Are there still limitations for the use of target-controlled infusion in children?:

Considerations for Intravenous Anesthesia Dose in Obese Children: Understanding PKPD

The intravenous induction or loading dose in children is commonly prescribed per kilogram. That dose recognizes the linear relationship between volume of distribution and total body weight. Total body weight comprises both fat and fat-free mass. Fat mass influences the volume of distribution and the use of total body weight fails to recognize the impact of fat mass on pharmacokinetics in children. Size metrics alternative to total body mass (e.g., fat-free and normal fat mass, ideal body weight and lean body weight) have been proposed to scale pharmacokinetic parameters (clearance, volume of distribution) for size. Clearance is the key parameter used to calculate infusion rates or maintenance dosing at steady state. Dosing schedules recognize the curvilinear relationship, described using allometric theory, between clearance and size. Fat mass also has an indirect influence on clearance through both metabolic and renal function that is independent of its effects due to increased body mass. Fat-free mass, lean body mass and ideal body mass are not drug specific and fail to recognize the variable impact of fat mass contributing to body composition in children, both lean and obese. Normal fat mass, used in conjunction with allometry, may prove a useful size metric but computation by clinicians for the individual child is not facile. Dosing is further complicated by the need for multicompartment models to describe intravenous drug pharmacokinetics and the concentration effect relationship, both beneficial and adverse, is often poorly understood. Obesity is also associated with other morbidity that may also influence pharmacokinetics. Dose is best determined using pharmacokinetic-pharmacodynamic (PKPD) models that account for these varied factors. These models, along with covariates (age, weight, body composition), can be incorporated into programmable target-controlled infusion pumps. The use of target-controlled infusion pumps, assuming practitioners have a sound understanding of the PKPD within programs, provide the best available guide to intravenous dose in obese children.

The relationship between the effect-site concentration of propofol and sedation scale in children: a pharmacodynamic modeling study

Background

Continuous infusion of propofol has been used to achieve sedation in children. However, the relationship between the effect-site concentration (C_e) of propofol and sedation scale has not been previously examined. The objective of this study was to investigate the relationship between the C_e of propofol and the University of Michigan Sedation Scale (UMSS) score in children with population pharmacodynamic modeling.

Methods

A total of 30 patients (aged 3 to 6 years) who underwent surgery under general anesthesia with propofol and remifentanil lasting more than 1 h were enrolled in this study. Sedation levels were evaluated using the UMSS score every 20 s by a 1 μg/mL stepwise increase in the C_e of propofol during the induction of anesthesia. The pharmacodynamic relationship between the C_e of propofol and UMSS score was analyzed by logistic regression with nonlinear mixed-effect modeling.

Results

The estimated C_e50 (95% confidence interval) of propofol to yield UMSS scores equal to or greater than n were 1.84 (1.54–2.14), 2.64 (2.20–3.08), 3.98 (3.66–4.30), and 4.78 (4.53–5.03) μg/mL for n = 1, 2, 3, and 4, respectively. The slope steepness for the relationship of the C_e versus sedative response to propofol (95% confidence interval) was 5.76 (4.00–7.52).

Conclusions

We quantified the pharmacodynamic relationship between the C_e of propofol and UMSS score, and this finding may be helpful to predict the sedation score at the target C_e of propofol in children.

Trial registration

http://www.clinicaltrials.gov (No.: NCT03195686, Date of registration: 22/06/2017).

A review of perioperative anesthesia and analgesia for infants: updates and trends to watch

This review focuses on pharmacokinetics and pharmacodynamics of opioid and non-opioid analgesics in neonates and infants. The unique physiology of this population differs from that of adults and impacts drug handling. Morphine and remifentanil are described as examples of older versus recently developed opiates to compare and contrast pharmacokinetics and pharmacodynamics in infants. Exploration of genetics affecting both pharmacokinetics and pharmacodynamics of opiates is an area of active research, as is the investigation of a new class of mu-opiate-binding agents which seem selective for analgesic pathways while having less activity in pathways linked to side effects. The kinetics of acetaminophen and of ketorolac as examples of parenteral non-steroidal analgesics in infants are also discussed. The growth in regional anesthesia for peri-operative analgesia in infants can fill an important role minimizing intra-operative anesthetic exposure to opioids and transitioning to post-operative care. Use of multi-modal techniques is recommended to decrease undesirable opiate-related side effects in this vulnerable population.

