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Intraoperative monitoring of blood flow insufficiency in the anterior choroidal artery during aneurysm surgery.
OBJECT: The lack of a specified intraoperative method for monitoring anterior choroidal artery (AChA) blood flow insufficiency (BFI) led the authors to devise a method for checking the BFI in this artery during aneurysm surgery. To this end, the authors relied on the intraoperative motor evoked potentials (MEPs) elicited by electrical stimulation of the hand motor cortex. METHODS: The study population consisted of 108 patients with internal carotid artery (ICA) aneurysms who underwent surgery via a standard frontotemporal craniotomy. After the dura mater had been opened, a grid electrode strip with 16 small electrodes was inserted subdurally into the hand motor cortex from the edge of the craniotomy. To check BFI in the AChA, the hand motor cortex was stimulated at an intensity level between 10 and 18 mA. The MEPs were successfully recorded from the contralateral thenar muscles in all 108 patients. There was no postoperativemotor paresis in 88 patients in whom the MEPs remained unchanged during the performance of various surgical maneuvers. Among the other 20 patients, 19 manifested transient MEP changes, but 15 of those patients experienced no postoperative motor paresis. In four patients who exhibited transient MEP changes, either after aneurysm clipping or during temporary occlusion of the ICA and/or AChA, hemiparesis occurred postoperatively but disappeared within 24 hours. In one patient with an ICA-posterior communicating artery aneurysm, the MEP disappeared and did not reappear by the time of dural closure. Severe hemiplegia developed in this patient and a computerized tomography scan obtained postoperatively revealed a new low-density area in the internal capsule. CONCLUSIONS: The findings of this study suggest that the monitoring method that is introduced here is safe and reliable for detecting intraoperative BFI in the AChA.
Threshold-level repetitive transcranial electrical stimulation for intraoperative monitoring of central motor conduction.
OBJECT: The authors conducted a study to evaluate repetitive transcranial electrical stimulation (TES) to assess spinal cord motor tract function in individuals undergoing spine surgery, with emphasis on safety and efficacy. METHODS: Somatosensory evoked potentials (SSEPs) were elicited using standard technique. Muscle electromyographic values were measured in response to a three- or four-pulse train of stimulation delivered to the motor cortex via subdermal electrodes. They also evaluated whether changes in the minimum stimulus intensity (that is, threshold level) needed to elicit a response from a given muscle predict motor status immediately postoperatively, as well as whether changes in SSEP response amplitude and latency predict sensory status immediately postoperatively. Anesthesia was routinely induced with intravenous propofol and remifentanil, supplemented with inhaled nitrous oxide. Use of neuromuscular block was avoided after intubation. Satisfactory monitoring of muscle response to threshold-level repetitive TES was achieved in all but nine of the 194 patients studied. In contrast, cortical SSEP responses could not be elicited in 42 of 194 individuals. In cases in which responses were present, TES-based evoked responses proved to be extremely accurate for predicting postoperative motor status. Somatosensory evoked potential monitoring was nearly as accurate for predicting postoperative sensory status. There were frequent instances of postoperative motor or sensory deficit that were not predicted by SSEP- and TES-based monitoring, respectively. There were no adverse events attributable to TES-based monitoring, although since this study ended we have had a single adverse event attributable to threshold-level repetitive TES. CONCLUSIONS: Intraoperative threshold-level repetitive TES-based monitoring of central motor conduction has proven to be a simple, safe, and highly accurate technique for the prevention or minimization of inadvertent motor deficit during surgery involving the spine or spinal cord.
Intraoperative monitoring of myocardial ischemia.
Cardiovascular complications are commonly observed in surgical patients, and myocardial ischemia is the most important determinant of perioperative morbidity. The clinical criteria defining a patient population at increased risk for cardiovascular events are presented. The authors review the principles of monitoring and diagnosing myocardial ischemia, focusing on eletrocardiography and TransEsophageal Echocardiography. These patients must be closely followed long after the end of surgery, since the risk for cardiac morbidity is high for several hours postoperatively.
Intraoperative monitoring in neurosurgery.
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Intraoperative monitoring of motor function by magnetic motor evoked potentials.
