Opioid-volatile anesthetic synergy: a response surface model with remifentanil and sevoflurane as prototypes

Remifentanil-induced hyperalgesia: the current state of affairs

Remifentanil-induced hyperalgesia (RIH) is a part of a general opioid-induced hyperalgesia (OIH) syndrome, seemingly resulting from abrupt cessation of continuous remifentanil infusion at rates equal or exceeding 0.3 mcg/kg/min. The intricate mechanisms of its development are still not completely understood. However, hyperactivation of the N -methyl d -aspartate receptor system, descending spinal facilitation and increased concentration of dynorphin (a κ-opioid ligand) are commonly proposed as possible mechanisms. Several ways of prevention and management have been suggested, such as slow withdrawal of remifentanil infusion, the addition of propofol, pretreatment with or concomitant administration of ketamine, buprenorphine, cyclooxygenase-2 inhibitors (NSAIDs), methadone, dexmedetomidine. In clinical and animal studies, these strategies exhibited varying success, and many are still being investigated.

Antinociceptive Agents as General Anesthetic Adjuncts: Supra-additive and Infra-additive Interactions

The hypothesis "General anesthesia consists of producing both loss of consciousness and the inhibition of noxious stimuli reaching the brain and causing arousal" was used as a basis for the review of published data on general anesthetic interactions with antinociceptive agents: opioids, α 2 adrenergic agonists, and systemic sodium channel blockers. This review is focused on a specific type of anesthetic interaction-the transformation of antinociceptive agents into general anesthetic adjuncts. The primary aim is to answer 2 questions. First, how does an antinociceptive agent transform the effect of an anesthetic in providing a certain component of anesthesia-hypnosis, immobility, or hemodynamic response to noxious stimulation? Second, does a combination of an anesthetic with an adjunct result in a simple summation of their respective effects or in a supra-additive or infra-additive interaction? The Medline database was searched for data describing the interactions of antinociceptive agents and general anesthetics. The following classes of antinociceptive agents were considered: opioids, α 2 adrenergic agonists, and systemic sodium channel blockers. Drugs used in combination with antinociceptive agents were general anesthetics and benzodiazepines. The following terms related to drug interactions were used: anesthetic interactions, synergy, antagonism, isobolographic analysis, response surface analysis, and fractional analysis. The interactions of antinociceptive agents with general anesthetics result in a decrease of general anesthetic requirements, which differ for each of the components of general anesthesia: hypnosis, immobility, and hemodynamic response to noxious stimulation. Most studies of the nature of anesthetic interactions are related to opioid-general anesthetic combinations, and their conclusions usually confirm supra-additivity.

The nuts and bolts of multimodal anaesthesia in the 21st century: a primer for clinicians

PURPOSE OF REVIEW

This review article explores the application of multimodal anaesthesia in general anaesthesia, particularly in conjunction with locoregional anaesthesia, specifically focusing on the importance of EEG monitoring. We provide an evidence-based guide for implementing multimodal anaesthesia, encompassing drug combinations, dosages, and EEG monitoring techniques, to ensure reliable intraoperative anaesthesia while minimizing adverse effects and improving patient outcomes.

RECENT FINDINGS

Opioid-free and multimodal general anaesthesia have significantly reduced opioid addiction and chronic postoperative pain. However, the evidence supporting the effectiveness of these approaches is limited. This review attempts to integrate research from broader neuroscientific fields to generate new clinical hypotheses. It discusses the correlation between high-dose intraoperative opioids and increased postoperative opioid consumption and their impact on pain indices and readmission rates. Additionally, it explores the relationship between multimodal anaesthesia and pain processing models and investigates the potential effects of nonpharmacological interventions on preoperative anxiety and postoperative pain.

SUMMARY

The integration of EEG monitoring is crucial for guiding adequate multimodal anaesthesia and preventing excessive anaesthesia dosing. Furthermore, the review investigates the impact of combining regional and opioid-sparing general anaesthesia on perioperative EEG readings and anaesthetic depth. The findings have significant implications for clinical practice in optimizing multimodal anaesthesia techniques (Supplementary Digital Content 1: Video Abstract, http://links.lww.com/COAN/A96 ).

Pharmacokinetic and pharmacodynamic drug display and simulation systems in anesthesia practice

PURPOSE OF REVIEW

This review explores the use of tools and displays based on pharmacokinetic and pharmacodynamic (PK/PD) modelling of drugs used in anesthesia. The primary focus is on those tools designed to illustrate the interactions between two or more drugs, or classes of drugs, and in particular, their use in a real-time clinical support role. Off-line, educational tools are also explored.

RECENT FINDINGS

Despite initial promise and encouraging supporting data, the use of real-time display of PK/PD is not common except in target-controlled infusion (TCI) pumps.

SUMMARY

PK/PD simulation is a useful tool for exposition of the relationship between drug dosing and effect. The initial promise of real-time tools has yet to be realized in routine clinical practice.

The Effect of Ramosetron on Remifentanil in Preventing Emergence Cough from Sevoflurane Anesthesia in Female Patients

BACKGROUND

Remifentanil reduces cough during extubation. Ramosetron, a 5-HT3 receptor antagonist, is a potent antiemetic. Regarding the antitussive property of 5-HT receptor agonists, ramosetron can mediate the cough reflex, as increasing the remifentanil requirement. The aim of this study was to evaluate the effect of ramosetron on the optimal effect-site concentration (Ce) of remifentanil for preventing emergence cough from sevoflurane anesthesia in female patients.

