Balanced anaesthesia today

Balanced anesthesia in pigeons (Columba livia): a protocol that ensures stable vital parameters and feasibility during long surgeries in cognitive neuroscience

In neuroscience, numerous experimental procedures in animal models require surgical interventions, such as the implantation of recording electrodes or cannulas before main experiments. These surgeries can take several hours and should rely on principles that are common in the field of research and medicine. Considering the characteristics of the avian respiratory physiology, the development of a safe and replicable protocol for birds is necessary to minimize side effects of anesthetic agents, circumvent technical limitations due to the insufficient availability of patient monitoring, and to maintain stable intraoperative anesthesia. Through the consistent and responsible implementation of the three R principle of animal welfare in science ("Replace, Reduce, Refine"), we aimed to optimize experimental methods to minimize the burden on pigeons (Columba livia) during surgical procedures. Here, surgeries were conducted under balanced anesthesia and perioperative monitoring of heart rate, oxygen saturation, body temperature, and the reflex state. The protocol we developed is based on the combination of injectable and inhalative anesthetic drugs [ketamine, xylazine, and isoflurane, supported by the application of an opiate for analgesia (e.g., butorphanol, buprenorphine)]. The combination of ketamine and xylazine with a pain killer is established in veterinary medicine across a vast variety of species. Practicability was verified by survival of the animals, fast and smooth recovery quantified by clinical examination, sufficiency, and stability of anesthesia. Independent of painful stimuli like incision or drilling, or duration of surgery, vital parameters were within known physiological ranges for pigeons. Our approach provides a safe and conservative protocol for surgeries of extended duration for scientific applications as well as for veterinary medicine in pigeons which can be adapted to other bird species.

Using the TI.VA algorithm to titrate the depth of general anaesthesia: a first-in-humans study

Background

The dose of anaesthetic and opioid drugs must be continuously adjusted after the induction of general anaesthesia to maintain an adequate depth of anaesthesia. The TI.VA algorithm is a multiple-input/multiple-output algorithm designed to optimise the balance between anaesthetic and opioid concentrations during general anaesthesia. It applies vector analysis to a two-dimensional matrix to quantify any inadequacy of the depth of anaesthesia at any given moment and determine any drug dose adjustments required to achieve an adequate depth of anaesthesia. This study aimed to capture preliminary data on the performance and safety of the TI.VA algorithm during total i.v. anaesthesia in patients.

Methods

This prospective study enrolled nine patients with breast cancer scheduled to undergo surgery. General anaesthesia was induced under manual control using propofol and remifentanil. Anaesthesia was guided using the TI.VA algorithm from skin incision until surgical resection was completed. The quality of anaesthesia was assessed through an analysis of performance errors. A bispectral index global score (GSBIS) <50 was considered an acceptable target for algorithm performance.

Results

All nine procedures were completed without any adverse events and none of the patients recalled any intraoperative event. Overall, we analysed 3417 monitoring points corresponding to 285 min of surgery. All patients presented a GSBIS below the cut-off value of 50.

Conclusions

The TI.VA algorithm provides adequate control of clinical anaesthesia. A more sophisticated prototype needs to be developed before the trial is expanded to include larger patient populations.

Clinical trial registration

NCT05199883.

Evaluation of an automatic approach device to the epidural space of Beagle dogs

OBJECTIVE

To compare the epidural anesthesia device (EPIA), which facilitates an automatic approach to location of the epidural space, with the performance of clinicians using tactile sensation and differences in pressure when inserting an epidural needle into the epidural space of a dog.

STUDY DESIGN

Prospective, crossover experiment.

ANIMALS

A total of 14 Beagle dogs weighing 7.5 ± 2.4 kg (mean ± standard deviation).

METHODS

Each dog was anesthetized three times at 2 week intervals for three anesthesiologists (two experienced, one novice) to perform 14 epidural injections (seven manual and EPIA device each). The sequence of methods was assigned randomly for each anesthesiologist. The dogs were anesthetized with medetomidine (10 μg kg^-1), alfaxalone (2 mg kg^-1) and isoflurane and positioned in sternal recumbency with the pelvic limbs extended cranially. Epidural puncture in the manual method was determined by pop sensation, hanging drop technique and reduced injection pressure, whereas using the device a sudden decrease in reaction force on the device was detected. A C-arm identified needle placement in the epidural space, and after administration of iohexol (0.3 mL), the needle length in the epidural space was defined as the mean value measured by three radiologists. Normality was tested using the Kolmogorov-Smirnov test, and significant differences between the two methods were analyzed using an independent sample t test.

RESULTS

In both methods, the success rates of epidural insertion were the same at 95.2%. The length of the needle in the epidural space using the device and manual methods was 1.59 ± 0.50 and 1.68 ± 0.88 mm, respectively, with no significant difference (p = 0.718).

