Introduction
Intraoperative neurophysiologic monitoring is becoming standard monitoring in neurosurgeries. Motor evoked potential (MEP) monitoring is useful tool for precision of spinal surgeries minimising post-operative neurological complication and ensures better outcome. Evoked Potentials- Stimulus of nervous system produces the electrical potentials which measured as evoked potentials.1
These are of 2 type-
Sensory Evoked Potentials (SEP)- is the response to sensory stimulus.
Motor Evoked Potentials (MEP)- Stimulus to motor pathway is given and muscle activity is recorded. Muscle MEP allow selective assessment of the functional integrity of descending motor tracts, from the motor cortex to muscles.
For eliciting MEP, current is applied to the cerebral cortex or spinal cord directly or trans-cranially. Fine wire electrodes were placed within the muscles innervated by the motor nerve or surface electrodes over the muscles which help in recording peripheral response of MEP by measuring Compound Muscle Action Potential (CMAP).
The responses can be recorded in the spinal cord, peripheral nerve or in muscle as CMAPs.2 Reduction in motor response in the nerve and muscle occurs by the anesthetic agent and they may also affect anterior horn cells or neuromuscular junction.3 Narcotics have less effect than volatile anesthetics on MEP, responses may be obtunded completely by neuromuscular blocking drugs. Dexmedetomidine with TIVA has minimal effect on neuromonitoring.4 MEP amplitude was greater with Ketamine and propofol compared to only Propofol.5 There are no studies available comparing effect of Ketamine and Dexmedetomidine on MEP. Anesthetic agents have a dose dependent adverse effect on the ability to record evoked potential responses.6
Materials and Methods
This prospective, single blind, randomized comparative study was conducted after Institutional Ethical Committee Clearance and written informed consent from sixty adult patients of either sex, ASA grade I & II scheduled for elective thoracic or lumbar spine surgeries included in this study, were randomly divided into two groups- 30 in each using chit and box method. Group D- 30 patients received dexmedetomidine 0.5 microgram/kg lean body weight & Group K- 30 patients received ketamine 0.6 mg/kg lean body weight. Complete pre-anesthetic evaluation with necessary investigations were done a day before surgery. Before start of surgery all standard monitors attached and intravenous line secured. All patients received- injection glycopyrrolate 0.004 mg/kg, injection fentanyl 3microgm/kg and no anxiolytics. Induced with injection propofol 1.5-2mg/kg and endotracheal intubation was facilitated with injection succinylcholine 2mg /kg. Maintenance was done by infusion propofol @ 60mg/hr and 50% oxygen with air. A soft bite block was placed to avoid tongue bite. All electrodes for MEP monitoring were placed. Two corkscrew electrodes were placed 2 cm antero-lateral to coronal sutures for transcranial stimulation. Needle electrodes were placed in target belly muscle abductor pollicis brevis (thenar muscle), rectus abdominis, quadriceps, tibialis anterior and adductor hallucis longus based on the surgical procedure and spinal level involved for CMAP recording. Transcranial electrical stimulus (6 pulses, 4 mili-second (ms) apart; intensity, 750 V; duration of each pulse, 0.5 ms) given. CMAP are recorded with needle electrodes from target belly muscle in all four limbs. Based on the surgical procedure and spinal level involved, muscles were selected. Readings of MEP recordings in abductor pollicis brevis (thenar muscle) of upper limb were used for the study. Though MEP changes were observed bilaterally in rectus abdominis, quadriceps, tibialis anterior and adductor hallucis longus. After positioning of patient, transcranial stimulus was given to record baseline MEP. In all patients the current of stimulus (750V) was kept same. Study drug prepared by anaesthetic technician in 100 ml Normal Saline was infused over a period of 10minutes. At completion of the infusion MEP recorded at 0 min and every 5 min. for 30 min.
