Does Patient Position Influence the Reading of the Bispectral Index Monitor?

Effect of patient position on the EEG bispectral index and entropy index under general anaesthesia

BACKGROUND

Perioperative depth monitoring techniques, such as electroencephalography bispectral index (BIS), entropy index, and auditory evoked potential, are commonly used to assess anesthesia depth. However, the influence of patient positioning changes, particularly in gynecological surgeries where a head-down position is often required, on the accuracy of these monitoring indices remains unexplored.

OBJECTIVE

The aim of the our study was to observe the impact of patient position changes on the monitoring value of entropy and BIS to identify a more sensitive method of anaesthesia depth monitoring for gynaecological surgery patients.

METHODS

We conducted a study involving 40 women undergoing general anesthesia, during which routine monitoring of vital signs, including electrocardiogram (ECG), heart rate (HR), noninvasive arterial blood pressure (NIBP), oxyhemoglobin saturation (SpO2), and end-expiratory carbon dioxide (PetCO2), was initiated. Entropy and BIS devices were affixed to the patients' foreheads after alcohol sterilization to record brain activity. Tracheal intubation was performed following anesthesia induction. Throughout anesthesia maintenance, the value of BIS and response entropy (RE) were monitored and maintained between 40 and 50 by adjusting the infusion rate of propofol and remifentanil with Target Controlled Infusion (TCI, Mintopharmacokinetics model). Dosing for infusion control utilized corrected weight (height-105). Data were recorded before and after position changes, including tilting the operating table to head-down positions of 15 and 25 degrees, returning to a supine position, and elevating the head to 15 and 25-degree angles. BIS and entropy values at different time points were compared between the groups.

RESULTS

Both BIS and entropy values increased from supine to head-down position and decreased from supine to head-up position, with entropy changes preceding those of BIS. Heart rate increased after head-up and decreased after head-down, while mean blood pressure (MBP) exhibited the opposite effect on heart rate. Significant correlations were found between heart rate and BIS (correlation coefficient: -0.43) and RE (correlation coefficient: -0.416), as well as between MBP and BIS (correlation coefficient: 0.346) and RE (correlation coefficient: 0.384).

CONCLUSION

Changes in patient position can significantly affect the value of RE and BIS, as changes in entropy occur earlier than changes in the BIS.

Effect of Continuous Infusion of Different Doses of Esketamine on the Bispectral Index During Sevoflurane Anesthesia: A Randomized Controlled Trial

Purpose

To investigate and quantify the effect of continuous esketamine infusion at different doses on the bispectral index (BIS) during sevoflurane anesthesia.

Methods

A total of 120 patients scheduled for elective laparoscopic renal surgery were randomly divided into three groups. Under steady anesthesia and surgical situations, the patient was started on continuous infusion of the study drug: 0.125 mg/kg/h esketamine (group E1), 0.25 mg/kg/h esketamine (group E2), and the same volume of saline (group C). The primary outcome was changes in BIS value after 15 min (T15), 30 min (T30), 45 min (T45), and 60 min (T60) of drug infusion. The secondary outcomes were 95% spectral edge frequency (SEF95), electromyogram (EMG), heart rate (HR), and mean arterial pressure (MAP) from T0 to T60. Furthermore, postoperative pain, postoperative recovery, and perioperative adverse events were evaluated.

Results

Compared with group C, group E1 exhibited significant BIS elevation at T30-T60 and group E2 at T15-T60 (P < 0.001). Compared with group E1, group E2 showed a more significant BIS elevation at T15-T60 (P < 0.001). The area under the curve (AUC) of BIS and SEF95 were significantly higher in group E2 than in groups C and E1 (P < 0.05). BIS value for any of the three groups was significantly correlated with SEF95 (P < 0.001). No significant differences were observed in the AUC of EMG, HR, and MAP among the three groups. Intraoperative remifentanil consumption and postoperative NRS of pain on movement were significantly reduced in group E2 compared with groups C and E1 (P < 0.05).

Conclusion

Continuous infusion of both 0.125 and 0.25 mg/kg/h of esketamine increased the BIS value during sevoflurane anesthesia, and the BIS value gradually stabilized with the prolongation of the infusion time.

