Effects of propofol, propofol-nitrous oxide and midazolam on cortical somatosensory evoked potentials during sufentanil anaesthesia for major spinal surgery

Recording of cortical somatosensory evoked potentials (CSEP) enables monitoring of spinal cord function. We studied the effects of propofol, propofol-nitrous oxide or midazolam during sufentanil anaesthesia on CSEP monitoring during major spinal surgery. Thirty patients with normal preoperative CSEP were allocated randomly to one of the following anaesthesia regimens: propofol (2.5 mg kg-1 followed by 10-6 mg kg-1 h-1) with or without nitrous oxide, or midazolam (0.3 mg kg-1 followed by 0.15 mg kg-1 h-1) combined with sufentanil 0.5 microgram kg-1 h-1 in the propofol and midazolam groups, or 0.25 microgram kg-1 h-1 in the propofol-nitrous oxide group. CSEP were elicited by alternate right and left tibial posterior nerve stimulation and recorded before and after induction (15 min, 1, 2 and 3 h), and during skin closure. CSEP latencies were not significantly modified in the three groups. CSEP amplitude decreased significantly in the propofol-nitrous oxide group (from mean 2.0 (SEM 0.3) to 0.6 (0.1) microV; P < 0.05) but not in the propofol (from 1.8 (0.6) to 2.2 (0.3) microV) or midazolam (1.7 (0.5) to 1.6 (0.5) microV) groups. The time to the first postoperative voluntary motor response (recovery) delay was significantly greater in the midazolam group (115 (19) min) compared with the propofol and propofol-nitrous oxide groups (43 (8) and 41 (3) min, respectively). Consequently, the use of propofol without nitrous oxide can be recommended during spinal surgery when CSEP monitoring is required.

Comparison of the effects of ketamine-midazolam with those of fentanyl-midazolam on cortical somatosensory evoked potentials during major spine surgery

Cortical somatosensory evoked potentials (CSEP) allow monitoring of spinal cord function during surgery. Ketamine has been shown to enhance CSEP amplitude, but there is no previous study comparing its effects with those of other anaesthetic regimens. Therefore, we have compared the effects of ketamine with those of fentanyl, both combined with midazolam, on CSEP monitoring during major spine surgery. Twenty patients with normal preoperative CSEP were allocated randomly to a ketamine or fentanyl group. Anaesthesia was induced with ketamine 3 mg kg-1 or fentanyl 6 micrograms kg-1 i.v., and midazolam 0.3 mg kg-1 i.v in both groups, and maintained with continuous i.v infusion of ketamine 2 mg kg-1 h-1 or fentanyl 3 micrograms kg-1 h-1, combined in both groups with midazolam 0.15 mg kg-1 h-1 and 60% nitrous oxide in oxygen. CSEP were elicited by tibial posterior nerve stimulation and measured P1 and N1 latencies, and P1-N1 amplitude, CSEP were recorded before and after induction, at 15 min, 1 and 2 h after induction, during skin closure and after removal of nitrous oxide. Both groups were comparable in characteristics, duration of surgery, mean arterial pressure and temperature. CSEP latencies were not significantly affected in either group. CSEP amplitude decreased significantly over time in the fentanyl group (from mean 2.02 (SEM 0.41) to 0.95 (0.17) microV, P < 0.05), but not in the ketamine group (from 1.33 (0.36) to 1.05 (0.31) microV, ns). Nevertheless, we did not observe any significant differences in amplitudes or latencies between the two groups. The delay in obtaining the first voluntary postoperative motor response was significantly greater in the ketamine group (170 (54) vs 55 (17) min, P < 0.01). Both ketamine and fentanyl allowed us to obtain reliable CSEP during major spine surgery, and there were no significant difference between these two anaesthetic regimens for CSEP monitoring, but a longer delay for voluntary postoperative motor assessment was observed in the ketamine group.

