Hala El-Habashy et al.

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1 Hala El-Habashy et al. Role of Motor Evoked Potential in The Predictability of Surgical Outcome of Herniated Disc Induced Cervical Myelopathy Under Different Anesthetic Techniques Hala El-Habashy 1, Ayman M. El-Badrawy 2, Mohamed Esawy 2, Hisham Hozian 3, Yasser El-Gohary 2 Departments of Clinical Neurophysiology 1, Anesthesia 2, Neurosurgery 3, Cairo University ABSTRACT Background: Intraoperative motor evoked potentials (MEPs) application provides a method for monitoring the functional integrity of motor pathways. However, these potentials are sensitive to suppressive effect by most anesthetic agents. The aim of the work: To evaluate the role of transcranial electrical motor evoked potentials (TceMEPs) in predicting motor system affection and surgical outcome during anterior cervical microdiscectomy operations and comparing the outcome under two anesthetic regimens (propofolfentanyl) versus (sevoflurane-n 2 O). Subjects and Methods: This study included 60 patients divided into two groups (I, II). Anesthetic plane was induction by propofol and use of atracurium for intubation and muscle relaxation in predetermined doses. Maintenance of anesthesia in group (I) was by (propofol-fentanyl) infusion and in group II by (sevoflurane-n 2 O). During operation TceMEPs monitoring with myogenic recoding of compound motor action potentials (CMAPs) from the four limbs was done. Results and Conclusions: we found that; (CMAPs) recorded under (sevoflurane-n 2 O) anesthesia had statistically significant lower amplitude than that recorded during (propofol-fentanyl) one, whereas both regimens had minimal non-significant prolongation of latencies. However, multipulse TceMEPs monitoring with myogenic recording remained stable throughout the operation under both regimens provided that the degree of anesthesia and analgesia were kept constant. Also, TceMEPs monitoring with myogenic recording of CMAPs alone could only point to harmful surgical manipulations but could not determine how much these manipulations will progress to permanent postoperative motor deficit. Recommendations: It is suggested that multipulse TceMEPs with epidural and myogenic recordings will show high degree of accuracy in predicting post-operative motor deficit. (Egypt J. Neurol. Psychiat. Neurosurg., 2006, 43(1): 49-62) INTRODUCTION Concerning MEPs, monitoring of the functional integrity of motor tract within the spinal cord is a technique with great benefit. Loss of motor function during spinal or vascular surgery without loss of sensory function or change in somatosensory evoked potentials (SSEPs) can occur 1. As SSEPs recorded from the brain are carried solely within the dorsal column of the spinal cord, SSEP monitoring may fail to detect damage to the spinal cord motor pathways, and techniques for directly monitoring the motor pathways have been developed, Transcranial magnetic brain stimulation is useful for extraoperative evaluation of the motor system but anesthetic effects on cortical synaptic activity limit its usefulness for intraoperative monitoring 2. 49

