Performance evaluation of paediatric propofol pharmacokinetic models in healthy young children

Clinical evaluation of bispectral index-guided closed-loop infusion of propofol for preschool children: A multi-center randomized controlled study

Importance

The closed-loop infusion system can automatically adjust and maintain the depth of anesthesia by using the propofol target-controlled infusion (TCI) model under the feedback guidance of the bispectral index (BIS).

Objective

To evaluate the safety and superiority of closed-loop TCI of propofol guided by BIS during maintenance of generalized intravenous anesthesia for preschool children.

Methods

A total of 120 children aged 1-6 years were enrolled and were divided into a closed-loop feedback group (Group C) and an open-loop manual control group (Group O), with 60 participants in each group. For anesthesia maintenance, the propofol infusion rate was adjusted by the injection system under the guidance of BIS in Group C and was manually adjusted by anesthesiologists according to the BIS and clinical experience in Group O, to maintain a BIS level of 50. The time ratio of adequate anesthesia (40 ≤ BIS ≤ 60), light anesthesia (BIS > 60), and deep anesthesia (BIS < 40) were recorded.

Results

A total of 119 patients (59 in Group C and 60 in Group O) were enrolled in the study. Group C demonstrated a higher time ratio of adequate anesthesia (P = 0.014) compared to Group O. The time ratio of light anesthesia and the global score was lower in Group C than in Group O (P = 0.010, P = 0.015, respectively). The frequency of adjustment per unit of time was higher in Group C for propofol (P < 0.001), while it was lower for remifentanil (P = 0.010).

Interpretation

BIS-guided closed-loop infusion of propofol is safe and effective for preschool children. The depth of anesthesia is controlled more accurately and smoothly.

Electroencephalographic Indices for Clinical Endpoints during Propofol Anesthesia in Infants: An Early-phase Propofol Biomarker-finding Study

BACKGROUND

Unlike expired sevoflurane concentration, propofol lacks a biomarker for its brain effect site concentration, leading to dosing imprecision particularly in infants. Electroencephalography monitoring can serve as a biomarker for propofol effect site concentration, yet proprietary electroencephalography indices are not validated in infants. The authors evaluated spectral edge frequency (SEF95) as a propofol anesthesia biomarker in infants. It was hypothesized that the SEF95 targets will vary for different clinical stimuli and an inverse relationship existed between SEF95 and propofol plasma concentration.

METHODS

This prospective study enrolled infants (3 to 12 months) to determine the SEF95 ranges for three clinical endpoints of anesthesia (consciousness-pacifier placement, pain-electrical nerve stimulation, and intubation-laryngoscopy) and correlation between SEF95 and propofol plasma concentration at steady state. Dixon's up-down method was used to determine target SEF95 for each clinical endpoint. Centered isotonic regression determined the dose-response function of SEF95 where 50% and 90% of infants (ED50 and ED90) did not respond to the clinical endpoint. Linear mixed-effect model determined the association of propofol plasma concentration and SEF95.

RESULTS

Of 49 enrolled infants, 44 evaluable (90%) showed distinct SEF95 for endpoints: pacifier (ED50, 21.4 Hz; ED90, 19.3 Hz), electrical stimulation (ED50, 12.6 Hz; ED90, 10.4 Hz), and laryngoscopy (ED50, 8.5 Hz; ED90, 5.2 Hz). From propofol 0.5 to 6 μg/ml, a 1-Hz SEF95 increase was linearly correlated to a 0.24 (95% CI, 0.19 to 0.29; P < 0.001) μg/ml decrease in plasma propofol concentration (marginal R2 = 0.55).

CONCLUSIONS

SEF95 can be a biomarker for propofol anesthesia depth in infants, potentially improving dosing accuracy and utilization of propofol anesthesia in this population.

EDITOR’S PERSPECTIVE

Target-controlled infusion - Past, present, and future

Target-controlled infusion (TCI) is a novel drug delivery system wherein a microprocessor calculates the rate of drug to be infused based upon the target plasma or effect site concentration set by the operator. It has found its place in the operation theaters and intensive care units (ICUs) for safe administration of intravenous anesthesia and analgosedation using drugs like propofol, dexmedetomidine, opioids, and so on. Operating a TCI device requires the user to have a primitive understanding of drug pharmacokinetics and pharmacodynamics and an awareness of the practical problems that can arise during its administration. Ongoing research supports their usage in other clinical settings and for various other drugs such as antibiotics, vasopressors, and so on. In this article, we review the underlying principles and commonly used drugs for TCI, the practical aspects of its implementation, and the scope of this technology in future. TCI technology is increasingly being used in the field of anesthesiology and critical care due to the myriad advantages it offers when compared to manual infusions. It is, therefore, essential for the reader to understand the relevant principles and practical aspects related to TCI technology, as well as to be aware of the commonly used TCI models.

External Evaluation of Population Pharmacokinetic Models for Precision Dosing: Current State and Knowledge Gaps

Predicting drug exposures using population pharmacokinetic models through Bayesian forecasting software can improve individual pharmacokinetic/pharmacodynamic target attainment. However, selecting the most adapted model to be used is challenging due to the lack of guidance on how to design and interpret external evaluation studies. The confusion around the choice of statistical metrics and acceptability criteria emphasises the need for further research to fill this methodological gap as there is an urgent need for the development of standards and guidelines for external evaluation studies. Herein we discuss the scientific challenges faced by pharmacometric researchers and opportunities for future research with a focus on antibiotics.

