Effect-site Concentration Of Propofol Research Articles

Sensitivity to volatile anesthetics in patients with dementia: a case-control analysis.

Patients with dementia are thought to be more sensitive to anesthesia, although volatile anesthetic requirement has not specifically been evaluated in this population. We tested the hypothesis that patients with dementia having non-cardiac surgery have a lower ratio of bispectral index (BIS) to minimal alveolar concentration (MAC) during the five minutes immediately preceding incision, thus exhibiting deeper hypnotic levels at a given MAC fraction. We obtained records from our database registry on patients who had volatile general anesthesia during their most recent operation. We excluded patients premedicated with midazolam. Patients with dementia were identified and their diagnosis was confirmed by chart review. Each patient with dementia was successfully matched with a maximum of five patients without dementia using a multivariate nearest-neighbor distance-matching algorithm restricted to the following criteria: American Society of Anesthesiologists physical status, age, five-minute pre-incision time-weighted average (TWA) estimated effect-site concentration of propofol and fentanyl, and use of remifentanil. Our primary outcome was the TWA BIS-to-MAC ratio during the five minutes immediately preceding incision. We analyzed 31 patients with dementia matched with 151 patients without dementia. Median [quartiles] TWA BIS-to-MAC ratios for the matched patients were 85 [73, 100] for the patients with dementia and 78 [73, 84] for the patients without dementia. The percent difference in mean BIS-to-MAC ratios between patients with dementia and patients without dementia was 9% (95% confidence interval: -9% to 29%) (P=0.35, Wald test). Our results do not support the hypothesis that patients with dementia are more sensitive to volatile anesthetics than patients without dementia.

A novel technique to determine an 'apparent ke0 ' value for use with the Marsh pharmacokinetic model for propofol.

Debate continues over the most appropriate blood-brain equilibration rate constant (ke0) for use with the Marsh pharmacokinetic model for propofol. We aimed to define the optimal ke0 value. Sixty-four patients were sedated with incremental increases in effect-site target concentration of propofol while using six different ke0 values within the range 0.2-1.2 min(-1). Depth of sedation was assessed by measuring visual reaction time. A median 'apparent ke0' value of 0.61 min(-1) (95% CI 0.37-0.78 min(-1)) led to the greatest probability of achieving a stable clinical effect when the effect-site target was fixed at the effect-site concentration displayed by the target-controlled infusion system, at the time when a desired depth of sedation had been reached. By utilising a clinically relevant endpoint to derive this value, inter-individual pharmacokinetic and pharmacodynamic variability may be accounted for.

Intrathecal fentanyl decreases the optimal effect site concentration of propofol during spinal anaesthesia

The aim of this study was to assess the possible difference in the optimal effect site concentration of propofol for conscious sedation during spinal anaesthesia with or without intrathecal fentanyl in patients undergoing urologic surgery. The hypothesis was that intrathecal fentanyl would decrease the effect site concentration of propofol needed for conscious sedation. Among 43 patients, 23 patients received fentanyl 25 mcg and 20 patients received normal saline in addition to hyperbaric bupivacaine 10 mg during spinal anaesthesia. Propofol was infused at a dose determined by a modified Dixon's up-and-down method. The Cerebral State Index was recorded once target effect site concentration was reached to determine the effect of the successfulness of the conscious sedation. The half maximal effective concentration (EC50) of the effect-site concentration of propofol for sedation was 1.67 ± 0.28 mcg/ml in the control group and 0.87 ± 0.15 mcg/ml in the fentanyl group (P = 0.02). The propofol dose for conscious sedation during spinal anaesthesia was decreased by 48% when intrathecal fentanyl 25 mcg was added to local anaesthetics. The EC50 of the effect-site concentration of propofol for sedation decreased from 1.67 ± 0.28 mcg/ml to 0.87 ± 0.15 mcg/ml with the addition of 25 mcg fentanyl to a spinal anaesthetic in patients undergoing urologic surgery.