2 Egypt J. Neurol. Psychiat. Neurosurg. Vol. 43 (1) Jan 2006 Multipulse transcranial electrical stimulation uses a short train of high-frequency stimuli producing several corticospinal volleys that summate to depolarize spinal motor neurons, producing muscle responses specific to motor pathways 3-7. This method provides individual limb assessment throughout the entire procedure, and is applicable to all levels. These responses benefit from Total Intravenous Anesthesia (TIVA) using narcotic with propofol, midazolam, ketamine, or etomidate 8. In neurosurgical spinal endovascular and thoracoabdominal aortic aneurysm procedures, multiple-pulse TceMEPs has been shown to provide rapid and sensitive motor assessment and correlated with outcome, but has been applied infrequently in orthopedics 9,8. Anatomical, theoretical, experimental, and clinical foundations and the absence of reported adverse effects have prompted the authors institution to adopt transcranial electrical stimulation for intraoperative motor pathway monitoring. Contrary to SSEP methods, Transcranial electrical stimulation for MEPs does not use supra-maximal stimuli. Consequently, when anesthesia deepens or accumulates, additional lower motor neuron suppression may cause fading or disappearance of muscle responses to the initially chosen stimulus parameters. Therefore, it is not surprising that increasing intensity or pulse number may sometimes be necessary to maintain responses in the face of evolving systemic effects. Paired pulses or a train of pulses have been effectively used for stimulation in intraoperative MEP monitoring 10,11. PATIENTS AND METHODS Patients This study included two groups of patients each 30 in number and carried out in the neurosurgical theater in Kasr El-Aini Hospital after achieving the consent of the patients and the approval of the Ethics and Research Committee (ERC) of Anesthesia Department of faculty of medicine in Cairo University. The age of patients in group I (propofol- fentanyl) ranges from year (mean 43.10, standard deviation 8.45). The age of patients in group (II) (Sevoflurane N 2 O ) ranges from year (mean SD 10.57). Group I included 21, 9. Group II included 20, 10. The patient in this study fulfilled a number of inclusion, exclusion criteria and certain preparation which were: I. Inclusion Criteria: Patient with motor affection due to herniated disc induced cervical myelopathy. The surgery was anterior cervical microdiscectomy. Age between years old. American Society of Anesthesiologist (ASA) class I or Π. II. Exclusion Criteria: History of epilepsy. Hypertensive patient. Neurological disorder other than cervical compression myelopathy. Previous cranial operation. Patient with intracardiac pacing devices. III. Preoperative Preparation: All patients would be cannulated with 18- gauge peripheral venous cannula. Premedication with midazolam 2 mg I.V. 15 minutes before induction of anesthesia. Site of insertion of stimulating and recording devices would be cleaned out by alcohol 70% then brushed with Ether. IV. Anesthetic Management: A. Induction of Anesthesia Induction of anesthesia in all patients in the two groups would be the same as follows: Propofol 1-2 mg/kg I.V. Fentanyl 2-3 µg/kg I.V. Muscle relaxation with atracurium mg/kg to facilitate tracheal intubation followed by mechanical ventilation with tidal volume of 7-10 ml/kg, respiratory rate breaths/min, inspiration to expiration ration (I:E ratio) 1: 3 50

3 Hala El-Habashy et al. B. Maintenance of Anesthesia: Patients divided into two groups each group includes 30 patients: 1. Group I: In this group, anesthesia would be maintained with propofol infusion (200 µg/kg/min. for 10 min.), then 150 µg/kg/min for another 10 min. followed by 100 µg/kg/min till end of operation. Analgesia would be provided with incremental doses of fentanyl 50 µg I.V. when needed as indicated. 2. Group II: Anesthesia in this group will be maintained by sevoflurane 1%, N 2 O 60% and oxygen 40%. N.B.: In the two groups, putting a paded oral airway with suitable size would be a must as during stimulation the patient might pit his or her tongue due to contraction of masseter muscles. V. Monitoring: All patients in this study monitored as following: ECG: 5 lead ECG. Blood pressure: non-invasive. Pulse oximetry: Oxygen saturation, heart rate. End tidal CO 2. Temperature: Core temperature through nasopharyngeal probe. Neuromuscular block monitoring: Partial neuromuscular blockade was necessary in order to prevent patient movement (either from transcranial stimulation or surgical maneuvers) that may interfere with the micro surgical procedure. VI. Evaluation and Grading of Motor Power of Patients: Each patient was evaluated pre and postoperatively. It was a must to find one grading system which was familiar to all persons participated in this study (anesthetist, Neurosurgeon, neurophysiologist). This system of grading was obtained from British Medical Research Council Scale 12. It would applied on each limb Equipments: I. The Stimulating device: The stimulating device in this study was EPOCH 2000 (Axon Systems Hauppauge, New York). II. The stimulating electrodes: We used cork-screw subdermal stimulating electrodes. The sites of these stimulating electrodes were as follow: A. For upper limb stimulation: The negative electrode was at Cz. The positive electrode of right upper limb was at 1 cm in front of C3. The positive electrode of left upper limb was at 1 cm in front of C4. B. For lower limb: The negative electrode was at Cz. The positive electrode of both lower limbs was at 6 cm in front Cz. N.B.: Cz, C3, C4 from international system of electrode placement for recording EEG III. Recording Electrodes: For recording, we used subdermal needle electrodes (1.5 cm stainless steel needle) The sites of these recording electrode were as follows: A. Upper limb: Two needles would be inserted in each thenar muscle 3 cm a part. The positive electrode is distal to reference electrode B. Lower limbs: Two needle electrodes would be inserted in each tibialis anterior muscle 3 cm apart. The positive electrode is distal to reference electrode 51

