Further studies of nimodipine in experimental spinal cord injury in the rat.

Previously in our laboratory, nimodipine was effective in reversing posttraumatic ischemia and promoting electrophysiologic recovery in a rat spinal cord injury (SCI) model. However, these beneficial effects were achieved when nimodipine was combined with adjuvant therapy to reverse posttraumatic hypotension, by either volume expansion or vasopressor therapy. The present experiments determined if nimodipine alone can increase spinal cord blood flow (SCBF) and improve function after SCI. The hydrogen clearance technique was used to measure SCBF, and motor and somatosensory evoked potentials (MEP and SSEP) were used to quantitate electrophysiologic function. SCBF, MEP, and SSEP were recorded before and after a 52 g clip compression injury at the T1 segment and then repeated after a 35 minute infusion of nimodipine. Twenty-five rats were allocated randomly to five equal groups, each of which received 35 minute infusions of one of the following doses of nimodipine: (1) 0 mg/kg, (2) 0.005 mg/kg, (3) 0.01 mg/kg, (4) 0.025 mg/kg, or (5) 0.05 mg/kg. SCBF decreased after injury in all groups, and there was no increase in SCBF after nimodipine infusion in any group. MEP and SSEP were abolished by the injury in all rats, and there was no recovery of the evoked potentials in any group. It is concluded that adjuvant therapy for posttraumatic hypotension may be necessary for nimodipine to improve SCBF and promote recovery of function in the injured spinal cord.     

术中无肌松全静脉麻醉用于联合神经电生理监护脊柱手术的可行性

［摘要］ 目的 比较全静脉麻醉下术中使用或不使用肌松药对脊柱手术中联合神经电生理监测结果的影响,探讨安全有效的神经电生理监测麻醉方案。方法 选择拟行联合神经电生理监测的择期脊柱手术病人 40 例,分为A、B两组。两组病人均采用丙泊酚、瑞芬太尼和右美托咪定全凭静脉麻醉,A组病人术中使用小剂量阿曲库铵维持肌松,B组病人术中不使用肌松药。同时监测体感诱发电位（SEP）和运动诱发电位（MEP）评判脊髓功能。记录术中不同时间点两组病人的生命体征和SEP和MEP的波幅和潜伏期,同时记录经颅电刺激时病人是否出现剧烈体动和自主呼吸。比较两组病人术毕后麻醉苏醒时间和质量。结果 两组病人不同时间点的生命体征差异无统计学意义。两组病人的SEP的波幅和潜伏期差异无统计学意义,MEP的潜伏期差异无统计学意义,MEP的波幅差异有显著性统计学意义。两组病人在电刺激时均无自主呼吸和剧烈体动发生。结论 术中不使用肌松药的全静脉麻醉方案可安全有效地用于行神经电生理监测的脊柱手术,并且在电生理监测信号质量和术后苏醒方面具有明显优势。     

Anesthetic management of corpus callosotomy with electrophysiological monitoring: a case report

We report anesthetic management of a 5-year-old girl for corpus callosotomy indicated for the treatment of intractable epilepsy. The procedure mandated intraoperative monitoring of evoked potentials and electrocorticogram. During the first half of the surgery until the corpus callosum was exposed, anesthesia was maintained with continuous infusion of propofol. Motor and somatosensory evoked potentials were monitored and diagnosed as intact throughout the procedure, with no epileptic activity observed in 32-lead electrocorticogram. Then propofol infusion was replaced with the inhalation of sevoflurane, 2.0% in air/oxygen mixture, which induced epileptic spike-and-wave activities, synchronized between the hemispheres, in electrocorticogram. After the completion of corpus callosotomy, we observed interhemispheric desynchronization of epileptic activities indicating successful surgical intervention. The patient emerged from anesthesia uneventfully with no neurological deficits, and thereafter with decreased incidence of generalized epileptic episodes. We suggest that such switch of anesthetic agents between propofol and sevoflurane should be helpful in intraoperative electrophysiological monitoring for ascertaining both functional preservation and successful intervention during epileptic surgery.     