[Sympathetic skin responses and variability of the R-R interval: correlation with the severity stages of diabetic polyneuropathy]

The sympathetic skin responses (SSR) and the variations of the R-R interval of the electrocardiogram (the difference between the maximum and minimum heart rates at rest, the ratio between the maximum and minimum heart rates during the Valsalva manoeuvre or Valsalva ratio, and during an active orthostatic test or orthostatic ratio) have been measured in 32 control subjects and 53 diabetic patients. These latter ones were classified according to the existence and the increasing severity of a polyneuropathy (PNP) into 4 grades (0 to III) based on Dyck's classification modified depending on the presence or the absence of cutaneous impairments in grade II. There was an important inter-individual variability for SSR as well as R-R interval results, in the control group. In the absence of PNP, the vegetative tests showed normal values. These tests were severely degraded in the diabetic patients with a PNP grade III, ov even could not be performed. The SSR amplitude was decreased in all diabetic patients. In the presence of clinical signs of dysautonomia, the SSR amplitude, the heart rate variability at rest and the orthostatic ratio were significantly different from those of the control subjects. The presence of trophic disorders appearing at PNP grade II did not significantly modify the results of the tests. Although they did not allow any differentiation of the PNP intermediary grades. SSR and R-R intervals are of interest in appreciating the infra-clinical existence and the importance of the neurovegetative disorders occurring during diabetic polyneuropathies.

[Combination of propofol-sufentanil on somatosensory evoked potentials in surgery of the spine]

OBJECTIVES

Most anaesthetics depress cortical somatosensory evoked potentials (CSEPs). However, the modification of CSEPs during total intravenous anaesthesia using propofol remaining still unknown, justified this trial.

TYPE OF STUDY

Open, prospective, clinical study.

METHODS

Nine consecutive patients requiring CSEPs monitoring for spine surgery, were studied. Anaesthesia was induced with propofol (2.5 mg.kg-1 then 10 mg.kg-1.h-1) and sufentanil (0.50 micrograms.kg-1 then 0.25 micrograms.kg-1.h-1). Maximum positive (P40) and negative (N50) waweform latencies, and the peak to peak amplitude of CSEPs (posterior tibial nerve stimulation, cortical recording), were recorded before induction, 30 min, 1 and 2 h after induction, and at the end of surgery. Data are means +/- SD.

RESULTS

Duration of anaesthesia was 260 +/- 73 min. Propofol induced significant lengthening of CSEPS (P40: from 37 +/- 10 up to 41 +/- 11 ms; N50: from 45 +/- 11 up to 51 +/- 14 ms), and a significant decrease in amplitude (from 1.9 +/- 0.9 down to 0.8 +/- 0.4 microV), but these changes were stable from 30 min after the induction to the end of spine surgery. A motor response was obtained 29 +/- 14 min after the end of anaesthetic administration.

CONCLUSIONS

Total intravenous anaesthesia with propofol and sufentanil induces a small but stable lengthening of CSEPs latency and a stable decrease of its amplitude, which enable an appropriate monitoring of CSEPs during spine surgery.

Evoked potentials in workers occupationally exposed to organic solvents

Somatosensory, Brainstem Auditory and Pattern Reversal Evoked Potentials (SEPs, BAEPs, PREPs) are recorded in workers occupationally exposed to mixtures of organic solvents, in order to specify the levels of the nervous system affected by a long term exposure to solvents, and to analyze the effects of age and gender. The most significant differences are found for SEPs; they objectivate peripheral impairments magnifying the differential effects of age observed in the control subjects, and show the higher sensitivity of women. The central impairment is pointed out by the latency delay of P22 component mainly, whose age-related increase is amplified by solvent exposure.