4 Egypt J. Neurol. Psychiat. Neurosurg. Vol. 43 (1) Jan 2006 N.B.: The recording electrodes would be 50 cm apart from the earthing pad of diathermy. The earthing cable of the stimulating device would be away from the earthing pad of diathermy by 50 cm. IV. Stimulus Parameters: The stimulus parameters were as follows: Type: Train Stimulation mode: manual (non repetitive) Polarity: Normal Train rate (pulse/sec.): 200 Train duration: 25 m.sec Pulse duration: 0.5 m.sec Train count: 5 Inter pulse duration: 4.5 m.sec Voltage: 350 volt Current: 100 ma Time between each train 30 seconds as safety margin locking time V. The recording parameters The recording parameters were as follows: Sweep length: 100 m.sec. Time base: 5-10 m.sec/div. Delay: Zero Signal to Noise Ratio (SNS) 100/10 µv Number: 1 Filtering: - Low frequency filter LFF: 100 Hz - High frequency filter HFF: 5000 Hz Artifact rejection level: 10 µv. Methodology & Data Collection and Data Analysis: I. Methodology and Data Collection The stimuli and so the recordings of (CMAPs) have collected at five different time intervals: - 1 st reading (baseline I): before induction of anesthesia. - 2 nd reading (baseline II): 5 min. after induction of anesthesia and before surgical manipulation and instrumentation - 3 rd reading: During surgical manipulation and instrumentation - 4 th reading: after completion of surgical manipulations on the spine. - 5 th reading: 5 min. after reversal of muscle relaxant N.B.: As the transcranial electrical stimulation is severely painful the first stimulus (before induction of anaesthesia) has been done under analgesic dose of ketamine mg/kg I.V. as ketamine in the only drug which does not affect the amplitude or latency of MEP (CMAPs) 13. II. Statistical Analysis: Data will be analyzed on an IBM compatible computer using SPSS win, Ver. 9 statistical package. Numerical data will be described in terms of means and medians for central tendency and standard deviation and range for dispersion. Categorical data will be described in terms of count and percentages. For comparison between the two study groups student t-test, Chi-square or their nonparametric counterpart will be used as appropriate. Probability (p-value) of less than 0.05 will be considered to be significant. RESULTS Data Description: I. Age: On comparison between the group I (propofol-fentanyl) and group II (Sevoflurane-N 2 O) as regard the age P. value was (i.e. > 0.05) II. Sex: On comparison between group I, group II as regard sex the P. value was (i.e. >0.05). III. ASA class: On comparison between group I, II as regard ASA class P. value was (i.e. >0.05) N.B.: For the following records (latency & amplitude & motor Power grading) we consider each limb as a separate entity i.e. each patient considered four patient (as every patient had four limbs), so by this method we had two groups each contained 52

5 Hala El-Habashy et al. 120 patient. (30 X 4=120). Also we divide each group (120 limb) into two subgroup (a, b) (a: upper limbs, b: Lower limbs) each of them contain IV. Latency: Readings of latencies in each group shows that: a. On comparison between mean latency change after all stimuli in group I (a, b) p. Value was < b. On comparison between mean latency change after all stimuli in group II (a, b) p. value was <0.05 c. On comparison between percentage of mean latency change in group I after all stimuli, results were as follow, table 1 and 2. d. On comparison between percentage of mean latency change in group II after all stimuli results were as follow in table 3 and 4. e. On comparison of percentage of mean latency change between group I, II before and after use of anesthetics p. value was > 0.05 (insignificant). V. Amplitude: Readings of amplitudes of (CMAP) in each group shows that: a. On comparison between mean amplitude after all stimuli in group I (a, b) p. Value was < b. On comparison between mean amplitude after all stimuli in group II (a, b) p. Value was <0.05. c. On comparison between percentage of mean amplitude change in group I after all stimuli, results were as follow, table 5 and 6. d. On comparison between percentage of mean amplitude change in group II after all stimuli, results were as follow, table 7 and 8. e. On comparison of percentage of mean amplitude change between group I,II before and after use of anesthetics, p. value was < 0.05 (significant) with incidence of decrease in mean amplitude of (CMAPs) in group II more than that group I. VI. Motor Power grading: The records of motor power grading for each group (group I: Propofol-fentanyl / Group II: sevoflurane-n 2 O) are listed as follow: Important Observations: 1. There was one patient (4 limbs) in whom we could not perform this test (TceMEPs) with myogenic recording, this most probably attributed to technical errors (earthing, amplification, filtering,. etc). 2. On comparison between patient (limbs) as regard changes in latencies recorded after stimulus (2), stimulus (3) and stimulus (4) we found that as in Table (13). 3. On comparison between patient (limbs) as regard changes in amplitude recorded after stimulus (2), stimulus (3) and stimulus (4) we found as in Table (14). The forty patients deteriorated during surgical manipulation progress as follows in Table (15). Table 1. Shows% of mean latency change in group I for upper limbs. Group I (Propofol fentanyl) a: upper limbs Median % Minimum % Maximum % Latency %change 1 (from stim. 1 to stim. 2) Latency %change 2 (from stim. 2 to stim. 3) Latency %change 3 (from stim. 3 to stim. 4) Latency %change 4 (from stim. 4 to stim. 5) Latency %change 5 (from stim. 1 to stim. 5) Latency %change 6 (from stim. 2 to stim. 4)

