Recovery of memory after general anaesthesia: clinical findings and somatosensory evoked responses

BACKGROUND

Mid-latency somatosensory evoked responses are used to monitor the integrity of the sensory pathways intra-operatively. They can quantify the effects of anaesthetics on the central nervous system. Mid-latency auditory evoked responses have been related to cognition during anaesthesia, but there are no detailed studies using median nerve somatosensory evoked responses (MnSSER).

METHODS

We studied 49 patients during recovery from general anaesthesia (isoflurane/nitrous oxide or propofol) to assess implicit and explicit memory function in relation to mid-latency MnSSER. The MnSSER recordings were made before anaesthesia, during steady-state anaesthesia, and at the end of the recovery period. The patients were interviewed 24 h later about their memory for the immediate wake up phase. Statistical analysis was by multivariate analysis of variance.

RESULTS

Out of 49 patients, 23 recalled the recovery period, 11 had implicit memory for an object shown to them during the recovery period, and 15 did not have any memory for the recovery period. At RECOVERY the patients with recall had significantly shorter MnSSER latencies N45 and P50 and inter-wave conduction times LatN35-LatP45 than patients without memory (P<0.05).

CONCLUSIONS

We conclude that MnSSER components warrant further investigation for studying the effects of anaesthetic drugs on cognitive function.

Skin sympathetic neuroeffector response is attenuated dose-dependently by systemic prostaglandin E1 injection in humans

To clarify the effects of prostaglandin E1 (PGE1) on the vasoconstrictive responses, we compared the correlation between the amplitude of integrated skin sympathetic nerve activity (SSNA) and per cent reduction in skin blood flow (SBF) before and after the infusion of lipo PGE1 and placebo (bolus one-shot infusion, single blind study), and constant rate infusion of PGE1 (10 and 50 ng kg(-1) min(-1) by infusion pump, dose-dependency study) in ten healthy men. SSNA was recorded microneurographically from the median nerve simultaneously with SBF by laser Doppler flowmetry at the index fingertip. The measurement was conducted 30 min after injection of lipo PGE1 or placebo, and during the drip infusion of 10 and 50 ng kg(-1) min(-1) of PGE1 with maneuvers to enhance SSNA. The resting and activated skin blood flow were not significantly different between 10 ng lipo PGE1 and placebo administration, and between baseline and 10, 50 ng kg(-1) min(-1) of PGE1 injection. The vascular response, defined as the slope of regression line between logarithm of amplitude of integrated SSNA bursts and the reduction in SBF, was significantly suppressed by injection of lipo PGE1 as compared with that by placebo. It was also decreased dose-dependently by the constant rate infusion of PGE1 (10 and 50 ng kg(-1) min(-1)). We concluded that the intravenous injection of PGE1 attenuates vasoconstrictive responses to SSNA, and analysis of the relations between SSNA and vasoconstrictive response, i.e. the neuroeffector response, is suggested to be an important tool to assess the drug effect.

Median nerve evoked responses and explicit memory during recovery from isoflurane/nitrous oxide anesthesia

PURPOSE

To evaluate median nerve somatosensory evoked responses during recovery from anesthesia in relation to clinical findings.

METHODS

Twenty-two gynecologic patients received isoflurane in nitrous oxide for anesthesia. Midlatency somatosensory evoked responses (N20, P25, N35, P45, N50) were recorded the day before surgery (AWAKE), during steady state anesthesia (STABLE), and every five minutes after discontinuation of anesthesia until the patients were able to name a shown object correctly (RECOVERY). Next day the patients were questioned with a structured interview about their explicit memory of the immediate recovery period and classified into groups: No-MEM (no memory) and MEM (memory). Multivariate analysis of variance compared electrophysiological parameters at the different time points and between the two memory groups.

RESULTS

During STABLE isoflurane/N2O anesthesia, all cortical amplitudes were reduced (P< or =0.003) and all latencies were prolonged compared with AWAKE (P<0.001). At RECOVERY the latencies N35, P45, N50 remained prolonged (P< or =0.001), while the amplitudes N20P25 and P45N50 were reduced in comparison to AWAKE (P< or =0.02). The latencies P45 (48+/-8 vs. 61+/-9 msec) and N50 (67+/-12 vs. 81+/-10 msec) were shorter in the patients of the group MEM (P< or =0.03) at RECOVERY.

CONCLUSION

The reversibility of anesthetic induced changes in amplitudes and latencies of median nerve somatosensory evoked responses reflected clinical awakening during emergence from isoflurane/nitrous oxide anesthesia. In the patients who had recall for the immediate recovery period, the reversibility of anesthetic induced changes of components P45 and N50 was faster than in patients without recall.

Midlatency median nerve evoked responses during recovery from propofol/sufentanil total intravenous anaesthesia

BACKGROUND

Median nerve somatosensory evoked responses (MnSSER) are frequently used to monitor the integrity of the somatosensory pathway during surgery. We investigated MnSSER components during the wakeup phase from anaesthesia with propofol/sufentanil, because detailed information is lacking about the reversibility of anaesthetic induced changes of MnSSER. The aim of the study was to document precisely the MnSSER waves in relation to the clinical awakening. The hypothesis was that anaesthetic induced MnSSER changes are reversed when the patient becomes responsive after anaesthesia.

METHODS

In 20 gynaecological patients anaesthesia was maintained with propofol 8 mg kg(-1) h(-1) supplemented by bolus injections of sufentanil. MnSSER were recorded at C4' (N20, P25, N35, P45, N50) following electrical median nerve stimulation on the day before surgery, after the end of surgery during anaesthesia and every 5 min during recovery, till the patients were responsive again and able to identify a shown object.

RESULTS

While the primary cortical MnSSER complex N20P25 regained baseline values, the cortical latencies > or =35 ms remained prolonged (P<0.001) and the amplitudes P45N50 were suppressed (P< or =0.013), when the patients were responsive after 26+/-7 min following anaesthesia. However, the amplitudes P25N35 exceeded their corresponding baseline value (P<0.01)

CONCLUSION

Persistent changes of MnSSER waves > or =35 ms reflect impaired signal processing along the somatosensory pathway following propofol/sufentanil anaesthesia when the patients are responsive again. Further studies combining MnSSER recording with distinct neuro-psychological tests are needed to define the clinical relevance of these findings.

[Occupational N-hexane neuropathy: clinical and neurophysiological investigation]

A group of 37 patients (26 men and 11 women), aged 18-49 (mean: 29.7) with subacute toxic polyneuropathy was investigated clinically and electrophysiologically. In all cases the disease was induced by occupational exposure to n-hexane in a small enterprise of purse makers. Toxicological investigations revealed a highly increased concentration of n-hexane in glue used in the manufacture process. The clinical course, including delayed worsening of symptoms after cessation of exposure, was typical when compared with previously reported cases of n-hexan-induced neuropathy after glue sniffing and industrial exposure. Electroneurographic (ENeG) studies showed a predominately decreased motor nerve conduction velocity (MNCV) with focal conduction block followed by dramatically diminished CMAPs. Recovery of EneG abnormalities paralled the clinical improvement.

