External validation of the modified Marsh and Schnider models for medium-chain triglyceride propofol in target-controlled infusion anesthesia.

BACKGROUND: Propofol formulated with medium- and long-chain triglycerides (MCT/LCT propofol) has rapidly replaced propofol formulated with long-chain triglycerides (LCT propofol). Despite this shift, the modified Marsh and Schnider pharmacokinetic models developed using LCT propofol are still widely used for target-controlled infusion (TCI) of propofol. This study aimed to validate the external applicability of these models by evaluating their predictive performance during TCI of MCT/LCT propofol in general anesthesia. METHODS: Adult patients (n = 48) undergoing elective surgery received MCT/LCT propofol via a TCI system using either the modified Marsh or Schnider models. Blood samples were collected at various target propofol concentrations and at specific time points, including the loss of consciousness and the recovery of consciousness (13 samples per patient). The actual plasma concentration of propofol was determined using high-performance liquid chromatography. The predictive performance of each pharmacokinetic model was assessed by calculating four parameters: inaccuracy, bias, divergence, and wobble. RESULTS: Both the modified Marsh and Schnider models demonstrated predictive performances within clinically acceptable ranges for MCT/LCT propofol. The inaccuracy values were 24.4% for the modified Marsh model and 26.9% for the Schnider model. Both models showed an overall positive bias, 16.4% for the modified Marsh model and 16.6% for the Schnider model. The predictive performance of MCT/LCT propofol was comparable to that of LCT propofol, suggesting formulation changes might exert only a minor impact on the reliability of the TCI system during general anesthesia. Additionally, both models exhibited higher bias and inaccuracy at target concentrations ranging from 3.5 ~ 5 ug/ml than at concentrations between 2 ~ 3 ug/ml. CONCLUSIONS: The modified Marsh and Schnider models, initially developed for LCT propofol, remain clinically acceptable for TCI with MCT/LCT propofol. TRIAL REGISTRATION: This study was registered at the Clinical Research Information Service of the Korean National Institute of Health ( https://cris.nih.go.kr ; registration number: KCT0002191; 06/01/2017).

Population pharmacokinetic and pharmacodynamic model of propofol externally validated in Korean elderly subjects.

The Eleveld propofol pharmacokinetic (PK) model, which was developed based on a broad range of populations, showed greater bias (- 27%) in elderly subjects in a previous validation study conducted by Vellinga and colleagues. We aimed to develop and externally validate a new PK-pharmacodynamic (PK-PD) model of propofol for elderly subjects. A population PK-PD model was constructed using propofol plasma concentrations and bispectral index (BIS) values that were obtained from 31 subjects aged 65 years older in previously published phase I studies. The predictive performance of the newly-developed PK-PD model (Choi model) was assessed in a separate Korean elderly population and compared with that of the Eleveld model. A three-compartment mammillary model using an allometric expression and a sigmoid Emax model well-described the time courses of propofol concentrations and BIS values. The V1, V2, V3, Cl, Q1, Q2, E0, Emax, Ce50, γ, and ke0 of a 60-kg subject were 8.36, 58.0, 650 L, 1.26, 0.917, 0.669 L/min, 92.1, 18.7, 2.21 µg/mL, 2.89, and 0.138 /min, respectively. In the Choi model and Eleveld model, pooled biases (95% CI) of the propofol concentration were 7.78 ( 3.09-12.49) and 16.70 (9.46-23.93) and pooled inaccuracies were 22.84 (18.87-26.81) and 24.85 (18.07-31.63), respectively. The Choi PK model was less biased than the Eleveld PK model in Korean elderly subjects (age range: 65.0-79.0 yr; weight range: 45.0-75.3 kg). Our results suggest that the Choi PK model, particularly, is applicable to target-controlled infusion in non-obese Korean elderly subjects.

Nongenetic and genetic predictors of haemodynamic instability induced by propofol and opioids: A retrospective clinical study.

