Performance of propofol target-controlled infusion models in the obese: pharmacokinetic and pharmacodynamic analysis

Pharmacokinetics of propofol in severely obese surgical patients

BACKGROUND

Existing PK models of propofol include sparse data from very obese patients. The aim of this study was to develop a PK model based on standardised surgical conditions and spanning from normal-weight up to, and including, a high number of very obese patients.

METHODS

Adult patients scheduled for laparoscopic cholecystectomy or bariatric surgery were studied. Anaesthesia was induced with propofol 2 mg/kg adjusted body weight over 2 min followed by 6 mg/kg/h adjusted body weight over 30 min. For the remainder of the operation anaesthesia was maintained with sevoflurane. Remifentanil was dosed according to clinical need. Eight arterial samples were drawn in a randomised block sampling regimen over a span of 24 h. Time-concentration data were analysed by population PK modelling using non-linear mixed-effects modelling.

RESULTS

Four hundred and seventy four serum propofol concentrations were collected from 69 patients aged 19-60 years with a BMI 21.6-67.3 kg/m2. Twenty one patients had a BMI above 50 kg/m2. A 3-compartment PK model was produced wherein three different body weight descriptors and sex were included as covariates in the final model. Total body weight was found to be a covariate for clearance and Q3; lean body weight for V1, V2 and Q2; predicted normal weight for V3 and sex for V1. The fixed allometric exponent of 0.75 applied to all clearance parameters improved the performance of the model. Accuracy and precision were 1.4% and 21.7% respectively in post-hoc performance evaluation.

CONCLUSION

We have developed a new PK model of propofol that is suitable for all adult weight classes. Specifically, it is based on data from an unprecedented number of individuals with very high BMI.

Feasibility of calculating rocuronium dosage by skeletal muscle weight in patients with obesity

This study aimed to investigate the dose-response relationship of rocuronium administered based on skeletal muscle weight and to assess the feasibility of calculating rocuronium dosage by skeletal muscle weight in short surgeries for patients with obesity. This single-center, randomized controlled clinical trial included 71 patients with obesity aged 28-70 years, with body fat percentages (PBF) >20% in men and > 28% in women, ASA status I-III, scheduled for tracheoscopy. Patients were randomly allocated into two groups: skeletal muscle group (SM group) received rocuronium based on the skeletal muscle content (1.0 mg/kg, n = 31), and the conventional administration group (conventional group) received rocuronium based on total body weight (0.45 mg/kg, n = 30). General anesthesia was administered using the same protocol. Parameters recorded included patients' general condition, muscle relaxant usage, onset time of muscle relaxants, non-response time, clinical effect time, 75% recovery time, and recovery index. Additionally, occurrences of body movement, choking, and incomplete muscle relaxation during surgery were recorded. Compared to the conventional group, the SM group required significantly less rocuronium dosage, resulting in significantly lower non-response time, clinical effect time, 75% recovery time, and recovery index (p < 0.05), and the onset time is slightly longer. Neither group experienced body movement, choking, or incomplete muscle relaxation (p > 0.05). Utilizing skeletal muscle weight to calculate rocuronium dosage in short surgeries for patients with obesity can reduce dosage, shorten recovery time, and prevent residual muscle relaxation while achieving satisfactory muscle relaxation to meet surgical requirements.

Neuromonitoring Changes in Spinal Deformity Surgery

Spinal cord injury is one of the most feared complications in spinal deformity surgery. The surgeon must be vigilant of direct and indirect sources of injury at all points during surgery. The incidence of complications has greatly decreased with the ability to monitor the motor and sensory pathways. Changes in signaling of these pathways provide context for what the insult is, and how to correct it before it becomes irreversible. There are well-established protocols that provide an algorithmic response to changes that can help all in the room determine the source of injury, and the appropriate reaction.

How obesity affects the disposition of intravenous anesthetics

PURPOSE OF REVIEW

Understanding the changes in drug disposition of intravenous anesthetics in patients with obesity and administering appropriate doses are critical to avoid intraoperative awareness with recall because of underdosing and over-sedation and delayed emergence due to overdosing. Pharmacokinetic simulation or target-controlled infusion (TCI) using models that have been adapted to patients with obesity are necessary to select appropriate dosing regimens. This review aimed to describe the pharmacokinetic concepts underpinning the use of intravenous anesthetics, including propofol, remifentanil, and remimazolam, in patients with obesity.

RECENT FINDINGS

In the last 5 years, a series of pharmacokinetic models for propofol, remifentanil, and remimazolam that were estimated from populations that included obese patients have been published. These new pharmacokinetic models can be considered 'second generation' compared with earlier models in that they expand the range of covariate effects (e.g. the extremes of body weight and age) accounted for by the models. The predictive performances of each pharmacokinetic model have been shown in the literature to be within clinically acceptable limits. Among them, the propofol model by Eleveld et al. has been externally validated and has shown reasonable predictive accuracy.

SUMMARY

Pharmacokinetic simulations or TCI using pharmacokinetic models that account for the influence of obesity on a drug's disposition are essential to predict plasma/effect-site concentrations of intravenous anesthetics and understand the temporal profile of drug concentrations and effect in patients with obesity, particularly severe obesity.

Effects of Different Injection Rates of Propofol on Postoperative Cognition in Elderly Patients Undergoing Laparoscopic Inguinal Hernia Repair

Purpose

This study aimed to explore the effects of different injection rates of propofol on postoperative cognition in elderly patients undergoing laparoscopic inguinal hernia repair.

Methods

A total of 180 elderly patients who planned to undergo laparoscopic inguinal hernia repair were randomly divided into three groups: slow injection of propofol (V_S-Group, 30 mg kg^-1 h^-1); medium injection of propofol (V_M-Group, 100 mg kg^-1 h^-1) or fast injection of propofol (V_F-Group, 300 mg kg^-1 h^-1). Propofol was induced by microinfusion pump, and the depth of anesthesia was monitored by bispectral index (BIS). Propofol and remifentanil were continuously infused during anesthesia maintenance and adjusted according to BIS. The primary outcome was the use of the Mini-Mental State Examination (MMSE) and the Montreal Cognitive Assessment (MoCA) to measure the incidence of postoperative cognitive decline (POCD) in elderly patients on the first and seventh postoperative day. Secondary outcomes included induced dose of propofol, incidence of burst suppression and maximum electroencephalographic (EEG) effect of propofol (BIS-min) during induction.

Results

The incidence of POCD on the first and seventh day postoperatively was similar among the three groups (P > 0.05). However, with the increase of propofol injection rate, induced dose of propofol, incidence of burst suppression and BIS-min during induction, the number of patients requiring vasoactive agents were significantly increased (P < 0.001). Multivariate regression analysis showed that the brief duration of burst suppression during induction did not affect the occurrence of POCD, while age and duration of hospitalization were risk factors for POCD.

