Somatosensory evoked potential monitoring during carotid surgery

Controversy exists over the value of intraoperative monitoring and shunting in patients undergoing carotid endarterectomy. Although it is widely believed that contralateral carotid occlusion and previous stroke mandate intraoperative shunting, the susceptibility of these two groups of patients to cerebral ischemia during carotid artery endarterectomy is not well defined. Somatosensory evoked potentials (SSEPs) were monitored in 113 carotid artery endarterectomy patients. Of these, 32 (28.3%) had a previous stroke, 24 (21.2%) had a contralateral carotid occlusion and 33 (29.2%) were diabetic. There were no deaths and only one perioperative stroke (0.9%). Cerebral ischemia occurred in 14 patients (12.4%). Six of these patients had a contralateral carotid occlusion. Some 29 patients (25.7%) were shunted, including 10 with contralateral carotid occlusions that did not have major SSEP changes. In the latter half of the study, 14 patients with contralateral carotid occlusions were selectively shunted (six shunted, eight not shunted) with no neurological complications. Thirty-two patients with prior strokes were selectively shunted (nine shunted, 23 not shunted); of these, one shunted patient undergoing combined carotid artery endarterectomy and coronary artery bypass grafting had a perioperative stroke. Intraoperative monitoring with SSEPs accurately identifies cerebral ischemia secondary to carotid clamping as well as patients requiring shunts. With the use of intraoperative SSEP monitoring, selective shunting may be safely performed in patients with a contralateral carotid occlusion or a previous stroke.     

Comparison of cerebral oximeter and evoked potential monitoring in carotid endarterectomy

Purpose

To assess the cerebral oximeter, which measures regional oxygen saturation (rSO₂) continuously and noninvasively, as a cerebral monitor during carotid endarterectomy (CEA). The rSO₂ was compared with Somatosensory Evoked Potentials (SSEPs) as an indicator for shunting and as a predictor of postoperative neurological deficits.

Methods

Seventy-two consenting patients undergoing CEA with general anaesthesia were studied. Normocarbia, normothermia and normotension were maintained. Cerebral monitoring consisted of bilateral median nerve SSEPs and the INVOS 3100 cerebral oximeter with the sensor pad placed on the ipsilateral forehead. Decreases in SSEP amplitude of 50% and in rSO₂ of 10% were considered clinically significant. Neurological assessment was performed at emergence from anaesthesia, 24 hr postoperatively and at discharge. The rSO₂ changes were compared with SSEP changes and with neurological deficits. Statistical analysis was with chi square and analysis of variance. P < 0.05 was considered significant.

Results

During carotid artery clamping, rSO₂ decreased from 72 ±8% to 68 ±9% and mean arterial blood pressure increased from 92 ±14 mmHg to 98 ±14 mmHg. In four patients, the carotid artery was shunted because of SSEP changes after cross-clamping. Five patients had ≥10% decreases in rSO₂ following clamp application. Changes in both SSEP and rSO₂ occurred in two patients. Three of the four shunted patients had transient postoperative neurological deficits. One patient had a transient deficit without changes in either monitor. There were no persistent postoperative deficits. Compared with SSEPs, rSO₂ had a sensitivity of 50% and a specificity of 96%.

Conclusion

Clinical experience with this evolving technology is ongoing. Its role in neurovascular procedures has yet to be established.     

The role of cranial computed tomography in carotid surgery

In patients who present with TIA, RIND, or CVA, the cranial CT scan can rule out other etiologies for neurologic symptoms. In addition to the clinical presentation, the CT scan allows further stratification of patients being considered for carotid endarterectomy. We propose that patients be classified as TIA (+), TIA (-), RIND (+), or CVA (-). The CT scan has defined a new subgroup of patients, TIA (+) and RIND (+)--the Silent Cerebral Infarction. Patients who are categorized as TIA (+), RIND (+), and CVA (+) (cerebral infarction on CT or by history) are at increased risk for intraoperative ischemia and postoperative neurologic deficit. As such, they should be selectively shunted based on intraoperative EEG monitoring or routinely shunted. There is a strong association between ulcerative plaque at the carotid bifurcation and cerebral infarction on CT. The CT scan is a critical diagnostic procedure in evaluating the patient with an acute neurologic event. Patients with negative CT scans are candidates for early operation. Carotid endarterectomy should generally be delayed for 4 to 6 weeks in patients with positive CT scans.     