METHODS

Forty-seven female patients undergoing laparoscopic cholecystectomy randomly received either ramosetron 0.3 mg (n = 23) or the same volume of normal saline (n = 24) intravenously at the end of surgery. The remifentanil Ce using target controlled infusion in 50% of patients (EC50) and 95% of patients (EC95) were assessed using Dixon's up-and-down or isotonic regression method with a boot¬strapping approach.

RESULTS

Using Dixon's up-and-down method, the EC50 of remifentanil in the control group (1.33 ± 0.38 ng/mL) was comparable to that of ramosetron group (1.50 ± 0.69 ng/mL) (P = 0.615). Using isotonic regression analysis, the EC50 (83% confidence interval) did not differ between the two groups (1.17 [0.86-1.43] ng/mL and 1.13 [0.68-1.56] ng/mL in control and ramosetron groups). However, the EC95 (95% confidence interval) was significantly lower in the control group than in the ramosetron group (1.90 [1.45-1.96] ng/mL and 2.92 [2.35-2.97] ng/mL).

CONCLUSION

Remifentanil Ce for preventing emergence cough was higher in the ramosetron group than the control group. It may indicate the lowering effect of ramosetron on antitussive activity of remifentanil.

A Response Surface Analysis of the Combination of Dexmedetomidine and Sufentanil for Attenuating the Haemodynamic Response to Endotracheal Intubation

Purpose

Dexmedetomidine combined with opioids has been extensively used to blunt cardiovascular responses to endotracheal intubation. To determine their interaction, we aimed to develop a response surface model between dexmedetomidine and sufentanil.

Methods

One hundred and twenty patients undergoing scheduled gynaecological surgery were recruited. According to a simulation of slice design, patients received different dose pairs of dexmedetomidine (0 to 1.1 μg/kg) and sufentanil (.1 to .5 μg/kg). The mean arterial blood pressure and heart rate of patients were recorded just before endotracheal intubation, immediately after intubation, and during the first 3 min after intubation. The primary outcomes were haemodynamic changes. The full dose–response relationship between dexmedetomidine and sufentanil was analysed using a logit model.

Results

This response surface model revealed that the interaction between dexmedetomidine and sufentanil was additive. The dose pairs that could effectively attenuate the haemodynamic response to endotracheal intubation primarily ranged from .3 to .4 μg/kg and .5 to 1.1 μg/kg for sufentanil and dexmedetomidine, respectively.

Conclusion

When used propofol as the main hypnotic drug during anaesthesia induction, dexmedetomidine could effectively reduce the requirement of sufentanil in an additive manner. However, it is not an effective drug for ablating the cardiovascular response to endotracheal intubation when used alone. The clinical trial registry. The trial registry name: Chinese Clinical Trial Registry. Registration number: ChiCTR1800015273. URL: http://www.chictr.org.cn

The usefulness of Smart Pilot View for fast recovery from desflurane general anesthesia

INTRODUCTION

Smart Pilot View (SPV) (Dräger Medical) provide information about the estimated drug effect of anesthetic drugs. We conducted a prospective randomized trial to evaluated the recovery time in SPV-guided general anesthesia compared with usual practice in patients with desflurane general anesthesia.

METHOD

Thirty-four American Society of Anesthesiologist's physical status I-II patients scheduled for elective surgery under general anesthesia were enrolled in the study. The patients were allocated to one of the following two groups: the Smart Pilot View group (group SPV) or the control group (group C). General anesthesia was induced by propofol and maintained by desflurane end-tidal concentration of 4.2%. During the procedure, desflurane concentration was adjusted to maintain BIS values between 40 and 60 and above MAC 90. In group SPV, desflurane concentration and infusion rate of remifentanil were decreased to achieve MAC 90 about 10 min before the end of the procedure. In group C, the desflurane concentration and infusion rate of remifentanil were maintained unchanged until the end of the procedure.

RESULTS

Fifteen patients were enrolled in group C, and seventeen of these were enrolled in group SPV. The time taken for the opening of the patient's eyes was 292 ± 53 s in group C and 218 ± 44 s in group SPV. The time taken for recovery of orientation was 451 ± 100 s in group C and 316 ± 57 s in group SPV. Both times were significantly faster in the group SPV.

CONCLUSION

Smart Pilot View guided anesthesia enabled faster recovery from desflurane general anesthesia.

Comparison of bispectral index-guided and fixed-gas concentration techniques in desflurane and remifentanil anesthesia: A randomized controlled trial

Anesthesia with desflurane and remifentanil can be maintained with either fixed or titrated desflurane concentration. We hypothesized that the fixed-gas concentration (FG) method would reduce the number of anesthetic titrations without hypnotic and hemodynamic instability compared to the bispectral index (BIS)-guided (BG) method. Forty-eight patients were randomly allocated to the FG or BG groups. In the FG group, desflurane vaporizer setting was fixed at 1 age-corrected minimum alveolar concentration (MAC). In the BG group, desflurane was titrated to target a BIS level at 50. Remifentanil was titrated to maintain a systolic arterial pressure (SAP) of 120 mmHg in both groups. Our primary endpoint was the hypnotic stability measured by the wobble of BIS in performance analysis, and the secondary endpoints included the wobble of SAP, mean BIS value during surgery, and the number of anesthetic titrations. The BIS in the FG group showed significantly less wobble (3.9 ± 1.1% vs 5.5 ± 1.5%, P <0.001) but lower value (33 ± 6 vs 46 ± 7, P <0.001) than BG group. The wobble of SAP showed no difference between groups [median (inter-quartile range), 5.0 (4.1-7.5)% vs 5.2 (4.2-8.3)%, P = 0.557]. The numbers of anesthetic titrations in the FG group were significantly lower than the BG group (0 ± 0 vs 8 ± 5, P<0.001 for desflurane, 13 ± 13 vs 22 ± 17, P = 0.047 for remifentanil). Less wobble in BIS and reduced anesthetic titration without hemodynamic instability during the FG technique may be practical in balanced anesthesia using desflurane and remifentanil anesthesia. Clinical trial: This study was registered at ClinicalTrials.gov (NCT02283866).