Conclusion

For elderly patients undergoing laparoscopic inguinal hernia repair, lowering the injection rate of propofol (such as 30 mg kg^-1 h^-1) cannot decrease the incidence of early POCD, but reduces induction dose of propofol and use of vasoactive drugs, making the patient's hemodynamics more stable.

Considerations for Satisfactory Sedation during Dental Implant Surgery

Implant surgery is a lengthy dental procedure, and sedation is often used to reduce discomfort. The effectiveness of sedation has traditionally been evaluated in terms of patient and surgeon satisfaction, but the most important goal is not to induce a deep sleep in the patient, but rather to ensure that the surgery is performed safely and as planned. Additionally, adequate pain control is a necessary requirement for patient and surgeon satisfaction. Most patients undergoing implant surgery are middle-aged or older, and a relatively large number of them have cardiovascular disease. Infiltration anesthesia using articaine or lidocaine in combination with adrenaline is widely used, but its use in patients with cardiovascular disease is limited because of adrenaline’s effects on the cardiovascular system. The use of long-acting local anesthetics and the potential efficacy of ultrasound-guided jaw nerve block have been investigated to enhance analgesia without resorting to adrenaline. Midazolam and propofol are usually used for sedation, but dexmedetomidine, which causes less respiratory depression, and the ultrashort-acting benzodiazepine remimazolam are emerging as potential alternatives. Monitoring of anesthetic depth using electroencephalography is effective in maintaining a constant level of sedation. In addition, sedation promotes the stabilization of heart rate and blood pressure, reducing the risks associated with adrenaline and allowing for safer management.

A population pharmacokinetic model of remimazolam for general anesthesia and consideration of remimazolam dose in clinical practice

BACKGROUND

Remimazolam besylate is a novel short-acting benzodiazepine. An appropriate pharmacokinetic model of remimazolam is desirable in anesthesia practice. The aim of the study was to develop a pharmacokinetic model using plasma samples from patients anesthetized with remimazolam. Influence of patient characteristics, context-sensitive decrement-times, and dose regimens were also examined.

METHODS

Data were obtained from four trials on patients, and seven trials on healthy volunteers. The characteristics of 416 male and 246 female subjects were as follows: age, 18-93 years; body weight, 34-149 kg; and American Society of Anesthesiologists physical status (ASA-PS), I-IV. 2231 arterial and 3200 venous samples were used for the final model. The equilibration rate constant between arterial plasma and effect-site was estimated using the concept of time to peak effect. The final model was used to generate context-sensitive decrement times and dose regimens for general anesthesia.

RESULTS

A three-compartment model plus virtual venous compartment with allometric scaling of adjusted body weight (ABW), age, sex, and ASA-PS as covariates were selected as the final model. Elimination clearance was lower in males, and in subjects with higher ABW and ASA-PS scores. Approximately 10% or 20% higher dose rate was necessary in females than in males or ASA-PS I/II than III/IV patient. The context-sensitive half-time for effect-site concentration in a 55-year-old, 70-kg, 170-cm male or female ASA-PS I/II patient after > 6-h infusion was 16.7 or 15.9 min.

CONCLUSION

Remimazolam pharmacokinetic model for general anesthesia was successfully developed. ABW, ASA-PS, and sex has a considerable impact on the remimazolam concentration.

Current Applications of Artificial Intelligence in Bariatric Surgery

The application of artificial intelligence technologies is growing in several fields of healthcare settings. The aim of this article is to review the current applications of artificial intelligence in bariatric surgery. We performed a review of the literature on Scopus, PubMed and Cochrane databases, screening all relevant studies published until September 2021, and finally including 36 articles. The use of machine learning algorithms in bariatric surgery is explored in all steps of the clinical pathway, from presurgical risk-assessment and intraoperative management to complications and outcomes prediction. The models showed remarkable results helping physicians in the decision-making process, thus improving the quality of care, and contributing to precision medicine. Several legal and ethical hurdles should be overcome before these methods can be used in common practice.

Online exhaled propofol monitoring in normal-weight and obese surgical patients

Background

Ion mobility spectrometry (IMS) allows for online quantification of exhaled propofol concentrations. We aimed to validate a bedside online IMS device, the Edmon^®, for predicting plasma concentrations of propofol in normal‐weight and obese patients.

Methods

Patients with body mass index (BMI) >20 kg/m² scheduled for laparoscopic cholecystectomy or bariatric surgery were recruited. Exhaled propofol concentrations (C_A), arterial plasma propofol concentrations (C_P) and bispectral index (BIS) values were collected during target‐controlled infusion (TCI) anaesthesia. Generalised estimation equation (GEE) was applied to all samples and stable‐phase samples at different delays for best fit between C_P and C_A. BMI was evaluated as covariate. BIS and exhaled propofol correlations were also assessed with GEE.

Results

A total of 29 patients (BMI 20.3–53.7) were included. A maximal R² of 0.58 was found during stable concentrations with 5 min delay of C_A to C_P; the intercept a = −0.69 (95% CI −1.7, 0.3) and slope b = 0.87 (95% CI 0.7, 1.1). BMI was found to be a non‐significant covariate. The median absolute performance error predicting plasma propofol concentrations was 13.4%. At a C_A of 5 ppb, the model predicts a C_P of 3.6 μg/ml (95% CI ±1.4). There was a maximal negative correlation of R² = 0.44 at 2‐min delay from C_A to BIS.

Conclusions

Online monitoring of exhaled propofol concentrations is clinically feasible in normal‐weight and obese patients. With a 5‐min delay, our model outperforms the Marsh plasma TCI model in a post hoc analysis. Modest correlation with plasma concentrations makes the clinical usefulness questionable.

Guidelines for Perioperative Care in Bariatric Surgery: Enhanced Recovery After Surgery (ERAS) Society Recommendations: A 2021 Update

Background

This is the second updated Enhanced Recovery After Surgery (ERAS®) Society guideline, presenting a consensus for optimal perioperative care in bariatric surgery and providing recommendations for each ERAS item within the ERAS® protocol.

Methods

A principal literature search was performed utilizing the Pubmed, EMBASE, Cochrane databases and ClinicalTrials.gov through December 2020, with particular attention paid to meta-analyses, randomized controlled trials and large prospective cohort studies. Selected studies were examined, reviewed and graded according to the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) system. After critical appraisal of these studies, the group of authors reached consensus regarding recommendations.