The hemodynamic effect of an intravenous antispasmodic on propofol requirements during colonoscopy: A randomized clinical trial

PurposeHemodynamic status during induction of anesthesia may modify the amount of propofol needed to induce loss of consciousness (LOC). This study was aimed to evaluate the effect of antispasmodic-induced tachycardia on the concentration of propofol at the effect-site for inducing LOC when deep sedation was executed for colonoscopy. MethodsOne hundred and sixteen adult patients were randomly assigned to receive either 20 mg of the antispasmodic Buscopan intravenously (Buscopan group; n = 58) or normal saline (control group; n = 58) for colonoscopy. After administration of Buscopan, the antispasmodic or normal saline, propofol was given by means of target-controlled infusion to induce LOC. We recorded patient characteristics, hemodynamic profiles, effect-site propofol concentration upon LOC, total propofol dosage for colonoscopy, and colonoscopy outcomes. ResultsThere were no significant differences in the characteristics between the two groups. Although the patients receiving Buscopan had a higher heart rate than those of the control group (101 ± 15 beats/minute vs. 77 ± 13 beats/minute; p < 0.001), we found no significant difference between two groups in the effect-site propofol concentration for inducing LOC (3.9 ± 0.6 μg/mL vs. 3.8 ± 0.6 μg/mL; p = 0.261) nor total propofol dosage required for colonoscopy (3.2 ± 1.4 mg/kg vs. 3.1 ± 1.1 mg/kg; p = 0.698). Both groups had comparable colonoscopy outcomes, including percentage of patients completing the procedure and total procedure time. ConclusionThe hemodynamic responses to intravenous Buscopan neither affected the effect-site propofol concentration needed to induce LOC, nor the total propofol dosage required for colonoscopy in this study. There is no need to modify the dosage of propofol in patients subject to Buscopan premedication in colonoscopy.

Propofol EC50 for inducing loss of consciousness is lower in the luteal phase of the menstrual cycle

BackgroundVarying levels of female sex hormones during the menstrual cycle were found to influence the central nervous system. The goal of the present study was to investigate whether the median (50%) effective effect-concentration (EC50) of propofol inducing loss of consciousness (LOC) varies between the luteal and the follicular phases of the menstrual cycle. MethodsTwenty-two patients (follicular phase) and 20 patients (luteal phase) undergoing gynaecological procedures under general anaesthesia were enrolled on the study. Anaesthesia was conducted with a target-controlled infusion (TCI) of propofol. The initial target effect-site propofol concentration (Ceprop) was 3.5 µg ml−1 and was adjusted stepwise by 0.5 µg ml−1 at 4 min intervals by an up–down sequential method to reach LOC. Anaesthesia was maintained with a propofol TCI guided by the bispectral index. The correlation between female sex hormones and predicted Ceprop at the time of LOC was analysed and emergence time from anaesthesia was recorded. ResultsPropofol EC50 to induce LOC was higher in patients in the follicular phase than those in the luteal phase (4.17 vs 3.58 µg ml−1, P<0.05). Progesterone correlated significantly with Ceprop at LOC. Emergence time was also longer in the follicular group than in the luteal group (6.5 vs 5.0 min, P<0.05). ConclusionsDuring general anaesthesia, patients in the luteal phase of the menstrual cycle had a lower propofol EC50 for LOC and a shorter emergence time compared with those in the follicular phase. Differences in progesterone levels between menstrual phases may contribute to these anaesthetic effects. Registry number of clinical trialChiCTR-RCH-12002755.