Recovery from neuromuscular blockade after either bolus and prolonged infusions of cisatracurium or rocuronium using either isoflurane or propofol-based anesthetics

We examined the recovery characteristics of cisatracurium or rocuronium after bolus or prolonged infusion under either isoflurane or propofol anesthesia. Sixty patients undergoing neurosurgical procedures of at least 5 h were randomized to receive either isoflurane with fentanyl (Groups 1 and 2) or propofol and fentanyl (Groups 3 and 4) as their anesthetic. Groups 1 and 3 received cisatracurium 0.2 mg/kg IV bolus, spontaneously recovered, after which time an infusion was begun. Groups 2 and 4 received rocuronium 0.6 mg/kg IV, spontaneously recovered, and an infusion was begun. Before the end of surgery, the infusion was stopped and recovery of first twitch (T(1)), recovery index, clinical duration, and train-of-four (TOF) recovery was recorded and compared among groups by using appropriate statistical methods. Clinical duration was shorter for rocuronium compared with cisatracurium using either anesthetic. Cisatracurium T(1) 75% recovery after the infusion was shorter with propofol compared with isoflurane. Cisatracurium TOF 75% recovery was similar after either bolus or infusion, but rocuronium TOF 75% recovery after the infusion was delayed. Infusion rates decreased for cisatracurium but remained relatively constant for rocuronium regardless of the anesthetic used. Isoflurane enhances the effect of both muscle relaxants but prolonged cisatracurium recovery more than rocuronium. Of the two muscle relaxants studied, rocuronium's recovery was most affected by length of the infusion. Cisatracurium may be a more desired muscle relaxant for prolonged procedures because recovery was least affected by prolonged infusion. Implications: This study describes the effect of different anesthetic techniques on the recovery of two different muscle relaxants, cisatracurium and rocuronium, when administered as either a single bolus or prolonged infusion during neurosurgery. This study demonstrates the feasibility of using these relaxants for these prolonged procedures.     

Influence of fentanyl, alfentanil, and sufentanil on motor evoked potentials

The effects of the opioids fentanyl, alfentanil, and sufentanil on motor pathways were studied in a total of 30 rabbits. Compound muscle action potentials (CMAP) were recorded from the extensor muscles of the upper extremity as well as evoked spinal cord potentials (ESCP) from the thoracic epidural space in response to electrical stimulation of the motor cortex. After establishing stable baseline values, an equipotent intravenous bolus of one of the three opioids was applied that abolished reflex motor response to noxious stimulation. Motor evoked potentials (MEP) were recorded from the time of bolus administration until recovery of MEP amplitudes and latencies. Afterwards, the opioids were administered continuously with cumulative dosage up to total absence of motor evoked response. Our results show a dose-dependent suppression of the CMAP: When reflex movement to noxious stimulation was extinguished, we found a significant (P < .001) reduction of the amplitudes to 34+/-18% (mean +/- SD) in the fentanyl group, to 43+/-24% in the alfentanil group, and to 53+/-20% of baseline values in the sufentanil group. Increasing opioid plasma levels were associated with complete extinction of the CMAP. We hypothesize that the descending volleys within motor pathways are mainly inhibited at a spinal level, because ESCP, particularly the number of spinal I-waves, are not severely affected even when CMAP are completely suppressed. In conclusion, intraoperative monitoring of descending pathways by means of MEP during anesthesia with opioids is feasible at anesthetic plasma concentrations maintaining a surgical level of analgesia. Even with high opioid plasma levels, a valid MEP monitoring could be performed evaluating neural activity of spinal MEP.     

Sustained spinal cord compression: part II: effect of methylprednisolone on regional blood flow and recovery of somatosensory evoked potentials