6 Egypt J. Neurol. Psychiat. Neurosurg. Vol. 43 (1) Jan 2006 Table 2. Shows % of mean latency change in group I for lower limbs. Group I (Propofol fentanyl) a: lower limbs Median % Minimum % Maximum % Latency %change 1 (from stim. 1 to stim. 2) Latency %change 2 (from stim. 2 to stim. 3) Latency %change 3 (from stim. 3 to stim. 4) Latency %change 4 (from stim. 4 to stim. 5) Latency %change 5 (from stim. 1 to stim. 5) Latency %change 6 (from stim. 2 to stim. 4) Table 3. Shows % of mean latency change in group II for upper limbs. Group II (sevoflurane N 2 O) a: upper limbs Median % Minimum % Maximum % Latency %change 1 (from stim. 1 to stim. 2) Latency %change 2 (from stim. 2 to stim. 3) Latency %change 3 (from stim. 3 to stim. 4) Latency %change 4 (from stim. 4 to stim. 5) Latency %change 5 (from stim. 1 to stim. 5) Latency %change 6 (from stim. 2 to stim. 4) Table 4. Shows % of mean latency change in group II for lower limbs. Group II (sevoflurane N 2 O) a: lower limbs Median % Minimum % Maximum % Latency %change 1 (from stim. 1 to stim. 2) Latency %change 2 (from stim. 2 to stim. 3) Latency %change 3 (from stim. 3 to stim. 4) Latency %change 4 (from stim. 4 to stim. 5) Latency %change 5 (from stim. 1 to stim. 5) Latency %change 6 (from stim. 2 to stim. 4) Table 5. Shows % of mean amplitude change in group I for upper limbs. Group I (Propofol fentanyl) a: upper limb Median % Minimum % Maximum % Amplitude %change 1 (from stim. 1 to stim. 2) Amplitude %change 2 (from stim. 2 to stim. 3) Amplitude %change 3 (from stim. 3 to stim. 4) Amplitude %change 4 (from stim. 4 to stim. 5) Amplitude %change 5 (from stim. 1 to stim. 5) Amplitude %change 6 (from stim. 2 to stim. 4)

7 Hala El-Habashy et al. Table 6. Shows% of mean amplitude change in group I for lower limbs. Group I (Propofol fentanyl) b: lower limb Median % Minimum % Maximum % Amplitude %change 1 (from stim. 1 to stim. 2) Amplitude %change 2 (from stim. 2 to stim. 3) Amplitude %change 3 (from stim. 3 to stim. 4) Amplitude %change 4 (from stim. 4 to stim. 5) Amplitude %change 5 (from stim. 1 to stim. 5) Amplitude %change 6 (from stim. 2 to stim. 4) Table 7. Shows % of mean amplitude change in group II for upper limbs. Group I (sevoflurane N 2 O) a: Upper limb Median % Minimum % Maximum % Amplitude %change 1 (from stim. 1 to stim. 2) Amplitude %change 2 (from stim. 2 to stim. 3) Amplitude %change 3 (from stim. 3 to stim. 4) Amplitude %change 4 (from stim. 4 to stim. 5) Amplitude %change 5 (from stim. 1 to stim. 5) Amplitude %change 6 (from stim. 2 to stim. 4) Table 8. Shows% of mean amplitude change in group II for lower limbs. Group I (sevoflurane N 2 O) b: lower limb Median % Minimum % Maximum % Amplitude %change 1 (from stim. 1 to stim. 2) Amplitude %change 2 (from stim. 2 to stim. 3) Amplitude %change 3 (from stim. 3 to stim. 4) Amplitude %change 4 (from stim. 4 to stim. 5) Amplitude %change 5 (from stim. 1 to stim. 5) Amplitude %change 6 (from stim. 2 to stim. 4) Table 9. Preoperative motor power grading (group I). Group I (Propofol + fentanyl) Frequency Percent Grade % Grade % Grade % Grade % Grade % Total % 55