Effect Site Concentrations of Propofol for Dental Treatment under Deep Sedation in Intellectually Disabled Patients

Effect Site Concentrations of Propofol for Dental Treatment under Deep Sedation in Intellectually Disabled Patients

Comparison of Efficacy of Propofol When Used with or without Remifentanil during Conscious Sedation with a Target-Controlled Infuser for Impacted Teeth Extraction

【Background: Clinical use of propofol along with remifentanil for intravenous sedation is increasing in these days, but there are not enough researches to evaluate proper target concentration when these drugs are infused by using target controlled infusion (TCI) pump in dental treatment cases. In this study, we compared efficacy of TCI conscious sedation and target concentration of propofol when it used with or without remifentanil during conscious sedation with the help of a TCI for the surgical extraction of impacted teeth. Methods: After IRB approval, all the charts of patients who had undergone surgical extraction of impacted teeth under propofol TCI sedation for 6 months were selected and reviewed for this study. After reviewal of charts, we could divide patients in two groups. In one group (group 1), only propofol was selected for sedation and initial effect site concentration of propofol was $1{\mu}g/ml$ (n = 33), and in another group (group 2), both propofol and remifentanil was infused and initial effect site concentration of each drug was $0.6{\mu}g/ml$ and 1 ng/ml respectively (n = 25). For each group, average propofol target concentration was measured. In addition, we compared heart rate, respiratory rate, and systolic and diastolic blood pressure as well as oxygen saturation. Besides, BIS, sedation scores (OAAS/S), and subjective satisfaction scores were compared. Results: Between group 1 and 2, there were no significant differences in demographics (age, weight and height), and total sedation time. However, total infused dose and the effect site target concentration of propofol was $163.8{\pm}74.5mg$ and $1.13{\pm}0.21{\mu}g/ml$ in group 1, and $104.3{\pm}46.5mg$ and $0.72{\pm}0.26{\mu}g/ml$ in the group 2 with $1.02{\pm}0.21ng/l$ of the effect site target concentration of remifentanil, respectively. During sedation, there were no differences between overall vital sign, BIS and OAAS/S in 2 groups (P > 0.05). However, we figured out patients in group 2 had decreased pain sensation during sedation. Conclusions: Co-administration of propofol along with remifentanil via a TCI for the surgical extraction of impacted teeth may be safe and effective compared to propofol only administration.】

Correction of target-controlled infusion following wrong selection of emulsion concentrations of propofol.

BackgroundWe investigated the correction methods following wrong-settings of emulsion concentrations of propofol as a countermeasure against erroneous target-controlled infusions (TCI).MethodsTCIs were started with targeting 4.0 µg/ml of effect-site concentration (Ceff) of propofol, and the emulsion concentrations were selected for 2.0% instead of 1.0% (FALSE1-2, n = 24), or 1.0% instead of 2.0% (FALSE2-1, n = 24). These wrong TCIs were corrected at 3 min after infusion start. During FALSE1-2, the deficit was filled up while injecting after equilibrium (n = 12), or while overriding (n = 12). During FALSE2-1, the overdose was evacuated while targeting Ceff (n = 12) or targeting plasma concentration (Cp) (n = 12). The gravimetrical measurements of TCI reproduced the Cp and Ceff using simulations. The reproduced Ceff at 3 min (Ceff-3min) and the time to be normalized within ± 5% of target Ceff (T±5%), were compared between the correction methods.ResultsDuring the wrong TCI, Ceff-3min was 1.98 ± 0.01 µg/ml in FALSE1-2, and 7.99 ± 0.05 µg/ml in FALSE2-1. In FALSE1-2, T±5% was significantly shorter when corrected while overriding (3.9 ± 0.25 min), than corrected after equilibrium (6.9 ± 0.05 min) (P < 0.001). In FALSE2-1, T±5% was significantly shorter during targeting Cp (3.6 ± 0.04 min) than targeting Ceff (6.7 ± 0.15 min) (P < 0.001).ConclusionsThe correction methods, based on the pharmacokinetic and pharmacodynamic characteristics, could effectively and rapidly normalize the wrong TCI following erroneously selections of the emulsion concentration of propofol.

Sevoflurane versus propofol for interventional neuroradiology: a comparison of the maintenance and recovery profiles at comparable depths of anesthesia.