Effects of chronic lithium treatment on the peripheral nervous system

BACKGROUND

Although lithium carbonate is widely used in the treatment of mood disorders, symptoms suggesting toxic effects on the peripheral nervous system may emerge even in subjects whose serum lithium levels remain within the recommended therapeutic range.

METHOD

Electroneuronographic (ENG) parameters (motor nerve conduction velocity of peroneal and median nerves, sensory nerve conduction velocity of sural and median nerves, amplitude of motor potential of peroneal and median nerves, and amplitude of sensory action potential of the median nerve at the wrist and the sural nerve) were investigated in 2 groups (N = 34) of patients suffering from bipolar affective disorder (DSM-III-R, DSM-IV) undergoing maintenance treatment with lithium carbonate for at least 1 year (mean = 2.06 years) in monotherapy. For 12 patients, ENG results were compared with pretreatment values, whereas in the other 22 cases, only data relevant to posttreatment were available. Fifty-four healthy subjects and 20 patients with recurrent major affective disorder (unipolar and bipolar) never treated with lithium made up the comparison groups.

RESULTS

Compared with the 2 comparison groups, patients on chronic lithium treatment showed significant reduction of motor nerve conduction velocity of peroneal and median nerves, sensory nerve conduction velocity of sural and median nerves, amplitude of motor potential of peroneal and median nerves, and amplitude of sensory action potential of the median nerve at the wrist and the sural nerve. The comparison with the assessment made prior to lithium treatment also showed significant changes; after a period of treatment with lithium varying from 2 to 8 years (mean = 5.2 years), significant reductions were found on motor and sensory nerve conduction velocity and on amplitude motor potentials and sensory action potentials.

CONCLUSION

Chronic maintenance treatment with lithium affects the peripheral nerves, even if the impairment rarely is such as to warrant discontinuation of treatment. Monitoring of ENG results could be useful for the early detection of neurotoxicity of lithium.

Acute mercury vapour poisoning in a shipyard worker--a case report

Acute mercury vapour poisoning is a serious, potentially fatal but fortunately rarely encountered problem. It is most commonly due to industrial accidents. The vapour is a direct respiratory tract irritant as well as a cell poison, exerting its greatest effects in the lungs, nervous system, kidneys and liver. We present a case of mercury vapour poisoning in a shipyard workers presenting as an acute chemical pneumonitis, which resolved with aggressive supportive therapy. Further investigations later revealed transient mild neuropsychiatric symptoms, and residual peripheral neuropathy. No chelation therapy was instituted. The detailed investigative work that led to the discovery of the source of mercury is also presented. This case alerts us to the potential hazard to shipyard workers who may work in ships previously carrying oil contaminated with mercury. There have been no previous reports of mercury poisoning in shipyard workers. A high index of suspicion leading to early diagnosis and institution of appropriate supportive measures in suspected cases can be life-saving.

[1% mepivacaine and axillary block: duration of the sensory and motor blockade]

OBJECTIVES

To assess the duration of both sensory and motor blockade of brachial plexus with 40 mL 1% mepivacaine after axillary or midhumeral approach.

STUDY DESIGN

Prospective, open, non-comparative, multicentric study.

PATIENTS

One hundred and eighty patients, ASA physical class 1 and 2, scheduled for hand or forearm surgery under brachial plexus block were included.

METHODS

A midhumeral or axillary brachial plexus block using a nerve stimulator was performed with 40 mL of 1% mepivacaine. Sensory blockade was tested for each cutaneous area (median, radial, ulnar, musculocutaneous and medial cutaneous nerve of the forearm) using pin-prick. Motor blockade was assessed by grip strength of the hand. Incidence and duration of analgesia, anaesthesia and motor blockade were assessed. The incidence of tourniquet pain and the time when pain occurred were determined.

RESULTS

According to the nerve area tested, analgesia and anaesthesia were obtained in 98% and 85% of cases respectively; duration of anaesthesia was between 150 +/- 40 to 167 +/- 49 minutes and duration of analgesia was from 184 +/- 50 to 205 +/- 51 minutes. Duration of paralysis was 144 +/- 40 minutes and duration of paresis was 190 +/- 51 minutes. Pain occurred in three out of 138 patients at tourniquet inflation and in six patients after completion of surgery.

CONCLUSIONS

Mid humeral or axillary block with 40 mL of 1% mepivacaine is highly successful and provides efficient surgical anaesthesia for various surgical procedures of intermediary duration.

Infraclavicular brachial plexus block effects on respiratory function and extent of the block

BACKGROUND AND OBJECTIVES

Axillary block is devoid of severe respiratory complications. However, incomplete anesthesia of the upper limb is the main disadvantage of the technique. Theoretically, the more proximal infraclavicular approach would produce a more extensive block without the risk of pneumothorax. However, neither its effects on respiratory function nor a detailed characterization of the extent of neural block has been assessed. The goal of this study was to evaluate the possible changes in respiratory function and also the extent of the block after infraclavicular block.

METHODS

We performed an infraclavicular block with a mixture of 40 mL 1.5% plain mepivacaine and 4 mL 8.4% sodium bicarbonate in 20 patients. Forced expiratory volumes were measured before and 15 minutes after the injection of local anesthetic, and sensory and motor block were evaluated at 10 and 20 minutes.

RESULTS

We did not find significant differences from baseline in the forced expiratory volumes in any of the patients. Axillary and musculocutaneous nerve distributions had the lowest rate of sensory block at 20 minutes.

CONCLUSIONS

Infraclavicular block does not produce a reduction in respiratory function.

Modulation of somatosensory evoked potentials under various concentrations of desflurane with and without nitrous oxide

Continuous measurement of somatosensory evoked potentials (SEP) by means of characteristic changes in the signal pattern makes it possible to identify cerebral or spinal cord ischemia during critical phases of the operative procedure. A correct interpretation of the measurements is only possible, however, if the influence of drugs acting on the central nervous system is known. The authors were able to show that inhaled anesthetics have an impact on latencies and response amplitudes. This study examined the influence of various concentrations of desflurane on the conduction of SEP of the Median nerve. In addition, the authors determined how the supplementation of nitrous oxide (N2O) influences the stimulus response of the medianus nerve's SEP. Desflurane has been shown to produce dose-dependent increases in SEP latency (data in part for latency N2O: 0.5 minimum alveolar concentration [MAC] = 20.8 +/- 0.9; 1.5 MAC = 22.2 +/- 1.5; 1.5 MAC/N2O= 23.8 +/- 1.5) and decreases in amplitude, whereas cervically recorded subcortical SEP components are minimally influenced by desflurane. When nitrous oxide is added, there were marked reductions in amplitude (p<0.01) of the cortical stimulus response (1.5 MAC = 2.4 +/- 0.9; 1.5 MAC/N2O = 1.1 +/- 1). It can therefore be recommended that supplementation with N2O should be avoided in the presence of low initial amplitudes. Based on the study's results, the use of desflurane (up to 1.0 MAC) seems to be compatible with intraoperative monitoring of median somatosensory evoked potentials.

