Effects of epidural anesthesia with 0.2% and 1% ropivacaine on predicted propofol concentrations and bispectral index values at three clinical end points

Do we have today a reliable method to detect the moment of loss of consciousness during induction of general anaesthesia?

This review aims to give an overview of the current state of monitoring depth of anaesthesia and detecting the moment of loss of consciousness, from the first clinical signs involved in anaesthesia to the latest technologies used in this area. Such techniques are extremely important for the development of automatic systems for anaesthesia control, including preventing intraoperative awareness episodes and overdoses. A search in the databases Pubmed and IEEE Xplore was performed using terms such anaesthetic monitoring, depth of anaesthesia, loss of consciousness, as well as anaesthesia indexes, namely BIS. Despite the several methods capable of monitoring the hypnotic state of anaesthesia, there is still no methodology to accurate detect the moment of loss of consciousness during induction of general anaesthesia.

[Anesthetic requirements measured by bilateral bispectral analysis and femoral blockade in total knee arthroplasty]

BACKGROUND AND OBJECTIVES

A continuous peripheral nerve blockade has proved benefits on reducing postoperative morphine consumption; the combination of a femoral blockade and general anesthesia on reducing intraoperative anesthetic requirements has not been studied. The objective of this study was to determine the relevance of timing in the performance of femoral block to intraoperative anesthetic requirements during general anesthesia for total knee arthroplasty.

METHODS

A single-center, prospective cohort study on patients scheduled for total knee arthroplasty, were sequentially allocated to receive 20mL of 2% mepivacaine throughout a femoral catheter, prior to anesthesia induction (Preoperative) or when skin closure started (Postoperative). An algorithm based on bispectral values guided intraoperative anesthetic management. Postoperative analgesia was done with an elastomeric pump of levobupivacaine 0.125% connected to the femoral catheter and complemented with morphine patient control analgesia for 48hours. The Kruskall Wallis and the chi-square tests were used to compare variables. Statistical significance was set at p<0.05.

RESULTS

There were 94 patients, 47 preoperative and 47 postoperative. Lower fentanyl and sevoflurane were needed intraoperatively in the Preoperative group; median values and range: 250 (100-600) vs 450 (200-600)μg and 21 (12-48) vs 32 (18-67)mL p=0.001, respectively. There were no differences in the median verbal numeric rating scale values 4 (0-10) vs 3 (0-10); and in median morphine consumption 9 (2-73) vs 8 (0-63)mg postoperatively.

CONCLUSIONS

A preoperative femoral blockade is useful in decreasing anesthetic requirements in total knee arthroplasty surgery but no added effect in the postoperative analgesic control.

Epidural ropivacaine with dexmedetomidine reduces propofol requirement based on bispectral index in patients undergoing lower extremity and abdominal surgeries

BACKGROUND AND AIM

To assess the amount of propofol required for induction based on bispectral index (BIS) after administering epidural anesthesia with ropivacaine alone and ropivacaine with dexmedetomidine in patients undergoing lower extremities and abdominal surgeries.

SUBJECTS AND METHODS

A double-blinded randomized clinical trial was carried out in 60 patients over a period of 2 years in a tertiary care hospital. American Society of Anaesthesiologists I or II in age group 18-65 years were included in the study. Group R received epidural anesthesia with ropivacaine alone, and Group D received ropivacaine and dexmedetomidine. General anesthesia was induced with propofol under BIS monitoring after 15 min. Onset of sensory and motor block, time for loss of consciousness and total amount of propofol used during induction to achieve the BIS value < 55 were recorded. Student's t-test and Chi-square test were used to find the significance of study parameters.

RESULTS

Time of onset of sensory block (Group R 11.30 ± 1.64/Group D 8.27 ± 0.83 min), motor block (Group R 14.16 ± 1.33/Group D 12.63 ± 1.22 min), time for loss of consciousness (Group R 90.57 ± 11.05/Group D 73.67 ± 16.34 s), and total amount of propofol (Group R 129.83 ± 22.38/Group D 92.13 ± 12.93 s) were reduced in Group D which was statistically significant with P < 0.001.

CONCLUSION

Epidural ropivacaine with dexmedetomidine significantly reduces the total propofol dose required for induction of anesthesia. Also, it decreases the onset time of sensory and motor block and provides good hemodynamic stability.