The Impact of Low Cardiac Output on Propofol Pharmacokinetics across Age Groups-An Investigation Using Physiologically Based Pharmacokinetic Modelling

BACKGROUND

pathophysiological changes such as low cardiac output (LCO) impact pharmacokinetics, but its extent may be different throughout pediatrics compared to adults. Physiologically based pharmacokinetic (PBPK) modelling enables further exploration.

METHODS

A validated propofol model was used to simulate the impact of LCO on propofol clearance across age groups using the PBPK platform, Simcyp^® (version 19). The hepatic and renal extraction ratio of propofol was then determined in all age groups. Subsequently, manual infusion dose explorations were conducted under LCO conditions, targeting a 3 µg/mL (80-125%) propofol concentration range.

RESULTS

Both hepatic and renal extraction ratios increased from neonates, infants, children to adolescents and adults. The relative change in clearance following CO reductions increased with age, with the least impact of LCO in neonates. The predicted concentration remained within the 3 µg/mL (80-125%) range under normal CO and LCO (up to 30%) conditions in all age groups. When CO was reduced by 40-50%, a dose reduction of 15% is warranted in neonates, infants and children, and 25% in adolescents and adults.

CONCLUSIONS

PBPK-driven, the impact of reduced CO on propofol clearance is predicted to be age-dependent, and proportionally greater in adults. Consequently, age group-specific dose reductions for propofol are required in LCO conditions.

General Purpose Pharmacokinetic-Pharmacodynamic Models for Target-Controlled Infusion of Anaesthetic Drugs: A Narrative Review

Target controlled infusion (TCI) is a clinically-available and widely-used computer-controlled method of drug administration, adjusting the drug titration towards user selected plasma- or effect-site concentrations, calculated according to pharmacokinetic-pharmacodynamic (PKPD) models. Although this technology is clinically available for several anaesthetic drugs, the contemporary commercialised PKPD models suffer from multiple limitations. First, PKPD models for anaesthetic drugs are developed using deliberately selected patient populations, often excluding the more challenging populations, such as children, obese or elderly patients, of whom the body composition or elimination mechanisms may be structurally different compared to the lean adult patient population. Separate PKPD models have been developed for some of these subcategories, but the availability of multiple PKPD models for a single drug increases the risk for invalid model selection by the user. Second, some models are restricted to the prediction of plasma-concentration without enabling effect-site controlled TCI or they identify the effect-site equilibration rate constant using methods other than PKPD modelling. Advances in computing and the emergence of globally collected databases has allowed the development of new “general purpose” PKPD models. These take on the challenging task of identifying the relationships between patient covariates (age, weight, sex, etc) and the volumes and clearances of multi-compartmental pharmacokinetic models applicable across broad populations from neonates to the elderly, from the underweight to the obese. These models address the issues of allometric scaling of body weight and size, body composition, sex differences, changes with advanced age, and for young children, changes with maturation and growth. General purpose models for propofol, remifentanil and dexmedetomidine have appeared and these greatly reduce the risk of invalid model selection. In this narrative review, we discuss the development, characteristics and validation of several described general purpose PKPD models for anaesthetic drugs.

Propofol context-sensitive decrement times in children

Plasma drug concentration is the variable linking dose to effect. The decrement time required for plasma concentration of anesthetic agents to decrease by 50% (context-sensitive half-time) correlates with the time taken to regain consciousness. However, the decrement time to consciousness may not be 50%. An effect compartment concentration is associated more closely with return of consciousness than plasma concentration. An alternative decrement time, the time required for propofol to decrease to a predetermined effect compartment concentration associated with movement (eg, 2 µg.ml^-1 ), was used to simulate time for the concentration to decrease from steady state at a typical targeted effect compartment concentration 3.5 µg.ml^-1 in children. These times were short and reflected a decrement time to consciousness (CST_AWAKE ) increase that was small with longer infusion time. CST_AWAKE ranged from 7.5 min in 1-year-old infant given propofol for 15 min to 13.5 min in a 15-year-old adolescent given a 2-hour infusion. Changes in decrement time with age reflect maturation of drug clearance. Neonates had prolonged increment times, 10 min after 15 min infusion and 18 min after 120 min infusion using a target concentration of 3.5 µg.ml^-1 . Decrement times to a targeted arousal concentration are context-sensitive. Use of a higher target concentration of 6 µg.ml^-1 doubled decrement times. Decrement times are associated with variability: delayed recovery beyond these simulated times is likely more attributable to the use of adjuvant drugs or the child's clinical status. An understanding of propofol decrement times can be used to guide recovery after anesthesia.