CONCLUSIONS AND CLINICAL RELEVANCE

EPIA device was comparable to human tactile sense for an epidural needle insertion in Beagle dogs. Further research should be conducted for application of the device in clinical environments.

Opioid Free Anesthesia in Thoracic Surgery: A Systematic Review and Meta Analysis

Introduction: Recent studies showed that balanced opioid-free anesthesia is feasible and desirable in several surgical settings. However, in thoracic surgery, scientific evidence is still lacking. Thus, we conducted the first systematic review and meta-analysis of opioid-free anesthesia in this field. Methods: The primary outcome was the occurrence of any complication. Secondary outcomes were the length of hospital stay, recovery room length of stay, postoperative pain at 24 and 48 h, and morphine equivalent consumption at 48 h. Results: Out of 375 potentially relevant articles, 6 studies (1 randomized controlled trial and 5 observational cohort studies) counting a total of 904 patients were included. Opioid-free anesthesia compared to opioid-based anesthesia, was associated with a lower rate of any complication (74 of 175 [42%] vs. 200 of 294 [68%]; RR = 0.76; 95% CI, 0.65−0.89; p < 0.001; I2 = 0%), lower 48 h morphine equivalent consumption (MD −14.5 [−29.17/−0.22]; p = 0.05; I2 = 95%) and lower pain at 48 h (MD −1.95 [−3.6/0.3]; p = 0.02, I = 98%). Conclusions: Opioid-free anesthesia in thoracic surgery is associated with lower postoperative complications, and less opioid demand with better postoperative analgesia at 48 h compared to opioid-based anesthesia.

Breath-by-breath measurement of intraoperative propofol by unidirectional anisole-assisted photoionization ion mobility spectrometry via real-time correction of humidity

Humidity as a major issue affects the quantitative performance of ion mobility spectrometry (IMS) in field applications. According to the kinetic equations of ion-molecular reaction, the intensity ratio of the product ion peak (PIP) over the reactant ion peak (RIP) is proposed as a quantitative factor to correct real-time humidity variation. By coupling this method with a unidirectional anisole-assisted photoionization IMS, direct breath-by-breath measurement of intraoperative propofol was achieved for the first time, which provided more clinical information for studying the anesthetics pharmacokinetics. Although the signal intensities of the RIP and the propofol PIP both declined along with the increase of humidity, the intensity ratio of Propofol/(RIP + Propofol) kept almost constant in a wide relative humidity range of 0%-98%, enabling direct quantitation of exhaled propofol with varying humidity. Furthermore, interfering ion peaks resulted from the high concentration humidity and anesthetics in single exhalation were eliminated during the balanced anesthesia as the exhaled sample was diluted by the unidirectional gas flow scheme. As a demonstration, breath-by-breath variation profiles of propofol were obtained via monitoring end-tidal propofol concentration of intraoperative anesthetized patients (n = 7). The analyses were quantitative, corrected for humidity in real-time, without measuring the humidity content of each breath sample during operation, which show potential for the quantitative analysis of other high humidity samples.

Systematic Review: Anesthetic Protocols and Management as Confounders in Rodent Blood Oxygen Level Dependent Functional Magnetic Resonance Imaging (BOLD fMRI)-Part B: Effects of Anesthetic Agents, Doses and Timing

Simple Summary

To understand brain function in rats and mice functional magnetic resonance imaging of the brain is used. With this type of “brain scan” regional changes in blood flow and oxygen consumption are measured as an indirect surrogate for activity of brain regions. Animals are often anesthetized for the experiments to prevent stress and blurred images due to movement. However, anesthesia may alter the measurements, as blood flow within the brain is differently affected by different anesthetics, and anesthetics also directly affect brain function. Consequently, results obtained under one anesthetic protocol may not be comparable with those obtained under another, and/or not representative for awake animals and humans. We have systematically searched the existing literature for studies analyzing the effects of different anesthesia methods or studies that compared anesthetized and awake animals. Most studies reported that anesthetic agents, doses and timing had an effect on functional magnetic resonance imaging results. To obtain results which promote our understanding of brain function, it is therefore essential that a standard for anesthetic protocols for functional magnetic resonance is defined and their impact is well characterized.

Abstract

In rodent models the use of functional magnetic resonance imaging (fMRI) under anesthesia is common. The anesthetic protocol might influence fMRI readouts either directly or via changes in physiological parameters. As long as those factors cannot be objectively quantified, the scientific validity of fMRI in rodents is impaired. In the present systematic review, literature analyzing in rats and mice the influence of anesthesia regimes and concurrent physiological functions on blood oxygen level dependent (BOLD) fMRI results was investigated. Studies from four databases that were searched were selected following pre-defined criteria. Two separate articles publish the results; the herewith presented article includes the analyses of 83 studies. Most studies found differences in BOLD fMRI readouts with different anesthesia drugs and dose rates, time points of imaging or when awake status was compared to anesthetized animals. To obtain scientifically valid, reproducible results from rodent fMRI studies, stable levels of anesthesia with agents suitable for the model under investigation as well as known and objectively quantifiable effects on readouts are, thus, mandatory. Further studies should establish dose ranges for standardized anesthetic protocols and determine time windows for imaging during which influence of anesthesia on readout is objectively quantifiable.

