The Effect of Neuromuscular Block and Noxious Stimulation on Hypnosis Monitoring During Sevoflurane Anesthesia

The arousal effect of sugammadex reversal of neuromuscular blockade differs with anesthetic depth in propofol-remifentanil anesthesia: a randomized controlled trial

Sugammadex reverses neuromuscular blockade by encapsulating steroidal neuromuscular blockers; therefore, it does not pharmacologically affect sedation levels. However, some clinicians avoid using it because of sudden unwanted acting out or patient arousal. Previous studies suggested sugammadex-induced awakening, but frontal muscle contraction after sugammadex administration compromised reliability of results obtained from EEG-based anesthesia depth monitoring tools like bispectral index (BIS). We hypothesized that sugammadex would affect patients' arousal depending on their baseline levels of sedation. We evaluated arousal signs after sugammadex administration with BIS between 25 - 35 and 45 - 55 under steady-state propofol-remifentanil anesthesia at the end of a surgery (n = 33 in each group). After sugammadex administration, twelve patients with a BIS of 45 - 55 showed clinical signs of awakening but none with a BIS of 25 - 35 (36.4% vs. 0%, P = 0.001). The distribution of the modified observer's assessment of alertness/sedation scale scores was also significantly different between the two groups (P < 0.001). Changes in the BIS were significantly greater in the BIS 45 - 55 than in the 25 - 35 group (median difference, 7; 95% CI 2 - 19, P = 0.002). Arousal after sugammadex was affected by patient sedation levels, and clinical signs of awakening appeared only in those with BIS 45 - 55. Unwanted arousal of the patient should be considered when using sugammadex under shallow anesthesia.Clinical trial registry number: Clinical Trial Registry of Korea ( https://cris.nih.go.kr ; Principal investigator: Jieae Kim; Registration number: KCT0006248; Date of first registration: 11/06/2021).

Changes in bispectral index and patient state index during sugammadex reversal of neuromuscular blockade under steady-state sevoflurane anesthesia

Few studies have investigated the changes in patient state index (PSI) and bispectral index (BIS) in response to abrupt increase in electromyographic (EMG) activity. These were performed using intravenous anesthetics or reversal agents for neuromuscular blockade (NMB) other than sugammadex. We compared the changes in BIS and PSI values caused by the sugammadex reversal of NMB during steady-state sevoflurane anesthesia. We enrolled 50 patients with American Society of Anesthesiologists physical status 1 and 2. At the end of the surgery, we administered 2 mg kg-1 sugammadex while maintaining sevoflurane for a 10-min study period. The changes in BIS and PSI from baseline (T0) to train of four ratio of 90% were not significantly different (median difference 0; 95% CI - 3 to 2; P = 0.83), neither were the changes in BIS and PSI values from T0 to their maximum values (median difference 1; 95% CI - 1 to 4; P = 0.53). Maximum BIS and PSI were significantly higher than their baseline values (median difference 6; 95% CI 4-9; P < 0.001 and median difference 5; 95% CI 3-6; P < 0.001, respectively). We found weak positive correlations between BIS and BIS-EMG (r = 0.12, P = 0.01), as well as PSI and PSI-EMG (r = 0.25, P < 0.001). Both PSI and BIS were affected to some extent by EMG artifacts after sugammadex administration.

Effects of noxious stimulation on the electroencephalogram during general anaesthesia: a narrative review and approach to analgesic titration