Clinical Importance of Potential Genetic Determinants Affecting Propofol Pharmacokinetics and Pharmacodynamics

Interindividual variability in response to drugs used in anesthesia has long been considered the rule, not the exception. It is important to mention that in anesthesiology, the variability in response to drugs is multifactorial, i.e., genetic and environmental factors interact with each other and thus affect the metabolism, efficacy, and side effects of drugs. Propofol (2,6-diisopropylphenol) is the most common intravenous anesthetic used in modern medicine. Individual differences in genetic factors [single nucleotide polymorphisms (SNPs)] in the genes encoding metabolic enzymes, molecular transporters, and molecular binding sites of propofol can be responsible for susceptibility to propofol effects. The objective of this review (through the analysis of published research) was to systematize the influence of gene polymorphisms on the pharmacokinetics and pharmacodynamics of propofol, to explain whether and to what extent the gene profile has an impact on variations observed in the clinical response to propofol, and to estimate the benefit of genotyping in anesthesiology. Despite the fact that there has been a considerable advance in this type of research in recent years, which has been largely limited to one or a group of genes, interindividual differences in propofol pharmacokinetics and pharmacodynamics may be best explained by the contribution of multiple pathways and need to be further investigated.

Midlatency auditory evoked potentials during anesthesia in children: A narrative review

The brain is considered as the major target organ of anesthetic agents. Despite that, a reliable means to monitor its function during anesthesia is lacking. Mid latency auditory evoked potentials are known to be sensitive to anesthetic agents and might therefore be a measure of hypnotic state in pediatric patients. This review investigates the available literature describing various aspects of mid latency auditory evoked potential monitoring in pediatric anesthesia.

Why do We Use the Concepts of Adult Anesthesia Pharmacology in Developing Brains? Will It Have an Impact on Outcomes? Challenges in Neuromonitoring and Pharmacology in Pediatric Anesthesia

BACKGROUND

Pediatric sedation and anesthesia techniques have plenty of difficulties and challenges. Data on the pharmacologic, electroencephalographic, and neurologic response to anesthesia at different brain development times are only partially known. New data in neuroscience, pharmacology, and intraoperative neuromonitoring will impact changing concepts and clinical practice. In this article, we develop a conversation to guide the debate and search for a view more attuned to the updated knowledge in neurodevelopment, electroencephalography, and clinical pharmacology for the anesthesiologic practice in the pediatric population.

Population pharmacokinetics of propofol in neonates and infants: Gestational and postnatal age to determine clearance maturation

AIMS

Develop a population pharmacokinetic model describing propofol pharmacokinetics in (pre)term neonates and infants, that can be used for precision dosing (e.g. during target-controlled infusion) of propofol in this population.

METHODS

A nonlinear mixed effects pharmacokinetic analysis (Monolix 2018R2) was performed, based on a pooled study population in 107 (pre)term neonates and infants.

RESULTS

In total, 836 blood samples were collected from 66 (pre)term neonates and 41 infants originating from 3 studies. Body weight (BW) of the pooled study population was 3.050 (0.580-11.440) kg, postmenstrual age (PMA) was 36.56 (27.00-43.00) weeks and postnatal age (PNA) was 1.14 (0-104.00) weeks (median and min-max range). A 3-compartment structural model was identified and the effect of BW was modelled using fixed allometric exponents. Elimination clearance maturation was modelled accounting for the maturational effect on elimination clearance until birth (by gestational age [GA]) and postpartum (by PNA and GA). The extrapolated adult (70 kg) population propofol elimination clearance (1.64 L min^-1 , estimated relative standard error = 6.02%) is in line with estimates from previous population pharmacokinetic studies. Empirical scaling of BW on the central distribution volume in function of PNA improved the model fit.

CONCLUSIONS

It is recommended to describe elimination clearance maturation by GA and PNA instead of PMA on top of size effects when analyzing propofol pharmacokinetics in populations including preterm neonates. Changes in body composition in addition to weight changes or other physio-anatomical changes may explain the changes in central distribution volume. The developed model may serve as a prior for propofol dose finding and target-controlled infusion in (preterm) neonates.

Case Studies Using the Electroencephalogram to Monitor Anesthesia-Induced Brain States in Children

For this child, at this particular moment, how much anesthesia should I give? Determining the drug requirements of a specific patient is a fundamental problem in medicine. Our current approach uses population-based pharmacological models to establish dosing. However, individual patients, and children in particular, may respond to drugs differently. In anesthesiology, we have the advantage that we can monitor our patients in real time and titrate drugs to the desired effect. Examples include blood pressure management or muscle relaxation. Although the brain is the primary site of action for sedative-hypnotic drugs, the brain is not routinely monitored during general anesthesia or sedation, a fact that would surprise many patients. One reason for this is that, until recently, physiologically principled approaches for anesthetic brain monitoring have not been articulated. In the past few years, our knowledge of anesthetic brain mechanisms has developed rapidly. We now know that anesthetic drug effects are clearly visible in the electroencephalogram (EEG) of adults and reflect underlying anesthetic pharmacology and brain mechanisms. Most recently, similar effects have been characterized in children. In this article, we describe how EEG monitoring could be used to guide anesthetic management in pediatric patients. We review previous evidence and present multiple case studies showing how drug-specific and dose-dependent EEG signatures seen in adults are visible in children and infants, including those with neurological disorders. We propose that the EEG can be used in the anesthetic care of children to enable anesthesiologists to better assess the drug requirements of individual patients in real time and improve patient safety and experience.

The predictive performance of propofol target-controlled infusion during robotic-assisted laparoscopic prostatectomy with CO2 pneumoperitoneum in the head-down position

PURPOSE

Propofol clearance can be reduced when cardiac output (CO) is decreased. This clearance reduction may alter the pharmacokinetics of propofol and worsen the predictive performance of target-controlled infusion (TCI) of propofol. The head-down position (HDP) and CO₂ pneumoperitoneum, which are required for robotic-assisted laparoscopic prostatectomy (RALP), may cause changes in CO. We investigated the predictive performance of propofol TCI during CO₂ pneumoperitoneum in patients who underwent RALP in the HDP.

