The effect of fentanyl on sevoflurane requirements for somatic and sympathetic responses to surgical incision

Consistency of the anesthesia consciousness index versus the bispectral index during laparoscopic gastrointestinal surgery with sevoflurane anesthesia: A prospective multi-center randomized controlled clinical study

Background

This study aimed to compare the consistency of anesthesia consciousness index (Ai) with that of bispectral index (BIS) in monitoring the depth of anesthesia (DOA) during sevoflurane anesthesia, to reveal the optimal cutoff values in different states of consciousness, and explore the stability of DOA monitoring during intraoperative injurious stimulation.

Methods

We enrolled 145 patients (97 men and 48 women) from 10 medical centers. General anesthesia was induced using intravenous anesthetics and maintained with sevoflurane. Ai and BIS values were recorded.

Results

The mean difference between the Ai and BIS was-0.1747 (95% confidence interval, −0.6660 to 0.3166; p = 0.4857). The regression equation of Ai and BIS from the Deming regression analysis was y = 5.6387 + 0.9067x (y is BIS, x is Ai), and the slope and intercept were statistically significant. Meanwhile, the receiver operating characteristic curve analysis of anesthesia-induced unconsciousness, loss of consciousness, and recovery of consciousness revealed that the accuracy of Ai and BIS were similar. In addition, the optimal cutoff values of the different states of consciousness were not sensitive to age, and both Ai and BIS had no correlation with hemodynamics.

Conclusion

We conclude that Ai and BIS show no systematic deviation in readings with high consistency, similar accuracy, and good stability; these insights provide more data for clinical application.

An electroencephalogram biomarker of fentanyl drug effects

Opioid drugs influence multiple brain circuits in parallel to produce analgesia as well as side effects, including respiratory depression. At present, we do not have real-time clinical biomarkers of these brain effects. Here, we describe the results of an experiment to characterize the electroencephalographic signatures of fentanyl in humans. We find that increasing concentrations of fentanyl induce a frontal theta band (4 to 8 Hz) signature distinct from slow-delta oscillations related to sleep and sedation. We also report that respiratory depression, quantified by decline in an index of instantaneous minute ventilation, occurs at ≈1700-fold lower concentrations than those that produce sedation as measured by reaction time. The electroencephalogram biomarker we describe could facilitate real-time monitoring of opioid drug effects and enable more precise and personalized opioid administration.

End-tidal Anesthetic Concentration: Monitoring, Interpretation, and Clinical Application

Age-adjusted fraction of minimum alveolar concentration derived from end-tidal anesthetic partial pressure measurement remains a useful drug advisory display to help prevent awareness if interpreted with proper understanding of the quantal and probabilistic nature of minimum alveolar concentration, semantics, drug interactions, and hysteresis.

Ethanol reduces the minimum alveolar concentration of sevoflurane in rats

A high number of trauma patients are under the influence of alcohol. Since many of them need immediate surgical procedures, it is imperative to be aware of the interaction of alcohol with general anesthesia. To counter challenges that arise from clinical studies, we designed an animal experiment in which 48 adult Wistar rats either received 1 g · kg-1 ethanol, 2 g · kg-1 ethanol or placebo via intraperitoneal application. Subsequently, they were anesthetized with an individual concentration of sevoflurane. The minimum alveolar concentration (MAC) of the different groups was assessed using Dixon's up-and-down design and isotonic regression methods. The bootstrap estimate of the MAC of sevoflurane in the placebo group was 2.24 vol% (95% CI 1.97-2.94 vol%). In the low dose ethanol group, the bootstrap estimate was 1.65 vol% (95% CI 1.40-1.98 vol%), and in the high dose ethanol group, it was 1.08 vol% (95% CI 0.73-1.42 vol%). We therefore report that intraperitoneal application of 1 g · kg-1 or 2 g · kg-1 ethanol both resulted in a significant reduction of the MAC of sevoflurane in adult Wistar rats: by 26.3% and 51.8% respectively as compared to placebo.

The effect of a ketamine constant rate infusion on cardiovascular variables in sheep anesthetized at the minimum alveolar concentration of sevoflurane that blunts adrenergic responses

OBJECTIVE

To evaluate the effect of a constant rate infusion of ketamine on cardiac index (CI) in sheep, as estimated using noninvasive cardiac output (NICO) monitoring by partial carbon dioxide rebreathing, when anesthetized with sevoflurane at the previously determined minimum alveolar concentration that blunts adrenergic responses (MACBAR).

ANIMALS

12 healthy Dorset-crossbred adult sheep.

PROCEDURES

Sheep were anesthetized 2 times in a balanced placebo-controlled crossover design. Anesthesia was induced with sevoflurane delivered via a tight-fitting face mask and maintained at MACBAR. Following induction, sheep received either ketamine (1.5 mg/kg IV, followed by a constant rate infusion of 1.5 mg/kg/h) or an equivalent volume of saline (0.9% NaCl) solution (placebo). After an 8-day washout period, each sheep received the alternate treatment. NICO measurements were performed in triplicate 20 minutes after treatment administration and were converted to CI. Blood samples were collected prior to the start of NICO measurements for analysis of ketamine plasma concentrations. The paired t test was used to compare CI values between groups and the ketamine plasma concentrations with those achieved during the previous study.

RESULTS

Mean ± SD CI of the ketamine and placebo treatments were 2.69 ± 0.65 and 2.57 ± 0.53 L/min/m2, respectively. No significant difference was found between the 2 treatments. Mean ketamine plasma concentration achieved prior to the NICO measurement was 1.37 ± 0.58 µg/mL, with no significant difference observed between the current and prior study.

CLINICAL RELEVANCE

Ketamine, at the dose administered, did not significantly increase the CI in sheep when determined by partial carbon dioxide rebreathing.

Effects of different remifentanil target concentrations on MACBAR of sevoflurane in patients with liver dysfunction under carbon dioxide pneumoperitoneum stimulus: A randomized controlled trial

WHAT IS KNOWN AND OBJECTIVE

Remifentanil can effectively decrease the sevoflurane concentration to block sympathetic adrenergic response to CO₂ pneumoperitoneum stimulus,and liver dysfunction will significantly reduce the MAC_BAR (minimum alveolar concentration for blocking adrenergic response) of sevoflurane. However, the effects of different remifentanil concentrations on the MAC_BAR of sevoflurane in patients with liver dysfunction are unclear. The aim of this study was to observe the effects of different remifentanil concentrations by intravenous target-controlled infusion on the MAC_BAR of sevoflurane in patients with grade B liver dysfunction under carbon dioxide pneumoperitoneum stimulus.

