What is the most sensitive non-invasive strategy for the diagnosis of intracranial aneurysms?
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Acute Disease↗
Biomedical subjects
P J Kirkpatrick
Publications and source records attributed to P J Kirkpatrick.
Evaluation of a near-infrared spectrometer (NIRO 300) for the detection of intracranial oxygenation changes in the adult head.
BACKGROUND AND PURPOSE: The clinical application of intracranial near-infrared spectroscopy in adults has been hampered by concerns over contamination from extracranial tissues. The NIRO 300 (Hamamatsu Photonics) provides continuous online measurements of hemoglobin and cytochrome oxidase concentrations and a calculated tissue oxygen index (TOI). The present study seeks confirmation of the anatomic source of TOI in the adult cranium. METHODS: Sixty patients undergoing carotid endarterectomy were studied. The NIRO 300 was incorporated into an established multimodal monitoring system. TOI, oxyhemoglobin, and deoxyhemoglobin changes were assessed and compared with (1) frontal cutaneous laser-Doppler flowmetry and (2) transcranial Doppler measurement of the ipsilateral middle cerebral artery flow velocity. RESULTS: Changes in TOI were seen during cross-clamping of the carotid vessels in 49 patients (mean DeltaTOI=-9.4%, SD=7.1). Significant correlation was seen between TOI and flow velocity (r=0.56) but not with laser-Doppler flowmetry (r=0.13). In 31 patients, oxyhemoglobin and deoxyhemoglobin concentrations were recorded, showing significant changes during both external carotid artery and internal carotid artery clamping. A change in TOI was predominantly associated with internal carotid artery clamping (n=41). When TOI changed during external carotid artery clamping (n=8), significant blood pressure changes occurred, or extracranial-to-intracranial anastomosis was evident. In the absence of such variables, the sensitivity of TOI to intracranial and extracranial changes was 87.5% and 0%, respectively, and specificity was 100% and 0%, respectively. CONCLUSIONS: The NIRO 300 reflects changes in cerebral tissue oxygenation when TOI is calculated, with a high degree of sensitivity and specificity.
Adult↗
The influence of hemodynamic stress factors on intracranial aneurysm formation.
OBJECT: Applanation tonometry is a noninvasive method of assessing both peripheral and central arterial blood pressure (BP) profiles. In this study the authors examine whether there are differences in these profiles in patients with intracranial aneurysms when compared with age-matched controls. METHODS: Carotid artery (CA) and derived aortic BP waveforms were obtained using a pulse wave analysis system. The ratio of the pressure wave amplitude above the systolic shoulder to the total systolic BP (augmentation index [AI]) was recorded. One hundred seventy-three patients with intracranial aneurysms (23 unruptured lesions) and 173 healthy control volunteers were examined. For the patients with aneurysms the right and left CA AIs (mean +/- standard deviation) were 125.6 +/- 23.1% and 128.3 +/- 22.1%, respectively. Corresponding values for the control group were 118.4 +/- 22.6% and 119.4 +/- 21.8%. The calculated AI for the ascending aorta was 29.8 +/- 10.5% and 25.6 +/- 12.2% for patients with aneurysms and control volunteers, respectively. Significant asymmetry in CA AI was seen in patients with aneurysms, the left being greater (p = 0.002). No significant differences were seen in mean BP (108 +/- 14 mm Hg in patients with aneurysms compared with 106 +/- 16 mm Hg in controls; p = 0.2). Multivariate analysis excluded the influence of BP and other potential confounding vascular risk factors for increased AI. CONCLUSIONS: Significant differences in AI, both in magnitude and symmetry, were identified in patients with intracranial aneurysms when compared with matched controls.
Adolescent↗
Continuous assessment of cerebral autoregulation--clinical verification of the method in head injured patients.