Results

The quality of evidence for many ERAS interventions remains relatively low in a bariatric setting and evidence-based practices may need to be extrapolated from other surgeries.

Conclusion

A comprehensive, updated evidence-based consensus was reached and is presented in this review by the ERAS® Society.

Obesity and anesthetic pharmacology: simulation of target-controlled infusion models of propofol and remifentanil

The prevalence of obesity is increasing, resulting in an increase in the number of surgeries performed to treat obesity and diseases induced by obesity. The associated comorbidities as well as the pharmacokinetic and pharmacodynamic changes that occur in obese patients make it difficult to control the appropriate dose of anesthetic agents. Factors that affect pharmacokinetic changes include the increase in adipose tissue, lean body weight, extracellular fluid, and cardiac output associated with obesity. These physiological and body compositional changes cause changes in the pharmacokinetic and pharmacodynamic parameters. The increased central volume of distribution and alterations in the clearance of drugs affect the plasma concentration of propofol and remifentanil in the obese population. Additionally, obesity can affect pharmacodynamic properties, such as the 50% of maximal effective concentration and the effect-site equilibration rate constant (ke0). Conducting a simulation of target-controlled infusions based on pharmacokinetic and pharmacodynamic models that include patients that are obese can help clinicians better understand the pharmacokinetic and pharmacodynamic changes of anesthetic drugs associated with this population.

Application of Intravenous Lidocaine in Obese Patients Undergoing Painless Colonoscopy: A Prospective, Randomized, Double-Blind, Controlled Study

OBJECTIVE

Propofol for procedural sedation and analgesia (PSA) for colonoscopy can result in a high prevalence of severe respiratory depression. Studies have shown that intravenous (IV) infusion of lidocaine can reduce propofol requirements significantly and increase the ventilatory response to carbon dioxide in humans. We tested the hypothesis that IV lidocaine could improve propofol-induced respiratory depression in obese patients during colonoscopy.

METHODS

Ninety obese patients scheduled for painless colonoscopy were randomized to receive lidocaine (1.5 mg/kg, then 2 mg/kg/h, IV) or the same volume of 0.9% saline. Intraoperative sedation was provided by propofol. The primary outcome was the number of oxygen-desaturation episodes. Secondary outcomes were: the number of apnea episodes; total propofol consumption; time to the first hypoxia episode; time to consciousness loss; intraoperative hemodynamic parameters; awakening time; adverse events; duration of post-anesthesia care unit (PACU) stay; satisfaction of endoscopists and patients.

RESULTS

Demographic characteristics between the two groups were comparable. The number of oxygen-desaturation episodes in group L (1.49±1.12) decreased by 0.622 (P=0.018) compared with that in group N (2.11±1.32), and the number of apnea episodes in group L decreased by 0.533 (P<0.001). Kaplan-Meier curves showed that the median time to the first hypoxia episode was longer in group L (86.78 s) than that in group N (63.83 s) (Log rank P=0.0008). The total propofol consumption, awakening time, and duration of PACU stay were reduced in group L. There was no significant difference in the prevalence of adverse events (P>0.05 for all). Satisfaction scores for endoscopists and patients in group L were higher than that in group N (P<0.001).

CONCLUSION

Intravenous infusion of lidocaine could significantly reduce the number of oxygen-desaturation and apnea episodes in obese patients during painless colonoscopy. This method is worthy of clinical promotion.

CLINICAL TRIALS REGISTRATION

ChiCTR2000028937.

The effect of cardiac output on the pharmacokinetics and pharmacodynamics of propofol during closed-loop induction of anesthesia

BACKGROUND AND OBJECTIVE

Intraoperative hemodynamic stability is essential to safety and post-operative well-being of patients and should be optimized in closed-loop control of anesthesia. Cardiovascular changes inducing variations in pharmacokinetics may require dose modification. Rigorous investigational tools can strengthen current knowledge of the anesthesiologists and support clinical practice. We quantify the cardiovascular response of high-risk patients to closed-loop anesthesia and propose a new application of physiologically-based pharmacokinetic-pharmacodynamic (PBPK-PD) simulations to examine the effect of hemodynamic changes on the depth of hypnosis (DoH).

METHODS

We evaluate clinical hemodynamic changes in response to anesthesia induction in high-risk patients from a study on closed-loop anesthesia. We develop and validate a PBPK-PD model to simulate the effect of changes in cardiac output (CO) on plasma levels and DoH. The wavelet-based anesthetic value for central nervous system monitoring index (WAV_CNS) is used as clinical end-point of propofol hypnotic effect.

RESULTS

The median (interquartile range, IQR) changes in CO and arterial pressure (AP), 3 min after induction of anesthesia, are 22.43 (14.82-36.0) % and 26.60 (22.39-35.33) % respectively. The decrease in heart rate (HR) is less marked, i.e. 8.82 (4.94-12.68) %. The cardiovascular response is comparable or less enhanced than in manual propofol induction studies. PBPK simulations show that the marked decrease in CO coincides with high predicted plasma levels and deep levels of hypnosis, i.e. WAV_CNS < 40. PD model identification is improved using the PBPK model rather than a standard three-compartment PK model. PD simulations reveal that a 30% drop in CO can cause a 30% change in WAV_CNS.

CONCLUSIONS

Significant CO drops produce increased predicted plasma concentrations corresponding to deeper anesthesia, which is potentially dangerous for elderly patients. PBPK-PD model simulations allow studying and quantifying these effects to improve clinical practice.

Effect of intra-operative intravenous lidocaine on opioid consumption after bariatric surgery: a prospective, randomised, blinded, placebo-controlled study

Peri-operative lidocaine infusion warrants investigation in bariatric surgery because obese patients present different physiological and pharmacological risks. This single-centre, prospective, randomised double-blind placebo-controlled study enrolled obese patients scheduled for laparoscopic bariatric surgery using an enhanced recovery protocol. Patients received either lidocaine (bolus of 1.5 mg.kg^-1 , then a continuous infusion of 2 mg.kg^-1 .h^-1 until the end of the surgery, then 1 mg.kg^-1 .h^-1 for 1 h in the recovery area) or identical volumes and rates of 0.9% saline. The primary outcome was the consumption of the equivalent of oxycodone consumption over the first 3 postoperative days. Secondary outcomes were: postoperative pain; incidence of nausea and vomiting; bowel function recovery; and lengths of stay in the recovery area and in hospital. Plasma concentrations of lidocaine were measured. On the 178 patients recruited, data were analysed from 176. The median (IQR [range]) equivalent intravenous oxycodone consumption was 3.3 mg (0.0-6.0 [0.0-14.5]) and 5.0 mg (3.3-7.0 [3.3-20.0]) in the lidocaine and saline groups, respectively (difference between medians (95%CI): 1.7 (0.6-3.4) mg; p = 0.004). Length of stay in the recovery area, postoperative pain, nausea and vomiting, day of recovery of bowel function, and length of stay in hospital were not different between groups. Mean (SD) lidocaine plasma concentrations were 2.44 (0.70) µg.ml^-1 and 1.77 (0.51) µg.ml^-1 at the end of surgery and 1 hour after the end of infusion, respectively. Lidocaine infusion during bariatric surgery resulted in a clinically non-relevant difference in postoperative oxycodone consumption.