METHODS

Seventy-five patients with grade B liver dysfunction undergoing elective laparoscopic surgery were selected, and randomly divided into three groups with remifentanil plasma target concentrations of 0 (group R₀ ), 1 (group R₁ ) and 2 (group R₂ ) ng/ml. Anaesthesia was induced by intravenous injection of propofol 2-3 mg/kg, remifentanil 2 μg/kg and cisatracurium 0.15 mg/kg. All groups were inhaled different concentrations of sevoflurane. The determination of sevoflurane MAC_BAR in each group was used a method of sequential-allocation technique, and venous blood samples were taken before and after the creation of carbon dioxide pneumoperitoneum to determine plasma adrenaline and noradrenaline concentrations.

RESULTS AND DISCUSSIONS

The MAC_BAR of sevoflurane in groups R₀ , R₁ and R₂ was 4.83%, 3.00% and 2.10%, respectively. The MAC_BAR of sevoflurane was significantly difference among the three groups. When a similar effect of MAC_BAR had achieved in each group, no significant differences were found in the changes of plasma adrenaline and noradrenaline concentrations before and after the creation of pneumoperitoneum. What is new and conclusion Target-controlled infusion of different concentrations of remifentanil can reduce sevoflurane MAC_BAR during pneumoperitoneum stimulation in patients with liver dysfunction in some degree. However, the changes of plasma adrenaline and noradrenaline concentrations are consistent in the three groups when patient's stress response was inhibited at the same degree.

The effect of oral Δ-9-tetrahydrocannabinol on the minimal alveolar concentration of sevoflurane: A randomised, controlled, observer-blinded experimental study

BACKGROUND

Cannabis has increasingly been used for medical and recreational purposes. The main pharmacological compound in cannabis is tetrahydrocannabinol (THC), which has sedative, anxiolytic and analgesic effects. In some animal models, THC has also been shown to reduce the minimum alveolar concentration (MAC) of halothane and cyclopropane, but its effect on sevoflurane, currently the most commonly used inhalational anaesthetic agent, has not been investigated.

OBJECTIVE

To investigate the effect of THC on the MAC of sevoflurane in rats.

METHODS

Observer-blinded, randomised controlled trial.

SETTING

Centre for Biomedical Research of the Medical University of Vienna, 2019.

INDIVIDUALS

Thirty-eight adult Wistar rats.

INTERVENTIONS

The rats were allocated randomly into one of two groups. Group A received THC 10 mg kg and group B received the corresponding volume of placebo via gastric gavage (administration through a tube placed in the distal oesophagus). The rats were then individually anaesthetised in an airtight sevoflurane-flooded chamber, and the MAC in both groups was determined using Dixon's up-and-down method. Blood samples were drawn to measure serum concentrations of THC.

MAIN OUTCOME MEASURES

The primary outcome was the MAC of sevoflurane in Groups A and B.

RESULTS

The bootstrap estimate of the MAC of sevoflurane was 2.1 (95% confidence interval 1.8 to 2.4) vol% in the THC group and 2.8 (95% confidence interval 2.7 to 2.9) vol% in the placebo group, corresponding to a significant MAC reduction of 26% in response to THC.

CONCLUSION

Gastric administration of THC 10 mg kg significantly reduced the MAC of sevoflurane by 26%.

TRIAL REGISTRATION

Not applicable.

Prediction of Postoperative Pain and Opioid Consumption Using Intraoperative Surgical Pleth Index After Surgical Incision: An Observational Study

Background

We evaluated whether the surgical pleth index (SPI) following surgical incision was related to postoperative pain and opioid consumption.

Methods

This prospective observational study was performed in 50 patients undergoing laparotomy under sevoflurane-based general anesthesia. We recorded the highest SPI during surgical incision. The postoperative pain with a numerical rating scale (NRS) and opioid consumption during postoperative 24 h were compared in patients who showed SPI over 50 (Group H) or 20–50 (Group L). The relationship between postoperative opioid consumption and SPI values (pre-incision, post-incision SPI value, change of SPI value, and post-incision SPI minus pre-incision SPI) was evaluated using receiver-operating characteristic analysis.

Results

The mean of the highest SPI value during surgical incision was 56 (SD, 12; range, 26–85). Twenty-nine (63%) patients were included in Group H and 17 (37%) patients in Group L. There was a significant difference in NRS during recovery room stay and on postoperative 24 h in two groups (5 [5, 6] vs 7 [6, 8], p=0.007 and 3.5 [3, 5] vs 5 [5,6], p=0.006, Group L vs Group H). Group H used higher fentanyl via patient control analgesia during postoperative 24 h (573 (253) µg vs 817 (305) µg, p=0.008). A change of pre-incision and post-incision SPI value of 23, which showed the highest sensitivity (67%) and specificity (68%), was defined post hoc as the cut-off for fentanyl consumption during postoperative 24 h ≥1000 µg.

Conclusion

Our finding suggests that the SPI response to nociceptive stimuli during surgery is closely related to the degree of patient postoperative pain and opioid requirements. This information may be used to provide proper intraoperative analgesia and individual postoperative pain management.

Effect of low-dose ketamine on MACBAR of sevoflurane in laparoscopic cholecystectomy: A randomized controlled trial

WHAT IS KNOWN AND OBJECTIVE

Low-dose ketamine can reduce the minimum alveolar concentration of sevoflurane necessary to block the adrenergic response (MAC_BAR ) in animals. However, the effects of low-dose ketamine on the sevoflurane MAC_BAR in patients undergoing laparoscopic surgery are unclear. The aim of this study was to investigate the effects of three different low doses of ketamine on the MAC_BAR of sevoflurane in patients undergoing laparoscopic cholecystectomy.

METHODS

One hundred patients who underwent laparoscopic cholecystectomy were enrolled. After general anaesthesia induction and tracheal intubation, patients received sevoflurane anaesthesia in combination with a loading dose of saline followed by infusion or a loading dose of 0.5 mg/kg ketamine followed by a continuous infusion of 5 (K₁ group), 10 (K₂ group) and 20 μg/kg/min (K₃ group). The target concentration of end-tidal sevoflurane was maintained for at least 20 minutes before carbon dioxide pneumoperitoneum stimulus. The MAC_BAR of sevoflurane in each group was determined by using an up-and-down sequential allocation technique.

