Changes In Depth Of Anesthesia Research Articles

Using the Perfusion Index to predict changes in the depth of anesthesia in children compared with the A-line Autoregression Index: an observational study

BackgroundWe investigated the performance of the Perfusion Index (PI) derived from pulse oximetry waveform as a tool for assessment of anesthetic depth in comparison with A-line Autoregression Index (AAI) derived from analysis of Middle-Latency Auditory Evoked Potentials (MLAEP) waveform integrated by aepEXplus monitor in children receiving sevoflurane anesthesia for tonsillectomy. MethodsForty-one patients (4...12 years old) were included in this study. The PI and AAI were recorded simultaneously every minute during different stages of anesthesia delivery. The statistical tests included descriptive analysis, significance tests, correlation tests, and Receiver Operating Characteristic (ROC) curve. The AAI served as a reference. ResultsThe PI significantly decreased during light anesthesia and recovery, and significantly increased during deeper planes of anesthesia, with an inverse mirror-image relationship with the AAI. A negative correlation of low to moderate degree was detected between PI and AAI during the study (p.ß>.ß0.05), that reached a statistical significance at the 5th minute during sevoflurane mask induction (r.ß=.ß...0.457, p.ß=.ß0.008). ROC analysis at an AAI < 25 extracted the best cut-off value for PI before intubation as 1.48 (AUC.ß=.ß0.698 [0.537...0.859], 94.4% sensitivity, 44.5% specificity) and at 10-minute intraoperatively as 2.4 (AUC.ß=.ß0.537 [0.354...0.721], 91.7% sensitivity, 31% specificity). During recovery, at an AAI.ß....ß50, the best cutoff was 1.82 (AUC.ß=.ß0.661 [0.46...0.863], 100% sensitivity and 50% specificity) 2 minutes before spontaneous eye opening. ConclusionsCompared with the AAI, the PI can track changes in depth of anesthesia in pediatric patients undergoing tonsillectomy under sevoflurane anesthesia. Trial registrationClinical Trials. Gov. Identifier: NCT03412214.

20. Correlation between blink reflex (br) and corticobulbar motor evoked potentials (comeps) in skull base surgery and role as a predictor of clinical outcome

In 2009, Deletis et al. were the first to describe a method for eliciting the R1 component of BR in patients under general anaesthesia. The R1 includes trigeminal afferents, brainstem connections between trigeminal and facial nuclei and facial nerve. Therefore this technique might be considered a tool to intraoperatively monitor the involved structures in the reflex arc. In this work we compare the neurophysiologic behaviour of R1 component of BR and facial and/or trigeminal CoMEPs in 21 patients. The study includes 21 patients diagnosed of skull base tumours that underwent surgery by the retrosigmoidal approach. Multimodal intraoperative monitoring was performed including: BR, lower facial and trigeminal CoMEPs, SEPs, MEPs and cranial nerve mapping. We used the published methodology by Deletis et al. to elicit BR and CoMEPs. Of the 21 patients, two patients with previous facial paresis did not have a BR. Of the 19 who had a BR; nine did not show changes in BR or CoMEPs during surgery. None of those had facial or trigeminal deficit postoperatively. Eight patients lost BR and presented significant decrement in amplitude of CoMEPs. Of these eight, five recovered all responses after stopping surgery momentarily, the other three didn’t recover responses and presented postoperative facial paresis. The last two patients lost BR during the surgery while CoMEPs didn’t show any change. We assumed that these changes in BR were due to changes in depth of anaesthesia. There is a strong correlation between BR and CoMEPs changes during skull base surgery. BR and CoMEPs help to predict the clinical outcome of facial and trigeminal nerve function. BR should be included in the routine methodology for intraoperative monitoring skull base surgeries since is a reliable tool to monitor the structures involved in the reflex arc.

Highlights of recent clinically relevant papers

Highlights of recent clinically relevant papers

Time delay of electroencephalogram index calculation: analysis of cerebral state, bispectral, and Narcotrend indices using perioperatively recorded electroencephalographic signals

Monitoring of anaesthetic depth with EEG-derived indices may detect EEG changes associated with awareness and thereby help to decrease the incidence of intraoperative awareness with postoperative recall. All currently available monitors need varying time periods to calculate a new index when reacting to changes in anaesthetic depth. The exact time delay for calculation of new index values is unknown. In a previous study, we used simulated EEG signals and found considerable time lags for the cerebral state index (Danmeter, Odense, Denmark), the bispectral index (Aspect Medical Systems Inc., Newton, MA, USA), and the Narcotrend index (MonitorTechnik, Bad Bramstedt, Germany). The aim of this study was to investigate whether the time delays observed with simulated EEG signals also applied to real EEG data. We used perioperatively recorded EEG data from a database corresponding to the awake state, general anaesthesia, and suppression of cortical activity, respectively. After a switch from one state of consciousness to another, the time necessary for all indices to adjust the index value to the underlying input signal was measured. We found time delays for all indices between 24 (7) and 122 (23) s before the new state was indicated. In accordance with our previous results, these time delays were not constant and depended on the particular starting and target index value. Results were different for decreasing and increasing values. Our results may show a limitation of the value of electronic EEG indices in prevention of awareness with recall. Furthermore, due to different time delays for ascending and descending values, the results of pharmacodynamic studies may be influenced by this phenomenon.

