml (Remi_0); 1 ng/mL (Remi_1); and 2 ng/mL (Remi_2). We recorded both raw EEG and EEG-derived parameters on a computer. After reaching remifentanil equilibrium, we administered propofol using a target-controlled infusion pump such that propofol Ce increased to about 0.3 μg/mL/min. After determining Ce-LOR, we administered 0.6 mg/kg of rocuronium and started mask ventilation. The study protocol ended after observation of BS.

RESULTS

Three participants were excluded. Ce-LOR in each group (Remi_0, Remi_1, Remi_2) was 2.00 ± 0.58 μg/mL, 1.43 ± 0.49 μg/mL, and 1.37 ± 0.42 μg/mL. Ce-alpha was 2.91 ± 0.63 μg/mL, 2.30 ± 0.41 μg/mL, and 2.12 ± 0.39 μg/mL. Ce-OBS was 3.80 ± 0.69 μg/mL, 3.25 ± 0.68 μg/mL, and 2.90 ± 0.57 μg/mL. In three other instances, Ce was decreased by remifentanil. Generalized linear model analysis revealed that remifentanil had no influence on the relationship between the three Ces.

CONCLUSION

During propofol anesthesia, even low concentrations of remifentanil shifted concentration-related electroencephalographic changes.

Using the TI.VA algorithm to titrate the depth of general anaesthesia: a first-in-humans study

Background

The dose of anaesthetic and opioid drugs must be continuously adjusted after the induction of general anaesthesia to maintain an adequate depth of anaesthesia. The TI.VA algorithm is a multiple-input/multiple-output algorithm designed to optimise the balance between anaesthetic and opioid concentrations during general anaesthesia. It applies vector analysis to a two-dimensional matrix to quantify any inadequacy of the depth of anaesthesia at any given moment and determine any drug dose adjustments required to achieve an adequate depth of anaesthesia. This study aimed to capture preliminary data on the performance and safety of the TI.VA algorithm during total i.v. anaesthesia in patients.

Methods

This prospective study enrolled nine patients with breast cancer scheduled to undergo surgery. General anaesthesia was induced under manual control using propofol and remifentanil. Anaesthesia was guided using the TI.VA algorithm from skin incision until surgical resection was completed. The quality of anaesthesia was assessed through an analysis of performance errors. A bispectral index global score (GSBIS) <50 was considered an acceptable target for algorithm performance.

Results

All nine procedures were completed without any adverse events and none of the patients recalled any intraoperative event. Overall, we analysed 3417 monitoring points corresponding to 285 min of surgery. All patients presented a GSBIS below the cut-off value of 50.

Conclusions

The TI.VA algorithm provides adequate control of clinical anaesthesia. A more sophisticated prototype needs to be developed before the trial is expanded to include larger patient populations.

Clinical trial registration

NCT05199883.

Bioelectrical impedance analysis of body composition for the anesthetic induction dose of propofol in older patients

Background

Older people are currently the fastest growing segment of the worldwide population. The present study aimed to estimate propofol dose in older patients based on size descriptors measured by bioelectrical impedance analysis (BIA).

Methods

A cross sectional study in adult and older patients with body mass index equal to or lower than 35 kg/m² was carried out. BIA and Clinical Frail Scale scoring were performed during pre-operative evaluation. Propofol infusion was started at 2000 mg/h until loss of consciousness (LOC) which was defined by “loss of eye-lash reflex” and “loss of response to name calling”. Total dose of propofol at LOC was recorded. Propofol plasma concentration was measured using gas chromatography/ion trap-mass spectrometry.

Results

Forty patients were enrolled in the study. Total propofol dose required to LOC was lower in Age ≥ 65 group and a higher plasma propofol concentration was measured in this group. 60% of old patients were classified as “apparently vulnerable” or “frail” and narrow phase angle values were associated with increasing vulnerability scores. In the Age ≥ 65 group, the correlation analysis showed that the relationship between propofol dose and total body weight (TBW) scaled by the corresponding phase angle value is stronger than the correlation between propofol dose and TBW or fat free mass (FFM).

Conclusions

This study demonstrates that weight-based reduction of propofol is suitable in older patients; however FFM was not seen to be more effective than TBW to predict the propofol induction dose in these patients. Guiding propofol induction dose according to baseline frailty score should also be considered to estimate individualized dosage profiles. Determination of phase angle value appears to be an easy and reliable tool to assess frailty in older patients.

Trial registration

ClinicalTrials.gov Identifier: NCT02713698. Registered on 23 February 2016.

Practicalities of Total Intravenous Anesthesia and Target-controlled Infusion in Children

Propofol administered in conjunction with an opioid such as remifentanil is used to provide total intravenous anesthesia for children. Drugs can be given as infusion controlled manually by the physician or as automated target-controlled infusion that targets plasma or effect site. Smart pumps programmed with pharmacokinetic parameter estimates administer drugs to a preset plasma concentration. A linking rate constant parameter (keo) allows estimation of effect site concentration. There are two parameter sets, named after the first author describing them, that are commonly used in pediatric target-controlled infusion for propofol (Absalom and Kataria) and one for remifentanil (Minto). Propofol validation studies suggest that these parameter estimates are satisfactory for the majority of children. Recommended target concentrations for both propofol and remifentanil depend on the type of surgery, the degree of surgical stimulation, the use of local anesthetic blocks, and the ventilatory status of the patient. The use of processed electroencephalographic monitoring is helpful in pediatric total intravenous anesthesia and target-controlled infusion anesthesia, particularly in the presence of neuromuscular blockade.

