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PubMed2000

Conscious and preconscious adaptation to rhythmic auditory stimuli: a magnetoencephalographic study of human brain responses.

This study was triggered by the experimental evidence that subjects required to tap in synchrony with a heard rhythm spontaneously time their tapping to variations in rhythm frequency even when these variations are so small that they are not consciously detectable. We performed a series of magnetoencephalographic (MEG) measurements, aimed at investigating whether the response of the auditory cortex discriminates randomly administered series of brief tones differing from each other only by their interstimulus intervals (ISI). Moreover, by combining psychophysical measurements, conscious and preconscious adjustments of tapping to rhythm variations were compared with brain cortical responses. The ISIs were varied by 2% or 20% from a "central" value of 500 ms. Subjects always consciously detected the 20% ISI changes and easily adjusted their tapping accordingly, whereas they never consciously detected the 2% ISI changes, even though they always correctly adjusted their tapping to them. Analysis of the auditory evoked fields (AEFs) showed that the intensity of the M100 component decreased with decreasing ISI both for 20% and 2% variations in a statistically significant manner, despite the fact that the 2% variation was not consciously perceived. The M100 behavior indicated that connections between auditory and motor cortexes may exist that are able to use the information on rhythm variations in the stimuli even when these are not consciously identified by the subject. The ability of the auditory cortex to discriminate different time characteristics of the incoming rhythmic stimuli is discussed in this paper in relation to the theories regarding the physiology of time perception and discrimination.

Acoustic Stimulation↗
PubMed2005

Neural processes underlying conscious perception: experimental findings and a global neuronal workspace framework.

One striking property of perception is that it can be achieved in two seemingly different ways: either consciously or non-consciously. What distinguishes these two types of processing at the neural level? So far, empirical findings suggest that conscious perception is associated with an increase in activity at the sensory level, the specific involvement of a fronto-parietal network and an increase in long-distance functional connectivity and synchrony within a broad network of areas. We interpret these data in the framework of the global neuronal workspace model which proposes that the neural basis of conscious access is a sudden self-amplifying process leading to a global brain-scale pattern of activity. In contradiction with several theories which assume that there is a continuum of perception, associated with a gradual change in the intensity of brain activation, the model predicts a sharp non-linear transition between non-conscious and conscious processing.

Animals↗
PubMed2004

Consciousness absent and present: a neurophysiological exploration.

Backward masking was used to investigate the amount of neuronal activity that occurs in the macaque inferior temporal visual cortex when faces can just be identified. It is shown that the effect of the pattern mask is to interrupt neuronal activity in the inferior temporal visual cortex. This reduces the number of action potentials that occur to a given stimulus, and decreases even more the information that is available about which stimulus was shown because the variance of the spike counts is increased. When the onset of the mask follows the onset of the test stimulus by 20 ms, each neuron fires for approximately 30 ms, provides on average 0.06 bits of information, and human observers perform at approximately 50% better than chance in forced choice psychophysics, yet say that they are guessing, and frequently report that they are unable to consciously see the face and identify which face it is. At a longer Stimulus Onset Asynchrony of 40 ms, the neurons fire for approximately 50 ms, the amount of information carried by a single neuron is 0.14 bits, and human observers are much more likely to report conscious identification of which face was shown. The results quantify the amount of neuronal firing and information that is present when stimuli can be discriminated but not reported on consciously, and the additional amount of neuronal firing and information that is required for humans observers to consciously identify the faces. It is suggested that the threshold for conscious visual perception may be set to be higher than the level at which small but significant information is present in neuronal firing, so that the systems in the brain that implement the type of information processing involved in conscious thoughts are not interrupted by small signals that could be noise in sensory pathways.

Animals↗
PubMed2005

Behavioral evaluation of consciousness in severe brain damage.

This paper reviews the current state of bedside behavioral assessment in brain-damaged patients with impaired consciousness (coma, vegetative state, minimally conscious state). As misdiagnosis in this field is unfortunately very frequent, we first discuss a number of fundamental principles of clinical evaluation that should guide the assessment of consciousness in brain-damaged patients in order to avoid confusion between vegetative state and minimally conscious state. The role of standardized behavioral assessment tools is particularly stressed. The second part of this paper reviews existing behavioral assessment techniques of consciousness, showing that there are actually a large number of these scales. After a discussion of the most widely used scale, the Glasgow Coma Scale, we present several new promising tools that show higher sensitivity and reliability for detecting subtle signs of recovery of consciousness in the post-acute setting.