Propofol: a review of its role in pediatric anesthesia and sedation

Propofol is an intravenous agent used commonly for the induction and maintenance of anesthesia, procedural, and critical care sedation in children. The mechanisms of action on the central nervous system involve interactions at various neurotransmitter receptors, especially the gamma-aminobutyric acid A receptor. Approved for use in the USA by the Food and Drug Administration in 1989, its use for induction of anesthesia in children less than 3 years of age still remains off-label. Despite its wide use in pediatric anesthesia, there is conflicting literature about its safety and serious adverse effects in particular subsets of children. Particularly as children are not "little adults", in this review, we emphasize the maturational aspects of propofol pharmacokinetics. Despite the myriad of propofol pharmacokinetic-pharmacodynamic studies and the ability to use allometrical scaling to smooth out differences due to size and age, there is no optimal model that can be used in target controlled infusion pumps for providing closed loop total intravenous anesthesia in children. As the commercial formulation of propofol is a nutrient-rich emulsion, the risk for bacterial contamination exists despite the Food and Drug Administration mandating addition of antimicrobial preservative, calling for manufacturers' directions to discard open vials after 6 h. While propofol has advantages over inhalation anesthesia such as less postoperative nausea and emergence delirium in children, pain on injection remains a problem even with newer formulations. Propofol is known to depress mitochondrial function by its action as an uncoupling agent in oxidative phosphorylation. This has implications for children with mitochondrial diseases and the occurrence of propofol-related infusion syndrome, a rare but seriously life-threatening complication of propofol. At the time of this review, there is no direct evidence in humans for propofol-induced neurotoxicity to the infant brain; however, current concerns of neuroapoptosis in developing brains induced by propofol persist and continue to be a focus of research.

Effect of butorphanol on thermal nociceptive threshold in healthy pony foals

REASONS FOR PERFORMING STUDY

Pain management is an important component of foal nursing care, and no objective data currently exist regarding the analgesic efficacy of opioids in foals.

OBJECTIVES

To evaluate the somatic antinociceptive effects of 2 commonly used doses of intravenous (i.v.) butorphanol in healthy foals. Our hypothesis was that thermal nociceptive threshold would increase following i.v. butorphanol in a dose-dependent manner in both neonatal and older pony foals.

METHODS

Seven healthy neonatal pony foals (age 1-2 weeks), and 11 healthy older pony foals (age 4-8 weeks). Five foals were used during both age periods. Treatments, which included saline (0.5 ml), butorphanol (0.05 mg/kg bwt) and butorphanol (0.1 mg/kg bwt), were administered i.v. in a randomised crossover design with at least 2 days between treatments. Response variables included thermal nociceptive threshold, skin temperature and behaviour score. Data within each age period were analysed using a 2-way repeated measures ANOVA, followed by a Holm-Sidak multiple comparison procedure if warranted.

RESULTS

There was a significant (P<0.05) increase in thermal threshold, relative to Time 0, following butorphanol (0.1 mg/kg bwt) administration in both age groups. No significant time or treatment effects were apparent for skin temperature. Significant time, but not treatment, effects were evident for behaviour score in both age groups.

CONCLUSIONS

Butorphanol (0.1 mg/kg bwt, but not 0.05 mg/kg bwt) significantly increased thermal nociceptive threshold in neonatal and older foals without apparent adverse behavioural effects.

POTENTIAL RELEVANCE

Butorphanol shows analgesic potential in foals for management of somatic painful conditions.

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.

Performance evaluation of paediatric propofol pharmacokinetic models in healthy young children

BACKGROUND

The performance of eight currently available paediatric propofol pharmacokinetic models in target-controlled infusions (TCIs) was assessed, in healthy children from 3 to 26 months of age.

METHODS

Forty-one, ASA I-II children, aged 3-26 months were studied. After the induction of general anaesthesia with sevoflurane and remifentanil, a propofol bolus dose of 2.5 mg kg(-1) followed by an infusion of 8 mg kg(-1) h(-1) was given. Arterial blood samples were collected at 1, 2, 3, 5, 10, 20, 40, and 60 min post-bolus, at the end of surgery, and at 1, 3, 5, 30, 60, and 120 min after stopping the infusion. Model performance was visually inspected with measured/predicted plots. Median performance error (MDPE) and the median absolute performance error (MDAPE) were calculated to measure bias and accuracy of each model.

RESULTS

Performance of the eight models tested differed markedly during the different stages of propofol administration. Most models underestimated propofol concentration 1 min after the bolus dose, suggesting an overestimation of the initial volume of distribution. Six of the eight models tested were within the accepted limits of performance (MDPE<20% and MDAPE<30%). The model derived by Short and colleagues performed best.

CONCLUSIONS

Our results suggest that six of the eight models tested perform well in young children. Since most models overestimate the initial volume of distribution, the use for TCI might result in the administration of larger bolus doses than necessary.

