Intraoperative myogenic motor evoked potentials induced by direct electrical stimulation of the exposed motor cortex under isoflurane and sevoflurane

Microscale Physiological Events on the Human Cortical Surface

Despite ongoing advances in our understanding of local single-cellular and network-level activity of neuronal populations in the human brain, extraordinarily little is known about their "intermediate" microscale local circuit dynamics. Here, we utilized ultra-high-density microelectrode arrays and a rare opportunity to perform intracranial recordings across multiple cortical areas in human participants to discover three distinct classes of cortical activity that are not locked to ongoing natural brain rhythmic activity. The first included fast waveforms similar to extracellular single-unit activity. The other two types were discrete events with slower waveform dynamics and were found preferentially in upper cortical layers. These second and third types were also observed in rodents, nonhuman primates, and semi-chronic recordings from humans via laminar and Utah array microelectrodes. The rates of all three events were selectively modulated by auditory and electrical stimuli, pharmacological manipulation, and cold saline application and had small causal co-occurrences. These results suggest that the proper combination of high-resolution microelectrodes and analytic techniques can capture neuronal dynamics that lay between somatic action potentials and aggregate population activity. Understanding intermediate microscale dynamics in relation to single-cell and network dynamics may reveal important details about activity in the full cortical circuit.

Motor Evoked Potential Warning Criteria in Supratentorial Surgery: A Scoping Review

During intraoperative monitoring of motor evoked potentials (MEP), heterogeneity across studies in terms of study populations, intraoperative settings, applied warning criteria, and outcome reporting exists. A scoping review of MEP warning criteria in supratentorial surgery was conducted in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR). Sixty-eight studies fulfilled the eligibility criteria. The most commonly used alarm criteria were MEP signal loss, which was always a major warning sign, followed by amplitude reduction and threshold elevation. Irreversible MEP alterations were associated with a higher number of transient and persisting motor deficits compared with the reversible changes. In almost all studies, specificity and Negative Predictive Value (NPV) were high, while in most of them, sensitivity and Positive Predictive Value (PPV) were rather low or modest. Thus, the absence of an irreversible alteration may reassure the neurosurgeon that the patient will not suffer a motor deficit in the short-term and long-term follow-up. Further, MEPs perform well as surrogate markers, and reversible MEP deteriorations after successful intervention indicate motor function preservation postoperatively. However, in future studies, a consensus regarding the definitions of MEP alteration, critical duration of alterations, and outcome reporting should be determined.

Intraoperative Neuromonitoring for Tethered Cord Surgery in Infants: Challenges and Outcome

OBJECTIVE

The aim of this study was to evaluate the efficacy and safety of intraoperative neuromonitoring (IONM) in surgery for tethered cord in infants.

MATERIALS AND METHODS

The study included 87 infants who underwent surgery for closed spinal dysraphism under IONM. Their preoperative neurological and urological statuses were compared with postoperative status clinically. The study design was prospective, and the study's duration was from January 2011 to February 2020. IONM was performed (TcMEP and direct mapping) with an Xltek Protektor 32 IOM system, Natus Neurology/medical Inc., Middleton, USA. Statistical analysis in the form of χ2 is conducted using SPSS.

RESULTS

Overall, among 87 patients, clinical improvement was seen in 28 (28/29) patients with motor deficits, 17 (17/24) with bladder deficits, and 18 (18/24) with bowel deficits. The monitorability for motor and sphincter was 97.3% and 90.7%, respectively. The sensitivity of IONM in predicting new motor deficit was 100%, whereas the specificity was 100%. The negative predictive value of predicting motor deficit was 100%, with a diagnostic accuracy of 100%. There were no complications in this cohort related to the IONM.

CONCLUSIONS

The study has highlighted that the use of IONM is sensitive in identifying motor injury in infants with reliable outcome correlation. Assessment, monitoring, and outcome correlation of bladder and sphincteric functions are a challenge in this cohort.

Desflurane - revisited

The search for an ideal inhalational general anesthetic agent continues. Desflurane, which was recently introduced in the Indian market, possesses favorable pharmacokinetic and pharmacodynamic properties and is closer to the definition of an ideal agent. It offers the advantage of precise control over depth of anesthesia along with a rapid, predictable, and clear-headed recovery with minimal postoperative sequelae, making it a valuable anesthetic agent for maintenance in adults and pediatric patients in surgeries of all durations. The agent has advantages when used in extremes of age and in the obese. Its use may increase the direct costs of providing anesthetic care. Methods or techniques, such as low-flow anesthesia, to reduce the overall cost and along with minimal environmental implications must be followed.

Anesthesia and intraoperative neurophysiological monitoring in children

PURPOSE

Anesthesia for pediatric patients undergoing surgery where intraoperative neurophysiological monitoring (IONM) is performed is based on an understanding of the anesthetic influence on the neural pathways involved and the physiology that supplies nutrients to the neural systems. Anesthesia in pediatric patients may be different than in adults due to the specific anesthesia considerations in children, notably the propofol infusion syndrome (PRIS) and the need to monitor immature neural pathways. This review was done to determine if the anesthesia protocols used were different than those used in adults.