AIM: Propofol and opioids are commonly used in anaesthesia, but are highly susceptible to haemodynamic instability, thereby threatening the patient's surgical safety and prognosis. The purpose of this study was to investigate the predictors of haemodynamic instability and establish its predictive model. METHODS: A total of 150 Chinese patients undergoing thyroid or breast surgery participated in the study, with target-controlled infusion concentrations of propofol, opioids dosage, heart rate (HR), mean arterial pressure (MAP) and Narcotrend Index recorded at key points throughout the procedure. The Agena MassARRAY system was used to genotype candidate single nucleotide polymorphisms related to pharmacodynamics and pharmacokinetics of propofol and opioids. RESULTS: Among nongenetic factors, baseline HR (R = -.579, P < .001) and baseline MAP (R = -.725, P < .001) had a significant effect on the haemodynamic instability. Among genetic factors, the CT/CC genotype of GABRB1 rs4694846 (95% confidence interval [CI]: -11.309 to -3.155), AA/AG of OPRM1 rs1799971 (95%CI: 0.773 to 10.290), AA of CES2 rs8192925 (95%CI: 1.842 to 9.090) were associated with higher HR instability; the AA/GG genotype of NR1I2 rs6438550 (95%CI: 0.351 to 7.761), AA of BDNF rs2049046 (95%CI: -9.039 to -0.640) and GG of GABBR2 rs1167768 (95%CI: -10.146 to -1.740) were associated with higher MAP instability. The predictive models of HR and MAP fluctuations were developed, accounting for 45.0 and 59.2% of variations, respectively. CONCLUSION: We found that cardiovascular fundamentals and genetic variants of GABRB1, GABBR2, OPRM1, BDNF, CES2 and NR1I2 are associated with cardiovascular susceptibility, which can provide a reference for haemodynamic management in clinical anaesthesia.

Clinical Validation of the Covariates Pharmacokinetic Model for Propofol in an Adult Population.

BACKGROUND AND OBJECTIVE: Pharmacokinetic or pharmacokinetic-pharmacodynamic models have been instrumental in facilitating the clinical use of propofol in target-controlled infusion systems in anaesthetic practice. There has been debate over which model should be recommended for practice. The covariates model is an updated pharmacokinetic model for propofol. The aim of this study was to prospectively validate this model in an adult population. METHODS: Twenty-nine patients were included, with a range of ages to assess model performance in younger and older individuals. Subjects received propofol through a target-controlled infusion device programmed with the covariates model. Subjects were randomised to one of two increasing/decreasing regimes of propofol plasma target concentrations between 2 and 5 µg.mL-1. After the start of the infusion, arterial and venous blood samples were drawn at pre-specified timepoints between 1.5 and 20 min and between 1.5 and 45 min, respectively. Predictive performance was assessed using established methodology. RESULTS: The model achieved a bias of 9 (- 45 to 82) and precision of 24 (9-82) for arterial samples and bias of - 8 (- 64 to 70) and precision of 23 (9-70) for venous samples. Predicted concentrations tended to be higher than the measured concentrations in female individuals but lower in male individuals. There was no clear systematic difference in the bias between younger and older patients. CONCLUSIONS: The covariates propofol pharmacokinetic model achieved an acceptable level of predictive performance, as assessed by both arterial and venous sampling, for use in target-controlled infusion in clinical practice. CLINICAL TRIAL REGISTRATION: NCT01492712 (15 December, 2011).

Pharmacokinetic models can estimate the changes in the concentration of a drug in the body over time. These have been instrumental in facilitating the clinical use of anaesthetic agents such as propofol in target-controlled infusions, which aim to achieve a set concentration in either plasma or the brain to achieve anaesthesia. The covariates model is a previously described pharmacokinetic model for propofol. The aim of the described study was to validate the performance of the model in an independent adult population. Participants received anaesthesia with propofol through a target-controlled infusion device programmed with the covariates model. The concentration of propofol in the blood was measured at various timepoints and compared to the target concentration specified by the target-controlled infusion device. The analysis showed that overall, the covariates model performed to a level acceptable for use in clinical practice and compared favourably to other pharmacokinetic models.