Reliability of body-weight scalars on the assessment of propofol induction dose in obese patients

BACKGROUND

Obese patients require specific perioperative care when compared with non-obese patients. The present study aimed to analyse the ability of size descriptors to estimate propofol induction dose in class II and III obese patients.

METHODS

A cross-sectional study on adult patients with body mass index (BMI) equal to or greater than 35 kg/m² and on adult patients with BMI lower than 35 kg/m² was carried out. General anaesthesia was induced with remifentanil, propofol and rocuronium. Propofol infusion was started at 2000 mg/h until loss of consciousness. Bioelectrical impedance analysis and Brice modified interview was completed during pre- and post-operative evaluation, respectively. Measurements of propofol plasma concentration were performed using gas chromatography/ion trap-mass spectrometry.

RESULTS

Forty patients were enrolled in the study. The median values of fat free mass (FFM) in BMI < 35 kg/m² and BMI ≥ 35 kg/m² groups were 70% and 55% of total body weight, respectively. Our results did not demonstrate a strong correlation level between the studied size descriptors and propofol induction dose in both groups. Nevertheless, when propofol doses were normalized by FFM, an apparent convergence of the empirical cumulative distribution functions was observed.

CONCLUSION

None of the size descriptors was seen to be an effective predictor of the propofol induction dose in class II and III obese patients when a fixed infusion rate was used. Due to the observed variability between patients, guiding propofol induction dose against a clinical endpoint of unconsciousness appears more appropriate in order to avoid side effects related both with under or overdosing of propofol.

Effects of remifentanil with or without midazolam pretreatment on the 95% effective dose of propofol for loss of consciousness during induction: A randomized, clinical trial

BACKGROUND

Propofol is a rapid, efficient hypnotic agent with antiemetic effects. However, a high dosage is related to hemodynamic abnormalities such as hypotension and bradycardia. Pretreatment with remifentanil can decrease injection pain and stabilize hemodynamics during the induction period. Remifentanil or midazolam in combination with propofol can provide synergistic or additive effects during anesthesia induction. However, the hypnotic doses of propofol required in patients who receive pretreatment with remifentanil or midazolam remain unclear.

METHODS

Patients aged 20 to 50 years who were scheduled to undergo surgery under general anesthesia were enrolled in this study. The patients were randomized into 3 groups using a computer-generated randomization table. Patients in Group P (Propofol) received only propofol for loss of consciousness, those in Group PR (Propofol-Remifentanil) received remifentanil prior to propofol, and those in Group PMR (Propofol-Midazolam-Remifentanil) received remifentanil and midazolam prior to propofol. After propofol administration, loss of both the eyelash reflex and verbal response represented success. The 95% effective dose of propofol for loss of consciousness in each group, which was the primary outcome, was determined using a modified biased coin up-and-down method.

RESULTS

A total of 124 patients were initially enrolled. Of these, 4 were excluded, and the remaining 120 patients were randomized to each (n = 40) of the 3 groups. The 95% effective dose of propofol for loss of consciousness was 1.74 , 1.38, and 0.92 mg/kg in Groups P, PR, and PMR, respectively. Blood pressure decreased at 2 minutes after propofol administration in all the groups. However, compared with Group P, Groups PR and PMR exhibited a significant decrease in blood pressure.

CONCLUSIONS

The effective dose of propofol for loss of consciousness could be decreased by 21% and 47% when remifentanil pretreatment was used without and with midazolam, respectively. However, the decrease in blood pressure was greater with pretreatment than sole propofol use. These findings suggest that the combination of remifentanil with or without midazolam may have no benefit on hemodynamic stability during induction using propofol.

TRIAL REGISTRATION

NCT02536690 (clinicaltrials.gov).

Remifentanil in Combination With Propofol Is Suitable for Use in the Dental Outpatient Setting

Although several adjuncts to the general anesthetic propofol have been proposed, there is insufficient research identifying the ideal agent, and in what dosage, to combine with propofol in dental outpatient anesthesia. Here we examined the combination of remifentanil or nitrous oxide and propofol in patients with severe dental avoidance undergoing dental treatment in the outpatient setting. Eighty patients were randomized to 4 groups and administered propofol/saline solution (PS; n = 20), propofol/remifentanil 0.25 μg/kg/min (PRe-0.25; n = 20), propofol/remifentanil 0.125 μg/kg/min (PRe-0.125; n = 20), or propofol/66% nitrous oxide (PN; n = 20). During anesthesia, the bispectral index value was kept between 40 and 60. Body movements and hemodynamic changes during anesthesia, emergence, and recovery as well as anesthetic cost were compared between the combinations. Body movements were observed in all patients administered PS but in no patients administered PRe-0.25, PRe-0.125, or PN. Postoperative nausea was observed in 5 patients (25%) administered PRe-0.25 and in 1 patient (5%) administered PN. Although both PRe-0.125 and PN were useful clinically, PRe-0.125 was the least expensive combination.

Impact of effect-site concentration of propofol on cardiac systolic function assessed by tissue Doppler imaging

Objective

To evaluate the relationship between effect-site concentration (C_E) of propofol during total intravenous anaesthesia (TIVA) and cardiac systolic function using tissue Doppler imaging (TDI) in patients undergoing cardiovascular procedures.

Methods

Stepwise increments of C_E of propofol of 1.0, 2.0, 3.0 and 4.0 µg/ml (modified Marsh model) were achieved using a target-controlled infusion device. Transthoracic echocardiographic assessments using TDI were performed for each C_E of propofol and corresponding systolic myocardial velocity (s′), mean arterial blood pressure (MAP), heart rate (HR) and bispectral index (BIS) were evaluated.