Comparison of haemodynamic- and electroencephalographic-monitored effects evoked by four combinations of effect-site concentrations of propofol and remifentanil, yielding a predicted tolerance to laryngoscopy of 90

This prospective study evaluates haemodynamic and electroencephalographic effects observed when administering four combinations of effect-site concentrations of propofol (Ce_PROP) and remifentanil (Ce_REMI), all yielding a single predicted probability of tolerance of laryngoscopy of 90% (P_TOL = 90%) according to the Bouillon interaction model. We aimed to identify combinations of Ce_PROP and Ce_REMI along a single isobole of P_TOL that result in favourable hypnotic and haemodynamic conditions. This knowledge could be of advantage in the development of drug advisory monitoring technology. 80 patients (18–90 years of age, ASA I–III) were randomized into four groups and titrated towards Ce_PROP (Schnider model, ug⋅ml⁻¹) and Ce_REMI (Minto model, ng⋅ml⁻¹) of respectively 8.6 and 1, 5.9 and 2, 3.6 and 4 and 2.0 and 8. After eleven minutes of equilibration, baseline measurements of haemodynamic endpoints and bispectral index were compared with three minutes of responsiveness measurements after laryngoscopy. Before laryngoscopy, bispectral index differed significantly (p < 0.0001) between groups in concordance with Ce_PROP. Heart rate decreased with increasing Ce_REMI (p = 0.001). The haemodynamic and arousal responses evoked by laryngoscopy were not significantly different between groups, but Ce_PROP = 3.6 μg⋅ml⁻¹ and Ce_REMI = 4 ng⋅ml⁻¹ evoked the lowest median value for ∆HR and ∆SAP after laryngoscopy. This study provides clinical insight on the haemodynamic and hypnotic consequences, when a model based predicted P_TOL is used as a target for combined effect-site controlled target- controlled infusion of propofol and remifentanil. Heart rate and bispectral index were significantly different between groups despite a theoretical equipotency for P_TOL, suggesting that each component of the anaesthetic state (immobility, analgesia, and hypnotic drug effect) should be considered as independent neurophysiological and pharmacological phenomena. However, claims of (in)accuracy of the predicted P_TOL must be considered preliminary because larger numbers of observations are required for that goal.

A pharmacokinetic-pharmacodynamic real-time display may change anesthesiologists' behavior

We have developed a real-time graphical display that presents anesthetic pharmacology data (drug effect site concentrations (Ce) and probability of anesthetic effects including hypnosis, loss of response to tracheal intubation), improving a previous prototype. We hypothesized that the use of the display alters (1) clinical behavior of anesthesiologists (i.e., Ce of isoflurane and fentanyl at the end of anesthesia), (2) fentanyl dose during the first 30 min of recovery in the post anesthesia care unit (PACU), and that the response of clinicians to the display in terms of workload and utility is favorable. The display was evaluated in a two-group, non-randomized prospective observational study of 30 patients undergoing general anesthesia using isoflurane and fentanyl. The isoflurane-predicted Ce was lower in the display group (without-display: 0.64% ± 0.06%; with-display: 0.42 ± 0.04%; t_23.9 = 3.17, P = 0.004 < adjusted alpha 0.05/2). The difference in fentanyl-predicted Ce did not achieve statistical significance (without-display: 1.5 ± 0.1 ng/ml; with-display: 2.0 ± 0.2 ng/ml; t_25.5 = 2.26, P = 0.03 > adjusted alpha 0.05/2) (means ± standard error). A joint test of isoflurane and fentanyl Ce with respect to the display condition rejected the null hypothesis of no differences (Hotelling T2, P = 0.01), supporting our primary hypothesis. The total fentanyl per patient during the first 30 min in the PACU with the display was 75.0 ± 62.7 µg and that without the display was 83.0 ± 74.7 µg. There was no significant difference between the groups (means ± standard deviation, P = 0.75). There were no differences in perceived workload. Use of the display does not appear to be cognitively burdensome and may change the anesthesiologist's dosing regimen.

Dynamic Cortical Connectivity during General Anesthesia in Surgical Patients

BACKGROUND

Functional connectivity across the cortex has been posited to be important for consciousness and anesthesia, but functional connectivity patterns during the course of surgery and general anesthesia are unknown. The authors tested the hypothesis that disrupted cortical connectivity patterns would correlate with surgical anesthesia.

METHODS

Surgical patients (n = 53) were recruited for study participation. Whole-scalp (16-channel) wireless electroencephalographic data were prospectively collected throughout the perioperative period. Functional connectivity was assessed using weighted phase lag index. During anesthetic maintenance, the temporal dynamics of connectivity states were characterized via Markov chain analysis, and state transition probabilities were quantified.