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).

Does Equi–Minimum Alveolar Concentration Value Ensure Equivalent Analgesic or Hypnotic Potency?

Background

Minimum alveolar concentration (MAC) has traditionally been used to compare the potency of volatile anesthetics. However, as it reflects the spinal mechanism of immobility rather than the cerebral mechanism of analgesia and hypnosis, it is doubtful that equi-MAC connotes equivalent analgesic or hypnotic potency. The level of analgesia and hypnosis can be assessed using surgical pleth index and bispectral index (BIS) values, respectively. This study was designed to compare the surgical pleth index and BIS values produced by equi-MAC of desflurane and sevoflurane in patients undergoing single-agent volatile anesthesia.

Methods

Eighty-nine patients were randomly allocated to two groups receiving either desflurane (n = 44) or sevoflurane (n = 45). Anesthesia was only maintained with assigned volatile anesthetic of age-corrected 1.0 MAC. Surgical pleth index values as an analgesic estimate and BIS values as a hypnotic estimate were obtained under standard tetanic stimulation.

Results

Post-stimulation surgical pleth index values (mean ± SD), the primary outcome, were significantly lower for the desflurane group than those for the sevoflurane group (49 ± 10 vs. 64 ± 14, difference, 15 [95% CI, 10 to 20], P &lt; 0.001). The desflurane group showed significantly lower poststimulation BIS values (median [interquartile range]) than the sevoflurane group (36 [31 to 41] vs. 41 [38 to 47], difference, 6 [95% CI, 2 to 9], P = 0.001).

Conclusions

During a steady-state of 1.0 MAC, desflurane and sevoflurane did not cause similar surgical pleth index and BIS values under the standardized nociceptive stimulus. These findings suggest that equi-MAC of desflurane and sevoflurane may not ensure equivalent analgesic or hypnotic potency.

A randomized clinical trial comparing hemodynamic responses to ketamine-propofol combination (ketofol) versus etomidate during anesthesia induction in patients with left ventricular dysfunction undergoing coronary artery bypass graft surgery

INTRODUCTION

Anesthesia induction is often accompanied by a period of hemodynamic instability, which could be a significant problem in patients with compromised ventricular function. The aim of this study is to compare the hemodynamic responses to etomidate versus a combination of ketamine and propofol (ketofol) for anesthetic induction in patients with left ventricular dysfunction undergoing coronary artery bypass graft (CABG) surgery.

MATERIAL AND METHODS

In a double-blind randomized clinical study, a total of 84 patients with ischemic left ventricular dysfunction (EF < 40%) were randomly assigned to two groups (A and B). Patients in group A received etomidate 0.2 mg/kg and a placebo (normal saline); group B received a combination of ketamine (1 mg/kg) and propofol (1.5 mg/kg) at the induction of anesthesia. Two minutes after induction, hemodynamic variables, including systolic, diastolic, mean arterial pressure (SAP, DAP, MAP) and heart rate (HR), were measured immediately before and after the laryngoscopy, and before intubation and post-intubation at 1, 2, and 3 min.

RESULTS

The decrease in all hemodynamic parameters (SBP, DBP, MAP and HR) from induction time to laryngoscopy was greater in the ketofol group (group B) than in the etomidate group (group A) (p < 0.05). The ephedrine prescription rate due to hemodynamic changes was 24.4% (10 patients) and 5% (2 patients) in group B and group A, respectively (p = 0.03).

CONCLUSIONS

We found that etomidate provides superior hemodynamic stability as compared to ketofol in patients with left ventricular dysfunction undergoing CABG surgery under general anesthesia.

Postoperative nausea and vomiting after thyroidectomy: a comparison between dexmedetomidine and remifentanil as part of balanced anesthesia

BACKGROUND

Postoperative nausea and vomiting (PONV) is the major complication related to general anesthesia, occurring in 60-80% of patients after thyroidectomy. The objective of this study was to compare the effects of an intraoperative dexmedetomidine infusion with remifentanil, as anesthetic adjuvants of balanced anesthesia, on PONV in patients undergoing thyroidectomy.