METHODS

Fifteen male patients received propofol TCI using the Diprifusor model. Propofol concentrations were measured at seven time points: (T1) 15 min after anesthesia induction; (T2) before the insufflation; (T3, T4, and T5) 15, 60, and 90 min, respectively, after insufflation in the HDP; (T6) before the release of pneumoperitoneum in the HDP; and (T7) 15 min after the release of pneumoperitoneum in the supine position. Cardiac index (CI) was assessed using an arterial pulse contour CO monitor. The predictive performance of propofol TCI was evaluated by calculating the performance errors (PE) in propofol concentrations for each data point. The relationship between CI and PE was examined. Median PE (MDPE) and median absolute PE (MDAPE) were calculated as measures of bias and accuracy, respectively.

RESULTS

A total of 104 blood samples were analyzed. There was significantly negative correlation between CI and PE. The predictive performance of propofol TCI during pneumoperitoneum in the HDP was acceptable (MDPE = - 1.5% and MDAPE = 18.8%).

CONCLUSION

The predictive performance of propofol TCI during RALP with CO₂ pneumoperitoneum in the HDP was acceptable.

External Validation of a Pharmacokinetic Model of Propofol for Target-Controlled Infusion in Children under Two Years Old

BACKGROUND

Previously, a linked pharmacokinetic-pharmacodynamic model (the Kim model) of propofol with concurrent infusion of remifentanil was developed for children aged 2-12 years. There are few options for pharmacokinetic-pharmacodynamic model of propofol for children under two years old. We performed an external validation of the Kim model for children under two years old to evaluate whether the model is applicable to this age group.

METHODS

Twenty-four children were enrolled. After routine anesthetic induction, a continuous infusion of 2% propofol and remifentanil was commenced using the Kim model. The target effect-site concentration of propofol was set as 2, 3, 4, and 5 μg/mL, followed by arterial blood sampling after 10 min of each equilibrium. Population estimates of four parameters-pooled bias, inaccuracy, divergence, and wobble-were used to evaluate the performance of the Kim model.

RESULTS

A total of 95 plasma concentrations were used for evaluation of the Kim model. The population estimate (95% confidence interval) of bias was -0.96% (-8.45%, 6.54%) and that of inaccuracy was 21.0% (15.0%-27.0%) for the plasma concentration of propofol.

CONCLUSION

The pooled bias and inaccuracy of the pharmacokinetic predictions are clinically acceptable. Therefore, our external validation of the Kim model indicated that the model can be applicable to target-controlled infusion of propofol in children younger than 2 years, with the recommended use of actual bispectral index monitoring in clinical settings that remifentanil is present.

TRIAL REGISTRATION

Clinical Research Information Service Identifier: KCT0001752.

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.

Measuring the accuracy of propofol target-controlled infusion (TCI) before and after surgery with major blood loss

Target-controlled infusion (TCI) is based on pharmacokinetic models designed to achieve a desired drug level in the blood. TCI's predictive accuracy of plasma propofol levels at the end of surgery with major blood loss has not been well established. This prospective observational study included adult patients (BMI 20-35 kg/m²) undergoing surgery with expected blood loss ≥ 1500 mL. The study was conducted with the Schnider TCI propofol model (Alaris PK Infusion Pump, CareFusion, Switzerland). Propofol levels were assessed in steady-state at the end of anaesthesia induction (T_initial) and before the end of surgery (T_final). Predicted propofol levels (C_TCI) were compared to measured levels (C_blood). Twenty-one patients were included. The median estimated blood loss was 1600 mL (IQR 1000-2300), and the median fluid balance at T_final was + 3200 mL (IQR 2320-4715). Heart rate, mean arterial blood pressure, and blood lactate did not differ significantly between T_initial and T_final. The median bispectral index (0-100) was 50 (IQR 42-54) and 49 (IQR 42-56) at the two respective time points. At T_initial, median C_TCI was 2.2 µmol/L (IQR 2-2.45) and C_blood was 2.0 µmol/L (bias 0.3 µmol/L, limits of agreement - 1.1 to 1.3, p = 0.33). C_TCI and C_blood at T_final were 2.0 µmol/L (IQR 1.6-2.2) and 1 µmol/L (IQR 0.8-1.4), respectively (bias 0.6 µmol/L, limits of agreement - 0.89 to 1.4, p < 0.0001). Propofol TCI allows clinically unproblematic conduct of general anaesthesia. In cases of major blood loss, the probability of propofol TCI overestimating plasma levels increases.Trial registration German Clinical Trials Register (DRKS; DRKS00009312).

Predictive performance of eleven pharmacokinetic models for propofol infusion in children for long-duration anaesthesia

Background

Predictive performance of eleven published propofol pharmacokinetic models was evaluated for long-duration propofol infusion in children.

