Christoph Metz

Accuracy of Cerebral Monitoring in Detecting Cerebral Ischemia during Carotid Endarterectomy A Comparison of Transcranial Doppler Sonography, Near-infrared Spectroscopy, Stump Pressure, and Somatosensory Evoked Potentials

Background:This study compares the accuracy of cerebral monitoring systems in detecting cerebral ischemia during carotid endarterectomy. Methods:The authors compared transcranial Doppler sonography (TCD), near-infrared spectroscopy (NIRS), stump pressure (SP) measurement, and somatosensory evoked potentials (SEP) in 48 patients undergoing carotid surgery during regional anesthesia. Cerebral ischemia was assumed when neurologic deterioration occurred. During clamping, the minimum mean middle cerebral artery velocity (TCDmin), its percentage change (TCD%), the minimum regional saturation of oxygen (NIRSmin), its percentage change (NIRS%), the mean SP, and the changes of SEP amplitude were recorded. To analyze the corresponding sensitivity and specificity of each parameter, the authors performed receiver operating characteristic analysis. Results:Neurologic deterioration occurred in 12 patients. SP and NIRS were successfully performed in all patients. TCD monitoring was not possible in 10 (21%); SEP was not possible in 2 patients (4%). All parameters provided the ability to distinguish between ischemic and nonischemic patients. TCD% and NIRS% showed significantly better discrimination than TCDmin and NIRSmin (P < 0.05). The highest area under the curve (AUC) was found for TCD% (AUC = 0.973), but there was no significant difference compared with NIRS% (AUC = 0.905) and SP (AUC = 0.925). The lowest AUC was found for SEP (AUC = 0.749), which was significantly lower than that for TCD%, NIRS%, and SP. Conclusions:TCD%, NIRS%, and SP measurement provide similar accuracy for the detection of cerebral ischemia during carotid surgery. Lower accuracy was found for SEP monitoring. Because of the high rate of technical difficulties (21%), TCD monitoring was the least practical of the investigated monitoring devices.

Comparison of clinical, radiologic, and serum marker as prognostic factors after severe head injury.

BACKGROUND S-1OOB, a protein of astroglial cells, is described as a marker for neuronal damage. Reliable outcome prediction from severe head injury is still unresolved. Clinical scores such as the Glasgow Coma Scale score (GCS) and diagnostic scores such as the Marshall Computed Tomographic Classification are well established and investigated, but there are still some concerns about these tools. The aim of this study was to investigate the predictive value of the initial serum level of S-100B compared with the predictive value of the GCS score and the Marshall Computed Tomographic Classification to outcome after severe head injury. METHODS Forty-four patients with severe head injury (GCS score < 9) were included. Blood samples were drawn within 1 to 6 hours of injury. After a period of 11 months, their outcome was correlated by using the Glasgow Outcome Scale. Patients with an S-100B serum level above 2 microg/L, a GCS score between 3 and 5, and a computed tomographic scan in the categories 4 to 6 are predicted to have an unfavorable outcome. The predictive values of these tools were calculated according to these definitions. RESULTS The protein S-100B had with 17% the lowest total misclassification rate. When compared with the GCS score and Marshall Computed Tomographic Classification the S-100B serum level calculated on admission had the highest positive predictive value (87%) and negative predictive value (77%). CONCLUSION The serum level of S-100B calculated within 1 to 6 hours of a severe head injury is a useful additional outcome predictor.

S-100 serum levels after minor and major head injury.

BACKGROUND S-100, a protein of astroglial cells, is described as a marker for central nervous system damage. The aim of this study was to evaluate whether the marker could give information about the severity and possibility of functional recovery after minor and severe head injury. METHODS Thirty patients after severe head injury (Glasgow Coma Scale score < 9) and 11 patients after minor head injury (Glasgow Coma Scale score > 12) were included. In each case, blood samples were drawn within 6 hours after injury. Outcome was estimated at hospital discharge using the Glasgow Outcome Scale. RESULTS All patients who sustained minor head injury had reached a favorable outcome by the time they were discharged from the hospital. Their mean S-100 serum level was 0.35 microg/L. Patients who sustained severe head injury and were classified as having an unfavorable outcome (31%) showed a mean serum concentration of 4.9 microg/L, whereas patients classified as having a favorable outcome (69%) had a mean S-100 level of 1.2 microg/L. All groups differed significantly (p < 0.05). CONCLUSION S-100 appears to be a promising marker for the severity of head injury and neuronal damage.