Suspected propofol infusion syndrome during normal targeted propofol concentration

To this day, the pathophysiology and risk factors of propofol infusion syndrome (PRIS) remain unknown. Moreover, there is no widely accepted definition of PRIS, even though it is a potentially fatal condition. While many suspected cases of PRIS have been reported in both pediatric and adult populations, the actual propofol plasma concentration (Cp) has never been clarified. In this clinical report, we described the first suspected PRIS case in which the propofol Cp was measured 25 min after 226 min of propofol infusion (7.2 µg/mL), which was 12 times higher than the predicted value (0.6 µg/mL). In the presented case, we observed gradually progressive uncontrollable hypercapnia and tachycardia, followed by severe lactic acidosis during surgical anesthesia based on the target-controlled infusion of propofol. Levels of liver enzymes were slightly elevated which suggests little or no liver damage though propofol is mainly metabolized by the liver. Meanwhile, renal impairment, a common secondary feature of PRIS, occurred concomitantly when hypercapnia and metabolic acidosis were manifested. In this case, low or delayed propofol clearance might have been a triggering factor causing severe lactic acidosis.

Choice of Perioperative Anesthetic Medications in Patients Undergoing Bariatric Surgery

The prevalence of obesity is increasing globally. Rational perioperative anesthetic drug selection and administration require knowledge of how obesity interacts with those drugs. In this review, we summarize different aspects of the anesthetic agents, including pharmacokinetics (PK), pharmacodynamics (PD) and clinical application of the most commonly used medications with particular focus on the enhanced recovery of the obese patient.

Influence of propofol-based total intravenous anaesthesia on peri-operative outcome measures: a narrative review

Propofol-based total intravenous anaesthesia is well known for its smooth, clear-headed recovery and anti-emetic properties, but there are also many lesser known beneficial properties that can potentially influence surgical outcome. We will discuss the anti-oxidant, anti-inflammatory and immunomodulatory effects of propofol and their roles in pain, organ protection and immunity. We will also discuss the use of propofol in cancer surgery, neurosurgery and older patients.

[Drugs for intravenous induction of anesthesia: propofol]

In a series of articles dealing with hypnotics for induction of anesthesia, this article describes the development and current value of propofol. Its significance far exceeds that of a pure induction hypnotic (sedation in diagnostic and therapeutic procedures and on the intensive care unit). Propofol is also used for sedation in diagnostic and therapeutic procedures and on the intensive care unit. In the field of induction of anesthesia, the alternatives are barely used. Some contraindications are still controversial whereas others are no longer sufficiently anchored in the users' awareness (widespread off-label use). Adverse effects, such as injection pain, infection risk and propofol-related infusion syndrome (PRIS) could be significantly reduced by pharmacovigilance. With appropriate caution nearly the whole spectrum of anesthesiology patients can be treated using propofol. The hemodynamic side effects and the rare but potentially fatal PRIS are limitations. Further developments address the water solubility and the solubilizing agents of propofol.

Adjusted vs Total Body Weight-Based Dosing of Sedation and Analgesia Used in the Intensive Care Unit

Background: The purpose of this study was to evaluate if dosing fentanyl, dexmedetomidine, and propofol based on ideal or adjusted vs actual weight in patients would decrease overall opioid and sedative use. Methods: This was a retrospective chart review comparing adjusted vs actual weight-based dosing protocol of mechanically ventilated (MV) intensive care unit (ICU) adult patients who required fentanyl and either propofol or dexmedetomidine. Results: A total of 261 patients were included in which 101 patients were in the actual weight group and 160 patients were in the adjusted weight group. Total doses per MV day of fentanyl was 1042 ± 1060 µg in the actual weight group vs 901 ± 1025 µg in the adjusted weight group (P = .13). Total doses per MV day of midazolam was 20 ± 19 mg in the actual group vs 15 ± 19 mg adjusted group (P = .02). Average MV days was 8.2 vs 7.1 days, ICU length of stay was 10.6 vs 9.4 days, and self-extubation rates were 17.8% vs 4.4% in the actual group and adjusted group, respectively. Conclusion: Total midazolam doses per MV day were lower in the adjusted group. No significant change was seen in MV days, ICU length of stay, or self-extubation rates.

Intraoperative immunomodulatory effects of sevoflurane versus total intravenous anesthesia with propofol in bariatric surgery (the OBESITA trial): study protocol for a randomized controlled pilot trial

Background

Obesity is associated with a chronic systemic inflammatory process. Volatile or intravenous anesthetic agents may modulate immune function, and may do so differentially in obesity. However, no study has evaluated whether these potential immunomodulatory effects differ according to type of anesthesia in obese patients undergoing laparoscopic bariatric surgery.

Methods/design

The OBESITA trial is a prospective, nonblinded, single-center, randomized, controlled clinical pilot trial. The trial will include 48 patients with a body mass index ≥ 35 kg/m², scheduled for laparoscopic bariatric surgery using sleeve or a Roux-en-Y gastric bypass technique, who will be allocated 1:1 to undergo general inhalational anesthesia with sevoflurane or total intravenous anesthesia (TIVA) with propofol. The primary endpoint is the difference in plasma interleukin (IL)-6 levels when comparing the two anesthetic agents. Blood samples will be collected prior to anesthesia induction (baseline), immediately after anesthetic induction, and before endotracheal extubation. Levels of other proinflammatory and anti-inflammatory cytokines, neutrophil chemotaxis, macrophage differentiation, phagocytosis, and occurrence of intraoperative and postoperative complications will also be evaluated.

Discussion

To our knowledge, this is the first randomized clinical trial designed to compare the effects of two different anesthetics on immunomodulation in obese patients undergoing laparoscopic bariatric surgery. Our hypothesis is that anesthesia with sevoflurane will result in a weaker proinflammatory response compared to anesthesia with propofol, with lower circulating levels of IL-6 and other proinflammatory mediators, and increased macrophage differentiation into the M2 phenotype in adipose tissue.

Trial registration

Registro Brasileiro de Ensaios Clínicos, RBR-77kfj5. Registered on 25 July 2018.