Anestesia total intravenosa libre de opioides guiada por qCON y qNOX en paciente obesa / Total Intravenous anesthesia in patients with intestinal occlusive syndrome

Introducción: En los últimos años la anestesia libre de opioides ha constituido una alternativa más a las técnicas tradicionales de anestesia general. Con la exclusión de este grupo de fármacos se evitan los múltiples efectos adversos y complicaciones asociados al mismo. A pesar de que la anestesia libre de opioides tiene sus indicaciones y que ha demostrado sus beneficios en cierto grupo de pacientes, existen aún controversias en relación con su utilidad en el paciente obeso. Características como la obesidad hacen que los modelos multimodales empleados para programar la anestesia libre de opioides sean cada vez más complejos. Objetivos: Describir un caso clínico realizado con la técnica de anestesia libre de opioides que constituye la primera experiencia en Ecuador. Presentación del caso: Se presenta el caso de una paciente obesa intervenida de colecistectomía laparoscópica mediante infusión de propofol, ketamina, lidocaína, sulfato de magnesio, y dexmedetomidina. La titulación de estos fármacos se realizó mediante cálculo de concentraciones plasmáticas a través de modelos farmacocinéticos y guiada por monitorización de profundidad anestésica y analgésica, con lo cual se logró optimizar el consumo de fármacos, disminuir las complicaciones y una evolución clínica favorable. Hasta donde se conoce a nivel local y de país (Ecuador) es la primera experiencia que se reporta con esta técnica. Conclusiones: La anestesia libre de opioides puede resultar una elección en el paciente obeso ya que asegura una adecuada recuperación sin efectos adversos asociados(AU)

Introduction: In recent years, opioid-free anesthesia has become another alternative in front of traditional general anesthesia techniques. The exclusion of this group of drugs avoids the numerous adverse effects and complications associated with its usage. Although opioid-free anesthesia has its indications and has showed its benefits in a certain group of patients, there is still controversy regarding its usefulness in the obese patient. Characteristics such as obesity make the multimodal models used to program opioid-free anesthesia increasingly complex. Objectives: To describe a clinical case involving the opioid-free anesthesia technique, which is the first experience in Ecuador. Case presentation: The case is presented of a female obese patient who underwent laparoscopic cholecystectomy by infusion of propofol, ketamine, lidocaine, magnesium sulfate and dexmedetomidine. Titration of these drugs was carried out by calculating plasma concentrations through pharmacokinetic models and guided by monitoring of anesthetic and analgesic depth, thus optimizing drug consumption, reducing complications and achieving a favorable clinical evolution. As far as known locally and in the country (Ecuador), this is the first reported experience with this technique. Conclusions: Opioid-free anesthesia may be a choice in the obese patient, since it ensures adequate recovery without associated adverse effects(AU)

Mechanism-based pharmacodynamic model for propofol haemodynamic effects in healthy volunteers☆.

BACKGROUND: The adverse haemodynamic effects of the intravenous anaesthetic propofol are well known, yet few empirical models have explored the dose-response relationship. Evidence suggests that hypotension during general anaesthesia is associated with postoperative mortality. We developed a mechanism-based model that quantitatively characterises the magnitude of propofol-induced haemodynamic effects during general anaesthesia. METHODS: Mean arterial pressure (MAP), heart rate (HR) and pulse pressure (PP) measurements were available from 36 healthy volunteers who received propofol in a step-up and step-down fashion by target-controlled infusion using the Schnider pharmacokinetic model. A mechanistic pharmacodynamic model was explored based on the Snelder model. To benchmark the performance of this model, we developed empirical models for MAP, HR, and PP. RESULTS: The mechanistic model consisted of three turnover equations representing total peripheral resistance (TPR), stroke volume (SV), and HR. Propofol-induced changes were implemented by Emax models on the zero-order production rates of the turnover equations for TPR and SV. The estimated 50% effective concentrations for propofol-induced changes in TPR and SV were 2.96 and 0.34 µg ml-1, respectively. The goodness-of-fit for the mechanism-based model was indistinguishable from the empirical models. Simulations showed that predictions from the mechanism-based model were similar to previously published MAP and HR observations. CONCLUSIONS: We developed a mechanism-based pharmacodynamic model for propofol-induced changes in MAP, TPR, SV, and HR as a potential approach for predicting haemodynamic alterations. CLINICAL TRIAL REGISTRATION: NCT02043938.

Pharmacokinetics, bioavailability, and bioequivalence of lower-sodium oxybate in healthy participants in two open-label, randomized, crossover studies.

