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]. / Réponses cutanées sympathiques et variabilité de l'intervalle R-R: corrélations avec le stade de gravité de la polyneuropathie diabétique.

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]. / Effets de l'association propofol-sufentanil sur les potentiels évoqués somesthésiques au cours de la chirurgie du rachis.

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.

Effects of occupational lead exposure on motor and somatosensory evoked potentials.

In order to objectivate the effects of inorganic lead compounds on the nervous system, 17 men occupationally exposed have been recorded for Motor Electric Potentials (MEPs) of the abductor policis brevis muscles with transcranial, cervical root and peripheral electrical stimulations, for Somatosensory Evoked Potentials (SEPs) of median and tibial posterior nerves, and for Electromyography (EMG). Considering each subject, 16 out of the 17 lead exposed ones exhibited electrophysiological abnormalities, occurring at both peripheral and central levels for the somatosensory as well as for the motor systems. As compared to a normal control group, the lead exposed one showed decreased sensory and motor peripheral conduction velocities, increased motor central conduction time, and delayed cortical P22 SEPs component that could be interpreted as a sensory-motor cortical dysfunction. The respective contributions of MEPs and SEPs are compared to clinical, biological and EMG examinations in the evaluation of the neurotoxic effects of inorganic lead compounds.

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]. / Potentiels évoqués somesthésiques au cours des interventions orthopédiques sur le rachis de l'adulte.

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?]. / Potentiels évoqués et âge: vieillissement différential selon le sexe?

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.

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]. / Rythmes électroencéphalographiques au cours de tests psychométriques à 50 et 70 ans.

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.