RESULTS AND DISCUSSION

Seventy-one patients completed the study. The values of MAC_BAR for sevoflurane were 5.3% in the K₀ , 4.8% in K₁ , 3.3% in K₂ and 3.2% in K₃ groups. The use of ketamine significantly reduced the MAC_BAR of sevoflurane compared to sevoflurane alone. The K₂ and K₃ groups showed significantly lower values of MAC_BAR than that in the K₁ group. However, a higher dose of ketamine in the K₃ group did not further reduce the sevoflurane MAC_BAR . The mean arterial blood pressure (MAP) values before pneumoperitoneum in the K₂ and the K₃ groups were significantly higher compared to those in the K₀ and K₁ groups. Compared with the values before pneumoperitoneum, the heart rate and MAP after pneumoperitoneum were significantly increased. Overall, the haemodynamics remained stable during the study period in all groups.

WHAT IS NEW AND CONCLUSION

A loading dose of 0.5 mg/kg ketamine followed by a continuous infusion of 10.0 μg/kg/min led to a significant decrease in the MAC_BAR of sevoflurane in patients undergoing laparoscopic cholecystectomy.

Effects of different sufentanil target concentrations on the MACBAR of sevoflurane in patients with carbon dioxide pneumoperitoneum stimulus

BACKGROUND

This study aims to observe the effects of different target controlled plasma sufentanil concentrations on the minimum alveolar concentration (MAC) of sevoflurane for blocking adrenergic response (BAR) in patients undergoing laparoscopic cholecystectomy with carbon dioxide pneumoperitoneum stimulation.

METHODS

Eighty-five patients undergoing laparoscopic cholecystectomy, aged 30-65 years, with American Society of Anesthesiologists physical status I-II, were enrolled in this study. All the patients were randomly divided into 5 groups (S₀, S₁, S₂, S₃, S₄) with different sufentanil plasma target concentration (0.0, 0.1, 0.3, 0.5, 0.7 ng ml^- 1). Anesthesia was induced by inhalation of 8% sevoflurane in 100% oxygen, and 0.6 mg kg^- 1 of rocuronium was intravenously injected to facilitate the insertion of a laryngeal mask airway. The end-tidal sevoflurane concentration and sufentanil plasma target concentration were adjusted according to respective preset value in each group. The hemodynamic response to pneumoperitoneum stimulus was observed after the end-tidal sevoflurane concentration had been maintained stable at least for 15 min. The MAC_BAR of sevoflurane was measured by a sequential method. Meanwhile, epinephrine (E) and norepinephrine (NE) concentrations in the blood were also determined before and after pneumoperitoneum stimulus in each group.

RESULTS

When the method of independent paired reversals was used, the MAC_BAR of sevoflurane in groups S₀, S₁, S₂, S₃, S₄ was 5.333% (confidence interval [CI] 95%: 5.197-5.469%), 4.533% (95% CI: 4.451-4.616%), 2.861% (95% CI: 2.752-2.981%), 2.233% (95% CI: 2.142-2.324%) and 2.139% (95% CI: 2.057-2.219%), respectively. Meanwhile, when the isotonic regression analysis was used, the MAC_BAR of sevoflurane in groups S₀, S₁, S₂, S₃, S₄ was 5.329% (95% CI: 5.321-5.343%), 4.557% (95% CI: 4.552-4.568%), 2.900% (95% CI: 2.894-2.911%), 2.216% (95% CI: 2.173-2.223%) and 2.171% (95% CI: 2.165-2.183%), respectively. The MAC_BAR was not significantly different between groups S₃ and S₄ when using 0.5 and 0.7 ng ml^- 1 of sufentanil plasma target concentrations. No significant difference was found in the change of E or NE concentration between before and after pneumoperitoneum stimulation in each group.

CONCLUSIONS

The MAC_BAR of sevoflurane can be decreased with increasing sufentanil plasma target concentrations. A ceiling effect of the decrease occurred at a sufentanil plasma target concentration of 0.5 ng ml^- 1. When the sympathetic adrenergic response was inhibited in half of the patients to pneumoperitoneum stimulation in each group, the changes of E and NE concentrations showed no significant differences.

TRIAL REGISTRATION

The study was registered at http://www.chictr.org.cn ( ChiCTR1800015819 , 23, April, 2018).

Clinical evaluation of postoperative analgesia, cardiorespiratory parameters and changes in liver and renal function tests of paracetamol compared to meloxicam and carprofen in dogs undergoing ovariohysterectomy

Background

In veterinary medicine, the administration of nonsteroidal anti-inflammatory analgesics (NSAIDs) for the control of postsurgical pain in dogs and cats is common given the anti-inflammatory, analgesic, and antipyretic effects of these drugs. This study compared the serum biochemical changes and postoperative analgesic effects of paracetamol, meloxicam, and carprofen in bitches submitted to an ovariohysterectomy using the Dynamic Interactive Visual Analog Scale (DIVAS) and Pain Scale of the University of Melbourne (UMPS) scoring systems.

Methods

Thirty bitches of different breeds underwent elective ovariohysterectomies and were randomly assigned to one of three treatment groups: a paracetamol group [15 mg kg^-1 intravenous (IV)], a carprofen group (4 mg kg^-1 IV), and a meloxicam group (0.2 mg kg^-1 IV). All treatments were administered 30 minutes prior to surgery. Paracetamol was administered every 8 hours postoperatively for 48 hours total, while carprofen and meloxicam were intravenously administered every 24 hours. An evaluation of post-surgical pain was done with the DIVAS and the UMPS. The first post-surgical pain measurement was performed 1 hour after surgery and then 2, 4, 6, 8, 12, 16, 20, 24, 36, and 48 hours after surgery.

Results

All groups exhibited a gradual reduction in pain throughout the postoperative period in both scales; however, neither scale significantly differed between the three treatment groups (P > 0.05) during the 48 postoperative hours.

Conclusions

Paracetamol was as effective as meloxicam and carprofen for post-surgical analgesia in bitches subjected to elective ovariohysterectomy. The present study demonstrates that paracetamol may be considered a tool for the effective treatment of acute perioperative pain in dogs. Furthermore, this drug led to no adverse reactions or changes in the parameters assessed in the present study, indicating its safety.

