Determination of sevoflurane alveolar concentration for tracheal intubation with remifentanil, and no muscle relaxant

Global sensitivity analysis in physiologically-based pharmacokinetic/pharmacodynamic models of inhaled and opioids anesthetics and its application to generate virtual populations

The integration between physiologically-based pharmacokinetics (PBPK) models and pharmacodynamics (PD) models makes it possible to describe the absorption, distribution, metabolism and excretion processes of drugs, together with the concentration-response relationship, being a fundamental framework with wide applications in pharmacology. Nevertheless, the enormous complexity of PBPK models and the large number of parameters that define them leads to the need to study and understand how the uncertainty of the parameters affects the variability of the models output. To study this issue, this paper proposes a global sensitivity analysis (GSA) to identify the parameters that have the greatest influence on the response of the model. It has been selected as study cases the PBPK models of an inhaled anesthetic and an analgesic, along with two PD interaction models that describe two relevant clinical effects, hypnosis and analgesia during general anesthesia. The subset of the most relevant parameters found adequately with the GSA method has been optimized for the generation of a virtual population that represents the theoretical output variability of various model responses. The generated virtual population has the potential to be used for the design, development and evaluation of physiological closed-loop control systems.

Supreme™ laryngeal mask airway insertion requires a lower concentration of sevoflurane than ProSeal™ laryngeal mask airway insertion during target-controlled remifentanil infusion: a prospective randomised controlled study

Background

ProSeal (PLMA) and Supreme (SLMA) laryngeal mask airways are effective ventilator devices with distinctive designs that may require different anaesthetics for insertion. Sevoflurane induction provides acceptable conditions for laryngeal mask insertion, and remifentanil significantly decreases the minimum alveolar concentration of sevoflurane required for that insertion. The study aimed to evaluate the optimal end-tidal (ET) sevoflurane concentration for successful insertion of PLMA versus SLMA in patients receiving a remifentanil infusion without a neuromuscular blocking agent.

Methods

Altogether, 45 patients ASA (American Society Anaesthesiologists) physical status I–II, aged 18–60 years were scheduled for elective ambulatory surgery. Exclusion criteria were a difficult airway, recent respiratory infection, reactive airway, obstructive sleep apnoea syndrome, gastric aspiration’s risk factors, pregnancy, and lactation. Patients were randomly allocated to receive the SLMA or the PLMA. Sevoflurane induction with co-administration of remifentanil was performed at an effect-site concentration of 4 ng mL^− 1. ET₅₀ was calculated with a modified Dixon’s up-and-down method (starting at 2.5% in steps of 0.5%). Predetermined sevoflurane concentration was kept constant during the 10 min before LMA insertion. Patient’s response to LMA insertion was classified as “movement” or “no movement”. Sevoflurane ET₅₀ was determined as the midpoint concentration of all the independent pairs that manifested crossover from “movement” to “no movement”.

Results

The ET₅₀ sevoflurane concentration co-administered with remifentanil required for PLMA insertion was 1.20 ± 0.41% (95% confidence interval 0.76 to 1.63%). For SLMA insertion, it was 0.55 ± 0.38% (95% confidence interval 0.14 to 0.95%) (p = 0.019).

Conclusions

The end-tidal sevoflurane concentration with co-administered remifentanil required to allow insertion of the SLMA was 54% lower than that needed for inserting the PLMA.

Trial registration

Clinicaltrials.gov identifier: NCT03003377. Retrospectively registered. Date of registration: December 28, 2016.

Sevoflurane at 1.0 MAC together with remifentanil and propofol produces clinically acceptable intubation conditions at the vocal cords: A prospective randomized study

Objective

The overall intubation conditions after tracheal intubation with remifentanil, propofol, and sevoflurane at 1.0 minimum alveolar concentration (MAC) are worse than with rocuronium at 0.45 mg/kg. Therefore, we compared the intubation conditions and laryngeal morbidity (vocal cord injuries, hoarseness, and sore throat) with sevoflurane at 1.2 and 1.4 MAC versus 1.0 MAC.

Methods

In this prospective clinical trial, 90 patients were randomized to 3 groups: the sevoflurane 1.0, 1.2, and 1.4 MAC groups. At 3 min, tracheal intubation was performed and the patients’ intubation conditions were assessed. The vocal cords were examined for injury by videolaryngoscopy. Additionally, the incidence and severity of laryngeal morbidity were compared between women and men.

Results

Acceptable intubation conditions were seen in 72% of the patients without significant differences between the groups. Overall, vocal cord injuries (oedema) occurred in three (4%) patients. Women reported sore throat more often than men (51% vs. 21%, respectively).

