EEG and SEMG monitoring during induction and maintenance of anesthesia with propofol

Sleep and Delirium in Older Adults

Purpose of Review

Poor sleep and delirium are common in older patients but recognition and management are challenging, particularly in the intensive care unit (ICU) setting. The purpose of this review is to highlight current research on these conditions, their inter-relationship, modes of measurement, and current approaches to management.

Recent Findings

Sleep deprivation and delirium are closely linked, with shared clinical characteristics, risk factors, and neurochemical abnormalities. Acetylcholine and dopamine are important neurochemicals in the regulation of sleep and wakefulness and their dysregulation has been implicated in development of delirium. In the hospital setting, poor sleep and delirium are associated with adverse outcomes; non-pharmacological interventions are recommended, but tend to be resource intensive and hindered by a lack of reliable sleep measurement tools. Delirium is easier to identify, with validated tools available in both ICU and non-ICU settings; however, an optimal treatment approach remains unclear. Antipsychotics are used widely to prevent and treat delirium, although the efficacy data are equivocal. Bundled non-pharmacologic approaches represent a promising framework for prevention and management.

Summary

Poor sleep and delirium are common problems in older patients. While these phenomena appear linked, a causal relationship is not clearly established. At present, there are no established sleep-focused guidelines for preventing or treating delirium. Novel interventions are needed that address poor sleep and delirium, particularly in older adults.

Sedation Analgesia and Neuromuscular Blockade in Pediatric Critical Care: Overview and Current Landscape

Sedation is a mainstay of therapy for critically ill children. Although necessary in the care of the critically ill child, sedative drugs are associated with adverse effects, such as disruption of circadian rhythm, altered sleep, delirium, potential neurotoxicity, and immunosuppression. Optimal approaches to the sedation of the critically ill child should include identification of sedation targets and sedation interruptions, allowing for a more individualized approach to sedation. Further research is needed to better understand the relationship between critical illness and sedation pharmacokinetics and pharmacodynamics, the impact of sedation on immune function, and the genetic implications on drug disposition and response.

Quantitative electroencephalography in a swine model of blast-induced brain injury

OBJECTIVE

Electroencephalography (EEG) was used to examine brain activity abnormalities earlier after blast exposure using a swine model to develop a qEEG data analysis protocol.

METHODS

Anaesthetized swine were exposed to 420-450 Kpa blast overpressure and survived for 3 days after blast. EEG recordings were performed at 15 minutes before the blast and 15 minutes, 30 minutes, 2 hours and 1, 2 and 3 days post-blast using surface recording electrodes and a Biopac 4-channel data acquisition system. Off-line quantitative EEG (qEEG) data analysis was performed to determine qEEG changes.

RESULTS

Blast induced qEEG changes earlier after blast exposure, including a decrease of mean amplitude (MAMP), an increase of delta band power, a decrease of alpha band root mean square (RMS) and a decrease of 90% spectral edge frequency (SEF90).

CONCLUSIONS

This study demonstrated that qEEG is sensitive for cerebral injury. The changes of qEEG earlier after the blast indicate the potential of utilization of multiple parameters of qEEG for diagnosis of blast-induced brain injury. Early detection of blast induced brain injury will allow early screening and assessment of brain abnormalities in soldiers to enable timely therapeutic intervention.

Sleep deprivation in critical illness: its role in physical and psychological recovery

Critically ill patients frequently experience poor sleep, characterized by frequent disruptions, loss of circadian rhythms, and a paucity of time spent in restorative sleep stages. Factors that are associated with sleep disruption in the intensive care unit (ICU) include patient-ventilator dysynchrony, medications, patient care interactions, and environmental noise and light. As the field of critical care increasingly focuses on patients' physical and psychological outcomes following critical illness, understanding the potential contribution of ICU-related sleep disruption on patient recovery is an important area of investigation. This review article summarizes the literature regarding sleep architecture and measurement in the critically ill, causes of ICU sleep fragmentation, and potential implications of ICU-related sleep disruption on patients' recovery from critical illness. With this background information, strategies to optimize sleep in the ICU are also discussed.

Sedation and sleep disturbances in the ICU

Sedation in the ICU is, paradoxically, both a cause and a potential treatment for the sleep disruption almost universally observed in the critically ill. A patient-focused sedation strategy that minimizes unnecessary medication, avoids medication withdrawal, addresses the specific impediments to sleep, and serves as an adjunct to attentive environmental control may ultimately serve patients best.