[Concentration-dependent changes in the latency and amplitude of somatosensory-evoked potentials by desflurane, isoflurane and sevoflurane]

PURPOSE

Comparison of the influence of desflurane, isoflurane, and sevoflurane on the parameters of cortical somatosensory evoked potentials (SEP).

METHODS

A total of 41 patients were randomly allocated to either the isoflurane, desflurane or sevoflurane group. Following induction with propofol and intubation, concentration of the volatile anaesthetic was kept constant at 1.3, 1.0, and 0.7 MAC for 15 minutes each in randomised sequences. No opioids or N2O were used. Cortical somatosensory evoked potentials were recorded following median nerve stimulation at the wrist with 1.5 times motor threshold current. SEP were evaluated for latencies of peak N20 and P25 as well as peak-to-peak amplitude N20P25. Measurements at the end of the 15 minute equilibration intervals were compared by analysis of variance for repeated measurements. Latencies and the logarithm of the amplitudes were assumed to be normally distributed.

RESULTS

SEP could be recorded in all patients and at all concentrations. Latency of cortical SEP increased with anaesthetic concentration in a linear manner. No differences in latency increase were found between the three anaesthetics (ANOVA). In contrast, the decrease in amplitude with increasing anaesthetic concentration was non-linear. It was large from control to 0.7 MAC, but small in the range between 0.7 and 1.3 MAC. Amplitude reduction was larger with isoflurane than with sevoflurane or desflurane.

CONCLUSION

1) Sevoflurane and desflurane are better suited for anaesthetic management during intraoperative electrophysiological monitoring than isoflurane, because SEP amplitudes are better preserved. 2) SEP amplitude is less altered by changing anaesthetic concentrations in the concentration range from 0.7 to 1.3 MAC than SEP latency.

The use of a selective axillary nerve block for outpatient hand surgery

Although no guidelines concerning discharge criteria after axillary plexus block are available, many institutions consider recovery of motor function as a critical factor. With the midhumeral approach, the four main nerves of the upper extremity can be blocked separately using a peripheral nerve stimulator. The aim of this double-blind study was to block the radial (R) and musculocutaneous (MC) nerves with lidocaine, and the median (M) and ulnar (U) nerves with bupivacaine to recover motor function of the elbow and wrist more rapidly while maintaining long-lasting postoperative analgesia at the operative site. Patients undergoing surgery for Dupuytren's contracture were randomized into two groups in a double-blind fashion: in the control group (n = 17), each of the four nerves was infiltrated with 10 mL of a mixture of 2% lidocaine and 0.5% bupivacaine, whereas in the selective group (n = 17), the R and MC nerves were blocked with 10 mL of 2% lidocaine each and the M and U nerves were blocked with 10 mL of 0.5% bupivacaine each. Recovery of motor block was significantly faster in the selective group (231 +/- 91 vs 466 +/- 154 min). However, time to first sensation of pain was not different between groups (707 +/- 274 vs 706 +/- 291 min). In conclusion, this new approach at the midhumeral level enables the anesthesiologist to selectively administer local anesthetics on different nerves.

IMPLICATIONS

In outpatients undergoing surgery for Dupuytren's contracture, a midhumeral block was used with the musculocutaneous and radial nerves blocked by lidocaine and the median and ulnar nerves blocked with bupivacaine. Recovery of motor function and time to discharge were shorter compared with patients who received the mixture on all four nerves.

Quinidine sulfate therapy for the slow-channel congenital myasthenic syndrome

The slow-channel congenital myasthenic syndrome (SCCMS) is caused by gain of function mutations in subunits of the end-plate acetylcholine receptor (AChR). The mutations prolong the opening episodes of the AChR channel, leading to a depolarization block and an end-plate myopathy. Because levels of quinidine sulfate attainable in clinical practice shorten the opening episodes of genetically engineered mutant SCCMS receptors in vitro, we tested the notion that the drug can be of benefit in SCCMS. We treated 6 SCCMS patients with quinidine sulfate in an open-label trial, using objective clinical measures of muscle strength and repetitive stimulation studies as end points. One patient became allergic to quinidine after 7 days. The remaining patients tolerated the drug well and after 30 days of continuous therapy showed statistically significant improvement in muscle strength and in decrement of the compound muscle action potential elicited by rapid rates of stimulation.

Reversal of reflex-induced myocardial ischemia by median nerve stimulation: a feline model of electroacupuncture

BACKGROUND

Acupuncture is reported to reduce myocardial ischemia, arrhythmias, and hypertension. To investigate the physiological mechanisms underlying these observations, a model of reflex-induced, reversible myocardial ischemia was developed to test the effects of median nerve stimulation as a surrogate for electroacupuncture.

METHODS AND RESULTS

Chloralose-anesthetized cats were instrumented to measure arterial blood pressure, left ventricular pressure, left ventricular dP/dt, heart rate, left anterior descending (LAD) coronary blood velocity, and regional wall motion. The LAD artery either was partially occluded or a small diagonal branch was ligated. Subsequently, transient reflex activation of the cardiovascular system was evoked by application of bradykinin (typically 1 microg/mL) to the gallbladder, which significantly increased myocardial oxygen demand (double product), left ventricular dP/dt, and coronary blood velocity and caused ischemia-induced regional dysfunction, evidenced by significant (P<.05) reduction in normalized wall thickening (10.7+/-4.2% versus -23.6+/-2.9%; control versus ischemia; n=7). However, when median nerves were stimulated with low frequency (5 Hz) to mimic electroacupuncture, bradykinin-induced change in normalized wall thickening was significantly improved (-23.6+/-2.9% versus 9.8+/-4.9%; ischemia versus median nerve stimulation, P<.05) and remained augmented > or = 1 hour. Results were similar in partial and complete occlusion groups. Significant improvement in wall thickening was associated with unchanged increment of coronary blood velocity and significantly diminished increments of double product and diastolic blood pressure.

CONCLUSIONS

These results suggest that stimulation of the median nerve to mimic electroacupuncture diminishes regional myocardial ischemia triggered by a sympathetically mediated increase in cardiac oxygen demand. The mechanism of this effect is related to reduction in cardiac oxygen demand, secondary to a diminished pressor response. These data provide the first documentation of the physiological mechanisms underlying the possible beneficial effect of electroacupuncture in the context of restricted coronary blood flow and augmented myocardial oxygen demand.