8 Egypt J. Neurol. Psychiat. Neurosurg. Vol. 43 (1) Jan 2006 Table 10. Post operative motor power grading (group I). Group I (Propofol + fentanyl) Frequency Percent Grade % Grade % Grade % Grade % Total % Table 11. Preoperative motor power grading (group II). Group II (Sevoflurane + N 2 O) Frequency Percent Grade % Grade % Grade % Grade % Grade % Grade % Total % Table 12. Post operative motor power grading group (II). Group II (Sevoflurane + N 2 O) Frequency Percent Grade 2 6 5% Grade % Grade % Grade % Grade % Grade % Missing system 4 3.3% Total % Table 13. No deterioration during surgical manipulations Deterioration during surgical manipulations (latency 10%) Return to 100% of base time II after stopping surgical manipulations 230 (from 236) 6 (from 236) 6 (from 236) 97.46% 2.54% 2.54% Table 14. No deterioration during surgical manipulations Deterioration during surgical manipulations (amplitude 50%) % 16.95% 56

9 Hala El-Habashy et al. Table 15. Return to 100% of base line II after stopping surgical manipulation Return to 75% of base line after stopping surgical manipulation % 50% 40% Sustained deterioration till end of surgery Stim. 3: During Decompression and Retraction Group II (Sevoflurane + N 2 O). Stim. 4: After Decompression and Stoppage Group II (Sevoflurane + N 2 O). 57

10 Egypt J. Neurol. Psychiat. Neurosurg. Vol. 43 (1) Jan 2006 DISCUSSION The intraoperative MEPs largely depends on the stimulation pattern and anesthetic technique, further improvement in intraoperative MEP recording requires exact knowledge of the modifying effects of each of these factors 14. The aim of this work is to evaluate the role of motor evoked potentials in response to multipulse transcranial electrical stimulation in predicting motor system affection and surgical outcome during anterior cervical microdiscectomy in patients with herniated disc induced cervical myelopathy and to compare the outcome under two anesthetic regiments (Propofol-fentanyl) versus (sevoflurane-n 2 O). This study included two groups of patients each 30 in number; group (I) under (Propofol-fentanyl) anesthesia and group (II) under (sevoflurane-n 2 O) anesthesia. On comparing between group I, group II there were no significant effect of age, sex, and ASA class on results as P. value was <0.05. There was one patient (four limbs) in whom this test (TceMEPs with myogenic recording) could not be performed, but, this may be attributed to technical errors, (earthing, amplification, filtering etc). The current study showed that, the presence of preoperative paresis had no significant influence on repetitive TceMEPs monitoring as a baseline (I) recording at start of operation and baseline (II) recording after induction of anesthesia could be obtained. These two baseline recordings used as reference for detecting any change after starting anesthesia and after starting surgical manipulations respectively. This is confirmed by other study which assumed that; in the presence of preoperative paresis, the TceMEPs monitoring applicability is reduced but there is no influence on the intraoperative pattern of MEPS 15. Concerning the effects of anesthesia on intraoperative TceMEPs monitoring; this study, showed that anesthesia in group I (Propofol- Fentanyl) did not prevent recording of (CMAPs) after multipulse TceMEPs, but (Propofol- Fentanyl) anesthesia produced statistically significant increase in latency of (CMAPs) [by median (+3%) for upper limbs and (+3.26%) for lower limbs]. Also (propofol-fentanyl) regiment of anesthesia produced statistically significant decrease in amplitude of (CMAPs) [by median ( 9.12%) for upper limbs and (-9.38%) for lower limbs]. With anesthesia in group II (Sevoflurane- N 2 O), recording of (CMAPs) after multipulse TceMEPs was not prevented but (Sevoflurane- N 2 O) produced statistically significant increase in latency of (CMAPs) [by median (+2.94%) for upper limbs and (+3.28%) for lower limbs]. Also (Sevoflurane-N 2 O) anesthesia produced statistically significant decrease in amplitude of (CMAPs) [by median (-11.99%) for upper limbs and (-12%) for lower limbs]. On comparing the effects of anesthetics between group I and group II, it is noticed that (Propofol-Fentanyl) regiment produced statistically insignificant prolongation of latency of (CMAPs) compared to the recorded under (Sevoflurane-N 2 O) regiment. Also (Sevoflurane-N 2 O) regiment produced statistically significant decrease in (CMAPs) amplitude more than that recorded under (Propofol-Fentanyl) regiment. These results are in agree with many previes studies In another study 16 which performed intraoperative TceMEPs monitoring using multipulse stimulation under propofol anesthesia and demonstrated that propofol anesthesia caused a reduction of (CMAPs) amplitude to 7% of baseline recording. It was found that propofol reduced TceMEP amplitude in a dose dependant manner when using a multipulse stimulation with a constant intensity and number of stimuli. Indeed, doubling the propofol concentration in blood from 0.7 mg litre -1 to 1.4 mg litre -1 may reduce (CMAPs) amplitude by 30-50% 20. Previous authors found that motor neuron excitability is markedly impaired when target propofol concentrations reaching 0.9 mg litre On the other hand TceMEP latencies were minimally influenced by propofol concentrations commonly used to maintain a deep anesthesia and remained stable during the whole operations 16. Previous studies using multipulse TceMEPs reported that nitrous oxide at concentrations 58