Electronic supplementary material

The online version of this article (10.1186/s13063-019-3399-z) contains supplementary material, which is available to authorized users.

Evaluating Propofol Concentration in Blood From Exhaled Gas Using a Breathing-Related Partition Coefficient

BACKGROUND

The anesthetic side effects of propofol still occur in clinical practice because no reliable monitoring techniques are available. In this regard, continuous monitoring of propofol in breath is a promising method, yet it remains infeasible because there is large variation in the blood/exhaled gas partial pressure ratio (RBE) in humans. Further evaluations of the influences of breathing-related factors on RBE would mitigate this variation.

METHODS

Correlations were analyzed between breathing-related factors (tidal volume [TV], breath frequency [BF], and minute ventilation [VM]) and RBE in 46 patients. Furthermore, a subset of 10 patients underwent pulmonary function tests (PFTs), and the parameters of the PFTs were then compared with the RBE. We employed a 1-phase exponential decay model to characterize the influence of VM on RBE. We also proposed a modified RBE (RBEM) that was not affected by the different breathing patterns of the patients. The blood concentration of propofol was predicted from breath monitoring using RBEM and RBE.

RESULTS

We found a significant negative correlation (R = -0.572; P < .001) between VM and RBE (N = 46). No significant correlation was shown between PFTs and RBE in the subset (N = 10). RBEM demonstrated a standard Gaussian distribution (mean, 1.000; standard deviation [SD], 0.308). Moreover, the predicted propofol concentrations based on breath monitoring matched well with the measured blood concentrations. The 90% prediction band was limited to within ±1 μg·mL.

CONCLUSIONS

The prediction of propofol concentration in blood was more accurate using RBEM than when using RBE and could provide reference information for anesthesiologists. Moreover, the present study provided a general approach for assessing the influence of relevant physiological factors and will inform noninvasive and accurate breath assessment of volatile drugs or metabolites in blood.

Influence of Bayesian optimization on the performance of propofol target-controlled infusion

Background

Target controlled infusion (TCI) systems use population-based pharmacokinetic (PK) models that do not take into account inter-individual residual variation. This study compares the bias and inaccuracy of a population-based vs a personalized TCI propofol titration using Bayesian adaptation. Haemodynamic and hypnotic stability, and the prediction probability of alternative PK models, was studied.

Methods

A double-blinded, prospective randomized controlled trial of 120 subjects undergoing cardiac surgery was conducted. Blood samples were obtained at 10, 35, 50, 65, 75 and 120 min and analysed using a point-of-care propofol blood analyser. Bayesian adaptation of the PK model was applied at 60 min in the intervention group. Median (Absolute) Performance Error (Md(A)PE) was used to evaluate the difference between bias and inaccuracy of the models. Haemodynamic (mean arterial pressure [MAP], heart rate) and hypnotic (bispectral index [BIS]) stability was studied. The predictive performance of four alternative propofol PK models was studied.

Results

MdPE and MdAPE did not differ between groups during the pre-adjustment period (control group: 6.3% and 16%; intervention group: 5.4% and 18%). MdPE differed in the post-adjustment period (12% vs. -0.3%), but MdAPE did not (18% vs. 15%). No difference in heart rate, MAP or BIS was found. Compared with the other models, the Eleveld propofol PK model (patients) showed the best prediction performance.

Conclusions

When an accurate population-based PK model was used for propofol TCI, Bayesian adaption of the model improved bias but not precision.

Clinical trial registration

Dutch Trial Registry NTR4518.

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.

Pharmacokinetic and pharmacodynamic interactions in anaesthesia. A review of current knowledge and how it can be used to optimize anaesthetic drug administration

This review describes the basics of pharmacokinetic and pharmacodynamic drug interactions and methodological points of particular interest when designing drug interaction studies. It also provides an overview of the available literature concerning interactions, with emphasis on graphic representation of interactions using isoboles and response surface models. It gives examples on how to transform this knowledge into clinically and educationally applicable (bedside) tools.

Advances in pharmacokinetic modeling: target controlled infusions in the obese

PURPOSE OF REVIEW

The use of conventional pharmacokinetic parameters sets 'models' derived from nonobese patients has proven inadequate to administer intravenous anesthetics in the obese population and is commonly associated with higher than anticipated plasma propofol concentrations when used with target (plasma or effect site) controlled infusion pumps. In this review we will describe recent modeling strategies to characterize the disposition of intravenous anesthetics in the obese patient and will show clinically relevant aspects of new model's performance in the obese population.

RECENT FINDINGS

Because clearance of a drug increases in a nonlinear manner with weight, nonlinear relationships better scale infusion rates between lean and obese individuals. Allometric concepts have been successfully used to describe size-related nonlinear changes in clearances. Other nonlinear scaling options include the use of descriptors such as body surface area, lean body weight, fat-free mass, and normal fat mass. Newer pharmacokinetic models, determined from obese patient data, have been developed for propofol and remifentanil using allometric concepts and comprehensive size descriptors.

SUMMARY

Pharmacokinetic models to perform target-controlled infusion in the obese population should incorporate descriptors that reflect with greater precision the influence of body composition in volumes and clearances of each drug. It is our hope that commercially available pumps will soon incorporate these new models to improve the performance of this technique in the obese population.

Pharmacokinetic-pharmacodynamic model for propofol for broad application in anaesthesia and sedation

BACKGROUND

Pharmacokinetic (PK) and pharmacodynamic (PD) models are used in target-controlled-infusion (TCI) systems to determine the optimal drug administration to achieve a desired target concentration in a central or effect-site compartment. Our aim was to develop a PK-PD model for propofol that can predict the bispectral index (BIS) for a broad population, suitable for TCI applications.

METHODS

Propofol PK data were obtained from 30 previously published studies, five of which also contained BIS observations. A PK-PD model was developed using NONMEM. Weight, age, post-menstrual age (PMA), height, sex, BMI, and presence/absence of concomitant anaesthetic drugs were explored as covariates. The predictive performance was measured across young children, children, adults, elderly, and high-BMI individuals, and in simulated TCI applications.

RESULTS

Overall, 15 433 propofol concentration and 28 639 BIS observations from 1033 individuals (672 males and 361 females) were analysed. The age range was from 27 weeks PMA to 88 yr, and the weight range was 0.68-160 kg. The final model uses age, PMA, weight, height, sex, and presence/absence of concomitant anaesthetic drugs as covariates. A 35-yr-old, 170 cm, 70 kg male (without concomitant anaesthetic drugs) has a V₁, V₂, V₃, CL, Q₂, Q₃, and k_e0 of 6.28, 25.5, 273 litres, 1.79, 1.75, 1.11 litres min^-1, and 0.146 min^-1, respectively. The propofol TCI administration using the model matches well with recommendations for all age groups considered for both anaesthesia and sedation.