RESULTS

Compared to baseline (weighted phase lag index, 0.163, ± 0.091), alpha frontal-parietal connectivity was not significantly different across the remaining anesthetic and perioperative epochs, ranging from 0.100 (± 0.041) to 0.218 (± 0.136) (P > 0.05 for all time periods). In contrast, there were significant increases in alpha prefrontal-frontal connectivity (peak = 0.201 [0.154, 0.248]; P < 0.001), theta prefrontal-frontal connectivity (peak = 0.137 [0.091, 0.182]; P < 0.001), and theta frontal-parietal connectivity (peak = 0.128 [0.084, 0.173]; P < 0.001) during anesthetic maintenance. Additionally, shifts occurred between states of high prefrontal-frontal connectivity (alpha, beta) with suppressed frontal-parietal connectivity, and high frontal-parietal connectivity (alpha, theta) with reduced prefrontal-frontal connectivity. These shifts occurred in a nonrandom manner (P < 0.05 compared to random transitions), suggesting structured transitions of connectivity during general anesthesia.

CONCLUSIONS

Functional connectivity patterns dynamically shift during surgery and general anesthesia but do so in a structured way. Thus, a single measure of functional connectivity will likely not be a reliable correlate of surgical anesthesia.

Effect of remifentanil infusion on the hemodynamic response during induction of anesthesia in hypertensive and normotensive patients: a prospective observational study

Background

The induction of general anesthesia may cause hemodynamic instability. Remifentanil is often administered to suppress the hemodynamic response. We aimed to evaluate the effect of remifentanil infusion on the hemodynamic response to induction of anesthesia in hypertensive and normotensive patients.

Methods

Patients were divided into two groups: Group H (n = 102) were hypertensive patients and Group C (n = 107) were normotensive patients. During induction, all patients received 1 µg/kg of remifentanil as a loading dose over 2 minutes, followed by a continuous infusion at 0.05 µg/kg/minute. We analyzed the systolic, diastolic, and mean pressures and heart rate pre-induction, pre-intubation, immediately post-intubation, and at 2, 4, 6, 8, and 10 minutes after intubation.

Results

The systolic, diastolic, and mean pressures before induction were significantly higher in group H compared with group C, but there was no significant difference between the two groups immediately after intubation. Blood pressures immediately after intubation were similar to the pre-induction blood pressure. There was no significant difference in heart rate between the two groups at any time point.

Conclusions

Remifentanil infusion effectively attenuates the hemodynamic response to induction of general anesthesia in hypertensive and normotensive patients.

Paradox of age: older patients receive higher age-adjusted minimum alveolar concentration fractions of volatile anaesthetics yet display higher bispectral index values

BACKGROUND

Minimum alveolar concentration (MAC) and MAC-awake decrease with age. We hypothesised that, in clinical practice, (i) end-tidal MAC fraction in older patients would decline by less than the predicted age-dependent MAC decrease (i.e. older patients would receive relatively excessive anaesthetic concentrations), and (ii) bispectral index (BIS) values would therefore be lower in older patients.

METHODS

We examined the relationship between end-tidal MAC fraction, BIS values, and age in 4699 patients > 30 yr in age at a single centre using unadjusted local regression (locally estimated scatterplot smoothing), Spearman's correlation, stratification, and robust univariable and multivariable linear regression.

RESULTS

The end-tidal MAC fraction in older patients declined by 3.01% per decade (95% confidence interval [CI]: 2.56-3.45; P<0.001), less than the 6.47% MAC decrease per decade that we found in a meta-regression analysis of published studies of age-dependent changes in MAC (P<0.001), and less than the age-dependent decrease in MAC-awake. The BIS values correlated positively with age (ρ=0.15; 95% CI: 0.12-0.17; P<0.001), and inversely with the age-adjusted end-tidal MAC (aaMAC) fraction (ρ= -0.13; 95% CI: -0.16, -0.11; P<0.001).

CONCLUSIONS

The age-dependent decline in end-tidal MAC fraction delivered in clinical practice at our institution was less than the age-dependent percentage decrease in MAC and MAC-awake determined from published studies. Despite receiving higher aaMAC fractions, older patients paradoxically showed higher BIS values. This most likely suggests that the BIS algorithm is inaccurate in older adults.

Are opioids indispensable for general anaesthesia?

The drug-induced, reversible coma of anaesthesia requires three clinical outcomes: unconsciousness, immobility, and the control of autonomic nervous system (ANS) responses to surgical stimulation. Producing the anaesthetised state with a single anaesthetic agent, such as an inhaled vapour or propofol, is challenging, primarily because suppressing ANS responses requires very high anaesthetic concentrations, resulting in haemodynamic depression and prolonged recovery. The antinociceptive effects of opioids (i.e. minimum alveolar concentration reduction) are thus central to the well-entrenched 'balanced anaesthesia' concept. In recent years, the notion of 'multimodal general anaesthesia' has extended the concept of balanced anaesthesia to include more drugs that target different neuroanatomical circuits and multiple neurophysiologic mechanisms. The opioid epidemic has provided some of the motivation to move away from opioids toward other adjunct drugs. Persistent opioid use after surgery is a component of the opioid epidemic and is a major concern for perioperative physicians. Potential solutions to the problem of persistent opioid use after surgery have focused on proper 'opioid stewardship' after operation, wherein opioids are used conservatively in combination with other analgesic adjuncts, and excessive opioid prescribing for home use is avoided. But there is a paucity of data on how intraoperative opioid usage patterns may be contributing to persistent opioid use after surgery. There are cogent reasons to moderate perioperative opioid use, including intraoperative opioids, but whether these changes in practice integral to the multimodal general anaesthesia concept will improve anaesthesia outcomes, including persistent opioid use after surgery, is unknown. Studies investigating these issues are an important research priority.

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.

