Anesthesia.
Anesthesiology as the Practice of Perioperative Medicine.
- The role of the Neuro-Anesthesiologist during procedures where intraoperative neuro-electrophysiological monitoring {IONM} is being performed involves anesthetic titration, attaining physiological homeostasis, and medical management of the patient. Further the anesthesiologist participates in mitigating neural injury when the monitoring indicates that the nervous system may be at risk for injury. More specifically, the choice of anesthetic agents directly impacts the ability to reliably record IONM responses, and the physiological management {like blood pressure} impacts on the reserve of the nervous system to tolerate procedural trespass. When altered responses indicate the health of the nervous system may be compromised, the insights of the anesthesiologist and the ability to improve the physiological reserve are keys to reducing neurological risk.
Types of Anesthesia.
General Anesthesia divided in two category .
- MAC -Monitored anesthesia care.
- TIVA- Total Intravenous Anesthesia .
- LA-Local Anesthesia .
Inhalation Drugs {like Sevoflurane, Desflurane ,Isoflurane,N2O etc}.
- These type of drugs are known to affect evoked potentials, such as SSEPs and MEPs, by dose-dependently decreasing their amplitudes and increasing latency.
- Higher doses of inhaled anesthetics can result in more pronounced effects on evoked potentials, potentially leading to global changes of signal or difficulty interpreting the monitoring data accurately.
- Careful titration of inhaled anesthetics is crucial to maintain an appropriate balance between anesthesia depth and preserving neurophysiological signals during surgery.
- As per literature 0.5 MAC acceptable to record MEP only in intact neurological conditions like cosmetic surgery { scoliosis } but will not be preferable in moderate to severe myelopathy type of spine surgery also not acceptable in direct motor cortical stimulation because of its, threshold of stimulation will require more. possibility of high electrical discharges cause seizure.
Intravenous Anesthesia {like Propofol, Dexmedetomidine, Etomidate, ketamine etc}
- Intravenous drugs like propofol generally have less impact on evoked potentials compared to inhaled anesthetics because this is less potent drug compare gas . However, high doses can still suppress these signals. usually acceptable dose of propofol 120mcg-150mcg/kg/minute.
- Propofol, for instance, may decrease SSEP amplitudes but usually has a minor effect on MEPs.
- Etomidate is known for its relatively stable effects on evoked potentials, making it a preferred choice in some neurosurgical procedures where IONM is critical.
- Dexmedetomidine also very good drug along with propofol as a supplementary , only draw back of this drug is poor amnesia and if you running for long time subject may present with hypotension . usually preferable in epilepsy surgery along with relaxant if there is no any requirement of motor mapping while disconnecting between frontal to posterior region to isolate the epileptic foci.
- Ketamine low dose usually we preferer along with above drugs as a mixture but high dose cause again may interfere the signal and traumatic hallucination .
- Remifentanil is a gold standard drug along with propofol for intraoperative neurophysiological monitoring .
Muscle Relaxants {like Rocuronium, Atracurium, Vecuronium etc}.
- Muscle relaxants are often used during surgery to facilitate intubation and provide muscle relaxation. They can affect MEPs by reducing muscle activity, leading to decreased MEP amplitudes.
- Sugammadex as a antidote for relaxant but its act on Rocuronium type of drug.
- some center prefer to use muscle relaxants in surgeries involving MEP monitoring, it’s essential to consider their impact and adjust dosages accordingly to maintain adequate signal quality for monitoring.
μ-opioid receptor mOR .{like Fentanyl, Remifentanil}.
- Opioids generally have minimal direct effects on evoked potentials if its constant infusion rate, but can indirectly impact if you giving bolus dose means, monitoring by altering due to activating other type of receptor like GABA.
- Changes in blood pressure, heart rate, or ventilation due to opioid administration can influence neurophysiological signals and should be closely monitored during surgery.
Local Anesthesia drugs {like Lidocaine, Bupivacaine}.
- Local anesthetics can be used in regional anesthesia techniques, such as epidural or nerve blocks, which may affect IONM by blocking sensory or motor pathways.
- Major role of local anesthesia drugs in scalp block for awake craniotomy like speech mapping ,motor mapping , DBS surgery etc.
The Neuro-Anesthesiologist is clearly an important member of the team to facilitate Intraoperative Neurophysiological Monitoring . Their knowledge of the patient and the pathophysiology of the medical comorbidities are essential to understanding the neural physiology and impact of the surgery and procedure. The choice of anesthesia and management of the physiology is paramount for the success of the IONM. When IONM changes occur, their role is paramount since the
etiology can usually be categorized as effects of anesthesia, physiology, positioning, technical, and of the procedure. As above, the anesthesiologist plays a key role helping identifying the possible etiologies and assisting in improving the neural conditions to favor an improved outcome.
This emphasizes the close working relationship between the IONM team, the anesthesiologist, and
the surgeon or proceduralist.
- Can be used Sugammadex drugs in all IONM cases.
- How can be used antidote muscle relaxant drugs in IONM cases.
- What are the correct Blood pressure to interpretate the IONM signals.
- Why core temperature is important in IONM Cases
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