Previously, using transcranial Doppler ultrasonography, we investigated whether the hemodynamic response to spontaneous variations in cerebral perfusion pressure (CPP) provides reliable information about cerebral autoregulatory reserve. In the present study we have verified this method in 166 patients after head trauma. Waveforms of intracranial pressure (ICP), arterial pressure and transcranial Doppler flow velocity (FV) were captured daily over 0.5-2.0 hour periods. Time-averaged mean flow velocity (FV) and CPP were resolved. The correlation coefficient indices between FV and CPP (Mx) were calculated over 3 minutes epochs, and averaged for each investigation. An index of CBF (flow velocity diastolic to mean ratio) was calculated independently for each investigation. Mx depended on CPP (p < 0.0001) increasing to positive values when CPP decreased below 60 mm Hg. This threshold coincided with an averaged breakpoint for autoregulation, expressed by the index of CBF. Mx depended on outcome following head injury stronger than the Glasgow Coma Score on admission (ANOVA, F values 18 and 15 respectively; N = 166). In patients who died, cerebral autoregulation was disturbed during the first two days following injury. These results indicate an important role for the continuous monitoring of autoregulation following head trauma.
Blood Flow Velocity↗
On-line monitoring of substrate delivery and brain metabolism in head injury.
Head injury is associated with complex pathophysiological changes in metabolism. The objective of the study was to investigate these changes by applying on-line bedside monitoring of cerebral metabolism using microdialysis. Following approval by the Local Ethics Committee and consent from the next of kin, a microdialysis catheter was inserted into the frontal cortex of patients with severe head injury. Twenty-one patients were studied for 102.3 +/- 26.9 hours (mean +/- 95% confidence interval; total 89.4 patient monitoring days). The overall cerebral glucose (mean of means) was 1.63 +/- 0.31 mM with periods of undetectable glucose recorded. The cerebral lactate and lactate/pyruvate ratio were 4.69 +/- 0.61 mM and 29.9 +/- 3.73 respectively. Patients who died (n = 4) or who were severely disabled (not proceeding to rehabilitation, n = 5) had a tendency towards lower glucose (1.39 +/- 0.35 mM), higher lactate (5.10 +/- 1.02 mM) and higher lactate/pyruvate ratios (35.5 +/- 7.67) compared to patients with good outcome (home or proceeding to rehabilitation, n = 12, glucose 1.80 +/- 0.49 mM, lactate 4.38 +/- 0.85 mM, lactate/pyruvate ratio 27.9 +/- 4.33). Trends in these metabolic parameters relating to outcome were identifiable. In the majority of patients, cerebral glutamate levels (overall mean of means 9.47 +/- 4.59 microM) were initially high and then declined to stable levels. Patients in whom the glutamate level remained elevated or in whom secondary rises in glutamate were seen had a poor outcome. The application of bedside analysis of microdialysis enables the progress of the patient to be monitored on-line. In addition to establishing trends of improving and deteriorating metabolism, the technique has the potential to monitor the effects of therapeutic manoeuvres on the biochemistry.
Adolescent↗
Immune responses to Chlamydia antigens in atherosclerosis.
Aim of this study was to isolate T lymphocytes from atheromatous plaques and to determine they respond to Chlamydia antigens. Atheromatous plaques from carotid endarterectomy patients, were cultured in vitro with the T cell growth factor, IL-2. This rarely allowed outgrowth of T cell lines. However, when combined with a mitogenic or antigenic stimulus to T cells, T cell lines were obtained from most patients, and from approximately 30% of replicate plaque tissue fragments. Chlamydia organisms were as effective in allowing the establishment of T cell lines as other recall antigens. T cell lines were tested for their ability to recognize antigens presented by autologous macrophages. Some lines responded to Chlamydia organisms, and also to the recombinant Chlamydia proteins hsp60 and OMP2. However, other lines recognized recall antigens. These results indicate that the atheromatous plaque contains memory T lymphocytes, and amongst the antigens they recognize are Chlamydia proteins. Stimulation of T cells was required to allow outgrowth in vitro, suggesting that the T cells were not in an activated state in vivo. However, since Chlamydia pneumoniae is present in the atheromatous plaque, activation of Chlamydia-reactive T cells by local antigen is a potential pro-inflammatory mechanism which could contribute to the pathogenesis of atherosclerosis.