METHODS

Eighty patients scheduled for thyroidectomy were randomized into the following two groups: 1) The dexmedetomidine group (Group D), who received an initial loading dose of dexmedetomidine (1 µg/kg over 10 min) during the induction of anesthesia, followed by a continuous infusion at a rate of 0.3-0.5 µg/kg/h; 2) the remifentanil group (group R), who received remifentanil at an initial target effect site concentration of 4 ng/ml during the induction of anesthesia, followed by a target effect site concentration of 2-3 ng/ml. PONV was assessed during the first 24 hours in 2 time periods (0-2 h and 2-24 h). The pain intensity, sedation score, extubation time, and hemodynamics were also assessed.

RESULTS

During the 2 time periods, the incidence and severity of PONV in group D were significantly lower than in group R. In addition, the need for rescue antiemetics was significantly lower in group D than in group R. The effect of dexmedetomidine on postoperative pain relief (2-24 h) was superior to that of remifentanil. The hemodynamics were similar in both groups, whereas eye opening and extubation time were delayed in group D.

CONCLUSIONS

Adjuvant use of intraoperative dexmedetomidine infusion may be effective for the prevention of PONV.

Comparison of the Analgesic Properties of Sevoflurane and Desflurane Using Surgical Pleth Index at Equi-Minimum Alveolar Concentration

Background: Traditionally, minimum alveolar concentration (MAC) has been used as the standard measure to compare the potencies of volatile anesthetics. However, it reflects the spinal mechanism of immobility rather than the subcortical mechanism of analgesia. Recently, the surgical pleth index (SPI) derived from photoplethysmographic waveform was shown to reflect the intraoperative analgesic component. This study was designed to compare the SPI values produced by equi-MAC of two commonly used volatile anesthetics, sevoflurane and desflurane. Methods: Seventy-two patients undergoing arthroscopic shoulder surgery were randomly assigned to two groups receiving either sevoflurane (n = 36) or desflurane (n = 36). General anesthesia was maintained with the respective volatile anesthetic only. A vaporizer was adjusted to maintain end-tidal anesthetic concentration at age-corrected 1.0 MAC throughout the study period. The SPI value as an analgesic estimate and the bispectral index (BIS) value as a hypnotic estimate were recorded at predefined time points during the standardized surgical procedure. Results: During the steady state of age-corrected 1.0 MAC, mean SPI values throughout the entire study period were significantly higher in the sevoflurane group than in the desflurane group (38.1 ± 12.8 vs. 30.7 ± 8.8, respectively, P = 0.005), and mean BIS values were significantly higher in the sevoflurane group than in the desflurane group (40.7 ± 5.8 vs. 36.8 ± 6.2, respectively, P = 0.008). Conclusions: Equi-MAC of sevoflurane and desflurane did not produce similar surgical pleth index values. Therefore, sevoflurane and desflurane may have different analgesic properties at equipotent concentrations.

Effect of midazolam and butorphanol premedication on inhalant isoflurane anesthesia in mice

Isoflurane is a representative inhalant anesthesia used in laboratory animals. However, isoflurane mediates respiratory depression and adverse clinical reactions during induction. In the present study, we established a novel balanced anesthesia method in mice that combined isoflurane anesthesia with midazolam and butorphanol (MB). Thirty-four male C57BL/6J mice received either isoflurane alone or isoflurane with an intra-peritoneal MB premedication (3 mg/kg midazolam and 4 mg/kg butorphanol). The minimum alveolar concentration (MAC) in each group was evaluated. Induction time and adverse clinical reactions were recorded in each group. Core body temperature, heart rate, respiratory rate, and oxygen saturation (SPO(2)) were assessed before and for 1 h after induction. Premedication with MB achieved a significant reduction in MAC compared with isoflurane monoanesthesia (isoflurane, 1.38 ± 0.15%; isoflurane with MB, 0.78 ± 0.10%; P<0.05). Induction time was significantly shortened with MB premedication, and adverse reactions such as excitement or incontinence were observed less frequently. Furthermore, isoflurane anesthesia with MB premedication caused increase of respiratory rates compared to isoflurane monoanesthesia. No significant decrease of SPO(2) was observed in MBI anesthesia, while a decrease in SPO(2) was apparent with isoflurane monoanesthesia (baseline, 98.3% ± 1.1; 10 min after induction, 91.8 ± 6.4%; P<0.05). In conclusion, premedication with MB was effective for the mitigation of respiratory depression induced by isoflurane in mice, with rapid induction and fewer adverse clinical reactions.

Hemodynamic responses to etomidate versus ketamine-thiopental sodium combination for anesthetic induction in coronary artery bypass graft surgery patients with low ejection fraction: a double-blind, randomized, clinical trial

BACKGROUND

During induction of anesthesia and intubation, hemodynamic changes are very important; especially in patients with coronary artery disease (CAD) and left ventricular dysfunction. A little information is available on the hemodynamic effects of a combination of ketamine-thiopental for induction of anesthesia in patients undergoing coronary artery bypass graft (CABG) surgery, with impaired ventricular function.