Conclusions

Intubation conditions were not improved with higher sevoflurane concentrations. The incidence and severity of sore throat were greater in women than men.

Trial registration: ClinicalTrials.Gov: NCT 01896245

The optimal exhaled concentration of sevoflurane for intubation without neuromuscular blockade using clinical bolus doses of remifentanil: A randomized controlled trial

BACKGROUND

The aim of this study was to investigate the optimal exhaled sevoflurane concentration that produces adequate endotracheal intubation conditions when sevoflurane is combined with the different bolus doses of remifentanil used in clinical practice.

METHODS

The patients were randomized to 3 groups (groups 1.0, 1.5, and 2.0), receiving remifentanil bolus doses of 1.0, 1.5, and 2.0 μg/kg, respectively. For each group, the concentration of sevoflurane used for each consecutive patient was increased or decreased using the "up-and-down" method based on the success or failure to achieve adequate conditions for intubation in the previous patient. The remifentanil bolus dose was administered 90 s before intubation and after the target sevoflurane concentration was achieved.

RESULTS

In groups 1.0, 1.5, and 2.0, the effective concentration in 50% (EC50) of the sevoflurane concentration required to perform successful intubation was 3.0, 2.0, and 1.29 vol% and the effective concentration in 95% was 3.45, 2.91, and 1.89 vol%, respectively. When sevoflurane was administered for the induction, the increase in heart rate (HR) of group 1.0 was the highest among the groups. The highest number of adverse events occurred in group 2.0, including vocal cord rigidity, hypotension, and bradycardia.

DISCUSSION

The EC50 of the sevoflurane concentration was 3.0, 2.0, and 1.29 vol% when it was combined with a bolus dose of remifentanil of 1.0, 1.5, and 2.0 μg/kg, respectively. Of the 3 different bolus doses of remifentanil, the dose of 1.5 μg/kg was least associated with changes in the HR/mean blood pressure during intubation without increasing adverse effects.

Comparison of the effects of remifentanil and remifentanil plus lidocaine on intubation conditions in intellectually disabled patients

BACKGROUND AND OBJECTIVES

This is a prospective, randomized, single-blind study. We aimed to compare the tracheal intubation conditions and hemodynamic responses either remifentanil or a combination of remifentanil and lidocaine with sevoflurane induction in the absence of neuromuscular blocking agents.

METHODS

Fifty intellectually disabled, American Society of Anesthesiologists I-II patients who underwent tooth extraction under outpatient general anesthesia were included in this study. Patients were randomized to receive either 2 μg kg(-1) remifentanil (Group 1, n=25) or a combination of 2 μg kg(-1) remifentanil and 1 mg kg(-1) lidocaine (Group 2, n=25). To evaluate intubation conditions, Helbo-Hansen scoring system was used. In patients who scored 2 points or less in all scorings, intubation conditions were considered acceptable, however if any of the scores was greater than 2, intubation conditions were regarded unacceptable. Mean arterial pressure, heart rate and peripheral oxygen saturation (SpO2) were recorded at baseline, after opioid administration, before intubation, and at 1, 3, and 5 min after intubation.

RESULTS

Acceptable intubation parameters were achieved in 24 patients in Group 1 (96%) and in 23 patients in Group 2 (92%). In intra-group comparisons, the heart rate and mean arterial pressure values at all-time points in both groups showed a significant decrease compared to baseline values (p=0.000) CONCLUSION: By the addition of 2 μg/kg remifentanil during sevoflurane induction, successful tracheal intubation can be accomplished without using muscle relaxants in intellectually disabled patients who undergo outpatient dental extraction. Also worth noting, the addition of 1mg/kg lidocaine to 2 μg/kg remifentanil does not provide any additional improvement in the intubation parameters.

Intubating conditions and side effects of propofol, remifentanil and sevoflurane compared with propofol, remifentanil and rocuronium: a randomised, prospective, clinical trial

BACKGROUND

Tracheal intubation without muscle relaxants is usually performed with remifentanil and propofol or sevoflurane. Remifentanil 1.0 to 4.0 μg·kg(-1) and propofol 2.0-3.0 mg·kg(-1) or sevoflurane up to 8.0 Vol% provide acceptable, i.e. excellent or good intubating conditions. We hypothesized that sevoflurane 1.0 MAC would provide acceptable intubating conditions when combined with propofol and remifentanil.