CONCLUSIONS

We developed a PK-PD model to predict the propofol concentrations and BIS for broad, diverse population. This should be useful for TCI in anaesthesia and sedation.

Impact of clinical factors and UGT1A9 and CYP2B6 genotype on inter-individual differences in propofol pharmacokinetics

PURPOSE

Propofol is one of the most widely used fast-acting intravenously administered anesthetics. However, although large inter-individual differences in dose requirements and recovery time have been observed, there are few previous studies in which the association between several potential covariates, including genetic factors such as the UGT1A9 and CYP2B6 genotypes, and propofol pharmacokinetics was simultaneously examined. This study aimed to identify factors determining propofol pharmacokinetics.

METHODS

Eighty-three patients were enrolled, and their blood samples were collected 1, 5, 10, and 15 min after administering a single intravenous bolus of propofol at a dose of 2.0 ml/kg to measure propofol plasma concentration. Area under the time-plasma concentration curve from zero up to the last measurable time point (AUC_15min) was determined from the concentration data. The inter-individual variability of the propofol pharmacokinetics was evaluated by investigating relationships between AUC_15min and genotype of UGT1A9 and CYP2B6; clinical factors, such as age, sex, body mass index (BMI), and preoperative hematological examination; and hemodynamic variables measured by a pulse dye densitogram analyzer. The Spearman rank correlation coefficient and the Mann-Whitney U test were used for the statistical analysis of continuous and categorical values, respectively. Subsequently, clinical factors that had p values of < 0.05 in the univariate analysis were examined in a multivariate analysis using multiple linear regression analysis.

RESULTS

Age, BMI, indocyanine green disappearance ratio (K-ICG), hepatic blood flow (HBF), preoperative hemoglobin level, and sex were correlated with AUC_15min (p < 0.05) in univariate analysis. Multivariate analysis performed to adjust for age, BMI, K-ICG, HBF, preoperative hemoglobin level, and sex revealed only BMI as an independent factor associated with AUC_15min.

CONCLUSIONS

This study demonstrated that BMI influences propofol pharmacokinetics after its administration as a single intravenous injection, while UGT1A9 and CYP2B6 SNPs, other clinical factors, and hemodynamic variables do not. These results suggest that BMI is an independent factor associated with propofol pharmacokinetics in several potential covariates.

CLINICAL TRIALS REGISTRATION NUMBER

University Hospital Medical Information Network (UMIN000022948).

Model-based drug administration: current status of target-controlled infusion and closed-loop control

PURPOSE OF REVIEW

Drug administration might be optimized by incorporating pharmacokinetic-dynamic (PK/PD) principles and control engineering theories. This review gives an update of the actual status of target-controlled infusion (TCI) and closed-loop computer-controlled drug administration and the ongoing research in the field.

RECENT FINDINGS

TCI is becoming mature technology clinically used in many countries nowadays with proven safety. Nevertheless, changing populations might require adapting the established PK/PD models. As TCI requires accurate PK/PD models, new models have been developed which should now be incorporated into the pumps to allow more general use of this technology. Closed-loop administration of hypnotic drugs using an electro-encephalographic-derived-controlled variable has been well studied and has been shown to outperform manual administration. Computer administration for other drugs and fluids have been studied recently. Feasibility has been shown for systems controlling multiple components of anaesthesia, but more work is required to show clinical safety and efficiency.

SUMMARY

Evidence in the literature is increasing that TCI and closed-loop technology could assist the anaesthetists to optimize drug administration during anaesthesia.

Effect-Site Target-Controlled Infusion in the Obese: Model Derivation and Performance Assessment

BACKGROUND

The aim of this study is to derive a propofol pharmacokinetic (PK) pharmacodynamic (PD) model to perform effect-site target-controlled infusion (TCI) in obese patients, and to analyze its performance along with that of other available PK models.

METHODS

In the first step of the study, a 3-compartment PK model linked to a sigmoidal inhibitory Emax PD model by a first-order rate constant (keo) was used to fit propofol concentration-bispectral index (BIS) data. Population modeling analysis was performed by nonlinear mixed effects regression in NONMEM (ICON, Dublin, Ireland). PK data from 3 previous studies in obese adult patients (n = 47), including PD (BIS) data from 1 of these studies (n = 20), were pooled and simultaneously analyzed. A decrease in NONMEM objective function (ΔOBJ) of 3.84 points, for an added parameter, was considered significant at the 0.05 level. In the second step of the study, we analyzed the predictive performance (median predictive errors [MDPE] and median absolute predictive errors [MDAPE]) of the current model and of other available models using an independent data set (n = 14).

RESULTS

Step 1: The selected PKPD model produced an adequate fit of the data. Total body weight resulted in the best size scalar for volumes and clearances (ΔOBJ, -18.173). Empirical allometric total body weight relationships did not improve model fit (ΔOBJ, 0.309). A lag time parameter for BIS response improved the fit (ΔOBJ, 89.593). No effect of age or gender was observed. Step 2: Current model MDPE and MDAPE were 11.5% (3.7-25.0) and 26.8% (20.7-32.6) in the PK part and 0.4% (-10.39 to 3.85) and 11.9% (20.7-32.6) in the PD part. The PK model developed by Eleveld et al resulted in the lowest PK predictive errors (MDPE = <10% and MDAPE = <25%).

CONCLUSIONS

We derived and validated a propofol PKPD model to perform effect-site TCI in obese patients. This model, derived exclusively from obese patient's data, is not recommended for TCI in lean patients because it carries the risk of underdosing.

A Comparative Study of Midazolam and Target-Controlled Propofol Infusion in the Treatment of Refractory Status Epilepticus

Background:

The recommended treatment for refractory status epilepticus (RSE) is the use of anesthetic agents, but evidence regarding the agent of choice is lacking. This study was designed to compare target-controlled infusion of propofol versus midazolam for the treatment of RSE regarding seizure control and complications.

Methods:

This prospective, randomized study recruited 23 adult patients with RSE due to any etiology and treated with either propofol or midazolam titrated to clinical seizure cessation and gradual tapering thereafter. The primary outcome measure was seizure control and the secondary outcomes were duration of the Intensive Care Unit stay and duration of mechanical ventilation, occurrence of super RSE (SRSE), and complications.

