Hironobu Hayashi

Evaluation of Reliability of Post-tetanic Motor-evoked Potential Monitoring During Spinal Surgery Under General Anesthesia

Study Design. A prospective research. Objective. Compare the reliability of post-tetanic motor-evoked potential (p-MEP) monitoring in the detection of motor injury during spinal surgery with that of conventional MEP (c-MEP). Summary of Background Data. Myogenic MEPs are sensitive to suppression by anesthetics and neuromuscular blockade. Recently, we reported a new technique for MEP recording, called “p-MEP” in which MEP amplitude can be enlarged by tetanic stimulation of peripheral nerve before transcranial stimulation in comparison with that of c-MEP. The purpose of this study is to compare the reliability of p-MEP monitoring in the detection of motor injury during spinal surgery with that of c-MEP. Methods. Eighty patients undergoing elective spinal surgery were enrolled in the study. Both c-MEP and p-MEP monitoring were performed throughout the operation in each patient. For recording c-MEPs, transcranial electrical train of five pulses stimulation with an interstimulus interval of 2 milliseconds was performed and compound muscle action potentials were bilaterally recorded from abductor pollicis brevis, abductor hallucis, tibialis anterior, and soleus muscles. For recording p-MEPs, tetanic stimulation (50 Hz, 50 mA, 5 sec) was applied to the left median nerve and bilateral tibial nerves 1 second before transcranial stimulation and compound muscle action potentials were recorded from the same muscles. The false positive, false negative, and accuracy of MEP monitoring in the detection of change in motor function were compared between p-MEP and c-MEP. Results. At the baseline, success rates of baseline c-MEP and p-MEP recording were 66.3% (53/80) and 92.5% (74/80), respectively. The false positive, false negative, and accuracy of p-MEP monitoring were 0%, 0%, and 100%, respectively, whereas c-MEP were 4%, 20%, and 95%, respectively. Conclusion. The results indicate that p-MEP is a more reliable method to detect changes in motor function during spinal surgery under general anesthesia in comparison with c-MEP.

Assessment of intraoperative motor evoked potentials for predicting postoperative paraplegia in thoracic and thoracoabdominal aortic aneurysm repair

PurposeMonitoring motor evoked potentials (MEPs) has been recognized as a highly reliable method to detect intraoperative spinal cord ischemia (SCI) in aortic repair. However, the data regarding the sensitivity and specificity of MEPs for predicting postoperative paraplegia are limited. We retrospectively assessed the value of intraoperative MEP amplitudes for predicting postoperative paraplegia.MethodsThe medical records of 44 patients were reviewed. A train-of-five stimulation was delivered to C3–C4, and MEPs were recorded from the abductor pollicis brevis and the tibialis anterior muscles. The cutoff point for detecting SCI was set at 75% decrease of the baseline MEP. Receiver operating characteristic curves were applied at various cutoff points.ResultsThree patients (6.8%) had postoperative paraplegia. The minimum MEP during surgery had 100% sensitivity and 64.9% specificity in predicting paraplegia, and the MEP at the end of surgery had 66.7% sensitivity and 78.0% specificity in predicting paraplegia: only 1 patient, who had borderline paraplegia (right monoparesis), showed a false-negative result. Receiver operating characteristic curves indicated that adequate cutoff points for the minimum MEP during surgery and for the MEP amplitude at the end of surgery were a 75–90% decrease and a 64–75% decrease of the baseline MEP, respectively.ConclusionMonitoring MEPs had relatively high sensitivity and acceptable specificity, with the cutoff point set at 75% decrease of the baseline MEP, for predicting paraplegia and paraparesis. Because of the small sample in our study, further investigations would be necessary to investigate an adequate cutoff point that could predict postoperative paraplegia.

Changes in intraocular pressure during prone spine surgery under propofol and sevoflurane anesthesia.

Background: Intraocular pressure (IOP) has been shown to increase during prone spine surgery. Although propofol and sevoflurane have been widely used during such surgery, there have been no data to compare the IOP changes under propofol and sevoflurane anesthesia. The present study was therefore conducted to investigate IOP changes under propofol and sevoflurane anesthesia during prone spine surgery. Method: After institutional approval and informed consent, 24 patients undergoing prone spine surgery were studied. Patients were randomly allocated to 1 of 2 groups: the propofol or sevoflurane group. Propofol or sevoflurane was administered to maintain the bispectral index between 40 and 60. The IOP was measured using a Tonopen XL hand-held tonometer 10 minutes after induction of anesthesia in the supine position (baseline), 10, 60, and 120 minutes after positioning in the prone position, and 10 minutes after returning to the supine position. Results: There were no significant differences in IOP values at baseline between the 2 groups. IOP values after positioning in the prone position were significantly higher than those at baseline in both groups (propofol group: from 8.9±3.5 to 21.9±5.0 mm Hg; sevoflurane group: from 11.6±3.9 to 24.8±3.4 mm Hg; P<0.05). Although IOP values were higher in the sevoflurane group than in the propofol group, the differences in IOP values were not statistically significant. Conclusions: The results indicated that the choice of anesthetic agent, sevoflurane or propofol, did not have significant effects on IOP changes during a relatively short interval of prone spine surgery.