[Somatosensory evoked potentials during spinal orthopedic surgery in adult patients]

Somatosensory evoked potentials (SEPs) were recorded in 165 patients from 185 operations for scoliosis and major spinal distortions, lumbar or cervical stenosis, post-traumatic malunions, or tumors. They were obtained by percutaneous stimulation of right and left median and tibial posterior nerves, and recorded on the scalp as recently, motor potentials (MPs) have also been obtained, by a trans-spinous stimulation rostral to the level of intervention. The protocol consists of pre- and post-operative recordings, as well as a continuous intra-operative monitoring. Neuromonitoring is justified in operations implying neurological risks, particularly scoliosis. A durable disappearance of SEPs and MPs was always associated with post-operative neurological disorders. Transient disappearances, not associated with neurological disorders, have been observed during certain manoeuvres such as vertebral traction, osteosynthesis, placing trans-pedicular screws or hooks, leading the surgeon to modify the operation. The role of medullary ischemia on the degradation of electrophysiological signals, obvious in cardiovascular decompensations, seems predominant in the post-operative occurrence of neurological impairment. During the post-operative period, SEPs allow one to discriminate between organic disorders and subjective complaints; they help in diagnosing hematomas, and distinguish between radicular and spinal cord injuries.

Evoked potentials and cerebral blood flow in solvent induced psycho-organic syndrome

Epidemiological studies have provided evidence that neuropsychiatric symptoms are induced by long term exposure to solvents; individual diagnosis with psychometric tests, however, is not always possible (for example, when the patient has linguistic difficulties). Therefore evoked potentials and cerebral blood flow were studied in 50 patients occupationally exposed to solvents who were referred to our department and for whom a solvent induced psycho-organic syndrome was suspected. Degree of exposure was evaluated by its duration (mean 13.9, range 1 to 37 years) and its intensity (from an interview). At the group level, P22 and N35 latencies and amplitude N20-P22 of somatosensory evoked potentials were higher in cases than in controls (p < 0.05), whereas there was no difference for brainstem and visual evoked potentials, nor for hemispheric cerebral blood flow (but a higher distribution in the left occipital region was seen in patients, p < 0.05). Some parameters were linked to degree of exposure (amplitude N20-P22 of somatosensory evoked potentials, interpeak latency I-V of brainstem evoked potentials, distribution of cerebral blood flow in the internal frontal left region). At the individual level, these examinations were not of diagnostic value because sensitivity was low.

[Evoked potentials and age: different aging by sex?]

Brainstem Auditory Evoked Responses, Pattern-Shift Visual Evoked Potentials, and Short-latency Somatosensory Evoked Potentials for upper and lower limbs have been recorded in 60 male and female normal control subjects, aged 20-84 years. Age and gender effects were analyzed from the comparison of linear regressions with age and from the comparison of the mean values calculated in 3 age groups (20-40 years, 40-60 years, over 60 years). No noticeable effect of age was observed on Brainstem Auditory Evoked Responses. A gender-differential aging process is discussed for some of the short-latency Somatosensory Evoked Potentials. The constitution of reference norms which differ for male and female subjects is considered to be necessary.

Sensory and cognitive event related potentials in workers chronically exposed to solvents

To obtain objective measures of possible impairment due to organic solvents, auditory, visual and somatosensory evoked potentials and cognitive event related potentials were recorded in a group of 13 workers occupationally exposed to a mixture of various solvents. The patients were compared to healthy subjects and to chronic alcoholics seen during post-alcohol withdrawal. Auditory and visual evoked potentials were almost normal but somatosensory evoked potentials showed a slight decrease of peripheral conduction velocities and an increase of central conduction times more marked in the solvent exposed workers who were also alcoholics. The late "cognitive" components reflecting attention processes (N2 and P3) were normal. Solvent-exposed workers and alcoholics were both characterized by some difficulty in modulating their attentional resources according to task demands, as reflected by a tendency to responses (N1, N2 and P3) of similar amplitudes whether the stimulus was or was not the target. These findings support the presence, in solvent exposed workers, of minor dysfunction of the nervous system at both peripheral and cortical levels potentiated by alcohol as well as of mild cognitive impairments concerning attention processes.