Computer simulations of propofol infusions for total intravenous anaesthesia in dogs : review article

The volatile anaesthetic agents halothane, isoflurane and enflurane are all chlorofluorocarbons and according to international treaties, their emission into the atmosphere will be prohibited from the year 2030. The agents desflurane and sevoflurane are fluorinated hydrocarbons and act as greenhouse gases. The future of veterinary anaesthesia could be dependent on the development of total intravenous anaesthesia. Drugs utilised in total intravenous anaesthesia (TIVA) should have a short duration of action and no tendency to accumulate in the body. Propofol has been the dominant agent used. Computer technology has enabled targeted plasma concentration controlled infusions to replace manual infusion regimens. This study simulated the pharmacokinetics of various infusion regimens similar to those used in clinical practice using previously published pharmocokinetic data. Bolus doses of 0, 4, 6 and 8 mg/kg were simulated in combination with infusion rates of 0, 0.2, 0.3 and 0.4 mg/kg/min for either 240 or 1440 min. The computer was also programmed to maintain a steady state plasma concentration based on the previous simulated data. Generated data were then compared with published data. Changes in the context-sensitive half-life for propofol were also evaluated. Results showed that the generated data were similar to published data. A decrease in plasma concentration to levels associated with a light plane of anaesthesia was evident even when the highest bolus dose and infusion rate were used. There was a slow rise in plasma concentration when only an infusion was used. A lightening of anaesthetic plane may be evident early in the course of TIVA and careful monitoring of anaesthetic depth is required. As the duration of the infusion increased, plasma concentration steadily rose but achieved 95% of the steady state by 204 min. The most dramatic changes in plasma concentration occurred in the first hour of an infusion. Similarly, the infusion rates decreased most in the first 70 min. Most changes in anaesthetic depth are likely to occur early in the course of TIVA and careful observation of anaesthetic depth is required.

Use of bispectral index to monitor depth of anesthesia in isoflurane-anesthetized dogs

To evaluate the correlation between the bispectral index (BIS) and end-tidal isoflurane (ET(ISO)) concentration and compare the use of 3 BIS sensor positions in dogs. 6 adult dogs. Mechanically ventilated dogs received pancuronium, and depth of anesthesia was altered by increasing ET(ISO) concentration from 1.5% to 2.3% and 3.0%. The BIS, suppression ratio (relative percentage of isoelectric electroencephalographic waveforms), and signal quality index (SQI) were recorded at each ET(ISO) concentration for each of 3 BIS sensor positions (frontal-occipital, bifrontal, and frontal-temporal positions). The BIS and ET(ISO) concentration were poorly correlated; regardless of sensor positioning, mean BIS values did not change significantly as ET(ISO) was increased. At 3% isoflurane, regardless of sensor positioning, there was an increase in suppression ratio coincident with BIS < 40 in some dogs, whereas paradoxic increases in BIS (> 60) were recorded in others. Furthermore, at 3.0% isoflurane, the SQI was significantly lower for the bifrontal sensor position (compared with values for the other positions), but low SQI values prevented recording of BIS values from the frontal-occipital sensor position in 2 dogs. Overall, BIS values derived from the 3 sensor positions did not differ. In dogs, BIS values may not reflect changes in depth of isoflurane anesthesia in the absence of noxious stimulation. Of the 3 sensor positions, frontal-temporal positioning provided better correlation with changes in depth of anesthesia induced via changes in isoflurane concentrations. However, the sensor placements yielded similar results at SQI values > 50.

Bispectral index, spectral edge frequency 95% and median frequency recorded at varying desflurane concentrations in pigs

The objective of this study is to evaluate the usefulness of bispectral index (BIS), spectral edge frequency 95% (SEF) and median frequency (MED) in relation to a simple descriptive scale (SDS) as indicators of anaesthetic depth at different desflurane concentrations in swine. Sixteen pigs were randomly allocated to four groups. Electroencephalograms (EEG) were recorded during desflurane anaesthesia, and BIS, SEF and MED were calculated from the EEG. The agent was administered in pure oxygen at 1, 1.25, 1.5 and 1.7 MAC in randomized order. Anaesthetic depth was evaluated on a SDS. BIS decreased significantly ( P < 0.001) at the different anaesthetic dosages used. SEF decreased significantly ( P < 0.001) from basal to 1 MAC of desflurane. MED decreased significantly ( P < 0.001) from basal to 1 MAC and from 1 to 1.75 MAC. Good correlation was seen between SDS scores and BIS values and between SDS scores and MED values. BIS appeared to be useful to predict changes in anaesthetic depth at clinically used dosages of inhalant anaesthesia.