Results

Data from 31 patients were analysed in this prospective study. The s′ velocity decreased with increasing propofol C_E and values recorded at propofol C_E 3.0 and 4.0 µg/ml were near or below 8 cm/s indicating abnormal cardiac systolic function. MAP, HR and BIS also decreased with each propofol C_E increment.

Conclusion

Although the recommended dosage for propofol is up to 4.0 µg/ml, caution should be taken when using propofol concentrations above 2.0 µg/ml during TIVA in patients with underlying cardiovascular diseases.

Comparative Evaluation of Remifentanil and Dexmedetomidine in General Anesthesia for Cesarean Delivery

Background

Use of remifentanil and dexmedetomidine in general anesthesia for cesarean section have been described. This study was designed to evaluate the effects of remifentanil and dexmedetomidine on maternal hemodynamics and bispectral index, and neonatal outcomes in elective caesarean delivery.

Material/Methods

Forty-four women undergoing elective cesarean delivery with ASA I or II and term or near-term singleton pregnancies were randomly assigned to receive remifentanil at a loading dose of 2 μg/kg over 10 min followed by a continuous infusion of 2 μg/kg/h until about 6 min before fetal delivery (Group REM), or dexmedetomidine at a loading dose of 0.4 μg/kg over 10 min followed by a continuous infusion of 0.4 μg/kg/h until about 6 min before fetal delivery (Group DEX). Maternal hemodynamics and BIS values were recorded. Neonatal effects were assessed using Apgar scores and umbilical cord blood gas analysis.

Results

Mean arterial pressure (MAP) increased after intubation in both groups, and the change magnitude of the MAP was higher in Group DEX (P<0.05). Patients in Group DEX had a lower BIS value at recovery and consumed less propofol during surgery (P<0.05). The incidences of neonatal resuscitation at 1 min were 81.8% in Group REM and 54.5% in Group DEX (P=0.052). There was no significant difference in either group in Apgar scores at 1 and 5 min and umbilical cord blood gas values.

Conclusions

Both remifentanil and dexmedetomidine are effective to blunt hemodynamic responses to intubation and also seem safe for neonates at the administrated doses, but remifentanil still has the potential to cause neonatal transient respiratory depression.

Total intravenous anesthesia will supercede inhalational anesthesia in pediatric anesthetic practice

Inhalational anesthesia has dominated the practice of pediatric anesthesia. However, as the introduction of agents such as propofol, short-acting opioids, midazolam, and dexmedetomidine a monumental change has occurred. With increasing use, the overwhelming advantages of total intravenous anesthesia (TIVA) have emerged and driven change in practice. These advantages, outlined in this review, will justify why TIVA will supercede inhalational anesthesia in future pediatric anesthetic practice.

Impact of deep sedation on the accuracy of hepatic and portal venous pressure measurements in patients with cirrhosis

BACKGROUND & AIMS

Measurement of the hepatic venous pressure gradient (HVPG) offers valuable prognostic information in patients with cirrhosis. In specific circumstances, (children, agitated patients, TIPS placement) deep sedation is required. This study aims to assess the impact of deep sedation on the accuracy of hepatic/portal pressure measurements.

METHODS

Forty-four patients were included. Measurements of baseline HVPG (n = 30), HVPG response to i.v. propranolol (n = 11), portal pressure gradient (PPG) after TIPS (n = 27) and of cardio-pulmonary pressures (n = 25) were obtained in awake conditions and under deep sedation with propofol and remifentanil.

RESULTS

During deep sedation, a marked oscillation within respiratory cycle was observed in abdominal pressures. End-expiratory sedated HVPG showed a better agreement with awake HVPG (intra-class correlation coefficient - ICC 0.864) than end-inspiratory HVPG (ICC 0.796). However, in almost half of the patients both values differed by more than 10%. Accuracy was not improved by using mean HVPG along the respiratory cycle. Similarly, changes in HVPG caused by propranolol while under sedation had a poor agreement to those obtained in awake conditions. Indeed, about a half of patients were misclassified according to the 10% HVPG reduction target. After TIPS, PPG values obtained under sedation were significantly different to awake PPG, usually underestimating the awake value. The systemic hemodynamic changes induced by sedation were not associated to a greater variability of PPG/HVPG measurements.

CONCLUSION

Deep sedation with propofol and remifentanil adds substantial variability and uncertainty to HVPG/PPG measurements. This must be considered when using these values to estimate prognosis, or targeting HVPG/PPG reductions.

Lessons learned from closed loops in engineering: towards a multivariable approach regulating depth of anaesthesia

In this paper is presented a brief state of art regarding the multivariable formulation for controlling the depth of anaesthesia by means of two intravenously administrated drugs, i.e. propofol and remifentanil. In a feasibility study of determining a suitable variable to quantify analgesia levels in patients undergoing cardiac surgery, the bispectral index and an electromyogram-based surrogate variable are proposed as the controlled variables. The study is carried on in the context of implementing a multivariable predictive control algorithm. The simulation results show that such a paradigm is feasible, although it does not guarantee perfect knowledge of the analgesia level-in other words, the variable is not validated against typical evaluations of the pain levels (e.g. clinical scores).

Modelling propofol pharmacodynamics using BIS-guided anaesthesia

Using Schnider's pharmacokinetic model, propofol pharmacodynamics were modelled during total intravenous anaesthesia. The method involved adjusting a pharmacokinetic/pharmacodynamic model according to data obtained from 42 patients having operative procedures with remifentanil analgesia. Parameters Ce50 and γ were estimated for induction and maintenance by analysing patients' bispectral index. The pharmacodynamic models were different for induction and maintenance. The mean (95% CI) Ce50 for induction and maintenance was Ce50 = 3.35 (2.79-3.91) mg.l(-1) and 2.23 (1.95-2.51) mg.l(-1) , respectively, with a higher concentration required to achieve the same effect during induction, even during remifentanil co-administration. During induction and maintenance, γ was 1.24 (1.44-2.00) and 1.58 (1.32-1.84), respectively. As γ is related to the concentration-effect slope, patient response is accentuated during maintenance compared with induction. The influence of sex and age on the model was analysed. Sex had no significant influence on the model, although a linear relation was found between age and Ce50 .