METHODS

Eighty-three patients to be intubated were randomised to two groups. The SEVO group received propofol 1.5 mg kg(-1), remifentanil 0.30 μg kg min(-1) and sevoflurane 1.0 MAC; the MR group received the same doses of propofol and remifentanil plus rocuronium 0.45 mg kg(-1). We evaluated intubation and extubation conditions, mean arterial pressure (MAP), heart rate (HR) and bispectral index (BIS). The vocal cords were examined for injury by videolaryngoscopy before and 24 hours after surgery.

RESULTS

ACCEPTABLE INTUBATING CONDITIONS WERE SEEN MORE FREQUENTLY WITH ROCURONIUM THAN WITH SEVOFLURANE: 97% versus 82%; p = 0.03; the subscore for vocal cords was comparable: 100% versus 98%. MAP before intubation decreased significantly compared with the MAP at baseline to the same extent in both groups; ephedrine IV was given in 15 (SEVO) versus 16 (MR) patients; p = 0.93. BIS at tracheal intubation was 27 (13-65) in the SEVO group, 29 (14-62) in the MR group; p = 0.07. Vocal cord injuries (oedema, haematoma) were similar: 4 patients in each group.

CONCLUSIONS

Overall intubating conditions were better when rocuronium was used; the subscore for vocal cords was comparable. The incidence of side effects was the same in the two groups.

TRIAL REGISTRATION

ClinicalTrials.Gov: NCT 01591031.

Tracheal intubation in intellectually disabled patients: clinical usefulness of remifentanil and sevoflurane without a muscle relaxant

OBJECTIVE

To compare two remifentanil doses (1 µg/kg and 2 µg/kg) in order to determine the preferred dose in intellectually disabled patients undergoing day care dental surgery under sevoflurane-induced general anaesthesia.

METHODS

Patients were randomly assigned to receive either 1 µg/kg (group 1) or 2 µg/kg (group 2) remifentanil; both groups received 8% sevoflurane anaesthesia induction. All other conditions were identical in both groups. Heart rate (HR), mean arterial pressure (MAP) and intubation conditions were assessed.

RESULTS

A total of 27/30 (90.0%) patients in group 1 and 29/30 patients (96.7%) in group 2 had acceptable intubation conditions. Remifentanil administration resulted in significant reductions in HR compared with baseline levels, in both groups. There were no significant between-group differences in HR at any timepoint. MAP decreased significantly compared with baseline in group 2 only.

CONCLUSION

Successful tracheal intubation in intellectually disabled patients can be accomplished with a combination of 1 µg/kg or 2 µg/kg remifentanil and 8% sevoflurane anaesthesia induction, without the requirement for neuromuscular blocking drugs.

The optimal dose of remifentanil for acceptable intubating conditions during propofol induction without neuromuscular blockade

STUDY OBJECTIVE

To determine the optimal remifentanil dose required to provide acceptable intubating conditions following induction of anesthesia with propofol without using neuromuscular blockade.

DESIGN

Dose-response study.

SETTING

Operating room of a university hospital.

PATIENTS

50 ASA physical status 1 men, aged between 20 and 40 years, who were scheduled for general anesthesia.

INTERVENTIONS

Intubating conditions were evaluated according to the scoring system described by Viby-Mogensen et al. Successful intubation was defined as excellent or good.

MEASUREMENTS

For induction of anesthesia, an intravenous (IV) bolus dose of propofol 2.0 mg/kg was given over 30 seconds followed by the administration of predetermined IV remifentanil over 30 seconds; intubation was performed 90 seconds after completion of the remifentanil administration. The dose of remifentanil used for each patient was determined by the response of the previously tested patients, using the modified Dixon's up-and-down method (using 0.2 μg/kg as a step size). The first patient was tested with remifentanil 1.0 μg/kg. If intubation failed, the remifentanil dose was increased by 0.2 μg/kg; if intubation was successful, the dose was decreased by 0.2 μg/kg. Mean arterial pressure (MAP), heart rate (HR), and peripheral oxygen saturation were recorded during the study period.

MAIN RESULTS

According to probit analysis, the effective dose of remifentanil in 50% (ED(50)) and 95% (ED(95)) of patients were 1.40 μg/kg and 2.40 μg/kg, respectively. Preintubation and postinduction HR and MAP values were lower than preinduction values (P < 0.001).

CONCLUSION

The optimal bolus dose of remifentanil for acceptable intubating conditions was 2.40 μg/kg (95% confidence interval, 1.90-9.0 μg/kg) in 95% of patients during induction of anesthesia with propofol 2.0 mg/kg without neuromuscular blocking agents.