Results
The collected data were analysed with IBM.SPSS statistics software 23.0 Version and p value < .05 was considered significant. To describe about the data descriptive statistics frequency analysis, percentage analysis was used for categorical variables and the mean & S.D were used for continuous variables. To find the significant difference between the bivariate samples in Independent groups the unpaired sample t-test was used. To find the significance in categorical data Chi-Square test was used.
The demographic data with respect to age, sex, height, weight and ASA grading were similar in both the groups. There was no significant change in MAP in both the groups and mild variations in SBP observed in ketamine group. Amplitude was significantly higher in ketamine group.
Table 1
Demographic distribution
Table 2
Intraoperative monitoring
Table 3
Amplitude and percentage with baseline
Discussion
Motor Evoked Potentials (MEP) is used for assessment of functions of motor cortex and descending tracts and for monitoring the prevention of neuronal injury during neurosurgical procedures.
Unsuspected and unpleasant neurological deficit after spinal surgery can be prevented by the use of intraoperative MEP monitoring. Various pharmacological and physiological factors affects MEP, such as – Inhaled anaesthetics reduce the amplitude and increases latency, intravenous anaesthetics have the same effect but to a lesser degree, barbiturates suppresses myogenic MEP etc.
There was no significant change in MAP in both the group at any point of time in our study while a study done by P. Chauhan et al7 found more than 20% fall in HR and no change in their study using ketamine with dexmedetomidine and fentanyl.
In our study we found that the SBP (mm/hg) of both the groups at different times varied in their statistical significance. In both groups, baseline, at 0min, 5mn, 20min, & 25 min SBP values were statistically insignificant. At 10 & 30 min SBP value of both the groups were statistically significant. At 15 min the SBP value of both drugs was highly significant. In ketamine group SBP was significantly higher than dexmedetomidine while DBP (mm/hg) of both the groups at different times of observation were statistically insignificant from baseline to 30 min.
In both groups, baseline Amplitude were similar. At 0min & 30 min amplitude was significantly higher in the ketamine group than dexmedetomidine group. At 5min, 10min, 15 min, 20 min, 25 min the amplitude was higher in the ketamine group than dexmedetomidine group which was highly significant. In a study done by Tobias et al4 found decrease in the MEP amplitude using dexmedetomidine, similar result was shown in our study. A study done by Kalkaman8 using ketamine found increase in the amplitude of MEP by 150-250% within 10 minutes of injection, we also found similar rise in amplitude.
The changes in Amplitude of both the groups according to the percentage with baseline were insignificant. In a study done by Sheng Lin et al9 to elicit the effect on somatosensory and motor evoked potentials in patients undergoing spinal surgery using dexmedetomidine- etomidate – fentanyl combined anesthesia. They concluded that TIVA using combined agents as mentioned above may be safely administered in spine surgeries. In our study we used ketamine with propofol (Group K) and propofol with dexmedetomidine (GroupD) and found that these drugs can be used safely in spinal surgeries. Penney et al10 in their case report stated that dexmedetomidine and ketamine infusions as a combination can be used as an alternative to propofol based TIVA during scoliosis repair surgery with intraoperative somatosensory evoked potential and MEP monitoring. We did a similar study in spinal surgeries using ketamine with propofol and dexmedetomidine with propofol and found both drugs can be used safely during TIVA. Kawaguchi et al11 in their study concluded that if a train of pulses were used for transcranial stimulation, low dose propofol can be effectively used as a supplement to ketamine-based anesthesia during intraoperative monitoring of myogenic MEPs. And also, they concluded that addition of propofol significantly reduced the ketamine induced psychedelic effects. In our study also we found similar results using ketamine with propofol.
Regarding the use of dexmedetomidine and ketamine for MEP recording during general anesthesia with TIVA, the results of most of the above-mentioned studies matches to the result our study.
Conclusion
We concluded that mean amplitude was higher in ketamine than dexmedetomidine group but when amplitude was compared with baseline of respective group there was no statistically significant difference between both the groups. Also, both the agents are equally good as they cause minimal depression and are equally efficient in measuring the amplitude of MEP.