Antigens, Bacterial↗
T lymphocyte lines isolated from atheromatous plaque contain cells capable of responding to Chlamydia antigens.
Chlamydia pneumoniae infection is associated with atherosclerosis and the organism has been identified in arterial lesions. To determine whether T lymphocyte-mediated immune responses to Chlamydia antigens within plaque could contribute to pathogenesis, we have derived T cell lines from atherosclerotic plaques of 32 patients. Culture with IL-2 alone proved insufficient for cellular activation and expansion, but additional stimulation with phytohaemagglutinin (PHA) or recall antigens allowed consistent establishment of T cell lines. Furthermore, in cultures of approx. 500 tissue fragments, Chlamydia organisms proved as effective as other recall antigens in producing outgrowth of arterial T cells (20-25% wells produced T cell lines). Testing the antigen responsiveness of T cell lines showed that those derived using Chlamydia organisms were more likely to respond to Chlamydia (5/29+) than those isolated using other stimuli (6/69+ for PHA; 5/57+ for PPD and tetanus toxoid (TT)). However, lines responsive to each of the recall antigens were observed. Using recombinant Chlamydia antigens, some Chlamydia-specific T cell lines were shown to respond to OMP2 and/or hsp60. Those recognizing Chlamydia hsp60 did not cross-react with human hsp60, but human hsp60-responsive lines were also observed. Thus, atherosclerotic plaque tissue contains a variety of memory T lymphocytes, and amongst these are cells capable of recognizing Chlamydia antigens. In a C. pneumoniae-infected plaque, such T cells may be activated by local antigen and could contribute to the inflammatory process in the arterial wall through CD40 ligand expression and cytokine secretion.
Aged↗
Multiparameter brain tissue monitoring--correlation between parameters and identification of CPP thresholds.
Continuous monitoring of brain interstitial gas concentrations allows direct regional evaluation of the pathophysiology of cerebral tissues. We have incorporated the Paratrend 7 (P7) multiparameter sensor into our established multimodal monitoring of head injured patients, to investigate the relationship between brain and arterial pO2, pCO2, and pH, as well as defining thresholds for cerebral perfusion pressure (CPP). A P7 sensor was inserted into the brain tissue of 40 adult head injured patients via a modified Camino bolt or triple lumen bolt. A second sensor was placed in the femoral artery for continuous monitoring of blood gases. Data signals from 19 monitored parameters were collected onto computer at the bedside for up to 14 days. No complications were seen. For individual patients the changes in brain tissue parameters showed large variations over 24 hours and the relationship between parameters varied considerably both between patients and during the period of monitoring any one individual. Changes related to periods of arterial desaturation, cerebral hypoperfusion and therapeutic manoeuvres could be seen. Good correlation was seen between brain pCO2 and arterial pCO2 (r = 0.58). Poor correlation was seen between CPP and brain pO2, and between brain pO2 and ICP. However, by grouping values for intracranial pressure (ICP) and CPP, thresholds for brain tissue pO2 were identified in 16 patients where CPP fell below 60 mmHg. No patients where CPP was always > 60 mmHg showed a significant threshold for a drop in brain pO2 (n = 16). In conclusion, the P7 shows potential as a monitor of regional brain oxygenation and for detection of potentially damaging secondary insults. The results must be interpreted whilst considering catheter position, autoregulation and systemic arterial changes for each individual.
Adolescent↗
Head injury monitoring using cerebral microdialysis and Paratrend multiparameter sensors.