Under etomidate anesthesia, motor evoked potentials produced by magnetic stimulation were successfully recorded from 10 thenar muscles and 10 anterior tibial muscles of eight patients who had undergone surgery on the medulla oblongata and the cervical and thoracic spinal cords. Recordings taken before placing the neural tissue at risk were assessed for variability in amplitude and latency. The lower limit in amplitude was approximately one-third (25-43%) of the baseline. The latencies were more difficult to monitor than were the amplitudes. The latency variations were 2.56 +/- 0.50 milliseconds for the hand and 6.84 +/- 1.37 milliseconds for the leg. During surgery, the unilateral recordings of two patients were transiently lost but partially recovered after a pause in the operation. No obvious postoperative weaknesses in the corresponding limbs occurred. One patient, who showed a permanent loss of unilateral recording, had transient monoplegia with a complete recovery. None of the remaining five patients who had amplitudes larger than one-third of the baseline at the end of the operation had additional motor deficits. Our conclusions are that under etomidate anesthesia, the magnetic motor evoked potentials can be convenient and reliable monitors of motor function, that changes in the amplitude may be superior to those in the latency for intraoperative warning, that the criterion for potential neural damage under magnetic motor evoked potential monitoring might be an amplitude reduction of two-thirds of the control value, and that the magnetic stimulation seems to be more sensitive than the electrical stimulation in the monitoring of motor function and also allows more time and opportunities for the motor function to recover.
[Intraoperative monitoring of facial electromyographic responses during neurovascular decompressive surgery for hemifacial spasm].
UNLABELLED: In this paper, we reported our experience of intraoperative facial electromyographic recordings obtained during microvascular decompression for hemifacial spasm. MATERIALS AND METHODS: Intraoperative electromyographic recordings from the mentalis muscle during stimulation of the temporal branch of the facial nerve has been attempted in 31 patients. No muscle relaxants were used except for those before intubation. Of 31 patients, 22 were female and 9 were male. The age on admission ranged from 31 to 60 years with a mean of 54 years. RESULTS: 1. Abnormal response appeared with a latency of about 10 msec after stimulation. This response disappeared in 30 out of 31 patients at the end of operation. In 4 patients, the abnormal response disappeared prior to decompression of the nerve. 2. 30 patients in whom the abnormal response disappeared were free of spasm immediately after surgery. Hemifacial spasm has been relieved in 28 patients with a follow up period of 6 months to 2 years and 7 months. The remaining two patients had mild spasm. The one patient in whom the abnormal response did not disappear had persistent hemifacial spasm. CONCLUSION: The authors think that intraoperative facial electromyographic recording is useful to identify the blood vessel that is causing the spasm and to ensure that decompression of the nerve has been accomplished.
Posterior fossa intraoperative monitoring.
Monitoring of brainstem structures is requested of the neurophysiologist for both intra-axial and extra-axial surgeries of the posterior fossa. A variety of techniques to include upper extremities somatosensory evoked potentials, short latency auditory evoked potentials, spontaneous and evoked electromyographic activity, and recordings from the cochlea and the eighth nerve are available. The indication, implementation, and interpretation of each of these modalities are delineated. The efficacy and utility of these techniques are also discussed.
Intraoperative monitoring of nerve repairs.
These examples illustrate the interplay of the electrophysiologic techniques of SEP, EMG, NCAPs, and nerve conduction studies to achieve the goals of monitoring, guiding, identifying and localizing, and assessing nerve function. Through their successful application, intraoperative neurophysiology moves from solely monitoring to serving as an electrophysiologic aid to the surgeon. Using all of these techniques provides a comprehensive analysis of nerve function. The overall goal is both to prevent intraoperative neural compromise and to optimize postoperative outcome by providing the surgeon with the best possible information regarding the functional condition of the nerves under investigation.
Intraoperative monitoring of brain tissue oxygen and carbon dioxide pressures reveals low oxygenation in peritumoral brain edema.