American Academy of Sleep Medicine practice parameters designate sodium oxybate (SXB) as a standard of care for cataplexy, excessive daytime sleepiness (EDS), and disrupted night-time sleep in narcolepsy. Recently, a lower-sodium oxybate (LXB) with 92% less sodium than SXB was approved in the United States for the treatment of cataplexy or EDS in patients 7 years of age and older with narcolepsy. Two phase I, open-label, randomized, single-dose crossover pharmacokinetic studies in healthy adults were conducted. Single 4.5-g oral doses of LXB and SXB were administered in a fasted or fed state. In the fasted state at equivalent oxybate doses, LXB, compared with SXB, had a lower maximum plasma concentration (Cmax ; study 1 [total aqueous volume, 240 ml]: 101.8 vs. 135.7 µg/ml; study 2 [60 ml]: 94.6 vs. 123.0 µg/ml), delayed time to Cmax (Tmax ; study 1: 0.75 vs. 0.5 h; study 2: 1.0 vs. 0.5 h), but similar area under the curve (AUC; study 1: AUC0-t , 235.4 vs. 263.9 µg∙h/ml; AUC0-∞ , 236.5 vs. 265.2 µg∙h/ml; study 2: AUC0-t , 241.5 vs. 254.7 µg∙h/ml; AUC0-∞ , 243.1 vs. 256.3 µg∙h/ml). Bioequivalence criteria were met for AUC but not Cmax (both studies). Cmax and AUC were lower under fed than fasted conditions (LXB and SXB); differences between fed versus fasted were smaller for LXB than SXB. These pharmacokinetic differences between LXB and SXB are likely due to the lower sodium content in LXB. Pooled analyses demonstrated that a higher Cmax is associated with a higher incidence of nausea and vomiting.

Correlation of exhaled propofol with Narcotrend index and calculated propofol plasma levels in children undergoing surgery under total intravenous anesthesia - an observational study.

BACKGROUND: Exhaled propofol concentrations correlate with propofol concentrations in adult human blood and the brain tissue of rats, as well as with electroencephalography (EEG) based indices of anesthetic depth. The pharmacokinetics of propofol are however different in children compared to adults. The value of exhaled propofol measurements in pediatric anesthesia has not yet been investigated. Breathing system filters and breathing circuits can also interfere with the measurements. In this study, we investigated correlations between exhaled propofol (exP) concentrations and the Narkotrend Index (NI) as well as calculated propofol plasma concentrations. METHODS: A multi-capillary-column (MCC) combined with ion mobility spectrometry (IMS) was used to determine exP. Optimal positioning of breathing system filters (near-patient or patient-distant) and sample line (proximal or distal to filter) were investigated. Measurements were taken during induction (I), maintenance (M) and emergence (E) of children under total intravenous anesthesia (TIVA). Correlations between ExP concentrations and NI and predicted plasma propofol concentrations (using pediatric pharmacokinetic models Kataria and Paedfusor) were assessed using Pearson correlation and regression analysis. RESULTS: Near-patient positioning of breathing system filters led to continuously rising exP values when exP was measured proximal to the filters, and lower concentrations when exP was measured distal to the filters. The breathing system filters were therefore subsequently attached between the breathing system tubes and the inspiratory and expiratory limbs of the anesthetic machine. ExP concentrations significantly correlated with NI and propofol concentrations predicted by pharmacokinetic models during induction and maintenance of anesthesia. During emergence, exP significantly correlated with predicted propofol concentrations, but not with NI. CONCLUSION: In this study, we demonstrated that exP correlates with calculated propofol concentrations and NI during induction and maintenance in pediatric patients. However, the correlations are highly variable and there are substantial obstacles: Without patient proximal placement of filters, the breathing circuit tubing must be changed after each patient, and furthermore, during ventilation, a considerable additional loss of heat and moisture can occur. Adhesion of propofol to plastic parts (endotracheal tube, breathing circle) may especially be problematic during emergence. TRIAL REGISTRATION: The study was registered in the German registry of clinical studies (DRKS-ID:  DRKS00015795 ).

Optimization, and in vitro and in vivo evaluation of etomidate intravenous lipid emulsion.

