Benefit of neurophysiologic monitoring for pediatric cardiac surgery.

BACKGROUND: Pediatric patients undergoing repair of congenital cardiac abnormalities have a significant risk of an adverse neurologic event. Therefore this retrospective cohort study examined the potential benefit of interventions based on intraoperative neurophysiologic monitoring in decreasing both postoperative neurologic sequelae and length of hospital stay as a cost proxy. METHODS: With informed parental consent approved by the institutional review board, electroencephalography, transcranial Doppler ultrasonic measurement of middle cerebral artery blood flow velocity, and transcranial near-infrared cerebral oximetry were monitored in 250 patients. An interventional algorithm was used to detect and correct specific deficiencies in cerebral perfusion or oxygenation or to increase cerebral tolerance to ischemia or hypoxia. RESULTS: Noteworthy changes in brain perfusion or metabolism were observed in 176 of 250 (70%) patients. Intervention that altered patient management was initially deemed appropriate in 130 of 176 (74%) patients with neurophysiologic changes. Obvious neurologic sequelae (i.e., seizure, movement, vision or speech disorder) occurred in five of 74 (7%) patients without noteworthy change, seven of 130 (6%) patients with intervention, and 12 of 46 (26%) patients without intervention (p = 0.001). Survivors' median length of stay was 6 days in the no-change and intervention groups but 9 days in the no-intervention group. In addition, the percentage of patients in the no-intervention group discharged from the hospital within 1 week (32%) was significantly less than that in either the intervention (51%, p = 0.05) or no-change (58%, p = 0.01) groups. On the basis of an estimated hospital neurologic complication cost of $1500 per day, break-even analysis justified a hospital expenditure for neurophysiologic monitoring of $2142 per case. CONCLUSIONS: Interventions based on neurophysiologic monitoring appear to decrease the incidence of postoperative neurologic sequelae and reduce the length of stay. Inasmuch as the break-even cost for neurophysiologic monitoring is more than four times the actual average charge, both patients and hospital may profit from this service. Because this study was not a truly randomized clinical trial, unintentional statistical bias may have occurred and caution is urged in interpreting the magnitude of apparent intergroup outcome differences.

Evoked potentials from direct cerebellar stimulation for monitoring of the rodent spinal cord.

Although the assessment of spinal cord function by electrophysiological techniques has become important in both clinical and research environments, current monitoring methods do not completely evaluate all tracts in the spinal cord. Somatosensory and motor evoked potentials primarily reflect dorsal column and pyramidal tract integrity, respectively, but do not directly assess the status of the ventral funiculus. The present study was undertaken to evaluate the use of evoked potentials, elicited by direct cerebellar stimulation, in monitoring the ventral component of the rodent spinal cord. Twenty-nine rats underwent epidural anodal stimulation directly over the cerebellar cortex, with recording of evoked responses from the lower thoracic spinal cord, both sciatic nerves, and/or both gastrocnemius muscles. Stimulation parameters were varied to establish normative characteristics. The pathways conducting these "posterior fossa evoked potentials" were determined after creation of various lesions of the cervical spinal cord. The evoked potential recorded from the thoracic spinal cord consisted of five positive (P1 to P5) and five negative (N1 to N5) peaks. The average conduction velocity (+/- standard deviation) of the earliest wave (P1) was 53 +/- 4 m/sec, with a latency of 1.24 +/- 0.10 msec. The other components followed within 4 msec from stimulus onset. Unilateral cerebellar stimulation resulted in bilateral sciatic nerve and gastrocnemius muscle responses; there were no significant differences (p greater than 0.05) in the thresholds, amplitudes, or latencies of these responses elicited by right- versus left-sided stimulation. Recordings performed following creation of selective lesions of the cervical cord indicated that the thoracic response was carried primarily in the ventral funiculus while the sciatic and gastrocnemius responses were mediated through the dorsal half of the spinal cord. It is concluded that the posterior fossa evoked potential has research value as a method of monitoring pathways within the ventral spinal cord of the rat, and should be useful in the study of spinal cord injury.

Spinal sensory and motor tract activation after epidural electrical stimulation in the cat.

Somatosensory evoked potentials (SEPs) after peripheral nerve stimulation and motor evoked potentials (MEPs) after transcranial stimulation have been routinely used as monitors of the viability of pathways in the posterior and anterior spinal cord, respectively, in patients undergoing spinal cord surgery. To assess total spinal cord function, both of these procedures must be performed simultaneously, which is both cumbersome and technically difficult. The objectives of this study were to demonstrate both sensory and motor spinal tract activation after epidural electrical stimulation of the cat spinal cord. Thirty-seven adult mongrel cats were anesthetized with ketamine, intubated, and maintained with Ethrane and nitrous oxide. Stimulating electrodes were placed over the right dorsolateral spinal cord epidurally at T7 after a laminectomy. Recording electrodes were placed over the right L3 spinal cord epidurally, on the right L7 dorsal and ventral nerve roots, on the right and left sciatic nerves in the popliteal fossa, and in the right gastrocnemius muscle. After epidural stimulation of the spinal cord at T11, distinct reproducible potentials were recorded at each site. Activity in the L7 dorsal root implicated activation of spinal sensory tracts. Activity in the L7 ventral root and in the gastrocnemius implicated activation of spinal motoneurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Swallowing and upper esophageal sphincter contraction with transcranial magnetic-induced electrical stimulation.

This study in three dogs explores the effect of magnetically induced electrical stimulation of the brain to induce swallowing and produce contraction of the upper esophageal sphincter (UES). Single stimuli were delivered at intervals from 15 s to 3 min. Studies were performed with and without perfusion of fluid into the pharynx and upper esophagus. Results showed that magnetic stimulation produced a twitch contraction of the UES when stimulus intensity was above a threshold that varied between 14 and 20% of the stimulator output. Increasing stimulus intensity progressively increased twitch amplitude. Magnetic stimulation also induced swallowing, above a stimulus threshold similar to that for induction of the UES twitch contraction. Fluid perfusion augmented the ability of the magnetic stimulus to induce swallowing. We concluded that a magnetically induced single electrical stimulus of the cerebral cortex produces UES contraction and induces swallowing. The effect on swallowing is facilitated by sensory stimulation of the pharynx. This technique holds the potential for further study of 1) motor and sensory neural mechanisms involved in the control of swallowing and 2) the assessment and management of oropharyngeal dysphagia in humans.