Results:

We recruited 23 patients (male:female = 18:5) into this study (propofol Group-11; midazolam Group-12). Overall, seizure control was noted in 34.8%, with successful seizure control in 45% of patients in the propofol group and 25% in midazolam group (P = 0.4). Mortality was similar in both the groups (propofol group [8/11; 72.7%] compared to the midazolam group [7/12; 58.3%] [P = 0.667]). The duration of hospital stay was significantly shorter in the propofol group compared to midazolam (P = 0.02). The overall incidence of SRSE was 69.5% in this study. The complication rate was not significantly different between the groups.

Conclusions:

The choice of anesthetic agent does not seem to affect the overall outcome in RSE and SRSE. Target-controlled propofol infusion was found to be equal in its efficacy to midazolam for the treatment of RSE. High mortality might be due to SRSE secondary to the underlying brain pathology.

An Allometric Model of Remifentanil Pharmacokinetics and Pharmacodynamics

BACKGROUND

Pharmacokinetic and pharmacodynamic models are used to predict and explore drug infusion schemes and their resulting concentration profiles for clinical application. Our aim was to develop a pharmacokinetic-pharmacodynamic model for remifentanil that is accurate in patients with a wide range of age and weight.

METHODS

Remifentanil pharmacokinetic data were obtained from three previously published studies of adults and children, one of which also contained pharmacodynamic data from adults. NONMEM was used to estimate allometrically scaled compartmental pharmacokinetic and pharmacodynamic models. Weight, age, height, sex, and body mass index were explored as covariates. Predictive performance was measured across young children, children, young adults, middle-aged, and elderly.

RESULTS

Overall, 2,634 remifentanil arterial concentration and 3,989 spectral-edge frequency observations from 131 individuals (55 male, 76 female) were analyzed. Age range was 5 days to 85 yr, weight range was 2.5 to 106 kg, and height range was 49 to 193 cm. The final pharmacokinetic model uses age, weight, and sex as covariates. Parameter estimates for a 35-yr-old, 70-kg male (reference individual) are: V1, 5.81 l; V2, 8.82 l; V3, 5.03 l; CL, 2.58 l/min; Q2, 1.72 l/min; and Q3, 0.124 l/min. Parameters mostly increased with fat-free mass and decreased with age. The pharmacodynamic model effect compartment rate constant (ke0) was 1.09 per minute (reference individual), which decreased with age.

CONCLUSIONS

We developed a pharmacokinetic-pharmacodynamic model to predict remifentanil concentration and effect for a wide range of patient ages and weights. Performance exceeded the Minto model over a wide age and weight range.

Comparison in anesthetic effects of propofol among patients with different ABO blood groups

Our study was aimed to investigate anesthetic effects of propofol in patients with different blood groups.A total of 72 participants were enrolled from patients arranged for surgeries of cholecystectomy, tonsillectomy, and spinal operation. Each blood group (A, B, AB, and O) contained 18 participants. Mean arterial pressure (MAP), heart rate (HR), and bispectral index (BIS) were assayed with Philips monitor. These indexes were observed before propofol anesthesia (T0), and then were recorded when concentration of propofol was 1 μg/mL (T1), 2 μg/mL (T2), 3 μg/mL (T3), and 4 μg/mL (T4). The differences in MAP, HR, and BIS at T0 among groups were compared with the χ test. Multiple comparisons were adopted to calculate the differences in MAP, HR, and BIS between groups at T1, T2, T3, and T4.No significant differences in age, sex, and weight of all groups were found (P > .05). Before propofol anesthesia (T0), all the participants exhibited no differences in MAP, HR, and BIS (P > .05). Subsequently, we found obvious differences in ΔMAP, ΔHR, and ΔBIS between groups. The patients in the B blood group showed highest ΔMAP and ΔHR at each time point (P < .05 for both). As for ΔBIS, patients in A blood group exhibited highest value at T3 and T4 (P < .05).The blood group remarkably affects the anesthetic effects of propofol.

Pharmacodynamic analysis of target-controlled infusion of propofol in patients with hepatic insufficiency

The effect of liver dysfunction on target-controlled infusion (TCI) of propofol remains poorly documented. The pharmacodynamic performance of propofol TCI was evaluated in a cohort of Chinese patients with hepatic insufficiency. Fifty-three patients with hepatic insufficiency were enrolled in the current prospective, observational study. Anesthesia was induced with propofol via TCI to a plasma concentration of 3 µg/ml. Following loss of consciousness (LOC), fentanyl and cisatracurium were administered. Pharmacodynamic parameters were recorded during TCI, including time to LOC, bispectral index (BIS), heart rate (HR) and blood pressure. Patients were divided into two groups based on model of end stage liver disease (MELD) score: Those with a MELD score of ≤9 and those with a MELD score of ≥10. BIS, mean arterial pressure and HR were demonstrated to vary according to time, but were not affected by liver dysfunction. Hypotension was prominent in patients with a MELD score of ≥10 30 min after induction. The proportion of bradycardia and hypotension at the other time points was not significantly different between MELD scores of ≤9 and ≥10. Notably, no bradycardia was observed in MELD of ≥10. Thus, bradycardia and hypotension was observed in patients with hepatic insufficiency over time, although patients with different severities of hepatic insufficiency did not present with different depths of anesthesia. TCI of propofol to 3 µg/ml may be not suitable for patients with hepatic insufficiency, particularly those with severe liver dysfunction. Predictive concentrations (Cp) of TCI propofol requires further investigation and adjustment in patients with hepatic insufficiency (trial registration no. ChiCTR-OCH-12002255).

Comparison of the Cortínez and the Schnider models with a targeted effect-site TCI of 3 mcg/ml in biophase in healthy volunteers

OBJECTIVE

To compare the Cortínez and Schnider models in effect-site TCI mode (3 mcg/ml) in healthy volunteers.

METHODS

Ten healthy volunteers were prospectively studied on 2 occasions. Propofol was administered with the Cortínez or the Schnider models, as randomly assigned. Times and predicted concentrations at the time of loss and recovery of consciousness (LOC and ROC), mass of drug administered, BIS, and haemodynamic variables were compared. Statistical analysis was with paired Wilcoxon test. A P<.05 was considered significant.

RESULTS

The propofol bolo was higher (1.4 [1.3-1.6] versus 0.9 [0.7-1.3] mg/kg, P=.005) and the LOC occurred earlier (1.33 [0.67-6.83] versus 3.87 [1.66-11.08] minutes, P=.02) with the Cortínez model compared to the Schnider model. With the Cortínez model, LOC occurred at an effect site concentrations of 2.6 (1.65-3.0) mcg/ml. With the Schnider model, LOC occurred at 3.87 min (1.66-11.8) after reaching the target of 3 mcg/ml. (P=.001). BIS values, infusion rates, and haemodynamic variables were similar between models after 20minutes of infusion (P>.5). Recovery (ROC) was longer with the Cortínez model (11.6 [8.1-16.2] vs. 8.5 [4.7-15.5] min, P=.003).