Behavior↗
PubMed1999

Acetylcholine in mind: a neurotransmitter correlate of consciousness?

The cholinergic system is one of the most important modulatory neurotransmitter systems in the brain and controls activities that depend on selective attention, which are an essential component of conscious awareness. Psychopharmacological and pathological evidence supports the concept of a 'cholinergic component' of conscious awareness. Drugs that antagonize muscarinic receptors induce hallucinations and reduce the level of consciousness, while the nicotinic receptor is implicated as being involved in the mechanism of action of general (inhalational) anaesthetics. In degenerative diseases of the brain, alterations in consciousness are associated with regional deficits in the cholinergic system. In Alzheimer's disease (AD), there is a loss of explicit (more than implicit) memory and hypoactivity of cholinergic projections to the hippocampus and cortex, while the visual hallucinations experienced by subjects with Dementia with Lewy bodies (DLB) are associated with reductions in neocortical ACh-related activity. In Parkinson's disease, the additional loss of pedunculopontine cholinergic neurones, which control REM (rapid eye movement) sleep or dreaming, is likely to contribute to REM abnormalities, which also occur in DLB. Widespread basal-forebrain and rostral brainstem cholinergic pathways, which include converging projections to the thalamus, appear to be located strategically for generating and integrating conscious awareness. Alleviation of a range of cognitive and non-cognitive symptoms by drugs that modulate the cholinergic system, which are being developed for the treatment of AD and related disorders, could be caused by changes in consciousness.

Acetylcholine↗
PubMed2000

Effect of Korea red ginseng on the blood pressure in conscious hypertensive rats.

The change of blood pressure and heart rate after intravenous injection of Korea red ginseng (KRG) were studied in the conscious normotensive and one-kidney, one-clip Goldblatt hypertensive (1K, 1C-GBH) rats. Crude saponin (CS) of KRG (50, 100 mg/kg i.v.) induced a hypotensive effect and bradycardia in a dose-dependent manner in the anesthetized rats. On the other hand, CS of KRG (100 mg/kg) induced a hypotensive effect and reflex tachycardia in the conscious rats. Saponin-free fraction (SFF) of KRG did not affect them in the anesthetized normotensive rats (P>.05). The maximal hypotensive effect by CS of KRG in the conscious 1K, 1C-GBH hypertensive rats and L-nitroarginine methyl ester (L-NAME, 40 mg/kg)-treated conscious hypertensive rats was not different from that of conscious normotensive rats (Delta 31.6+/-6.3, Delta 27.5+/-5.8 vs. Delta 26.7+/-4.3 mmHg, P>.05). However, pretreatment of L-NAME significantly inhibited the reflex tachycardia by CS of KRG (70.8+/-7.0 vs. 30.6+/-15.0 bpm, P<.05). Hemolysate-sensitive nitric oxide (NO) current by the CS of KRG was greater than that of the SFF of KRG (651.9+/-128.2 pA for CS and 164.9+/-92.5 pA for SFF, P<.001). These findings suggest that KRG has a hypotensive effect and its effect may be due to saponin fraction of KRG in the conscious rats. The releasing effect of NO of KRG, like NO donor, may be partly contributed to the hypotensive effect of KRG.

Animals↗
PubMed1985

Different relations between infarct size and occluded bed size in barbiturate-anesthetized versus conscious dogs.

The relation between infarct size and occluded bed size in barbiturate-anesthetized (n = 32) and conscious (n = 34) dogs was compared using models of the left anterior descending (n = 43) and circumflex (n = 23) coronary arteries with 2 day old infarcts. Infarct and occluded bed (postmortem coronary arteriography) masses were measured by computerized planimetry of weighed left ventricular rings. For either type of occlusion, infarcts were larger in anesthetized than in conscious dogs (56 versus 33% occluded bed, p less than 0.001), with greater slopes of the linear regressions between infarct size and occluded bed size (p less than 0.001) and less epicardial sparing (p less than 0.05) on topographic mapping. Although arterial and left atrial pressures were similar in the two groups, heart rates were higher in the anesthetized dogs, both before (127 versus 88 beats/min, p less than 0.001) and after (151 versus 109 beats/min, p less than 0.001) occlusion. Myocardial blood flow distribution (radioactive microspheres, n = 33) favored the epicardium in anesthetized dogs, with lower endocardial-epicardial flow ratios pre- and postocclusion. Also, the level of total plasma catecholamines (radioenzymatic assay) was higher in barbiturate-anesthetized (n = 5) than in conscious (n = 5) dogs. Increasing the heart rate in conscious dogs (n = 18) to that of the anesthetized group (139 beats/min) by pacing produced larger infarcts and greater linear regression slopes, as seen in anesthetized dogs. Decreasing the heart rate in anesthetized dogs (n = 7) to that of the conscious group (98 beats/min) by sinoatrial node destruction and pacing resulted in smaller infarcts and lower linear regression slope, as seen in conscious dogs. Thus, the larger infarcts in barbiturate-anesthetized dogs appeared to be related mainly to the tachycardia, although transmural maldistribution of flow and increased circulating catecholamines might have contributed.

