1 MAC-incision sevoflurane prevents explicit awareness during surgical skin incision and tracheal intubation

The incidence of intra-operative awareness during general anesthesia in China: a multi-center observational study

BACKGROUND

The incidence of awareness in patients undergoing general anesthesia is 0.1-0.2% in Western countries. The medical literatures about awareness during general anesthesia are still rare in China, but some previous studies have reported a higher incidence (1.4-6%) of intra-operative awareness. To find out the reason why the incidence reported in China is much higher than that in Western countries, we performed a prospective, multicenter, non-randomized observational study to determine the true incidence of intra-operative awareness in China.

METHODS

This is a prospective, non-randomized descriptive cohort study that was conducted at 25 academic medical centers in China. Eleven thousand one hundred and eighty-five patients were interviewed by research staff for evaluation of awareness at the first and fourth day after general anesthesia with muscle relaxation. An independent blinded committee evaluated the responses and determined whether awareness occurred. Necessary data were collected for a binary logistic regression analysis.

RESULTS

Data from 11,101 patients were presented. Forty-six cases (0.41%) were reported as definite awareness and 47 additional cases (0.41%) as possible awareness. Three hundred and fifty-five patients (3.19%) had dreams during general anesthesia. Awareness was associated with increased American Society of Anesthesiologists (ASA) physical status, a previous anesthesia, and anesthesia methods of total intravenous anesthesia.

CONCLUSION

The incidence of intra-operative awareness in China is approximately 0.41%, two to three times higher than that widely cited in Western countries. Inappropriately light anesthesia, and the population proportion of surgery and general anesthesia in China may account for the difference. (ClinicalTrials.gov Identifier, NCT00693875.).

The optimal bolus dose of alfentanil for tracheal intubation during sevoflurane induction without neuromuscular blockade in day-case anaesthesia

BACKGROUND

The purpose of this study was to determine the optimal bolus dose of alfentanil required to provide successful intubating conditions following inhalation induction of anaesthesia using 5% sevoflurane and 60% nitrous oxide without neuromuscular blockade in adult day-case anaesthesia.

METHODS

Twenty-four adults, aged 18-60 years, undergoing general anaesthesia for short ambulatory surgery were enroled into the study. After vital capacity induction, with sevoflurane 5% and 60% nitrous oxide in oxygen, pre-determined dose of alfentanil was injected over 30 s. The dose of alfentanil was determined by modified Dixon's up-and-down method (2 microg/kg as a step size). Ninety seconds after the end of bolus administration of alfentanil, the trachea was intubated. Systolic blood pressure, heart rate and SpO2 were recorded at anaesthetic induction, before, 1 min and 3 min after intubation.

RESULTS

The bolus dose of alfentanil for successful tracheal intubation was 10.7+/-2.1 microg/kg in 50% of patients during inhalation induction. From probit analysis, 50% effective dose (ED(50)) and ED(95) values (95% confidence limits) of alfentanil were 10.7 microg/kg (8.0-12.9 microg/kg) and 14.9 microg/kg (12.9-31.1 microg/kg), respectively.

CONCLUSIONS

Using the modified Dixon's up-and-down method, the bolus dose of alfentanil for successful tracheal intubation was 10.7+/-2.1 microg/kg in 50% of adult patients during inhalation induction using 5% sevoflurane and 60% nitrous oxide in oxygen without neuromuscular blocking agent in day-case anaesthesia.

Concentration of remifentanil needed for tracheal intubation with sevoflurane at 1 MAC in adult patients

BACKGROUND AND OBJECTIVE

Inhalation induction with sevoflurane provides acceptable conditions for tracheal intubation. Opioids significantly decrease the alveolar concentration needed to achieve tracheal intubation. The purpose of this study was to determine the target concentration of remifentanil providing excellent conditions for tracheal intubation with sevoflurane at 1 minimum alveolar concentration without muscle relaxant.

METHODS

Twenty-four consecutive patients, aged 18-50 yr, ASA I or II, were studied. Induction of anaesthesia was performed with sevoflurane at age-adjusted minimum alveolar concentration. Remifentanil was simultaneously administered using target-controlled infusion with the Minto model. Target plasma concentration of remifentanil was selected for each patient according to an up-and-down method.