The influence of the severity of chronic virus-related liver disease on propofol requirements during propofol-remifentanil anesthesia

PURPOSE

The purpose of this study was to investigate the influence of chronic virus- related liver disease severity on propofol requirements.

MATERIALS AND METHODS

In this study, 48 male patients with chronic hepatitis B infection were divided into three groups according to Child-Turcotte-Pugh classification of liver function (groups A, B, and C with mild, moderate and severe liver disease, respectively). After intubation, propofol concentration was adjusted by ± 0.3 μg/mL increments to maintain bispectral index in the range of 40-60. Target propofol concentrations at anesthesia initiation, pre-intubation and pre-incision were recorded.

RESULTS

The initial concentration used in group C was significantly lower than that used in group A or B (p<0.05), whereas no difference was observed between groups A and B. At pre-intubation, the actual required concentration of propofol increased significantly (3.2 μg/mL) in group A (p<0.05), which lead to significant differences between the groups (p<0.05). At pre-incision, the requirements for propofol decreased significantly in both groups A and B (3.0 μg/mL and 2.7 μg/mL, respectively) compared with those at pre-intubation (p<0.05), and were significantly different for all three groups (p<0.05), with group C demonstrating the lowest requirement (2.2 μg/mL). The required concentrations of propofol at pre-incision were similar to those at induction.

CONCLUSION

In this study, propofol requirements administered by target-controlled infusion to maintain similar depths of hypnosis were shown to depend on the severity of chronic virus-related liver dysfunction. In other words, patients with the most severe liver dysfunction required the least amount of propofol.

The effect of gender on EC(50) of remifentanil to prevent pain during injection of microemulsion propofol

Background

Propofol injection pain is an unpleasant experience to patients and its prevalence can be influenced by age and gender. We determined the half maximal effective concentration (EC₅₀) of remifentanil for preventing the microemulsion propofol injection pain in the male and female adult groups.

Methods

After institutional review board approval, a total of 60 patients were assigned into 2 groups depending on their gender: group M (male, 20-65 yr) and group F (female, 20-65 yr). Anesthesia was induced with propofol and remifentanil, by a target-controlled infusion. Target effect-site concentration (Ce) of propofol and remifentanil for the first patient started at 4.0 ug/ml and 4.0 ng/ml. Ce of remifentanil for each subsequent patient was determined by the response of the previous patient by the Dixon's up-and-down method (DUDM) with an interval of 0.2 ng/ml. After equilibration of plasma and effect site remifentanil concentration, propofol was administered, and the pain responses were observed.

Results

The remifentanil EC₅₀ was 3.8 ± 0.2 and 2.7 ± 0.2 ng/ml in groups M and F, respectively, by DUDM. From Probit regression model, the remifentanil EC₅₀ was 3.7 (3.0-4.3) and 2.7 (1.8-2.9) ng/ml in groups M and F, respectively.

Conclusions

The remifentanil EC₅₀ for preventing the moderate to severe injection pain of propofol was higher in males than in females.

Intravenous dexamethasone pretreatment reduces remifentanil induced cough

BACKGROUND

Remifentanil infusion is commonly used for general anesthesia but reflex cough can occur after an intravenous (IV) infusion. This study was designed to examine the effect of IV-dexamethasone on remifentanil-induced cough (RIC).

METHODS

One hundred thirty patients scheduled for elective surgery were randomly assigned into two groups that received by either 2 ml of IV 0.9% saline (Group C, n = 68) or 10 mg of dexamethasone (Group D, n = 62) 5 min before administration of remifentanil at a target effect-site concentration of 5 ng/ml. The incidence and severity of coughs of each patient were recorded.

RESULTS

The overall incidence of cough was 6.5% (4/62 patients) in Group D and 26.5% (18/68 patients) in the Group C (P = 0.002). The severity of cough observed was significantly different by dexamethasone pretreatment (P = 0.02) but there were no significant hemodynamic changes.

CONCLUSIONS

Pretreatment with dexamethasone after IV administration was effective in suppressing the reflex cough induced by remifentanil infusion.

Myocardial Injury in Remifentanil-Based Anaesthesia for off-Pump Coronary Artery Bypass Surgery: An Equipotent Dose of Sevoflurane versus Propofol

This randomised controlled trial compared the effect of equipotent anaesthetic doses of sevoflurane (S group) versus propofol (P group), during remifentanil-based anaesthesia for off-pump coronary artery bypass surgery, on myocardial injury. Either sevoflurane or propofol was titrated to maintain bispectral index values between 40 and 50. In both groups, a targeted concentration of remifentanil 20 ng.ml-1 was maintained during anaesthesia. The concentrations of creatine kinase MB and troponin I were measured before the start of surgery, on admission to the intensive care unit, and at 12 and 24 hours after intensive care unit admission. The postoperative values of creatine kinase MB (S group: 15.08±18.97, 20.78±20.92, 12.76±12.82 vs 2.09±1.54 ng.ml-1; P group: 10.99±13.15, 27.16±56.55, 11.88±18.80 vs 1.84±1.67 ng.ml-1) and troponin I (S group: 3.56±5.19, 5.66±7.89, 3.35±4.55 vs 0.52±1.90 ng.ml-1; P group: 2.42±3.33, 4.11±6.01, 3.04±5.31 vs 0.43±1.28 ng.ml-1) were significantly higher than preoperative values in both groups but there were no significant differences between the two groups. There were no significant differences in time to extubation (S group, 476±284 minutes; P group, 450±268 minutes) and intensive care unit length of stay (S group, 2775±1449 minutes; P group, 2797±1534 minutes) between the two groups. In conclusion, sevoflurane and propofol at equipotent doses guided by bispectral index with remifentanil 20 ng.ml-1 had similar creatine kinase MB and troponin I values.