Change in lateralization of the P22/N30 cortical component of median nerve somatosensory evoked potentials in patients with cervical dystonia after successful treatment with botulinum toxin A

The precentral P22/N30 cortical component of the median nerve somatosensory evoked potentials (SEPs) was recorded in 16 patients (11 women and five men) suffering from cervical dystonia before and after botulinum toxin therapy. Cervical dystonia was diagnosed as idiopathic in all patients: 13 patients suffered from right-sided torticollis, and three suffered from left-sided torticollis. The amplitude of the P22/N30 component and the side-to-side ratio of amplitude values were measured. Normal values were obtained by acquiring measurements in two groups of healthy volunteers (n1 = 20 and n2 = 20). The recordings in the first control group were done with the patient's head in a normal position, whereas, in the second control group, the patient kept the head intentionally rotated 60 degrees to the right. Patients were treated with local injections of botulinum toxin A (BTX-A). The mean duration of treatment was 8.3 months, and the mean total amount of BTX injected was 295 U. The P22/N30 precentral component was repeatedly recorded in patients after head posture had been corrected to the normal plane by BTX-A treatment. The recordings showed that the amplitude of the P22/N30 precentral component recorded contralaterally to the direction of head deviation was significantly higher in patients before treatment than after treatment. Contralateral pretreatment amplitudes were also significantly higher (p < 0.01 and p < 0.05, respectively) than amplitudes in both groups of healthy volunteers. The mean side-to-side ratio of precentral P22/N30 component amplitudes was significantly higher in patients before treatment compared with after treatment and also compared with both control groups. These changes in dystonic patients probably reflect the direction of head rotation, the muscle pattern of torticollis, and the change in force of dystonic contraction after the treatment. The changes presumably could be the result of higher excitability of the precentral cortex contralateral to head rotation in patients with cervical dystonia and its change after successful BTX-A treatment.

Nerve lesions after therapy for childhood acute lymphoblastic leukemia

BACKGROUND

The objective of the current study was to use somatosensory evoked potentials (SEP) to detect signs of nerve lesions in the peripheral nerve and in the central nervous system (CNS) after 3 years of treatment for childhood acute lymphoblastic leukemia (ALL).

METHODS

The somatosensory potentials evoked by stimulation of the median nerve and posterior tibial nerve were recorded in 31 children with ALL after 3 years of therapy. All patients were examined clinically. The 14 standard risk patients had been treated with chemotherapy according to the Nordic regimen, and the 17 intermediate risk or high risk patients had been treated with chemotherapy and cranial irradiation according to the ALL BFM-83 protocol.

RESULTS

A decrease in amplitudes was observed at the brachial plexus and spinal cord (C7) in the median SEP, and at the knee, spinal cord (Th12), and cortex in the tibial SEP, indicating axonal injury within the entire CNS in the patients with ALL compared with healthy age-, gender-, and height-matched controls. Prolongation of the SEP latencies was found within the spinal cord, indicating demyelination. These SEP changes had persisted for 2 years since the last injection/infusion of vincristine or methotrexate, which are the principal neurotoxic drugs used in chemotherapy for ALL. Clinical signs of nerve injury such as depressed deep tendon reflexes and gross or fine motor difficulties were found in approximately 33% of the patients and dysdiadochokinesia in 50%.

CONCLUSIONS

Treatment of ALL in children principally with vincristine and methotrexate causes long-standing axonal injury throughout the nervous system and demyelination within the spinal cord. These changes are associated with clinical neurologic findings.

[The effect of cigarettes on somatosensory potentials]

INTRODUCTION AND OBJECTIVE

The physiological and pathological effects of cigarettes on the nervous system have been widely studied, but none of the investigations carried out has enabled us to determine the degree to which nicotine may affect the central pathways of somatosensorial evoked potentials in humans.

MATERIAL AND METHODS

Following parameters established internationally for investigation of the effects of nicotine on the nervous system, we find that the N18 wave obtained by stimulation of the median nerve before smoking completely disappears after smoking for 3 minutes and reappears 10 minutes after smoking has stopped.

CONCLUSIONS

Therefore, we conclude that the action of nicotine on these evoked potentials is mainly subcortical, and for this reason it is essential to investigate the toxicological history before carrying out any clinical or neurophysiological study, since this might affect the results obtained.

Median nerve somatosensory evoked potentials during isoflurane anaesthesia

PURPOSE

The effect of isoflurane on the subcortical P14 component of the median nerve somatosensory evoked potential (SEP) is poorly known. We studied whether the P14 wave from the upper brainstem, recorded with a nasopharyngeal electrode, was attenuated at the isoflurane-induced EEG burst-suppression level. We also compared the effect of isoflurane on the P14, cervical N13 and cortical N20, N35 and N6, components.

METHODS

Seventeen elective patients were anaesthetized with isoflurane. Somatosensory evoked potentials were recorded prior to anaesthesia, at 0.5 MAC and 1 MAC end-tidal isoflurane as well as at the level when EEG was in burst-suppression (mean 1.9 vol% end-tidal isoflurane).

RESULTS

Isoflurane had varying effects on the subcortical components of median SEP. The amplitude of nasopharyngeal P14 was stable, but the mean latency increased from 14.4 +/- 1.2 msec at 0.5 MAC to 15.2 +/- 1.1 msec at burst-suppression level (P < 0.05). In contrast, the N13 neck response amplitude was attenuated from 3.3 +/- 0.6 microV to 2.6 +/- 0.5 microV (P < 0.005) without latency changes. The latency of the cortical N20 wave was increased from 19.7 +/- 1.1 msec at awake to 24.4 +/- 1.6 msec at burst-suppression level (P < 0.0001) and amplitude was reduced from 3.3 +/- 1.1 microV to 1.3 +/- 0.6 microV (P < 0.0001). The later cortical components were attenuated even during 0.5 MAC isoflurane and were not recordable during EEG burst-suppression.

CONCLUSION

We conclude that P14 can reliably be recorded with nasopharyngeal electrodes during isoflurane anaesthesia, even during EEG burst-suppression, when the N20 wave is attenuated. In contrast, the middle-latency SEP components are sensitive to isoflurane anaesthesia.

The effects of low median nerve block on thumb abduction strength

The relative contributions of the abductor pollicis longus (APL) and abductor pollicis brevis (APB) to thumb abduction strength (TAS) were determined after a selective nerve block in 21 normal volunteers. The median nerve was anesthetized (blocked) at the wrist. Needle electromyography verified paralysis of the APB and usually the opponens pollicis; in 6 study subjects, the superficial head of the flexor pollicis brevis (FPB) was also paralyzed. The APL, innervated by a branch of the posterior interosseous nerve, remained functionally intact. TAS was measured by a mechanical device before and after median nerve block. Median nerve block at the wrist resulted in a dramatic decrease in TAS in all volunteers. The mean loss of TAS was 70.3% in men and 74.3% in women. Postblock TAS tended to be greater in those subjects with retained function of the FPB. This study verifies that TAS is primarily a function of the APB.

Comparison of transthecal and subcutaneous single-injection digital block techniques

A randomized double-blinded study was performed on 20 normal volunteers to evaluate 2 different techniques of single-injection digital anesthesia. Single-injection transthecal digital block technique was used to anesthetize 1 index finger and single-injection subcutaneous technique to block the other index finger. Pain and light touch were evaluated and sensory nerve-conduction studies were performed on both index fingers. These data were obtained prior to the nerve blocks and then at 10-minute intervals until recovery from the anesthesia. The method of anesthesia was found to have no effect on the distribution, onset, and duration of anesthesia. Median and radial nerve sensory nerve action potential amplitude reductions following digital anesthesia were also not influenced by the technique of anesthesia. Single-injection subcutaneous block was found to be easier to administer and to produce less pain during and 24 hours after injection than did the single-injection transthecal technique.