BACKGROUND: The efficacy of methylprednisolone in the treatment of traumatic spinal cord injury is controversial. We examined the effect of methylprednisolone on regional spinal cord blood flow and attempted to determine whether recovery of electrophysiological function is dependent on reperfusion, either during sustained spinal cord compression or after decompression. METHODS: The effects of methylprednisolone therapy on recovery of somatosensory evoked potentials and on spinal cord blood flow were examined in a canine model of dynamic spinal cord compression. Methylprednisolone (30 mg/kg intravenous loading dose followed by 5.4 mg/kg/hr intravenous infusion) or saline solution was administered to thirty-six beagles (eighteen in each group) five minutes after cessation of dynamic spinal cord compression and loss of all somatosensory evoked potentials. After ninety minutes of sustained compression, the spinal cords were decompressed. Somatosensory evoked potentials and spinal cord blood flow were evaluated throughout the period of sustained compression and for three hours after decompression. RESULTS: Seven dogs treated with methylprednisolone and none treated with saline solution recovered measurable somatosensory evoked potentials during sustained compression. After decompression, three more dogs treated with methylprednisolone and seven dogs treated with saline solution recovered somatosensory evoked potentials. Four dogs treated with methylprednisolone lost their previously measurable somatosensory evoked potentials. In the methylprednisolone group, spinal cord blood flow was significantly higher (p < 0.05) in the dogs that had recovered somatosensory evoked potentials than it was in the dogs that had not. Reperfusion blood flow was significantly higher (p < 0.05) in the saline-solution group than it was in the methylprednisolone group. Spinal cord blood flow in the saline-solution group returned to baseline levels within five minutes after decompression. It did not return to baseline levels in the dogs treated with methylprednisolone. CONCLUSIONS: The methylprednisolone administered in this study did not provide a large or significant lasting benefit with regard to neurological preservation or restoration. Methylprednisolone may reduce regional spinal cord blood flow through mechanisms affecting normal autoregulatory blood-flow function.     

Effects of epidural diamorphine on the somatosensory evoked potential to posterior tibial nerve stimulation

We have studied the effects of the epidural administration of diamorphine 0.1 mg/kg at the L3-4 interspace on somatosensory evoked potentials in the cervical epidural space before corrective surgery for idiopathic adolescent scoliosis. A further eight patients in whom anaesthesia was maintained with a propofol infusion acted as a control group. Epidural diamorphine had no effect on the latency or amplitude of the evoked potentials. We conclude that epidural diamorphine is a suitable technique to use in scoliosis surgery because of its lack of effect on neurophysiological variables, although the potential respiratory problems need investigation.     

Total intravenous anesthesia with propofol, fentanyl and ketamine for carotid endarterectomy under somatosensory evoked potential monitoring--combination with intraoperative hypothermia]

We reported anesthetic management combined with hypothermia for carotid endarterectomy under somatosensory evoked potential monitoring. Anesthesia was induced by propofol, fentanyl and ketamine, and maintained by infusion of propofol and ketamine and intermittent injections of fentanyl. Perioperative hypothermia was induced by gradually reducing the temperature of a circulating water mattress underneath the body to 15 degrees C. Additionally, somatosensory evoked potential monitoring was performed and recordings were obtained immediately after induction of anesthesia, and before as well as during cross-clamping of the internal carotid artery. Rectal temperature was reduced to 33.7 degrees C when cross-clamping of carotid artery was carried out, but major changes between before and during the procedure was not observed. All procedures were done uneventfully and gradual rewarming was accomplished by electric blanket. No neurological deficits were observed following recovery from anesthesia. Total intravenous anesthesia with propofol, fentanyl and ketamine may be useful for carotid endarterectomy under hypothermia and somatosensory evoked potential monitoring. This method may provide neuronal protection against ischemia injuries induced by cross-clamping of the carotid artery.     

A comparison of target- and manually controlled infusion propofol and etomidate/desflurane anesthesia in elderly patients undergoing hip fracture surgery

Elderly patients have a higher risk of developing adverse drug reactions during anesthesia, especially anesthesia affecting cardiovascular performance. In this prospective randomized study we compared quality of induction, hemodynamics, and recovery in elderly patients scheduled for hip fracture surgery and receiving either etomidate/desflurane (ETO/DES) or target-controlled (TCI) or manually controlled (MAN) propofol infusion for anesthesia. Sixteen patients were anesthetized with ETO (0.4 mg/kg) followed by DES titrated from an initial end-tidal concentration of 2.5%. Eighteen patients received propofol TCI at an initial plasma concentration of 1 microg/mL and titrated upwards by 0.5-microg/mL steps. Fifteen patients received a bolus induction of propofol 1 mg/kg over 60 s followed by an infusion initially set at 5 mg . kg(-1) . h(-1). All received a bolus (20 microg/kg) followed by an infusion of 0.4 microg . kg(-1) . min(-1) alfentanil. According to hemodynamics, concentrations of DES or propofol (TCI group) and propofol infusion rate (MAN group) were respectively adjusted by a step of 20% and 50%. In the TCI and ETO/DES groups, the time spent at a mean arterial blood pressure within 15% and 30% of baseline values was more than 60% and 80% of anesthesia time, whereas in the MAN group it was <30% and 60%, respectively. In the MAN group more anesthetic drug adjustments were recorded (6.4 +/- 2.8 versus 2.5 +/- 1.2 [ETO/DES] and 2.6 +/- 1 [TCI]). TCI improves the time course of propofol's hemodynamic effects in elderly patients.     