The difficult-to-treat electroconvulsive therapy patient - Strategies for augmenting outcomes

BACKGROUND

Several treatment strategies for augmenting outcomes with ECT (concurrent antidepressant treatment, frequency of ECT treatments, hyperventilation and use of remifentanil) are discussed in the context of a difficult clinical case, accompanied by a review of the relevant existing literature.

METHODS

Literature on the above aspects of ECT technique was identified via a PubMed search and was critically reviewed.

RESULTS

There is preliminary evidence that concurrent administration of some antidepressant medications may be useful in the highly treatment resistant patient, though due attention should be given to potential risks in combining these with ECT; reduction of the treatment frequency to twice a week; hyperventilation prior to each treatment; and the use of remifentanil to minimise the dosage of induction anaesthetics with anticonvulsant properties, may be useful strategies to enhance seizure production in cases where a high or rapidly rising seizure threshold is a major impediment to ECT treatment.

LIMITATIONS

It should be noted that empirical evidence for the effectiveness of each of the above strategies in producing better outcomes with ECT is not definitive, pointing to the need for further research in these areas.

CONCLUSIONS

The above strategies may be useful in clinical ECT practice, particularly in patients who are apparently treatment resistant, but the practitioner should be aware that the level of evidence underpinning these approaches is at present, preliminary.

The effects of midazolam and remifentanil on induction of anesthesia and hemodynamics during tracheal intubation under target-controlled infusion of propofol

BACKGROUND

The combined induction using two or more agents has a potential benefit that anesthesia could be induced with smaller anesthetic agents with fewer side effects. We studied the effects of co-administration with midazolam and remifentanil on the dose of propofol, the time to loss of consciousness (LOC) and hemodynamics during tracheal intubation.

METHODS

Sixty patients were randomly assigned to three groups. Group 1 was induced with target-controlled propofol alone. Group 2 received midazolam (0.05 mg/kg) and target-controlled propofol. Group 3 received midazolam (0.025 mg/kg), remifentanil (2 ng/ml) and target-controlled propofol. The time to LOC, the infused propofol dose and the effect site concentration at LOC were recorded. After LOC, rocuronium (0.6 mg/kg) was given and tracheal intubation was performed. The noninvasive blood pressure, heart rate (HR) and bispectral index were recorded.

RESULTS

The time and the dose of propofol to LOC were significantly reduced in group 2, 3 than in group 1 (P < 0.05). Compared with pre-induction values, mean blood pressure at immediately after intubation was increased in group 1, 2 with no change in group 3. The HR immediately after intubation was significantly increased in all groups compared to the pre-induction values, but the rate of increase of HR in group 3 were significantly lower than those group 1, 2 (P < 0.05).

CONCLUSIONS

The co-administration with midazolam and remifentanil reduces the time to LOC and the dose of propofol. That also attenuates hemodynamics during tracheal intubation under target-controlled infusion of propofol.

Effects of the addition of remifentanil to propofol anesthesia on seizure length and postictal suppression index in electroconvulsive therapy

OBJECTIVE

Propofol is a widely used anesthetic agent for electroconvulsive therapy (ECT). However, there are concerns that its anticonvulsant effect may interfere with the efficacy of ECT. We aimed to investigate the effects on seizure activity of the addition of the opiate remifentanil to propofol anesthesia for ECT.

METHODS

A retrospective analysis of 633 treatments in 73 patients was conducted. At each treatment, patients had received anesthesia with propofol alone or propofol plus remifentanil, depending on which anesthetist was providing anesthesia. Analysis of variance was performed to examine the effects of the anesthetic used, the electrode placement, the dose of electricity administered, and the stage in the course of treatment. Dependent variables were electroencephalogram seizure length and postictal suppression index (PSI).

RESULTS

Addition of remifentanil resulted in a small but significantly lower dose of propofol being used to induce unconsciousness. Addition of remifentanil affected seizure length, mainly related to an effect when placement was right unilateral (F = 5.70; P = 0.017). There was also a significantly increased PSI (F = 4.3; P = 0.039), which was not dependent on dose or on placement.

CONCLUSIONS

The data suggest that addition of remifentanil to propofol anesthesia significantly alters seizure indices. This may be secondary to a reduction in the amount of propofol required or to an independent effect of remifentanil. The increase in PSI in particular suggests that addition of remifentanil may improve clinical response. However, this can only be examined in a randomized controlled trial.

[Target-controlled infusion (TCI) - a concept with a future?: state-of-the-art, treatment recommendations and a look into the future]

Over the last 10 years the technique of target-controlled infusion (TCI) has substantially influenced the development and practice of intravenous anaesthesia. It opened the possibility of many new and exciting applications of perioperative anaesthetic care. More recent and current developments, such as open TCI (target-controlled infusion) and the availability of generic anaesthetic agents combined with modern infusion pumps, means that TCI can become a standard procedure in anaesthesia and is no longer just a research tool for specialists and enthusiasts. This review explains the fundamentals and applications of intravenous drug delivery by TCI and gives practice guidelines to successfully implement the technique into clinical practice. The aim is to provide a comprehensive reference based on clinically proven evidence.