BackgroundSevoflurane and propofol are used widely for interventional neuroradiology (INR). Using the bispectral index (BIS), we compared the clinical properties of sevoflurane and propofol anesthesia in patients undergoing INR at comparable depths of anesthesia.MethodsThe patients were allocated randomly into two groups. The sevoflurane group received propofol (1.5 mg/kg), alfentanil (5 µg/kg), and rocuronium (0.6 mg/kg) for induction, and the propofol group was induced with a target effect-site concentration of propofol (4 µg/ml), alfentanil (5 µg/kg), and rocuronium (0.6 mg/kg). After intubation, anesthesia was maintained with sevoflurane or propofol with 67% nitrous oxide in 33% oxygen. Sevoflurane and propofol concentrations were titrated to maintain the BIS at 50-60. Phenylephrine or opioid was used to maintain the mean arterial pressure within 20% of the baseline values. The amounts of phenylephrine or alfentanil used, the number of patients showing movement during the procedure, and the recovery times were recorded.Results Compared to the propofol group, the sevoflurane group showed faster recovery in spontaneous ventilation, eye opening, extubation, and orientation (4 vs. 7 min, 7 vs. 9 min, 8 vs. 10 min, 10 vs. 14 min, respectively; P < 0.01). In the propofol group, significantly greater amounts phenylephrine were used (P < 0.05), and more patients moved during the procedure (P < 0.05).ConclusionsThe use of sevoflurane in maintaining anesthesia during INR was associated with faster recovery, less patient movement during the procedure, and a more stable hemodynamic response when compared to propofol.

The effect of desflurane versus propofol on regional cerebral oxygenation in the sitting position for shoulder arthroscopy

The sitting position may cause significant hemodynamic instability and cerebral hypoperfusion. We investigated the effects of desflurane and propofol on regional cerebral oxygenation (rSO2) in the sitting position during arthroscopic shoulder surgery. Forty patients undergoing arthroscopic shoulder surgery in the sitting position were randomly allocated to the desflurane group (n = 20) or the propofol group (n = 20). Anesthetic agents were maintained and adjusted with the effect-site concentration of propofol (2-3.5 μg/ml) or desflurane (4-7 vol%) to obtain a bispectral index (BIS) of 40-50. The hemodynamic variables, end-tidal carbon dioxide tension (ETCO2) and rSO2 were measured and evaluated. There were no differences in BIS, hemodynamic variables and ETCO2 between the groups. The rSO2 values in the desflurane group were higher compared to the propofol group at 3, 5, 7 and 9 min after the sitting position (P = 0.031, 0.047, 0.025 and 0.034, respectively). However, it decreased significantly from the baseline values at 3, 5, 7 and 9 min after the sitting position in both groups (P < 0.001). The change in rSO2 across time was not significantly different between the groups (P = 0.183). The incidence of rSO2 <75% of the baseline values after the sitting position was similar between the groups (0 and 10% in the desflurane and propofol group, respectively, P = 0.487). When anesthetized patients were raised to the sitting position, desflurane preserved cerebral oxygenation better than propofol at equipotent concentrations in terms of BIS. However, both anesthetics were associated with significant decrease in the rSO2 values during the sitting position.

Influence of a modified propofol equilibration rate constant (ke0) on the effect‐site concentration at loss and recovery of consciousness with the Marsh model

This study compared the predicted effect-site concentration of propofol at loss and recovery of consciousness when using target-controlled infusion devices with the same pharmacokinetic model (Marsh) but a different plasma effect-site equilibration rate constant (ke0 ), the Diprifusor(TM) (ke0 0.26 min(-1) ) and Base Primea™ (ke0 1.21 min(-1) ). We studied 60 female patients undergoing minor gynaecological surgery under general anaesthesia. Although the total dose of propofol and time until loss of consciousness were comparable, the effect-site concentration at loss of consciousness was significantly lower with the Diprifusor than with the Base Primea (1.2 (0.3) μg.ml(-1) vs 4.5 (0.9) μg.ml(-1) , respectively, p < 0.001). The effect-site concentration at recovery of consciousness was significantly higher with the Diprifusor than with the Base Primea (1.8 (0.4) μg.ml(-1) vs 1.5 (0.2) μg.ml(-1) , respectively, p = 0.01). In conclusion, the effect-site concentration of propofol differs depending on the ke0 , despite the use of the same pharmacokinetic model. Therefore, the ke0 should be considered when predicting loss and recovery of consciousness based on the effect-site concentration of propofol.