11 Hala El-Habashy et al. above 50% reduced significantly the amplitude of (CMAPs) but did not prevent monitoring in the large majority of operations 19. This is consistent with earlier studies using multipulse TceMEPs 18. Short trains of anodal stimuli delivered to the exposed motor cortex, succeeded in monitoring myogenic MEPs during sevoflurane-n 2 O anesthesia 22. It is likely that the depressant effect of sevoflurane-n 2 O during multipulse TceMEPs monitoring is dose dependant 23. CMAPs recorded under (Sevoflurane-N 2 O) anesthesia had lower amplitude and higher trial to trial variability than CMAPs recorded during (Propofol-Fentanyl) anesthesia. Sevoflurane had minimal effect on CMAP latencies 4.In conclusion it is assumed that "provided that the degree of general anesthesia and analgesia were kept constant" multipulse TceMEPs with myogenic recording remained stable throughout the operation under both regiment of anesthesia (Propofol-fentanyl/ Sevofuran-N 2 O). Nevertheless CMAPs recorded under (Sevoflurane-N 2 O) regiment of anesthesia had lower amplitude and higher trial to trial variability than CMAPs recorded during (Propofol-fentanyl) one whereas both regiment had minimal non-significant prolonging effect on latencies. These data are comparable with data obtained from current study except for effects of both regiment of anesthesia on latencies of CMAP that demonstrate statistically significant prolongation of latencies. This may be attributed to difference in doses of given anesthetics or differences in stimulus intensity. A dose effect relationship was not investigated in current study. Consequently, an exact knowledge of the effects of increasing concentrations of these anesthetics on TceMEPs with myogenic recording is needed to avoid the erroneous conclusion that intraoperative changes in TceMEPs during surgical maneuvers represent spinal cord injury. Concerning the role of intraoperative TceMEPs monitoring in prediction of new injury to spinal cord as regard motor pathways: on comparing between changes of mean latencies and mean amplitudes of CMAPs recorded before and during surgical manipulations (after stimuli 2 and 3 respectively). This study showed that the mean latencies did not increase by more than 10% and mean amplitude did nor decrease by more than 50%, so there were no significant risk of deterioration during this type of surgery (Anterior cervical microdiscectomy). This may be attributed to the high degree of safety of surgical maneuver. However, we could not calculate the sensitivity and specificity of this test (TceMEPs with myogenic recording) as we had no single patient with new postoperative motor deficit. Nevertheless we had less than 2% false positive recordings during surgical manipulations. Also we found that during decompression and surgical manipulation, 2.5% of cases showed deterioration by increase in latency of CMAP > 10% and all these patient returned to their original recordings of latency after completion of cervical spinal cord decompression with no new postoperative motor deficit. Also during decompression and surgical manipulation, 17% of cases showed deterioration by decrease in amplitude of CMAP > 50%, only 1.6% of them returned to 100% of their original recordings, 8% returned to 75% of their original recordings and 7.4% showed sustained deterioration till end of surgery with no new postoperative motor deficit in all patient. This apparently makes TceMEPs with myogenic recording a test that can only point to harmful manipulations but can not alone determine how much these harmful manipulations will progress to permanent postoperative motor deficit. Several investigators have reported clinical and experimental parameters of intraoperative TceMEPs monitoring using CMAPs recording. These authors referred to the threshold of the changes in CMAPs as indicators for the detection and prevention of neurologic injury 24,25. They insisted that an amplitude reduction of 50% should be the threshold. In another study 26, which performed a detailed experiment using animal models of scoliosis and concluded that a 10% delay in onset latency would be an appropriate threshold. Clinically the critical point should be defined at a point yielding a 10% latency delay or 59