Heart rate and blood pressure reactivity during active coping with a mental task in healthy 18- to 73-year-old subjects

Alterations with aging in the responses of heart rate (HR) and blood pressure (BP) reactivity were investigated during mild mental stress induced by undergoing a psychometric test, in 52 women and men aged 18-73 years, with no history of cardiovascular, renal or neurological deficits. HR and BP responses were measured before, during and after the test. Resting HR and diastolic BP (DBP) were not age-related while resting systolic BP (SBP) was. HR and SBP were increased during test performance. HR reactivity, measured during task execution as well as during recovery, was significantly decreased in older subjects. DBP recovery variation was lowered with age. These results indicate that age is an important determinant of the magnitude of cardiovascular adjustment during minor mental stress in women and men.

Effects of lead and mercury intoxications on evoked potentials

Pattern reversal, brain stem auditory and somatosensory evoked potentials (PREPs, BAEPs, SEPs) have been recorded on 13 patients occupationally exposed to inorganic lead compounds, in 9 patients occupationally or accidentally exposed to inorganic mercury compounds and in 26 chronic alcoholics. The results were compared to those of a normal control group. Peripheral conduction velocities were decreased in lead exposed workers and in alcoholics, but not modified in the mercury exposed patients. In the three exposed groups, an amplitude increase (PREPs and upper limb SEP cortical components), more important in the mercury group and an increase of central conduction time in case of lower limb stimulation, could be interpreted as early signs of nervous cortical impairment.

Data entry on a computer terminal: repetitive work strains on the oculomotor and central nervous systems

Continuous telemetric recordings including E.K.G., E.O.G., and E.E.G. were carried out on two subjects during 4 working days: 1 day of "reference work" or classical clerical activities, 3 days of "data entry work". Although the time allowed for the task was not limited, the performance assessed from oculomotor patterns remained stable throughout the day, from one day to the next and from one subject to another. This stability was reflected on the stereotyped E.E.G. patterns recorded during the work period, the differences occurring between reading and typing were more acute in the left cortical hemisphere than in the right. As a result of these stable patterns, the ultradian oscillations of the behavioural and physiological parameters were less during data entry than during work reference. The only possible time adjustments were the interruptions or breaks between two document pages and their variations could be considered as indicators of work load.

Effects of time and tasks upon auditory and somatosensory evoked potentials in man

Auditory evoked potentials (AEPs) recorded from the vertex and somatosensory evoked potentials (SEPs) recorded from the somatosensory and motor areas and vertex were examined during visual and auditory discrimination tasks, with and without motor responses, and during motor tasks alone in normal human subjects. These procedures allowed the separation of sensory discrimination from motor activity effects on the evoked potentials. It was observed that EPs were modified systematically by task and by temporal variables, even though vigilance, as evaluated through EEG recording and performance level, was stable throughout the experimental recording session. 1. AEPs were minimally influenced by time, but very sensitive to task. Inversely, the SEP amplitude decreased considerably with time and less with task. There was evidence of time/task interaction. 2. The magnitude of SEP attenuation in time was reduced by intervening rest periods. 3. The sensory modality in which the discrimination task was performed did not influence the effect on EPs. A discrimination task involving a motor response reduced EPs more than a pure discrimination or a pure motor task. The task effect seems to involve a general, mechanism (load imposed upon the subject) not dependent on the particular sensory channel used to deliver task-relevant information.

Heart rate, urinary catecholamines and anxiety responses during mental stress in men in their fifties and seventies

Alterations with ageing in the responses of heart rate (HR), urinary excretion of free epinephrine (E) and norepinephrine (NE) and anxiety were investigated during mild mental stress. Forty-eight normal male volunteers were studied: in control conditions; when subjected to psychometric tests; and during recovery. Men in their seventies had lower baseline levels of HR, E and NE than men in their fifties. Several anxiety indices were positively correlated with E. HR and NE were positively correlated. During stress, mean HR and E levels increased in the two age groups by the same percentages. Mean HR and E levels returned to pre-stress values more slowly in the older age group.

Heart rate reactivity during minor mental stress in men in their 50s and 70s

Modifications with aging in heart rate reactivity was investigated during minor mental stress. 27 normal male volunteers, aged 51-55 years (n = 10) and 71-74 years (n = 17), were studied in control conditions and while passing a series of 5 psychometric test measuring memory or intellectual speed. Men in their 70s had both lower heart rate baseline levels and lower reactivity during cognitive tasks.