Magnetic resonance imaging flow void changes after cerebrospinal fluid shunt in post-traumatic hydrocephalus: clinical correlations and outcome

The assessment of the flow-void in the cerebral aqueduct of patients with post-traumatic hydrocephalus on magnetic resonance imaging (MRI) evaluation could concur the right diagnosis and have a prognostic value. We analysed prospectively 28 patients after a severe head injury (GCS≤8), with radiological or clinical suspicion of post-traumatic hydrocephalus and a fast flow-void signal in the cerebral acqueduct on T2-weighted and proton density MRI. Twenty-two patients were shunted (n=19) or revised (n=3). Six patients were followed-up without surgery. Twenty out of 22 shunted patients (91%) showed variable reduction of the fast flow-void. Eighteen of the operated patients (82%) presented a significant clinical improvement at 6-month follow-up. All patients (n=2) who had no change of the fast flow-void after surgery did not clinically improve. The six non-shunted patients did not present any clinical or radiological improvement. In head-injured patients, fast flow-void in the cerebral aqueduct is diagnostic for post-traumatic hydrocephalus and its reduction after ventriculo-peritoneal shunt is correlated with a neurological improvement. In already shunted patients, a persistent fast flow-void is associated with a lack of or very slow clinical improvement and it should be considered indicative of under-drainage.     

Cerebral monitoring during carotid endarterectomy--a comparison between electroencephalography, transcranial cerebral oximetry and carotid stump pressure

OBJECTIVE: Various modalities are used for cerebral monitoring during carotid endarterectomy (CEA). The aim of this study was to evaluate whether transcranial cerebral oximetry (TCO) and carotid stump pressure (SP) are as accurate as electroencephalography (EEG) for monitoring cerebral ischaemia during carotid cross-clamping. METHODS: One hundred consecutive patients who underwent CEA were studied with continuous and simultaneous EEG and TCO. SP was measured for each patient. The percentage decrease of oxygenation on TCO was calculated during cross-clamping and surgery. EEG findings were used as the benchmark to detect cerebral ischaemia and were the indication for insertion of a temporary shunt. The relationship with TCO was observed in terms of percentage decrease in oxygenation. RESULTS: A total of 6 patients were shunted on the basis of their EEG changes. TCO changed more than 20% in these 6 patients, but an additional 12 patients had TCO changes with a normal EEG. This correlated with a decrease in blood pressure (BP) and was corrected by increasing the BP. The positive predictive values (PPVs) and negative predictive values (NPVs) for shunting based on TCO (as compared with EEG) were 33% and 100% respectively. Thirty-four patients had SP <50 mmHg, of whom 4 were shunted based on EEG changes. Two of 66 patients with SP >50 mmHg were shunted based on EEG changes. If a shunting policy had been based on a SP of 50 mmHg, 30 patients would have been shunted unnecessarily (PPV 12%), whereas the non-requirement for a shunt was predicted correctly in 64 of 66 patients (NPV 97%). There were 2 major strokes: 1 contralateral on day 3 in a patient with bilateral severe stenoses, and 1 ipsilateral in a nonshunted patient with normal EEG, TCO and SP >50 mmHg. CONCLUSION: Compared with EEG, TCO is a practical and non-invasive monitoring system with a high sensitivity (100%) but a low specificity. TCO is more sensitive to a drop in BP and responds earlier to these changes than EEG. SP should not be used as the sole predictor for shunting during CEA.     