INTRODUCTION: Following head injury complex pathophysiological changes occur in brain metabolism. The objective of the study was to monitor brain metabolism using the Paratrend multiparameter sensor and microdialysis catheters. PATIENTS, MATERIAL AND METHODS: Following approval by the Local Ethics Committee and consent from the relatives, patients with severe head injury were studied using a triple bolt inserted into the frontal region, transmitting an intracranial pressure monitor, microdialysis (10 mm or 30 mm membrane; glucose, lactate, pyruvate, glutamate) catheter and Paratrend multiparameter (oxygen, carbon dioxide, pH and temperature) sensor. A Paratrend sensor was also inserted into the femoral artery for continuous blood gas analysis. RESULTS: 21 patients were studied with cerebral microdialysis for a total of 91 monitoring days (range 19 hours to 12 days). Of these, 14 patients were also studied with cerebral and arterial Paratrend sensors. The mean (+/- 95% confidence intervals) arterial and cerebral oxygen levels were 123 +/- 10.9 mmHg and 27.9 +/- 5.71 mmHg respectively. The arterial and cerebral carbon dioxide levels were 34.3 +/- 2.35 mmHg and 45.3 +/- 3.07 mmHg respectively. Episodes of systemic hypoxia and hypotension resulting in falls in cerebral oxygen and rises in cerebral carbon dioxide were rapidly detected by the arterial and cerebral Paratrend sensors. Systemic pyrexia was reflected in the brain with the cerebral Paratrend sensor reading 0.17 degree C (mean) higher than the arterial sensor. Elevations of cerebral glucose were detected, but the overall cerebral glucose was low (mean 1.57 +/- 0.53 mM 10 mm membrane; mean 1.95 +/- 0.68 mM 30 mm membrane) with periods of undetectable glucose in 6 patients. Lactate concentrations (mean 5.08 +/- 0.73 mM 10 mm membrane; mean 8.27 +/- 1.31 mM 30 mm membrane) were higher than glucose concentrations in all patients. The lactate/pyruvate ratio was 32.1 +/- 5.16 for the 10 mm membrane and 30.6 +/- 2.17 for the 30 mm membrane. Glutamate concentrations varied between patients (mean 15.0 +/- 10.5 microM 10 mm membrane; mean 28.8 +/- 17.8 microM 30 mm membrane). CONCLUSION: The combination of microdialysis catheters and Paratrend sensors enabling the monitoring of substrate delivery and brain metabolism, and the detection of secondary metabolic insults has the potential to assist in the management of head-injured patients.
Accidents, Traffic↗
A new cranial access device for cerebral monitoring.
We report the design and clinical application of a new cranial access device (triple bolt) designed to transmit intracranial pressure monitors, multiparameter sensors, microdialysis catheters and laser doppler probes into the cerebral parenchyma. The objective was to achieve insertion on the Neuro-Critical Care Unit, imaging compatibility, angled trajectories and versatility of monitor application. The bolt has been successfully applied to 100 patients with severe head injury and subarachnoid haemorrhage.
Equipment Design↗
Outcome from poor grade aneurysmal subarachnoid haemorrhage--which poor grade subarachnoid haemorrhage patients benefit from aneurysm clipping?
Patients with poor grade aneurysmal subarachnoid haemorrhage (SAH) are associated with high mortality and morbidity, and hence are often treated conservatively. This study has set out to determine the outcome for all poor grade subarachnoid haemorrhage patients, and attempts to identify a subgroup with a more favourable prognosis. During a prospective audit of patients with aneurysmal SAH, patients of poor grade [World Federation of Neurological Surgeons (WFNS) IV (and not obeying commands) and V] were sedated, paralysed and ventilated for transfer to the Regional Neurosurgical Unit. Any intraventricular blood and/or hydrocephalus was treated by external ventricular drainage. Following a 24-h period for active blood gas, fluid and electrolyte resuscitation, patients were assessed after reversal of sedation. Selection for angiography and potential aneurysm surgery was restricted to those who showed a purposeful response to painful stimulation. Patients who could readily obey commands were not considered 'true' poor grade and were excluded from analysis. In 102 patients with 'true' poor grade SAH admitted between 1991 and 1997, the overall management outcome at 6 months was poor (favourable outcome 25%, mortality 67%). Following reversal of sedation, 55 patients demonstrated a purposeful response and proceeded to angiography, of whom 37 underwent clipping and three coiling of aneurysm. The outcome in this aneurysm treated subgroup was favourable in 53% (mortality 28%). If patients over the age of 65 years are excluded, the management outcome was favourable in 35% (mortality 58%), with those patients proceeding to clipping or coiling of aneurysms having a favourable outcome in 57% (mortality 27%). Patients over the age of 65 years with poor grade SAH had a favourable outcome in only 6% (mortality 85%). The mortality for poor grade SAH patients remains high. However, following resuscitation and correction of any acute hydrocephalus, a patient subgroup identified on simple clinical criteria can be identified who can expect a better outcome.