The effect of remifentanil on the minimum alveolar concentration (MAC) and MAC derivatives of sevoflurane in dogs

Remifentanil is an ultra-short-acting µ-opioid receptor agonist. The purpose of this study was to determine the relationship of the minimum alveolar concentration (MAC) of sevoflurane and other MAC derivatives, including the MAC for blocking adrenergic responses (MAC-BAR) and the MAC at which tracheal extubation is occurred (MAC-extubation), with or without remifentanil infusion. Six healthy adult beagle dogs were randomly anesthetized three times for determining the MAC-BAR (SEV_MAC-BAR), MAC (SEV_MAC), and MAC- extubation (SEV_{MAC-extubation}) of sevoflurane under infusion of saline and remifentanil at rates of 0.15, 0.30, 0.60, 1.20, and 2.40 µg/kg/min. The ratio of the SEV_MAC-BAR and SEV_MAC and that of the SEV_{MAC-extubation} and SEV_MAC were not significantly different at baseline and during treatment. The MAC-BAR₉₅ and MAC₉₅ decreased in a dose-dependent manner until reaching 1.20 µg/kg/min, and the MAC-extubation₅ decreased in a dose-dependent manner until reaching 0.60 µg/kg/min. The percentage reduction of SEV_MAC-BAR, SEV_MAC, and SEV_{MAC-extubation} increased in a dose-dependent manner during remifentanil infusion. The heart rate significantly decreased in the MAC-BAR and MAC groups, and the systolic and mean arterial pressures increased after remifentanil infusion compared with the baseline values. Remifentanil infusion caused reduction of the SEV_MAC-BAR, SEV_MAC, and SEV_{MAC-extubation} in a dose-dependent manner, and ceiling effects were observed in the dogs. Higher doses of remifentanil and sevoflurane were necessary for blocking the sympathetic response to the supramaximal stimulus to prevent movement and extubation in dogs.

Remifentanil Reduces Blood Loss During Orthognathic Surgery

Remifentanil is reported to reduce oral tissue blood flow. We performed a retrospective investigation using logistic regression analysis of anesthesia records to investigate whether the use of remifentanil infusion in a balanced anesthesia technique was useful as a primary technique to reduce blood loss during orthognathic surgery. Subjects were 80 patients who underwent Le Fort I osteotomy and sagittal split ramus osteotomy of the mandible. The variables included gender, age, weight, type of maintenance anesthetic, type and dose or infusion rate of opioid, mean systolic blood pressure (SBP-mean), coefficient of variation of systolic blood pressure (CVSBP) during surgery, mean heart rate (HR-mean), duration of surgery, total blood loss, volume of infusion used, amount of local anesthetic used, body temperature, and urine output. Gender, type of maintenance anesthetic, type of opioid, SBP-mean, CVSBP, HR-mean, and duration of surgery were used as candidates for independent variables. Logistic regression analysis was performed for the selected independent variables with the total blood loss as the dependent variable. The factors associated with the reduction of blood loss were the use of remifentanil (odds ratio, 3.112; 95% CI, 1.166-8.307; P = .023) and smaller CVSBP (odds ratio, 2.747; 95% CI, 1.07-7.053; P = .036). Use of remifentanil and smaller CVSBP were associated with a reduction of blood loss during orthognathic surgery.

The Effect of Chronic Opioid Use on End-Tidal Concentration of Sevoflurane Necessary to Maintain a Bispectral Index Below 50: A Prospective, Single-Blind Study

BACKGROUND

Opioid analgesics decrease the minimum alveolar concentration of inhalation agents during the acute phase response. However, the effect of chronic opioid exposure on minimum alveolar concentration of inhalation agents remains unknown. This study aimed to determine the concentration of sevoflurane necessary to maintain a bispectral index (BIS) <50 (SEVOBIS50) in patients with chronic opioid use compared with those naïve to opioid use.

METHODS

We included chronic opioid users who received a stable dose of oral morphine of at least 60 mg/d according to the morphine equivalent daily dose for at least 4 weeks and opioid-naïve patients. General anesthesia that included thiopental, vecuronium, and sevoflurane in oxygen was administered to all patients. Anesthesia was maintained using predetermined end-tidal sevoflurane concentrations. Fifteen minutes after achieving the determined end-tidal sevoflurane concentration through closed circuit anesthesia, BIS was measured for 1 minute in both groups. SEVOBIS50 was determined using Dixon's up-down method and probit analysis.

RESULTS

Nineteen and 18 patients from the chronic opioid and control groups, respectively, were included in the final analysis. SEVOBIS50values for the chronic opioid and control patients were 0.84 (95% confidence interval, 0.58-1.11) and 1.18 (95% confidence interval, 0.96-1.40), respectively (P = .0346).

CONCLUSIONS

Our results suggest that the end-tidal concentration of sevoflurane necessary to maintain a BIS <50 is lower for chronic opioid users than for opioid-naïve patients.

Awareness during anesthesia: Current status in Japan

Intraoperative awareness is the explicit recall of sensory perceptions during general anesthesia. I presume the epidemiology and characteristics of intraoperative awareness from these surveys in Japan. A questionnaire survey was conducted via the Internet. The first survey was conducted in 2008. Our survey showed 17% of anesthesiologists experienced definite or possible awareness. The second survey was conducted to evaluate the first survey in detail in 2008. A total of 172 anesthesiologists answered. The total number of reported anesthetic cases was 85156. Twenty-four cases of definite or possible awareness were reported by 21 anesthesiologists. The most surprising finding was total intravenous anesthesia (TIVA) was used in 21 of the 24 cases. The third survey was conducted in 2011 as a continuous survey. Six cases of definite or possible awareness were reported by six anesthesiologists (7%). Two cases were maintained by TIVA, and 2 cases were sevoflurane. The survey showed 76% anesthesiologists routinely use bispectral index (BIS) for TIVA, but for sevoflurane only 27% anesthesiologists routinely use BIS. The incidence of intraoperative awareness decreased in the third survey. The continuous survey revealed the current status of daily anesthesia and the results might be used to prevent the awareness during general anesthesia.