AIM

The aim of this study was to compare the hemodynamic responses to etomidate versus ketamine-thiopental sodium combination for anesthetic induction in CABG surgery patients with low ejection fraction (EF<45%).

MATERIALS AND METHODS

In a double blind randomized clinical trial, a total of 100 patients, scheduled for elective CABG surgery were randomly assigned into two groups. These patients received either etomidate or ketamine-thiopental sodium combination at induction of anesthesia. Hemodynamics variable were measured and recorded at baseline, immediately before and after laryngoscopy and intubation, one, two and three minutes after intubation. Also, muscle twitching incidence among patients in two groups was evaluated.

RESULTS

No significant differences between the two groups regarding the changes of hemodynamic variables including systolic and diastolic arterial blood pressure, mean arterial pressure and heart rate, were notice (p>0.05). Muscle twitching was not observed in the two groups.

CONCLUSION

Hemodynamic stability after administration of ketamine-thiopental sodium combination for induction of anesthesia in patients undergoing CABG surgery, with impaired ventricular function, supports the clinical impression that this combination is safe in CABG surgery patients with low EF.

Partial intravenous anaesthesia in the horse: a review of intravenous agents used to supplement equine inhalation anaesthesia. Part 1: lidocaine and ketamine

OBJECTIVE

To review the literature with regard to the use of different intravenous agents as supplements to inhalational anaesthesia in horses. These drugs include lidocaine, ketamine, opioids and α2 -agonists. The Part 1 of this review will focus in the use of lidocaine and ketamine.

DATABASES USED

Pubmed & Web of Science. Search terms: horse, inhalant anaesthesia, balanced anaesthesia, partial intravenous anaesthesia, lidocaine, ketamine.

CONCLUSIONS

Different drugs and their combinations can be administered systemically in anaesthetized horses, with the aim of reducing the amount of the volatile agent whilst improving the recovery qualities and providing a multimodal analgesic approach. However, full studies as to whether these techniques improve cardiopulmonary status are not always available and potential disadvantages should also be considered.

Relationship of bispectral index to minimum alveolar concentration during isoflurane, sevoflurane or desflurane anaesthesia

OBJECTIVE

To determine bispectral index (BIS) values produced by equipotent concentrations of commonly used volatile anaesthetics.

METHODS

Female patients undergoing thyroidectomy were randomly assigned to receive isoflurane, sevoflurane or desflurane anaesthesia. After induction, anaesthesia was maintained by the volatile agent at 1 minimum alveolar concentration and supplemented with remifentanil infusion. BIS values were recorded during 1 h surgical anaesthesia after a 15 min equilibrium phase.

RESULTS

Time-averaged BIS value during the study period was significantly lower in the desflurane group (n = 29) than the sevoflurane group (n = 27) (37.0 ± 4.9 vs 41.5 ± 5.9). Duration of deep hypnosis (BIS < 40) was significantly longer in the desflurane group than the sevoflurane group (40.2 ± 20.7 vs 24.3 ± 22.5 min). There were no significant differences in any parameter between the isoflurane group (n = 27) and any other group.

CONCLUSIONS

Desflurane produces a greater hypnotic effect than sevoflurane during equipotent anaesthesia. Management of volatile anaesthesia using predetermined minimum alveolar concentration targets can lead to an unnecessarily long duration of deep hypnosis.

Intravenous anaesthesia in goats: A review

Intravenous anaesthesia is gradually becoming popular in veterinary practice. Traditionally, general anaesthesia is induced with intravenous drugs and then maintained with inhalation agents. Inhalation anaesthetic agents cause more significant dose-dependent cardiorespiratory depression than intravenous anaesthetic drugs, creating a need to use less of the inhalation anaesthetic agents for maintenance of general anaesthesia by supplementing with intravenous anaesthesia drugs. Better still, if anaesthesia is maintained completely with intravenous anaesthetic drugs, autonomic functions remain more stable intra-operatively. Patient recovery from anaesthesia is smoother and there is less pollution of the working environment than happens with inhalation anaesthetic agents. Recently, a number of drugs with profiles (pharmacokinetic and pharmacodynamic) suitable for prolonged intravenous anaesthesia have been studied, mostly in humans and, to a certain extent, in dogs and horses. There is currently very little scientific information on total intravenous anaesthesia in goats, although, in the past few years, some scholarly scientific articles on drugs suitable for partial intravenous anaesthesia in goats have been published. This review article explored the information available on drugs that have been assessed for partial intravenous anaesthesia in goats, with the aim of promoting incorporation of these drugs into total intravenous anaesthesia protocols in clinical practice. That way, balanced anaesthesia, a technique in which drugs are included in anaesthetic protocols for specific desired effects (hypnosis, analgesia, muscle relaxation, autonomic stabilisation) may be utilised in improving the welfare of goats undergoing general anaesthesia.