Determination of the minimum alveolar concentration of sevoflurane that blunts adrenergic responses and the effect of a constant rate infusion of ketamine in sheep

Minimizing sympathetic stimulation under anesthesia prevents activation of the neuroendocrine stress response. The minimum alveolar concentration blunting adrenergic responses in 50% of the population when exposed to a noxious stimulus is defined as MAC-BAR. The purpose of this study was to determine the MAC-BAR of sevoflurane (MAC-BAR_sevo) in sheep and the MAC-BAR sparing effects of ketamine. Thirteen healthy Dorset-cross adult ewes, 4 ± 1 year old and weighing 74 ± 9 kg, were enrolled in a randomized blinded crossover study design. Ewes were anesthetized twice for MAC-BAR_sevo determination. After face mask induction with sevoflurane, sheep received intravenous ketamine at 1.5 mg/kg and a constant rate infusion of 1.5 mg/kg/h or an equivalent volume of saline (placebo). After 8 day washout, the other treatment was administered. A bracketing technique was used for MAC-BAR_sevo determination and values were collected in duplicate. The mechanical stimulus (sponge forceps) was applied at the coronary band for 1 min and blood was collected for ketamine plasma concentrations. The MAC-BAR_sevo values of each treatment were compared using a paired t-test. Mean MAC-BAR_sevo of the ketamine and placebo were 2.73 ± 0.23% and 2.77 ± 0.31%, respectively and no significant difference was found (p = .638). Average ketamine plasma concentrations was 1.54 ± 0.18 μg/mL maintained through the study. Ketamine at 1.5 mg/kg, followed by 1.5 mg/kg/h, did not decrease the MAC-BAR_sevo in sheep. Further studies to determine the effect of higher doses of ketamine on inhalational anesthetic agents and their potential adverse effects are warranted.

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.

Dose-finding study comparing three treatments of remifentanil in cats anesthetized with isoflurane undergoing ovariohysterectomy

Objectives Three infusion rates of remifentanil were used in isoflurane-anesthetized cats undergoing ovariohysterectomy. The aim of this study was to identify a dosage regimen that would provide optimal anesthetic and surgical conditions, as well as to compare cardiovascular response to surgical stimulation, postoperative analgesia, anesthetic duration and quality of recovery among the tested remifentanil infusion rates. Methods Twenty-seven client-owned, mixed-breed adult healthy female cats were randomized to receive remifentanil 0.1 µg/kg/min (REMI01), remifentanil 0.2 µg/kg/min (REMI02) or remifentanil 0.4 µg/kg/min (REMI04). After premedication with acepromazine and induction of anesthesia with propofol, cats were mechanically ventilated and anesthesia was maintained at approximately 1.0 minimum alveolar concentration (MAC) of isoflurane (1.63% end-tidal isoflurane [ETISO]). Remifentanil infusion rate was increased or decreased by 20% if blood pressure had increased or decreased by 20% from previous values. Pulse rate (PR), systolic arterial pressure (SAP), esophageal temperature, pulse oximetry, end-tidal partial pressure of CO2 and ETISO were recorded at different time points during surgery. Meloxicam was administered before the end of surgery. Data within each treatment group were analyzed using a mixed-model ANOVA and Friedman's test followed by the Wilcoxon signed rank test. Bonferroni or Dunnett's post-hoc tests were used. The Kruskal-Wallis test followed by Dunn's post-hoc test were used to compare data between groups; significance was set at P <0.05. Results Time to sternal recumbency and time to standing were significantly longer in REMI04 than in the other groups. SAP was higher when compared with baseline in REMI01 and REMI02 groups than in REMI04. No significant difference in PR among groups was observed. One cat in REMI01 and another in REMI02 required postoperative rescue analgesia. Conclusion and relevance The dosage regimen of 0.4 µg/kg/min seemed to be the most appropriate to be used in cats undergoing ovariohysterectomy and anesthetized with 1.0 MAC of isoflurane.

Pupillary reflex dilation in response to incremental nociceptive stimuli in patients receiving intravenous ketamine

Pupillometry is a non-invasive monitoring technique, which allows dynamic pupillary diameter measurement by an infrared camera. Pupillary diameter increases in response to nociceptive stimuli. In patients anesthetized with propofol or volatile agents, the magnitude of this pupillary dilation is related to the intensity of the stimulus. Pupillary response to nociceptive stimuli has never been studied under ketamine anesthesia. Our objective was to describe pupillary reflex dilation after calibrated tetanic stimulations in patients receiving intravenous ketamine. After written consent, 24 patients of our pediatric burn care unit were included. They received an oral morphine premedication (0.3 mg kg^-1) 1 h before their scheduled daily dressing change. Just before the procedure, they received 1 mg kg^-1 of intravenous ketamine. Two minutes after this bolus, tetanic stimulations of incremental intensities were performed on the arm of each patient (5-10-20-30-40-60 mA, 60 s interval between stimulations). Pupillary diameter, heart rate and movements were recorded before and after each stimulation. Tetanic stimulations were associated with changes in pupillary diameter and heart rate. The magnitude of these changes was significantly influenced by the intensity of stimulation (ANOVA for repeated measures, p < 0.001). Movement was associated with a 32% increase in diameter (ROC curves, AUC 0.758) with 65% sensitivity and 77% specificity. In children, pupillary reflex dilation to nociceptive stimuli persists under deep sedation obtained with 1 mg kg^-1 of intravenous ketamine combined with a 0.3 mg kg^-1 oral morphine premedication, and its magnitude depends on the intensity of the stimulation. Our results confirm that pupillometry could be a relevant way to monitor nociception in anaesthetised subjects, including those receiving ketamine. Trial registration clinicaltrials.gov, NCT 02648412.

Hemodynamic Responses at Intubation, Change of Position, and Skin Incision: A Comparison of Multimodal Analgesia with Conventional Analgesic Regime

Background:

Lumbar spine surgery is associated with hemodynamic variations at intubation, change of position, and skin incision. A balanced anesthesia with multimodal analgesia (MMA) is necessary to attenuate these changes.

Aim:

To assess the relative effectiveness of preemptive MMA compared with the conventional analgesic regime in suppressing the hemodynamic response to endotracheal intubation, prone positioning, and skin incision.

Settings and Design:

A randomized, prospective study involving 42 patients belonging to the American Society of Anesthesiologists Physical Status 1 and II scheduled to undergo elective lumbar spine surgery were allocated into two groups of 21 each.

Materials and Methods:

Forty-two patients were randomly allocated into Groups A and B. Group A (study group) received diclofenac, paracetamol, clonidine, and bupivacaine with adrenaline skin infiltration and Group B (control group) injection paracetamol and saline with adrenaline skin infiltration.

Statistical Analysis Used:

Hemodynamic parameters (heart rate [HR], systolic blood pressure [SBP], diastolic blood pressure [DBP], and mean arterial pressure [MAP]) between the groups following intubation, prone position, and skin incision were noted and compared using repeated measure analysis of variance. One sample t-test was used to compare the standard mean concentration with the means of the study and control groups. P < 5% being considered statistically significant.