Analysis of Variance↗
PubMed2002

Evidence of conscious and subconscious olfactory information processing during word encoding: a magnetoencephalographic (MEG) study.

The present study was meant to distinguish between unconscious and conscious olfactory information processing and to investigate the influence of olfaction on word information processing. Magnetic field changes were recorded in healthy young participants during deep encoding of visually presented words whereby some of the words were randomly associated with an odor. All recorded data were then split into two groups. One group consisted of participants who did not consciously perceive the odor during the whole experiment whereas the other group did report continuous conscious odor perception. The magnetic field changes related to the condition 'words without odor' were subtracted from the magnetic field changes related to the condition 'words with odor' for both groups. First, an odor-induced effect occurred between about 200 and 500 ms after stimulus onset which was similar in both groups. It is interpreted to reflect an activity reduction during word encoding related to the additional olfactory stimulation. Second, a later effect occurred between about 600 and 900 ms after stimulus onset which differed between the two groups. This effect was due to higher brain activity related to the additional olfactory stimulation. It was more pronounced in the group consisting of participants who consciously perceived the odor during the whole experiment as compared to the other group. These results are interpreted as evidence that the later effect is related to conscious odor perception whereas the earlier effect reflects unconscious olfactory information processing. Furthermore, our study provides evidence that only the conscious perception of an odor which is simultaneously presented to the visual presentation of a word reduces its chance to be subsequently recognized.

Adult↗
PubMed2006

From automatic antigay prejudice to behavior: the moderating role of conscious beliefs about gender and behavioral control.

Two experiments tested whether the relation between automatic prejudice and discriminatory behavior is moderated by 2 conscious processes: conscious egalitarian beliefs and behavioral control. The authors predicted that, when both conscious processes are deactivated, automatic prejudice would elicit discriminatory behavior. When either of the 2 processes is activated, behavioral bias would be eliminated. The authors assessed participants' automatic attitudes toward gay men, conscious beliefs about gender, behavioral control, and interactions with gay confederates. In Experiment 1, men's beliefs about gender were heterogeneous, whereas women's beliefs were mostly egalitarian; men's responses supported the predictions, but women's responses did not. In Experiment 2, the authors recruited a sample with greater diversity in gender-related beliefs. Results showed that, for both sexes, automatic prejudice produced biased behavior in the absence of conscious egalitarian beliefs and behavioral control. The presence of either conscious process eliminated behavioral bias.

Adult↗
PubMed2000

Homeostatic biophasal conscious regulation.

A new theory on consciousness is presented. According to our neuroscientific model, focal awareness is the result of neurophysiological patterns of voluntary or involuntary information, registration, storage and retrieval performed in accordance with organismic biphasal homeostatic rules and regulations that follow the demand-supply principle. The information-processing operation consists of three major elements: 1. Involuntary activated 'inherited schematic representation' (ISR) programs that monitor homeostatic negative feedback programs and remain inert during the storage period; 2. Voluntary activated 'acquired engram linkage' (AEL) programs that monitor the preferential self-efforts designed to maintain homeostasis and dynamic adaptational survival; this information remains fixed in the storage reservoir; and 3. Outer, nonselective sources of activation that derive from the assembly of the sensory information system. Consciousness is limited by the microneurostructural boundaries of 'conscious instrument panel' (CIP) needed to handle this unique biological experience. At any unit of time, the conscious subjectively identifies states of pleasure (first phase of homeostasis maintenance) or displeasure (second phase of homeostasis) which are associated with the alarm subsystem of the 'organismic defense system' (ODS).Thus, consciousness is a form of neurophysiological activity that excludes unconscious existence in order to monitor information. This model promotes our understanding of the biological essences of consciousness.

Consciousness↗
PubMed1997

Some neurophysiologic aspects of consciousness.

