Signal recapture in transcranial motor evoked potentials can herald early spinal cord reperfusion

Abstract INTRODUCTION Intraoperative neurophysiological monitoring of transcranial motor evoked potentials (MEPs) provides the most reliable method for assessing spinal cord functional integrity during deformity and other complex spinal surgeries. MEPs are affected by pharmacological and physiological parameters. It is the responsibility of the spine surgeon and neuroanesthesia team to understand how they can best maintain high quality MEP signals throughout surgery. Nevertheless, varying approaches to neuroanesthesia are seen in clinical practice. METHODS We identified 19 international spinal deformity expert teams for participation in our study. A modified Delphi process utilizing 2 rounds of surveying was performed. Greater than 50% and 75% agreement on the final statements was considered achieving “agreement” and “consensus,” respectively. RESULTS Anesthesia regimens and protocols were obtained from the expert centers. A large amount of variability in these centers was witnessed. Two rounds of consensus surveying were then performed, and all centers participated in both rounds of the surveying. Consensus was obtained in 12 of 15 statements and majority agreement in 2 of the remaining. Agreement on specific safe neuroanesthesia practices in the setting of MEP monitoring was obtained. Total intravenous anesthesia (TIVA) was identified as the optimal method of maintenance with few centers allowing for low MAC concentrations of inhaled anesthetic. While no strict cutoff values of propofol concentrations or opioid doses were identified, most centers advocated for less than 150 mcg/kg/min of propofol with titration to the lowest dose that maintains appropriate anesthesia depth based on bispectral index or electroencephalography awareness monitoring. Utilization of adjuvant intravenous anesthetics, including ketamine and lidocaine, may help to reduce propofol and opioid requirements without negatively impacting MEP signals. Low-dose dexmedetomidine was also routinely used with the same purpose, but with knowledge that higher doses may be suppressive. Maintenance of blood pressure parameters near the patient's preoperative baseline or with mean arterial pressure greater than 80 mmHg ensures appropriate spinal cord perfusion and prevents loss of MEPs. CONCLUSION Spine surgeons and their neuroanesthesia teams should be familiar with the methods for optimizing IOM of MEPs during deformity and complex spinal cases. While variability in practices exist, consensus exists among international deformity centers regarding best practices.

Download Full-text

1002 Differential response times of transcranial motor evoked potentials to selective thoracic or lumbal spinal cord ischemia

Journal of Neurosurgical Anesthesiology ◽

10.1097/00008506-199910000-00124 ◽

1999 ◽

Vol 11 (4) ◽

pp. 331

Author(s):

Jeroen Lips ◽

Cor J Kalkman ◽

Peter de Haan

Keyword(s):

Spinal Cord ◽

Evoked Potentials ◽

Response Times ◽

Motor Evoked Potentials ◽

Spinal Cord Ischemia ◽

Differential Response ◽

Transcranial Motor Evoked Potentials

Download Full-text

Effect of Hemorrhage and Hypotension on Transcranial Motor-evoked Potentials in Swine

Anesthesiology ◽

10.1097/aln.0b013e31829d4a92 ◽

2013 ◽

Vol 119 (5) ◽

pp. 1109-1119 ◽

Cited By ~ 10

Author(s):

Jeremy A. Lieberman ◽

John Feiner ◽

Russ Lyon ◽

Mark D. Rollins

Keyword(s):

Spinal Cord ◽

Multivariate Analysis ◽

Cardiac Output ◽

Evoked Potentials ◽

Tibialis Anterior ◽

Motor Evoked Potentials ◽

P Value ◽

Swine Model ◽

Paired Comparisons ◽

Transcranial Motor Evoked Potentials

Abstract Background: Transcranial motor-evoked potentials (TcMEPs) monitor spinal cord motor tract integrity. Using a swine model, the authors studied the effects of vasodilatory hypotension, hemorrhage, and various resuscitation efforts on TcMEP responses. Methods: Twelve pigs were anesthetized with constant infusions of propofol, ketamine, and fentanyl. Animals were incrementally hemorrhaged, until bilateral tibialis anterior TcMEP amplitude decreased to less than 40% of baseline or until 50% of the blood volume was removed. Mean arterial pressure (MAP), cardiac output (CO), and oxygen delivery (DO2) were examined. Resuscitation with phenylephrine, epinephrine, and colloid were evaluated. In seven animals, vasodilatory hypotension was examined. Paired comparisons and multivariate analysis were performed. Results: Hemorrhage significantly reduced (as a percentage of baseline, mean ± SD) TcMEPs (left, 33 ± 29%; right, 26 ± 21%), MAP (60 ± 17%), CO (49 ± 12%), and DO2 (43 ± 13%), P value less than 0.001 for all. Vasodilation reduced MAP comparably, but TcMEPs, CO, and DO2, were not significantly lowered. After hemorrhage, restoration of MAP with phenylephrine did not improve TcMEPs, CO, or DO2, but similar restoration of MAP with epinephrine restored (to percentage of baseline) TcMEPs (59 ± 40%), and significantly increased CO (81 ± 17%) and DO2 (72 ± 19%) compared with both hemorrhage and phenylephrine, P value less than 0.05 for all. Resuscitation with colloid did not improve TcMEPs. Multivariate analysis revealed that changes in TcMEPs were more closely associated with changes in CO and DO2 as compared with MAP. Conclusions: Hypotension from hemorrhage, but not vasodilation, is associated with a decrease in TcMEP amplitude. After hemorrhage, restoration of TcMEPs with epinephrine but not phenylephrine indicates that CO and DO2 affect TcMEPs more than MAP. Monitoring CO may be beneficial in major spine surgery when using TcMEP monitoring.

Download Full-text