Electroencephalographic (EEG) activity is used to monitor the neurophysiology of the brain, which is a target organ of general anaesthesia. Besides its use in evaluating hypnotic states, neurophysiologic reactions to noxious stimulation can also be observed in the EEG. Recognising and understanding these responses could help optimise intraoperative analgesic management. This review describes three types of changes in the EEG induced by noxious stimulation when the patient is under general anaesthesia: (1) beta arousal, (2) (paradoxical) delta arousal, and (3) alpha dropout. Beta arousal is an increase in EEG power in the beta-frequency band (12-25 Hz) in response to noxious stimulation, especially at lower doses of anaesthesia drugs in the absence of opioids. It is usually indicative of a cortical depolarisation and increased cortical activity. At higher concentrations of anaesthetic drug, and with insufficient opioids, delta arousal (increased power in the delta band [0.5-4 Hz]) and alpha dropout (decreased alpha power [8-12 Hz]) are associated with noxious stimuli. The mechanisms of delta arousal are not well understood, but the midbrain reticular formation seems to play a role. Alpha dropout may indicate a return of thalamocortical communication, from an idling mode to an operational mode. Each of these EEG changes reflect an incomplete modulation of pain signals and can be mitigated by administration of opioid or the use of regional anaesthesia techniques. Future studies should evaluate whether titrating analgesic drugs in response to these EEG signals reduces postoperative pain and influences other postoperative outcomes, including the potential development of chronic pain.

Effects of Neuromuscular Blockages on Entropy Monitoring During Sevoflurane Anesthesia

Background

There are no data available on the effects of different degrees of neuromuscular blockade on spectral entropy during sevoflurane anesthesia. This study aimed to observe the effects of different degrees of neuromuscular blockade on state and response entropy during sevoflurane anesthesia.

Material/Methods

Eighty-one female patients were randomized to 9 groups (n=9 per group) according to the concentration of sevoflurane and degree of neuromuscular blockade. Response and state entropy were monitored. The endpoints were: 1) impact of neuromuscular blockade on state entropy and response entropy, and the difference between response entropy and state entropy; and 2) the response of entropy after cutaneous tetanic electrical noxious stimulation to the ulnar nerve under different degrees of neuromuscular blockade and concentrations of sevoflurane.

Results

These were no significant differences in response entropy or state entropy, or differences between response entropy and state entropy among the groups in the awake state (P>0.05). Without noxious stimulation, sevoflurane concentrations and neuromuscular blockade had no significant effects on response entropy or state entropy, or on the difference between response entropy and state entropy (all P>0.05), but sevoflurane concentrations showed a significant effect on state entropy (P<0.05). After noxious stimulation, sevoflurane concentrations and neuromuscular blockade had significant effects on response entropy and state entropy, and on the difference between response entropy and state entropy.

Conclusions

Response entropy and state entropy decreased with increasing sevoflurane concentration. Neuromuscular blockade did not affect entropy without noxious stimulation. With stimulation, muscle relaxants significantly reduced the changes in entropy, and there were significant effects of neuromuscular blockade and sevoflurane on entropy.

Prolonged concurrent hypotension and low bispectral index ('double low') are associated with mortality, serious complications, and prolonged hospitalization after cardiac surgery

Background

Low bispectral index (BIS) and low mean arterial pressure (MAP) are associated with worse outcomes after surgery. We tested the hypothesis that a combination of these risk factors, a 'double low', is associated with death and major complications after cardiac surgery.

Methods

We used data from 8239 cardiac surgical patients from two US hospitals. The primary outcomes were 30-day mortality and a composite of in-hospital mortality and morbidity. We examined whether patients who had a case-averaged double low, defined as time-weighted average BIS and MAP (calculated over an entire case) below the sample mean but not in the reference group, had increased risk of the primary outcomes compared with patients whose BIS and/or MAP were at or higher than the sample mean. We also examined whether a prolonged cumulative duration of a concurrent double low (simultaneous low MAP and BIS) increased the risk of the primary outcomes.

Results

Case-averaged double low was not associated with increased risk of 30-day mortality {odds ratio [OR] 1.73 [95% confidence interval (CI) 0.94-3.18] vs reference; P =0.01} or the composite of in-hospital mortality and morbidity [OR 1.47 (95% CI 0.98-2.20); P =0.01] after correction for multiple outcomes. A prolonged concurrent double low was associated with 30-day mortality [OR 1.06 (95% CI 1.01-1.11) per 10-min increase; P =0.001] and the composite of in-hospital mortality and morbidity [OR 1.04 (95% CI 1.01-1.07), P =0.004].