Prediction of effect-site concentration of sufentanil by dose–response target controlled infusion of sufentanil and propofol for analgesic and sedation maintenance in burn dressing changes

This study was to investigate the feasibility and efficiency of by target-controlled infusion (TCI) for analgesia and sedation during burn dressing change, and to predict the effect-site concentration of sufentanil. Eighty burn patients were randomly and evenly divided into four groups according to target sufentanil effect-site concentration (0.2, 0.3, 0.4 and 0.5ng/ml). The sufentanil–propofol TCI was carried out during dressing changes. The effect-site concentration of propofol was maintained at 1.2μg/ml. The dose–response relationships of sufentanil for providing adequate analgesia were evaluated by visual analog scales and Ramsay sedation scores. The effect-site concentration of sufentanil was calculated by Probit regression analysis. Incidence of respiratory depression, doctors and patients’ satisfaction and adverse events were assessed. The EC50 and EC95 of sufentanil to maintain anesthesia for uncovering the inner layer dressings during TCI were 0.278ng/ml (95% CI 0.231–0.318ng/ml) and 0.394ng/ml (95% CI 0.366–0.530ng/ml), respectively, while the EC50 and EC95 of sufentanil to maintain anesthesia for wound management were 0.349ng/ml (95% CI 0.299–0.366ng/ml) and 0.465ng/ml (95% CI 0.430–0.563ng/ml), respectively. Doctors and patients’ satisfaction were significantly higher in the 0.4 and 0.5ng/ml groups than the 0.2ng/ml group. One and three patients had respiratory depression in the 0.4 and 0.5ng/ml groups, respectively. No adverse events occurred after operations. In conclusion, low dose sufentanil–propofol TCI for anesthesia and sedation maintenance in burn dressing changes is feasible and effective, and wound management requires higher effect-site concentrations of sufentanil than disclosing inner layer dressings.

Target‐Controlled Infusion of Propofol‐Induced Sleep Endoscopy for Patients with Obstructive Sleep Apnea

Objectives: Drug-induced sleep endoscopy (DISE) allows inspection of upper airway to accurately localize the anatomical region that collapses in obstructive sleep-apnea-hypopnea syndrome (OSAHS). The sedation technique adopted in most centers throughout Europe is the target controlled infusion (TCI) of propofol without oxygen supply. The goal of this paper is to compare the advantages of supplemental oxygen during this procedure. Methods: Medical records of 61 patients diagnosed with OSAHS by full-night PSG who underwent drug-induced sleep endoscopy (DISE) with propofol to evaluate the upper airway were retrospectively reviewed. No patients were on any premedication preoperatively before DISE. Besides applying standard anesthetic monitors, a bispectral index monitor (BIS) Quatro sensor was positioned on the forehead as per manufacturer’s instructions. If patients had brisk response of limb movement, the sedative dosage was adjusted by specialized anesthesiologists. The demographic variables of age, gender, BMI and intraoperative presentations of effect site concentration of Propofol ((µg/mL)), BIS level, infusion time, and involuntary movement were collected for analysis. Results: By achieving the same level of sedation detected by the BIS monitor, the severe OSAHS patients needed a higher effect site concentration of propofol (5.3 ± 1.1 μg/mL in severe OSAHS vs. 4.5 ± 1.4 μg/mL in mild/moderate OSAHS, p=0.025, Mann-Whitney U test) and obviously involuntary movement. No adverse effects or complications were noted during this procedure. Conclusions: Target controlled infusion of Propofol-induced sleep endoscopy for OSA patients is a feasible and safe procedure. Severe OSAHS patients experienced worse saturation during overnight sleep and obviously involuntary response in sedated endoscopy even with higher predicted concentration of Propofol.