The evaluation of mannitol therapy in acute ischemic stroke patients by serial somatosensory evoked potentials

The effects of mannitol infusion therapy on acute ischemic stroke were investigated by serial median nerve somatosensory evoked potentials (SEP) in 31 patients with abnormal SEP recordings within 72 hours after onset. In 10 patients with missing N20 waves mannitol had no effect. In 12 patients mannitol improved N20 and central conduction time (CCT) latencies. In 9 patients absent N20 waves appeared after mannitol. As regard to the location of infarcts, CT revealed 7 hemispheric infarcts in patients with absent N20 waves in spite of mannitol infusion. The remaining patients' CTs revealed cortical and subcortical infarcts. This study concludes that mannitol treatment improved microcirculatory flow in the ischemic penumbra of acute ischemic stroke patients. We suggest that SEPs can be used in evaluating the effects of drugs to be used in the therapy of acute cerebrovascular accidents.

Functional magnetic resonance imaging of median nerve stimulation in rats at 2.0 T

An animal model of sensory activation using fMRI at 2.0 T has been developed, demonstrating that fMRI studies on animals need not be limited to high field magnets. These methods produced reliable image intensity changes of 2% using median nerve stimulation in rats at 3 Hz and propofol as the anesthetic agent. At 6 Hz the activation was slightly but not statistically significantly greater. The feasibility of fMRI studies in animals using propofol suggests that it may be a useful anesthetic for fMRI studies in agitated adult patients or in children.

No effect of long-term vigabatrin treatment on central nervous system conduction in patients with refractory epilepsy: results of a multicenter study of somatosensory and visual evoked potentials. PMS Study Multicenter Group

PURPOSE

In dogs, vigabatrin (VGB) has been associated with intramyelinic edema producing delayed central conduction in somatosensory and visual evoked potentials (SEP, VEP). No such effects have been reported in humans. We assessed whether abnormalities of central conduction could be detected prospectively in patients with epilepsy treated with VGB as long-term add-on medication.

METHODS

Two hundred one patients with refractory partial epilepsy were enrolled and monitored for as long as 2 years. VGB was added to the treatment at an average dose of 2-3g/day. Conduction in somatosensory and visual pathways was assessed by median nerve SEP and pattern VEP recordings performed at inclusion and once every 6 months. The upper limit and test-retest variability of EP latencies were evaluated at time of enrollment in the patient group. Prolonged N13-N20 or P14-N20 SEP intervals and P100 VEP latency >2.5 SD above the baseline mean, observed on repeated runs in the same session and exceeding the test-retest variability at enrollment were considered to indicate central conduction slowing.

RESULTS

One hundred nine patients completed the 2-year study period, and 92 discontinued VGB, of whom 37 were monitored with regard to EP until the end of the study. No consistent change in SEP or VEP was observed in the entire group during VGB treatment. The number of occasional EP values outside the baseline range in patients treated with VGB similar to that in patients whose VGB treatment had been discontinued.

CONCLUSIONS

We detected no evidence of changes in SEP and VEP attributable to altered neuronal conduction in the CNS during long-term VGB treatment.

Injection injury to the median nerve

A case of injection injury to the median nerve is presented and the literature reviewed with respect to pathogenesis, prevention, and outcome. At the present time, all injectable anesthetic agents are neurotoxic. As this case illustrates, direct intrafascicular injection of these agents can result in devastating and permanent impairment. All clinicians must take steps in order to prevent these iatrogenic injuries from occurring.

Abnormal cutaneous nerve outgrowth: a secondary effect of methyl triazene teratology in developing mouse limb buds

The cutaneous branches originating from the superficial distal division of the ulnar nerve exhibit abnormal developmental features in 70.2% of the forelimb buds from embryos submitted 2 or 3 days earlier to methyl triazene administered to their pregnant mother. Similar abnormalities characterize the preaxial ventral cutaneous nerve of the thumb in 17.8% of forelimb primordia. The affected nerves undergo anticipated growth with respect to the normal schedule, follow abnormal pathways through areas of extensive cell death, and finally reach the apical ectoderm where they run in close contact with the basement membrane without forming a plexus. Histological observations gathered in pyronin-methyl green stained serial sections as well as in whole limb buds after cholinesterase method suggest that three factors probably contribute to modify nerve outgrowth: (1) a discrepancy between the rate of nerve progression and that of mesodermal growth in the prospective zeugopod territory which is preferentially affected by the teratogen; (2) facilitated nerve pathfinding into areas strongly hit by triazene-induced mesodermal cell death; and (3) alteration or abolition of some unknown ectodermal influence necessary to stimulate selective guidance of terminal sensory afferents and to maintain them transiently at some distance from the epidermis.

Three-year follow-up of serial nerve conduction among lead-exposed workers

OBJECTIVES

The purpose of this study was to investigate the serial nerve conduction parameters of a group of lead-exposed workers and determine their correlation with the serial blood lead results over a three-year period. A "nonresponse" level (defined as no significant changes in the nerve conduction in response to changes in the blood lead level of each exposed worker observed over the period of study) was also determined for blood lead in respect to the peripheral nerves.

METHODS

Seventy-two male workers from a lead battery manufacturing factory were followed at six-month intervals for three years. At each follow-up, the blood lead level was determined and nerve conduction tests (ulnar and median nerves) were conducted. A group of 82 unexposed subjects served as referents.

RESULTS

Significant differences were observed for some of the mean values of the median nerve conduction parameters between the exposed and reference groups. The 28 exposed workers who completed the follow-up were divided into the following two blood lead categories: < 40 micrograms. 100 ml-1 (< 1.93 micromol.l-1 and > or = 40 micrograms. 100 ml-1 (> or = 1.93 micromol.l-1. In the latter, the median motor conduction velocity, median distal latency, median amplitude, ulnar motor conduction velocity, and ulnar amplitude were significantly correlated (adjusted for age and within-subject variation) with the blood lead levels, but not so in the former.

CONCLUSIONS

According to the three-year serial results, the "nonresponse" level for blood lead with respect to the peripheral nerves would be < 40 micrograms.100 ml-1 (< 1.93 micromol. l-1).

Median nerve somatosensory evoked potentials in rubber factory workers

Somatosensory evoked potentials (SEPs) on median nerve stimulation were studied in 38 rubber factory workers to detect possible subclinical impairments in the somatosensory pathway as a result of exposure to rubber factory chemicals. Results showed trend towards the prolongation of latencies of all the major peaks of SEP such as P1, N1, P2, N2, P3, N3 in exposed workers besides changes in peak to peak amplitudes (higher P1-N1 and lower N2-P3). These changes may be attributed to synergistic action of solvents and other rubber factory chemicals on the generators of SEPs located higher up at the thalamo-cortical level.