A desflurane and fentanyl dosing regimen for wake-up testing during scoliosis surgery: Implications for the time-course of emergence from anesthesia

BACKGROUND/PURPOSE

The Stagnara wake-up test assesses neurological deficits during scoliosis surgery, and response surface interaction models for opioids and inhaled agents predicts anesthetic drug effects. We hypothesized that there is an optimal desflurane-fentanyl dosing regimen that can provide a faster and more predictable wake-up time, while also ensuring adequate analgesia during wake-up testing.

METHODS

Twenty-three American Society of Anesthesiologists Class I-II scoliosis patients who received desflurane-fentanyl anesthetic regimens were enrolled in this posthoc study, and their intraoperative drug administration data were collected retrospectively. Desflurane and fentanyl effect site concentrations were calculated using pharmacokinetic models, and converted to equivalent remifentanil-sevoflurane concentrations.

RESULTS

Results were fitted into Greco models for predicting the probability of an Observers Assessment of Alertness/Sedation score of <2. At time of wake-up, the models correctly predicted the probability that patients would respond to voice prompts and prodding was approximately 50%. The probability of pain intensity was distributed between 50% and 95%, indicating a low degree of pain at emergence. When comparing subgroups defined by calculated effect-site fentanyl concentrations, the wake-up time in the intermediate concentration group was significantly shorter than that in the high concentration group (p = 0.024).

CONCLUSION

This study provides evidence that desflurane-fentanyl-based anesthesia is conducive to rapid emergence followed by an immediate neurological evaluation. Intermediate fentanyl effect-site concentrations (1-2 ng/mL) at time of wake-up were associated with good balance between rapid emergence and adequate analgesia. Furthermore, we believe that generalizing response surface models to a variety of inhalation agent-opioid combinations using simple relative potency relationships is possible and practical.

Novel relaxant effects of RPL554 on guinea pig tracheal smooth muscle contractility

BACKGROUND AND PURPOSE

We investigated the effectiveness of RPL554, a dual PDE3 and 4 enzyme inhibitor, on airway smooth muscle relaxation and compared it with that induced by salbutamol, ipratropium bromide, glycopyrrolate or their combination on bronchomotor tone induced by different spasmogenic agents.

EXPERIMENTAL APPROACH

Guinea pig tracheal preparations were suspended under 1 g tension in Krebs-Henseleit solution maintained at 37°C and aerated with 95% O2 /5% CO2 and incubated in the presence of indomethacin (5 μM). Relaxation induced by cumulative concentrations of muscarinic receptor antagonists (ipratropium bromide or glycopyrrolate), β2 -adrenoceptor agonists (salbutamol or formoterol), PDE3 inhibitors (cilostamide, cilostazol or siguazodan) or a PDE4 inhibitor (roflumilast) was evaluated in comparison with RPL554. Maximal relaxation was calculated (% Emax papaverine) and expressed as mean ± SEM.

KEY RESULTS

Bronchomotor tone induced by the various spasmogens was reduced by the different bronchodilators to varying degrees. RPL554 (10-300 μM) caused near maximum relaxation irrespective of the spasmogen examined, whereas the efficacy of the other relaxant agents varied according to the contractile stimulus used. During the evaluation of potential synergistic interactions between bronchodilators, RPL554 proved superior to salbutamol when either was combined with muscarinic receptor antagonists.

CONCLUSIONS AND IMPLICATIONS

RPL554 produced near maximal relaxation of highly contracted respiratory smooth muscle and provided additional relaxation compared with that produced by other clinically used bronchodilator drugs. This suggests that RPL554 has the potential to produce additional beneficial bronchodilation over and above that of maximal clinical doses of standard bronchodilators in highly constricted airways of patients.

Comparison of false-negative/positive results of intraoperative evoked potential monitoring between no and partial neuromuscular blockade in patients receiving propofol/remifentanil-based anesthesia during cerebral aneurysm clipping surgery: A retrospective analysis of 685 patients

Although the elicited responses of motor evoked potential (MEP) monitoring are very sensitive to suppression by anesthetic agents and muscle relaxants, the use of neuromuscular blockade (NMB) during MEP monitoring is still controversial because of serious safety concerns and diagnostic accuracy. Here, we evaluated the incidence of unacceptable movement and compared false-negative MEP results between no and partial NMB during cerebral aneurysm clipping surgery. We reviewed patient medical records for demographic data, anesthesia regimen, neurophysiology event logs, MEP results, and clinical outcomes. Patients were divided into 2 groups according to the intraoperative use of NMB: no NMB group (n = 276) and partial NMB group (n = 409). We compared the diagnostic accuracy of MEP results to predict postoperative outcomes between both groups. Additionally, we evaluated unwanted patient movement during MEP monitoring in both groups. Of the 685 patients, 622 (90.8%) manifested no intraoperative changes in MEP and no postoperative motor deficits. Twenty patients showed postoperative neurologic deficits despite preserved intraoperative MEP. False-positive MEP results were 3.6% in the no NMB group and 3.9% in the partial NMB group (P = 1.00). False-negative MEP results were 1.1% in the no NMB group and 4.2% in the partial NMB group (P = 0.02). No spontaneous movement or spontaneous respiration was observed in either group. Propofol/remifentanil-based anesthesia without NMB decreases the stimulation intensity of MEPs, which may reduce the false-negative ratio of MEP monitoring during cerebral aneurysm surgery. Our anesthetic protocol enabled reliable intraoperative MEP recording and patient immobilization during cerebral aneurysm clipping surgery.