RESULTS

The mean target concentration of remifentanil for successful tracheal intubation was 3.3 ng mL(-1) (95% confidence interval: 2.6-3.9 ng mL(-1)). Arterial pressure, heart rate and bispectral index did not increase after tracheal intubation in the group of patients with successful intubation.

CONCLUSIONS

Remifentanil at 3.3 ng mL(-1) together with sevoflurane at 1 minimum alveolar concentration provides excellent conditions for tracheal intubation in 50% of patients.

Systolic blood pressure, not BIS, is associated with movement during laryngoscopy and intubation

OBJECTIVE

To compare bispectral index (BIS) values to hemodynamic variations, in order to evaluate adequacy of anesthesia during orotracheal intubation with muscle relaxants.

METHODS

Forty-one patients ASA I-II, scheduled for elective peripheral surgery under general anesthesia with tracheal intubation were enrolled in the study. Fentanyl/thiopental followed by vecuronium were used for induction. Onset of relaxation was monitored at the orbicularis occuli (OO) muscle using train-of-four stimulation. Intubation was performed when no response at the OO was detected visually. Intubating conditions were noted. The "isolated forearm" technique was used to detect movement during laryngoscopy/intubation. BIS values, pulse rate (PR), and systolic pressure were recorded before induction, during laryngoscopy/intubation and 60 sec after intubation.

RESULTS

Although intubating conditions were clinically adequate for all patients, ten out of 41 had movement of the isolated arm during laryngoscopy/intubation. BIS values were not significantly different for these patients: 67 (55-83) compared to those who had no movement: 60 (35-80), P = 0.6. During laryngoscopy, PR increased for all patients while systolic pressure increased significantly only in patients who moved: 125 (100-136) mmHg vs those who did not: 108 (67-140), P < 0.05.

CONCLUSION

Systolic pressure elevations were associated with inadequate anesthesia as evaluated by the "isolated forearm" technique, during laryngoscopy/intubation. BIS values were not different between groups, suggesting that systolic blood pressure may be a better predictor of inadequate anesthesia under the circumstances described.

Intraoperative awareness: detected by the structured Brice interview?

BACKGROUND

Awareness is a rare complication in general anesthesia, but its consequences are stressful. Efforts must be undertaken to prevent, diagnose, and, if occurring, treat it. The incidence of awareness is higher following anesthesia involving the use of muscle relaxants. As a part of a quality assurance program at our short-stay surgery all patients exposed to general anesthesia are routinely subjected to a Brice interview, which aims to evaluate our standard anesthetic technique regarding awareness.

METHODS

The Brice interview was used prospectively in 5216 patients given a propofol/opioid anesthetic for day-case or short-stay surgery. Neuromuscular blocks were used only for surgical needs, not routinely. All patients were interviewed on discharge from the recovery room. A second interview, according to Brice, was undertaken by telephone 3-7 days later in the case of a notable intraoperative event, or otherwise after postoperative patient complaints. All patients were also interviewed by telephone 1-2 days postoperatively.

RESULTS

None of the patient interviews indicated awareness. This was also the case in five non-relaxed patients who had an incident of light anesthesia with eye opening and gross motor response without forewarning. Neuromuscular blockade was used in 7% of patients.

DISCUSSION

We were unable to detect intraoperative awareness. The anesthetic regimen, including minimal use of muscle relaxants, might be beneficial for awareness prevention. Alternatively, the diagnostic power, the timing of the Brice interview, or the number of interviews performed may be questioned.

Muscle relaxation does not alter hypnotic level during propofol anesthesia

Electromyographic (EMG) activity can contaminate electroencephalographic signals. Paralysis may therefore reduce the Bispectral Index (BIS) by alleviating artifact from muscles lying near the electrodes. Paralysis may also reduce signals from muscle stretch receptors that normally contribute to arousal. We therefore tested the hypothesis that nondepolarizing neuromuscular block reduces BIS. Ten volunteers were anesthetized with propofol at a target effect site concentration of 3.8 plus/minus 0.4 microg/mL. A mivacurium infusion was adjusted to vary the first twitch (T1) in a train-of-four to 80%, 30%, 20%, 15%, 10%, 5%, or 2% of the prerelaxant intensity. At each randomly assigned T1, we measured BIS and frontal-temporal EMG intensity. BIS averaged 95 plus/minus 4 before induction of anesthesia, and decreased significantly to 40 plus/minus 5 after propofol administration. However, there were no significant differences at the designated block levels. Frontal-temporal EMG intensity averaged 47 plus/minus 3 dB before induction of anesthesia, and decreased significantly to 27 plus/minus 1 dB after propofol administration. However, there were no significant differences at the designated block levels. These data suggest that the BIS level and EMG tone are unaltered by mivacurium administration during propofol anesthesia.