Anesthetic management of four cases of craniotomy with alternate monitoring of motor and somatosensory evoked potentials

We experienced four cases of craniotomy in which motor evoked potential (MEP) and somatosensory evoked potential (SEP) were monitored alternately. Anesthesia was induced with propofol and fentanyl, and it was maintained with continuous infusion of propofol. Intermittently, propofol and fentanyl were administered as needed. Inhalation of 66% nitrous oxide did not prolong latency, but significantly reduced the amplitude of MEP. We could obtain the largest amplitude of MEP using five consecutive stimuli of which duration and frequency were 0.5 milliseconds and 500 Hz, respectively. Anesthetic management using propofol and fentanyl is useful for craniotomy with monitoring of MEP and SEP.     

Progressive suppression of motor evoked potentials during general anesthesia: the phenomenon of "anesthetic fade"

Transcranial motor evoked potentials (MEPs) are useful for assessing the integrity of spinal cord motor tracts during major spine surgery. Anesthetic agents depress the amplitude of MEPs in a dose-dependent fashion. Anecdotal reports suggest that MEP responses degrade or "fade" over the duration of a surgery, despite unchanged anesthetic levels or other physiologic variables. This phenomenon has not been systematically analyzed. We performed a retrospective study of 418 patients who underwent spine surgery at UCSF using intraoperative MEP monitoring. We excluded patients who experienced variations in physiologic parameters that might affect MEP signals and those who developed new neurologic deficits. We identified 46 neurologically intact patients and 16 myelopathic patients who had surgery performed using a constant desflurane/N2O/narcotic or desflurane/propofol/narcotic anesthetic regimen. The minimum voltage threshold needed to produce an MEP response of at least 50 microV in amplitude was recorded at the beginning ("baseline") and end of surgery. The voltage threshold was higher at the end of the case than at baseline for each patient, regardless of anesthetic regimen. In normal patients, the rate of rise of the threshold was similar for those receiving propofol (11.4 +/- 6.9 V/hr) or N2O (9.7 +/- 5.9 V/hr) (P = not significant). Myelopathic patients demonstrated a larger rate of rise in voltage threshold, 23.4 +/- 12.2 V/hr, versus normal subjects (P < 0.01). The rate of rise of voltage threshold is inversely proportional to anesthetic duration. Prolonged exposure to anesthetic agents necessitates higher stimulating thresholds to elicit MEP responses, separate from the dose-dependent depressant effect. This retrospective study is limited and cannot explain the mechanism for this observed fade in signals. Recognition of anesthetic fade is essential when interpreting changes to the MEP response to avoid false-positive findings.     

Low dose propofol as a supplement to ketamine-based anesthesia during intraoperative monitoring of motor-evoked potentials