Sedation and sleep disturbances in the ICU

The need for compassionate care of the critically ill often compels clinicians to treat these patients with pharmacologic sedation. Although patients may appear to be asleep under the influence of these sedating medications, the relationship between sleep and sedation is complex and not fully understood. These medications exert their effects at different points along the central nervous system's natural sleep pathway, leading to similarities and differences between the two states. This relationship is important because critically ill patients sleep poorly and this phenomenon has been linked to poor intensive care unit outcomes. Therefore, greater awareness of the effects of these medications on sleep may lead to sedation protocols that further improve outcomes. This article reviews the relationship between sedation and sleep from physiologic and clinical perspectives.

Pharmacology I: effects on sleep of commonly used ICU medications

Critically ill patients are almost universally administered medications to treat their acute illnesses and to maximize their comfort. The effects of many of these medications on their sleep, however, may be important. It is known that critically ill patients have severely disrupted sleep and that this disrupted sleep has a negative impact on ICU outcomes. This article reviews how some commonly used ICU medications may affect patients' sleep.

Classic electroencephalographic parameters: Median frequency, spectral edge frequency etc

Even today many anaesthesiologists rely on parameters of the autonomic nervous system, such as blood pressure and heart rate to decide if a patient is adequately anaesthetized. It is thought that the electroencephalogram (EEG) may provide more information on the state of anaesthesia. Because full EEG analysis is not possible in the operating room, processed EEG parameters have been developed comprising complex information into a single value. Time and frequency domain parameters are calculated. The power spectrum results from a Fourier analysis and can be described by parameters such as median frequency, spectral edge frequency and others. It was noted, however, that anaesthetics at low doses increase frequency of the EEG, whereas at high doses the EEG is depressed. This biphasic response makes it difficult to clearly distinguish the exact anaesthetic state of a patient. Median frequency and spectral edge frequency have been studied in numerous studies. However, no sole indicator has been derived from the EEG that could serve as a descriptor of anaesthetic depth.

The electroencephalographic effects of IV anesthetic doses of melatonin: comparative studies with thiopental and propofol

We have demonstrated that large-dose IV melatonin can exert hypnotic effects similar to those caused by thiopental and propofol. In this study, we compared the electroencephalographic (EEG) effects of melatonin with those of thiopental and propofol. Sprague-Dawley rats were assigned to receive equipotent bolus doses of thiopental (23.8 mg/kg), propofol (14.9 mg/kg), or melatonin (312 mg/kg). EEG effects were recorded at periodic intervals over 10 minutes. Of eight processed EEG variables analyzed, only relative total power (rTP), relative spectral edge 95% (rSE95), and relative approximate entropy (rAE) were altered by all drugs compared with their control vehicles. Drug administration decreased the values relative to baseline, with subsequent return toward baseline during the 10-min time course. Thiopental significantly increased rTP, whereas propofol and melatonin did not. All drugs significantly decreased rSE95. However, the time course of peak effect and duration differed for each, with melatonin exhibiting a slower onset and a more sustained EEG effect. All drugs significantly decreased rAE, with similar time courses for thiopental and propofol and a slower onset/longer duration for melatonin. Melatonin produced effects on processed EEG variables similar to those of thiopental and propofol, specifically a decrease in the rSE95 and a decrease in the rAE.

IMPLICATIONS

Anesthetic doses of melatonin produced effects on processed electroencephalographic variables similar to those of thiopental and propofol.

Esmolol promotes electroencephalographic burst suppression during propofol/alfentanil anesthesia