Results:

In the study group, HR, SBP, DBP, and MAP were lower at intubation and change of position as compared to the control group and were statistically significant.

Conclusion:

Preemptive MMA with balanced anesthesia is effective in attenuating the hemodynamic responses to multiple noxious stimuli during lumbar spine surgery.

Sevoflurane-induced isoelectric EEG and burst suppression: differential and antagonistic effect of added nitrous oxide

The objective of this study was to investigate whether nitrous oxide influenced the ED50 of sevoflurane for induction of isoelectric electroencephalogram (ED50_isoelectric ) differently from its influence on the ED50 of sevoflurane for electroencephalogram burst suppression (ED50_burst ). In a prospective, randomised, double-blind, parallel group, up-down sequential allocation study, 77 ASA physical status 1 and 2 patients received sevoflurane induction and, after tracheal intubation, were randomly allocated to receive sevoflurane with either 40% oxygen in air (control group) or 60% nitrous oxide in oxygen mixture (nitrous group). The ED50_isoelectric in the two groups was determined using Dixon's up and down method, starting at 2.5% with 0.2% step size of end-tidal sevoflurane. The electroencephalogram was considered as isoelectric when a burst suppression ratio of 100% lasted > 1 min. The subsequent concentrations of sevoflurane administered were determined by the presence or absence of isoelectric electroencephalogram in the previous patient in the same group. The ED50_isoelectric in the nitrous group 4.08 (95%CI, 3.95-4.38)% was significantly higher than that in the control group 3.68 (95%CI, 3.50-3.78)% (p < 0.0001). The values for ED50_burst were 3.05 (95%CI, 2.66-3.90)% and 3.02 (95%CI, 3.00-3.05)% in nitrous group and control group, respectively (p = 0.52). The addition of 60% nitrous oxide increases ED50_isoelectric , but not the ED50_burst of sevoflurane. Neither result indicates an additive effect of anaesthetic agents, as might be expected, and possible reasons for this are discussed.

Interaction between maropitant and carprofen on sparing of the minimum alveolar concentration for blunting adrenergic response (MAC-BAR) of sevoflurane in dogs

Maropitant, a neurokinin-1 receptor antagonist, may provide analgesic effects by blocking pharmacological action of substance P. Carprofen is a non-steroidal anti-inflammatory drug commonly used for pain control in dogs. The purpose of this study was to evaluate the effect of a combination of maropitant and carprofen on the minimum alveolar concentration for blunting adrenergic response (MAC-BAR) of sevoflurane in dogs. Six healthy adult beagle dogs were anesthetized with sevoflurane four times with a minimum of 7-day washout period. On each occasion, maropitant (1 mg/kg) alone, carprofen (4 mg/kg) alone, a combination of maropitant (1 mg/kg) and carprofen (4 mg/kg), or saline (0.1 ml/kg) was subcutaneously administered at 1 hr prior to the first electrical stimulation for the sevoflurane MAC-BAR determination. The sevoflurane MAC-BAR was significantly reduced by maropitant alone (2.88 ± 0.73%, P=0.010), carprofen alone (2.96 ± 0.38%, P=0.016) and the combination (2.81 ± 0.51%, P=0.0003), compared with saline (3.37 ± 0.56%). There was no significant difference in the percentage of MAC-BAR reductions between maropitant alone, carprofen alone and the combination. The administration of maropitant alone and carprofen alone produced clinically significant sparing effects on the sevoflurane MAC-BAR in dogs. However, the combination of maropitant and carprofen did not produce any additive effect on the sevoflurane MAC-BAR reduction. Anesthetic premedication with a combination of maropitant and carprofen may not provide any further sparing effect on anesthetic requirement in dogs.

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.

Prediction of Movement to Surgical Stimulation by the Pupillary Dilatation Reflex Amplitude Evoked by a Standardized Noxious Test

Background:

Individual assessment of the amplitude of a physiologic reflex evoked by a standardized noxious test (SNT) before surgical stimulation has been suggested to predict movement upon the forthcoming surgical stimulation. This study aimed to compare the ability of pupillary dilatation reflex amplitude (PDRA) evoked by an SNT and estimated remifentanil effect-site concentration (Ce) to predict movement upon surgical stimulation.

Methods:

Eighty female patients were anesthetized for vacuum aspiration with propofol (Ce 4 μg/ml) and remifentanil. Remifentanil Ce was randomized to 0, 1, 3, or 5 ng/ml. SNT was a 60-mA, 5-s, 100-Hz tetanus applied on median nerve before cervix dilatation. PDRA was calculated as the difference in pupillary diameter after and before SNT. Movement upon cervix dilatation was recorded by an independent observer. Ability of PDRA and estimated remifentanil Ce to discriminate movers from non-movers during cervix dilatation was measured as the area under the receiver operating characteristics curve.

Results:

Twenty-one of the 76 patients analyzed moved during cervix dilatation. Mean PDRA (±1 SD) evoked by SNT was 2.0 ± 1.2 mm in movers and 0.6 ± 0.7 in non-movers (P &lt; 0.0001). Remifentanil Ce was 0.2 ± 0.4 ng/ml in movers and 3.0 ± 1.7 in non-movers (P &lt; 0.0001). Area under the receiver operating characteristics curve for PDRA was 0.90 (95% CI, 0.83 to 0.96) and for remifentanil Ce 0.94 (0.89 to 0.98), without any significant difference between the two areas.

Conclusions:

PDRA evoked by an SNT is as accurate as the estimated remifentanil Ce to predict movement upon cervix dilatation. PDRA could be valuable when estimated opioid Ce is not available or reliable.

1-1-12 one-step wash-in scheme for desflurane low flow anesthesia: performance without nitrous oxide

Background

We reported a 1-1-12 wash-in scheme for desflurane-nitrous oxide (N₂O) low flow anesthesia that is simple, rapid, and predictable. There remain some situations where N₂O should be avoided, which limits the generalizability of this wash-in scheme. The objective of our study was to determine the performance of this scheme in contexts where N₂O is not used.

Methods

We recruited 106 patients scheduled for elective surgery under general anesthesia. After induction and intubation, wash-in was started with a fresh gas flow of air:O₂ 1:1 L/min and a vaporizer concentration of desflurane of 12%. Controlled ventilation was then adjusted to maintain P_ACO₂ at 30–35 mmHg.

Results

The alveolar concentration of desflurane (F_AD) rose rapidly from 0% to 6% in 4 minutes in the same pattern as observed in our previous study in which N₂O was used. An F_AD of 7% was achieved in 6 minutes. An F_AD of 1% to 7% occurred at 0.6, 1, 1.5, 2, 3, 4, and 6 minutes. The rise in heart rate during wash-in was statistically significant, although not clinically so. There was a slight but statistically significant decrease in blood pressure, but this had no clinical significance.

