The influence of depth of anesthesia and blood pressure on muscle recorded motor evoked potentials in spinal surgery. A prospective observational study protocol

Abstract

For high-risk spinal surgeries, intraoperative neurophysiological monitoring (IONM) is used to detect and prevent intraoperative neurological injury. The motor tracts are monitored by recording and analyzing muscle transcranial electrical stimulation motor evoked potentials (mTc-MEPs). A mTc-MEP amplitude decrease of 50–80% is the most common warning criterion for possible neurological injury. However, these warning criteria often result in false positive warnings. False positives may be caused by inadequate depth of anesthesia and blood pressure on mTc-MEP amplitudes. The aim of this paper is to validate the study protocol in which the goal is to investigate the effects of depth of anesthesia (part 1) and blood pressure (part 2) on mTc-MEPs. Per part, 25 patients will be included. In order to investigate the effects of depth of anesthesia, a processed electroencephalogram (pEEG) monitor will be used. At pEEG values of 30, 40 and 50, mTc-MEP measurements will be performed. To examine the effect of blood pressure on mTc-MEPs the mean arterial pressure will be elevated from 60 to 100 mmHg during which mTc-MEP measurements will be performed. We hypothesize that by understanding the effects of depth of anesthesia and blood pressure on mTc-MEPs, the mTc-MEP monitoring can be interpreted more reliably. This may contribute to fewer false positive warnings. By performing this study after induction and prior to incision, this protocol provides a unique opportunity to study the effects of depths of anesthesia and blood pressure on mTc-MEPs alone with as little confounders as possible.Trial registration number NL7772.

Evaluation of the effect of preoperative anxiety on intraoperative hemodynamic stability and drug consumption in patients who underwent BIS-guided total intravenous anesthesia (TIVA) for neurophysiological monitoring in spine surgery

“…Since there is no method that can directly measure the perfusion of these tissues, the measurement and regulation of blood pressure is of great importance. In a recent study, the depth of anesthesia and mean arterial pressure values were stated to affect the optimal measurements of MEP [14]. In our study, the target MAP values were determined as 55-110 mmHg.…”

Validation of the 18F-FDG PET Image Biomarker Model Predicting Late Xerostomia after Head and Neck Cancer Radiotherapy

“…4 Distribution of optimal ISI when measuring mTc-MEPs using supramaximal stimulation with a pulse duration of 0.075ms (n = 29) The x-axis denotes the different muscles used for mTc-MEP monitoring and the y-axis denotes the number of patients. The optimal ISI's ranging from 1ms to 4ms are presented by the different colored bars for the AH left, AH right, TA left and TA right separately the effects of higher anesthetic drug doses, anesthetic fade, and significant blood pressure decreases on mTc-MEP amplitudes [20][21][22]. Although, the ≥ 20 V cut-off value chosen in this study is arbitrary, in our experience, it was sufficient to counteract for anesthetic events.…”

“…In three patients, supramaximal stimulation was not achieved although the subsequent analyses showed that there had still been the possibility to increase the voltage without reaching the maximal current output. These three anesthetic fade, or significant blood pressure decreases cause reductions in mTc-MEP amplitudes then it is desirable to increase the stimulation voltage or current [20,21]. Therefore, we evaluated if there was the possibility to increase the stimulation voltage with ≥ 20 V below maximum output to address for these possible anesthetic events.…”

Anesthesia and intraoperative neurophysiological spinal cord monitoring

“…It is currently not clear what blood pressure is sufficient to ensure spinal cord perfusion [23 ▪▪ ] but decreasing the pressure below this level (of autoregulation) leads to progressive mTc-MEP and SSEP amplitude decreases without affecting latency [21,24]. Adhering to the generally accepted population-based lower and upper MAP threshold of 60–70 mm Hg and 160 mm Hg [25] and adjusting these targets by monitoring the EPs is advisable.…”