Comparative study of propofol and midazolam effects on somatosensory evoked potentials during surgical treatment of scoliosis

How to assess prognosis after cardiac arrest and therapeutic hypothermia

The prognosis of patients who are admitted in a comatose state following successful resuscitation after cardiac arrest remains uncertain. Although the introduction of therapeutic hypothermia (TH) and improvements in post-resuscitation care have significantly increased the number of patients who are discharged home with minimal brain damage, short-term assessment of neurological outcome remains a challenge. The need for early and accurate prognostic predictors is crucial, especially since sedation and TH may alter the neurological examination and delay the recovery of motor response for several days. The development of additional tools, including electrophysiological examinations (electroencephalography and somatosensory evoked potentials), neuroimaging and chemical biomarkers, may help to evaluate the extent of brain injury in these patients. Given the extensive literature existing on this topic and the confounding effects of TH on the strength of these tools in outcome prognostication after cardiac arrest, the aim of this narrative review is to provide a practical approach to post-anoxic brain injury when TH is used. We also discuss when and how these tools could be combined with the neurological examination in a multimodal approach to improve outcome prediction in this population.

Somatosensory Evoked Potentials suppression due to remifentanil during spinal operations; a prospective clinical study

BACKGROUND

Somatosensory evoked potentials (SSEP) are being used for the investigation and monitoring of the integrity of neural pathways during surgical procedures. Intraoperative neurophysiologic monitoring is affected by the type of anesthetic agents. Remifentanil is supposed to produce minimal or no changes in SSEP amplitude and latency. This study aims to investigate whether high doses of remifentanil influence the SSEP during spinal surgery under total intravenous anesthesia.

METHODS

Ten patients underwent spinal surgery. Anesthesia was induced with propofol (2 mg/Kg), fentanyl (2 mcg/Kg) and a single dose of cis-atracurium (0.15 mg/Kg), followed by infusion of 0.8 mcg/kg/min of remifentanil and propofol (30-50 mcg/kg/min). The depth of anesthesia was monitored by Bispectral Index (BIS) and an adequate level (40-50) of anesthesia was maintained. Somatosensory evoked potentials (SSEPs) were recorded intraoperatively from the tibial nerve (P37) 15 min before initiation of remifentanil infusion. Data were analysed over that period.

RESULTS

Remifentanil induced prolongation of the tibial SSEP latency which however was not significant (p > 0.05). The suppression of the amplitude was significant (p < 0.001), varying from 20-80% with this decrease being time related.

CONCLUSION

Remifentanil in high doses induces significant changes in SSEP components that should be taken under consideration during intraoperative neuromonitoring.

Neurophysiological monitoring under anesthesia to position a child with extreme lumbar spine flexion for MRI and CT scan

A novel application of neurophysiological monitoring enabled us safely to anesthetize and position a child with severe lumbosacral spine flexion for diagnostic MRI and CT scan. We conducted a propofol-based anesthetic to optimize somatosensory (SSEP) and transcranial electric motor (tceMEP) evoked potential amplitudes, thereby facilitating dynamic neurological monitoring while fully extending the patient supine. In cases outside the operating room involving extraordinary changes in patient position, anesthesia providers may consider utilizing neurophysiological monitoring.

Somatosensory evoked potentials in coma prognosis

SEPs provide useful prognostic information regarding outcome after coma. Use of the summary data presented here should allow clinicians caring for these patients to provide families with a greater degree of certainty regarding outcome than previously has been available.

Predictive value of somatosensory evoked potentials for awakening from coma

OBJECTIVES

A systematic review of somatosensory evoked potentials performed early after onset of coma, to predict the likelihood of nonawakening. The pooled results were evaluated for rates of awakening, confidence intervals, and the possibility of rare exceptions.

DATA SOURCES

Forty-one articles reporting somatosensory evoked potentials in comatose patients and subsequent outcomes, from 1983 to 2000.

STUDY SELECTION

Studies were included if they reported coma etiology, age group, presence or absence of somatosensory evoked potentials, and coma outcomes.

DATA EXTRACTION

We separated patients into four groups: adults with hypoxic-ischemic encephalopathy, adults with intracranial hemorrhage, adults and adolescents with traumatic brain injury, and children and adolescents with any etiologies. Somatosensory evoked potentials were categorized as normal, abnormal, or bilaterally absent. Outcomes were categorized as persistent vegetative state or death vs. awakening.

DATA SYNTHESIS

For each somatosensory evoked potential result, rates of awakening (95% confidence interval) were calculated: adult hypoxic-ischemic encephalopathy: absent 0% (0%-1%), abnormal 22% (17%-26%), normal 52% (48%-56%); adult intracranial hemorrhage: absent 1% (0%-4%), present 38% (27%-48%); adult-teen traumatic brain injury: absent 5% (2%-7%), abnormal 70% (64%-75%), normal 89% (85%-92%); child-teen: absent 7% (4%-10%), abnormal 69% (61%-77%), normal 86% (80%-92%).

CONCLUSIONS

Somatosensory evoked potential results predict the likelihood of nonawakening from coma with a high level of certainty. Adults in coma from hypoxic-ischemic encephalopathy with absent somatosensory evoked potential responses have <1% chance of awakening.

[Anesthetic particularities of stereotaxic neurosurgery]

Functional neurosurgery procedures are long and specific. Cooperation of the patient may be necessary during surgery. The interference of anaesthetic agents with electrophysiological monitoring should be as little as possible. Local anaesthesia combined with intravenous sedation is often used, but general anaesthesia is more comfortable and secure. Since awakening during the procedure is generally planed, it has to be quick, reliable and of excellent quality. These requirements are fulfilled by the association of propofol by target-controlled infusion (TCI) and a continuous infusion of remifentanil.

Individually optimizing posterior tibial somatosensory evoked potential P37 scalp derivations for intraoperative monitoring

This investigation sought the optimal (highest amplitude) derivation for monitoring the posterior tibial P37 for each side in each individual, and determined whether this may change intraoperatively. Fifty monitored patients were studied using a partial P37 map consisting of FPz, Fz, Cz, Cz', Pz, POz, C4', and C3' to a noncephalic reference. From this, the highest amplitude scalp derivation was determined for each side. Of 100 tibial nerves, the initial optimal input 1 was Cz' in 52%, Pz in 28%, and Cz or iC' in 10%, and optimal input 2 was cC' in 69% and FPz in 31%. The optimal derivation was the same for each side in 34% of patients and different in 66%. Of 31 patients with at least one subsequent trial later during surgery, P37 topography changed in 14 and affected optimal inputs in 12. This occurred regularly during sitting-position posterior fossa surgery because of intracranial air, but sometimes occurred during other surgeries as well. The most common change consisted of FPz replacing cC' as optimal input 2. Input 1 changes were predominantly in an anterior or posterior sagittal direction. The results demonstrate great inter- and intraindividual P37 variability, and document intraoperative topographic changes. Both phenomena can be addressed by a practical method to refine intraoperative monitoring by individually optimizing scalp derivations and identifying topographic P37 changes during surgery.