Brain edema and swelling often complicate surgery for brain tumors. Its pathophysiology is unclear, as is the relationship with brain tissue oxygenation. Our hypothesis was that brain edema around tumor is cytotoxic type caused by impaired local tissue oxygenation due to increased local tissue pressure. Therefore, we monitored brain tissue oxygen pressure (p(ti)O2) and carbon dioxide pressure (p(ti)CO2) in 19 patients undergoing craniotomy for removal of a brain tumor and specifically studied the effect of decompression by dura opening and by tumor removal with respect to the presence of brain swelling. Before craniotomy, multiparameter sensors were inserted into the peritumoral brain tissue guided by MRI-based stereotaxy. In eight patients who had severe brain swelling upon opening of the dura mater, p(ti)O2 immediately rose from 7 +/- 8 mm Hg to 24 +/- 15 mm Hg ( < 0.05), whereas in patients who did not have swelling, p(ti)O2 went from 16 +/- 9 to 18 +/- 10 mm Hg after opening of the dura. The mean p(ti)O2 of all patients at the start of resection of the tumor was 18 +/- 11 mm Hg, and increased to 30 +/- 15 mm Hg after resection was completed ( < 0.05). The effect on p(ti)O2 of raising the FiO2 to 1.0 was limited in this group of patients, as an increase greater than 50% was found in only six of twelve patients. Notably, in six patients, sensor malfunctions or associated hardware problems occurred, prohibiting useful data acquisition. We conclude that brain tissue oxygenation is reduced in the peritumoral area and improves after local tissue pressure relief, especially in patients with brain swelling. Thus, ischemic processes may contribute to brain edema around tumors. Intraoperative p(ti)O2 monitoring may enhance the safety of neuroanesthesia, but the high incidence of failures with this type of sensor remains a matter of concern.
Validity of pelvic autonomic nerve stimulation with intraoperative monitoring of bladder function following total mesorectal excision for rectal cancer.
PURPOSE: This prospective study was designed to clarify whether the results of the intraoperative stimulation of parasympathetic pelvic nerves performed in 31 patients after mesorectal excision for rectal carcinoma allowed predictions in terms of the postoperative bladder function of the patients. METHODS: After monopolar stimulation of the splanchnic pelvic nerves using a constant voltage stimulator (Screener 3625), intravesical pressure increase was measured manometrically. The results were related to the postoperative residual urine volume, requirement of recatheterization and long-term catheterization, just as to the results of the validated International Prostatic Symptom Scores and the Quality of Life Index caused by urinary symptoms. The median follow-up period was nine (range, 2-14) months. RESULTS: Parasympathetic nerve stimulation was performed at 61 sites and results in intravesical pressure increase up to 6 cm water column in median. In 11 patients (33.3 percent), a negative test result was achieved: 5 with unilateral and 6 with bilateral pressure increases of < or = 2 cm water column. Recatheterization was necessary in four patients, and all of them showed negative neuromonitoring results. Two of these patients were discharged with an in situ urinary bladder catheter. Postoperative increased residual urine volumes (> or =100 ml) resulted more frequently in the group with negative test results (63.6 vs. 21.1 percent; P = 0.047), and the International Prostatic Symptom Score and Quality of Life Index showed the worst results (9.9 +/- 6.7 vs. 3 +/- 4.9, P = 0.021; 2.4 +/- 1.7 vs. 0.7 +/- 1.3, P = 0.021). CONCLUSIONS: Intraoperative neurostimulation and manometric measurement of bladder pressure may contribute to the identification of parasympathetic pelvic nerves during total mesorectal excision. This method is suitable for intraoperative recording of nerve preservation and therefore associated with postoperative bladder function.
Tibial somatosensory evoked potential intraoperative monitoring: recommendations based on signal to noise ratio analysis of popliteal fossa, optimized P37, standard P37, and P31 potentials.