Monitoring of Cerebral Oxygen Metabolism in the Jugular Bulb: Reliability of Unilateral Measurements in Severe Head Injury

To investigate the reliability of unilateral jugular venous monitoring and to determine the appropriate side, we performed bilateral jugular venous monitoring in 22 head-injured patients. Fiberoptic catheters were placed in both jugular bulbs. Arterial and bilateral jugular venous blood samples were obtained simultaneously for in vitro determination of jugular venous oxygen saturation (SJO2), arterial minus jugular venous lactate content difference (AJDL), and modified lactate-oxygen index (mLOI). Ischemia was assumed if one of the following pathologic values occurred at least unilaterally: SJO2 <54%, AJDL <−0.37 mmol/L, mLOI >0.08. The sensitivity of calculated unilateral monitoring in detecting ischemia was evaluated by comparing the incidence detected unilaterally with that disclosed bilaterally. The mean and maximum bilateral SJO2 differences varied between 1.4% and 21.0%, and 8.1% and 44.3%, respectively. The bias and limits of agreement (mean differences ± 2 SD) between paired samples were 0.4% ± 12.8%. There was no significant variation in bilateral SJO2 differences with time. Decreasing cerebral perfusion pressure (r = −0.559, P < 0.001) and arterial Pco2 (r = −0.342, P < 0.001) were associated with increasing bilateral SJO2 differences. Regarding AJDL, the maximum bilateral differences varied between 0.04 mmol/L and 1.52 mmol/L. The bias and limits of agreement were −0.01 ± 0.18 mmol/L. At best, 87% of ischemic events were disclosed by monitoring on the side of predominant lesion or, in diffuse injuries, on the side of the larger jugular foramen (computed tomographic [CT] approach). We conclude that in severe head injury, even calculated unilateral jugular venous monitoring has an unpredictable risk for misleading or missing data. Therefore, the reliability of unilateral jugular venous monitoring appears suspicious. For diagnosing ischemia the CT approach is recommended.

Dynamic changes of cerebral oxygenation measured by brain tissue oxygen pressure and near infrared spectroscopy.

The aim of this study was to find out whether a correlation exists between changes in brain tissue oxygen pressure (ti-pO2) and hemoglobin oxygenation (HbO2) measured by near-infrared spectroscopy. We studied 10 patients with severe head injury. A ti-pO2 monitoring device was introduced in the frontal white matter as soon as possible after administration. Additionally a NIRS sensor was placed at the forehead. All data were recorded simultaneously. Changes of the ti-pO2 curve were defined as events with the following criteria: > 10% change from the baseline value, > 3 min duration, clearly not an artifact. 137 events were found with a mean change of ti-pO2 of 8.3 +/- 10.2 mmHg. In 77.4% we observed a corresponding change of the HbO2. In 7 patients we found a good correlation (r > 0.7) between change ti-pO2 and change HbO2. In 3 patients the correlation was poor. The reason for poor correlation might be poor signal quality of the NIRS sensor or inhomogenous distribution of ischemic areas in the whole brain. We conclude that under the condition of a stable NIRS signal and a diffuse brain lesion, changes of ti-pO2 are well reflected by NIRS.

Cardiovascular and pulmonary effects of aerosolized prostacyclin administration in severe respiratory failure using a ventilator nebulization system

We investigated the effects of aerosolized prostacyclin (PGI2) administration on hemodynamics and pulmonary gas exchange in 8 patients with severe respiratory failure and acute pulmonary hypertension. Nebulization of epoprostenol (5 ng/kg body weight for 15 min) decreased mean pulmonary blood pressure from 41.2 +/- 6.7 mm Hg (mean +/- SD, before administration) to 36.1 +/- 6 mm Hg < or = 15 min (p < 0.05). The effect was reversed 10 min after discontinuation of PGI2 (40.9 +/- 6.3 mm Hg). Pulmonary vascular resistance index (339 +/- 138 dynes.s.cm-5.m2, before administration) was significantly (p < 0.05) reduced < or = 15 min (260 +/- 89 dynes.s.cm-5.m2) and increased again after discontinuation of PGI2 (341 +/- 142 dynes.s.cm-5.m2). The ratio of arterial oxygen to the fraction of inspired oxygen (PaO2/FiO2) increased from 119 +/- 34 mm Hg (before administration) to 163 +/- 76 mm Hg (15 min after initiation of administration p < 0.05) and was reduced after PGI2 discontinuation (116 +/- 35 mm Hg). Heart rate, mean blood pressure, central venous pressure, and pulmonary arterial wedge pressure remained unchanged, whereas cardiac index was slightly reduced. We assume that PGI2 aerosolization is a beneficial technique, applied with a ventilator nebulization system. The beneficial effect might be caused by selective pulmonary vasodilatation in well-ventilated areas of the lung.

Rapid evaluation of S-100 serum levels. Case report and comparison to previous results

The aim of this case report is to describe the time course of S-100 serum levels of a patient, after severe head injury, whose blood sample could be drawn very soon after injury. The results were compared to a group of patients in which a correlation between S-100 serum levels and outcome after traumatic brain injury could be demonstrated. Blood samples were taken on admission (mean 2.3 hours), 6, 12 and 24 hours after trauma and then every 24 hours up until and including the fifth day. The outcome was estimated on discharge using the Glasgow Outcome Scale. The S-100 serum level of the patient described in the case report with a favourable outcome had initially risen to 10.0 micrograms/l and showed a rapid decline. In the previous group, patients with unfavourable outcome had a S-100 serum level of 7 micrograms/l mean concerning the first probe (after 2.3 hours mean) compared to 1.5 micrograms/l mean (after 2.23 hours mean) in patients with favourable outcome (p < 0.05). In comparison to the literature, there seems to be differences regarding the enzyme liberation in stroke and head injury. Therefore, S-100 serum levels need to be interpreted with regard to collection time and underlying pathology.