An anatomico-physiologic approach to consciousness is facilitated by recognizing that the various meanings of consciousness have in common a crucial core C variously called subjectivity, awareness, consciousness-as-such, or consciousness per se. A sharp distinction is made between the property C and the contents of consciousness, partial loss of which is typical of cerebro-cortical lesions. The neuronal mechanism producing subjectivity also acts as an attention-action coordinator, hence must have specific connectivity requirements. These requirements are best met by the thalamic intralaminar nuclei (ILN). Whereas large lesions elsewhere leave C undisturbed, quite small bilateral lesions in ILN engender immediate unresponsiveness. This combination of anatomic and neurologic evidence is bolstered by a variety of physiologic evidence leading to the conclusion that further investigations of the ILN, and their interaction with lower centers as well as cerebral cortex, are most apt to yield a better understanding of consciousness.

Attention↗
PubMed2004

Neurohumoral mechanisms involved in the hypertensive response elicited by bilateral carotid occlusion in conscious intact or chronically sympathectomized rats.

Bilateral carotid occlusion (BCO) increases the sympathetic drive to the circulatory system in conscious intact rats, producing a hypertensive response characterized by two components, i.e., an initial peak followed by a sustained response of lower intensity. The neurohumoral mechanisms involved in the hypertensive response to BCO were evaluated in conscious intact (INTACT) or chronic guanethidine sympathectomized (SYMPX) rats. To accomplish this, the receptor antagonists, prazosin for alpha1-adrenergic receptor, losartan for AT1 angiotensin II receptor and [d(CH2)5Tyr(Me)AVP] for vascular V1 vasopressin receptor were used. A saline control group was studied as well. Conscious rats were equipped with cuffs around the common carotid arteries plus arterial and venous catheters. The results indicate that the sympathetic nervous system is the main mechanism controlling the basal arterial pressure in conscious INTACT rats, whereas in chronically SYMPX rats the renin-angiotensin system plays this role. In INTACT rats prazosin abolished the initial peak and blunted the sustained hypertensive response due to BCO, while the other antagonists exhibited no effect. SYMPX rats did not present the initial peak but displayed an enhanced sustained response, which was blunted by prazosin or the vasopressin antagonist. In conclusion, activation of the sympathetic drive is responsible for both the initial peak and the sustained hypertensive response due to BCO in conscious INTACT rats. On the other hand, vasopressin acting in concert with the sympathetic nervous system, plays a key role in the potentiation of the sustained hypertensive response due to BCO in conscious chronically SYMPX rats.

Adrenal Glands↗
PubMed2006

The Narcotrend 'depth of anaesthesia' monitor cannot reliably detect consciousness during general anaesthesia: an investigation using the isolated forearm technique.

BACKGROUND: During general anaesthesia in the presence of neuromuscular blocking drugs clinical criteria cannot detect the presence of consciousness. Various 'depth of anaesthesia' monitors are available which claim to prevent consciousness and/or reduce anaesthetic drug use. This study uses the Narcotrend anaesthesia brain monitor to guide anaesthetic administration but at the same time checks for the presence of intra-operative consciousness by using the 'isolated forearm' technique throughout the whole surgical/anaesthetic procedure. METHODS: Twelve women presenting for major gynaecological surgery under general anaesthesia, which included the use of neuromuscular blocking drugs, had a target controlled infusion of propofol adjusted according to the anaesthetic 'stage' indicated by a Narcotrend 'Depth of Anaesthesia Monitor'. Throughout surgery the isolated forearm technique was used to detect for the presence of consciousness at 1 min intervals. RESULTS: Isolated forearm responses to commands occurred in all 12 patients at some time during surgery, frequently in the absence of any significant changes in the usually monitored clinical variables. Overall, the 12 patients responded a total of 92 times during surgery. Only 41 (45%) responses were associated with an increase in the Narcotrend stage to a level suggesting consciousness (above stage C(0)). For the remaining responses, either there was no significant increase in the Narcotrend stage (above C(0)) or there was no change at all in the Narcotrend stage before, during, or after the patient responded to the taped command. CONCLUSIONS: The Narcotrend was unable to differentiate reliably between conscious and unconscious patients during general anaesthesia when neuromuscular blocking agents were used.

Acoustic Stimulation↗
PubMed2003

The neural correlates of conscious vision.