Relationship between age and spontaneous ventilation during intravenous anesthesia in children

BACKGROUND

Maintaining spontaneous ventilation in children, using total intravenous anesthesia (TIVA), is often desirable, particularly for airway endoscopy. The aim of this study was to evaluate the effect of age on the dose of remifentanil tolerated during spontaneous ventilation under anesthesia maintained with infusions of propofol and remifentanil and to provide guidelines for the administration of remifentanil and propofol to maintain spontaneous ventilation in children.

METHODS

Forty-five children scheduled for strabismus surgery were divided by age into three groups (group I: 6 months-3 years, group II: 3 years-6 years, and group III: 6 years-9 years). The propofol infusion was titrated using State Entropy as a pharmacodynamic endpoint and remifentanil infused, using a modified up-and-down method, with respiratory rate depression as a pharmacodynamic endpoint. A respiratory rate of just greater than 10, stable for 10 min, determined the final remifentanil infusion rate. The group mean was estimated from the final remifentanil infusion rate tolerated (RD(50)).

RESULTS

The RD(50) of groups I, II, and III were 0.192 (0.08), 0.095 (0.04), and 0.075 (0.03) microg x kg(-1) x min(-1) respectively. Pair-wise comparisons between the groups for the rate of remifentanil tolerated revealed a statistically significant increase in the RD(50) in children less than 3 years of age compared with older children in groups II and III (P < 0.001). The relationship between remifentanil dose and age, weight or height was not linear.

CONCLUSIONS

Younger children, especially those aged less than 3 years, tolerate a higher dose of remifentanil while still maintaining spontaneous respiration. TIVA with spontaneous ventilation is readily achieved in younger children and infants.

Propofol and remifentanil effect-site concentrations estimated by pharmacokinetic simulation and bispectral index monitoring during craniotomy with intraoperative awakening for brain tumor resection

Different anesthetic techniques have been suggested for craniotomy with intraoperative awakening. We describe an asleep-awake-asleep technique with propofol and remifentanil infusions, with pharmacokinetic simulation to predict the effect-site concentrations and to modulate the infusion rates of both drugs, and bispectral index (BIS) monitoring. Five critical moments were defined: first loss of consciousness (LOC1), first recovery of consciousness (ROC1), final of neurologic testing (NT), second loss of consciousness (LOC2), and second recovery of consciousness (ROC2). At LOC1, predicted effect-site concentrations of propofol and remifentanil were, respectively, 3.6+/-1.2 microg/mL and 2.4+/-0.4 etag/mL. At ROC1, predicted effect-site concentrations of propofol and remifentanil were, respectively, 2.1+/-0.3 microg/mL and 1.8+/-0.3 etag/mL. At NT, predicted effect-site concentrations of propofol and remifentanil were, respectively, 0.9+/-0.3 microg/mL and 1.8+/-0.2 etag/mL. At LOC2, predicted effect-site concentrations of propofol and remifentanil were, respectively, 2.1+/-0.2 microg/mL and 2.5+/-0.2 etag/mL. At ROC2, predicted effect-site concentrations of propofol and remifentanil were, respectively, 1.2+/-0.5 microg/mL and 1.4+/-0.2 etag/mL (data are mean+/-SE). A significative correlation was found between BIS and predicted effect-site concentrations of propofol (r=0.547, P<0.001) and remifentanil (r=0.533, P<0.001). Multiple regression analysis between BIS and propofol and remifentanil predicted effect-site concentrations at the different critical steps of the procedure was done and found also significative (r=0.7341, P<0.001).

Target-controlled infusion of propofol combined with variable rate infusion of remifentanil for anaesthesia of a dog with patent ductus arteriosus

An 18-month-old Lurcher was anaesthetized for surgical ligation of a patent ductus arteriosus using a target-controlled infusion (TCI) of propofol and a variable rate infusion of remifentanil. Before anaesthesia, radiographic and echocardiographic examination indicated that the dog had left-sided congestive heart failure and impaired left ventricular systolic function. Ramipril and furosemide were administered pre-operatively. Following pre-anaesthetic medication with morphine, 0.5 mg kg(-1), by intramuscular injection, and pre-oxygenation, remifentanil was infused for 5 minutes at 0.2 microg kg(-1) minute(-1), followed by induction of anaesthesia using intravenous propofol administered by TCI, set at a target concentration of 3.5 microg mL(-1) of propofol in blood. Tracheal intubation was performed and 100% oxygen delivered through a non-rebreathing (Bain) system and then a circle system in the operating theatre. Anaesthesia was maintained with propofol and remifentanil, adjusted according to clinical requirements. Peri-operative analgesia consisted of intercostal bupivacaine nerve block, with meloxicam, morphine and remifentanil.

Feasibility study for the administration of remifentanil based on the difference between response entropy and state entropy †

BACKGROUND

Facial electromyography (FEMG) may have utility in the assessment of nociception during surgery. The difference between state entropy (SE) and response entropy (RE) is an indirect measure of FEMG. This study assesses an automated algorithm for remifentanil administration that is based on maintaining an entropy difference (ED) that is less than an upper boundary condition and greater than a lower boundary condition.

METHODS

The algorithm was constructed with a development set (n = 40), and then automated and studied with a validation set (n = 20) of patients undergoing anterior cruciate ligament repair. The percentage of time that the ED was maintained between the two boundary conditions was determined. Remifentanil and propofol predicted effect-site concentrations (Ce) were determined at surgical milestones and, after drug discontinuation, the time to response to verbal stimulation and orientation was measured.