OBJECTIVE: To compare the intraoperative signal-to-noise ratio (SNR), reproducibility and rapidity of popliteal fossa (PF), optimized P37, standard P37 and P31 potentials. METHODS: Raw sweeps and 11 averages doubling sweep number from 2 to 2048 were compared in 37 patients undergoing scoliosis surgery. Optimized (highest amplitude or SNR) P37 derivations were Cz-CPc (22), CPz-CPc (27), Pz-CPc (7), iCPi-CPc (8), CPi-CPc (1), Cz-Pz (2) or Pz-FPz (3), and in two patients with non-decussation, Cz-CPi (1) or CPz-CPi (3). Standard P37 and P31 derivations were CPz-FPz and FPz-C5S. Signal amplitude was measured in 2048-sweep averages; peak noise was measured in raw sweeps and +/- averages; SNR was amplitude/noise. Visual superimposability and < 20-30% amplitude variation determined reproducibility. Sweeps to reproducibility determined rapidity. RESULTS: The SNR order was PF >> optimized P37 > standard P37 > P31. Mean optimized P37 SNR advantages over the standard P37 and P31 were 2.1:1 and 4.9:1. SNR had powerful non-linear correlations to reproducibility and rapidity. Median sweeps to reproducibility were PF: 2, optimized P37: 128, standard P37: 512 and P31: 1024. EEG noise was greatest in FPz derivations. Burst-suppression increased scalp potential SNR and rapidity. CONCLUSIONS: Optimized P37 and PF recordings are most rapidly reproducible due to superior SNRs and are recommended. FPz should be avoided. Burst-suppression may be desirable. SIGNIFICANCE: CPz-FPz and FPz-C5S should no longer be standard.
Intraoperative monitoring of the biliary tracts as a means of preventing choledocholithiasis oversight.
The aim of the work is to assess the performance and effectiveness of intraoperative cholangiography or choledochoscopy in the prevention of choledocholithiasis oversight. The effectiveness of choledochoscopy was assessed in 50 patients during the years 2001-2002. Since 2000 intraoperative cholangiography has been performed on all patients after classic cholecystostomy in the absence of indications to choledochotomy. The effectiveness of intraoperative cholangiography was assessed in 50 patients in 2001. Both groups underwent ultrasonographic control and tests of biochemical parameters a year after surgery. The advisability of performing intraoperative cholangiography or choledochoscopy and their high degree of effectiveness in the prevention of choledocholithiasis oversight was confirmed.
The role of intraoperative monitoring of oculomotor and trochlear nuclei -safe entry zone to tegmental lesions.
OBJECTIVE: A safe entry zone to tegmental lesions was identified based on intraoperative electrophysiological findings, the compound muscle action potentials (CMAP) from the extraocular muscles, and anatomic considerations. This entry zone is bordered caudally by the intramesencephalic path of the trochlear, laterally by the spinothalamic tract, and rostrally by the caudal margin of the brachium of the superior colliculus. METHODS: Four intrinsic midbrain lesions were operated upon via the safe entry zone using the infratentorial paramedian supracerebellar approach. All lesions involved the tegmentum and included an anaplastic astrocytoma, a metastatic brain tumor, a radiation necrosis, and a cavernous angioma. CMAP were bilaterally monitored from the inferior recti (for oculomotor function) and superior oblique (for trochlear nerve function) muscles. RESULTS: In three of four cases, CMAP related to the oculomotor nerve were obtained upon stimulation at the cavity wall after removal of the tumor. Stimulation at the surface of the quadrigeminal plate, however, did not cause any CMAP response. Using this monitoring as an indicator, the lesions were totally removed. CONCLUSIONS: In the surgery of tegmental lesions, CMAP monitoring from extraocular muscles is particularly helpful to prevent damage to crucial neural structures during removal of intrinsic lesions, but less so to select the site of the medullary incision. The approach via the lateral part of the colliculi is considered to be a safe route to approach the tegmental lesions.
Intraoperative monitoring of the recurrent laryngeal nerve using acoustic, free-run, and evoked electromyography.
The purpose of this study was to explore advantages and disadvantages of electrodes used for monitoring of the recurrent laryngeal nerve (RLN) and to determine the postoperative outcome in 135 patients. A pilot study examined 11 patients to compare the clinical performance of two commercially available recording electrodes and three stimulation electrodes for RLN neuromonitoring. After determining the most reliable and consistent stimulating/recording electrode combination, 124 patients were then monitored. In a total of 135 patients there was no permanent iatrogenic nerve damage to the RLN, although 2 patients developed transient vocal hoarseness that resolved shortly postoperatively. An initial "searching" current for evoked electromyography (EMG) was delivered at 0.7 mA and then decreased to a value of 0.35 mA, which reliably elicited RLN stimulation with a minimal incidence of false-positive results. The combination of auditory feedback from the mechanically elicited EMG and a control channel involving EMG monitoring of an additional peripheral muscle improved the detection of artifact and improved the clinical efficacy of intraoperative electromyography. A video camera showed the surgical manipulation on the EMG screen, allowing the neurophysiologist to correlate dissection with RLN status and location. Auditory responses from the nerve helped to determine the type of distress the RLN was encountering.