Effect of sugammadex on processed EEG parameters in patients undergoing robot-assisted radical prostatectomy

BACKGROUND

Sugammadex has been associated with increases in the bispectral index (BIS). We evaluated the effects of sugammadex administration on quantitative electroencephalographic (EEG) and electromyographic (EMG) measures.

METHODS

We performed a prospective observational study of adult male patients undergoing robot-assisted radical prostatectomy. All patients received a sevoflurane-based general anaesthetic and a continuous infusion of rocuronium, which was reversed with 2 mg kg-1 of sugammadex i.v. BIS, EEG, and EMG measures were captured with the BIS Vista™ monitor.

RESULTS

Twenty-five patients were included in this study. Compared with baseline, BIS increased at 4-6 min (β coefficient: 3.63; 95% confidence interval [CI]: 2.22-5.04; P<0.001), spectral edge frequency 95 (SEF95) increased at 2-4 min (β coefficient: 0.29; 95% CI: 0.05-0.52; P=0.016) and 4-6 min (β coefficient: 0.71; 95% CI: 0.47-0.94; P<0.001), and EMG increased at 4-6 min (β coefficient: 1.91; 95% CI: 1.00-2.81; P<0.001) after sugammadex administration. Compared with baseline, increased beta power was observed at 2-4 min (β coefficient: 93; 95% CI: 1-185; P=0.046) and 4-6 min (β coefficient: 208; 95% CI: 116-300; P<0.001), and decreased delta power was observed at 4-6 min (β coefficient: -526.72; 95% CI: -778 to -276; P<0.001) after sugammadex administration. Neither SEF95 nor frequency band data analysis adjusted for EMG showed substantial differences. None of the patients showed clinical signs of awakening.

CONCLUSIONS

After neuromuscular block reversal with 2 mg kg-1 sugammadex, BIS, SEF95, EMG, and beta power showed small but statistically significant increases over time, while delta power decreased.

A, Kalia R, Kaur J. Effect of Change of Position (Supine vs. Steep Trendelenburg) on Bispectral Index Value During Robotic Surgery

Background: Bispectral Index (BIS) is used to monitor anesthetic depth and is a useful instrument to keep a check on intraoperative awareness. But there are various situations in which it shows false readings. Our aim of the study was to observe the changes in BIS value with steep Trendelenburg position, which is usually done, in robotic pelvic surgeries.

Methods: We included 100 patients in our study who underwent robotic prostatectomies and hysterectomies. After anesthetizing the patient, the patient's heart rate, systolic blood pressure, mean arterial pressure, end-tidal desflurane, end-tidal CO₂, and BISwere recorded at three min. intervals, for 15 minutes before and 15 minutes after the Trendelenburg position without surgical stimulus.

Results: We found a significant increase in BIS values (p <0.05) after the change of position from supine to steep Trendelenburg. Heart rate, systolic blood pressure, and mean arterial pressure were almost constant.

Conclusion: Our study concluded that the BIS value increases when patients were shifted from the supine to Trendelenburg position, which might raise the concern of a decrease in anesthetic depth.

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

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

A Prospective, double-blinded randomized controlled study comparing two different Trendelenburg tilts in laparoscopically assisted vaginal hysterectomy positioning

BACKGROUND

Bispectral index (BIS) used for intra-operative depth assessment under general anesthesia (GA) can be altered by different factors. This study was designed to detect the alteration in BIS reading with two different Trendelenburg (TBG) tilt in laparoscopically assisted vaginal hysterectomy (LAVH) procedure.

MATERIALS AND METHODS

A prospective, double-blinded, randomized controlled study was designed involving 40 American Society of Anesthesiologists Grade I and II female patients, aged 35-60 years, scheduled to undergo LAVH under GA. Patients were divided into two groups with TBG >30° and TBG <30°. BIS readings; systolic and diastolic blood pressure, heart rate were recorded in supine position. Patients were then shifted to desired TBG position either (>30°) or (<30°) as per group allotment. Data were recorded at 30 min intervals and all the patients were followed upto 24 h postoperatively for any recall.