The aim of this investigation was to develop an etomidate intravenous lipid emulsion (ETM-ILE) and evaluate its properties in vitro and in vivo. Etomidate (ETM) is a hydrophobic drug, and organic solvents must be added to an etomidate injectable solution (ETM-SOL) to aid dissolution, that causes various adverse reactions on injection. Lipid emulsions are a novel drug formulation that can improve drug loading and reduce adverse reactions. ETM-ILE was prepared using high-pressure homogenization. Univariate experiments were performed to select key conditions and variables. The proportion of oil, egg lecithin, and poloxamer 188 (F68) served as variables for the optimization of the ETM-ILE formulation by central composite design response surface methodology. The optimized formulation had the following characteristics: particle size, 168.0 ± 0.3 nm; polydispersity index, 0.108 ± 0.028; zeta potential, -36.4 ± 0.2 mV; drug loading, 2.00 ± 0.01 mg/mL; encapsulation efficiency, 97.65% ± 0.16%; osmotic pressure, 292 ± 2 mOsmol/kg and pH value, 7.63 ± 0.07. Transmission electron microscopy images showed that the particles were spherical or spheroidal, with a diameter of approximately 200 nm. The stability study suggested that ETM-ILE could store at 4 ± 2 °C or 25 ± 2 °C for 12 months. Safety tests showed that ETM-ILE did not cause hemolysis or serious vascular irritation. The results of the pharmacokinetic study found that ETM-ILE was bioequivalent to ETM-SOL. However, a higher concentration of ETM was attained in the liver, spleen, and lungs after administration of ETM-ILE than after administration of ETM-SOL. This study found that ETM-ILE had great potential for clinical applications.

Asymmetric neural dynamics characterize loss and recovery of consciousness.

Anesthetics are known to disrupt neural interactions in cortical and subcortical brain circuits. While the effect of anesthetic drugs on consciousness is reversible, the neural mechanism mediating induction and recovery may be different. Insight into these distinct mechanisms can be gained from a systematic comparison of neural dynamics during slow induction of and emergence from anesthesia. To this end, we used functional magnetic resonance imaging (fMRI) data obtained in healthy volunteers before, during, and after the administration of propofol at incrementally adjusted target concentrations. We analyzed functional connectivity of corticocortical and subcorticocortical networks and the temporal autocorrelation of fMRI signal as an index of neural processing timescales. We found that en route to unconsciousness, temporal autocorrelation across the entire brain gradually increased, whereas functional connectivity gradually decreased. In contrast, regaining consciousness was associated with an abrupt restoration of cortical but not subcortical temporal autocorrelation and an abrupt boost of subcorticocortical functional connectivity. Pharmacokinetic effects could not account for the difference in neural dynamics between induction and emergence. We conclude that the induction and recovery phases of anesthesia follow asymmetric neural dynamics. A rapid increase in the speed of cortical neural processing and subcorticocortical neural interactions may be a mechanism that reboots consciousness.

Arginase II polymorphisms modify the hypotensive responses to propofol by affecting nitric oxide bioavailability.

PURPOSE: Propofol anesthesia is usually accompanied by hypotensive responses, which are at least in part mediated by nitric oxide (NO). Arginase I (ARG1) and arginase II (ARG2) compete with NO synthases for their common substrate L-arginine, therefore influencing the NO formation. We examined here whether ARG1 and ARG2 genotypes and haplotypes affect the changes in blood pressure and NO bioavailability in response to propofol. METHODS: Venous blood samples were collected from 167 patients at baseline and after 10 min of anesthesia with propofol. Genotypes were determined by polymerase chain reaction. Nitrite concentrations were measured by using an ozone-based chemiluminescence assay, while NOx (nitrites + nitrates) levels were determined by using the Griess reaction. RESULTS: We found that patients carrying the AG + GG genotypes for the rs3742879 polymorphism in ARG2 gene and the ARG2 GC haplotype show lower increases in nitrite levels and lower decreases in blood pressure after propofol anesthesia. On the other hand, subjects carrying the variant genotypes for the rs10483801 polymorphism in ARG2 gene show more intense decreases in blood pressure (CA genotype) and/or higher increases in nitrite levels (CA and AA genotypes) in response to propofol. CONCLUSION: Our results suggest that ARG2 variants affect the hypotensive responses to propofol, possibly by modifying NO bioavailability. TRIAL REGISTRATION: NCT02442232.

Do epoch lengths of hypnotic depth indicators affect estimated of blood-brain equilibration rate constants of propofol?