Medication errors--new approaches to prevention

Medication errors in pediatric anesthesia represent an important risk to children. Concerted action to reduce harm from this cause is overdue. An understanding of the genesis of avoidable adverse drug events may facilitate the development of effective countermeasures to the events or their effects. Errors include those involving the automatic system of cognition and those involving the reflective system. Errors and violations are distinct, but violations often predispose to error. The system of medication administration is complex, and many aspects of it are conducive to error. Evidence-based practices to reduce the risk of medication error in general include those encompassed by the following recommendations: systematic countermeasures should be used to decrease the number of drug administration errors in anesthesia; the label on any drug ampoule or syringe should be read carefully before a drug is drawn up or injected; the legibility and contents of labels on ampoules and syringes should be optimized according to agreed standards; syringes should always be labeled; formal organization of drug drawers and workspaces should be used; labels should be checked with a second person or a device before a drug is drawn up or administered. Dosage errors are particularly common in pediatric patients. Causes that should be addressed include a lack of pediatric formulations and/or presentations of medication that necessitates dilution before administration or the use of intravenous formulations for oral administration in children, a frequent failure to obtain accurate weights for patients and a paucity of pharmacokinetic and pharmacodynamic data. Technological innovations, including the use of bar codes and various cognitive aids, may facilitate compliance with these recommendations. Improved medication safety requires a system-wide strategy standardized at least to the level of the institution; it is the responsibility of institutional leadership to introduce such strategies and of individual practitioners to engage in them.

Optimizing intravenous drug administration by applying pharmacokinetic/pharmacodynamic concepts

This review discusses the ways in which anaesthetists can optimize anaesthetic-analgesic drug administration by utilizing pharmacokinetic and pharmacodynamic information. We therefore focus on the dose-response relationship and the interactions between i.v. hypnotics and opioids. For i.v. hypnotics and opioids, models that accurately predict the time course of drug disposition and effect can be applied. Various commercial or experimental drug effect measures have been developed and can be implemented to further fine-tune individual patient-drug titration. The development of advisory and closed-loop feedback systems, which combine and integrate all sources of pharmacological and effect monitoring, has taken the existing kinetic-based administration technology forwards closer to total coverage of the dose-response relationship.

Total intravenous anesthesia (TIVA) in pediatric cardiac anesthesia

Although inhalational anesthesia with moderate- to high-dose opioid analgesia has been the mainstay of pediatric cardiac anesthesia, the availability of new short-acting drugs, new concepts in pharmacokinetic modeling and computer technology, and advances in surgery and perfusion have made total intravenous anesthesia (TIVA) an attractive option. In this article, we review some of the TIVA techniques used in pediatric cardiac anesthesia.

Aspects of pharmacokinetics and pharmacodynamics of sufentanil in pediatric practice

Sufentanil is a potent synthetic opioid. Like other opioids, sufentanil creates a stable hemodynamic environment in cardiovascularly compromised pediatric patients. Clearance, expressed as per kilogram, is increased in children compared to adults. The P450 CYP3A4 enzyme is responsible for the major metabolic N-dealkylation pathway. Enzyme activity is reduced in neonates but the maturation of sufentanil clearance is not described. The free active fraction is affected by age because of the reduced α(1) -acid glycoprotein plasma concentrations in neonates. Intranasal administration of sufentanil is a possible option for premedication, procedural sedation and analgesia in children, as this option has been found to be safe and effective. Studies concerning the pharmacokinetics and dynamics of sufentanil administered as a bolus or continuous infusion in children are few.

Administration and monitoring of intravenous anesthetics

PURPOSE OF REVIEW

The importance of accuracy in controlling the dose-response relation for intravenous anesthetics is directly related to the importance of optimizing the efficacy and quality of anesthesia while minimizing adverse drug effects. Therefore, it is important to measure and control all steps of the pharmacokinetic and dynamic cascade influencing this dose-effect relationship.

RECENT FINDINGS

The ultimate goal when administering a particular dose of a drug is to obtain the desired clinical effect, taking into account interindividual pharmacokinetic and dynamic variability. Recent findings suggest that effect compartment-controlled target-controlled infusion systems and measurement of (surrogate) clinical drug effects might be helpful in an attempt to optimize the administration intravenous anesthetics and opioids. Additionally, recent findings suggest that the pharmacokinetic and dynamic interaction between anesthetics and opioids is important and such be taking into account when optimizing drug administration. Hereby, feedback control technology and advisory displays depicting these interactions have been studied.

SUMMARY

Anesthetic drug administration might be optimized by applying knowledge from clinical pharmacokinetics and dynamics.