Adolescent↗
Prediction of cerebral ischaemia during carotid endarterectomy with preoperative CO2-reactivity studies and angiography.
The objective of this study was to assess the value of combining the preoperative CO2 cerebrovascular reactivity index (CO2RI) with carotid and cerebral angiography in predicting the risk of severe cerebral ischaemia (SCI) during carotid endarterectomy (CEA). Seventy-four consecutive patients scheduled for CEA underwent preoperative digital subtraction angiography and CO2-reactivity tests. During CEA, cerebral function monitor (CFM) was used to document cortical electrical activity, whilst transcranial Doppler measured the middle cerebral artery flow velocity (FV). A persistent fall in CFM voltage and/or a fall in FV > or = 60% on internal carotid artery (ICA) clamping were used as criteria for defining SCI. Complete data from 59 patients were obtained for final analysis. Twelve cases showed a fall in FV > or = 60%; 11 of these also showed a sustained fall in CFM voltage. Using logistic regression, the risk of SCI was found to be negatively associated with (1) contralateral CO2RI, (2) the percentage stenosis of the contralateral ICA, and (3) the difference between ipsilateral and contralateral CO2RI. Using these factors, a logistic regression model for predicting the risk of SCI was established which provided a sensitivity of 75% and specificity of 100%. The risk of SCI during CEA was related to the contralateral ICA stenosis and the CO2RI of both cerebral hemispheres. This information may assist in presurgical planning and help to select asymptomatic carotid lesions for surgery.
Aged↗
Deficits in decision-making in patients with aneurysms of the anterior communicating artery.
Patients with aneurysmal subarachnoid haemorrhage (SAH) secondary to ruptured anterior communicating artery aneurysms (ACoA) often suffer from neuropsychological sequelae including personality and behavioural changes. In this study, 31 patients with ruptured aneurysms of the ACoA resulting in SAH [mean age 50.9 years, NART (National Adult Reading Test) IQ 108.7] were compared with a group of 29 normal controls (mean age 51.9 years, NART IQ 109.7) on a specific task of decision-making. A similar task has been imaged previously and shown to activate regions involving the ventromedial prefrontal cortex. Patients with ACoA rupture showed no significant difference from controls on the task in their speed or quality of decision-making. They did, however, exhibit increased risk-taking behaviour, placing higher bets in a measure of the task which involved choices between actions associated with differing magnitudes of reward and punishment. ACoA patients demonstrated true risk-taking behaviour as opposed to simple impulsivity. Such a deficit in decision-making may be a result of direct damage to the orbital prefrontal cortex itself (as a result of micro-ischaemia or infarction after ACoA aneurysmal rupture) or to a disconnection in the ventromedial circuits from distant or generalized brain damage.
Aneurysm, Ruptured↗
Potential role of NovoSeven in the prevention of rebleeding following aneurysmal subarachnoid haemorrhage.
Rebleeding following aneurysmal subarachnoid haemorrhage is a major factor contributing to unfavourable outcome. Antifibrinolytic agents reduce the rate of rebleeding but increase the risk of cerebral ischaemia and infarction and hence provide no overall benefit. To address the theoretical concern that recombinant activated factor VII (NovoSeven, Novo Nordisk A/S, Bagsvaerd, Denmark) might increase the risk of cerebral ischaemia while stabilizing the clot at the site of aneurysmal rupture, an open-label, dose-escalation safety study has been developed in collaboration with the UK Spontaneous Intracranial Haemorrhage Group. The trial design includes the recruitment of 15 patients (aged 18 years or over) in good grade with subarachnoid haemorrhage verified by computerized tomography scan or lumbar puncture. Safety evaluation includes clinical observation, monitoring of laboratory variables, positron emission tomography (PET) scanning (rCBF, rOEF, rCMRO2) and transcranial Doppler ultrasound. To date, ten patients have been recruited [NovoSeven 80 microg/kg single bolus (n = 2), NovoSeven 80 microg/kg single bolus followed by continuous infusion at 3.5 microg/kg per h (n = 2) or 7 microg/kg per h (n = 1), or control (n = 5)]. Clinical observation, transcranial Doppler ultrasound and PET studies revealed no evidence of cerebral ischaemia in the first nine patients treated with NovoSeven. The last patient developed middle cerebral artery branch thrombosis contralateral to the aneurysm. The study is currently suspended pending further investigation.