[Tracheal intubation quality under remifentanil-propofol with sevoflurane compared with remifentanil-propofol with rocuronium: a randomized double-blind clinical trial]

OBJECTIVE

To determine whether intubation conditions under remifentanil-propofol plus sevoflurane rather than a nondepolarizing neuromuscular blocker are similar to those obtained when a neuromuscular blocker is used.

MATERIAL AND METHODS

In this double-blind controlled trial, 100 patients undergoing outpatient surgery were randomized to 2 groups. Intubation in one group was performed under remifentanil, propofol and sevoflurane. In the other, intubation was performed under remifentanil, propofol, and the nondepolarizing neuromuscular blocker rocuronium. We recorded dysphonia at 24 hours, Cormack-Lehane classification at laryngoscopy, mandibular relaxation, vocal cord position and mobility, and cough or movement during laryngoscopy, on intubation and on cuff inflation. Blood pressure and heart rate before and after tracheal intubation were also recorded.

RESULTS

No significant between-group differences were observed in dysphonia 24 hours after surgery, Cormack-Lehane classification at laryngoscopy, mandibular relaxation, the position or mobility of vocal cords, or cough or movement during laryngoscopy, intubation or cuff inflation. After intubation the mean (SD) systolic blood pressure was 119.7 (75.4) mm Hg in the rocuronium group and 97.5 (54.5) mm Hg in the sevoflurane group. Mean heart rate was 80.7 beats/min in the rocuronium group and 66.7 beats/min in the sevoflurane group. The differences were significant (P < .05).

CONCLUSIONS

Adequate doses of remifentanil, propofol, and sevoflurane provide intubation conditions that are similar to those achieved by using a nondepolarizing neuromuscular blocker, without exposing patients to additional risk. Avoiding use of a neuromuscular blocker would circumvent the development of complications associated with use of these agents or their antagonists and costs would be lower.

The effects of sevoflurane with propofol and remifentanil on tracheal intubation conditions without neuromuscular blocking agents

Background

Propofol and remifentanil are used for tracheal intubation in the absence of neuromuscular blocking agents. We hypothesized that the addition of sevoflurane to propofol and remifentanil would improve intubation conditions and provide hemodynamic stability.

Methods

Seventy-six patients scheduled for elective surgery were randomly allocated to be ventilated with either 4% (group I) or 7% sevoflurane (group II) after propofol injection (2 mg/kg). All patients received remifentanil (1 µg/kg) 30 seconds after administration of propofol. Ninety seconds after remifentanil was given, laryngoscopy and tracheal intubation were performed. Intubation conditions and hemodynamic changes were evaluated.

Results

The overall incidence of clinically acceptable intubation conditions was significantly higher in group II (92%) than group I (58%) (P = 0.001). Scores for vocal cord position, coughing, and limb movement were significantly better in group II (P < 0.05). Mean blood pressure remained significantly lower than the pre-induction level throughout the investigation in both groups (P < 0.001), but there was no incidence of bradycardia or hypotension requiring treatment.

Conclusions

Tracheal intubation without neuromuscular blocking agents can be achieved safely and reliably by adding 7% sevoflurane to propofol (2 mg/kg) and remifentanil (1 µg/kg).

[Implications of anesthetic techniques on patients' recovery in laparoscopic cholecystectomy]

BACKGROUND/AIM

Different techniques of general anesthesia are used for laparoscopic cholecystectomy (LC). The aim of the study was to establish the best anesthetic technique for achieving better results during awakening affecting not only patient's recovery, but activities of anesthesiological team, as well.

METHODS

The study was conducted as a prospective comparative clinical trial. The patients (n=90) were classified according to the applied anesthetic technique into two groups: Volatile Induction and Maintenance Anaesthesia (VIMA) with sevofluran and Target Controlled Infusion (TCI). The results relating to parameters of recovery after anesthesia and surgery were compared between these two groups. The following parameters were analysed: demographic patients' characteristics, duration of anesthesia, the times to eye opening, to respond to a command, to extubation, and to orientation, from the last anesthetic dose receiving until post anesthesia discharge (PAD), frequency of postoperative nausea, vomiting and agitation (PONVA).

RESULTS

In the examined groups there were no statistically significant differences in the duration of anesthesia (68.29 +/- 6.47 vs 66.29 +/- 11.97 min, p = 0.327). The time to eye opening was significantly shorter in the group VIMA compared to the group TCI (4.49 +/- 1.20 vs 7.42 +/- 1.25 min, p = 0.000), as well as the time to respond to a command (5.93 +/- 1.12 vs 8.47 +/- 1.08 min, p = 0.000). The patients anesthetised with VIMA technique wer estatistically significantly extubated earlier (6.84 +/- 1.19 vs 9.69 +/- 1.31 min, p = 0.000). Considering orientation time, there was also statistically significant difference between the two groups (7.51 +/- 0.97 vs 11.60 +/- 1.75 min, p = 0.000). There was no statistically significant difference in PAD time duration (19.42 +/- 5.99 vs 20.80 +/- 1.59 min, p = 0.142). There were no statistically significant differences in PONVA events between the examined groups.