Methods

Twenty-one aged three-11 yr ASA I-II patients were included. Anaesthesia was induced with propofol or sevoflurane, and maintained with propofol, remifentanil, and fentanyl. Propofol was continuously infused at rates of 4-14 mg kg  - 1 h - 1 after an initial bolus of 1.5-2.0 mg kg  - 1 . Venous blood samples were obtained every 30-60 min for five h and then every 60-120 min after five h from the start of propofol administration, and immediately after the end of propofol administration. Model performance was assessed with prediction error (PE) derivatives including divergence PE, median PE (MDPE), and median absolute PE (MDAPE) as time-related PE shift, measures for bias, and inaccuracy, respectively.

Results

We collected 85 samples over 270 (130) (88-545), mean (SD) (range), min. The Short model for children, and the Schüttler general-purpose model had acceptable performance (-20%≤MDPE ≤ 20%, MDAPE ≤ 30%, -4% h - 1  ≤   divergence PE ≤ 4% h - 1 ). The Short model showed the best performance with the maximum predictive performance metric. Two models developed only using bolus dosing (Shangguan and Saint-Maurice models) and the Paedfusor of the remaining nine models had significant negative divergence PE (≤-6.1% h - 1 ).

Conclusions

The Short model performed well during continuous infusion up to 545 min. This model might be preferable for target-controlled infusion for long-duration anaesthesia in children.

Clinical Pharmacokinetics and Pharmacodynamics of Propofol

Propofol is an intravenous hypnotic drug that is used for induction and maintenance of sedation and general anaesthesia. It exerts its effects through potentiation of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) at the GABAA receptor, and has gained widespread use due to its favourable drug effect profile. The main adverse effects are disturbances in cardiopulmonary physiology. Due to its narrow therapeutic margin, propofol should only be administered by practitioners trained and experienced in providing general anaesthesia. Many pharmacokinetic (PK) and pharmacodynamic (PD) models for propofol exist. Some are used to inform drug dosing guidelines, and some are also implemented in so-called target-controlled infusion devices, to calculate the infusion rates required for user-defined target plasma or effect-site concentrations. Most of the models were designed for use in a specific and well-defined patient category. However, models applicable in a more general population have recently been developed and published. The most recent example is the general purpose propofol model developed by Eleveld and colleagues. Retrospective predictive performance evaluations show that this model performs as well as, or even better than, PK models developed for specific populations, such as adults, children or the obese; however, prospective evaluation of the model is still required. Propofol undergoes extensive PK and PD interactions with both other hypnotic drugs and opioids. PD interactions are the most clinically significant, and, with other hypnotics, tend to be additive, whereas interactions with opioids tend to be highly synergistic. Response surface modelling provides a tool to gain understanding and explore these complex interactions. Visual displays illustrating the effect of these interactions in real time can aid clinicians in optimal drug dosing while minimizing adverse effects. In this review, we provide an overview of the PK and PD of propofol in order to refresh readers' knowledge of its clinical applications, while discussing the main avenues of research where significant recent advances have been made.

Population pharmacokinetics of intravenous acetaminophen in Japanese patients undergoing elective surgery

INTRODUCTION

Intravenous (i.v.) acetaminophen is administered during surgery for postoperative analgesia. However, little information is available on the pharmacokinetics of i.v. acetaminophen in Japanese patients undergoing surgery under general anesthesia.

METHODS

The study was approved by the Institutional Review Board and registered at UMIN-CTR (UMIN000013418). Patients scheduled to undergo elective surgery under general anesthesia were enrolled after obtaining written informed consent. During surgery, 1 g of i.v. acetaminophen was administered over 15, 60, or 120 min. Acetaminophen concentrations (15 or 16 samples per case) were measured at time points from 0-480 min after the start of administration (liquid chromatography-mass spectrometry/tandem mass spectrometry; limit of quantitation 0.1 μg/mL). The predictive performance of three published pharmacokinetic models was evaluated. Population pharmacokinetics were also analyzed using a nonlinear mixed-effect model based on the NONMEM program.

RESULTS

Data from 12 patients who underwent endoscopic or lower limb procedures were analyzed (male/female = 7/5, median age 55 years, weight 63 kg). Anesthesia was maintained with remifentanil and propofol or sevoflurane. The pharmacokinetic model of i.v. acetaminophen reported by Würthwein et al. worked well. Using 185 datapoints, the pharmacokinetics of i.v. acetaminophen were described by a two-compartment model with weight as a covariate but not age, sex, or creatinine clearance. The median prediction error and median absolute prediction error of the final model were -1 and 10%, respectively.

CONCLUSION

A population pharmacokinetic model of i.v. acetaminophen in Japanese patients was constructed, with performance within acceptable ranges.

Optimization of initial propofol bolus dose for EEG Narcotrend Index-guided transition from sevoflurane induction to intravenous anesthesia in children

BACKGROUND

Sevoflurane induction followed by intravenous anesthesia is a widely used technique to combine the benefits of an easier and less traumatic venipuncture after sevoflurane inhalation with a recovery with less agitation, nausea, and vomiting after total intravenous anesthesia (TIVA). Combination of two different anesthetics may lead to unwanted burst suppression in the electroencephalogram (EEG) during the transition phase.

OBJECTIVE

The objective of this prospective clinical observational study was to identify the optimal initial propofol bolus dose for a smooth transition from sevoflurane induction to TIVA using the EEG Narcotrend Index (NI).