STUDY DESIGN: Motor-evoked potentials (MEPs) were analyzed using transcranial electrical stimulation during spinal surgery in patients under ketamine-based anesthesia, with and without propofol. OBJECTIVE: To investigate the effects of propofol on MEPs and ketamine-induced adverse effects during spinal surgery in patients under ketamine-based anesthesia. SUMMARY OF BACKGROUND DATA: Intraoperative monitoring of transcranial motor-evoked responses provides a method for monitoring the functional integrity of descending motor pathways. However, because these responses are sensitive to suppression by most anesthetic agents, anesthetic technique is limited during the monitoring of MEPs. Ketamine has been reported to have little effect on MEPs but may produce adverse effects such as psychedelic effect and hypertension. Recently, it has been reported that propofol may be able to inhibit ketamine-induced adverse effects. METHODS: Intraoperative monitoring of MEPs was performed in 58 patients who underwent elective spinal surgery. Anesthesia was maintained with nitrous oxide-fentanyl-ketamine without or with low-dose (1-3 mg/kg/hr) of propofol (K group; n = 34, KP group; n = 24, respectively). Transcranial stimulation with single or paired pulses or a train of three or five pulses (interstimulus interval, 2 msec) were delivered to the scalp, and compound muscle action potentials were recorded from the left and right tibialis anterior muscles. To investigate the dose effects of propofol on MEPs, propofol was administered at an infusion rate of 6, 4, and 2 mg/kg/hr and then discontinued in 14 patients. RESULTS: Results of MEPs were comparable between the K and KP groups. The incidence of postoperative psychedelic effect was significantly less in the KP group (14%) than in the K group (41%). Although propofol inhibited MEPs dose dependently, the use of a train of pulses for stimulation could overcome such inhibition. CONCLUSIONS: If a train of pulses were used for transcranial stimulation, low-dose propofol can be effectivelyused as a supplement to ketamine-based anesthesia during intraoperative monitoring of myogenic MEPs. Addition of propofol significantly reduced the ketamine-induced psychedelic effects.     

Comparison of recovery of propofol and methohexital sedation using an infusion pump.

Two sedative anesthetic agents administered by an infusion pump were compared during third molar surgery. Forty American Society of Anesthesiologists (ASA) class I or II volunteers were randomly allocated to two groups. All subjects received supplemental oxygen via a nasal hood, fentanyl (0.0007 mg/kg intravenous [i.v.] bolus), and midazolam (1 mg/2 min) titrated to effect. Patients then received either 0.3 mg/kg of methohexital or 0.5 mg/kg of propofol via an infusion pump. Upon completion of the bolus, a continuous infusion of 0.05 mg/kg/min methohexital or 0.066 mg/kg/min propofol was administered throughout the procedure. Hemo-dynamic and respiratory parameters and psychomotor performance were compared for the two groups and no significant differences were found. The continuous infusion method maintained a steady level of sedation. Patients receiving propofol had a smoother sedation as judged by the surgeon and anesthetist.     

Intraoperative transcranial electrical motor evoked potential monitoring during spinal surgery under intravenous ketamine or etomidate anaesthesia

Summary Motor evoked potentials (MEPs), monitoring the motor function directly, are superior to somatosensory evoked potentials (SSEPs) in monitoring the motor system during spinal surgery. Reliable MEPs are difficult to elicit under normal anaesthesia. Using intravenous anaesthesia with either ketamine or etomidate infusion, we performed intraoperative MEP monitoring in 12 spinal operations for 11 cases from February 1992 to May 1992. For anaesthesia, ketamine was used in 5, etomidate in 7, fentanyl was supplemented in all, muscle relaxation at 30% to 50% of pre-anaesthetic muscle power was maintained with atracurium or vencuronium infusion. Transcranial bipolar electrical stimulation was used to induce MEPs. Concomitant SSEP monitoring was performed in 3. No significant anaesthesia related side effects were noted except one episode of unpleasant dream occurred in the ketamine anaesthesia group.Successful monitoring was achieved in 10 sessions. In 5 of which warning to the surgeons was made due to sudden MEP deterioration, which recovered followed by definite management in four and persisted in one. In the other 5 sessions, no warning was made due to stationary or gradual change in MEPs. Bilateral two-channel recordings were used in 3 sessions. In 2 of which unilateral transient change was noted. Loss of SSEPs was noted in one despite unchanged MEPs, in whom only new sensory deficits occurred postoperatively. Compared to the baseline MEPs in terms of latency and amplitude, the final MEPs improved in 5 sessions, did not change significantly in 4 sessions, deteriorated in one session, and were correlated well with the immediate postoperative motor status.In our small series, the intraoperative MEP monitoring showed neither false negative nor false positive result. It is concluded that the intraoperative MEP monitoring is feasible under intravenous ketamine or etomidate anaesthesia and valuable in spinal surgery.     