Comparison of changes in cerebral blood flow and cerebral oxygen saturation measured by near infrared spectroscopy (NIRS) after acetazolamide.

SummaryThe present study compares the change of cerebral blood flow and HbO2 measured by near-infrared spectroscopy (NIRS) after administration of 1000 mg acetazolamide intravenously. CBF studies in 21 patients with ischaemic cerebrovascular disease were performed routinely with the133Xenon technique. Additionally the local HbO2 was recorded by NIRS. A rest study was followed by a second study after the administration of 1000 mg acetazolamide. In 18 patients we observed an increase of 30.8% of CBF and 4.7% of HbO2, 3 patients showed a decrease of CBF and 2 patients a simultaneous decrease of HbO2. We did not find a correlation between the absolute values of CBF and HbO2 at rest or after stimulation. However, a positive correlation (r=0.71, p < 0.05) between the change of CBF and HbO2 could be detected. Assuming a threshold value of normal CBF reactivity of 30% and 4% HbO2 reactivity we found for NIRS a sensitivity of 0.88 and a specificity of 0.75.The results demonstrate that changes of CBF can be detected with NIRS and the algorithm of the used monitor is able to calculate the intracranial part of the signal. So, NIRS can be used as non-invasive screening method to test the cerebrovascular reserve capacity.

Neuromonitoring in carotid surgery: are the results obtained in awake patients transferable to patients under sevoflurane/fentanyl anesthesia?

Background Diagnostic accuracy studies of neuromonitoring devices during carotid endarterectomy in awake patients are limited by the question of the transferability to anesthetized patients. This study was designed to compare the different neuromonitoring parameters in patients under regional and general anesthesia with stump pressure as the primary endpoint and the courses of cerebral blood flow velocity (Vmca) measured by transcranial Doppler sonography, regional cerebral oxygen saturation (rSO2) measured by near-infrared spectroscopy, and the amplitude of somatosensory evoked potentials (SEP) as the secondary endpoints. Materials and Methods Ninety-six patients undergoing carotid endarterectomy were randomized to regional (n=48) or sevoflurane/fentanyl anesthesia (n=48) group. Absolute and relative changes of Vmca and rSO2 and the SEP amplitude were recorded at baseline, during carotid artery clamping, and after declamping. Intergroup differences (ß) were calculated by generalized estimation equations and linear regression analysis. Results Mean arterial pressure (P<0.001) and heart rate (P<0.001) were significantly higher in the regional anesthesia group. SP did not differ between both the groups (ß=−1.6; P=0.71). Vmca (ß=9.2; P<0.01) and rSO2 (ß=4.1; P<0.01) values were higher in the awake patients. After adjustment for mean arterial pressure, the differences of Vmca remained consistent (ß=9.3; P<0.01) whereas these of rSO2 during clamping (ß=2.9; P=0.105) and during reperfusion (ß=2.7; P=0.095) disappeared. No significant differences were found for Vmca(%) (ß=−1.0; P=0.80), rSO2(%) (ß=−1.4; P=1.8) and SEP (ß=−2.6; P=0.29). Conclusion Carotid artery clamping leads to similar results of stump pressure and similar relative changes of transcranial Doppler sonography, near-infrared spectroscopy, and SEP monitoring in patients under regional and sevoflurane/fentanyl anesthesia.

The accuracy of jugular bulb venous monitoring in detecting cerebral ischemia in awake patients undergoing carotid endarterectomy.

To investigate the accuracy of jugular bulb venous monitoring in detecting cerebral ischemia, we performed ipsilateral jugular bulb venous monitoring in 48 patients undergoing carotid surgery under regional anesthesia. Cerebral ischemia was assumed when neurologic deterioration occurred. During carotid clamping, the maximal arterial-jugular venous oxygen content difference [AJDO2 (max)], the minimal jugular venous oxygen saturation [SjO2 (min)], the maximal arterial-jugular venous lactate content difference [AJDL (max)], the maximal lactate oxygen index [LOI (max)], and the maximal modified LOI [mLOI (max)] were determined. To quantify the selectivity of each parameter, we performed receiver operating characteristic analysis and determined the area under the curve. The cutoff points providing the highest accuracy and the corresponding sensitivity (Se) and specificity (Spec) were determined. Neurologic deterioration occurred in 12 patients. All parameters, except AJDO2 (max), showed significant ability to distinguish between ischemic and nonischemic patients. The area under the curve for AJDL (max) was 0.840, for SjO2 (min) 0.766, for LOI 0.745, for mLOI 0.748, and for AJDO2 (max) 0.672. We found cutoff points of ≥0.16 mmol/L for AJDL (max) (Se=67%; Spec=86%) and ≤55% for SjO2 (Se=75%; Spec=83%). In conclusion, the present investigation shows that AJDL, SjO2, LOI, and mLOI provide the ability to detect cerebral hypoperfusion. The highest accuracy was found for AJDL. Neither the calculation of LOI nor of mLOI showed improved results.