METHODS

Fifty children aged 1-8 years scheduled for elective pediatric surgery were studied. After sevoflurane induction and establishing of an intravenous access, a propofol bolus dose range 0-5 mg·kg^-1 was administered at the attending anesthetist's discretion to maintain a NI between 20 and 64, and sevoflurane was stopped. Anesthesia was continued as TIVA with a propofol infusion dose of 15 mg·kg^-1 ·h^-1 for the first 15 min, followed by stepwise reduction according to McFarlan's pediatric infusion regime, and remifentanil 0.25 μg·kg^-1 ·min^-1 . Endtidal concentration of sevoflurane, NI, and hemodynamic data were recorded during the whole study period using a standardized case report form. Propofol plasma concentrations were calculated using the paedfusor dataset and a TIVA simulation program.

RESULTS

Median endtidal concentration of sevoflurane at the time of administration of the propofol bolus was 5.1 [IQR 4.7-5.9] Vol%. The median propofol bolus dose was 1.2 [IQR 0.9-2.5] mg·kg^-1 and median NI thereafter was 33 [IQR 23-40]. Nine children presented with a NI 13-20 and three children with burst suppression in the EEG (NI 0-12); all of them received an initial propofol bolus dose >2 mg·kg^-1 . Regression equation demonstrated that NI 20-64 was achieved with a 95% probability when using a propofol bolus dose of 1 mg·kg^-1 after sevoflurane induction. Decrease in mean arterial blood pressure correlated significantly with propofol bolus dose (P = 0.038). After 25 min of TIVA, children younger than 2 years had a higher NI (median difference 14.0, 95%CI: 6.0-20.0, P = 0.001), higher deviations from the expected Narcotend Index (median difference 4.1, 95%CI: 3.9-4.2, P < 0.001) and lower calculated propofol plasma concentrations (median difference 0.2 μg·ml^-1 , 95% CI: 0.1-0.3 μg·ml^-1 , P < 0.001) than older children.

CONCLUSION

After sevoflurane induction, a reduced propofol bolus dose of 1 mg·kg^-1 followed by TIVA according to McFarlan's regime resulted in a NI within the recommended range in children aged 1-8 years. During the course of TIVA, children younger than 2 years displayed higher NI values and more pronounced interindividual variation. Processed EEG monitoring is recommended to find adequate individual age-dependent doses.

Bispectral index under propofol anesthesia in children: a comparative randomized study between TIVA and TCI

BACKGROUND

In children, only a few studies have compared different modes of propofol infusion during a total intravenous anesthesia (TIVA) with propofol and remifentanil. The aim of this study was to compare Bispectral Index (BIS) profiles (percentage of time spent at adequate BIS values) between four modes of propofol infusion: titration of the infusion rate on clinical signs (TIVA0 ), titration of the infusion rate on the BIS (TIVABIS ), target controlled infusion (TCI) guided by the BIS either with the Kataria model (TCI KBIS ) or the Schnider model (TCI SBIS ).

METHODS

Sixty-six children (aged from 4 to 14 years) were prospectively randomized into one of the four groups. In the TIVA0 group, the anesthesiologist was blinded to the BIS. In each group, the percentage of time with adequate BIS values (45-55), the bias, and imprecision were calculated.

RESULTS

The propofol consumption was similar in the four groups. During the maintenance phase, the percentage of time spent in the targeted BIS range was significantly lower in the TIVA0 group compared to the three other groups (TIVA0 : 31% ± 22, TIVABIS : 59% ± 17, TCI KBIS : 53% ± 12, TCI SBIS : 56% ± 17). The bias was not statistically different between the four groups, but the imprecision was larger for the TIVA0 group. Compared to the Kataria model, the Schnider model was associated with shorter time delay to reach the desired BIS, to eyes opening, and to tracheal extubation.

CONCLUSIONS

Propofol administration using manual infusion guided by clinical signs was associated with higher risks of over- or underdosage when compared to BIS-guided administrations. When propofol infusion was guided by the BIS, no major difference was found between TIVA and TCI (either with the Kataria or the Schnider model). This study highlights the need of a pharmacodynamic feedback during propofol anesthesia in children.

Auditory functional magnetic resonance in awake (nonsedated) and propofol-sedated children

BACKGROUND

Functional Magnetic Resonance Imaging (fMRI) is often used in preoperative assessment before epilepsy surgery, tumor or cavernous malformation resection, or cochlear implantation. As it requires complete immobility, sedation is needed for uncooperative patients.

OBJECTIVE

The aim of this study was to compare the fMRI cortical activation pattern after auditory stimuli in propofol-sedated 5- to 8-year-old children with that of similarly aged nonsedated children.

METHODS

When possible, children underwent MRI without sedation, otherwise it was induced with i.v. propofol 2 mg·kg(-1) and maintained with i.v. propofol 4-5 mg·kg(-1) ·h(-1) . Following diagnostic MRI, fMRi was carried out, randomly alternating two passive listening tasks (a fairy-tale and nonsense syllables).

RESULTS

We studied 14 awake and 15 sedated children. During the fairy-tale task, the nonsedated children's blood-oxygen-level-dependent (BOLD) signal was bilaterally present in the posterior superior temporal gyrus (STG), Wernicke's area, and Broca's area. Sedated children showed similar activation, with lesser extension to Wernicke's area, and no activation in Broca's area. During the syllable task, the nonsedated children's BOLD signal was bilaterally observed in the STG and Wernicke's area, in Broca's area with leftward asymmetry, and in the premotor area. In sedated children, cortical activation was present in the STG, but not in the frontal lobes. BOLD signal change areas in sedated children were less extended than in nonsedated children during both the fairy-tale and syllable tasks. Modeling the temporal derivative during both the fairy-tale and syllable tasks, nonsedated children showed no response while sedated children did.