Effects of nicotine gum on F waves in non-smokers

The effects of chewing gum, containing 0 and 4 mg nicotine, on F waves were studied in healthy volunteers in a repeated measure design. F responses were recorded from the abductor pollicis brevis muscle following stimulation of the median nerve at the wrist. The persistence and various amplitude measures were analysed. Chewing a 4 mg nicotine gum, with a considerable rise in systemic nicotine (6.4-37.4 ng/ml), failed to produce significant effects on F wave parameters in relation to the placebo baseline. The analysis of different F wave amplitude ranges, however, revealed significant nicotine-induced changes: a dose-related decrease of F responses > or = 500 microV and an increase of F waves between 200-290 microV. This may be due to an activation of Renshaw cells in the spinal cord.

Intraoperative myogenic motor evoked potentials induced by direct electrical stimulation of the exposed motor cortex under isoflurane and sevoflurane

We monitored myogenic motor evoked potentials (MEPS) during intracranial surgery in 21 patients anesthetized with nitrous oxide in oxygen, fentanyl, and 0.75-1.5 minimum alveolar anesthetic concentration (MAC) isoflurane (n = 11) or sevoflurane (n = 10). The exposed motor cortex was stimulated with a single or train-of-five rectangular pulses at a high frequency (500 Hz), while the compound muscle action potentials (CMAPS) were recorded from the abductor pollicis brevis muscle. Neuromuscular block was monitored by recording the CMAPs from the abductor pollicis brevis muscle in response to electrical stimulation of the median nerve at the wrist (M-response). Stimulation of the motor cortex with a single pulse elicited MEPs in none of the patients, while stimulation with a train-of-five rectangular pulses at high frequency elicited MEPs in all patients. The relationship between MEP amplitude and the level of neuromuscular block induced by vecuronium infusion was evaluated in seven patients. For comparison of the individual measurements, the MEP amplitude at a M-response amplitude of 100% was calculated by means of the individual regression curve as 100% of MEP amplitude. There was a linear correlation between percent MEP amplitude and percent M-response amplitude (r = 0.81; P < 0.01). Intraoperative monitoring of MEP could be performed at a M-response amplitude above 90 % of the baseline value in 10 patients and at a M-response amplitude of 20%-50% of the baseline value in 11 patients. During monitoring of the 21 patients, MEPs did not change in 18 patients and disappeared in two patients. In the remaining patient, MEP amplitudes were attenuated to approximately 10% of the baseline value and recovered after cessation of surgical manipulation. In the two patients in whom MEPs disappeared, motor paresis developed postoperatively. We conclude that 1) intraoperative myogenic MEP monitoring is feasible during isoflurane or sevoflurane anesthesia if stimulation is performed with a short train of rectangular pulses, and 2) that electromyographic monitoring of neuromuscular block is useful to assess intraoperative MEP changes under partial neuromuscular block.

Functional preservation of benzodiazepine receptors of the primary somatosensory cortex in Creutzfeldt-Jakob disease: a pharmacologic-evoked potential study

In previous studies, we demonstrated that the benzodiazepine (BZP) receptors of the visual system are functionally preserved in Creutzfeldt-Jakob disease (CJD). We hypothesized that such a functional preservation is not confined to the visual system. In a 74-year-old woman suffering from CJD, three consecutive recording sessions of somatosensory cortical evoked potentials (SEPs) by right median nerve stimulation were carried out: (a) basal condition, without any pharmacologic treatment; (b) 1 min after i.v. administration of 10 mg diazepam (DZP); (c) 2.5 min after i.v. administration of 3 mg FMZ, a high-affinity receptor benzodiazepine antagonist. DZP greatly decreased the amplitude of SEP early components, whereas flumazenil (FMZ) reversed such an effect. The results of this study, paralleling our previous findings on the visual system in CJD, demonstrated functional preservation of BZP receptors in the somatosensory pathways as well.

Cortical reactivity during isoflurane burst-suppression anesthesia

We studied cortical reactivity to auditory, visual, and somatosensory stimuli during moderate and deep levels of isoflurane anesthesia at which the electroencephalogram (EEG) showed burst suppression patterns, defined as alternating high amplitude bursts and periods of suppressed background activity. Fifteen patients scheduled for gynecologic surgery were anesthetized with isoflurane until burst suppression appeared in the EEG. During steady state burst suppression at 1.5 end-tidal isoflurane concentration (ETisof), each patient was given a 5-min interval each of episodes of visual, auditory, and somatosensory stimulation. During the 5-min interval of visual stimulation the patient was given 3-s episodes of 60 flashes, 4 ms duration each, at a 20-Hz frequency via redlight-emitting diode goggles. Corresponding auditory and somatosensory stimulation consisted of 60 clicks (80 dB, 0.1 ms, 20 Hz) via earphones and 60 pulses to the median nerve at the wrist (20 mA, 0.2 ms, 20 Hz). The 3-s episodes of stimulation were given at irregular intervals ranging from 5 to 20 s. End-tidal isoflurane was then increased by 0.3 vol% and 15 min later the stimulation sequence was repeated. During anesthesia at 1.5 +/- 0.1 ETisof all stimulus modalities readily evoked bursts. One hundred percent of visual stimuli, 98% +/- 4% of somatosensory stimuli, and 94% +/- 9% of auditory stimuli, given during EEG suppression, evoked bursts. Somatosensory and visual stimulation evoked bursts at both onset and offset of the 3-s episodes of stimuli. The responses to auditory stimuli were related mainly to the ending of the 3-s episode of clicks.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuromuscular recovery after peripheral nerve repair: effects of an orally-administered peptide in a primate model

Oral delivery of the tripeptide calpain inhibitor, leupeptin, after median nerve transection and epineural nerve repair in primates (Cebus apella) was studied for its potential benefits to neuromuscular recovery. Results of a controlled, dose-response study indicated that leupeptin was absorbed into plasma by the oral route of administration. When plasma leupeptin concentrations were 3 micrograms/ml or greater, morphologic and functional motor recovery were facilitated after nerve repair. Serial testing in hematology, clotting, and serum biochemistry showed that there were no adverse effects, when leupeptin was administered twice daily for 6 months following nerve repair. These data indicate that leupeptin is an effective and safe pharmaceutic adjunct to nerve repair and may have clinical benefits in humans, where the oral route is a much preferred method of delivery.

The orthogonal two-needle technique: a new axillary approach to the brachial plexus

Ninety-eight patients scheduled for elbow, forearm, wrist or hand surgery were allocated randomly to one of two different techniques of brachial plexus block, both using the axillary approach. The blocks were all performed at the level of the insertion of the lateral margin of the pectoralis major muscle on the humerus. The same mixture and volume of anaesthetic solution (30 mL of a mixture of equal parts of 0.5% bupivacaine with adrenaline 1:200 000 and 2% lignocaine) was injected through two needles positioned above and below the axillary artery, in the fascial compartments containing the median and ulnar nerves, respectively. Confirmation of correct needle placement was obtained by elicitation of paraesthesias. In one group of patients (n = 40) the needles were inserted parallel to the axillary artery pathway and the anaesthetic solution was injected toward the apex of the axilla. In a second group (n = 58) the needles were inserted orthogonally with respect to the neurovascular bundle pathway, aimed towards the posterior fascial compartment containing the radial nerve. Using the second technique, all the terminal branches of the brachial plexus were more frequently involved in the block, including the distribution of the musculocutaneous nerve. It seems likely that the inclination of the needles causes a preferential spread of the anaesthetic solution which follows the direction of the needle shaft.