The Effects of the Neuromuscular Blockade Levels on Amplitudes of Posttetanic Motor-Evoked Potentials and Movement in Response to Transcranial Stimulation in Patients Receiving Propofol and Fentanyl Anesthesia

BACKGROUND: Patient movement in response to transcranial stimulation during monitoring of myogenic motor-evoked potentials (MEPs) may interfere with surgery. We recently reported a new technique to augment the amplitudes of myogenic MEPs, called “post-tetanic MEPs (p-MEPs),” in which tetanic stimulation of a peripheral nerve was applied prior to transcranial stimulation. We conducted the present study to determine an appropriate level of neuromuscular blockade during the monitoring of p-MEPs with a focus on patient movement. METHODS: In 15 patients under propofol/fentanyl anesthesia, conventional MEPs (c-MEPs) and p-MEPs in response to transcranial electrical stimulation were recorded from the abductor hallucis muscle. For p-MEP recording, tetanic stimulation to the posterior tibial nerve at an intensity of 50 mA for 5 s was started 6 s prior to transcranial stimulation. The level of neuromuscular blockade was assessed by recording the amplitude of compound muscle action potentials (T1) from the abductor hallucis brevis muscle in response to supramaximal electrical stimulation of the median nerve at the wrist. After the baseline recordings of c-MEP and p-MEP at a T1 of 50% of control, 0.1 mg/kg of vecuronium was injected and the amplitudes of c-MEPs and p-MEPs were recorded. Patient movement was also assessed with the movement score ranging from 1 to 4 (1 = no movement, 4 = severe movement). RESULTS: T1, %T1, the amplitudes of c-MEPs and p-MEPs, and the movement score changed in parallel after the administration of vecuronium. The amplitudes of p-MEPs before and 15–45 min after the administration of vecuronium were significantly higher than those of c-MEPs. When T1 and %T1 were less than and equal to 1 mV and 10%, respectively, the movement score was 1 or 2 in all patients, indicating that microscopic surgery was possible without the interruption of surgical procedures. When T1 was around 1 mV (0.8–1.2 mV), the success rates of recording of c-MEPs and p-MEPs were 73% (11 of 15) and 100% (15 of 15), respectively. CONCLUSIONS: Under propofol/fentanyl anesthesia, p-MEP could be recorded at a T1 of 1 mV, in which patient movement in response to transcranial stimulation did not interfere with surgery. This technique may be used in patients without preoperative motor deficits, in which patient movement during surgical procedures is not preferable.

The application of tetanic stimulation of the unilateral tibial nerve before transcranial stimulation can augment the amplitudes of myogenic motor-evoked potentials from the muscles in the bilateral upper and lower limbs.

BACKGROUND: Recently, we reported a new technique to augment motor-evoked potentials (MEPs) under general anesthesia, posttetanic MEP (p-MEP), in which tetanic stimulation of the peripheral nerve before transcranial stimulation enlarged amplitudes of MEPs from the muscle innervated by the nerve subjected to tetanic stimulation. In the present study, we tested whether tetanic stimulation of the left tibial nerve can also augment amplitudes of MEPs from the muscles which are not innervated by the nerve subjected to tetanic stimulation. METHODS: Thirty patients undergoing spinal surgery under propofol-fentanyl anesthesia with partial neuromuscular blockade were examined. For conventional MEP (c-MEP) recording, transcranial stimulation with train-of-five pulses was delivered to C3-4, and the compound muscle action potentials were bilaterally recorded from the abductor pollicis brevis, abductor hallucis (AH), tibialis anterior, and soleus muscles. For p-MEP recording, tetanic stimulation (50 Hz, 50 mA of stimulus intensity) with a duration of 5 s was applied to the left tibial nerve at the ankle 1 s before transcranial stimulation. Transcranial stimulation and recording of compound muscle action potentials were performed in the same manner as c-MEP recording. Amplitudes of c-MEP and p-MEP were compared using Wilcoxons signed rank test. RESULTS: Amplitudes of p-MEPs from the left AH muscle innervated by the left tibial nerve with tetanic stimulation were significantly larger compared with those of c-MEPs. Amplitudes of p-MEPs from the bilateral abductor pollicis brevis and soleus muscles and right AH and tibialis anterior muscles, which were not innervated by the left tibial nerve with tetanic stimulation, were also significantly larger compared with those of c-MEPs. CONCLUSION: In patients under propofol and fentanyl anesthesia with partial neuromuscular blockade, the application of tetanic stimulation to the left tibial nerve augmented the amplitudes of MEPs from the muscles without tetanic nerve stimulation and those with stimulation.