METHODS

After reviewing the implications of anesthetic action, a survey of pediatric anesthesia practitioners in 40 North American centers was conducted to determine the anesthesia protocols used in pediatric surgery with IONM and if these were specifically modified over concerns about PRIS.

RESULTS

Twenty-five centers responded with 35 different protocols used by practitioners. These protocols are similar to protocols used in adult patients. Although no centers specifically avoided propofol in all patients, several strategies were used to reduce the dosage, avoid its use in selected patients, or monitor for the onset of the syndrome.

CONCLUSION

Anesthesia for pediatric patients undergoing surgery where IONM is being performed is consistent with the practice and principles of anesthesia for adults. Although PRIS has not caused major alterations in most patients, concern has modified the practice of some anesthesiologists.

Amplitudes and intrapatient variability of myogenic motor evoked potentials to transcranial electrical stimulation during ketamine/N2O- and propofol/N2O-based anesthesia

The aim of the current study was to investigate whether there are differences in amplitudes and intrapatient variability of motor evoked potentials to five pulses of transcranial electrical stimulation between ketamine/N2O- and propofol/N2O-based anesthesia. Patients in the propofol group (n = 13) and the ketamine group (n = 13) were anesthetized with 50% N2O in oxygen, fentanyl, and 4 mg/kg/hr of propofol or 1 mg/kg/hr of ketamine, respectively. The level of neuromuscular blockade was maintained at an M-response amplitude of approximately 50% of control. Motor evoked potentials in response to multipulse transcranial electrical stimulation were recorded from the right adductor pollicis brevis muscle, and peak-to-peak amplitude and onset latency of motor evoked potentials were evaluated. To estimate intrapatient variability, the coefficient of variation (standard deviation/mean x 100%) of 24 consecutive responses was determined. Motor evoked potential amplitudes in the ketamine group were significantly larger than in the propofol group (mean, 10th-90th percentile: 380 microV, 129-953 microV; 135 microV, 38-658 microV, respectively; P <.05). There were no significant differences in motor evoked potential latency (mean +/- standard deviation: 20.9 +/- 2.2 msec and 21.4 +/- 2.2 msec, respectively) and coefficient of variation of amplitudes (median [range]: 32% [22-42%] and 26% [18-41%], respectively) and latencies (mean +/- standard deviation: 2.1 +/- 0.7% and 2.1 +/- 0.7%, respectively) between the ketamine and propofol groups. In conclusion, intrapatient variability of motor evoked potentials to multipulse transcranial stimulation is similar between ketamine/N2O- and propofol/N2O-based anesthesia, although motor evoked potential amplitudes are lower during propofol/N2O-based anesthesia than ketamine/N2O-based anesthesia.

Convergent and reciprocal modulation of a leak K+ current and I(h) by an inhalational anaesthetic and neurotransmitters in rat brainstem motoneurones

Neurotransmitters and volatile anaesthetics have opposing effects on motoneuronal excitability which appear to reflect contrasting modulation of two types of subthreshold currents. Neurotransmitters increase motoneuronal excitability by inhibiting TWIK-related acid-sensitive K+ channels (TASK) and shifting activation of a hyperpolarization-activated cationic current (I(h)) to more depolarized potentials; on the other hand, anaesthetics decrease excitability by activating a TASK-like current and inducing a hyperpolarizing shift in I(h) activation. Here, we used whole-cell recording from motoneurones in brainstem slices to test if neurotransmitters (serotonin (5-HT) and noradrenaline (NA)) and an anaesthetic (halothane) indeed compete for modulation of the same ion channels - and we determined which prevails. When applied together under current clamp conditions, 5-HT reversed anaesthetic-induced membrane hyperpolarization and increased motoneuronal excitability. Under voltage clamp conditions, 5-HT and NA overcame most, but not all, of the halothane-induced current. When I(h) was blocked with ZD 7288, the neurotransmitters completely inhibited the K+ current activated by halothane; the halothane-sensitive neurotransmitter current reversed at the equilibrium potential for potassium (E(K)) and displayed properties expected of acid-sensitive, open-rectifier TASK channels. To characterize modulation of I(h) in relative isolation, effects of 5-HT and halothane were examined in acidified bath solutions that blocked TASK channels. Under these conditions, 5-HT and halothane each caused their characteristic shift in voltage-dependent gating of I(h). When tested concurrently, however, halothane decreased the neurotransmitter-induced depolarizing shift in I(h) activation. Thus, halothane and neurotransmitters converge on TASK and I(h) channels with opposite effects; transmitter action prevailed over anaesthetic effects on TASK channels, but not over effects on I(h). These data suggest that anaesthetic actions resulting from effects on either TASK or hyperpolarization-activated cyclic nucleotide-gated (HCN) channels in motoneurones, and perhaps at other CNS sites, can be modulated by prevailing neurotransmitter tone.