The effects of xenon on myogenic motor evoked potentials in rabbits: a comparison with propofol and isoflurane

We compared the effects of xenon on myogenic motor evoked potentials (MEPs) with those of propofol and isoflurane in rabbits under ketamine/fentanyl anesthesia. Thirty animals were randomly allocated to one of 3 groups (n = 10 in each group). In the propofol group, propofol was administered at a rate of 0.4 mg x kg(-1) x min(-1) (small) and 0.8 mg x kg(-1) x min(-1) (large). In the isoflurane group, isoflurane was administered at 0.8% (small) and 1.6% (large). In the xenon group, xenon was administered at 35% (small) and 70% (large). Myogenic MEPs in response to stimulation with single pulse and a train of 5 pulses were recorded from the soleus muscle before, during (at small and large doses), and after the administration of each anesthetic. With single-pulse stimulation, MEPs were recorded in 90% and 50% of animals at small and large doses of xenon, respectively, and MEP amplitudes in the xenon and isoflurane groups were significantly lower compared with those in the propofol group. With train pulse stimulation, MEPs were recorded in 100% and 90% of animals at small and large doses of xenon, respectively, and a reduction in MEP amplitudes by xenon was more prominent than by propofol but less than isoflurane at large doses. These results suggest that MEP recording may be feasible under xenon anesthesia if multipulse stimulation is used, although xenon has suppressive effects on myogenic MEPs.     

异丙酚复合芬太尼对患者拇短展肌运动诱发电位的影响

目的 探讨异丙酚复合芬太尼对患者拇短展肌运动诱发电位(MEP)的影响.方法 择期普通外科手术患者11例,ASA Ⅰ或Ⅱ级,年龄26～48岁.以第6颈椎棘突为刺激线圈的中点进行磁刺激,周期20s.试验Ⅰ:经30 s匀速静脉注射异丙酚2mg/kg.记录给药即刻至患者出现睁眼或体动反应期间右拇短展肌MEP波幅的基础值、最低值和最后值,及其对应的潜伏期,以及波幅下降至最低值的时间(时程).试验Ⅱ:试验Ⅰ结束后30 min,经大隐静脉依次匀速注射异丙酚2 mg/kg和芬太尼5 μg/kg,每种药物注射时间为30 s.记录给药即刻开始拇短展肌MEP波幅的基础值、最低值和最后值,及其对应的潜伏期,以及时程,记录时间为360 s.结果 与基础值比较,两试验拇短展肌MEP波幅的最低值和最后值降低(P<0.01);与试验Ⅰ比较,试验Ⅱ拇短展肌MEP波幅的最后值降低(P<0.05).结论 与静脉注射异丙酚比较,异丙酚复合芬太尼对患者拇短展肌MEP的抑制作用更强.     

Propofol infusion for the maintenance of short-term anesthesia

The administration of propofol by infusion for maintenance of anesthesia has attracted much attention recently. We investigated the necessary infusion rate of propofol to maintain anesthesia for short surgical procedures without loss of the evident advantages of this substance. Forty unpremedicated female patients aged 18-59, scheduled for minor gynecological procedures, were randomly assigned to four groups. Anesthesia was induced with 2.0 mg/kg propofol i.v. and simultaneously an infusion of 0.05, 0.10, 0.15, or 0.20 mg propofol/kg per minute was started. The patients were breathing N2O/O2 with FIO2 33%. Additional propofol was administered as a bolus of 10 to 20 mg when the patients moved. With 0.05 mg propofol/kg per minute all patients required additional bolus injections of propofol; with 0.10 mg 8 patients, with 0.15 mg 5 patients, and with 0.20 mg 1 patient required bolus injection. Therefore, 0.15 mg/kg per minute can be considered as an approximate ED50 value. The total propofol consumption (infusion + bolus) increased from 0.102 +/- 0.028 (+/- SD) with the lowest infusion rate to 0.202 +/- 0.006 mg/kg per minute with the highest infusion rate and recovery time from 5.2 +/- 1.4 to 9.9 +/- 2.6 min. There was a significant correlation between propofol consumption and recovery time. After induction, arterial blood pressure decreased by systolic/diastolic 20/10-15 mmHg. With the low infusion rate, arterial pressure increased to its control value during operation; it remained at the postinduction value with high infusion rates. Side-effects: 10 patients had salivation that in some instances lead to coughing, 9 reported pain at the injection site during induction, and 9 reported dreams of a pleasant nature.(ABSTRACT TRUNCATED AT 250 WORDS)     

Variability of somatosensory cortical evoked potentials during spinal surgery. Effects of anesthetic technique and high-pass digital filtering