This study aimed to investigate the effect of epoch length of hypnotic depth indicators on the blood-brain equilibration rate constant (ke0) estimates of propofol. Propofol was administered by zero-order infusion (1.5, 3.0, 6, and 12 mg·kg-1·h-1) for one hour in 63 healthy volunteers. The ke0 of propofol was estimated using an effect-compartment model linking pharmacokinetics and pharmacodynamics, in which response variables were electroencephalographic approximate entropy (ApEn) or bispectral index (BIS) (n = 32 each for propofol infusion rates of 6 and 12 mg·kg-1·h-1). Epoch lengths of ApEn were 2, 10, 30, and 60 seconds (s). The correlations between plasma propofol concentrations (Cp) and BIS and ApEn 2, 10, 30, and 60 s were determined, as was the Ce associated with 50% probability of unconsciousness (Ce50,LOC). The pharmacokinetics of propofol were well described by a three-compartment model. The correlation coefficient between Cp and ApEn 2, 10, 30, and 60 s were -0.64, -0.54, -0.39, and -0.26, respectively, whereas correlation coefficient between Cp and BIS was -0.74. The blood-brain equilibration half-life based on the ke0 estimates for ApEn at 2, 10, 30, 60 s and BIS were 4.31, 3.96, 5.78. 6.54, 5.09 min, respectively, whereas the Ce50,LOC for ApEn at 2, 10, 30, 60 s and BIS were 1.55, 1.47, 1.28, 1.04, and 1.55 µg·ml-1, respectively. Since ke0, which determines the onset of drug action, varies according to the epoch length, it is necessary to consider the epoch length together when estimating ke0.

Effective dose of intravenous oxycodone depending on sex and age for attenuation of intubation-related hemodynamic responses

Background/aim: Preoperative intravenous oxycodone may help to prevent or attenuate intubation-related hemodynamic responses (IRHRs), but its pharmacokinetics differs according to age and sex. Therefore, we investigated the 95% effective dose (ED95) of intravenous oxycodone for attenuating all IRHRs, depending on the age and sex of the study population. Materials and methods: All patients were allocated to one of 6 groups: 1) 20­40 year old males, 2) 41­65yearold males, 3) 66­80 year old males, 4) 20­40 year old females, 5) 41­65yearold females, and 6) 66­80 year old females (groups YM, OM, EM, YF, OF, and EF, respectively). Using Dixon's up-and-down method, the first patient in each group was slowly injected with intravenous oxycodone (0.1 mg kg­1) 20 min before intubation. The subsequent patient received the next oxycodone dose, which was decreased or increased by 0.01 mg kg­1, depending on the "success" or "failure" of attenuation of all IRHRs to within 20% of the baseline values at 1 min after intubation in the previous patient. After obtaining 8 crossover points, predictive ED95 was estimated with probit regression analysis. Results: ED95 varied greatly according to age and sex. ED95was 0.133 mg kg­1, 0.181 mg kg­1, 0.332 mg kg­1, 0.183 mg kg­1, 0.108 mg kg­1, and 0.147 mg kg­1in groups YM, OM, EM, YF, OF, and EF, respectively. Conclusion: ED95 is higher in males with increasing age but is ambiguous for females. ED95 is higher in males than in females over 40 years of age but is higher in females than in males under 41 years of age. However, after considering the age and sex of the study population, these results can be used as reference doses for further studies to verify the clinical effects of oxycodone for attenuating all IRHRs.

Prospective clinical validation of the Eleveld propofol pharmacokinetic-pharmacodynamic model in general anaesthesia.

BACKGROUND: Target-controlled infusion (TCI) systems incorporating pharmacokinetic (PK) or PK-pharmacodynamic (PK-PD) models can be used to facilitate drug administration. Existing models were developed using data from select populations, the use of which is, strictly speaking, limited to these populations. Recently a propofol PK-PD model was developed for a broad population range. The aim of the study was to prospectively validate this model in children, adults, older subjects, and obese adults undergoing general anaesthesia. METHODS: The 25 subjects included in each of four groups were stratified by age and weight. Subjects received propofol through TCI with the Eleveld model, titrated to a bispectral index (BIS) of 40-60. Arterial blood samples were collected at 5, 10, 20, 30, 40, and 60 min after the start of propofol infusion, and every 30 min thereafter, to a maximum of 10 samples. BIS was recorded continuously. Predictive performance was assessed using the Varvel criteria. RESULTS: For PK, the Eleveld model showed a bias < ±20% in children, adults, and obese adults, but a greater bias (-27%) in older subjects. Precision was <30% in all groups. For PD, the bias and wobble were <5 BIS units and the precision was close to 10 BIS units in all groups. Anaesthetists were able to achieve intraoperative BIS values of 40-60 using effect-site target concentrations about 85-140% of the age-adjusted Ce50. CONCLUSIONS: The Eleveld propofol PK-PD model showed predictive precision <30% for arterial plasma concentrations and BIS predictions with a low (population) bias when used in TCI in clinical anaesthesia practice.