CONCLUSIONS

After auditory stimuli, propofol-sedated 5- to 8-year-old children exhibit an fMRI cortical activation pattern which is different from that in similarly aged nonsedated children.

The administration of high-dose propofol sedation with manual and target-controlled infusion in children undergoing radiation therapy: a 7-year clinical investigation

Background

Radiation therapy requires the patient to remain immobile for a long time, which is challenging in children. This study therefore aimed to determine the adequate target concentration and dosage of propofol in target-controlled infusion (TCI) and manual infusion (MI) in children requiring sedation for proton radiation therapy. Our hypothesis is that the adequate dose of propofol sedation required for proton radiation therapy in pediatric patients was larger than that seen in previous studies.

Methods

We retrospectively analyzed the medical records of Korean children who received proton therapy under propofol sedation. The average target concentration at induction and during maintenance with TCI and the dose with MI were analyzed as primary outcomes.

Results

A total of 1296 procedures in 54 children were analyzed (TCI group, 26; MI group, 28). The median bolus dose of propofol in the MI group was 2.6 (2.2–3.0) mg/kg, while the pump speed was 17.0 (13.6–25.8) mg/kg/h. The median target concentration of propofol in the TCI group was 5.3 (4.4–5.7) mcg/mL at induction and 4.2 (3.1–5.1) mcg/mL during maintenance. There were no cases of life-threatening complications in either group over 7 years. There were six cases of transient desaturation, which were managed by using the jaw thrust maneuver.

Conclusions

Compared with those in previous studies, the target concentration of propofol with TCI and the propofol dose with MI required for adequate sedation in children undergoing proton radiation therapy were larger in the present study. Despite concerns regarding overdosage, the complications were managed well. However, safe and adequate sedation for proton radiation therapy remains a challenge. The development of monitoring tools to evaluate the depth of sedation is necessary to adjust the propofol dose and sedation level.

Propofol concentration to induce general anesthesia in children aged 3-11 years with the Kataria effect-site model

BACKGROUND

The propofol pharmacokinetic model derived by Kataria et al. was recently modified to perform effect-site target-controlled infusion (TCI). Effect-site concentration (Ce) targets to induce general anesthesia with this model in children have not been described. The aim of this study was to identify propofol Ce targets associated with success rates of 50% (Ce50) and 95% (Ce95) among children 3-11 years of age.

METHODS

Forty-two children were assigned to one of seven groups of six patients each according to propofol target Ce. After fentanyl administration propofol TCI was started with an assigned Ce target. A successful response was defined as loss of eyelash reflex and bispectral index < 50, 45 s after reaching the assigned Ce. Logistic regression analysis was performed to calculate propofol Ce50 and Ce95.

RESULTS

Twenty-eight children had a successful response with the assigned propofol Ce. In these patients, a significant decrease in mean arterial blood pressure (79-59, P < 0.0001) and in heart rate (95-83, P < 0.0001) was observed. Propofol Ce and age showed a statistically significant effect in the logistic regression model. The overall calculated propofol Ce50 and Ce95 were 3.8 μg·ml(-1) (95% CI: 3.1-4.4 μg·ml(-1) ) and 6.1 μg·ml(-1) (95% CI: 4.6-7.6 μg·ml(-1) ), respectively.

CONCLUSION

Our results identified useful propofol targets to be used with the Kataria effect-site model to induce anesthesia in children between 3 and 11 years. The recommended targets should be reduced progressively with increasing age most probably due to PK model misspecifications.

Target-controlled infusion and population pharmacokinetics of landiolol hydrochloride in patients with peripheral arterial disease

PURPOSE

We previously determined the pharmacokinetic (PK) parameters of landiolol in healthy male volunteers and gynecological patients. In this study, we determined the PK parameters of landiolol in patients with peripheral arterial disease.

METHODS

Eight patients scheduled to undergo peripheral arterial surgery were enrolled in the study. After inducing anesthesia, landiolol hydrochloride was administered at target plasma concentrations of 500 and 1,000 ng/mL for 30 minutes each. A total of 112 data points of plasma concentration were collected from the patients and used for the population PK analysis. A population PK model was developed using a nonlinear mixed-effect modeling software program (NONMEM).

RESULTS

The patients had markedly decreased heart rates at 2 minutes after initiation of landiolol hydrochloride administration; however, systolic blood pressures were lower than the baseline values at only five time points. The concentration time course of landiolol was best described by a two-compartment model with lag time. The estimates of PK parameters were as follows: total body clearance, 30.7 mL/min/kg; distribution volume of the central compartment, 65.0 mL/kg; intercompartmental clearance, 48.3 mL/min/kg; distribution volume of the peripheral compartment, 54.4 mL/kg; and lag time, 0.633 minutes. The predictive performance of this model was better than that of the previous model.

CONCLUSION

The PK parameters of landiolol were best described by a two-compartment model with lag time. Distribution volume of the central compartment and total body clearance of landiolol in patients with peripheral arterial disease were approximately 64% and 84% of those in healthy volunteers, respectively.

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.