The median effective effect-site concentration of remifentanil for minimizing the cardiovascular changes to endotracheal intubation during desflurane anesthesia in pediatric patients

Background

Desflurane has the most rapid onset and offset of action among the volatile anesthetic agents used for general anesthesia, but it can cause airway reactivity, tachycardia, and hypertension during induction, especially in pediatric patients. This study was designed to determine a median effective effect-site concentration (EC₅₀) of remifentanil to prevent the cardiovascular changes due to tracheal intubation during the 1 minimum alveolar concentration (MAC) desflurane inhalation, which was required to prevent movement in response to a noxious stimulus in 50% of subjects, in pediatric patients.

Methods

Twenty-four pediatric patients between the ages 5-15 years were enrolled in this study. We injected thiopental intravenously, at the same time remifentanil was infused by Target Controlled Infusion (TCI) device. When the target effect-site concentration (Ce) of remifentanil reached a preset level, desflurane was administrated through the facial mask. Then, we assessed the signs of desflurane related airway reactivity and cardiovascular changes for 2 min. The up-and-down criteria was a 20% change in systolic blood pressure (SBP) and a heart rate (HR) between just prior to intubation and 1 min after intubation. The EC₅₀ of remifentanil was calculated from 8 independent pairs using Dixon's up-and-down method.

Results

We studied 24 pediatric patients in range of 1-5 ng/ml of the Ce of remifentanil. No patient showed airway reactivity during the study. The EC₅₀ of remifentanil to suppress the hemodynamic changes after tracheal intubation during desflurane anesthesia was calculated as 3.4 ± 0.9 ng/ml.

Conclusions

In pediatric anesthesia, the EC₅₀ of remifentanil to minimize the cardiovascular changes due to tracheal intubation during 1 MAC desflurane anesthesia was 3.4 ± 0.9 ng/ml.

Intratesticular lidocaine reduces the response to surgical castration in dogs

OBJECTIVE

To investigate whether intratesticular injection of lidocaine pre-surgery would reduce the intraoperative responses to elective castration in dogs.

STUDY DESIGN

Double-blinded, randomized, controlled, prospective clinical study.

ANIMALS

Forty-two client-owned dogs weighing 2.2-38.4 kg and aged between 4.5 and 56 months.

METHODS

Group L dogs received an intratesticular injection of 2% lidocaine (2 mg kg(-1)) and Group S an identical volume of saline prior to surgery. Premedication was with acepromazine and morphine intramuscularly. Anaesthesia was induced with propofol intravenously and maintained with isoflurane vaporized in oxygen. Heart rate (HR), mean arterial pressure (MAP), respiratory rate (f(R)), end-tidal isoflurane (Fe'ISO) and carbon dioxide concentrations, oxygen saturation and ECG were monitored during surgery. Fe'ISO was maintained at 1.0±0.1%. Supplemental propofol was given in response to gross movement.

RESULTS

Group L had significantly lower maximum values for both HR and MAP. Group L displayed significantly smaller increases in HR during exteriorization of the first testis than Group S. There was an overall significant difference in MAP between groups during all surgical events (p=0.041) and time points (p=0.002). In univariate analysis, Group L showed significantly less changes in MAP during skin incision, exteriorization of the first testis and clamping of both spermatic cords. Group S reached its highest f(R) significantly earlier. Group L (eight dogs) required additional propofol 33±18 minutes after the start of surgery and Group S (seven dogs) at 19±17 minutes; this difference was not statistically significant. Seven dogs in Group L and 12 dogs in Group S required rescue analgesia with morphine (GCMPS-SF score ≥6); this difference was not statistically significant. No adverse effects were reported postoperatively.

CONCLUSIONS AND CLINICAL RELEVANCE

Based on this study, the authors recommend the use of intratesticular lidocaine for surgical castration in dogs.

Anesthetic management for small bowel enteroscopy in a World Gastroenterology Organization Endoscopy Training Center

AIM

To study the anesthetic management of patients undergoing small bowel enteroscopy in the World Gastroenterology Organization (WGO) Endoscopy Training Center in Thailand.

METHODS

Patients who underwent small bowel enteroscopy during the period of March 2005 to March 2011 in Siriraj Gastrointestinal Endoscopy Center were retrospectively analyzed. The patients' characteristics, pre-anesthetic problems, anesthetic techniques, anesthetic agents, anesthetic time, type and route of procedure and anesthesia-related complications were assessed.