English

The aim of this study was to determine the target-controlled concentration of propofol required for successful laryngeal mask airway (LMA) placement after dexmedetomidine pre-injection. Twenty ASA physical status I–II patients aged 20–60 years old, who were scheduled for general anesthesia, were studied. After receiving a loading dose of 1.0 μg/kg dexmedetomidine over 10 min, propofol was infused using a target-controlled infusion as determined by a modified Dixon's up-and-down method. The first patient received a target-controlled infusion of 3.0 μg/ml propofol. The response of each patient determined the propofol concentration given to the next patient. Cough, body movement, laryngospasm, intentional movement, mouth opening, and difficulty of LMA insertion indicated failure, and the propofol concentration was increased by a step of 0.2 μg/ml. If the insertion of the LMA was successful, then the target concentration was decreased by the same dose. The effect-site propofol concentration for successful LMA insertion was determined to be 2.351 μg/ml in 50% of the patients (EC50) with pre-injection of dexmedetomidine without muscle relaxant. Subsequent probit analysis showed an EC95 (95% CI) of 2.854 μg/ml (2.588–2.944 μg/ml).Thus, dexmedetomidine combined with target-controlled infusion of propofol can be used for LMA placement, with few adverse reactions. In addition, dexmedetomidine sedation can effectively reduce the target-controlled plasma concentration of propofol. Key words: Dexmedetomidine, propofol, target-controlled infusion, laryngeal airway mask.

The Effective Effect-Site Propofol Concentration for Induction in Morbidly Obese Patients Using Total Body Weight with a New Pharmacokinetic Model

To the Editor: Recently Echevarría et al.1 from our group described the effect-site propofol concentration (Ce) required to be set in propofol effect-site target-controlled infusion mode to induce and intubate the tracheas of morbidly obese patients using total body weight (TBW) with the Marsh and the Schnider pharmacokinetic (PK) models.2,3 These models, however, were not derived from obese patient data and their use in obese patients is controversial. Using the same data from Echevarría et al.’s1 study, we estimated the propofol Ce to be set for induction and tracheal intubation with a new PK model available for obese patients.4 The data of 66 morbidly obese subjects aged from 18 to 50 years were analyzed. All patients were monitored with a bispectral index electroencephalographic monitor (A2000 BIS® XP monitor, version 3.2; Aspect Medical Systems Inc., Newton, MA). Fentanyl 3 μg/kg TBW was administered before starting propofol infusion. The Ce (CI95%) producing a bispectral index <60 until intubation for 50% (Ce50) and 95% (Ce95) of patients was calculated with logistic regression. The target values obtained were 3.8 (3.2–4.2) μg/mL and 5.6 (5.0–7.6) μg/mL, respectively. The mean dose of propofol estimated to reach the Ce within the range of confidence interval 95% of the Ce50 (n = 19) was 0.9 ± 0.1 and 1.6 ± 0.2 mg/kg for the Ce95 (n = 16). Mean maximum decrease of mean arterial blood pressure was around 30% with the 2 estimated Ces. Heart rate variations ranged from −22% to 12% from baseline. Figure 1 shows the concentration versus effect curves estimated for the 3 PK models.Figure 1: Dose-response curve fitted to Cortínez, Marsh, and Schnider pharmacokinetic models using logit analysis, based on total body weight. The y-axis corresponds to the probability of no response until tracheal intubation (TI) and the x-axis to the predicted propofol effect-site concentration (Ce).This new analysis suggests that when using propofol target-controlled infusion with the Cortínez PK model4 in morbidly obese patients receiving fentanyl 3 μg/kg TBW, the Ce for induction and intubation should be around 5.5 μg/mL. A significant decrease in arterial blood pressure must be expected with this recommended dosingscheme.