Conflicting accounts of the neurobiology of consciousness have emerged from previous imaging studies. Some studies suggest that visual consciousness relates to a distributed network of frontal and partietal regions while others point to localized activity within individual visual areas. While the two positions seem mutually exclusive, timing issues may help reconcile the two. Networks that appear unified in functional magnetic resonance imaging (fMRI) studies may reflect processes that are widely distributed in time. To help resolve this issue, we have investigated timing across a network correlating with consciousness in parallel fMRI and evoked potential (EP) studies of grating stimuli. At threshold, a stimulus is perceived on some occasions but not on others, dissociating sensory input and perception. We have found correlates of consciousness in the occipital lobe at 100 ms and in parietal, frontal, auditory and motor regions from 260 ms onwards. The broad temporal and spatial distribution of activity argues against a unified, distributed fronto-parietal correlate of consciousness. Instead, it suggests that correlates of consciousness are divided into primary and secondary network nodes, with early activity in the occipital lobe correlating with perception and later activity in downstream areas with secondary processes contingent on the outcome of earlier perceptual processing.

Adult↗
PubMed2006

Human ventral parietal cortex plays a functional role on visuospatial attention and primary consciousness. A repetitive transcranial magnetic stimulation study.

In this paper, we used repetitive transcranial magnetic stimulation (rTMS) in 18 normal subjects to investigate whether the ventral posterior parietal cortex (PPC) plays a causal role on visuospatial attention and primary consciousness and whether these 2 functions are linearly correlated with each other. Two distinct experimental conditions involved a similar visual stimuli recognition paradigm. In "Consciousness" experiment, number of consciously perceived visual stimuli was lower by about 10% after rTMS (300 ms, 20 Hz, motor threshold intensity) on left or right PPC than after sham (pseudo) rTMS. In "Attentional" Posner's experiment, these stimuli were always consciously perceived. Compared with sham condition, parietal rTMS slowed of about 25 ms reaction time to go stimuli, thus disclosing effects on endogenous covert spatial attention. No linear correlation was observed between the rTMS-induced impairment on attention and conscious perception. Results suggest that PPC plays a slight but significant causal role in both visuospatial attention and primary consciousness. Furthermore, these high-level cognitive functions, as modulated by parietal rTMS, do not seem to share either linear or simple relationships.

Adult↗
PubMed1994

Pulmonary vasoregulation by arginine vasopressin in conscious, halothane-anesthetized, and pentobarbital-anesthetized dogs with increased vasomotor tone.

BACKGROUND: Arginine vasopressin (AVP) is an important "stress" hormone that is known to play a key role in cardiovascular homeostasis of the systemic circulation. In contrast, the effects of AVP on the pulmonary circulation have not been extensively investigated, and the extent to which general anesthesia alters the pulmonary vascular response to AVP is entirely unknown. Our first objective was to assess the effects of AVP on the pulmonary vascular pressure-flow relation in chronically instrumented conscious dogs in the setting of an acute elevation in pulmonary vasomotor tone. Our second objective was to investigate the effects of halothane and pentobarbital anesthesia on the pulmonary vascular response to AVP after inducing the same degree of pulmonary preconstriction achieved in the conscious state. METHODS: Conditioned, mongrel dogs were chronically instrumented to measure the left pulmonary vascular pressure-flow (LPQ) relation. LPQ plots were generated by continuously measuring the pulmonary vascular pressure gradient (pulmonary arterial pressure minus left atrial pressure) and left pulmonary blood flow during gradual (approximately 1 min) inflation of a hydraulic occluder around the right pulmonary artery, which directed total pulmonary blood flow through the left pulmonary circulation. LPQ plots were generated in conscious (n = 10), halothane-anesthetized (n = 9) and pentobarbital-anesthetized (n = 7) dogs. In each condition, LPQ plots were measured at baseline, during the intravenous administration of the thromboxane analog U46619 and during the cumulative administration of AVP (2-19 ng.kg-1.min-1, intravenous) in the presence of U46619 preconstriction. RESULTS: U46619 caused acute pulmonary vasoconstriction (P < 0.01) in conscious dogs. In this setting of U46619 preconstriction, AVP caused pulmonary vasodilation (P < 0.05) in the conscious state. In contrast, despite identical levels of U46619 preconstriction, the pulmonary vasodilator response to AVP was either reversed to vasoconstriction (P < 0.05) or abolished during halothane and pentobarbital anesthesia. CONCLUSIONS: These results indicate that AVP exerts a significant pulmonary vasodilator response in the setting of acute pulmonary vasoconstriction in conscious dogs. However, the pulmonary vascular response to this stress hormone is markedly altered during halothane and pentobarbital anesthesia.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1994

Levosimendan (OR-1259), a myofilament calcium sensitizer, enhances myocardial contractility but does not alter isovolumic relaxation in conscious and anesthetized dogs.