RESULTS

One hundred and forty-four patients underwent this procedure during the study period. The mean age of the patients was 57.6 ± 17.2 years, and most were American Society of Anesthesiologists (ASA) class II (53.2%). Indications for this procedure were gastrointestinal bleeding (59.7%), chronic diarrhea (14.3%), protein losing enteropathy (2.6%) and others (23.4%). Hematologic disease, hypertension, heart disease and electrolyte imbalance were the most common pre-anesthetic problems. General anesthesia with endotracheal tube was the anesthetic technique mainly employed (50.6%). The main anesthetic agents administered were fentanyl, propofol and midazolam. The mean anesthetic time was 94.0 ± 50.5 min. Single balloon and oral (antegrade) intubation was the most common type and route of enteroscopy. The anesthesia-related complication rate was relatively high. The overall and cardiovascular-related complication rates including hypotension in the older patient group (aged ≥ 60 years old) were significantly higher than those in the younger group.

CONCLUSION

During anesthetic management for small bowel enteroscopy, special techniques and drugs are not routinely required. However, for safety reasons anesthetic personnel need to optimize the patient's condition.

The target concentration of remifentanil to suppress the hemodynamic response to endotracheal intubation during inhalational induction with desflurane

Background

Anesthesia induction with desflurane is troublesome because of the frequent sympathetic hyperactivity during desflurane administration. We thought that a low concentration of desflurane combined with a target-controlled infusion (TCI) of remifentanil would eliminate the desflurane-related complications and provide hemodynamic stability during desflurane induction. An up-and-down study was planned to find the target effect-site concentration of remifentanil to block the hemodynamic response to endotracheal intubation, the highest level of stimulus, during anesthesia induction with administering desflurane at 1 MAC.

Methods

Remifentanil TCI was initiated before desflurane administration. When the preset target was achieved, spontaneous inhalation of desflurane 1 MAC was performed until the patients became unconscious. Laryngoscopic tracheal intubation was facilitated with rocuronium injection. The starting concentration of remifentanil and the test space were 5 and 1 ng/ml, respectively. The criteria for up-and-down was a 20% increase of the mean arterial pressure or heart rate after intubation. The median effective concentration (EC₅₀) of remifentanil was calculated from 6 independent pairs. The complications related with remifentanil and desflurane were assessed during the study.

Results

We studied 20 patients using 2-5 ng/ml of the effect-site concentrations of remifentanil. The EC₅₀ of remifentanil was 3.7 ng/ml. Loss of consciousness was achieved at 125 ± 22 s after desflurane inhalation and this was irrespective of the combined remifentanil concentrations. Any remifentanil-related complication was not observed. Transient cough was seen in one patient who received 2 ng/ml of remifentanil.

Conclusions

We demonstrated that uncomplicated induction with desflurane was possible by the use of target-controlled remifentanil. The EC₅₀ of remifentanil to block the hemodynamic response to tracheal intubation was 3.7 ng/ml during inhalational induction with 1 MAC desflurane.

Peak and averaged bicoherence for different EEG patterns during general anaesthesia

BACKGROUND

Changes in nonlinear neuronal mechanisms of EEG generation in the course of general anaesthesia have been extensively investigated in research literature. A number of EEG signal properties capable of tracking these changes have been reported and employed in anaesthetic depth monitors. The degree of phase coupling between different spectral components is a marker of nonlinear EEG generators and is claimed to be an important aspect of BIS. While bicoherence is the most direct measure of phase coupling, according to published research it is not directly used in the calculation of BIS, and only limited studies of its association with anaesthetic depth and level of consciousness have been published. This paper investigates bicoherence parameters across equal band and unequal band bifrequency regions, during different states of anaesthetic depth relating to routine clinical anaesthesia, as determined by visual inspection of EEG.

METHODS

41 subjects scheduled for day surgery under general anaesthesia were recruited into this study. EEG bicoherence was analysed using average and smoothed-peak estimates calculated over different regions on the bifrequency plane. Statistical analysis of associations between anaesthetic depth/state of consciousness and bicoherence estimates included linear regression using generalised linear mixed effects models (GLMs), ROC curves and prediction probability (Pk).

RESULTS

Bicoherence estimates for the δ_θ region on the bifrequency plane were more sensitive to anaesthetic depth changes compared to other bifrequency regions. Smoothed-peak bicoherence displayed stronger associations than average bicoherence. Excluding burst suppression and large transients, the δ_θ peak bicoherence was significantly associated with level of anaesthetic depth (z = 25.74, p < 0.001 and R2 = 0.191). Estimates of Pk for this parameter were 0.889(0.867-0.911) and 0.709(0.689-0.729) respectively for conscious states and anaesthetic depth levels (comparable BIS estimates were 0.928(0.905-0.950) and 0.801(0.786-0.816)). Estimates of linear regression and areas under ROC curves supported Pk findings. Bicoherence for eye movement artifacts were the most distinctive with respect to other EEG patterns (average |z| value 13.233).