A Response Surface Model Exploration of Dosing Strategies in Gastrointestinal Endoscopies Using Midazolam and Opioids

Classical midazolam-opioid combination for gastrointestinal endoscopy sedation has been adopted for decades. Dosing regimens have been studied but most require fixed dosing intervals. We intend to use a sophisticated pharmacodynamic tool, response surface model (RSM), to simulate sedation using different regimens. RSM can predict patient's response during different phases of the examination and predict patient's wake-up time with precision and without the need for fixed dosing intervals. We believe it will aid physicians in guiding their dosing strategy and timing.The study is divided into 2 parts. The first part is the full Greco RSMs development for 3 distinct phases: esophagogastroduodenoscopy (EGD), colonoscopy, and intersession (the time lapse between procedures). Observer's Assessment of Alertness Score (OAA/S) is used to assess patient response. The second part simulates 6 regimens with different characteristics using the RSMs: midazolam only, balanced midazolam and opioids, high-dose opioids and midazolam, low-dose midazolam with high-dose opioids, high-dose midazolam and low-dose opioids, and finally midazolam with continuous opioid infusion. Loss of response at 95% probability for adequate anesthesia during examination and return of consciousness at 50% probability during intersession was selected for simulation purposes.The average age of the patient population is 49.3 years. Mean BMI is 21.9 ± 2.3 kg/m. About 56.7% were females and none received prior abdominal surgery. The cecal intubation rate was 100%. Only 1 patient (3%) developed temporary hypoxemia, which was promptly managed with simple measures. The RSMs for each phase showed significant synergy between midazolam and alfentanil. The balanced midazolam and alfentanil combination provided adequate anesthesia and most rapid return of consciousness. The awakening time from the final drug bolus was 7.4 minutes during EGD and colonoscopy stimulation, and 9.1 minutes during EGD simulation.Simulation of regimens with different characteristics gives insights on dosing strategies. A balanced midazolam-alfentanil regimen is adequate in providing good anesthetic depth and most rapid return of consciousness. We believe with the aid of our RSM, clinicians can perform sedation with more flexibility and precision.

Pharmacodynamic interaction models in pediatric anesthesia

Pharmacokinetic (PK) and pharmacodynamic (PD) models are important tools for summarizing drug dose, concentration, and effect relationships. Co-administration of drugs may alter PK and PD relationships. Traditional methods of evaluating PD interactions include using isoboles, shifts in dose-response curves, or interaction indices based on parameters of potency derived from separate monotherapy and combination therapy analyses. These methods provide an estimation of the magnitude of effect for dose or concentration combinations, but they do not inform us on the time course of that effect, or its associated variability. A better way to investigate PD interactions is to use modeling, and to take advantage of the benefits of population analyses. A population analysis is a statistical method in which a model describing the typical (or population) response, and the variability between individuals within that population, is developed. Models for monotherapy, derived using a population approach, can be combined and extended to incorporate PD interactions between two or more drugs. The purpose of this article was to provide a general road map for understanding and interpreting PD interaction models, including the 'response surface' models. Several types of response surface models exist, and here we review these with examples taken from the literature. We also consider current and future applications for this type of analysis for clinical anesthesia and pediatrics.

Response surface models in the field of anesthesia: A crash course

Drug interaction is fundamental in performing anesthesia. A response surface model (RSM) is a very useful tool for investigating drug interactions. The methodology appeared many decades ago, but did not receive attention in the field of anesthesia until the 1990s. Drug investigations typically start with pharmacokinetics, but it is the effects on the body clinical anesthesiologists really care about. Typically, drug interactions are divided into additive, synergistic, or infra-additive. Traditional isobolographic analysis or concentration-effect curve shifts are limited to a single endpoint. Response surface holds the complete package of isobolograms and concentration effect curves in one equation for a given endpoint, e.g., loss of response to laryngoscopy. As a pharmacodynamic tool, RSM helps anesthesiologists guide their drug therapy by navigating the surface. We reviewed the most commonly used models: (1) the Greco model; (2) Reduced Greco model; (3) Minto model; and (4) the Hierarchy models. Each one has its unique concept and strengths. These models served as groundwork for researchers to modify the formula to fit their drug of interest. RSM usually work with two drugs, but three-drug models can be constructed at the expense of greatly increasing the complexity. A wide range of clinical applications are made possible with the help of pharmacokinetic simulation. Pharmacokinetic-pharmcodynamic modeling using the RSMs gives anesthesiologists the versatility to work with precision and safe drug interactions. Currently, RSMs have been used for predicting patient responses, estimating wake up time, pinpointing the optimal drug concentration, guide therapy with respect to patient's well-being, and aid in procedures that require rapid patient arousal such as awake craniotomy or Stagnara wake-up test. There is no other model that is universally better than the others. Researches are encouraged to find the best fitting model for different occasions with an objective measure.

Intraoperative Blood Loss During Orthognathic Surgery: A Comparison of Remifentanil-Based Anesthesia With Sevoflurane or Isoflurane

PURPOSE

The aim of the present study was to compare the blood loss with remifentanil-based anesthesia with sevoflurane or isoflurane during orthognathic surgery.