Conclusion

Performance of the 1-1-12 wash-in scheme is independent of the use of N₂O. Respective F_ADs of 1%, 2%, 3%, 4%, 5%, 6%, and 7% can be expected at 0.6, 1, 1.5, 2, 3, 4, and 6 minutes.

Clinical comparison of propofol-remifentanil TCI with sevoflurane induction/maintenance anesthesia in laparoscopic cholecystectomy

Objective : We aimed to compare the anesthetic characteristics between total intravenous anesthesia (TIVA) using propofol-remifentanil with target control infusion (TCI) and volatile induction and maintenance anesthesia (VIMA) using sevoflurane and sufentanyl for patients undergoing laparoscopic cholecystectomy.

METHODS

A total of 120 patients undergoing laparoscopic cholecystectomy were randomly assigned to two groups. Patients in group T received TCI of propofol-remifentanil for induction and maintenance. Patients in group S received sevoflurane-sufentanyl for induction and maintenance.

RESULTS

Patients in group S had a significantly faster induction time than patients in group T (109s vs.44s). The emergence time in terms of time to extubation was comparable between the two groups, while the time to eyes opening (419s vs.483s, p=0.006) and duration in PACU were longer in group S (44 min vs.53 min, p=0.017). Ten (17.2%) patients in group S were administered an antihypertensive drug when gallbladder issues were present, while only 1(1.7%) patient needed this drug in group T (p=0.004).More patients in group T than in group S received fentanyl for analgesia in PACU (88%vs.70%, p=0.013). The incidence of postoperative nausea and vomiting (PONV) in PACU was higher in group S than in group T (20% vs.38%, p=0.027).

CONCLUSION

Both techniques had advantages and disadvantages in laparoscopic cholecystectomy; none of the techniques studied was superior.

Minimal alveolar concentration of sevoflurane for induction of isoelectric electroencephalogram in middle-aged adults

BACKGROUND

We determined the minimal alveolar concentration (MAC) of sevoflurane inducing an isoelectric EEG in 50% of adult subjects (MACie).

METHODS

We included 31 middle-aged subjects; 30 subjects finished the study protocol and received sevoflurane at preselected concentrations according to a modified Dixon 'up-and-down' design starting at 1.7 vol% with 0.2 vol% steps size. General anaesthesia was induced and maintained with sevoflurane; tracheal intubation was facilitated with cisatracurium. After a period of 30 min before skin incision, the state of isoelectric EEG was considered as significant when a burst suppression ratio of 100% lasted for >1 min. The haemodynamic responses to skin incision and the vasopressor requirement to maintain stable haemodynamic status were also analysed according to the EEG state.

RESULTS

MACie was 3.5% (95% confidence interval, 3.4-3.7%) in middle-aged subjects. When compared with subjects not in isoelectric EEG state, subjects in isoelectric EEG state received more phenylephrine to maintain stable haemodynamics (10 of 10 compared with 7 of 20 subjects, P=0.001) and experienced less sympathetic responses to skin incision (1 of 10 compared with 11 of 20 subjects, P=0.024).

CONCLUSIONS

MACie for sevoflurane was ∼2.1 times MAC for immobilization in phenobarbital premedicated middle-aged adults. Sevoflurane-induced isoelectric EEG state is associated with significant cardiovascular depression but reduced haemodynamic responses to skin incision.

Interaction between nitrous oxide, sevoflurane, and opioids: a response surface approach

BACKGROUND

The interaction of sevoflurane and opioids can be described by response surface modeling using the hierarchical model. We expanded this for combined administration of sevoflurane, opioids, and 66 vol.% nitrous oxide (N2O), using historical data on the motor and hemodynamic responsiveness to incision, the minimal alveolar concentration, and minimal alveolar concentration to block autonomic reflexes to nociceptive stimuli, respectively.

METHODS

Four potential actions of 66 vol.% N2O were postulated: (1) N2O is equivalent to A ng/ml of fentanyl (additive); (2) N2O reduces C50 of fentanyl by factor B; (3) N2O is equivalent to X vol.% of sevoflurane (additive); (4) N2O reduces C50 of sevoflurane by factor Y. These four actions, and all combinations, were fitted on the data using NONMEM (version VI, Icon Development Solutions, Ellicott City, MD), assuming identical interaction parameters (A, B, X, Y) for movement and sympathetic responses.

RESULTS

Sixty-six volume percentage nitrous oxide evokes an additive effect corresponding to 0.27 ng/ml fentanyl (A) with an additive effect corresponding to 0.54 vol.% sevoflurane (X). Parameters B and Y did not improve the fit.

CONCLUSION

The effect of nitrous oxide can be incorporated into the hierarchical interaction model with a simple extension. The model can be used to predict the probability of movement and sympathetic responses during sevoflurane anesthesia taking into account interactions with opioids and 66 vol.% N2O.

Incidence of and risk factors for postoperative nausea and vomiting at a Japanese Cancer Center: first large-scale study in Japan

Purpose

The first purpose of this study was to determine the incidence of postoperative nausea and/or vomiting (PONV) 0–48 h after anesthesia at a Japanese cancer center. The second purpose of this study was to collect information on PONV risk factors, independently, in the categories of patient-related, anesthesia-related, and surgery-related factors.

Methods

The frequency of nausea and vomiting was prospectively investigated from 0 to 48 h after anesthesia in 1645 patients (11–94 years of age) at a single medical institution. The occurrence of nausea and vomiting and the use of antiemetics were recorded up to 48 h after anesthesia. Patient-related, anesthesia-related, and surgery-related factors were also recorded and submitted to multiple logistic regression analysis to determine the relationship of these factors to nausea and vomiting.

Results

The incidences of nausea and vomiting from 0 to 24 h after anesthesia were 40 and 22 %, respectively. The incidences 24–48 h after anesthesia were 10 and 3 %, respectively. Female sex, previous history of PONV, prolonged anesthesia, and remifentanil use during surgery were identified as risk factors for both nausea and vomiting. The use of a volatile anesthetic, use of fentanyl during surgery, postoperative use of opioids, nonsmoking status, and drinking alcohol on 4 or fewer days per week were identified as risk factors for nausea alone.

Conclusion

The incidence of and risk factors for PONV at a Japanese cancer center according to this study are comparable to those reported elsewhere.