CONCLUSION

This study showed that VIMA technique with sevofluran in LC provides faster and more qualitative recovery of patients. Thus this technique should be applied in everyday anesthesiological procedures in LC, as well as in other minimally invasive videoendoscopic surgical procedures.

Effect of Remifentanil on Tracheal Intubation Conditions and Haemodynamics in Children Anaesthetised with Sevoflurane and Nitrous Oxide

This study examined the effect of remifentanil added to inhalation agents on intubating conditions in children (aged one to seven years). As is our routine, all patients were premedicated with 0.004 mg/kg glycopyrrolate intramuscularly 30 minutes before anaesthesia to prevent bradycardia and salivary secretion, and received intravenous 1 mg/kg ketamine prior to transfer into the operating room to facilitate separation of the child from the parents. Laryngoscopy was attempted after ventilation with 8% sevoflurane in 50% nitrous oxide and 50% oxygen for two minutes, and intravenous administration of either a placebo bolus of saline (Group S) or one of two doses of remifentanil, 1 μg/kg (Group R1) or 2 μg/kg (Group R2) given over 30 seconds, commenced at the beginning of the sevoflurane administration. Only 18 of 32 patients (56.3%) in Group S had acceptable intubating conditions compared with 31 of 32 patients (96.9%) in Group R1 and 32 of 32 patients (100%) in Group R2 (P <0.001). Mean blood pressure was lower in Group R1 and R2 compared with Group S (P <0.005). Our routine use of ketamine and glycopyrrolate may have influenced the relative lack of significant hypotension and bradycardia. Sevoflurane, nitrous oxide and remifentanil provided acceptable conditions for tracheal intubation in children and could be an acceptable alternative to intravenous induction and neuromuscular blocking agents.

The optimal effect site concentration of remifentanil for tracheal intubation without muscle relaxant during inhalation anesthetic induction using sevoflurane in adult

BACKGROUND

Sevoflurane has been shown to be suitable for inhalation induction of anesthesia in adults. The addition of remifentanil during sevoflurane induction allows for rapid and smooth tracheal intubation without muscle relaxant. The high concentration of remifentanil can result in improved conditions for tracheal intubation but also caused a cardiovascular instability. We tried to estimate optimal effect site concentration of remifentanil for tracheal intubation without muscle relaxants during inhalation anesthetic induction with 8 vol% sevoflurane and 50% N2O.

METHODS

One hundred five ASA I and II patients were randomly allocated to receive an effect site concentration of remifentanil 2, 4, or 6 ng/ml. Trachea was intubated without muscle relaxant after 3 minutes of inhalation induction with 8 vol% sevoflurane and 50% N2O. The intubating conditions for tracheal intubation were assessed and blood pressure and heart rate were recorded at the baseline, before intubation, just after intubation, 1, and 3 minute after intubation.

RESULTS

Tracheal intubation was successful in all patients. Clinically acceptable intubation conditions were 60%, 94%, and 100% in 2 ng/ml, 4 ng/ml, and 6 ng/ml group respectively. However, the number of patient who requested rescue medication for bradycardia in 6 ng/ml group was significantly higher than that in the other group (P < 0.05).

CONCLUSIONS

We concluded that 4 ng/ml effect site concentration of remifentanil is adequate concentration for tracheal intubation without muscle relaxants during inhalation induction using sevoflurane.

Target-controlled inhalation induction with sevoflurane in children: a prospective pilot study

BACKGROUND

Target-controlled inhalation induction (TCII) with sevoflurane is becoming possible with new anesthesia platforms. Although TCII has already been performed in adults, it remains to be evaluated in children.

METHODS

In a prospective study, we compared TCII using the Felix AInOC anesthetic station (Taema, Anthony, France) to our standard protocol inhalation induction in children scheduled for elective surgery under general anesthesia. After preoxygenation, sevoflurane induction was performed in both groups without priming of the circuit. Sufentanil was administered after venous line placement.