Ocular Blood Flow Measured Using Laser Speckle Flowgraphy During Aortic Arch Surgery With Antegrade Selective Cerebral Perfusion

OBJECTIVE The objective of this study was to evaluate the validity of ocular blood flow measured using laser speckle flowgraphy (LSFG) for the assessment of cerebral perfusion during aortic arch surgery. DESIGN A prospective study. SETTING A single university hospital. PARTICIPANTS The study included 17 patients undergoing aortic arch surgery with cardiopulmonary bypass (CPB) using antegrade selective cerebral perfusion (ASCP). INTERVENTIONS Measurement of ocular blood flow using LSFG. MEASUREMENTS AND MAIN RESULTS Measurement of ocular perfusion that is supplied mainly from the ophthalmic artery might be useful as an indicator of cerebral blood flow because the ophthalmic artery is the first branch of the internal carotid artery. Recently, LSFG has been developed for noncontact estimation of ocular perfusion using the laser speckle phenomenon. In this study, the LSFG system was used to measure blood flow in the optic nerve head during aortic arch surgery with CPB using ASCP. The blood flow in the optic nerve head during ASCP was statistically significantly reduced by 40.6% compared with the baseline value after anesthetic induction. CONCLUSIONS Ocular blood flow measured using LSFG showed favorable validity for assessment of cerebral perfusion during aortic arch surgery with ASCP.

Evaluation of the applicability of sevoflurane during post-tetanic myogenic motor evoked potential monitoring in patients undergoing spinal surgery

PurposeRecent evidence has indicated that post-tetanic motor evoked potentials (p-MEPs) can be used to improve the reliability of the monitoring of motor function during spinal surgery. However, data on p-MEP monitoring are limited to those in subjects under propofol anesthesia. The present study was conducted to assess the applicability of sevoflurane during p-MEP monitoring in patients undergoing spinal surgery.MethodsThirty-five patients undergoing spinal surgery under sevoflurane anesthesia were enrolled in the study and classified as being without preoperative motor deficits (n = 25) or with preoperative motor deficits (n = 10). For conventional MEP (c-MEP), transcranial train-pulse stimulation was delivered and the compound muscle action potentials were bilaterally recorded from the abductor pollicis brevis, abductor hallucis, tibialis anterior, and soleus muscles. For p-MEP, tetanic stimulation (50 Hz, 50 mA stimulus intensity) for 5 s was applied to the bilateral median and left tibial nerves 1 s prior to transcranial stimulation.ResultsThe amplitudes of p-MEP were significantly higher in all muscle recording sites than those of c-MEP in patients without motor deficits, whereas these amplitudes were significantly higher in only four of the eight muscles in patients with motor deficits (P < 0.05). The success rates of c-MEP and p-MEP recording were 48% and 64%, respectively, in patients without motor deficits and 30% and 60%, respectively, in patients with motor deficits. There were no statistically significant differences in success rates between c-MEP and p-MEP recording.ConclusionAlthough the application of tetanic stimulation prior to transcranial stimulation did not significantly increase the success rates of MEP recording, it significantly enlarged MEP amplitude under sevoflurane anesthesia in patients without preoperative motor deficits.