Reaction time‐monitored patient‐maintained propofol sedation: a pilot study in oral surgery patients

Previous volunteer studies of an effect-site controlled patient-maintained sedation system using propofol have demonstrated a risk of oversedation. We have incorporated a reaction time monitor into the handset to add an individualised patient-feedback mechanism. This pilot study assessed if the reaction time-feedback modification would prove safe and effective in 20 healthy patients receiving sedation while undergoing oral surgery. All patients successfully sedated themselves without reaching any unsafe endpoints. All 20 maintained verbal contact throughout. The mean (SD) lowest peripheral blood oxygen saturation was 98.0 (2.1)% breathing room air. No patient required supplementary oxygen. The mean (SD) maximum effect-site propofol concentration reached was 1.6 (0.5)μg.ml(-1). The present system was found to be safe and effective, allowing oral surgery treatment under conscious sedation, but preventing oversedation.

Robust closed‐loop control of induction and maintenance of propofol anesthesia in children

During closed-loop control, a drug infusion is continually adjusted according to a measure of clinical effect (e.g., an electroencephalographic depth of hypnosis (DoH) index). Inconsistency in population-derived pediatric pharmacokinetic/pharmacodynamic models and the large interpatient variability observed in children suggest a role for closed-loop control in optimizing the administration of intravenous anesthesia. To clinically evaluate a robustly tuned system for closed-loop control of the induction and maintenance of propofol anesthesia in children undergoing gastrointestinal endoscopy. One hundred and eight children, aged 6-17, ASA I-II, were enrolled. Prior to induction of anesthesia, NeuroSENSE™ sensors were applied to obtain the WAVCNS DoH index. An intravenous cannula was inserted and lidocaine (0.5mg·kg(-1) ) administered. Remifentanil was administered as a bolus (0.5μg·kg(-1) ), followed by continuous infusion (0.03μg·kg(-1) ·min(-1) ). The propofol infusion was closed-loop controlled throughout induction and maintenance of anesthesia, using WAVCNS as feedback. Anesthesia was closed-loop controlled in 102 cases. The system achieved and maintained an adequate DoH without manual adjustment in 87/102 (85%) cases. Induction of anesthesia (to WAVCNS ≤60) was completed in median 3.8min (interquartile range (IQR) 3.1-5.0), culminating in a propofol effect-site concentration (Ce ) of median 3.5μg·ml(-1) (IQR 2.7-4.5). During maintenance of anesthesia, WAVCNS was measured within 10 units of the target for median 89% (IQR 79-96) of the time. Spontaneous breathing required no manual intervention in 91/102 (89%) cases. A robust closed-loop system can provide effective propofol administration during induction and maintenance of anesthesia in children. Wide variation in the calculated Ce highlights the limitation of open-loop regimes based on pharmacokinetic/pharmacodynamic models.

The ability of bispectral index to detect intra‐operative wakefulness during total intravenous anaesthesia compared with the isolated forearm technique

It has been suggested that monitoring during total intravenous anaesthesia should include aspects of brain function. The current study used a manually adjusted target-controlled infusion of propofol for anaesthesia, guided to a bispectral index range of 55-60. Intra-operative responsiveness, as assessed by the isolated forearm technique, was compared with whether the bispectral index predicted/identified a patient's appropriate hand movements in responses to commands. Twenty-two women underwent major gynaecological surgery with total intravenous anaesthesia, propofol, remifentanil and atracurium. Sixteen women responded, on 80 occasions, with appropriate hand movements to commands during surgery, of which the bispectral index detected 47 (sensitivity 59%). The bispectral index suggested consciousness 220 times in the absence of movement responses (specificity 85%). The positive predictive value of a bispectral index response was 18%. While two women had vague recall about squeezing fingers, none had recall of surgery. For patients who responded more than once during surgery the bispectral index value associated with a response was not constant. Although there was no difference in the median (IQR [range]) effect site propofol concentration between intra-operative responses (2.0 (1.5-2.3 [1.2-4.0]) μg.ml(-1)) and eye opening after surgery (2.1 (1.7-2.8 [1.5-3.9]) μg.ml(-1)), the median (IQR [range]) bispectral index value at eye opening after surgery was significantly higher than that associated with responses during surgery: 75 (70-78 [51-93]) vs 61 (52-67 [37-80]) respectively, (p < 0.001). The manual control of propofol intravenous anaesthesia to target a bispectral index range of 55-60 may result in an unacceptable number of patients who are conscious during surgery (albeit without recall).