The Effect of Epidural Bupivacaine on BIS Levels in the Awake Phase and on the Maintenance Doses of Propofol and Fentanyl During General Anesthesia

BACKGROUND

Simultaneous administration of epidural local anesthetic agents (LA) and general anesthetics (intravenous or inhaled) is a common procedure in patients undergoing major operations. The effects of epidural anesthesia during combined general-epidural anesthesia on the alertness level (CGEA) in the awake phase and the doses of anesthetics have been reported.

OBJECTIVES

The present study was designed to determine the effects of epidural bupivacaine on the alertness level measured by bispectral index (BIS) in the awake phase and the maintenance doses of propofol and fentanyl during general anesthesia for vascular operation on the lower limb.

PATIENTS AND METHODS

A double-blinded randomized clinical trial was conducted on patients awaiting vascular surgery on lower extremities in a teaching hospital from October 2007 to October 2008. During the epidural anesthesia, the control group received 0.9% NS while 0.125% bupivacaine was injected in the case group via the epidural route. No sedative drug was utilized for epidural catheter placement. The BIS measurement was performed in both groups during the awake phase, before performing epidural anesthesia, and 10 minutes after epidural injection at 1-min intervals for 15 min. After induction of general anesthesia in both groups, anesthesia maintenance was established using the infusion of propofol with the aim of keeping the BIS level between 40 and 50 throughout the anesthesia. At the end of the study period, maintenance dose requirements of propofol and fentanyl were measured.

RESULTS

Thirty-two patients were enrolled in the study. There was no difference in BIS levels of the two groups in the awake phase. There was a significant difference between the propofol and fentanyl requirements of the two groups.

CONCLUSIONS

Performing CGEA using bupivacaine was reported to reduce propofol and fentanyl doses required to maintain BIS levels between 40 and 50 considerably.

EEG under anesthesia--feature extraction with TESPAR

We investigated the problem of automatic depth of anesthesia (DOA) estimation from electroencephalogram (EEG) recordings. We employed Time Encoded Signal Processing And Recognition (TESPAR), a time-domain signal processing technique, in combination with multi-layer perceptrons to identify DOA levels. The presented system learns to discriminate between five DOA classes assessed by human experts whose judgements were based on EEG mid-latency auditory evoked potentials (MLAEPs) and clinical observations. We found that our system closely mimicked the behavior of the human expert, thus proving the utility of the method. Further analyses on the features extracted by our technique indicated that information related to DOA is mostly distributed across frequency bands and that the presence of high frequencies (> 80 Hz), which reflect mostly muscle activity, is beneficial for DOA detection.

Comparison of 1.5% lidocaine and 0.5% ropivacaine epidural anesthesia combined with propofol general anesthesia guided by bispectral index

OBJECTIVE

To compare the effects of epidural anesthesia with 1.5% lidocaine and 0.5% ropivacaine on propofol requirements, the time to loss of consciousness (LOC), effect-site propofol concentrations, and the hemodynamic variables during induction of general anesthesia guided by bispectral index (BIS) were studied.

METHODS

Forty-five patients were divided into three groups to receive epidurally administered saline (Group S), 1.5% (w/w) lidocaine (Group L), or 0.5% (w/w) ropivacaine (Group R). Propofol infusion was started to produce blood concentration of 4 mug/ml. Once the BIS value reached 40~50, endotracheal intubation was facilitated by 0.1 mg/kg vecuronium. Measurements included the time to LOC, effect-site propofol concentrations, total propofol dose, mean arterial blood pressure (MABP), and heart rate (HR) at different study time points.

RESULTS

During induction of anesthesia, both Groups L and R were similar for the time to LOC, effect-site propofol concentrations, total propofol dose, MABP, HR, and BIS. The total doses of propofol administered until 1 min post-intubation were significantly less in patients of Groups R and L compared with Group S. MABP and HR were significantly lower following propofol induction compared with baseline values in the three groups, or MABP was significantly increased following intubation as compared with that prior to intubation in Group S but not in Groups R and L while HR was significantly increased following intubation in the three groups.

CONCLUSION

Epidural anesthesia with 1.5% lidocaine and 0.5% ropivacaine has similar effects on the time to LOC, effect-site propofol concentrations, total propofol dose, and the hemodynamic variables during induction of general anesthesia.