Conclusions

A prolonged concurrent double low, but not a case-averaged double low, was associated with higher morbidity and mortality after cardiac surgery.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Pharyngeal function and breathing pattern during partial neuromuscular block in the elderly: effects on airway protection

BACKGROUND

Intact pharyngeal function and coordination of breathing and swallowing are essential for airway protection and to avoid respiratory complications. Postoperative pulmonary complications caused by residual effects of neuromuscular-blocking agents occur more frequently in the elderly. Moreover, elderly have altered pharyngeal function which is associated with increased risk of aspiration. The purpose of this study was to evaluate effects of partial neuromuscular block on pharyngeal function, coordination of breathing and swallowing, and airway protection in individuals older than 65 yr.

METHODS

Pharyngeal function and coordination of breathing and swallowing were assessed by manometry and videoradiography in 17 volunteers, mean age 73.5 yr. After control recordings, rocuronium was administered to obtain steady-state train-of-four ratios of 0.70 and 0.80 followed by spontaneous recovery to greater than 0.90.

RESULTS

Pharyngeal dysfunction increased significantly at train-of-four ratios 0.70 and 0.80 to 67 and 71%, respectively, compared with 37% at control recordings, and swallowing showed a more severe degree of dysfunction during partial neuromuscular block. After recovery to train-of-four ratio of greater than 0.90, pharyngeal dysfunction was not significantly different from the control state. Resting pressure in the upper esophageal sphincter was lower at all levels of partial neuromuscular block compared with control recordings. The authors were unable to demonstrate impaired coordination of breathing and swallowing.

CONCLUSION

Partial neuromuscular block in healthy elderly individuals causes an increased incidence of pharyngeal dysfunction from 37 to 71%, with impaired ability to protect the airway; however, the authors were unable to detect an effect of partial neuromuscular block on coordination of breathing and swallowing.

The EEG signal: a window on the cortical brain activity

The accurate assessment of the depth of anesthesia, allowing a more accurate adaptation of the doses of hypnotics, is an important end point for the anesthesiologist. It is a particularly crucial issue in pediatric anesthesia, in the context of the recent controversies about the potential neurological consequences of the main anesthetic drugs on the developing brain. The electroencephalogram signal reflects the electrical activity of the neurons in the cerebral cortex. It is thus the key to assessment of the level of hypnosis. Beyond visual analysis, several monitoring devices allow an automated treatment of the electroencephalographic (EEG) signal, combining time and frequency domain analysis. Each of these monitors focuses on a specific combination of characteristics of the signal and provides the clinician with useful information that remains, however, partial. For a comprehensive approach of the EEG-derived indices, the main features of the normal EEG, in adults and children, will be presented in the awake state and during sleep. Age-related modifications accompanying cerebral maturation during infancy and childhood will be detailed. Then, this review will provide an update on how anesthetic drugs, particularly hypnotics, influence the EEG signal, and how the main available monitors analyze these drug-induced modifications. The relationships between pain, memory, and the EEG will be discussed. Finally, this review will focus on some specific EEG features such as the electrical epileptoid activity observed under sevoflurane anesthesia. The EEG signal is the best window we have on cortical brain activity and provides a fair pharmacodynamic feedback of the effects of hypnotics. However, the cortex is only one of several targets of anesthesia. Hypnotics and opiates, have also subcortical primary targets, and the EEG performances in the evaluation or prediction of nociception are poor. Monitoring subcortical structures in combination with the EEG might in the future allow a better evaluation and a more precise adaptation of balanced anesthesia.

Limitations of anaesthesia depth monitoring

PURPOSE OF REVIEW

We critically review brain function monitors based on the processed electroencephalogram with regards to signal quality, artefacts and other limitations in clinical performance.