Adult↗
Predicting delayed ischemic deficits after aneurysmal subarachnoid hemorrhage using a transient hyperemic response test of cerebral autoregulation.
OBJECTIVE: To assess whether the development of delayed ischemic deficits (DIDs) after aneurysmal subarachnoid hemorrhage can be predicted using transcranial Doppler ultrasonography and the transient hyperemic response test (THRT). METHODS: An increase in the middle cerebral artery peak flow velocity (FV) of more than 9% of baseline values after 5 to 9 seconds of carotid artery compression was defined as a normal THRT result, indicating good autoregulatory reserve. The transcranial Doppler criteria for vasospasm were a FV of more than 120 cm/s and a Lindegaard ratio of more than 3. Twenty patients with no immediate postoperative neurological deficits were studied. The FVs at all of the major cerebral arteries were measured daily after surgery, and the THRT results were assessed bilaterally. RESULTS: Five of six patients with abnormal THRT results in the first examination after surgery (primary THRT impairment) developed DIDs; none of the remaining patients developed DIDs (Fisher exact test, P = 0.0004). All five patients with DIDs initially exhibited low FVs but all subsequently developed increases in FVs to values of more than 150 cm/s and four exhibited FVs of more than 200 cm/s. The time of onset of DIDs corresponded to the time of onset of moderate vasospasm (FV > 150 cm/s). None of the patients with initially normal THRT results developed DIDs, although four patients did exhibit late (secondary) THRT impairment, which was associated with FVs of more than 120 cm/s. CONCLUSION: When the effects of primarily impaired (after surgery) autoregulation are magnified by vasospasm, the risk of DIDs seems to be very high. Vasospasm alone does not seem to cause DIDs. The development of DIDs could therefore be predicted using the THRT for patients after aneurysm clipping.
Adult↗
Detection of intracranial aneurysms with unenhanced and echo contrast enhanced transcranial power Doppler.
OBJECTIVE: To assess transcranial power Doppler and the effect of an intravenous ultrasonic contrast agent for detecting intracranial aneurysms in patients admitted with a subarachnoid haemorrhage METHODS: 203 patients with subarachnoid haemorrhage were examined with the operator blind to the results of the admission CT and subsequent digital subtraction angiogram (DSA). In 98 cases patients were imaged using unenhanced transcranial power Doppler, and in 105 cases, patients were imaged both using unenhanced and echo contrast enhanced (Levovist, Schering AG) transcranial power Doppler. RESULTS: DSA detected 168 intracranial aneurysms in 128 patients (24 patients had multiple lesions) and 75 patients had an aneurysm negative DSA. There was agreement between DSA and transcranial power Doppler in 87 intracranial aneurysms of which 20 were only detected after infusion of contrast agent. Without contrast infusion, transcranial power Doppler showed a sensitivity of 40% and specificity of 91%. A significant increase in detection was noted when using a contrast agent (chi(2) = 9.49, p<0.001). With a contrast study the sensitivity increase to 55% with a specificity of 83%. Intracranial aneurysm detection by transcranial power Doppler was significantly dependent on position using a contrast infusion (chi(2) = 15.87, p<0.05). A positive correlation was also found between the size of intracranial aneurysms measured by transcranial power Doppler and DSA (r = 0.55, p<0.05). The transcranial power Doppler sensitivity and specificity increased with larger aneurysms and reached 100% for intracranial aneurysms greater than 12 mm diameter. Detection by transcranial power Doppler was also dependent on morphology (chi(2) = 14.46, p<0.001). CONCLUSIONS: The detection of intracranial aneurysm by transcranial power Doppler is dependent on aneurysm location, size, and morphology and is enhanced with the use of an intravenous contrast agent.