RESULTS

The median (25th-75th percentile) per cent of time that the ED was recorded between the boundary conditions was 99.3% (98.1-99.8%). Predicted propofol (microg ml(-1)) and remifentanil (ng ml(-1)) Ce (sd), respectively, were 3.5 and 4.0 at induction, 1.9 (0.8) and 7.2 (3.7) at the end of surgery, and 1.1 (0.5) and 3.2 (2.2) at eye opening. The median time to eye opening and orientation was 3.8 and 6.8 min, respectively.

CONCLUSION

This feasibility study supports the concept that remifentanil may be delivered using an algorithm that maintains the difference between SE and RE between the upper and lower boundary condition.

Spectral frequency index monitoring during propofol-remifentanil and propofol-alfentanil total intravenous anaesthesia

BACKGROUND

The aim of this study was to evaluate the usefulness of spectral frequency index (SFx) monitoring to assess the depth of anaesthesia during propofol-opioid total intravenous anaesthesia (TIVA).

METHODS

Thirty-three patients scheduled for laparoscopic cholecystectomy under propofol TIVA were prospectively and randomly allocated to receive either remifentanil (bolus of 1.0 microg/kg, followed by continuous infusion from 0.25 to 0.05 microg/kg/min) [n = 18] or alfentanil (bolus of 10 microg/kg, followed by continuous infusion from 2.0 to 0.5 microg/kg/min) [n = 15]. EEG activity was monitored to achieve the desired depth of anaesthesia, and intravenous propofol was titrated to keep the SFx at 70-80%. The remifentanil and alfentanil groups were compared in relation to the plasma propofol concentration required for an adequate level of hypnosis during maintenance of anaesthesia, Pearson correlation coefficient for the relationship between the plasma propofol concentration and SFx values, recovery parameters, and recall of events during anaesthesia.

RESULTS

The study groups were comparable with regard to demographic characteristics, type and duration of surgery, and time to resumption of spontaneous ventilation. No evidence of explicit recall was noted. The mean plasma propofol concentration required for an adequate level of hypnosis during maintenance of anaesthesia was significantly higher in the alfentanil group (3.20 microg/mL) compared with the remifentanil group (2.17 microg/L) [p < 0.05]. In both groups, the Pearson correlation coefficient test showed a linear correlation between SFx values and propofol concentration in the studied propofol concentration range. The mean time to orientation for name and place was significantly shorter (p < 0.05), the mean propofol concentration at orientation for name and place and at the resumption of spontaneous ventilation timepoints was significantly lower (both p < 0.01), and the mean SFx value at resumption of spontaneous ventilation timepoint was significantly higher (p < 0.01) in the remifentanil group.

CONCLUSIONS

As SFx is linearly related to plasma propofol concentration, this index may be used to measure anaesthetic effect during propofol anaesthesia. The results of this clinical trial are consistent with a previous computer-simulated opioid-propofol model with regard to intraoperative and recovery variables, although the recovery occurred at different propofol concentration and SFx values.

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.

A randomized, prospective double-blind comparison of the efficacy of generic propofol (sulphite additive) with Diprivan®

BACKGROUND AND OBJECTIVE

We compared the dose requirement and side effect profile of total intravenous anaesthesia using Diprivan to generic propofol at a specific anaesthetic target level utilizing the bispectral index monitor to determine efficacy differences between the two products.

METHODS

Sixty women undergoing abdominal hysterectomy were induced with propofol 2 mg kg-1 and maintained with infusion (20-200 microg kg-1 min-1) adjusted to maintain a bispectral index of 50-65. Plasma propofol concentration was measured at 1 and 2 h post induction in 25 patients.

RESULTS

Mean (SD) drug doses adjusted for weight and time were similar in the Diprivan and generic propofol groups: 90 (30) microg kg-1 min-1 vs. 90 (20) microg kg-1 min-1 respectively. Mean (SD) plasma propofol levels at 1 and 2 h were also similar (3.0 (1.0) microg mL-1 vs. 3.6 (1.4) microg mL-1, P = 0.2 and 3.0 (1.9) microg mL-1 vs. 3.4 (1.6) microg mL-1, P = 0.58).

CONCLUSIONS

Diprivan and generic propofol have similar efficacy at a specified, bispectral index-defined, depth of anaesthesia.

Closed loops in anaesthesia

Closed-loop systems are able to make their own decisions and to try to reach and maintain a preset target. As a result, they might help the anaesthetist to optimise the titration of drug administration without any overshoot, controlling physiological functions and guiding monitoring variables. Thanks to the development of fast computer technology and more reliable pharmacological effect measures, the study of automation in anaesthesia has regained popularity. This short review focuses on the most recently developed and tested feedback systems in anaesthesia. Various new approaches for controlling the administration of intravenous and inhaled hypnotic-anaesthetic drugs have recently been published. For analgesics, a framework for further research has been presented in the literature. For other drugs, such as muscle relaxants and haemodynamic agents, only short reviews can be found. Until now, most of these systems have had to be under development. The challenge is now fully to establish the safety, efficacy, reliability and utility of closed-loop anaesthesia so that it can be adopted in the clinical setting. Besides, their role in optimising the controlled variables and control models, these systems have to be tested in extreme circumstances in order to test their robustness.