RECENT FINDINGS

Several studies have been showing that depth of anaesthesia monitors based on processed electroencephalogram has limitations that can lead to a wrong interpretation of the level of anaesthesia. Processed electroencephalogram indices can be altered by nonanaesthetic influences ranging from artefacts that affect signal quality and signal processing, adverse effects of some anaesthetic and nonanaesthetic drugs, neuromuscular blocking agents to conditions inherent to the patient such as cerebral tumours, brain ischemia and temperature.

SUMMARY

Clinicians should be aware of the several limitations of the commercial devices intending to monitor the depth of anaesthesia, which may not reflect the real underlying level of unconsciousness.

Minimum alveolar concentrations of sevoflurane for maintaining bispectral index below 50 in children

OBJECTIVE

To determine minimum alveolar concentration (MAC) of sevoflurane for maintaining bispectral index (BIS) below 50 (MAC(BIS50) ) in children.

BACKGROUND

MAC(BIS50) of sevoflurane in adults was reported to be 0.97%, which has not been elucidated in children.

METHODS/MATERIALS

Twenty children, American Society of Anesthesiologists physical status I or II, aged 1-8, were induced and anesthetized with sevoflurane in oxygen. After tracheal intubation, we started maintenance of anesthesia with endtidal sevoflurane concentrations of 2.6%. The endtidal sevoflurane concentration at which BIS was measured was predetermined by the up-down method (with 0.2% as a step size). After 10 min at predetermined endtidal sevoflurane concentrations, BIS was measured for 1 min. MAC(BIS50) was determined using Dixon's up-down method and probit test.

RESULT

MAC(BIS50) of sevoflurane was 2.83% (95% confidence intervals: 2.70-3.14) in children.

CONCLUSIONS

MAC(BIS50) of sevoflurane in children was calculated to be three times as high as in adults. This indicates that high endtidal sevoflurane concentration is required to suppress electroencephalogram activity in children.

Reversal of neuromuscular blockade by sugammadex does not affect EEG derived indices of depth of anesthesia

OBJECTIVE

According to previous studies neuromuscular blockade may affect the depth of anesthesia. One theory states that neuromuscular blockade prevents disturbing EMG signals, arousing from the muscles of the forehead, from falsely elevating bispectral index (BIS)-levels. According to the afferentation theory signals generated in muscle stretch receptors, accessing the brain through afferent nerve pathways, induce arousal. By blocking these signals neuromuscular blockade would increase depth of anesthesia. Arousal has previously been associated with neostigmine reversal. This study investigates the possible effect of sugammadex on the level of anesthesia as defined by BIS and spectral entropy levels.

METHODS

Thirty elective patients were enrolled. All patients received propofol and remifentanil by target controlled infusion and an intermediate level neuromuscular blockade induced and maintained by bolus doses of rocuronium. Depth of anesthesia was monitored by BIS and spectral entropy. The patients were given 2 mg/kg sugammadex 5 min after finishing of surgery. Propofol and remifentanil infusions were kept unchanged for another 10 min while BIS and entropy values were recorded.

RESULTS

Mean BIS and Entropy™ values remained unchanged after reversal of the rocuronium block. The mean averaged BIS, state entropy and response entropy values were 31.7 ± 9.9, 35.3 ± 12.9 and 36.8 ± 13.3 before and 32.0 ± 11.9, 36.3 ± 15.9 and 38.4 ± 18.0 after sugammadex administration, respectively.

CONCLUSIONS

Sugammadex does not affect level of anesthesia as determined by BIS or entropy levels.

Depth of anaesthesia and post-operative cognitive dysfunction

BACKGROUND

A deep level of anaesthesia measured by the bispectral index has been found to improve processing speed as one aspect of cognitive function after surgery. The purpose of the present study was to assess the possible effect of the level of anaesthesia on post-operative cognitive dysfunction (POCD) 1 week after surgery, as assessed by a neuropsychological test battery.