CONCLUSIONS

The Cortínez model is a good alternative to the Schnider model for use in effect-site TCI mode in normal weight subjects. With the target used in this study (3 mcg/ml), the slower Ke0 incorporated into the Cortínez model better discriminated the LOC time.

Best anaesthetic drug strategy for morbidly obese patients

PURPOSE OF REVIEW

The purpose of this review is to describe an evidence-based drug strategy applicable to any obese patient, rather than to present one standard 'ideal' anaesthetic drug combination. The ultimate choice of specific drugs in any given situation will depend upon clinician experience, patient specifics, and drug availability. The fundamental principle in anaesthesia for the obese patient is to use the shortest acting, least fat soluble agents to ensure rapid recovery to safe levels of alertness and mobility.

RECENT FINDINGS

No new drugs have been introduced over the past few years, but we have seen an introduction of enhanced recovery after surgery-based protocols into bariatric surgery. Our understanding of how obesity affects pharmacokinetics/dynamics of our drugs is improving, with new and better use of established drugs. Allometric scaling is being tested in the different pharmacokinetic/dynamic models used in target controlled infusion devices, with improved performance as a result. Obstructive sleep apnoea has a significant impact upon outcome and utilization of clinical resources, including critical care beds. If an improved drug dosing strategy will reduce this impact, then this would be a step forward.

SUMMARY

This review introduces newer findings to help us use anaesthetic and analgesic drugs more safely in the morbidly obese. However, there remain many areas of uncertainty with a lack of consensus on many issues.

Propofol target-controlled infusion modeling in rabbits: Pharmacokinetic and pharmacodynamic analysis

This study aimed to establish a new propofol target-controlled infusion (TCI) model in animals so as to study the general anesthetic mechanism at multi-levels in vivo. Twenty Japanese white rabbits were enrolled and propofol (10 mg/kg) was administrated intravenously. Artery blood samples were collected at various time points after injection, and plasma concentrations of propofol were measured. Pharmacokinetic modeling was performed using WinNonlin software. Propofol TCI within the acquired parameters integrated was conducted to achieve different anesthetic depths in rabbits, monitored by narcotrend. The pharmacodynamics was analyzed using a sigmoidal inhibitory maximal effect model for narcotrend index (NI) versus effect-site concentration. The results showed the pharmacokinetics of propofol in Japanese white rabbits was best described by a two-compartment model. The target plasma concentrations of propofol required at light anesthetic depth was 9.77±0.23 μg/mL, while 12.52±0.69 μg/mL at deep anesthetic depth. NI was 76.17±4.25 at light anesthetic depth, while 27.41±5.77 at deep anesthetic depth. The effect-site elimination rate constant (ke0) was 0.263/min, and the propofol dose required to achieve a 50% decrease in the NI value from baseline was 11.19 μg/mL (95% CI, 10.25-13.67). Our results established a new propofol TCI animal model and proved the model controlled the anesthetic depth accurately and stably in rabbits. The study provides a powerful method for exploring general anesthetic mechanisms at different anesthetic depths in vivo.

Perioperative support reduces mortality of obese BALB/c mice after ovariectomy

The incidence of obesity is on the rise in most western countries and represents major risks to health. Obesity causes complex metabolic dysfunctions and can be associated with a large number of secondary diseases. To investigate causal mechanisms of obesity and develop better options for treatment, researchers study the condition in animal models. In addition to genetically engineered animal models, diet-induced obesity is often used because it occurs similarly in animals as it does in humans. For several types of investigations that use obesity models, investigators must carry out surgical interventions and they frequently encounter severe perioperative complications induced by anesthesia. In an example of this problem, we observed 100% mortality in obese BALB/c mice after ovariectomy, despite no obvious surgical complications. We supposed that a failure to recover from surgery was the primary cause of this increased mortality. Therefore, to support their recovery from surgery we administered atropine to obese mice in order to facilitate blood circulation, and we also increased the oxygen content of the ambient air. With this specific support before and after surgery, we increased the survival rate of obese ovariectomized mice up to 83%. These results confirm the assumption that obesity is a risk factor for the recovery of obese animal models after ovariectomy, and they highlight the need to provide additional interventions for such experimental animals.

Spontaneous Ventilation Using Target-Controlled Propofol Infusion for Microlaryngoscopy in Adults: A Retrospective Audit

Summary

We conducted a retrospective audit of 285 adult elective microlaryngoscopy cases in our institution over a three-and-a-half year period. Conventional anaesthesia with intubation and mechanical ventilation was the most common technique, used in 71% of cases. Tubeless spontaneous ventilation during total intravenous anaesthesia with a target-controlled infusion of propofol (SVTCI) was the most common alternative. Spontaneous ventilation with target-controlled infusion was used for 79 (27.7%) anaesthetic inductions and was continued through the maintenance phase for 60 patients (21.1%). Jet and intermittent ventilation were both used infrequently (1% each). The most common SVTCI technique since 2013 involved adjusting the target-controlled infusion rate during induction using a formula we developed based on intermittently increasing the target rate, such that the predicted plasma concentration minus the predicted effect site concentration was maintained at 1 μg/ml. We found that this method maintained ventilation during induction more reliably than other SVTCI strategies, and was associated with fewer complications than other spontaneous ventilation techniques or mechanical ventilation: it was associated with only one (3.1%) failed induction and one (3.9%) episode of apnoea. Jet ventilation was associated with the most severe complications, including two cases of barotrauma.

Obesity and chronic pain: systematic review of prevalence and implications for pain practice

The combination of obesity and pain may worsen a patient's functional status and quality of life more than each condition in isolation. We systematically searched PubMed/MEDLINE and the Cochrane databases for all reports published on obesity and pain. The prevalence of combined obesity and pain was substantial. Good evidence shows that weight reduction can alleviate pain and diminish pain-related functional impairment. However, inadequate pain control can be a barrier to effective lifestyle modification and rehabilitation. This article examines specific pain management approaches for obese patients and reviews novel interventional techniques for treatment of obesity. The infrastructure for simultaneous treatment of obesity and pain already exists in pain medicine (eg, patient education, behavioral medicine approaches, physical rehabilitation, medications, and interventional treatment). Screening for obesity, pain-related disability, and behavioral disorders as well as monitoring of functional performance should become routine in pain medicine practices. Such an approach requires additional physician and staff training. Further research should focus on better understanding the interplay between these 2 very common conditions and the development of effective treatment strategies.