This study examined the effects of an esmolol infusion on the electroencephalogram during propofol/alfentanil IV anesthesia. After informed consent, 20 patients were randomly assigned into four groups on the basis of two target alfentanil concentrations (alfentanil 50 or 150 ng/mL) and of a saline or esmolol infusion. Bispectral index (BIS), burst suppression ratio (SR), and physiologic variables were continuously monitored. A 30-min blinded infusion of saline or esmolol was started after establishing a stable baseline and followed by a washout period. The electroencephalogram was significantly suppressed by esmolol (BIS, 37 +/- 6 to 22 +/- 6, 40% decrease [mean +/- SD]; SR, 5 +/- 7 to 67 +/- 23, 13.4-fold increase) compared with baseline in the small-dose alfentanil groups. Discontinuation of esmolol reversed the response. BIS and SR were unaffected by placebo infusion. Twelve-minute to 16-min hysteresis between esmolol administration and the onset of half-maximal cortical suppression was observed. Physiologic variables and serum propofol and alfentanil concentrations were not significantly altered by esmolol. Although the mechanism remains unclear, significant cortical depression and the onset of burst suppression during a stable, computer-controlled propofol/alfentanil anesthetic was associated with esmolol infusion.

IMPLICATIONS

This study demonstrated the suppression of cerebral cortical electrical activity after blinded esmolol infusion during propofol/alfentanil anesthesia. A significant lag was noted between infusion and half-maximal effect (12-16 min). Whether esmolol, a metabolite, or a secondary process was responsible for this cortical suppression remains unknown and requires further study.

Craniofacial electromyogram activation response: another indicator of anesthetic depth

OBJECTIVE

After finding that craniofacial EMG preceding a stimulus was a poor predictor of movement response to that stimulus, we evaluated an alternative relation between EMG and movement: the difference in anesthetic depth between the endpoint of EMG responsiveness to a stimulus and endpoint of movement responsiveness to that stimulus. We expressed this relation as the increment of isoflurane between the two endpoints.

METHODS

We measured EMG over the frontalis muscle, over the corrugator muscle, and between the Fp2 and the mastoid process as patients emerged from general anesthesia during suture closing of the surgical incision. Anesthesia was decreased by controlled washout of isoflurane while maintaining 70% N2O, and brain isoflurane concentrations ((C)isoBrain) were calculated. We studied a control group of 10 patients who received only surgical stimulation, and 30 experimental patients who intermittently received test stimuli in addition to the surgical stimulation. Patients were observed for movement responses and EMG records were evaluated for EMG activation responses. We defined an EMG activation response to be a rapid voltage increase of at least 1.0 microV RMS above baseline, with a duration of at least 30 s, in at least one of the three EMG channels. Patient responses to stimuli were classified as either an EMG activation response without a move response (EMG+), a move response without an EMG activation response (MV+), both an EMG activation response and a move response (EMG+MV+), or no response. We defined the EMG+ endpoint to be the threshold between EMG+ response and nonresponse to a stimulus, and estimated (C)isoBrain at this endpoint. We similarly defined the move endpoint and estimated the move endpoint (C)isoBrain. We then calculated the increment of (C)isoBrain at the EMG+ endpoint relative to the move endpoint.

MAIN RESULTS

For the 30 experimental patients, the initial response to a test stimulus was an EMG+ in 14 patients (47%), an EMG+MV+ in 12 patients (40%), and a MV+ in 1 patient (3%); no response occurred by the time surgery was completed in 3 patients (10%). No response occurred in 7 of the control patients (70%). Of the 14 patients with an initial EMG+ response to a test stimulus, 9 patients later had a move response. For these 9 patients, the increment of (C)isoBrain between the EMG+ endpoint and move endpoint was 0.11 +/- 0.04 vol%, (mean +/- SD).

CONCLUSIONS

Our results suggest that, given the circumstances of our study, an EMG activation response by a nonmoving patient indicates that the patient is at an anesthetic level close to that at which movement could occur. However, because the first EMG activation response may occur simultaneously with movement, the EMG activation response cannot be relied upon to always herald a move response before it occurs. Our results also suggest that EMG responsiveness to a test stimulus may be used to estimate the anesthetic depth of an individual patient.

Electroencephalographic characteristics of emergence from propofol/sufentanil total intravenous anesthesia

We recorded the electroencephalogram (EEG) in 16 patients during propofol/sufentanil total intravenous anesthesia to determine whether EEG changes might predict imminent awakening during emergence. Changes in absolute and relative power in four frequency bands, median frequency (MF), 95th percentile frequency (F95), and two frequency band power ratios (beta/alpha and (alpha+beta)/delta) were quantified. One minute before eye opening, absolute power in the delta and alpha bands had decreased to 49% (25%-73%) and 42% (25%-58%) of the value during the infusion (P > 0.005). MF, F95, and the two frequency band power ratios increased during emergence (P > 0.05). Of the individual spectral variables, only a 50% decrease in absolute alpha power was more than 90% sensitive and specific in predicting eye opening. We conclude that, although pronounced EEG changes occur during emergence from propofol/sufentanil anesthesia, the EEG does not reliably predict eye opening.