Application of physiology-based pharmacokinetic and pharmacodynamic modeling to individualized target-controlled propofol infusions

This study compared the ability of the physiology-based pharmacokinetic (PBPK) model with that of compartmental models used in propofol infusion devices to predict the pharmacokinetics and pharmacodynamics of propofol in various patient groups (children, pregnant women, young men, normal weight adults, and obese adults). With a PBPK model, loss of consciousness (LOC) and recovery of consciousness (ROC) corresponded to a narrow range of brain tissue concentrations (2.2-4.0 mg/L). With the compartmental models, predicted effect concentrations were also within a narrow range at LOC, but were outside the range at ROC. In individuals of normal weight, coefficients of variation (CV) of the predicted brain or effect concentrations at LOC were in a similar range-between 18% and 32%. In obese individuals, however, interindividual CV values for brain or effect concentrations were 41% (PBPK) and 93% (compartmental). This comparison suggests the increased flexibility of PBPK models over compartmental models, the latter of which rely heavily on the patient group from which the model was derived. The incorporation of PBPK models may provide target-controlled infusions with enhanced ability to predict response in a wide variety of patients.

Remifentanil supplementation of propofol during electroconvulsive therapy: effect on seizure duration and cardiovascular stability

OBJECTIVES

Electroconvulsive therapy (ECT) is standard treatment of severe depression. The induction of a seizure is a core event in successful ECT. Although propofol is a frequently used anesthetic agent, one of its limitations is a reduction of seizure duration. No such effects have been reported regarding remifentanil, an ultrarapid-acting opioid that is used to induce and maintain anesthesia. The simultaneous administration of propofol and remifentanil may have similar safety and efficacy in terms of induction of anesthesia during ECT as propofol alone and significantly increase seizure duration.

METHODS

Twenty-one ECT patients (10 men, 11 women, aged 24 to 81 years) were recruited. Muscle paralysis was achieved with succinylcholine (0.5-0.75 mg/kg intravenously [IV]). Unconsciousness was induced by either propofol (1 mg/kg IV) or propofol (0.5 mg/kg IV) + remifentanil (1 microg/kg) in a crossover format. ECT was administered according to established clinical protocols at the Sheba Medical Center, Israel. No changes in ECT current were permitted in the 2 protocols of each patient. Statistical analysis was based on paired t tests.

RESULTS

In all but 2 cases, seizure duration was significantly longer in the remifentanil group than in the control group (motor seizure 53.7 +/- 28.3 seconds vs. 29.5 +/- 10.9 seconds, t = 4.017, P = 0.0007; Electroencephalographic (EEG) seizures 60.8 +/- 25.1 seconds vs. 40.1 +/- 17.0 seconds, t = 3.971, P = 0.001). No significant differences were found in mean recovery time, post-treatment elevation in blood pressure, heart-beat, or oxygen saturation.

CONCLUSION

During anesthesia, the addition of remifentanil to propofol appears to be as effective as propofol alone with regard to anesthesia efficacy and cardiovascular function while significantly increasing seizure duration. Whether this discovery is of relevance to the clinical efficacy of ECT remains to be tested.

Pitfalls and challenges when assessing the depth of hypnosis during general anaesthesia by clinical signs and electronic indices

The objective of this article was to review the present methods used for validating the depth of hypnosis. We introduce three concepts, the real depth of hypnosis (DHreal), the observed depth of hypnosis (DHobs), and the electronic indices of depth of hypnosis (DHel-ind). The DHreal is the real state of hypnosis that the patient has in a given moment during the general anaesthesia. The DHobs is the subjective assessment of the anaesthesiologist based on clinical signs. The DHel-ind is any estimation of the depth of hypnosis given by an electronic device. The three entities DHreal, DHobs and DHel-ind should in the ideal situation be identical. However, this is rarely the case. The correlation between the DHobs and the DHel-ind can be affected by a number of factors such as the stimuli used for the assessment of the level of consciousness or the administration of analgesic agents or neuro muscular blocking agents. Opioids, for example, can block the response to tactile and noxious stimuli, and even the response to verbal command could vanish, hence deeming the patient in a lower depth of hypnosis than the real patient state. The DHel-ind can be disturbed by the presence of facial muscular activity. In conclusion, although several monitors and clinical scoring scales are available to assess the depth of hypnosis during general anaesthesia, care should be taken when interpreting their results.

Recent advances in intravenous anaesthesia

Efforts to develop new hypnotic compounds continue, although several have recently failed in development. Propofol has been reformulated in various presentations with and without preservatives. Pharmacokinetic and pharmacodynamic differences exist between some of these preparations, and it is currently unclear whether any have substantial advantages over the original presentation. The use of target-controlled infusion (TCI) has been extended to include paediatric anaesthesia and sedation. Application of TCI to remifentanil is now licensed. Linking of electroencephalogram (EEG) monitoring to TCI for closed-loop anaesthesia remains a research tool, although commercial development may follow. The availability of stereoisomer ketamine and improved understanding of its pharmacology have increased non-anaesthetic use of ketamine as an adjunct analgesic. It may be useful in subhypnotic doses for postsurgical patients with pain refractory to morphine administration.

Remifentanil: an update

PURPOSE OF REVIEW

Remifentanil has now reached maturity, as reflected by the increasing number of clinical papers relating to its use. Its position among anaesthetic drugs is now better understood, and this review will attempt to place it in the context of current clinical practice.

RECENT FINDINGS AND SUMMARY

Propofol reduces the initial distribution of remifentanil, leading to higher concentrations during induction. Propofol and remifentanil administered together at sedative doses display a major synergistic interaction on the respiratory drive. Remifentanil accelerates the penetration of sevoflurane to its site of effect. The risk of intraoperative awareness seems to be low when remifentanil is associated to very low concentrations of hypnotic drugs, but this field warrants further investigation. Acute tolerance to opioids and its prevention remain controversial.

SUMMARY

Remifentanil is the opioid of choice for tracheal intubation without muscle relaxants. It provides an alternative to regional anaesthesia in labour pain control. Target-controlled infusion may further improve the administration of remifentanil.