Delayed treatment with magnesium: reduction of brain infarction and improvement of electrophysiological recovery following transient focal cerebral ischemia in rats

OBJECT: The authors examined whether delayed treatment with Mg++ would reduce brain infarction and improve electrophysiological and neurobehavioral recovery following cerebral ischemia-reperfusion. METHODS: Male Sprague-Dawley rats were subjected to right middle cerebral artery occlusion for 90 minutes followed by 72 hours of reperfusion. Magnesium sulfate (750 micromol/kg) or vehicle was given via intracarotid infusion at the beginning of reperfusion. Neurobehavioral outcome and somatosensory evoked potentials (SSEPs) were examined before and 72 hours after ischemia-reperfusion. Brain infarction was assessed after the rats had died. Before ischemia-reperfusion, stable SSEP waveforms were recorded after individual fore- and hindpaw stimulations. At 72 hours of perfusion the SSEPs recorded from ischemic fore- and hindpaw cortical fields were depressed in vehicle-injected animals and the amplitudes decreased to 19 and 27% of baseline, respectively (p < 0.001). Relative to controls, the amplitudes of SSEPs recorded from both ischemic fore- and hindpaw cortical field in the Mg++-treated animals were significantly improved by 23% (p < 0.005) and 39% (p < 0.001) of baselines, respectively. In addition, Mg++ improved sensory and motor neurobehavioral outcomes by 34% (p < 0.01) and 24% (p < 0.05), respectively, and reduced cortical (p < 0.05) and striatal (p < 0.05) infarct sizes by 42 and 36%, respectively. CONCLUSIONS: Administration of Mg++ at the commencement of reperfusion enhances electrophysiological and neurobehavioral recovery and reduces brain infarction after cerebral ischemia-reperfusion. Because Mg++ has already been used clinically, it may be worthwhile to investigate it further to see if it holds potential benefits for patients with ischemic stroke and for those who will undergo carotid endarterectomy.     

Somatosensory evoked potentials and cortical blood flow during craniotomy for vascular disease

It has been demonstrated that central conduction time (CCT) is slowed and that attenuation of cortical potentials occurs with reduced cerebral perfusion. During 11 craniotomies for aneurysm, arteriovenous malformation (AVM), or extracranial-intracranial (EC-IC) bypass, we continuously monitored somatosensory evoked potentials (SSEPs) and regional cortical blood flow (rCBF) as determined by a thermal flow probe. The CCT was calculated and correlated with the rCBF. In 8 of the 11 cases, the rCBF values varied within 1 SD of normal values derived from 25 measurements of nonischemic cerebral cortex. All initial CCT values were within 1 SD of normal, but 4 of 11 patients had a prolonged CCT intraoperatively. Three of these were associated with a low rCBF (14 to 31 ml/100 g/minute). One patient had postoperative confusion at the time of discharge. One patient who underwent AVM embolization had a permanent loss of SSEPs postoperatively, and his preexisting hemiparesis was more profound after operation. Finally, 1 patient's CCT improved after EC-IC bypass. This is a preliminary study that demonstrates the feasibility of monitoring CCT and rCBF during craniotomy. When rCBF values fall and the CCT slows, neurological deficit will probably occur.     

Topographical relationships between the brainstem auditory and somatosensory evoked potentials and the location of lesions in posterior fossa stroke

The topographical relationships between the location of brainstem lesions detected by magnetic resonance imaging and abnormality of brainstem auditory evoked potentials (BAEPs) and short-latency somatosensory evoked potentials (SSEPs) were studied in 57 patients with stroke in the posterior fossa. Abnormal BAEPs or SSEPs were associated with lesions involving the pontine tegmentum, and abnormal BAEPs also with lesions at the cerebellar peduncle. Absence of the V wave in BAEPs and N20 in SSEPs was associated with a localized overlapping area in the pontine tegmentum contralateral to stimulation. The overlapping area associated with loss of N20 coincided with the location of the medial lemniscus. Lesions widely involving the pontine tegmentum caused the disappearance of multiple waves in the BAEPs and SSEPs. Patients who entered prolonged coma or died had total loss of the III, IV, and V waves, bilateral absence to the contralateral response in BAEPs, or loss of N18 in SSEPs. The loss of N18 in SSEPs had a statistically significant correlation with bad outcome, which suggests the superiority of SSEPs for predicting the outcome of stroke and indicates the involvement of some system excluding the medial lemniscus in the generation of N18.     