[Electroencephalographic rhythms during psychometric tests at 50 and 70 years of age]

The experiments were conducted to investigate changes occurring between maturity and old age in variations of the EEG when performing a series of mental tasks. Forty three normal male volunteers, divided in two age groups separated by 2 decades (52.9 +/- 0.2 yr, N = 22; 72.2 +/- 0.2 yr, N = 21), were continuously recorded by telemetry in 3 conditions: control, tests, questionnaires. Beta, alpha and theta rhythms and the number of slow waves were measured after visual EEG interpretation. The study showed that: (1) theta rhythms and slow waves were in higher proportions in men in their 70s; (2) variations induced by the various mental tasks were very similar at ages 50 and 70; (3) the two groups differed mostly in theta rhythm responses during tests with a coding task; (4) test performances and EEG indices were correlated only in the older group for theta rhythms.

Variations in diurnal and nocturnal waking state in air traffic controllers

Physiological variables of 22 air traffic controllers (ATCs), mean age 32, were continuously telemetrically recorded from 08:00 to 17:30 and on the following day from 19:00 to either 00:00 or 0.3:00. EEG (alpha and theta indices, slow delta waves), EOG (palpebral blinks), EMG (from the neck muscles) and EKG (HR) were recorded. Comparison between day and night shows an increase at night of HR and slow waves, particularly after midnight. These results were compared with similar ones obtained from two other populations of the same age having very different professional activities (university personnel and factory workers). The EEG indices and HR are higher in ATCs. The work load imposed by the need in air traffic control to maintain a high level of vigilance, especially difficult after midnight, is in great part responsible for the high values of physiological parameters observed in this study.

Relationship between heart rate and sinus arrhythmia in air traffic controllers at work

Sinus arrhythmia and mean heart rate were calculated from continuous electrocardiogram recordings of ten air traffic controllers. The telemetric recordings were carried out during 1 day of work and the following day's night shift. The individual variations of sinus arrhythmia were very large. The different situations (rest, relaxed work, intense work, eating, movements within the control room) had no specific effect on sinus arrhythmia. For each subject and for each group it was the value of the mean heart rate and its temporal variations that had the greatest influence on variations of sinus arrhythmia.

[Health effects of night work]

Schedules of working times are related to various individual problems including the family, the quality of home and health problems. Only epidemiological studies can reveal the complexity of problems related to shift work. Night shifts ae increasing constantly and must be considered as a physiological, medical and social load of the worker.

[Synchronization of various physiological parameters during the waking state in man (author's transl)]

Various physiological parameters (EEG, EKG, EOG, EMG), and behavioural activities were measured during 8 working hours in 40 subjects divided into 4 groups according to their age and occupation (35 and 50 years, specially skilled workmen and university workers). Several moments of synchronization between the different parameters were defined; they were characterized by reduction or suppression of the theta index, an increase in the alpha index, an increase in number of blinkings, a drop in muscle tone, and variations in heart rate, accompanied by modifications in work activity. The variation observed during these synchronized moments is an overall change in all the parameters and is not systematically related to just one of them. The synchronized moments last for about 8 minutes and are more frequent and better individualized in university personnel than in workmen. The average interval between them is 93 minutes with large intra and inter-variability between individuals. They are longer in 50-year-old subjects whatever the type of activity. The authors compare these moments of synchronization with ultradian rhythms described by other authors.

Effect of ageing and occupational activity on active wakefulness

44 people were recorded by a telemetric system during 8 h of daily occupational activity. 24 were factory personnel (12: mean age 37 years, and 12: mean age 53 years) and 20 were univeristy researchers (10: mean age 39 years, and 10: mean age 53 years). Recordings were made concerning EEG, EOG, EMG, and EKG. At 35 years no differences were observed. At 50 years the organization of wakefulness was different for the two occupational activity groups. Although stable for the moment seemed to play a prominent role in the modulation of wakefulness.