METHODS

We included 70 patients >60 years of age scheduled for elective non-cardiac surgery with general anaesthesia. The depth of anaesthesia was monitored using the cerebral state monitor, which provided a cerebral state index (CSI) value. Cognitive function was assessed by the ISPOCD neuropsychological test battery before and at 1 week (or hospital discharge) after surgery and POCD was defined as a Z score above 1.96.

RESULTS

Five patients were not assessed after surgery. The mean CSI was 40 and 43 in patients with (N=9) and without POCD (N=56), respectively (P=0.41). The cumulated time of both deep anaesthesia (CSI<40) and light anaesthesia (CSI>60) did not differ significantly, and no significant correlation was found between the mean CSI and the Z score.

CONCLUSION

We were unable to detect a significant association between the depth of anaesthesia and the presence of POCD 1 week after the surgery.

Midazolam dose for loss of response to verbal stimulation during the unilateral or bilateral spinal anesthesia

BACKGROUND

We have conducted this study to investigate whether unilateral or bilateral spinal anesthesia with bupivacaine induces different sensitivity to intravenous (i.v.) midazolam for sedation.

METHODS

Forty-two patients undergoing various elective unilateral lower extremity surgeries were allocated into two groups: (1) unilateral spinal anesthesia group (Group US, n=21; heavy bupivacaine 5 mg/ml, 9 mg) and (2) bilateral spinal anesthesia group (Group BS, n=21; heavy bupivacaine 5 mg/ml, 9 mg). One milligram of midazolam was injected i.v. at 30-s intervals until the patients did not respond to the hand grasp test beginning 15 min after spinal anesthesia. The concentration of plasma bupivacaine was evaluated every 15 min for the first 75 min after the start of the spinal anesthesia, and the bispectral index was monitored continuously.

RESULTS

The mean venous plasma concentration of bupivacaine was not significantly different between Group US and BS. The dose of midazolam required to abolish responses to verbal commands was significantly lower in Group BS (mean 5.9+/-1.2 mg) vs. Group US (mean 9.0+/-1.4 mg).

CONCLUSIONS

A higher dosage of midazolam is required for loss of response to verbal stimulation during unilateral spinal anesthesia than during bilateral spinal anesthesia.

Validation of the index of consciousness during sevoflurane and remifentanil anaesthesia: a comparison with the bispectral index and the cerebral state index

BACKGROUND

The purpose of this study was to validate a new level of consciousness monitor derived from the EEG, called the index of consciousness (IoC), by comparing it with the bispectral index (BIS) and the cerebral state index (CSI) during general anaesthesia for cardiac surgery using sevoflurane, remifentanil, and atracurium.

METHODS

After ethical committee approval and written patient consent, data from 35 patients [31 males, four females, age 55 (10) yr] were recorded during general anaesthesia for elective cardiac bypass surgery. All patients were induced with sevoflurane 8%, until the Observer's Assessment of Alertness and Sedation (OAAS) scale level 1 was reached, and then was set at a 1% end-tidal sevoflurane concentration. Subsequently, remifentanil and atracurium were administered, the trachea was intubated, and the procedure continued as usual. To assess accuracy, the prediction probability (Pk) was calculated both during induction and during maintenance.

RESULTS

The Pk values [mean (se)] for IoC, BIS, and CSI during induction were 0.90 (0.01), 0.90 (0.01), and 0.88 (0.01), respectively, whereas the corresponding Pk values during maintenance were 0.95 (0.01), 0.94 (0.01), and 0.60 (0.01).

CONCLUSIONS

The three indices performed equally well during the induction phase and were able to predict the level of consciousness of the patients satisfactorily. During maintenance, the IoC and the BIS showed good agreement with the clinical signs. The CSI was significantly influenced by the administration of atracurium; therefore, the agreement with the OAAS scale during the maintenance phase was significantly less for CSI than for IoC and BIS.