Variability of predicted propofol concentrations and measured sevoflurane concentrations during general anaesthesia: a single-centre retrospective cohort study.

BACKGROUND: Variability is high in predicted propofol concentrations during clinical anaesthesia titrated by target-controlled infusion (TCI) to maintain a processed EEG parameter (bispectral index [BIS]) within a specified range. We have shown that the potential for improving the pharmacokinetic model is minimal. The drug titration paradox revealed that titration challenges the classical relationship between drug dose and effect in both individuals and the population. We hypothesised that dynamic factors during surgery beyond the static genetic, epigenetic, and other factors such as age, height, and weight affect the necessary dose. We compared the variability of measured end-tidal sevoflurane concentrations with predicted effect-site propofol concentrations when titrated to a BIS range of 40-60, with the hypothesis that the variability in measured sevoflurane concentrations would not be less than the variability in estimated propofol concentrations. METHODS: Clinical data from 2280 surgical procedures >1 h in duration were included in the analysis. Anaesthesia with sevoflurane or propofol was based on an institutional protocol. The titration performance for both drugs was assessed by comparing BIS values 30 min after skin incision. The variability of the required concentrations at the same time point was calculated and compared. RESULTS: The achieved 30-min post-incision BIS ranges were not significantly different for sevoflurane or propofol TCI (30 [99% CI: 28-33] and 31 [99% CI: 27-36], respectively). The variability of sevoflurane concentrations was not significantly different from measured predicted propofol concentrations during BIS-guided anaesthesia (normalized concentration range of 0.89 [99% CI: 0.78-0.99] and 0.93 [99% CI 0.87-1.02). CONCLUSIONS: Improvements in prediction accuracy of pharmacokinetic models beyond that of those already in clinical use are unlikely to reduce variability in target anaesthetic concentrations across patients in clinical practice.

Pro-Con Debate: Should All General Anesthesia Be Done Using Target-Controlled Propofol Infusion Guided by Objective Monitoring of Depth of Anesthesia?

In this Pro-Con commentary article, we discuss whether all general anesthesia should be done using target-controlled propofol anesthesia guided by monitoring of depth of anesthesia. This is an ongoing debate since more than 25 years, representing a scientific, cultural as well as geographical divide in the anesthesia community. The Pro side argues that total intravenous anesthesia causes less postoperative nausea and higher patient satisfaction than anesthesia using volatile anesthetics. Target-controlled infusion (TCI) of anesthetic agents allows for better titration of intravenous anesthesia using pharmacokinetic models. Processed EEG monitors, such as bispectral index monitoring, allows for better assessing the effect of TCI anesthesia than solely assessment of clinical parameters, such as ECG or blood pressure. The combination of TCI propofol and objective depth of anesthesia monitoring allows creating a pharmacokinetic-pharmacodynamic profile for each patient. Finally, anesthesia using volatile anesthetics poses health risks for healthcare professionals and contributes to greenhouse effect. The Con side argues that for procedures accompanied with ischemia and reperfusion injury of an organ or tissue and for patients suffering from a severe inflammation' the use of volatile anesthetics might well have its advantages above propofol. In times of sudden shortage of drugs, volatile anesthetics can overcome the restriction in the operating theater or even on the intensive care unit, which is another advantage. Volatile anesthetics can be used for induction of anesthesia when IV access is impossible, end-tidal measurements of volatile anesthetic concentration allows confirmation that patients receive anesthetics. Taking environmental considerations into account, both propofol and volatile anesthetics bear certain harm to the environment, be it as waste product or as greenhouse gases. The authors therefore suggest to carefully considering advantages and disadvantages for each patient in its according environment. A well-balanced choice based on the available literature is recommended. The authors recommend careful consideration of advantages and disadvantages of each technique when tailoring an anesthetic to meet patient needs. Where appropriate, anesthesia providers are encouraged to account for unique features of anesthetic drug behavior, patient-reported and observed postoperative outcomes, and economic and environmental considerations when choosing any of the 2 described techniques.

Analgesic efficacy of systemic lidocaine using lean body mass based dosing regime versus placebo in bariatric surgery: a prospective, randomised, double-blind, placebo-controlled, single-centre study.