RESULTS

In the TCII group, no overdosage or underdosage was observed except in two children where TCII failed owing to high agitation, and the number of adjustments was lower compared with our standard protocol inhalation induction (1(1-2.5[0-5]) vs 6(5-6[4-10]) respectively). Moreover, the delay to obtain target end-tidal sevoflurane concentration was shorter in the TCII group (2(1.6-2.7[1.3-4]) min vs 3.4(2.5-3.8[2.3-6.5]) min respectively). No significant difference in the delay of loss of consciousness or in the conditions for intubation or laryngeal mask placement was observed between the groups.

CONCLUSION

The Felix AInOC allows TCII to be performed satisfactorily in children. Manual inhalation induction induced a higher number of adjustments and overdosages.

The optimal bolus dose of alfentanil for tracheal intubation during sevoflurane induction without neuromuscular blockade in day-case anaesthesia

BACKGROUND

The purpose of this study was to determine the optimal bolus dose of alfentanil required to provide successful intubating conditions following inhalation induction of anaesthesia using 5% sevoflurane and 60% nitrous oxide without neuromuscular blockade in adult day-case anaesthesia.

METHODS

Twenty-four adults, aged 18-60 years, undergoing general anaesthesia for short ambulatory surgery were enroled into the study. After vital capacity induction, with sevoflurane 5% and 60% nitrous oxide in oxygen, pre-determined dose of alfentanil was injected over 30 s. The dose of alfentanil was determined by modified Dixon's up-and-down method (2 microg/kg as a step size). Ninety seconds after the end of bolus administration of alfentanil, the trachea was intubated. Systolic blood pressure, heart rate and SpO2 were recorded at anaesthetic induction, before, 1 min and 3 min after intubation.

RESULTS

The bolus dose of alfentanil for successful tracheal intubation was 10.7+/-2.1 microg/kg in 50% of patients during inhalation induction. From probit analysis, 50% effective dose (ED(50)) and ED(95) values (95% confidence limits) of alfentanil were 10.7 microg/kg (8.0-12.9 microg/kg) and 14.9 microg/kg (12.9-31.1 microg/kg), respectively.

CONCLUSIONS

Using the modified Dixon's up-and-down method, the bolus dose of alfentanil for successful tracheal intubation was 10.7+/-2.1 microg/kg in 50% of adult patients during inhalation induction using 5% sevoflurane and 60% nitrous oxide in oxygen without neuromuscular blocking agent in day-case anaesthesia.

Role of muscle relaxants in pediatric anesthesia

PURPOSE OF REVIEW

Changes in practice and the development of new anesthetic drugs have influenced the use of muscle relaxants in children. This article reviews these developments, and defines the current role and factors affecting the choice of muscle relaxant drugs in pediatric anesthesia.

RECENT FINDINGS

The introduction of the laryngeal mask airway as a means of controlling the pediatric airway has reduced the need for muscle relaxants. In cases requiring tracheal intubation, however, a balanced anesthetic technique incorporating a nondepolarizing relaxant provides the best intubating conditions with the minimal potential for adverse effects. The introduction of newer less-toxic, shorter-acting anesthetic drugs has reduced the requirement for muscle relaxants during surgery. Moderate anesthesia with sevoflurane-remifentanil or propofol-remifentanil can keep patients immobile without producing hypotension and facilitate controlled ventilation once the effects of the intubating dose of a muscle relaxant have worn off.

SUMMARY

Recent developments in clinical practice have reduced or obviated the need for muscle relaxants in pediatric anesthesia. Muscle relaxants are still indicated for intubation and procedures requiring profound muscle relaxation, and to minimize the amounts of anesthetic drugs given to infants and sick children. Specific relaxants and doses can be chosen to suit the clinical circumstances.

The optimal dose of remifentanil for intubation during sevoflurane induction without neuromuscular blockade in children

The optimal dose of remifentanil needed to produce successful intubating conditions following inhalation induction of anaesthesia using 5% sevoflurane without the use of neuromuscular blocking drugs, was investigated in 25 children aged 3-10 years. Sixty seconds after inhalation induction of anaesthesia using sevoflurane 5% in 100% oxygen, a predetermined dose of remifentanil was injected over 30 s. The dose of remifentanil was determined using the modified Dixon's up-and-down method (0.2 microg x kg(-1) as a step size). The first patient was tested at 1.0 microg x kg(-1) remifentanil. Ninety seconds following the bolus administration of remifentanil, the child's trachea was intubated. The optimal bolus dose of remifentanil required for successful tracheal intubation was 0.56 (0.15) microg x kg(-1) in 50% of children during inhalation induction using 5% sevoflurane in the absence of neuromuscular blocking drugs. Using probit analysis, the 95% effective dose (ED(95)) of remifentanil was 0.75 microg x kg(-1) (95% confidence limits 0.63-1.38 microg x kg(-1)).