Non-steroidal anti-inflammatory drugs reduce the stress response during sevoflurane anesthesia

BACKGROUND

Non-steroidal anti-inflammatory drugs are analgesics commonly used for post-operative pain. However, their effect on dosages of inhaled anesthetics during surgery is unclear. We investigated the effect of flurbiprofen axetil and parecoxib sodium on the minimum alveolar concentration of sevoflurane required to blunt stress responses to skin incision under general anesthesia.

METHODS

One hundred and five adult patients were randomly allocated to four treatment groups, each receiving sevoflurane: control (sevoflurane only), lidocaine (1 mg/kg bolus, followed by continuous infusion of 20 μg/kg/min after intubation), Intravenous (IV) flurbiprofen (1 mg/kg before skin incision), and IV parecoxib (40 mg before skin incision). Following anesthetic induction and stabilization of end-tidal sevoflurane concentration, mean arterial blood pressure and heart rate were recorded 2 min before and at 5-min intervals after skin incision. The stable end-tidal sevoflurane concentration was calculated using an up-and-down method.

RESULTS

The minimum alveolar concentration of sevoflurane required to blunt the stress responses to skin incision in the control, lidocaine, flurbiprofen, and parecoxib groups was 4.63 ± 0.08%, 2.67 ± 0.08%, 3.33 ± 0.08%, and 3.80 ± 0.11%, respectively. These figures for the later three groups were all significantly less than that of the control group (P = 0.021, P = 0.037, and P = 0.011, respectively); that of the flurbiprofen group was significantly less than the parecoxib (P = 0.034).

CONCLUSION

The non-steroidal anti-inflammatory drugs flurbiprofen axetil and parecoxib sodium decreased the minimum alveolar concentration of sevoflurane required to blunt the stress response to skin incision during general anesthesia.

Minimal alveolar concentration of sevoflurane inhibiting the reflex pupillary dilatation after noxious stimulation in children and young adults

BACKGROUND

In children, sevoflurane is the most commonly used anaesthetic. Its excellent haemodynamic tolerance gives it a wide therapeutic index. This halogenated agent can abolish movement [minimal alveolar concentration (MAC)] or haemodynamic responses (MACBAR) to noxious stimulus in children as in adults. Reflex pupillary dilatation (RPD) has been demonstrated as a very sensitive measure of noxious stimulation. In order to investigate the effect of sevoflurane on the RPD, a subcortical reflex, we determined the MAC of sevoflurane inhibiting the RPD in 50% of the subjects in response to skin incision (MACpup) in pre- and post-pubertal subjects.

METHODS

We included 30 pre-pubertal children and 19 post-pubertal subjects. Patients received sevoflurane at preselected concentrations according to an 'up and down' design, and after a steady-state period, skin incision was performed. The RPD was considered as significant when the pupillary diameter increased by more than 100%. Heart rate (HR) and bispectral index (BIS) changes were analysed according to the pupillary response.

RESULTS

The MACpup of sevoflurane was 4.8% (95% confidence interval, 4.6-5.1%) in pre-pubertal children vs 3.4% (3.5-3.3%) in post-pubertal subjects (P<0.001). Inhibition of RPD was always associated with lack of significant HR response. In pre-pubertal children receiving high concentrations of sevoflurane, RPD in response to noxious stimulation was frequently associated with lack of HR response and low BIS values.

CONCLUSIONS

MACpup was higher than MAC and close to the MACBAR. Inhibition of RPD in pre-pubertal children required higher sevoflurane concentrations compared with post-pubertal subjects, suggesting that the relationship between the brain structure sensitivities may differ with brain maturation.

Hemodynamic effects of butorphanol in desflurane-anesthetized dogs

OBJECTIVE

To evaluate the effects of butorphanol on cardiopulmonary parameters in dogs anesthetized with desflurane and breathing spontaneously.

STUDY DESIGN

Prospective, randomized experimental trial.

ANIMALS

Twenty dogs weighing 12 ± 3 kg.

METHODS

Animals were distributed into two groups: a control group (CG) and butorphanol group (BG). Propofol was used for induction and anesthesia was maintained with desflurane (10%). Forty minutes after induction, the dogs in the CG received sodium chloride 0.9% (0.05 mL kg(-1) IM), and dogs in the BG received butorphanol (0.4 mg kg(-1) IM). The first measurements of body temperature (BT), heart rate (HR), arterial pressures (AP), cardiac output (CO), cardiac index (CI), central venous pressure (CVP), stroke volume index (SVI), pulmonary arterial occlusion pressure (PAOP), mean pulmonary arterial pressure (mPAP), left ventricular stroke work (LVSW), systemic (SVR) and pulmonary (PVR) vascular resistances, respiratory rate (f(R) ), and arterial oxygen (PaO(2) ) and carbon dioxide (PaCO(2) ) partial pressures were taken immediately before the administration of butorphanol or sodium chloride solution (T0) and then at 15-minute intervals (T15-T75).

RESULTS

In the BG, HR, AP, mPAP and SVR decreased significantly from T15 to T75 compared to baseline. f(R) was lower at T30 than at T0 in the BG. AP and f(R) were significantly lower than in the CG from T15 to T75. PVR was lower in the BG than in the CG at T30, while PaCO(2) was higher compared with T0 from T30 to T75 in the BG and significantly higher than in the CG at T30 to T75.

CONCLUSIONS AND CLINICAL RELEVANCE

At the studied dose, butorphanol caused hypotension and decreased ventilation during desflurane anesthesia in dogs. The hypotension (from 86 ± 10 to 64 ± 10 mmHg) is clinically relevant, despite the maintenance of cardiac index.

Response surface model predictions of emergence and response to pain in the recovery room: An evaluation of patients emerging from an isoflurane and fentanyl anesthetic

INTRODUCTION

Sevoflurane-remifentanil interaction models that predict responsiveness and response to painful stimuli have been evaluated in patients undergoing elective surgery. Preliminary evaluations of model predictions were found to be consistent with observations in patients anesthetized with sevoflurane, remifentanil, and fentanyl. This study explored the feasibility of adapting the predictions of sevoflurane-remifentanil interaction models to an isoflurane-fentanyl anesthetic. We hypothesized that model predictions adapted for isoflurane and fentanyl are consistent with observed patient responses and are similar to the predictions observed in our previous work with sevoflurane-remifentanil/fentanyl anesthetics.

METHODS

Twenty-five patients scheduled for elective surgery received a fentanyl-isoflurane anesthetic. Model predictions of unresponsiveness were recorded at emergence, and predictions of a response to noxious stimulus were recorded when patients first required analgesics in the recovery room. Model predictions were compared with observations with graphical and temporal analyses. Results were also compared with our previous predictions after the administration of a sevoflurane-remifentanil/fentanyl anesthetic.