BACKGROUND: Intravenous lidocaine is used as an adjuvant analgesic agent in perioperative settings. It has been investigated in various patient populations and surgical interventions, but there are limited data on its efficacy, particularly for patients undergoing bariatric surgery. Obese patients are at high risk of postoperative respiratory complications and can be expected to benefit from anaesthetic techniques that minimise opioid administration. METHODS: We studied administration of lidocaine hydrochloride 1% i.v. to general anaesthesia at a dose of 1.5 mg kg-1 (lean body mass×1.28) or placebo in patients undergoing bariatric surgery. Subjects randomly assigned to each group were surveyed for 48 h after surgery for experienced pain (primary outcome), and administered opioids, postoperative nausea and vomiting (PONV), resumption of bowel function, and length of hospital stay (secondary outcomes). RESULTS: We recruited and randomised 140 subjects to either the lidocaine or placebo group; 137 completed the study. Subjects with pain numeric rating scale (NRS) >3 within the first 4 h postoperatively were similar in both groups (proportion of any NRS >3 within first 4 h lidocaine group: 47/68 (69%) vs placebo group: 44/69 (63%), P=0.507; within first h P=0.177, within second h P=0.513, within third h P=0.145, within fourth h P=0.510). There was no difference in maximal pain score, opioid consumption, recovery of bowel function, incidence of PONV, or length of hospital stay. CONCLUSIONS: Lidocaine does not improve postoperative pain scores, analgesia, or any secondary outcomes in patients undergoing bariatric surgery. CLINICAL TRIAL REGISTRATION: NCT03667001.

The drug titration paradox: more drug does not correlate with more effect in individual clinical data.

BACKGROUND: A fundamental concept in pharmacology is that increasing dose increases drug effect. This is the basis of anaesthetic titration: the dose is increased when increased drug effect is desired and decreased when reduced drug effect is desired. In the setting of titration, the correlation of doses and observed drug effects can be negative, for example increasing dose reduces drug effect. We have termed this the drug titration paradox. We hypothesised that this could be explained, at least in part, by intrasubject variability. If the drug titration paradox is simply an artifact of pooling population data, then a mixed-effects analysis that accounts for interindividual variability in drug sensitivity should 'flip' the observed correlation, such that increasing dose increases drug effect. METHODS: We tested whether a mixed-effects analysis could correctly reveal the underlying pharmacology using previously published data obtained during automatic feedback control of mean arterial pressure (MAP) with alfentanil (effect site concentration, CeAlf) during surgery. The relationship between MAP and CeAlf was explored with linear regression and a linear mixed-effects model. RESULTS: A linear mixed-effects model did not identify the correct underlying pharmacology because of the presence of the titration paradox in the individual data. CONCLUSIONS: The relationship between drug dose and drug effect must be determined under carefully controlled experimental conditions. In routine care, where the effect is profoundly influenced by varying clinical conditions and drugs are titrated to achieve the desired effect, it is nearly impossible to draw meaningful conclusions about the relationship between dose and effect.

Targeting Higher Intraoperative Blood Pressures Does Not Reduce Adverse Cardiovascular Events Following Noncardiac Surgery.

BACKGROUND: Intraoperative arterial hypotension is strongly associated with postoperative major adverse cardiovascular events (MACE); however, whether targeting higher intraoperative mean arterial blood pressures (MAPs) may prevent adverse events remains unclear. OBJECTIVES: This study sought to determine whether targeting higher intraoperative MAP lowers the incidence of postoperative MACE. METHODS: This single-center randomized controlled trial assigned adult patients at cardiovascular risk undergoing major noncardiac surgery to an intraoperative MAP target of ≥60 mm Hg (control) or ≥75 mm Hg (MAP ≥75). The primary outcome was acute myocardial injury on postoperative days 0-3 and/or 30-day MACE/acute kidney injury (AKI) (acute coronary syndrome, congestive heart failure, coronary revascularization, stroke, AKI, and all-cause mortality). The secondary outcome was 1-year MACE. RESULTS: In total, 458 patients were randomized (intention-to-treat population: 451). The cumulative intraoperative duration with MAP <65 mm Hg was significantly shorter in the MAP ≥75 group (median 9 minutes [interquartile range: 3 to 24 minutes] vs 23 minutes [interquartile range: 8-49 minutes]; P < 0.001). The primary outcome incidence was 48% for MAP ≥75 and 52% for control (risk difference -4.2%; 95% CI: -13% to +5%), the primary contributor being AKI (incidence 44%). Acute myocardial injury occurred in 15% (MAP ≥75) and 19% (control) of patients. The secondary outcome incidence was 17% for MAP ≥75 and 15% for control (risk difference +2.7; 95% CI: -4% to +9.5%). CONCLUSIONS: These findings do not support universally targeting higher intraoperative blood pressures to reduce postoperative complications. Despite a 60% reduction in hypotensive time with MAP <65 mm Hg, no significant reductions in acute myocardial injury or 30-day MACE/AKI could be found. (Biomarkers, Blood Pressure, BIS: Risk Stratification/Management of Patients at Cardiac Risk in Major Noncardiac Surgery [BBB]; NCT02533128).