Concentration of remifentanil needed for tracheal intubation with sevoflurane at 1 MAC in adult patients

BACKGROUND AND OBJECTIVE

Inhalation induction with sevoflurane provides acceptable conditions for tracheal intubation. Opioids significantly decrease the alveolar concentration needed to achieve tracheal intubation. The purpose of this study was to determine the target concentration of remifentanil providing excellent conditions for tracheal intubation with sevoflurane at 1 minimum alveolar concentration without muscle relaxant.

METHODS

Twenty-four consecutive patients, aged 18-50 yr, ASA I or II, were studied. Induction of anaesthesia was performed with sevoflurane at age-adjusted minimum alveolar concentration. Remifentanil was simultaneously administered using target-controlled infusion with the Minto model. Target plasma concentration of remifentanil was selected for each patient according to an up-and-down method.

RESULTS

The mean target concentration of remifentanil for successful tracheal intubation was 3.3 ng mL(-1) (95% confidence interval: 2.6-3.9 ng mL(-1)). Arterial pressure, heart rate and bispectral index did not increase after tracheal intubation in the group of patients with successful intubation.

CONCLUSIONS

Remifentanil at 3.3 ng mL(-1) together with sevoflurane at 1 minimum alveolar concentration provides excellent conditions for tracheal intubation in 50% of patients.

Comparison of propofol/remifentanil and sevoflurane/remifentanil for maintenance of anaesthesia for elective intracranial surgery

BACKGROUND

Propofol and sevoflurane are suitable agents for maintenance of anaesthesia during neurosurgical procedures. We have prospectively compared these agents in combination with the short-acting opioid, remifentanil.

METHODS

Fifty unpremedicated patients undergoing elective craniotomy received remifentanil 1 microg kg(-1) followed by an infusion commencing at 0.5 microg kg(-1) min(-1) reducing to 0.25 microg kg(-1) min(-1) after craniotomy. Anaesthesia was induced with propofol, and maintained with either a target-controlled infusion of propofol, minimum target 2 microg ml(-1) or sevoflurane, initial concentration 2%(ET). Episodes of mean arterial pressure (MAP) more than 100 mm Hg or less than 60 mm Hg for more than 1 min were defined as hypertensive or hypotensive events, respectively. A surgical assessment of operating conditions and times to spontaneous respiration, extubation, obey commands and eye opening were recorded. Drug acquisition costs were calculated.

RESULTS

Twenty-four and twenty-six patients were assigned to propofol (Group P) and sevoflurane anaesthesia (Group S), respectively. The number of hypertensive events was comparable, whilst more hypotensive events were observed in Group S than in Group P (P=0.053, chi-squared test). As rescue therapy, more labetolol [45 (33) vs 76 (58) mg, P=0.073] and ephedrine [4.80 (2.21) vs 9.78 (5.59) mg, P=0.020] were used in Group S. Between group differences in recovery times were small and clinically unimportant. The combined hourly acquisition costs of hypnotic, analgesic, and vasoactive drugs appeared to be lower in patients maintained with sevoflurane than with propofol.

CONCLUSION

Propofol/remifentanil and sevoflurane/remifentanil both provided satisfactory anaesthesia for intracranial surgery.

Low alfentanil target-concentrations improve hemodynamic and intubating conditions during induction with sevoflurane

PURPOSE

To investigate the effects of different alfentanil target-concentrations on hemodynamics, respiration and conditions of tracheal intubation during an inhalation induction with 8% sevoflurane.

METHODS

In this prospective randomized open-label study, 40 ASA I adult patients received alfentanil at the following target-concentrations: zero (Group 0), 25 (Group 25), 50 (Group 50) and 75 ng*mL(-1) (Group 75), starting five minutes before induction of anesthesia with 8% sevoflurane in 50% nitrous oxide. The ease of intubation was determined on fixed criteria and scored; arterial pressure, heart rate and bispectral index (BIS) were recorded at one-minute intervals.

RESULTS

Times to allow tracheal intubation were shortened only in Group 75 (94 +/- 8 sec) as compared to Group 0 (140 +/- 11 sec, P < 0.05). BIS values, tracheal intubation scores and number of attempts were not different between groups. However, more patients suffered from apnea in Group 75. Heart rate and mean arterial pressure remained stable in Group 75 whereas they increased significantly in the three other groups. No patient suffered hypotension.

CONCLUSION

Adding alfentanil at a 75 ng*mL(-1) target-concentration during an inhalation induction with 8% sevoflurane in 50% nitrous oxide allows intubation slightly earlier and provides stable hemodynamic conditions but the incidence of apnea during induction is higher. Lower concentrations are of little clinical interest.