BACKGROUND: Levosimendan is a myofilament calcium sensitizer with phosphodiesterase III inhibiting properties which increases contractile state in vitro by stabilizing calcium-induced changes in troponin C. This latter effect may produce positive inotropic actions but may also cause deleterious negative lusitropic effects. This investigation examined the effects of levosimendan on systemic and coronary hemodynamics and left ventricular systolic and diastolic function in conscious and anesthetized dogs. METHODS: Because autonomic nervous system activity may influence the actions of levosimendan and volatile anesthetics in vivo, experiments were conducted in the presence of pharmacologic blockade of the autonomic nervous system. A total of 24 experiments were performed in eight dogs chronically instrumented for measurement of aortic and left ventricular pressure, the peak rate of increase and decrease of left ventricular pressure, subendocardial segment length, diastolic coronary blood flow velocity, and cardiac output. The slope of the regional preload recruitable stroke work relation was used to assess myocardial contractility. Diastolic function was evaluated by the peak rate of decrease of left ventricular pressure, a time constant of isovolumic relaxation, maximum segment lengthening velocity during rapid ventricular filling, and a regional chamber stiffness constant. Systemic and coronary hemodynamics and left ventricular pressure-segment length diagrams and waveforms were recorded after 10 min equilibration at each dose of levosimendan (0.5, 1.0, 2.0, and 4.0 micrograms.kg-1.min-1) in the conscious state or during isoflurane or halothane anesthesia (1.0 MAC) on 3 days of experimentation. RESULTS: In conscious dogs, levosimendan increased heart rate, cardiac output, diastolic coronary blood flow velocity, and segment shortening and decreased left ventricular end-diastolic pressure, systemic vascular resistance, and diastolic coronary vascular resistance. Levosimendan caused dose-dependent increases in the slope of the regional preload recruitable stroke work relation (65 +/- 6 during control to 139 +/- 9 mmHg during the high dose), consistent with a direct positive inotropic effect. No changes in the peak rate of decrease of left ventricular pressure or in the time constant of isovolumic relaxation were produced by with levosimendan in conscious dogs, indicating that isovolumic relaxation was unaffected. In contrast, increases in rapid ventricular filling were observed (maximum segment lengthening velocity 34 +/- 3 during control to 47 +/- 5 mm.s-1 at the high dose). In the presence of isoflurane and halothane, levosimendan caused cardiovascular actions which were similar to those observed in the conscious state. Levosimendan increased, in a dose-related manner, the slope of the regional preload recruitable stroke work relation and in the maximum segment lengthening velocity during rapid ventricular filling in anesthetized dogs. However, there were no changes in the time constant of isovolumic relaxation or in the peak rate of decrease of left ventricular pressure. CONCLUSIONS: The results indicate that levosimendan causes systemic and coronary vasodilatation in conscious and anesthetized dogs during blockade of the autonomic nervous system. Levosimendan caused direct positive inotropic effects and improved rapid ventricular filling but did not alter indices of isovolumic relaxation, suggesting that levosimendan may selectively enhance systolic performance and diastolic filling without affecting left ventricular relaxation.

Anesthetics↗
PubMed1997

Recovery of consciousness after thiopental or propofol. Bispectral index and isolated forearm technique.

BACKGROUND: Currently, there exists no effective monitor that can predict the probability of a patient being conscious during general anesthesia. The electroencephalogram-derived bispectral index (BIS) is a promising new method to assess anesthetic adequacy. This study used the BIS to predict the probability of recovery of consciousness after a single bolus induction dose of propofol or thiopental. METHODS: Twenty unpremedicated surgical patients were anesthetized with 4 mg/kg thiopental and 20 patients with 2 mg/kg propofol. The BIS was monitored throughout the study. After induction, before administration of neuromuscular blocking agent, a tourniquet was applied to one arm and inflated above the systolic blood pressure. This allowed preservation of the ability to move the hand after neuromuscular blocking agent onset. Patients were then prompted to squeeze the investigator's hand every 30 s, until they responded to the request. At the time of response, anesthesia was reinduced and the study terminated. RESULTS: The BIS at loss of consciousness and recovery of a response was not statistically different between propofol and thiopental. No patient with a BIS less than 58 was conscious. In both groups, a BIS of less than 65 signified a less than 5% probability of return of consciousness within 50 s. CONCLUSION: The BIS can be used to predict probability of recovery of consciousness after a single injection of either thiopental or propofol.

Adult↗