[Posterior theta rhythms during waking state activity in man (author's transl)]

Telemetric recordings were made of 44 subjects divided into 4 groups according to age and occupation (35 and 50 years--skilled workers and university personel), during a period of 8 hours working activity. Short sequences of posterior theta rhythms were observed in all cases. They appear mainly during continuous work activity and diminish or disappear when work ceases. They are more frequent in the 50-year-old subjects than in those aged 35 years. They are neither pathological nor related to immaturity or emotion, and their etiology is related to visual perception and attention.

Spontaneous variations in level of arousal among aged individuals. Correlations with functional abilities and mental performances

The aim of this study was to assess whether spontaneous interindividual variations in arousal level appreciated by telemetric recordings of physiological variables were related to mental performance and functional ability in institutionalized aged subjects. The sample studied was made up of 18 subjects (16 women and 2 men) aged 82-97, living in an old age home in Paris. Telemetric recordings of EEG, EKG, EMG and EOG were obtained over 8-hour periods, during the subjects' normal daily activity schedule. The Stockton Geriatric Rating Scale (SGRS), Benton's Visual Retention Test (VRT) and the Trail Making Test (TMT) were independently used to assess behaviour and mental performance of these aged persons. All correlations between telemetric data and psychological evaluations (the psychometric tests as well as the rating scale) were highly significant, even once the influence of the cultural level was controlled.

[Determination of the degree of mental alertness in the enderly (author's transl)]

Telemetric polygraph recordings lasting from 10-18 hours were performed in 22 elderly and institutionalised patients whose ages ranged from 82 to 97 years in an attempt to determine whether they were able to maintain alertness throughout the course of the day. By combining the standard E.E.G. data with that from the telemetric recording it was possible to subdivide the patients into 4 groups: 1 Normal E.E.G. Stable state of awareness varying only between active waking and relaxed waking, apart from a clearly demarcated siesta period (8 subjects). 2 Normal E.E.G. State of awareness moderately stable but containing as well as one or two clearly defined, siestas some somnolent episodes (6 subjects). 3 Numerous fluctuations of alertness with several levels of drowsiness corresponding either to the classical stages of sleep or to undifferentiated stages (5 subjects, 4 with normal E.E.G.). 4 Abnormal E.E.G. and only two levels of alertness which were difficult to correlate with the behavioural state. All 4 subjects in this group had severe organic impairment. There was a good correlation between the data obtained from the standard E.E.G. and that from the telemetric recording. Patients having a normal E.E.G. maintained their alertness well, and those with the highest proportion of fast activity best of all. The possible limits of variation become very narrow in severe organic impairment.

Effect of voluntary self-paced movements upon auditory and somatosensory evoked potentials in man

The effect of voluntary self-paced movements upon auditory (AEPs) and somatosensory (SEPs) evoked potentials has been investigated according to the temporal relationship between movement and delivery of test stimuli. EPs were recorded in 7 subjects and averaged in 10 successive epochs extending from 880 msec before to 2500 msec after movement. AEPs were attenuated in all epochs. The decrease was greatest in the 220 msec epoch just following movement and involved components N85 and P170. SEPs were attenuated similarly to AEPs when movements were performed by the hand contralateral to somatosensory stimulation. Of the 5 SEP components, only P40 failed to reflect the attenuation, while P95 showed the greatest amplitude decrease. When stimulation was ipsilateral, SEP amplitude was attenuated only when close to the movement. N65 and P95 decreased while N130 increased. In all subjects the results were consistent for treatments of AEP and SEP (with contralateral movements), whereas large inter-individual differences were observed for the SEP with ipsilateral movements.

[Electroencephalographic problems in a department of infant resuscitation]

The authors analyse the technical problems encountered in using E.E.G. in children's reanimation. They show some examples which illustrate the importance of E.E.G. in diagnosis and therapy of such cases. Emphasis is laid upon the need for close collaboration between the EEGers and the reanimation staff.