The use of remifentanil for intubation in paediatric patients during sevoflurane anaesthesia guided by Bispectral Index (BIS) monitoring

We studied the intubating conditions, haemodynamic and endocrine changes following tracheal intubation during sevoflurane anaesthesia guided by Bispectral Index (BIS) monitoring in 40 children who received either remifentanil 1 microg.kg-1 (group R) or saline 1 ml.kg-1 (group S). Acceptable intubating conditions were found in all patients in group R (n = 20), compared to only 12 patients in group S (p = 0.002). There were no intergroup differences in heart rate, systolic blood pressure and plasma concentrations of epinephrine and norepinephrine at any time point and changes in haemodynamic variables throughout the study period were moderate. Titration of sevoflurane delivery to a target BIS of 35 +/- 5 led to almost equal end-tidal sevoflurane concentrations in either group and remifentanil did not affect the BIS. There were no side-effects in either group that required intervention. Intubating conditions during sevoflurane anaesthesia in children were found to be improved by a single bolus dose of remifentanil 1 microg.kg-1.

Inhalational techniques in ambulatory anesthesia

In the current health care environment, anesthesia practitioners are frequently required to reevaluate their practice to be more efficient and cost-effective. Although IV induction with propofol and inhalational induction with sevoflurane are both suitable techniques for outpatients, patients prefer IV induction. Maintenance of anesthesia with the newer inhaled anesthetics (ie, desflurane and sevoflurane) provide for a rapid early recovery as compared with infusion of propofol (ie, TIVA), while allowing easy titratability of anesthetic depth. Titration of hypnotic sedatives using BIS monitoring may reduce the time to awakening and thereby may facilitate fast tracking (ie, bypassing the PACU) and reduce hospital stay. Inhalational anesthesia is associated with a higher incidence of PONV, but no differences have been demonstrated with respect to late recovery (eg, PACU stay and home readiness). Although clinical differences between desflurane and sevoflurane appear to be small, desflurane may be associated with faster emergence, particularly in elderly and morbidly obese patients. Balanced anesthesia with IV propofol induction and inhalation anesthesia with N2O for maintenance, and an LMA for airway management, may be an optimal technique for ambulatory surgery. Inhalational anesthesia may have an economic advantage over a TIVA technique.

An inhalation bolus of sevoflurane versus an intravenous bolus of remifentanil for controlling hemodynamic responses to surgical stress during major surgery: a prospective randomized trial

We studied 120 patients scheduled for elective major thoracic or abdominal surgery, randomized into 2 groups: a Sevoflurane group (n = 63) and a Remifentanil group (n = 57). Heart rate (HR) and mean arterial pressure (MAP) are indicative of sympathetic response to surgical stress. A positive response was defined as a 15% increase in the HR and MAP above baseline measurements. When a positive response occurred, in the Sevoflurane group we administered a bolus dose of 8% sevoflurane (fresh gas flow 6 L/min) and in the Remifentanil group, an IV bolus dose of remifentanil 1 microg x kg(-1) x min(-1), which was maintained until MAP and HR returned to baseline measurements (effective bolus). If, after a bolus dose, a decrease in MAP and/or HR of >15% occurred with respect to baseline values, the response was considered to be excessive. The bolus dose was ineffective in 4.8% of the responses in the Sevoflurane group and in 17.8% of the responses in the Remifentanil group (P < 0.05). In the Sevoflurane group, an excessive effect occurred in 12% of responses, and in 26.7% in the Remifentanil group (P < 0.05). An inhalation bolus of sevoflurane seems to be more effective than an IV remifentanil bolus during maintenance, with more effective control of hemodynamic responses to surgical stress.

IMPLICATIONS

We compared an inhalation bolus of sevoflurane with remifentanil for managing hemodynamic responses to major abdominal or thoracic surgery. This prospective, randomized trial demonstrated better results with sevoflurane.

Inhalational anaesthesia

Sevoflurane and desflurane have important advantages over isoflurane and halothane. Disadvantages, which the clinician should keep in mind, include the degradation of both agents by soda lime under certain circumstances during closed circuit anaesthesia. As a result compound A and carbon monoxide (CO) may be generated in soda lime canisters and may be inhaled by patients. The extent to which this constitutes a significant problem during routine anaesthesia in humans is not clear. Recent developments in absorbent technology have the potential to reduce any hazard to negligible proportions. Other undesirable properties of the newer inhalation agents include agitation with sevoflurane in children and cardiovascular and airway effects with desflurane.