IMPLICATIONS

Neuromuscular block level did not alter Bispectral Index (BIS) during propofol anesthesia, either by reducing electromyographic artifact or by decreasing afferent neuronal input. The BIS will thus comparably estimate sedation in deeply unconscious patients who are paralyzed, partially paralyzed, or unparalyzed.

Tracheal lidocaine attenuates the cardiovascular response to endotracheal intubation

PURPOSE

In order to examine the efficacy of tracheal lidocaine (TL) for attenuation of the cardiovascular responses to endotracheal intubation (EI), we compared the cardiovascular responses to TL alone and EI with TL, with those to EI without TL.

METHODS

Seventy-five patients (ASA I-II) were studied. Anesthesia was induced with fentanyl 2 microg x kg(-1) iv, thiamylal 5 mg x kg(-1) iv and sevoflurane 1.0% in oxygen. Vecuronium 0.12 mg x kg(-1) was used to facilitate EI. In Group A (n=25), three minutes after induction, EI was performed. In Group B (n=25), three minutes after induction, the patients received TL (4% lidocaine, 4 mL). This was followed by immediate EI. In Group C (n=25), EI was performed two minutes after TL. Heart rate, arterial blood pressure and rate- pressure product (RPP) were measured from one minute before induction until five minutes after EI.

RESULTS

The changes of RPP caused by TL alone in Group C (TL; +34.6 +/- 29.0%, mean +/- SD) were significantly (P <0.01) less than those caused by EI without TL in Group A (+77.3 +/- 42.6%). EI after TL in Group C did not cause significant changes in RPP (+5.4 +/- 15.2%). There were no significant differences between Groups A and B (+58.3 +/- 36.6%).

CONCLUSION

We conclude that the cardiovascular responses to TL alone are half as great as those to EI without TL, and that TL is effective for attenuation of the cardiovascular responses to EI. EI should be performed more than two minutes after TL.

A case of awareness with sevoflurane and epidural anesthesia in ovarian tumorectomy

We experienced a case of awareness during ovarian tumorectomy in a patient who was anesthetized with sevoflurane and epidural anesthesia. A 74-year-old woman was scheduled for resection of an ovarian tumor. After epidural catheter insertion, anesthesia was induced with 60 mg of propofol and 6 mg of vecuronium, and anesthesia was maintained with epidural anesthesia (1% mepivacaine), 1 to 2% sevoflurane, and 66% nitrous oxide in oxygen. The operative course was uneventful and the total operation time was 2 hours and 50 minutes. Two days after the operation, we were surprised to learn that the patient complained of awareness during the surgery.

Determination of sevoflurane alveolar concentration for tracheal intubation with remifentanil, and no muscle relaxant

The sevoflurane alveolar concentration needed for tracheal intubation with remifentanil was studied in 26 adult patients premedicated with 100 mg hydroxyzine. Anaesthesia was induced with sevoflurane in oxygen. The concentration was determined by Dixon's up-and-down method. The first patient was tested at 4.5%. One minute after obtaining the preselected value, remifentanil 1 microg.kg-1 was injected for 60 s followed by an infusion of 0.25 microg.kg-1. min-1. Ventilation was then manually assisted for 2 min and tracheal intubation was attempted. Tracheal intubation conditions and responses to intubation were noted. Heart rate and mean arterial pressure were recorded before induction, before remifentanil injection, and before and 3 min after tracheal intubation. The concentration for acceptable intubating conditions was 2.5 +/- 0.7%. From logistic regression, ED50 and ED95 were 2.0% (95% CI 1.3-2.5) and 3.2% (95% CI 2.6-5.6), respectively. With sevoflurane 2.5%, heart rate and mean arterial pressure decreased by 18% and 15%, respectively, after remifentanil administration and increased slightly after tracheal intubation.