CONCLUSIONS

This study quantified associations between deepening anaesthesia and increase in bicoherence for different frequency components and bicoherence estimates. Increase in bicoherence was also established for eye movement artifacts. While identified associations extend earlier findings of bicoherence changes with increases in anaesthetic drug concentration, results indicate that the unequal band bifrequency region, δ_θ, provides better predictive capabilities than equal band bifrequency regions.

Pharmacoeconomics of Volatile Inhalational Anaesthetic Agents: An 11-Year Retrospective Analysis

With continuously increasing expenditure on health care resources, various cost containment strategies have been suggested in regard to controlling the cost of inhalational anaesthetic agents. We performed a cost identification analysis assessing inhalational anaesthetic agent expenditure at a tertiary level hospital, along with an evaluation of strategies to contain the cost of these agents.

The number of bottles of isoflurane, sevoflurane and desflurane used during the financial years 1997 to 2007 was retrospectively determined and the acquisition costs and cumulative drug expenditure calculated. Pharmacoeconomic modelling using low fresh gas flow anaesthesia was performed to evaluate practical methods of cost reduction.

The use of isoflurane decreased from 384 bottles during 1997 to 204 in 2007. In contrast, use of sevoflurane increased from 226 bottles during 1998 to 875 during 2007. Desflurane use increased from 34 bottles per year during 2002 (its year of introduction) to 163 bottles per year in 2007. While the inflation-adjusted cumulative expenditure for these inhalational agents (Australian dollars) increased from $132,000 in 1997 to over $326,000 in 2007, an increase of 168%, patient workload over the same period increased by only 11%. Pharmacoeconomic modelling demonstrated that sevoflurane at 2 l/minute costs 19 times more than isoflurane at 0.5 l/minute.

For the financial years 1997 to 2007, we found a progressive shift from the cheaper isoflurane to the more expensive agents, sevoflurane and desflurane, a shift associated with marked increases in costs. Low flow anaesthesia with isoflurane is one strategy to reduce costs.

Opioid-free balanced anesthesia for cervical ganglionectomy subsequent to recent ultra rapid opioid detoxification

OBJECTIVE

To perform an opioid-free, balanced anesthetic for an Active Duty soldier undergoing cervical ganglionectomy for intractable occipital neuralgia 7 days after ultra rapid opioid detoxification (UROD) under general anesthesia.

SETTING

Opioids have been a mainstay for both intraoperative and postoperative analgesia. With the emergence of newer non-opioid analgesics and the practice of the multimodal analgesia, opioid therapy will be complimented and, in some cases, replaced by these newer agents. The increasing knowledge in the literature of both pain mechanisms and chronic pain treatment can present anesthesiologists with a challenge when faced with opioid-tolerant patients in the acute perioperative setting. With an increased focus on adequate pain control among health care regulatory agencies, we may expect to see a growing number of patients who desire weaning from chronic opioid therapy. There have been many weaning protocols proposed in the literature, with UROD under general anesthesia being one of them. We report a case of successful non-opioid analgesia in a patient that presented for a cervical ganglionectomy 7 days after UROD.

CONCLUSIONS

This patient successfully completed a perioperative and postoperative course using ketamine and dexmedetomidine infusions, in addition to other non-opioid adjuncts. The patient returned to her Active Duty station, with increased functional capacity and remains opioid-free.

Influence of anesthesia on immune responses and its effect on vaccination in children: review of evidence

Anesthesia and surgery exert immunomodulatory effects and some authors argue that they may exert additive or synergistic influences on vaccine efficacy and safety. Alternatively, inflammatory responses and fever elicited by vaccines may interfere with the postoperative course. There is a lack of consensus approach among anesthesiologists to the theoretical risk of anesthesia and vaccination. Few studies have assessed the influence of anesthesia and surgery on pediatric vaccine responses. We have undertaken an extensive review of articles published in English between 1970 and 2006 meeting the criteria: measurement of immune parameters following general anesthesia in children. By searching the major medical databases (OVID Medline, PubMed, ISI Web of Science) and references cited in the articles themselves, among 277 articles obtained none examined directly the influence of anesthesia/surgery on vaccine responses. Only 16 original reports assessed the influence of several anesthetic agents on various markers of immunity including lymphocyte numbers and functions. These results are reinterpreted here in view of our current understanding of the immune mechanisms underlying vaccine efficacy and adverse events. We conclude that the immunomodulatory influence of anesthesia during elective surgery is both minor and transient (around 48 h) and that the current evidence does not provide any contraindication to the immunization of healthy children scheduled for elective surgery. However, respecting a minimal delay of 2 days (inactivated vaccines) or 14-21 days (live attenuated viral vaccines) between immunization and anesthesia may be useful to avoid the risk of misinterpretation of vaccine-driven adverse events as postoperative complications.