A general purpose pharmacokinetic model for propofol

BACKGROUND

Pharmacokinetic (PK) models are used to predict drug concentrations for infusion regimens for intraoperative displays and to calculate infusion rates in target-controlled infusion systems. For propofol, the PK models available in the literature were mostly developed from particular patient groups or anesthetic techniques, and there is uncertainty of the accuracy of the models under differing patient and clinical conditions. Our goal was to determine a PK model with robust predictive performance for a wide range of patient groups and clinical conditions.

METHODS

We aggregated and analyzed 21 previously published propofol datasets containing data from young children, children, adults, elderly, and obese individuals. A 3-compartmental allometric model was estimated with NONMEM software using weight, age, sex, and patient status as covariates. A predictive performance metric focused on intraoperative conditions was devised and used along with the Akaike information criteria to guide model development.

RESULTS

The dataset contains 10,927 drug concentration observations from 660 individuals (age range 0.25-88 years; weight range 5.2-160 kg). The final model uses weight, age, sex, and patient versus healthy volunteer as covariates. Parameter estimates for a 35-year, 70-kg male patient were: 9.77, 29.0, 134 L, 1.53, 1.42, and 0.608 L/min for V1, V2, V3, CL, Q2, and Q3, respectively. Predictive performance is better than or similar to that of specialized models, even for the subpopulations on which those models were derived.

CONCLUSIONS

We have developed a single propofol PK model that performed well for a wide range of patient groups and clinical conditions. Further prospective evaluation of the model is needed.

Evaluation of the aepEX™ monitor of hypnotic depth in pediatric patients receiving propofol-remifentanil anesthesia

BACKGROUND

The aepEX Plus monitor (aepEX) utilizes a mid-latency auditory evoked potential-derived index of depth of hypnosis (DoH).

OBJECTIVE

This observational study evaluates the performance of the aepEX as a DoH monitor for pediatric patients receiving propofol-remifentanil anesthesia.

METHODS

aepEX and BIS values were recorded simultaneously during surgery in three groups of 25 children (aged 1-3, 3-6 and 6-16 years). Propofol was administered by target-controlled infusion. The University of Michigan Sedation Scale (UMSS) was used to clinically assess the DoH during emergence. Prediction probability (P(k)) and receiver operating characteristics (ROC) analyses were performed to assess the accuracy of both DoH monitors. Nonlinear regression analysis was used to describe the dose-response relationships for the aepEX, the BIS, and propofol plasma concentrations (Cp).

RESULTS

The P(k) for the aepEX and BIS was 0.36 and 0.21, respectively (P = 0.010). ROC analysis showed an area under the curve of 0.77 and 0.88 for the aepEX and BIS, respectively (P = 0.644). At half-maximal effect (EC(50)), C(p) of 3.13 μg·ml(-1) and 3.06 μg·ml(-1) were observed for the aepEX and BIS, respectively. The r(2) for the aepEX and BIS was 0.53 and 0.82, respectively.

CONCLUSION

The aepEX performs comparable to the BIS in differentiating between consciousness and unconsciousness, while performing inferior to the BIS in terms of distinguishing different levels of sedation and does not correlate well with the C(p) in children receiving propofol-remifentanil anesthesia.

[Total intravenous anaesthesia in geriatrics: the example of propofol]

The aim of this review is to analyse the changes in the pharmacology of the elderly patient using, as examples, the existing pharmacokinetics and pharmacodynamics models of propofol and data provided in the literature.

Is indirect hyperbilirubinemia a useful biomarker of reduced propofol clearance in neonates?

AIM

Large interindividual variability in neonatal propofol clearance is documented which, in part, can be explained by postmenstrual age (PMA) and postnatal age (PNA). We aimed to document whether indirect bilirubin, instead of or in addition to PNA, could improve predictability of propofol clearance and serve as a useful biomarker of reduced propofol clearance in neonates.

METHODS

Indirect serum bilirubin was introduced as a dichotomous or continuous variable (both age-normalized) in a previously developed three-compartment pharmacokinetic model, based on 235 concentration-time points obtained in 25 neonates after single bolus administration of propofol. For pharmacokinetic analysis, nonlinear mixed effect modeling 6.2 was used.

RESULTS

The covariates PMA and PNA explained 67% of the interindividual variability compared with 45% in the model with PMA and bilirubin.

CONCLUSION

Age, reflected by PMA and PNA, is a more relevant clinical predictor of neonatal propofol clearance compared with PMA and raised indirect hyperbilirubinemia.

My child is unique; the pharmacokinetics are universal

The pharmacokinetic (PK) parameters that are important for dosing (e.g., clearance and volume) are well known. They are used in universal mathematical formulae that describe the time course of drug concentration. Additional formulae can be used to describe major covariate effects in children, such as size and maturation. PK parameters describing the time-concentration profile of a drug after administration are those for a typical individual in a population. These parameters are associated with variability. Further, any one individual may not be typical of the population studied. While size and maturation are two important considerations in children and assist with dosing estimation, there are also a number of additional PK covariates (e.g., organ function, disease, drug interactions, pharmacogenetics), and identifying these sources of variability allows us to individualize drug dose. Pharmacology is not simply an application of PK, and determinants of drug dose also require an understanding of the variability associated with pharmacodynamic response and a balancing of beneficial effects against unwanted effects. Each child is unique in this respect.