Clinical monitoring for depth of anesthesia: Bispectral index (BIS)

Bispectral index (BIS) is the first scientifically validated and commercially supported monitor for anesthetic drug effect on CNS. BIS integrates four EEG parameters into a single variable. This enables tracking of the EEG change associated with the changes in depth of anesthesia from awake state to electrical silence. However, we should note some pitfalls in clinical use of BIS. BIS is not a magic number but a value calculated from EEG. Checking raw EEG is still important when using BIS monitor.

Monitoring of anaesthesia in neurophysiological experiments.

Cortical activity can be substantially changed by the type of anaesthetic used, and by its dose level. For easy monitoring of depth of anaesthesia we describe the changes in electroencephalogram and electrocardiogram accompanying changes in depth of anaesthesia in the cat. Anaesthesia was induced by the volatile anaesthetic isoflurane. The high-frequency components (around 30 Hz) in the electroencephalogram disappear in deep anaesthesia. The electrocardiogram also shows substantial changes in contamination due to muscle fasciculations with anaesthesia level. Fasciculations appear as noise in the electrocardiogram. The amplitude of the electrical muscle activity contaminating the ECG can be easily used for the maintainance of a constant level of anaesthesia during a neurophysiological experiment.

Sevoflurane in elderly patients

An ideal anaesthetic should allow rapid, pleasant, and predictable induction, maintenance and emergence from anaesthesia. Little information is available about sevoflurane use in elderly patients. The pharmacological profile of sevoflurane may be advantageous in geriatric patients because low solubility in the blood is a prerequisite for rapid changes in anaesthetic depth. In addition, the pharmacological profile of sevoflurane may help to reduce the total amount of drug required. Using volatile anaesthetics with low blood solubility and rapid clearance may help in an early postoperative assessment of the neurological status. Because geriatric patients show a higher intraoperative variability of haemodynamic parameters when compared to younger patients a drug such as sevoflurane with rapid uptake and elimination may be advantageous for treatment of hyper- and hypotensive states. As a consequence, the need for vasoactive drugs may be reduced. Recovery from sevoflurane anaesthesia is faster when compared with isoflurane. However, there is still controversy if the occurrence of postoperative cognitive and mental impairment is reduced in elderly patients if drugs with fast elimination characteristics are use. Few data are available on the use of sevoflurane in geriatric patients with renal impairment. Further studies are needed to clarify if the administration of sevoflurane is safe in this population of patients.

Autoregressive Modeling with Exogenous Input of Middle-Latency Auditory-Evoked Potentials to Measure Rapid Changes in Depth of Anesthesia

Obtaining an adequate depth of anesthesia is a continuous challenge to the anesthetist. With the introduction of muscle-relaxing agents the traditional signs of awareness are often obscured, or difficult to interpret. These signs include blood pressure, heart rate, pupil size, etc. However, these factors do not describe the depth of anesthesia (DA) in a cerebral activity sense. Hence, a better measure of the DA is required. It has been suggested that Auditory-Evoked Potentials (AEP) can provide additional information about the DA. The general method of extracting AEP is by use of a Moving Time Average (MTA). However, the MTA is time consuming because a large number of repetitions is needed to produce an estimate of the AEP. Hence, changes occurring over a small number of sweeps will not be detected by the MTA average. We describe a system-identification method, an autoregressive model with exogeneous input (ARX) model, to produce a sweep-by-sweep estimate of the AEP. The method was clinically evaluated in 10 patients anesthetized with alfentanil and propofol. The time interval between propofol induction and the time when the Na-Pa amplitude was decreased to 25% of the initial amplitude was measured. These measurements showed that ARX-estimated compared to MTA-estimated AEP was significantly faster in tracing transition from consciousness to unconsciousness during propofol induction (p < 0.05).

Respiratory sinus arrhythmia: comparison with EEG indices during isoflurane anaesthesia at 0.65 and 1.2 MAC