Anestesia intravenosa en urgencia / Total intravenous anesthesia in emergency

In emergency settings, TIVA should be adjusted in accordance to the pharmacological changes observed in the hypovolemic patient. With the understanding that in those cases there is a decrease in drug requirements, there is a tendency to underdose these patients, increasing the possibility of awareness. Variation in central volume concentration and blood flow redistribution increase plasma drug concentration (Cp). Decreased liver and kidney perfusion, hemodilution and hypothermia, all affect metabolism and clearance of drugs. Changes in drug bioavailability are also observed secondary to changes in plasma protein concentration and acidosis. Changes in pharmacodynamic of target organs are the product of metabolic and temperature disturbances. Due to the nature of hypovolemic shock, most systematic studies have been done in animals. In this condition, the volume of distribution and clearance of fentanyl decreases, increasing decremental times hence requiring bolus and infusion adjustment. Similar changes are observed when using remifentanil, but in this case its contextual half-life is not altered. In the case of etomidate use, most changes are observed on V2 and V3, with a minimal pharmacodynamic variation is observed, thus, requiring no adjustment. When propofol is used, the increase in Cp is proportional to the degree of hypovolemia, adding an increased sensitivity when it reaches over 40%. Data fit to the Eleveld's model (from animal data extrapolation) and simulations in TIVA trainer are shown. Experience shows that these suggestions overestimate the dose, especially within the first 10 minutes. Therefore, it is recommended to reduce the target by 50% in the case of crystalloid-based resuscitation and by 20% when colloids are preferred. Finally, ketamine has been repositioned as an analgesic drug, and is not recommended as a hypnotic, except when used with propofol or benzodiazepines. For propofol, a staggered induction is recommended (together with remifentanil and a neuromuscular blocker), maintaining then the concentration at the site of effect with which the unconsciousness was achieved. The use of EEG monitoring will yield a better titration.

En escenarios de urgencia, la TIVA se debe ajustar a los cambios farmacológicos observados en el paciente hipovolémico. En el entendido de que los requerimientos de drogas bajan, se tiende a subdosificar y con ello, aumentar la posibilidad de recuerdo intraoperatorio. La concentración del volumen central y la redistribución de flujo, aumentan la concentración plasmática (Cp) de droga. La disminución del flujo hepático y renal, la hemodilución y la hipotermia afectan el metabolismo y la distribución de las drogas. Cambios en la biodisponibilidad de drogas también se observan secundario a cambios en la concentración de proteínas plasmáticas y acidosis. Cambios farmacodinámicos de los órganos blancos son producto de las alteraciones metabólicas y de temperatura. Por la naturaleza del hipovolémico, los estudios sistemáticos han sido fundamentalmente en animales. El volumen de distribución y aclaramiento del fentanilo disminuyen, aumentando los tiempos decrementales. Requiere ajuste de bolo e infusión. Los mismos cambios se observan en el remifentanilo, sin embargo, su vida media contextual no se altera. Para etomidato se observa una contracción centrada en V2 y V3 y una variación farmacodinámica mínima, por lo que no requiere ajuste. Con propofol el aumento de la Cp es proporcional a la hipovolemia, agregándose aumento de la sensibilidad cuando es mayor del 40%. Se muestran ajustes basados en el modelo de Eleveld (de la extrapolación de datos animales) y simulaciones en TIVAtrainer. La experiencia muestra que estas sugerencias sobrestiman la dosis, especialmente los primeros 10 minutos, por lo que se aconseja disminuir el target en 50% en el caso de la reanimación basada en cristaloides y en 20% cuando se prefieren coloides. Por último, la ketamina se ha reposicionado como droga analgésica, no se recomienda como hipnótico, salvo en presencia de propofol o benzodiacepinas. Para propofol, se recomienda una inducción escalonada (junto con remifentanilo y un bloqueador neuromuscular), manteniendo luego con la concentración en en el sitio de efecto (Ce) con la que se alcanzó el LOC. El monitoreo con EEG permitirá una mejor titulación.