Adult↗
Clinical cerebral microdialysis: a methodological study.
OBJECT: Clinical microdialysis enables monitoring of the cerebral extracellular chemistry of neurosurgical patients. Introduction of the technique into different hospitals' neurosurgical units has resulted in variations in the method of application. There are several variables to be considered, including length of the catheter membrane, type of perfusion fluid, flow rate of perfusion fluid, and on-line compared with delayed analysis of samples. The objects of this study were as follows: 1) to determine the effects of varying catheter characteristics on substance concentration; 2) to determine the relative recovery and true extracellular concentration by varying the flow rate and extrapolating to zero flow; and 3) to compare substance concentration obtained using a bedside enzyme analyzer with that of off-line high-performance liquid chromatography (HPLC). METHODS: A specially designed bolt was used to conduct two adjacent microdialysis catheters into the frontal cortex of patients with head injury or poor-grade subarachnoid hemorrhage who were receiving ventilation. One reference catheter (10-mm membrane, perfused with Ringer's solution at 0.3 microl/minute) was constant for all studies. The other catheter was varied in terms of membrane length (10 mm or 30 mm), perfusion fluid (Ringer's solution or normal saline), and flow rate (0.1-1.5 microl/minute). The effect of freezing the samples on substance concentration was established by on-line analysis and then repeated analysis after storage at -70 degrees C for 3 months. Samples assayed with the bedside enzyme analyzer were reassessed using HPLC for the determination of glutamate concentrations. CONCLUSIONS: Two adjacent microdialysis catheters that were identical in membrane length, perfusion fluid, and flow rate showed equivalent results. Variations in perfusion fluid and freezing and thawing of samples did not result in differences in substance concentration. Catheter length had a significant impact on substance recovery. Variations in flow rate enabled the relative recovery to be calculated using a modification of the extrapolation-to-zero-flow method. The recovery was approximately 70% at 0.3 microl/minute and 30% at 1 microl/minute (10-mm membrane) for all analytes. Glutamate results obtained with the enzyme analyzer showed good correlation with those from HPLC.
Adult↗
Biochemical changes related to hypoxia during cerebral aneurysm surgery: combined microdialysis and tissue oxygen monitoring: case report.
OBJECTIVE AND IMPORTANCE: The objective of this study was to monitor brain metabolism on-line during aneurysm surgery, by combining the use of a multiparameter (brain tissue oxygen, brain carbon dioxide, pH, and temperature) sensor with microdialysis (extracellular glucose, lactate, pyruvate, and glutamate). The case illustrates the potential value of these techniques by demonstrating the effects of adverse physiological events on brain metabolism and the ability to assist in both intraoperative and postoperative decision-making. CLINICAL PRESENTATION: A 41-year-old woman presented with a World Federation of Neurological Surgeons Grade I subarachnoid hemorrhage. Angiography revealed a basilar artery aneurysm that was not amenable to coiling, so the aneurysm was clipped. Before the craniotomy was performed, a multiparameter sensor and a microdialysis catheter were inserted to monitor brain metabolism. INTERVENTION: During the operation, the brain oxygen level decreased, in relation to biochemical changes, including the reduction of extracellular glucose and pyruvate and the elevation of lactate and glutamate. These changes were reversible. However, when the craniotomy was closed, a second decrease in brain oxygen occurred in association with brain swelling, which immediately prompted a postoperative computed tomographic scan. The scan demonstrated acute hydrocephalus, requiring external ventricular drainage. The patient made a full recovery. CONCLUSION: The monitoring techniques influenced clinical decision-making in the treatment of this patient. On-line measurement of brain tissue gases and extracellular chemistry has the potential to assist in the perioperative and postoperative management of patients undergoing complex cerebrovascular surgery and to establish the effects of intervention on brain homeostasis.
Adult↗