Intraoperative decrease in amplitude of somatosensory-evoked potentials of the lower extremities with interbody fusion cage placement during lumbar fusion surgery

STUDY DESIGN.: A retrospective analysis was performed. OBJECTIVE.: To characterize neurophysiological data of patients who had a decrease in amplitude of somatosensory-evoked potentials (SSEP) of the lower extremities secondary to interbody fusion cage placement during lumbar fusion surgery with no alert of the electromyography (EMG). SUMMARY OF BACKGROUND DATA.: The most consistently used and studied modalities of neurophysiological monitoring during spine surgery are SSEPs, motor-evoked potentials (MEPs), and EMG. In general, it is accepted that MEPs along with SSEPs are used to detect spinal cord injury and EMGs are used to detect nerve root injury. METHODS.: The medical records of a consecutive series of 115 patients who had undergone a transforaminal lumbar interbody fusion (TLIF) procedure in which SSEPs, MEPs, and EMGs were utilized for neurophysiological monitoring were retrospectively reviewed. RESULTS.: One hundred fifteen cases of TLIF procedures were reviewed. The follow-up was 2 years after the last procedure. A total of 5 cases that demonstrated intraoperative SSEP changes were found. The age range for these cases was from 39 to 81 years (mean age, 61 yr). All 5 patients developed SSEP changes that were secondary to interbody fusion cage placement. All 5 cases demonstrated reversal of the SSEP changes to baseline after removal of the interbody cage. Three of these cases had no new postoperative neurological findings. However, given that these 3 cases of SSEP change were associated with a surgical event that improved secondary to an intervention (in this case removal of the interbody cage), those cases were classified as presumed positive. Two of the 5 cases were in fact associated with a new postoperative neurological deficit. CONCLUSION.: To our knowledge this study demonstrates the first reported SSEP alerts that were associated with a posterior lumbar interbody cage placement without a corresponding EMG alert.     

Continuous automated monitoring of somatosensory evoked potentials in posttraumatic coma

Using a microcomputer system, 36 patients were continuously monitored with somatosensory evoked potentials (SSEPs) following closed head injury. The mean duration of monitoring was five days. The patients' GCS scores at the start of monitoring ranged from 3-10. Mortality was 44%. Of 14 patients who had initial absence of SSEP activity after the N20 wave or lost this activity during the period of monitoring, 12 died and two remained vegetative. Eighteen of 22 patients who had preservation or enhancement of this activity had a functional survival (3-month outcomes, p less than 0.001). The best outcomes were observed in the patients with the greatest number of peaks and highest amplitudes in the SSEPs, often in spite of increased intracranial pressure (ICP). The management of three patients was altered as a result of SSEP monitoring. We conclude that continuous monitoring of SSEPs is a useful adjunct in the management of comatose head-injured patients.     

What factors are related to impairment of cerebrovascular reserve before and after arteriovenous malformation resection? A cerebral blood flow study using xenon-enhanced computed tomography

