Prospective evaluation of the time to peak effect of propofol to target the effect site in children

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.

The influence of induction speed on the frontal (processed) EEG

The intravenous injection of the anaesthetic propofol is clinical routine to induce loss of responsiveness (LOR). However, there are only a few studies investigating the influence of the injection rate on the frontal electroencephalogram (EEG) during LOR. Therefore, we focused on changes of the frontal EEG especially during this period. We included 18 patients which were randomly assigned to a slow or fast induction group and recorded the frontal EEG. Based on this data, we calculated the power spectral density, the band powers and band ratios. To analyse the behaviour of processed EEG parameters we calculated the beta ratio, the spectral entropy, and the spectral edge frequency. Due to the prolonged induction period in the slow injection group we were able to distinguish loss of responsiveness to verbal command (LOvR) from loss of responsiveness to painful stimulus (LOpR) whereas in the fast induction group we could not. At LOpR, we observed a higher relative alpha and beta power in the slow induction group while the relative power in the delta range was lower than in the fast induction group. When concentrating on the slow induction group the increase in relative alpha power pre-LOpR and even before LOvR indicated that frontal EEG patterns, which have been suggested as an indicator of unconsciousness, can develop before LOR. Further, LOvR was best reflected by an increase of the alpha to delta ratio, and LOpR was indicated by a decrease of the beta to alpha ratio. These findings highlight the different spectral properties of the EEG at various levels of responsiveness and underline the influence of the propofol injection rate on the frontal EEG during induction of general anesthesia.

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.

Impact of propofol on mid-latency auditory-evoked potentials in children

BACKGROUND

Propofol is increasingly used in paediatric anaesthesia, but can be challenging to titrate accurately in this group. Mid-latency auditory-evoked potentials (MLAEPs) can be used to help titrate propofol. However, the effects of propofol on MLAEP in children are unclear. Therefore, we investigated the relationship between propofol and MLAEP in children undergoing anaesthesia.

METHODS

Fourteen healthy children aged 4-16 yr received anaesthesia for elective surgery. Before surgery, propofol was administered in three concentrations (3, 6, 9 µg ml(-1)) through a target-controlled infusion pump using Kataria and colleagues' model. MLAEPs were recorded 5 min after having reached each target propofol concentration at each respective concentration. Additionally, venous propofol blood concentrations were assayed at each measuring time point.

RESULTS

Propofol increased all four MLAEP peak latencies (peaks Na, Pa, Nb, P1) in a dose-dependent manner. In addition, the differences in amplitudes were significantly smaller with increasing propofol target concentrations. The measured propofol plasma concentrations correlated positively with the latencies of the peaks Na, Pa, and Nb.

CONCLUSIONS

Propofol affects MLAEP latencies and amplitudes in children in a dose-dependent manner. MLAEP measurement might therefore be a useful tool for monitoring depth of propofol anaesthesia in children.

The peak bispectral index time cannot predict early phase propofol pharmacodynamics with effect site-controlled infusion algorithm

Objectives:

The plasma-effect site equilibration rate constant (ke0) of propofol was determined with peak bispectral index (BIS) time (T_PEAK) in our previous study. The present study has been conducted to evaluate the ke0's performance with effect site-controlled infusion algorithm.

Materials and Methods:

Forty unpremedicated patients were randomized to group TE1 (Schnider's pharmacokinetic model with ke0 adapted to T_PEAK = 74s) and TE2 (T_PEAK = 96s). In stage 1, all patients received propofol with effect-site concentration (Ce) controlled infusion. Once the pump had injected the mass of propofol necessary to achieve pre-set Ce and while the infusion was stopped, target was reset at 0 μg/ml. When BIS returned to 80 or above, then, in stage 2, the patients received plasma concentration controlled infusion for 10 min. The time of loss of responsiveness (LOR) and BIS were recorded. The differences of Ce at the time of LOR, lowest BIS between stages 1 and 2, hysteresis loop were used to evaluate the performance of ke0.

Results:

In both groups, the calculated propofol Ce at the time of LOR in stages 1 and 2 differed significantly (P<0.01); the mean lowest BIS in stage 1 were significantly higher than those in stage 2 (P < 0.05).The relations of propofol Ce versus BIS revealed the apparent hysteresis loop.

Conclusions:

The study cannot clinically validate the accuracy of application of ke0 derived from the T_PEAK = 74 s of BIS with Schnider propofol pharmacokinetic model.

Optimum Bolus dose of Propofol for Tracheal Intubation during Sevoflurane Induction without Neuromuscular Blockade in Children

The purpose of this study was to determine the optimum bolus dose of propofol required to provide excellent conditions for tracheal intubation following inhalational induction of anaesthesia using 5% sevoflurane without neuromuscular blockade. Twenty-eight children, aged three to seven years, requiring anaesthesia for short duration surgery were recruited. Two minutes after beginning the inhalational induction with 5% sevoflurane and 60% nitrous oxide, a predetermined dose of propofol was injected over 10 seconds. Propofol dose was determined using the Dixon's up-and-down method, starting from 3 mg/kg (0.5 mg/kg as a step size). Laryngoscopy was performed 50 seconds after propofol injection. The optimum dose of propofol required for excellent intubating conditions was 1.39±0.37 mg/kg in 50% of children during inhalation induction using 5% sevoflurane and 60% nitrous oxide in the absence of neuromuscular blocking agents. From probit analysis, the 95% effective dose of propofol was 2.33 mg/kg (95% confidence interval 1.78 to 6.21 mg/kg).

Optimum Bolus Dose of Propofol for Tracheal Intubation during Sevoflurane Induction without Neuromuscular Blockade in Children

The purpose of this study was to determine the optimum bolus dose of propofol required to provide excellent conditions for tracheal intubation following inhalational induction of anaesthesia using 5% sevoflurane without neuromuscular blockade. Twenty-eight children, aged three to seven years, requiring anaesthesia for short duration surgery were recruited. Two minutes after beginning the inhalational induction with 5% sevoflurane and 60% nitrous oxide, a predetermined dose of propofol was injected over 10 seconds. Propofol dose was determined using the Dixon's up-and-down method, starting from 3 mg/kg (0.5 mg/kg as a step size). Laryngoscopy was performed 50 seconds after propofol injection. The optimum dose of propofol required for excellent intubating conditions was 1.39±0.37 mg/kg in 50% of children during inhalation induction using 5% sevoflurane and 60% nitrous oxide in the absence of neuromuscular blocking agents. From probit analysis, the 95% effective dose of propofol was 2.33 mg/kg (95% confidence interval 1.78 to 6.21 mg/kg).