Median nerve somatosensory evoked potentials. Apomorphine-induced transient potentiation of frontal components in Parkinson's disease and in parkinsonism

Somatosensory evoked potentials (SEPs) to median nerve stimulation have been recorded from parietal and frontal districts in 43 parkinsonians, 17 patients with parkinsonism and 35 healthy controls matched for age and sex. Latency/amplitude characteristics of the parietal P14-N20-P25 and of the frontal P20-N30-P40 wave complexes before and after (10, 20, 30 and 60 min) subcutaneous administration of apomorphine chloride were evaluated in all the 60 patients and in 3 controls. The frontal waves N30 and P40 were either absent or significantly smaller than normal in 31 patients with Parkinson's disease (PD) (72.1%) and in 9 with parkinsonism in baseline records (56.3%). Following apomorphine, the parietal deflections did not significantly vary in amplitude. On the contrary, the frontal complex showed a significant amplitude increase in 27 PD and 8 parkinsonisms (respectively 62.8 and 47.1%); 79.1% of PD and 35.3% of parkinsonisms were improved clinically. Amplitude increase was evident at 10 min after apomorphine, in parallel with clinical improvement, and vanished nearly in coincidence with the end of the clinical effect.

Is ACE inhibition with lisinopril helpful in diabetic neuropathy?

Thirteen diabetic patients with hypertension (mean diastolic blood pressure 96.2 +/- 1.1 mmHg) were included in a study to assess the effects of lisinopril (20 mg day-1) on measures of nerve function. Patients had nerve conduction velocity (NCV), temperature discrimination threshold (TDT), and vibration perception threshold (VPT) measurements. At the end of 12 weeks of treatment with lisinopril, there was a significant improvement in median motor NCV (mean change +/- SEM 2.7 +/- 0.6 m s-1, p < 0.0001), median sensory NCV (2.1 +/- 0.9 m s-1, p = 0.03), peroneal motor NCV (1.0 +/- 0.4 m s-1, p = 0.03), and sural sensory NCV (1.9 +/- 0.7 m s-1, p = 0.01) values. There were also significant improvements in warm TDT and VPT. Diastolic BP decreased significantly, but there was no significant change in HbA1. Double blind controlled studies are now needed to confirm the effect of lisinopril on measures of nerve function.

Radial or brachial artery injections for intraarterial regional anesthesia for hand surgery?

BACKGROUND AND OBJECTIVES

The aim of this study was to determine the optimal injection site for the intraarterial regional anesthesia for hand surgery.

METHODS

Forty-two adult patients undergoing elective hand surgery were studied. 0.5% lidocaine plain 1.5 mg/kg was injected over 3 minutes into the radial artery (group 1), or the brachial artery (group 2) through a 22 or 20 gauge Teflon catheter.

RESULTS

Two patients (one in each group) were excluded due to technical problems. Onset of analgesia in the hand was faster after radial artery injection (P < .05). Onset of analgesia in the forearm was similar in both groups. Catheterization time, operating conditions, motor block, offset of analgesia, injection, surgical and tourniquet pain scores, and patient's acceptance were similar. Ten patients in group 1 and nine patients in group 2 needed supplemental analgesia at the start of surgery. Median nerve paresthesias were unintentionally elicited during catheterization in three patients in group 2. Six patients (two in group 1 and four in group 2) had minor systemic adverse effects after tourniquet release. Seven patients in group 1 and five in group 2 developed minor bruises after catheterization. No permanent sequelae of injections were observed.

CONCLUSIONS

Radial artery is preferred for intraarterial regional anesthesia. Compared with the brachial artery, injection in the radial artery produces faster analgesia in the hand and reduces the risk of damage to the median nerve.

Neural blockade, urokinase and prostaglandin E1 combination therapy for acute digital ischemia of progressive systemic sclerosis

To treat severe painful digital ulcers on progressive systemic sclerosis (PSS) patients, we developed a new combination therapy which included neural blockade, intravenous urokinase, and prostaglandin E1 infusion. All of these are already recognized treatments for circulatory disturbances in PSS. Although each of them alone has a limited effect on the painful ischemic attack in PSS; in stepwise combination, neural blockade for release of vascular spasm and pain, prostaglandin E1 for further vasodilatation, and urokinase for thrombolysis were effective in the treatment of digital ischemia in two PSS patients. This therapy reduced the necrotic areas predicted before therapy and saved fingers from amputation. It also relieved the intolerable digital pain and effected the recovery of digital function.

Preferential channelling of anaesthetic solution injected within the perivascular axillary sheath

Preferential channelling of anaesthetic solution injected into the perivascular axillary sheath was investigated in 40 patients undergoing elective orthopaedic upper-limb surgery. Three needles, with different approaches and inclinations, were inserted near the three main terminal branches of the brachial plexus using an axillary approach. Separate boluses of anaesthetic solution (12 ml of a mixture of equal parts of 0.5% bupivacaine with 1:200,000 adrenaline and 2% lignocaine) were injected in random order through each needle, and back flow through the other two needles was noted. Back flow was observed, mainly in the needle nearest to the radial nerve during injection of the anaesthetic solution in the superior and inferior aspects of the brachial artery, and in the needle close to the ulnar nerve when the injection was performed posterior to the artery, near the radial nerve. These results could be related to the trapping of anaesthetic solution in unconnected compartments and to the slope of the needle injecting the anaesthetic solution which spreads preferentially along a gradient following the needle shaft direction.

Leukaemia inhibitory factor rescues motoneurones from axotomy-induced cell death

The death of spinal motoneurones after axotomy provides a useful model for studying novel factors which prevent motoneurone loss in vivo. Peripheral nerves of newborn rats were unilaterally transected and treated with either a vehicle solution or leukaemia inhibitory factor (LIF). Compared with the vehicle controls, treatment with a gelfoam containing LIF significantly reduced motoneurone loss: from 38% to 22% after 3 days and from 55% to 38% after 7 days. The loss of motoneurones was further reduced by placing the LIF-containing gelfoam inside a silicone chamber: from 39% to 15% after 7 days, which represented a 62% rescue. Thus, LIF is a potential therapeutic agent for preventing the loss of injured or diseased motoneurones.

Somatosensory evoked potentials during isoflurane anaesthesia

Short latency somatosensory evoked potentials (SEPs) to median nerve stimulation during isoflurane anaesthesia were recorded in 12 elective-surgery patients. The effect of isoflurane on the shape, amplitude and latency of SEPs was evaluated. SEPs were recorded at awake, 1 MAC, 1.5 MAC, at electroencephalogram (EEG) burst suppression and at continuous suppression levels. Finally, SEPs were recorded when anaesthesia was lightened back to 1 MAC. The peak latency and amplitude of the first cortical N20 wave were measured. The latencies increased with increasing isoflurane concentrations. At high concentrations only an almost monophasic N20 wave was recorded, reduced in shape and amplitude. No specific changes could be correlated with the burst suppression or suppression patterns. This suggests that EEG and SEP generators are differently affected with increasing isoflurane concentration. The results indicate that SEPs can also be recorded in drug-induced EEG suppression.