12 Egypt J. Neurol. Psychiat. Neurosurg. Vol. 43 (1) Jan 2006 disappearance of CMAPs. The parameter monitored in muscle MEP (CMAP) recording was the presence or absence of responses. This all-ornone concept has been adopted for two reasons. Firstly in contrast to epidural MEPs that show little amplitude variation 27, the variability of muscle MEP amplitude is tremendous 28. Thus, defining a threshold amplitude below which one expects an intraoperative injury would be extremely difficult. Secondly; the analysis of the available reports indicated that a motor deficit occurred only when the muscle response was lost 18. The repetitive trans-cranial electrical stimulation with epidural and myogenic recoding was found to be highly accurate for predicting postoperative motor deficit. The sensitivity and specificity values of this technique were 1 and 1 respectively 29. This is consistent with results of current study which showed that TceMEPs with myogenic recording of CMAPs alone could only point to harmful manipulations but could not determine how much these harmful manipulations will progress to permanent postoperative motor deficit. So it is assumed that multipulse TceMEPs with epidural and myogenic recordings will show high accuracy on predicting postoperative motor deficit. Using this highly reliable method, existing surgical procedures can be safely performed, and the possibility of performing more aggressive surgical procedures in the further is anticipated. Finally we conclude that, TceMEPs, monitoring is very labile test for many reasons, the most important of them are technical difficulties; therefore this test must be done with close attendance of experienced personells. A dose-effect relationship was not investigated in this study. Consequently, an exact knowledge of the effect of increasing concentrations of these anesthetics on TceMEPs with myogenic recording is needed to avoid the erroneous conclusion that intraoperative changes in TceMEPs during surgical maneuvers represent spinal cord injury. Also It is recommended to perform this test (TceMEPs) on other types of surgery that require spinal cord monitoring by both MEPs, SSEPs such as, operations on thoracoabdominal aorta, operations for correction of spinal deformity, operations for post-traumatic spine injury and operations within spinal cord (spinal cord tumors). With knowledge of physics, techniques and safety issues of neurophysiological monitoring, the field will continue to proliferate and assist surgeons alleviating human suffering. REFERENCES 1. Deletis V, Vodusek D, Abbott R, et al. (1992): Intraoperative monitoring of the dorsal sacral roots: Minimizing the risk of iatrogenic micturition disorders. Neurosurgery, 30: Legatt AD. (2004): Ellen R. Grass Lecture: Motor evoked potential monitoring. Am J Electroneurodiagnostic Technol; 44(4) : Rodi Z, Deletis V, Morota N, et al. (1996): Motor-evoked potentials during brain surgery. Pflugers Arch, 431 (6 Suppl 2):R Calancie B, Hams W, Bioton JG, el al. (1998): Threshold-level multipulse transcranial electrical stimulation of motor cortex for intraoperative monitoring of spinal motor tracts: description of method and comparison to somatosensory evoked potential monitoring J Neurosurgery 88: Cioni B, Meglio M, Rossi GF (1999): Intraoperative motor-evoked potentials monitoring in spinal neurosurgery. Arch Ital Biol, 137: Deletis V, Isgum V, Amassian VE (2001): Neurophysiological mechanisms underlying motor-evoked potentials in anesthetized humans: Part 1. Recovery time of corticospinal tract direct waves elicited by pairs of transcranial electrical stimuli. Clin Neurophysiol, 112: , 7. Deletis V, Rodi Z, Amassian VE (2001): Neurophysiological mechanisms underlying motor-evoked potentials in anesthetized humans: Part 2. Relationship between epidurally and muscle recorded MEPs in man. Clin Neurophysiol, 112: Pelosi L, Stevenson M, Hobbs GJ, Jardine A, Webb JK (2001): Intraoperative motor evoked potentials to transcranial electrical stimulation during two anaesthetic regimens. Clinical Neurophysiology 112:

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14 Egypt J. Neurol. Psychiat. Neurosurg. Vol. 43 (1) Jan 2006 الملخص العربي