The Drug Titration Paradox: Correlation of More Drug With Less Effect in Clinical Data.

While analyzing clinical data where an anesthetic was titrated based on an objective measure of drug effect, we observed paradoxically that greater effect was associated with lesser dose. With this study we sought to find a mathematical explanation for this negative correlation between dose and effect, to confirm its existence with additional clinical data, and to explore it further with Monte Carlo simulations. Automatically recorded dosing and effect data from more than 9,000 patients was available for the analysis. The anesthetics propofol and sevoflurane and the catecholamine norepinephrine were titrated to defined effect targets, i.e., the processed electroencephalogram (Bispectral Index, BIS) and the blood pressure. A proportional control titration algorithm was developed for the simulations. We prove by deduction that the average dose-effect relationship during titration to the targeted effect will associate lower doses with greater effects. The finding of negative correlations between propofol and BIS, sevoflurane and BIS, and norepinephrine and mean arterial pressure confirmed the titration paradox. Monte Carlo simulations revealed two additional factors that contribute to the paradox. During stepwise titration toward a target effect, the slope of the dose-effect data for the population will be "reversed," i.e., the correlation between dose and effect will not be positive, but will be negative, and will be "horizontal" when the titration is "perfect." The titration paradox must be considered whenever data from clinical titration (flexible dose) studies are interpreted. Such data should not be used naively for the development of dosing guidelines.

Relationship Between Propofol Target Concentrations, Bispectral Index, and Patient Covariates During Anesthesia.

BACKGROUND: Internationally, propofol is commonly titrated by target-controlled infusion (TCI) to maintain a processed electroencephalographic (EEG) parameter (eg, bispectral index [BIS]) within a specified range. The overall variability in propofol target effect-site concentrations (CeT) necessary to maintain adequate anesthesia in real-world conditions is poorly characterized, as are the patient demographic factors that contribute to this variability. This study explored these issues, hypothesizing that the variability in covariate-adjusted propofol target concentrations during BIS-controlled anesthesia would be substantial and that most of the remaining interpatient variability in drug response would be due to random effects, thus suggesting that the opportunity to improve on the Schnider model with further demographic data is limited. METHODS: With ethics committee approval and a waiver of informed consent, a deidentified, high-resolution, intraoperative database consisting of propofol target concentrations, BIS values, and vital signs from 13,239 patients was mined to identify patients who underwent general endotracheal anesthesia using propofol (titrated to BIS), fentanyl, remifentanil, and rocuronium that lasted at least 1 hour. The propofol target concentrations and BIS values 30 minutes after incision (CeT30 and BIS30) were considered representative of stable intraoperative conditions. The data were plotted and analyzed by descriptive statistics. Confidence intervals were computed using a bootstrap method. A linear model was fit to the data to test for correlation with factors of interest (eg, age and weight). RESULTS: A total of 4584 patients met inclusion criteria and were entered into the analysis. Of the propofol target concentrations, 95% were between 1.5 and 3.5 µg·mL-1. Higher BIS30 values were correlated with higher propofol concentrations. Except for age, all the patient-related variables analyzed entered the regression model linearly. Only 10.2% of the variability in CeT30 was explained by the patient factors of age and weight combined. CONCLUSIONS: Our hypothesis was confirmed. The variability in covariate-adjusted propofol CeT30 titrated to BIS in real-world conditions is considerable, and only a small portion of the remaining variability in drug response is explained by patient demographic factors. This finding may have important implications for the development of new pharmacokinetic (PK) models for propofol TCI.

Adverse events of postoperative thoracic epidural analgesia: A retrospective analysis of 7273 cases in a tertiary care teaching hospital.