Pharmacokinetic implications for the clinical use of propofol

Propofol, the recently marketed intravenous induction agent for anaesthesia, is chemically unrelated to earlier anaesthetic drugs. This highly lipophilic agent has a fast onset and short, predictable duration of action due to its rapid penetration of the blood-brain barrier and distribution to the CNS, followed by redistribution to inactive tissue depots such as muscle and fat. On the basis of pharmacokinetic-pharmacodynamic modelling, a mean blood-brain equilibration half-life of only 2.9 minutes has been calculated. In most studies, the blood concentration curve of propofol has been best fitted to a 3-compartment open model, although in some patients only 2 exponential phases can be defined. The first exponential phase half-life of 2 to 3 minutes mirrors the rapid onset of action, the second (34 to 56 minutes) that of the high metabolic clearance, whereas the long third exponential phase half-life of 184 to 480 minutes describes the slow elimination of a small proportion of the drug remaining in poorly perfused tissues. Thus, after both a single intravenous injection and a continuous intravenous infusion, the blood concentrations rapidly decrease below those necessary to maintain sleep (around 1 mg/L), based on both the rapid distribution, redistribution and metabolism during the first and second exponential phases (more than 70% of the drug is eliminated during these 2 phases). During long term intravenous infusions cumulative drug concentrations and effects might be expected, but even then the recovery times do not appear to be much delayed. The liver is probably the main eliminating organ, and renal clearance appears to play little part in the total clearance of propofol. On the other hand, because the total body clearance may exceed liver blood flow, an extrahepatic metabolism or extrarenal elimination (e.g. via the lungs) has been suggested. Approximately 60% of a radiolabelled dose of propofol is excreted in the urine as 1- and 4-glucuronide and 4-sulphate conjugates of 2.6-diisopropyl 1,4-quinol, and the remainder consists of the propofol glucuronide. Thus for hepatic and renal diseases, co-medication, surgical procedure, gender and obesity do not appear to cause clinically significant changes in the pharmacokinetic profile of propofol, but the decrease in the clearance value in the elderly might produce higher concentrations during a long term infusion, with an increased drug effect. In addition, the lower induction dose observed in relation to increased age might be partly explained by a smaller central volume of distribution.(ABSTRACT TRUNCATED AT 400 WORDS)

Propofol. A review of its pharmacodynamic and pharmacokinetic properties and use as an intravenous anaesthetic

Propofol is an intravenous anaesthetic which is chemically unrelated to other anaesthetics. Induction of anaesthesia with propofol is rapid, and maintenance can be achieved by either continuous infusion or intermittent bolus injections, with either nitrous oxide or opioids used to provide analgesia. Comparative studies have shown propofol to be at least as effective as thiopentone, methohexitone or etomidate for anaesthesia during general surgery. The incidence of excitatory effects is lower with propofol than with methohexitone, but apnoea on induction occurs more frequently with propofol than with other anaesthetics. Additionally, a small number of studies of induction and maintenance of anaesthesia have found propofol to be a suitable alternative to induction with thiopentone and maintenance with halothane, isoflurane or enflurane. Propofol is particularly suitable for outpatient surgery since it provides superior operating conditions to methohexitone (particularly less movement), and rapid recovery in the postoperative period associated with a low incidence of nausea and vomiting. When used in combination with fentanyl or alfentanil, propofol is suitable for the provision of total intravenous anaesthesia, and comparative studies found it to be superior to methohexitone or etomidate in this setting. Infusions of subanaesthetic doses of propofol have been used to sedate patients for surgery under regional anaesthesia, and also to provide sedation of patients in intensive care. In the latter situation it is particularly encouraging that propofol did not suppress adrenal responsiveness during short term studies. If this is confirmed during longer term administration this would offer an important advantage over etomidate. Thus, propofol is clearly an effective addition to the limited range of intravenous anaesthetics. While certain areas of its use need further study, as would be expected at this stage of its development, propofol should find a useful role in anaesthetic practice.