Respiratory sinus arrhythmia (RSA) is a cyclical variation in heart rate during breathing, where the heart rate increases during inspiration and decreases during expiration. RSA and the electroencephalogram (EEG) were monitored in 10 patients undergoing elective surgery with isoflurane and nitrous oxide in oxygen anaesthesia after induction with propofol. All patients were subject to controlled ventilation and recovery from competitive neuromuscular block was facilitated by neostigmine and glycopyrronium (seven patients) or atropine (three patients). Median and spectral edge (95%) frequencies of the raw EEG were derived off-line. RSA and EEG indices were obtained during preinduction (baseline), induction, incision, 0.65 and 1.2 MAC of isoflurane maintenance during surgery and recovery. Significant decreases in the level of RSA, median and spectral edge frequencies were observed during induction and significant increases in all indices were observed at recovery in all patients. Significant decreases in the median and spectral edge EEG frequencies occurred in patients treated with atropine both to counteract bradycardia after propofol induction and at antagonism of neuromuscular block (n = 3), compared with patients treated with glycopyrronium (n = 7). In contrast, the level of RSA did not decrease significantly with atropine. It is concluded that measurements of RSA could form the basis of a useful index of anaesthetic depth during isoflurane anaesthesia, even during the use of pharmacologically appropriate doses of atropine. However, any effects of atropine on the raw EEG and on indices derived from the EEG, should be characterized further so that these effects are not confused with changes in anaesthetic depth.

Laryngeal and Respiratory Responses to Tracheal Irritation at Different Depths of Enflurane Anesthesia in Humans

The effect of three different depths of enflurane anesthesia (1.0, 1.4, and 1.8 MAC) upon laryngeal and respiratory responses to tracheal instillation of distilled water in nine female patients in whom a double-cuffed endotracheal tube had been inserted was investigated. The laryngeal responses were monitored by measuring the pressure in the saline-filled cuff positioned within the larynx, and the respiratory responses were monitored by measuring ventilatory flow and tracheal airway pressure. Increases in laryngeal cuff pressure in response to tracheal irritation were 19.7 +/- 4.5 cmH2O (mean +/- SD) at 1.0 MAC, 13.9 +/- 3.6 cmH2O at 1.4 MAC, and 7.6 +/- 1.8 cmH2O at 1.8 MAC, respectively (P less than 0.01 for anesthetic dose). At 1.0 MAC of enflurane anesthesia, tracheal instillation of saline caused immediate laryngeal constriction and all components of the tracheal response, such as apnea, expiration reflex, cough reflex, and spasmodic panting. At 1.4 and 1.8 MAC, the same stimulation caused only apnea and constriction of the larynx in the majority of patients. These results indicate that changes in depth of anesthesia can modify the laryngeal and respiratory responses to tracheal irritation. The close association of laryngeal and respiratory responses may be an integral part of the defensive reflex synergism.

Anesthetic effect of CO2 on fish. I. Changes in depth of anesthesia of the carp anesthetized with a constant level of CO2.

Changes of respiration, behavior, and depth of anesthesia were examined in carp that were individually kept in a chamber supplied with water bubbled with an equi-mixture of CO2 and O2.CO2 had an anesthetic effect on all the carp at Pco2 ?? 125, 150, and 175mmHg, but these partial pressures in the ambient water were fatal in 10, 20, and 70% of the carp, respectively. Although all the carp survived in the experiment using Pco2 ?? 100mmHg, only 50% of them became anesthetized. The depth of anesthesia progressed with time and the Pco2. Recovery time from anesthetic state was 13-130min, the mean recovery time being about 40min in all experiments. The optimum anesthetic concentration for adult carp seemed to be between Pco2=100mmHg and 125mmHg.

Methoxyflurane (penthrane): a laboratory and clinical study.

Methoxyflurane is a new fluorinated and chlorinated saturated asymmetrical ether whose outstanding physical properties are an unusually high boiling point and the fact that it is non-flammable in anaesthetic concentrations. Its greatest usefulness seems to lie in its role as an adjuvant to nitrous oxide anaesthesia. Methoxyflurane is a potent respiratory depressant but has relatively little effect on the cardiovascular system. Profound hypotension will occur with undue depth of anaesthesia but changes in the electrocardiogram have not been observed. Methoxyflurane lacks a certain degree of flexibility as far as ready changes in depth of anaesthesia are concerned and on occasion recovery from anaesthesia is quite markedly delayed. There is some evidence that the drug concentration increases in the adipose tissue after administration has been discontinued, thus accelerating the lowering of plasma levels in the obese patient and decreasing wakening time. Since it is a rather long-acting agent, administration should be discontinued well before the end of operation and concentrations should be tapered off even earlier. Methoxyflurane is capable of producing a degree of abdominal muscle relaxation but it is recommended that small doses of muscle relaxants be used in order to reduce the amount of methoxyflurane required. The argent enhances the effect of the non-depolarizing muscle relaxants. Although induction of anaesthesia with nitrous oxide-oxygen-methoxyflurane is possible and is njot unpleasant, it is slow, implies the use of more methoxyflurane, and is undesirable from the point of view of awakening. It is therefore recommended that anaesthesia be induced with intravenous barbiturates and adequate premedication is desirable. Administration of a nitrous oxide-oxygen-methoxyflurane sequence was accompanied by few operative and postoperative complications and in that regard the drug compared favourably with other anaesthetic techniques.