BACKGROUND: Thoracic epidural analgesia is a well established technique for postoperative pain relief after major abdominal and thoracic surgery. Safety remains a major concern because of serious adverse events including epidural haematoma, abscess and permanent neurological deficit. OBJECTIVE: The aim of this study was to evaluate the incidence and the long-term outcome of serious adverse events associated with thoracic epidural analgesia. DESIGN: Retrospective cohort study. SETTING: The study was conducted at a single institution, a tertiary care teaching hospital. Data were collected over a 10-year period from 2003 until 2012. PATIENTS: Data from 7430 patients were prospectively entered into a standardised acute pain service database. A total of 7273 study participants met the inclusion criteria and were included in the final analyses. The inclusion criteria involved surgical patients receiving a postoperative thoracic epidural analgesia catheter treatment for pain control. Exclusion criteria were defined as obstetric, non-surgical, non-epidural analgesia patients and epidural analgesia catheters that had not been placed by an anaesthesiologist. MAIN OUTCOME MEASURES: The database was queried for serious adverse events which were defined as spinal or epidural haemorrhage; spinal or epidural abscess; permanent neurological deficits; cardiac arrest; death and incomplete removal of the epidural analgesia catheter. Patients' charts were comprehensively reviewed in case of a major adverse event. Patients with an unclear outcome received a mailed questionnaire or were contacted by telephone to determine long-term sequelae. RESULTS: Seven serious adverse events were identified: epidural abscess [n = 1; incidence 1 : 7273 (0.014%, 95% confidence interval, CI, 0 to 0.08%)], persistent neurological damage [n = 1; incidence 1 : 7273 (0.014%, 95% CI, 0 to 0.08%)], cardiac arrest [n = 1; incidence 1 : 7273 (0.014%, 95% CI, 0 to 0.08%)] and catheter breakage leaving a catheter fragment in situ [n = 4; incidence 1 : 1818 (0.055%, 95% CI, 0.01 to 0.14%)]. Apart from the one patient with persistent neurologic deficit, the patients with serious adverse events associated with thoracic epidural analgesia in our cohort suffered no long-term consequences. CONCLUSION: In our single-centre study of thoracic epidural analgesia, serious adverse events occurred in 0.1% cases (1 : 1000), whereas long-term outcome was compromised in 0.014% (1.4 : 10 000) which is similar to the serious adverse event rates and outcomes reported in the current literature.

Target-Controlled Infusion: A Mature Technology.

Target-controlled infusions (TCIs) have been used in research and clinical practice for >2 decades. Nonapproved TCI software systems have been used during the conduct of almost 600 peer-reviewed published studies involving large numbers of patients. The first-generation pumps were first approved in 1996, and since then an estimated 25,000 units have been sold and used. Second-generation pumps were first approved in 2003. During 2004 to 2013, >36,000 units were sold. Currently, TCI systems are approved or available in at least 96 countries. TCI systems are used to administer propofol and opioids for IV sedation and general anesthesia for millions of patients every year. In countries where TCI systems are approved, nonapproved software is still commonly used in studies of the pharmacology of hypnotics and opioids, because research software offers greater flexibility than approved TCI systems. Research software is also readily integrated into data management modules. Although TCI is a part of established practice around the world, TCI devices have not received regulatory approval in the United States. In the United States, TCI administration of propofol and opioids for sedation and anesthesia is only possible using research software in IRB-approved research studies.

The Safety of Target-Controlled Infusions.

Target-controlled infusion (TCI) technology has been available in most countries worldwide for clinical use in anesthesia for approximately 2 decades. This infusion mode uses pharmacokinetic models to calculate infusion rates necessary to reach and maintain the desired drug concentration. TCI is computationally more complex than traditional modes of drug administration. The primary difference between TCI and conventional infusions is that TCI decreases the infusion rate at regular intervals to account for the uptake of drug into saturable compartments. Although the calculated infusion rates are consistent with manually controlled infusion rates, there are concerns that TCI administration of IV anesthetics could introduce unique safety concerns. After approximately 2 decades of clinical use, it is appropriate to assess the safety of TCI. Our aim in this article was to describe safety-relevant issues related to TCI, which should have emerged after its use in millions of patients. We collected information from published medical literature, TCI manufacturers, and publicly available governmental Web sites to find evidence of safety issues with the clinical use of TCI. Although many case reports emphasize that IV anesthesia is technically more demanding than inhaled anesthesia, including human errors associated with setting up IV infusions, no data suggest that a TCI mode of drug delivery introduces unique safety issues other than selecting the wrong pharmacokinetic model. This is analogous to the risk of selecting the wrong drug with current infusion pumps. We found no evidence that TCI is not at least as safe as anesthetic administration using constant rate infusions.