The Performance of an Artificial Neural Network Model in Predicting the Early Distribution Kinetics of Propofol in Morbidly Obese and Lean Subjects.

BACKGROUND: Induction of anesthesia is a phase characterized by rapid changes in both drug concentration and drug effect. Conventional mammillary compartmental models are limited in their ability to accurately describe the early drug distribution kinetics. Recirculatory models have been used to account for intravascular mixing after drug administration. However, these models themselves may be prone to misspecification. Artificial neural networks offer an advantage in that they are flexible and not limited to a specific structure and, therefore, may be superior in modeling complex nonlinear systems. They have been used successfully in the past to model steady-state or near steady-state kinetics, but never have they been used to model induction-phase kinetics using a high-resolution pharmacokinetic dataset. This study is the first to use an artificial neural network to model early- and late-phase kinetics of a drug. METHODS: Twenty morbidly obese and 10 lean subjects were each administered propofol for induction of anesthesia at a rate of 100 mg/kg/h based on lean body weight and total body weight for obese and lean subjects, respectively. High-resolution plasma samples were collected during the induction phase of anesthesia, with the last sample taken at 16 hours after propofol administration for a total of 47 samples per subject. Traditional mammillary compartment models, recirculatory models, and a gated recurrent unit neural network were constructed to model the propofol pharmacokinetics. Model performance was compared. RESULTS: A 4-compartment model, a recirculatory model, and a gated recurrent unit neural network were assessed. The final recirculatory model (mean prediction error: 0.348; mean square error: 23.92) and gated recurrent unit neural network that incorporated ensemble learning (mean prediction error: 0.161; mean square error: 20.83) had similar performance. Each of these models overpredicted propofol concentrations during the induction and elimination phases. Both models had superior performance compared to the 4-compartment model (mean prediction error: 0.108; mean square error: 31.61), which suffered from overprediction bias during the first 5 minutes followed by under-prediction bias after 5 minutes. CONCLUSIONS: A recirculatory model and gated recurrent unit artificial neural network that incorporated ensemble learning both had similar performance and were both superior to a compartmental model in describing our high-resolution pharmacokinetic data of propofol. The potential of neural networks in pharmacokinetic modeling is encouraging but may be limited by the amount of training data available for these models.

The influence of cardiac output on propofol and fentanyl pharmacokinetics and pharmacodynamics in patients undergoing abdominal aortic surgery.

Cardiac output (CO) is expected to affect elimination and distribution of highly extracted and perfusion rate-limited drugs. This work was undertaken to quantify the effect of CO measured by the pulse pressure method on pharmacokinetics and pharmacodynamics of propofol and fentanyl administrated during total intravenous anesthesia (TIVA). The data were obtained from 22 ASA III patients undergoing abdominal aortic surgery. Propofol was administered via target-controlled infusion system (Diprifusor) and fentanyl was administered at a dose of 2-3 µg/kg each time analgesia appeared to be inadequate. Hemodynamic measurements as well as bispectral index were monitored and recorded throughout the surgery. Data analysis was performed by using a non-linear mixed-effect population modeling (NONMEM 7.4 software). Three compartment models that incorporated blood flows as parameters were used to describe propofol and fentanyl pharmacokinetics. The delay of the anesthetic effect, with respect to plasma concentrations, was described using a biophase (effect) compartment. The bispectral index was linked to the propofol and fentanyl effect site concentrations through a synergistic Emax model. An empirical linear model was used to describe CO changes observed during the surgery. Cardiac output was identified as an important predictor of propofol and fentanyl pharmacokinetics. Consequently, it affected the depth of anesthesia and the recovery time after propofol-fentanyl TIVA infusion cessation. The model predicted (not observed) CO values correlated best with measured responses. Patients' age was identified as a covariate affecting the rate of CO changes during the anesthesia leading to age-related difference in individual patient's responses to both drugs.

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.