The effects of anesthetic technique (nitrous oxide or propofol) and high-pass digital filtering on within-patient variability of posterior tibial nerve somatosensory cortical evoked potentials (PTN-SCEP) were compared prospectively in two groups of 20 patients undergoing spinal surgery. Average P1N1 amplitude was significantly higher and P1N1 amplitude variability lower during propofol/alfentanil anesthesia than during nitrous oxide/alfentanil anesthesia. Off-line 30-Hz high-pass digital filtering significantly reduced P1N1 amplitude variability without decreasing P1N1 amplitude. In 93 patients studied retrospectively, a significant negative logarithmic correlation (r = -0.77) was observed between P1N1 amplitude and P1N1 amplitude variability. This study shows the importance of maintaining the highest possible PTN-SCEP amplitudes during spinal surgery. Propofol/opioid anesthesia may be an alternative anesthetic technique to nitrous oxide/opioid anesthesia during spinal cord function monitoring.     

Recovery from rocuronium by sugammadex does not affect motor evoked potentials

Motor evoked potential (MEP) monitoring has been employed to detect the spinal cord injury during spinal, neurosurgical and cardiovascular operations. Muscle relaxants diminish the amplitude of MEP because MEP is the picture of electromyogram. In 5 cases undergoing MEP monitoring, we examined the effect of rocuronium followed by the administration of sugammadex on MEP Anesthesia was induced with propofol (target controlled infusion 3.0-3.5 microg x ml(-1)) and remifentanil 0.15-0.3 microg x kg(-1) x min(-1), and the trachea was intubated with the use of rocuronium 0.6 mg x kg(-1) without any muscle rigidity, bucking and laryngospasm. General anesthesia was maintained by total intravenous anesthesia using propofol and remifentanil with no muscle relaxants. Immediately after the tracheal intubation, sugammadex 4 mg x kg(-1) was intravenously given. The amplitude of MEP was measured just before the administration of rocuronium, immediately after the tracheal intubation, and 1, 2, 3, 5 min following the administration of sugammadex. Sugammadex restored the MEP amplitude, deteriorated by rocuronium, in 3 to 5 min to the level of non-paralytic muscles. In one case, it took 8 min to restore the MEP of hemiparetic leg. Taking these findings into consideration, it is likely that rocuronium might not affect the MEP when reversed by sugammadex, and should be safe for smooth tracheal intubation in patients who need MEP monitoring.     

Total intravenous anesthesia for intraoperative monitoring of the motor pathways: an integral view combining clinical and experimental data

OBJECT: Monitoring of descending corticospinal pathways by using motor evoked potentials (MEPs) has proven to be useful in preventing permanent neurological deficits during cranial and spinal procedures. Difficulties in interpretation of intraoperative changes in potentials may largely be attributed to the effects of anesthesia. Development of suitable intravenous anesthesia protocols specifically tailored for MEP monitoring, including plasma level target-controlled infusion (TCI), requires precise knowledge of the specific neurophysiological properties of the various agents. METHODS: The effects of alfentanil, sufentanil, fentanyl, remifentanil, thiopental, midazolam, etomidate, ketamine, and propofol on neurogenic and myogenic MEPs were evaluated in an integral study combining clinical data obtained in 40 patients and experimental investigations conducted in 140 animals. The dose-dependent modulation of MEPs after electrical and magnetoelectrical stimulation of the motor cortex was recorded from peripheral muscles and the spinal cord. The results were as follows: opioids, propofol, and thiopental suppressed myogenic, but not neurogenic MEPs in a dose-dependent fashion; remifentanil exerted the least suppressive effects. Etomidate and midazolam did not suppress myogenic MEP, even at plasma concentrations sufficient for anesthesia. Ketamine induced moderate reduction of compound muscle action potential amplitudes only at high doses. Remifentanil and propofol administered via TCI systems allowed recording of myogenic potentials within a defined target plasma concentration range. CONCLUSIONS: Development of standardized total intravenous anesthesia/TCI protocols by using anesthetic agents such as propofol, remifentanil, ketamine, and midazolam, which have favorable pharmacokinetic and neurophysiological properties, will enhance the quality of intraoperative MEPs and promote the use of MEP monitoring as a useful tool to reduce surgery-related morbidity.