Effects of different doses of dexmedetomidine on propofol-induced inhibition of responses to laryngeal mask airway insertion when combined with fentanyl in patients undergoing gynecological operation

Objective To evaluate the effects of different doses of dexmedetomidine on propofol-induced inhibition of responses to laryngeal mask airway （LMA） insertion when combined with fentanyl in patients undergo- ing gynecological operation. Methods One hundred and twenty-five ASA Ⅰ-Ⅱ female patients, aged 20-60 yr, scheduled for elective short-time surgery, were randomly divided into 5 groups （ n = 25 each） ： normal saline group （group NS） and different doses of dexmedetomidne groups （groups D1-4 ）. Normal saline 40 ml and dexmedeto- midne 0.4, 0.6, 0.8, 1.0 μg/kg （in 40 ml of normal saline） were infused over 10 min in groups NS and D1-4 re- spectively. 1% propofol was then given by target-controlled infusion. The concentration of propofol was determined by using modified Dixon＇s up-and-down method. The initial plasma concentration of propofol was 3.0 μg/ml and the ratio between the 2 successive concentrations was 1.1. Fentanyl 1. 5μg/kg was injected intravenously when the effect-site concentration of propofol reached the preset plasma concentration. LMA was inserted 4 min later. When LMA insertion was successful, the concentration of propofol was decreased in the next patient and when LMA inser- tion failed, the concentration of propofol was increased in the next patient. Failure of LMA insertion was defined asdifficulty in inserting LMA or body movement, corner of mouth movement, biting LMA, swallowing and/or lacrima- tion during insertion. The median effective target effect-site concentration and 95 % confidence interval of propofol blunting responses to LMA insertion when combined with fentanyl were calculated. Results The median effective target effect-site concentration （95% confidence interval） of propofol blunting responses to LMA insertion when combined with fentanyl were 3.09 （2.83-3.36）, 2.48 （2.26-2.73）, 2.29 （2.18-2.41）, 2.04 （1.95-2.12） and 1.67 （1.55-1.81 ）μg/ml in groups NS and D].4 , respectively. Conclusion Dexmedetomidine can enhance propo- fol-induced inhibition of responses to LMA insertion when combined with fentanyl in dose-dependent manner in pa- tients undergoing gynecological operation. Key words: Dexmedetomidine ; Propofol ; Piperidines ; Dose-response relationship, drug ; Laryngeal masks; Gynecologic surgical procedures

Low effect‐site concentration of propofol target‐controlled infusion reduces the risk of hypotension during endoscopy in a Taiwanese population

Target-controlled infusion (TCI) of propofol is an effective way of delivering propofol during endoscopy. However, the ideal effect-site concentration (Ce) of propofol has not yet been defined in an Asian population. This study aimed to determine the ideal Ce of propofol in painless gastrointestinal endoscopy in a Taiwanese population. A total of 121 consecutive patients undergoing diagnostic endoscopy were recruited for this study. The endoscopic procedure was carried out within 1 h. TCI of propofol was utilized during the procedure. All patients received the same regimen to induce conscious sedation, including a bolus of midazolam (0.04 mg/kg) and fentanyl (0.5 μg/kg). The Ce of propofol was calculated using the Schneider model. Patients were randomly assigned to either the low Ce group (1.5-2.5 μg/mL) or high Ce group (3.0-4.0 μg/mL). Their cardiovascular and respiratory events were monitored during the procedure and the patients' post-procedure satisfaction was evaluated. The mean requirement for propofol was 232.02 mg in the low Ce group and 329.56 mg in the high Ce group, respectively (P < 0.0001). No unexpected event was observed in either group. However, more episodes of hypotension were observed in the high Ce group (P = 0.026). The post-procedure satisfaction rate between the two groups was comparable. A low Ce of propofol TCI (1.5-2.5 μg/mL) achieved adequate anesthesia, reduced the risk of hypotension, and attained a high satisfaction rate in a Taiwanese population undergoing diagnostic painless endoscopy.