OBJECTIVE: To examine the incidence and possible determinants of impaired vascular reserve in arteriovenous malformation (AVM)-affected brain, before and after surgery. METHODS: In a prospective study of 30 patients, the regional cerebrovascular reserve capacity (rCRC) and the vasodilated regional cerebral blood flow (rCBF) were assessed during an acetazolamide challenge, using xenon-enhanced computed tomography, before and after complete AVM resection. Single brain slices at the level of the basal ganglia were examined, and scanning through the AVMs was avoided. Five regions of interest in the AVM-bearing hemisphere were compared with their counterparts in the unaffected hemisphere. Vasodilated rCBF reductions of at least 20% in one or more regions of interest and rCRC values of less than 10 ml/100 g/min were considered to be significant. RESULTS: Ipsilateral vasodilated rCBF was significantly reduced in 17 patients before surgery and 15 patients after surgery. Ipsilateral rCRC was impaired in 14 patients before surgery and 12 patients after surgery. Large AVM size, venous congestion, and AVM-related vascular territories were correlated with impaired vascular reserve in AVM-nonadjacent brain tissue before surgery. Similar correlations were observed after surgery, except that not AVM size but a large number of AVM-supplying vascular territories was correlated. Moreover, the smallest AVMs and those supplied by a single vascular territory, as well as hemorrhage and nonhemorrhagic neurological deficits as presenting symptoms, were correlated with reduced ipsilateral vasodilated rCBF before surgery. Among patients with AVMs and nonhemorrhagic epilepsy, a trend of impaired cerebrovascular reserve was observed. In the only case of postresectional "breakthrough," the preoperative rCRC was not impaired but abnormally high. CONCLUSION: Among the determinants of impaired cerebrovascular reserve, AVM size is already a constituent of current grading scales and decision-making paradigms, whereas factors such as venous congestion have been less closely considered or less obvious but may deserve increased attention in the future. Nonhemorrhagic epilepsy in patients with AVMs may constitute the clinical equivalent of chronic cerebral ischemia in a murine model. Postresectional breakthrough may be partly attributable to individual predisposition to excessive vasoreactivity in the whole brain.     

Somatosensory evoked potential

Summary Somatosensory evoked potentials (SSEPs) have been used to help minimize neurologic morbidity during spinal surgery. While this is a sensory test it has been used as an inference of motor function. The failure to always achieve the latter goal has resulted in some pessimism regarding the value of this test. In this series of 161 operations in 150 patients, it was demonstrated that SSEPs were recordable under anesthesia in 87% of patients. Of these patients, 12% had their spinal surgery interrupted due to significant neurophysiologic changes; of these patients, 18% had new neurologic deficits postoperatively. There were no cases with new neurologic deficits who had no changes in their SSEPs. It was concluded that SSEP monitoring may be helpful in identifying potentially neurologically threatening surgical maneuvers in a significant number of patients.     

Somatosensory evoked potentials in severe traumatic brain injury: a blinded study.

OBJECT: Beginning in 1979, the results of somatosensory evoked potential (SSEP) monitoring have been used to predict outcome in patients who have suffered severe brain trauma. The data indicate that if the cortical components of the SSEPs were bilaterally absent, the outcome was always death or a vegetative state, but previous studies have not been blinded. The aims of this study were to correlate the results of SSEP recordings with the outcome in a prospectively blinded manner and to assess whether monitoring of SSEPs was a useful adjunct to clinical judgment in the prediction of outcome. METHODS: The authors studied 105 severely head injured patients (median Glasgow Coma Scale score of 6) who were admitted to the Waikato Intensive Care Unit. The upper limb SSEPs were classified according to the central conduction time (CCT) as normal, of increased latency, or absent. The outcome as assessed using the Glasgow Outcome Scale (GOS) score was evaluated 12 months after the injury. CONCLUSIONS: Of 51 patients with a bilaterally normal CCT, 29 (57%) had a good outcome (GOS Score 5). Any delay in CCT was associated with a decreased incidence of good outcome (30%). Unilateral absence of the cortical component of the SSEP was usually associated with a poor outcome (death or severe disability), and bilateral absence was always associated with a poor outcome. The authors conclude that SSEPs correlate well with outcome and that this is not the result of investigator bias.     

Drug-induced hypotension SEP test and acetazolamide test using 133Xe SPECT in patients with occlusive carotid disease--selection of candidates for extracranial-intracranial bypass.

The correlation between the drug-induced hypotension somatosensory evoked potential (SEP) test and regional cerebral blood flow changes after acetazolamide administration was studied. Fourteen patients presenting with transient ischemic attack, reversible ischemic neurological deficits, or minor completed stroke were evaluated. All patients had no or only localized low-density areas on computed tomographic scans, and unilateral occlusion or severe stenosis of the internal carotid or middle cerebral artery on cerebral angiograms. The Diamox asymmetry enhancement (DAE) was studied to detect reduced cerebral perfusion reserve in the affected hemispheres. The DAE was 7.9 +/- 5.8% in seven patients positive in the SEP test, significantly higher than -1.5 +/- 2.9% in patients negative in the SEP test. Postoperative SEP tests were negative in all five patients who underwent extracranial-intracranial (EC-IC) bypass surgery, suggesting that the EC-IC bypass improved the cerebral perfusion reserve in the affected hemispheres. The DAE decreased significantly in four of these patients. This study disclosed a significant correlation between the drug-induced hypotension SEP test and DAE. These parameters are considered important for evaluating patients with hemodynamic compromise and/or suitable candidates for EC-IC bypass.     