PATIENTS AND METHODS

In this randomized controlled clinical trial, the patients who were scheduled for orthognathic surgery were divided into 2 groups: the sevoflurane (Sevo) group and isoflurane (Iso) group. Anesthesia was maintained using end-tidal concentrations of 1.4% sevoflurane or 0.9% isoflurane. Remifentanil was continuously infused at 0.05 to 0.5 μg/kg/min to maintain the mean blood pressure (MBP) at 60 to 65 mm Hg. The intraoperative blood loss was compared between the 2 groups. The Student t test for unpaired samples was used for statistical analysis. P < .05 was considered statistically significant.

RESULTS

The study sample included 19 men and 45 women (n = 64). The mean age was 25 years (range 16 to 50). The intraoperative blood loss tended to be greater in the Iso group (n = 32; 4.79 ± 3.22 mL/kg) than in the Sevo group (n = 32; 4.00 ± 1.98 mL/kg). However, the difference between the 2 groups was not significant.

CONCLUSION

In a comparison of intraoperative blood loss during remifentanil-based anesthesia with sevoflurane or isoflurane during orthognathic surgery, no difference was observed between the 2 groups.

Pharmacology of novel treatments for COPD: are fixed dose combination LABA/LAMA synergistic?

Bronchodilators are mainstay for the symptomatic treatment of chronic obstructive pulmonary disease (COPD) and the introduction of long-acting bronchodilators has led to an improvement in the maintenance treatment of this disease. Various clinical trials have evaluated the effects of fixed dose long-acting β2-agonists (LABA)/long-acting anti-muscarinics (LAMA) combinations and documented greater improvements in spirometry but such improvements do not always translate to greater improvements in symptom scores or reduction in the rates of exacerbation compared with a single component drug. An analysis of whether this significantly greater change in spirometry with combination therapy is additive or synergistic was undertaken and is the subject of this review. Bronchodilators are not disease modifiers and whilst glucocorticosteroids have been shown to reduce rates of exacerbation in moderate to severe COPD, the increase risk of pneumonia and bone fractures is a motivation enough to warrant developing novel anti-inflammatory and disease-modifying drugs and with the expectation of positive outcomes.

Comparison of emergence times with different fresh gas flow rates following desflurane anaesthesia

Objective

To investigate emergence times with different fresh gas flow rates, following desflurane anaesthesia.

Methods

Patients undergoing surgery with desflurane anaesthesia were randomly assigned to receive fresh gas flow rates of 100% oxygen during emergence of 2 l/min (group D2), 4 l/min (group D4) or 6 l/min (group D6). Time to eye opening, spontaneous movement and extubation (emergence time) were assessed after desflurane discontinuation. The end-tidal concentration of desflurane and bispectral index were recorded at each of these timepoints.

Results

A total of 105 patients were included in the study, with 35 in each of the three groups. Mean times to extubation were 17.6 min, 9.9 min and 9.1 min in groups D2, D4 and D6, respectively. Times to eye opening, spontaneous movement and extubation in group D2 were significantly longer than in groups D4 and D6.

Conclusions

These results suggest that there is the potential to predict emergence time based on fresh gas flow rate following desflurane anaesthesia. It should therefore be possible to use a low-flow technique during the emergence period, in addition to the maintenance period, without delaying recovery if the inhaled anaesthetic is stopped at the predicted time before the end of surgery.

Target-controlled infusion of remifentanil for laryngeal mask airway insertion during sevoflurane induction in adults

OBJECTIVE

This randomized, double-blind study investigated the suitable target effect-site concentration of remifentanil for laryngeal mask airway (LMA) insertion during inhalation induction with sevoflurane.

METHODS

Patients aged 18 - 60 years were randomly assigned to one of three groups receiving infusions of normal saline (control group), or infusions with target effect-site remifentanil concentrations of either 1 ng/ml (R1 group) or 2 ng/ml (R2 group), 1 min after the induction of anaesthesia with sevoflurane. LMA insertion was attempted 2 min after induction. Insertion conditions were graded using a six-variable, three-point scale (excellent, intermediate or poor).

RESULTS

A total of 102 patients were included. The proportion of patients ranked as excellent for the LMA insertion was significantly higher in groups R1 and R2 compared with the control group. The incidence of apnoea was significantly more frequent in the R2 group than in the control or R1 groups.

CONCLUSIONS

Compared with 1 ng/ml remifentanil or normal saline, target-controlled infusion of 2 ng/ml remifentanil significantly improved the LMA insertion conditions during sevoflurane inhalational induction, although apnoeic episodes were more frequently observed.

Understanding synergy

Analysis of the interactive effects of combinations of hormones or other manipulations with qualitatively similar individual effects is an important topic in basic and clinical endocrinology as well as other branches of basic and clinical research related to integrative physiology. Functional, as opposed to mechanistic, analyses of interactions rely on the concept of synergy, which can be defined qualitatively as a cooperative action or quantitatively as a supra-additive effect according to some metric for the addition of different dose-effect curves. Unfortunately, dose-effect curve addition is far from straightforward; rather, it requires the development of an axiomatic mathematical theory. I review the mathematical soundness, face validity, and utility of the most frequently used approaches to supra-additive synergy. These criteria highlight serious problems in the two most common synergy approaches, response additivity and Loewe additivity, which is the basis of the isobole and related response surface approaches. I conclude that there is no adequate, generally applicable, supra-additive synergy metric appropriate for endocrinology or any other field of basic and clinical integrative physiology. I recommend that these metrics be abandoned in favor of the simpler definition of synergy as a cooperative, i.e., nonantagonistic, effect. This simple definition avoids mathematical difficulties, is easily applicable, meets regulatory requirements for combination therapy development, and suffices to advance phenomenological basic research to mechanistic studies of interactions and clinical combination therapy research.