RESULTS

A rise in BIS value was noticed, when position was changed from supine to head down in both groups. During comparison between two groups with different angulations, TBG >30° showed a higher BIS value than TBG <30°. This statistically significant (P < 0.05) trend was observed at all the 30, 60, 90, and 120(th) min interval. Interestingly, BIS values returned to preoperative levels following adopting final supine position. No incidence of awareness was reported in both the series throughout the study.

CONCLUSION

Though awareness remains unaltered BIS value gets increased with higher angle of inclination in TBG position during LAVH operation.

Effect of beach chair position on bispectral index values during arthroscopic shoulder surgery

Background

Bispectral index (BIS) monitoring reduces the cases of intraoperative awareness. Several factors can alter BIS readings without affecting the depth of anesthesia. We conducted a study to assess the impact of beach chair position (sitting position) on BIS readings.

Methods

General anesthesia was administered to 30 patients undergoing arthroscopic shoulder surgery. Patients were kept in neutral position (supine) for 10 minutes and BIS readings, mean arterial blood pressure, heart rate, end-tidal carbon dioxide, and end-tidal sevoflurane were recorded. Patients were then shifted to beach chair position. After 15 minutes, data were recorded.

Results

A significant decrease in BIS values (P < 0.01) associated with a position change from neutral position to beach chair position was evident.

Conclusions

BIS values are significantly decreased in the beach chair position compared with the neutral position and might affect interpretation of the depth of anesthesia.

Randomized clinical trial on the influence of anaesthesia protocol on intestinal motility during laparoscopic surgery requiring small bowel anastomosis

Background

Hyperperistalsis of the small bowel during laparoscopic surgery may cause mucosal prolapse and reduce exposure, making laparoscopic suturing or stapling more demanding for the surgeon. Although it is commonly accepted that both opioids and volatile anaesthetics induce intestinal paralysis, intestinal hyperactivity during anaesthesia is not uncommon. This randomized trial investigated the effect of different volatile anaesthetics on intestinal motility and the impact on surgeon satisfaction.

Methods

Patients scheduled for laparoscopic gastric bypass surgery were randomized to receive sevoflurane or desflurane in a balanced anaesthetic regimen. After surgical exposure peristaltic waves were counted over 1 min in a segment of the jejunum. Following evaluation of intestinal motility, N-butylhyoscine, an antimuscarinic anticholinergic agent that relaxes bowel smooth muscle cells, could be administered if the surgeon judged the intestinal motility as disturbing. The endpoints were number of peristaltic waves and incidence of N-butylhyoscine administration, a surrogate for surgeon satisfaction.

Results

Twenty-two patients were randomized to each group. The groups were similar in age, sex and body mass index. There was a statistically significant difference in intestinal motility between the desflurane and sevoflurane groups: median (range) 7 (0–12) versus 1 (0–10) waves counted over 1 min respectively (P &lt; 0·001). A higher proportion of patients in the desflurane group received N-butylhyoscine (10 of 22 versus 1 of 22 in the sevoflurane group; P = 0·004).

Conclusion

Desflurane increased intestinal motility and decreased surgeon satisfaction compared with sevoflurane during laparoscopic gastric bypass surgery. A sevoflurane-based anaesthetic protocol can help to avoid disturbing hyperperistalsis. Registration number: B39620097060 (http://www.clinicaltrials.be).

Administration and monitoring of intravenous anesthetics

PURPOSE OF REVIEW

The importance of accuracy in controlling the dose-response relation for intravenous anesthetics is directly related to the importance of optimizing the efficacy and quality of anesthesia while minimizing adverse drug effects. Therefore, it is important to measure and control all steps of the pharmacokinetic and dynamic cascade influencing this dose-effect relationship.

RECENT FINDINGS

The ultimate goal when administering a particular dose of a drug is to obtain the desired clinical effect, taking into account interindividual pharmacokinetic and dynamic variability. Recent findings suggest that effect compartment-controlled target-controlled infusion systems and measurement of (surrogate) clinical drug effects might be helpful in an attempt to optimize the administration intravenous anesthetics and opioids. Additionally, recent findings suggest that the pharmacokinetic and dynamic interaction between anesthetics and opioids is important and such be taking into account when optimizing drug administration. Hereby, feedback control technology and advisory displays depicting these interactions have been studied.

SUMMARY

Anesthetic drug administration might be optimized by applying knowledge from clinical pharmacokinetics and dynamics.