Are CT infarcts a separate risk factor in patients with transient cerebral ischaemic episodes?

CT cerebral infarcts have been reported in a number of studies of patients with transient ischaemic episodes. The hypothesis that these asignomatic infarcts, i.e. without associated clinical neurological deficit reflect the ability of the brain to limit the extent of neuronal damage through its collateral circulation was tested in 50 patients undergoing both CT scanning and cerebral angiography. Out of 50 patients there were 15 patients with a total of 17 infarcts on CT scan. Fourteen of 50 patients had evidence of diminished collateral reserve capacity on cerebral angiography. Ten of these 14 patients (71%) had CT evidence of infarction, in contrast to an incidence of five out of 36 patients (14%) without evidence of diminished collateral reserve. These results indicate that CT infarcts and collateral cerebral circulation must be evaluated as prognostic factors in patients with T.I.A.s.     

Adenosine: A Sensitive Indicator of Cerebral Ischemia during Carotid Endarterectomy

Background: For the human brain, there are no data available concerning the significance of adenosine and its metabolites as biochemical indicators of cerebral ischemia. Since adenosine may counteract key pathogenetic mechanisms during cerebral ischemia, its sensitivity and specificity as a marker of cerebral ischemia was investigated in relation to hypoxanthine and lactate.

Methods: Arterial and jugular venous concentration changes of adenosine, hypoxanthine, and lactate were studied in 41 patients undergoing carotid endarterectomy. Cerebral tissue oxygenation was monitored continuously by somatosensory-evoked potentials. A carotid artery shunt (n = 6) was placed only after complete loss of somatosensory-evoked potentials.

Results: Before carotid artery clamping jugular venous concentrations of adenosine, hypoxanthine, and lactate in subsequently shunted patients were 229 +/- 88 nM, 1105 +/- 116 nM, and 0.85 +/- 0.52 mM, respectively (mean +/- SD). In patients who required shunting, carotid artery clamping induced a significant increase in jugular venous adenosine (389 +/- 114 nM) and jugular venous hypoxanthine (1444 +/- 168 nM). In contrast, the increase in jugular venous lactate (0.91 +/- 0.48 mM) did not reach statistical significance. Focal cerebral ischemia was indicated by jugular venous adenosine with a sensitivity and specificity of 0.83 and 0.71, respectively.     

Prevention of positional brachial plexopathy during surgical correction of scoliosis

Continuous intraoperative monitoring of spinal cord function using somatosensory evoked potentials (SSEP) has gained nearly universal acceptance as a reliable and sensitive method for detecting and possibly preventing neurologic injury during surgical correction of spinal deformities. In several reports, spinal cord injury was identified successfully based on changes in SSEP response characteristics, specifically amplitude and latency. Less well documented and used, however, is monitoring of peripheral nerve function with SSEPs to identify and prevent the neurologic sequelae of prolonged prone positioning on a spinal frame. The authors describe a patient who underwent surgical removal of spinal instrumentation but was not monitored. A brachial plexopathy developed in this patient from pressure on the axilla exerted by a Relton-Hall positioning frame during spinal surgery. In addition, data are presented from 15 of 500 consecutive pediatric patients who underwent surgical correction of scoliosis between 1993 and 1997 with whom intermittent monitoring of ulnar nerve SSEPs was used successfully to identify impending brachial plexopathy, a complication of prone positioning. A statistically significant reduction in ulnar nerve SSEP amplitude was observed in 18 limbs of the 500 patients (3.6%) reviewed. Repositioning the arm(s) or shoulders resulted in nearly immediate improvement of SSEP amplitude, and all awoke without signs of brachial plexopathy. This complication can be avoided by monitoring SSEPs to ulnar nerve stimulation for patients placed in the prone position during spinal surgery.     