RESULTS

Although patients were anesthetized, model predictions indicated a high likelihood that patients would be unresponsive (> or = 99%). After the termination of the anesthetic, model predictions of responsiveness well described the actual fraction of patients observed to be responsive during emergence. Half of the patients woke within 2 min of the 50% model-predicted probability of unresponsiveness; 70% woke within 4 min. Similarly, predictions of a response to a noxious stimulus were consistent with the number of patients who required fentanyl in the recovery room. Model predictions after the administration of an isoflurane-fentanyl anesthetic were similar to model predictions after a sevoflurane-remifentanil/fentanyl anesthetic.

DISCUSSION

The results confirmed our study hypothesis; model predictions for unresponsiveness and no response to painful stimuli, adapted to isoflurane-fentanyl were consistent with observations. These results were similar to our previous study comparing model predictions and patient observations after a sevoflurane-remifentanil/fentanyl anesthetic.

Desflurane versus sevoflurane to reduce blood loss in maxillofacial surgery

PURPOSE

In our study, desflurane was hypothesized to reduce blood loss more than sevoflurane, both used with targeted mild controlled hypotension.

PATIENTS AND METHODS

A total of 20 American Society of Anesthesiologists Class I patients undergoing maxillofacial elective surgery for maxillary and mandibular osteotomies were randomized to a desflurane group or a sevoflurane group. Anesthesia was performed with an end tidal value of the inhaled agent to obtain a bispectral index value <30 but without burst-suppression patterns (minimal alveolar concentration age-corrected between 0.7 and 0.9). Remifentanil was administered at a dose of 0.5 microg x kg(-1) x min(-1) to obtain analgesia and a <2 surgical field level in Fromme's modified scale. Sodium-nitroprusside was administered on demand to have a surgical field level of <2 when the anesthesia plan was not sufficient to achieve this target. The minimal value of the mean arterial pressure achievable was 60 mm Hg.

RESULTS

In the desflurane group, blood loss was more restricted. The hypotensive drug was used in 8 patients in the sevoflurane group and 2 patients in the desflurane group.

CONCLUSIONS

Anesthesia with desflurane can reduce blood loss and could give an acceptable surgical field with mild controlled hypotension and with a substantial reduction in the vasoactive drug requirement. These data need to be assessed with an enlargement of the statistical sample.

Is a new paradigm needed to explain how inhaled anesthetics produce immobility?

A paradox arises from present information concerning the mechanism(s) by which inhaled anesthetics produce immobility in the face of noxious stimulation. Several findings, such as additivity, suggest a common site at which inhaled anesthetics act to produce immobility. However, two decades of focused investigation have not identified a ligand- or voltage-gated channel that alone is sufficient to mediate immobility. Indeed, most putative targets provide minimal or no mediation. For example, opioid, 5-HT3, gamma-aminobutyric acid type A and glutamate receptors, and potassium and calcium channels appear to be irrelevant or play only minor roles. Furthermore, no combination of actions on ligand- or voltage-gated channels seems sufficient. A few plausible targets (e.g., sodium channels) merit further study, but there remains the possibility that immobilization results from a nonspecific mechanism.

Inhaled anesthetics do not combine to produce synergistic effects regarding minimum alveolar anesthetic concentration in rats

BACKGROUND

We hypothesized that pairs of inhaled anesthetics having divergent potencies [one acting weakly at minimum alveolar anesthetic concentration (MAC); one acting strongly at MAC] on specific receptors/channels might act synergistically, and that such deviations from additivity would support the notion that anesthetics act on multiple sites to produce anesthesia.

METHODS

Accordingly, we studied the additivity of MAC for 11 anesthetic pairs divergently (one weakly, one strongly) affecting a specific receptor/channel at MAC. By "divergently," we usually meant that at MAC the more strongly acting anesthetic enhanced or blocked the in vitro receptor or channel at least twice (and usually more) as much as did the weakly acting anesthetic. The receptors/channels included: TREK-1 and TASK-3 potassium channels; and gamma-aminobutyric acid type A, glycine, N-methyl-D-aspartic acid, and acetylcholine receptors. We also studied the additivity of cyclopropane-benzene because the N-methyl-D-aspartic acid blocker MK-801 had divergent effects on the MACs of these anesthetics. We also studied four pairs that included nitrous oxide because nitrous oxide had been reported to produce infraadditivity (antagonism) when combined with isoflurane.

RESULTS

All combinations produced a result within 10% of that which would be predicted by additivity except for the combination of isoflurane with nitrous oxide where infraadditivity was found.

CONCLUSIONS

Such results are consistent with the notion that inhaled anesthetics act on a single site to produce immobility in the face of noxious stimulation.

Landiolol, an Ultra–Short-Acting β1-Adrenoceptor Antagonist, Does Not Alter the Minimum Alveolar Anesthetic Concentration of Isoflurane in a Swine Model

BACKGROUND

We previously reported that landiolol, an ultra-short-acting beta1-adrenoceptor antagonist, does not alter the electroencephalographic effect of isoflurane. Here, we investigated the influence of landiolol on the minimum alveolar anesthetic concentration (MAC) of isoflurane required to prevent movement in response to a noxious stimulus in 50% of subjects.

METHODS

Ten swine (29.0 +/- 3.4 kg) were anesthetized by inhalation of isoflurane. MAC was determined using the dewclaw clamp technique, in which movement in response to clamping is recorded. After determination of MAC in the baseline period, an infusion of landiolol (0.125 mg x kg(-1) x min(-1) for 1 min, then 0.04 mg x kg(-1) x min(-1)) was started. After a 20-min stabilization period, MAC was again assessed (0.04 mg x kg(-1) x min(-1) landiolol). The infusion of landiolol was then increased from 0.04 to 0.2 mg x kg(-1) x min(-1), and after a 20-min stabilization period, MAC was again assessed (0.2 mg x kg(-1) x min(-1) landiolol). Finally, the infusion of landiolol was stopped, and after a 20-min stabilization period, MAC was assessed for a fourth time (Baseline 2).

RESULTS

Landiolol clearly attenuated the increases in heart rate and mean arterial blood pressure that occurred in response to the dewclaw clamp, but did not alter the MAC of isoflurane.

CONCLUSIONS

Landiolol does not alter the antinociceptive effect of isoflurane. This result, combined with that from our previous work, also suggests that landiolol does not influence the anesthetic potency of inhaled anesthetics.