Recent advances in the monitoring of myogenic motor-evoked potentials: development of post-tetanic motor-evoked potentials

In 1937, Penfi eld and Boldrey [6] fi rst reported that limb and face movements in humans could be elicited by the electrical stimulation of the exposed motor cortex at a frequency of 50–60 Hz. In this technique, patients needed to have a craniotomy to stimulate the motor cortex. In 1980, Merton and Morton [7] reported that a high-voltage single electrical stimulus applied over the skull could activate the motor cortex, and consequently, myogenic MEPs could be obtained from the limbs in patients without a craniotomy. These techniques using single pulses for stimulation have been successfully performed in awake subjects. However, MEPs in response to electrical stimulation with a single pulse were very easily suppressed by most anesthetic agents. Early anesthetic techniques were limited to light anesthesia using narcotic-based or ketamine-based anesthesia. To overcome the anesthetic-induced suppression of myogenic MEPs, multiple-stimulus setups, with paired pulses or a train of pulses for stimulation have been introduced [1–5]. When descending impulses are inhibited, the temporal accumulation of several excitatory postsynaptic potentials (EPSPs) is required to bring motor neurons from the resting state to the fi ring threshold. Kalkman et al. [2] examined the effects of paired transcranial electrical stimulation on myogenic MEPs in anesthetized patients and demonstrated that maximum amplitude augmentation was observed with intersti mulus intervals between 2 and 5 ms. When the interstimulus interval was increased to 7 ms, no further augmentation was observed. Subsequently, a short train of electrical pulses over the scalp and exposed motor cortex has been shown to elicit MEPs successfully even under general anesthesia [3,4]. Multipulse transcranial Introduction

Evaluation of posttetanic motor evoked potentials--the influences of repetitive use, the residual effects of tetanic stimulation to peripheral nerve, and the variability.

Background Recently, we developed a new technique to augment myogenic motor evoked potentials (MEPs), called as posttetanic MEPs (p-MEPs), in which tetanic stimulation is applied to peripheral nerve before transcranial stimulation. However, the data on p-MEPs are limited. This study was conducted; (1) to evaluate the influences of repetitive use of p-MEPs on p-MEP amplitudes, (2) to evaluate the residual effects of use of p-MEPs on subsequent conventional MEPs (c-MEPs), and (3) to compare the variability of p-MEPs with that of c-MEPs. Methods Sixty patients under propofol/fentanyl anesthesia with partial neuromuscular blockade were enrolled. For p-MEP measurements, tetanic stimulation was applied to posterior tibial nerve 1 second before transcranial stimulation. In study 1, p-MEPs were repetitively recorded with intervals of 10 or 60 seconds. In study 2, the amplitudes of c-MEPs recorded 15, 30, 60, and 120 seconds after p-MEP recordings were compared with those of control. In study 3, the coefficients of variation of c-MEP and p-MEP responses were compared. Results The repetitive use of p-MEP with an interval of 10 seconds, but not 60 seconds, induced a significant reduction of p-MEP amplitude. Amplitudes of c-MEP were significantly increased when applied within 60 seconds after p-MEP recordings. The coefficient of variations of p-MEPs was similar to those of c-MEPs. Conclusions The results indicated that the amplitudes of p-MEP and c-MEP might be affected when applied with a short interval after p-MEP recording.

Asymptomatic and Symptomatic Postoperative Visual Dysfunction After Cardiovascular Surgery With Cardiopulmonary Bypass: A Small-Sized Prospective Observational Study

OBJECTIVE Postoperative visual dysfunction (POVD) after cardiovascular surgery rarely is reported, since it is more likely underdetected and underreported. This study was designed to verify the presence of POVD, including a variety of asymptomatic as well as symptomatic visual dysfunctions after cardiovascular surgery with cardiopulmonary bypass (CPB). DESIGN A prospective observational study. SETTING Cardiothoracic surgery in a medical university hospital. PARTICIPANTS Seventy-one patients undergoing elective cardiovascular surgery with CPB. INTERVENTIONS None. MEASUREMENTS AND MAIN RESULTS All patients were assessed by a battery of 7 neuro-ophthalmic examinations preoperatively and postoperatively, including fundus, visual field, eye movement, color vision, visual acuity, intraocular pressure, and critical flicker frequency. Patients were considered to have POVD if they had postoperative new abnormal findings of neuro-ophthalmic examinations. One patient was excluded due to a failure of postoperative neuro-ophthalmic examinations. In 16 of 70 patients analyzed in this study, selective cerebral perfusion was required for aortic arch surgery. Of 70 patients, a total of 8 patients (11.4%) had postoperative new abnormal findings in neuro-ophthalmic examinations, including new visual field deficits in 4, reduced visual acuity in 4, and/or increased intraocular pressure in 1 patient. Of these 8 patients, symptomatic POVD was recognized in 1 patient (1.4%) with postoperative visual field deficit and reduced visual acuity. There were no new abnormal findings compared with preoperative results in postoperative funduscopy, eye movement, color vision, and critical flicker frequency. CONCLUSIONS These results indicated that the asymptomatic as well as symptomatic POVD can develop after cardiovascular surgery with CPB, and their incidence may be relatively high.