Adenosine: a sensitive indicator of cerebral ischemia during carotid endarterectomy.

BACKGROUND: For the human brain, there are no data available concerning the significance of adenosine and its metabolites as biochemical indicators of cerebral ischemia. Since adenosine may counteract key pathogenetic mechanisms during cerebral ischemia, its sensitivity and specificity as a marker of cerebral ischemia was investigated in relation to hypoxanthine and lactate. METHODS: Arterial and jugular venous concentration changes of adenosine, hypoxanthine, and lactate were studied in 41 patients undergoing carotid endarterectomy. Cerebral tissue oxygenation was monitored continuously by somatosensory-evoked potentials. A carotid artery shunt (n = 6) was placed only after complete loss of somatosensory-evoked potentials. RESULTS: Before carotid artery clamping jugular venous concentrations of adenosine, hypoxanthine, and lactate in subsequently shunted patients were 229+/-88 nM, 1105+/-116 nM, and 0.85+/-0.52 mM, respectively (mean +/- SD). In patients who required shunting, carotid artery clamping induced a significant increase in jugular venous adenosine (389+/-114 nM) and jugular venous hypoxanthine (1444+/-168 nM). In contrast, the increase in jugular venous lactate (0.91+/-0.48 mM) did not reach statistical significance. Focal cerebral ischemia was indicated by jugular venous adenosine with a sensitivity and specificity of 0.83 and 0.71, respectively. CONCLUSIONS: Carotid artery clamping induced significant increases in jugular venous adenosine and hypoxanthine in patients with inadequate collateral blood flow. In addition, focal cerebral ischemia was reflected by changes in adenosine concentrations.     

Continuous monitoring of cerebral hemodynamic reserve in acute brain injury: relationship to changes in brain swelling.

A new concept of cerebral hemodynamic and metabolic physiology, cerebral hemodynamic reserve (CHR), was evaluated in 20 comatose adults with acute traumatic brain swelling who were undergoing continuous monitoring of the arteriojugular difference in oxyhemoglobin saturation, along with cerebral perfusion pressure and expired PCO2. The CHR was measured as the ratio of relative (percent) changes in cerebral oxygen extraction to relative changes in cerebral perfusion pressure during spontaneous increases in intracranial pressure. In patients with initially severe brain swelling, the CHR was more frequently abnormal (compromised) on the first day, and tended to improve on the second day. In patients with initially moderate brain swelling, the CHR was more frequently normal (preserved) on the first day, but tended to become compromised on the second day if the brain swelling exacerbated. It is concluded that cerebral hemodynamic reserve abnormalities very closely associate with signs of increased intracranial "tightness" on computed tomographic scans of the head. Cerebral hemodynamic reserve could therefore become an important guide in the functional evaluation and management of acute brain swelling (focusing on cerebral oxygenation and perfusion pressure) in a variety of predominantly diffuse acute intracranial disorders.     

Subdural effusions re-appearing after shunts in patients with non-tumoural stenosis of the aqueduct

Three patients shunted for non-tumoural stenosis of the aqueduct suffered from progressive clinical symptoms about four months after the shunting. Computed tomography (CT) showed bilateral subdural effusions. The effusions were evacuated, and the shunts revised. One month later all patients suffered from symptoms of increased intracranial pressure, and CT showed enlargement of the supratentorial cerebral ventricles. The effusions had disappeared. After shunt revision the symptoms decreased again. The fluctuation in the ventricular size, the thickness of the subdural effusions, and the clinical deterioration were related to the change in the opening pressure of the shunt valve in all patients. Patients with large supratentorial cerebral ventricles (Evans index over 0.40) should be monitored by intraventricular pressure recording in order to select the exact opening pressure of the shunt valve before inserting a relieving shunt; a clinical check-up and a CT examination should be carried out about three months after the operation in order to investigate any changes in the function of the shunt.