Intraoperative monitoring of intact PTH in surgery for renal hyperparathyroidism as an indicator of complete parathyroid removal.
In the setting of total parathyroidectomy and autotransplantation surgery (TPT x AS) as treatment for secondary hyperparathyroidism (SHPT), we evaluated whether intraoperative parathyroid hormone (iPTH) monitoring is useful as a reference for total parathyroid removal. We conducted a prospective, open, single value measurement efficacy study of the intraoperative (i.o.) diagnostic monitoring of iPTH in a cohort of surgical patients. All patients (n = 25) underwent TPT x AS at the Department of Surgery, Donostia Hospital from January 2002 to October 2004. The primary outcome measures were kinetics of serum levels of iPTH during surgery and prediction time of the of descent of PTH levels (measured in the clinic on the day of admission and intraoperatively during induction of anesthesia, every 5 and 10 minutes after removal of the adenoma, and again 24 hours thereafter). iPTH levels returned to normal in all 25 patients, decreasing from pathological levels at the beginning of the operation (1302.24 + 424.9 pg/ml) to half (50%) values at the third intraoperative determination, minute 10 (614.8 +/- 196.62), becoming undetectable at 24 hours. Frozen sections were conclusive for parathyroid tissue (20.56 + 10.3 minutes after removal). Intraoperative measurement of iPTH is useful in the prediction complete removal of all parathyroid tissue prior to autotransplantation, thus avoiding persistence of disease because of incomplete surgery.
Intraoperative monitoring of spinal cord SEPs during microsurgical DREZotomy (MDT) for pain, spasticity and hyperactive bladder.
Since 1972, MDT has been performed in 234 patients with chronic pain, 140 with hyperspasticity and 12 with hyperactive neurogenic bladder. In the last 64 patients, the evoked electrospinogram has been recorded intraoperatively from the surface of the spinal cord, to monitor the electrophysiological effects produced by the surgical lesioning, not only on the conduction of lemniscal fibers when entering the dorsal column, but also on the postsynaptic responses of the dorsal horn cells. The decrease in amplitude of the latter responses (N13 or N22) was well correlated with (1) the depth and the width of the DREZ lesion, and (2) the number of spinal segments operated on. In most cases, amplitude was reduced in the order of 2/3, which was considered the best value.
Intraoperative monitoring of motor pathways during operative fixation of acute acetabular fractures.
OBJECTIVE: To determine whether intra-operative spontaneous electromyography (EMG) was superior to somatosensory evoked potentials (SSEP) in the prevention of iatrogenic sciatic nerve injury. DESIGN: Prospective, consecutive. SETTING: Tertiary referral, teaching Hospital in New York City. PATIENTS: Seventy-four patients with acutely displaced acetabular fractures. MAIN OUTCOME MEASURE: Group A consisted of 24 patients who underwent intraoperative sciatic nerve monitoring using SSEP only. Group B consisted of 50 patients who underwent monitoring using both SSEP and spontaneous EMG. Motor potentials were recorded from the tibialis anterior, peroneus longus, abductor hallucis, and flexor hallucis longus muscles. All patients had independent preoperative and postoperative evaluations by the same neurologist. RESULTS: One iatrogenic sciatic nerve injury occurred in group A and none in group B. Prolonged sciatic nerve compromise, demonstrated by significant intraoperative SSEP changes, occurred 2.4 times per case in group A and only 0.8 times per case in group B. In group B, spontaneous EMG noted compromise an average of 3.6 times per case (p < 0.0001). CONCLUSIONS: The results of this study support spontaneous EMG as feasible and superior to SSEP monitoring in detecting intraoperative sciatic nerve comprise in acute acetabular fracture surgery. Spontaneous EMG permits earlier detection of intraoperative sciatic nerve comprise, allowing a more rapid response of the surgical team to noxious nerve stimuli. This may prevent permanent neurologic sequellae.