Conduction block in vasculitic neuropathy

We describe a 28-year-old man who developed a mononeuropathy with a conduction block of the median nerve in the forearm, during the acute stage of a polyarteritis nodosa. Sequential studies show progressive disappearance of the conduction block (together with the clinical symptoms), without signs of axonotmesis.

Lithium and peripheral nervous system function in manic-depressive patients

INTRODUCTION

Lithium salts are widely used in treatment of affective disorders, but lithium may cause electrophysiologically detectable changes in peripheral nervous system even with lithium concentrations within recommended therapeutic limits. The risk of lithium treatment against other risks to peripheral nervous system in psychiatric patients with affective psychoses was tested in our study.

MATERIAL AND METHOD

Electrophysiologic parameters of motor and sensory peripheral nerve fibre function were measured in two age-matched groups of psychiatric patients (20 lithium-treated and 20 affective psychotic patients without lithium treatment) and a group of 20 healthy age-matched volunteers.

RESULTS

Lower amplitudes of M waves (p < 0.015) and sensory nerve action potentials (p < 0.020) on stimulation of the median nerve have been found in both groups of patients. On peroneal nerve stimulation lower M wave amplitudes have been found only in the group of lithium-treated patients (p < 0.055). No significant differences in conduction parameters of motor and sensory fibres were demonstrated.

CONCLUSION

Our results demonstrate subclinical involvement of motor and sensory axons in affective-psychotic patients, which is only slightly more pronounced in lithium-treated patients. We suggest that lithium (within therapeutic plasma concentrations) is just one among the factors leading towards minor axonopathy in psychiatric patients.

Effects of adenosine triphosphate (ATP) on somatosensory evoked potentials in humans anesthetized with isoflurane and nitrous oxide

In order to examine the usefulness of adenosine triphosphate (ATP) as an adjuvant to anesthesia for surgery requiring intraoperative somatosensory evoked potential (SSEP) monitoring, we have studied the effects of ATP on SSEPs in patients anesthetized with isoflurane and nitrous oxide (N2O). A control recording of SSEP was performed while anesthesia was maintained with 0.5% end-tidal concentration of isoflurane in 60% N2O. The recordings were repeated after an ATP infusion had been added to this basal anesthesia at the rates of 100 micrograms.kg bw-1.min-1 and 200 micrograms.kg bw-1.min-1. SSEP was also studied when end-tidal isoflurane concentration was increased to 1.5% after cessation of ATP infusion. An infusion of ATP combined with 0.5% isoflurane and 60% N2O effectively inhibited an increase in blood pressure during surgery. The amplitude of the cortical component of SSEP was lowered by 1.5% isoflurane, which also increased both cortical and spinal latencies as well as central conduction time (CCT). In contrast ATP infusions at both rates induced no significant changes in latencies, amplitude and CCT. The results indicate that ATP infusion combined with 0.5% isoflurane in 60% N2O can be a useful anesthetic technique for intraoperative SSEP monitoring because adequate anesthetic depth can be maintained by a low concentration of anesthetics without further suppression of SSEPs.

Radial and median nerve conduction velocities in workers exposed to lead, copper, and zinc: a follow-up study for 2 years

To evaluate the interactive effects of lead, zinc, and copper on the peripheral nervous system in man, we measured maximal motor and sensory conduction velocities (MCV and SCV) in the distal radial and median nerves in 19 gun metal foundry workers with asymptomatic increased absorption of these metals twice at a 12-month interval. The workers' initial blood lead (BPb) concentrations ranged from 16 to 64 (mean, 42) micrograms/dl. The principal findings in the present study indicated that (1) radial and median nerve conduction velocities were significantly slowed in the gun metal foundry workers; (2) indicators of lead absorption were inversely related to radial nerve conduction velocities, whereas indicators of copper and zinc absorption were positively correlated with the radial and median nerve conduction velocities; and (3) yearly changes in MCV in the radial nerve and in SCV in the median nerve were positively correlated with the changes in indicators of copper and zinc absorption. These findings suggest that zinc and copper antagonize the subclinical neurologic effects of lead. Also, the radial and median nerve conduction velocities provide important indicators of subclinical lead toxicity.

[Unmasking congenital myotonia by hypothyroidism]

A case with the combination of hypothyroidism and true myotonia is reported, in which the latter first became manifest clinically together with the thyroid disorder and improved with L-thyroxine therapy. The hypothyroidism itself caused very few symptoms, and the diagnosis was not made until examination for myotonia. The effect of each disorder on muscle function seems to be additive.

[Effects of isoflurane, sevoflurane and enflurane on median nerve somatosensory evoked potentials in humans]

Median nerve somatosensory evoked potentials (SEPs) were recorded over neck (N13) and scalp (N20) in 18 neurologically normal subjects anesthetized with isoflurane, sevoflurane or enflurane for abdominal or lower limb surgery. SEP recordings were made at 0.5, 1.0 and 1.5 MAC of each volatile agent without nitrous oxide. These three agents did not change N13 latency and amplitude. Increasing concentrations of isoflurane and sevoflurane were associated with graded reductions in N20 amplitude and increases in N20 latency and N13-N20 interpeak latency. During enflurane anesthesia N20 amplitude was smaller than that at increased in dose related manner. At 1.0 MAC of enflurane N20 amplitude was smaller than that at 0.5 MAC, but further decrease was not produced at 1.5 MAC. The data suggest that effects of sevoflurane on SEPs were more similar to those of isoflurane than those of enflurane.

Midazolam and somatosensory evoked potentials

The effect of intravenous midazolam on the somatosensory evoked potentials (SEP's) elicited from median nerve stimulation was investigated in a study on 20 volunteers. SEP's were recorded from contralateral scalp before and at 5, 30, and 60 min after drug administration. Relative amplitudes of the early components (N18-N20) were essentially stable, while relative amplitudes of the late components (N50-P90, P90-N160, N160-P250 and P250-N380) were reduced significantly after midazolam administration and had not returned to baseline 60 min after administration. Given the correlation between late SEP amplitude and subjective reports of experimental pain, the data support the possibility that administration of midazolam in conscious sedation doses may have some effect on pain in addition to its better documented sedative and amnesic properties.

Topographic analysis of the effects of isoflurane anesthesia on SEP

Isoflurane anesthesia induces a striking increase in the P22 potential recorded over the precentral scalp whereas the amplitude of the N20 is reduced. It is not known whether the increased "P22" enhanced by isoflurane arises from the same generator as the small precentral P22 potential recorded in the normal awake subject. Multi-channel recordings of SEP before and during isoflurane anesthesia were performed in 13 normal subjects. Isopotential topographic maps showed that isoflurane did not change the distribution of the precentral "P22" despite its clear amplitude increase. Our data confirm that isoflurane enhances the precentral P22 and that the enhanced "P22" arises from the same generator as the P22 recorded before isoflurane anesthesia.