Monitoring cerebral perfusion after subarachnoid hemorrhage using CT.

The aim of this prospective study was to assess the feasibility and diagnostic relevance of repetitive dynamic (contrast-enhanced) CT measurements of cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT) in the first 3 weeks after aneurysmal subarachnoid hemorrhage (SAH). In 15 patients with SAH, 59 dynamic CT studies including 944 regions of interest (ROI) were analyzed. The results were correlated with the clinical course and time after the event and the occurrence of vasospasm. Values for the entire series were 33.8+/-19.3 ml/100 g/min (CBF), 3.3+/-1.3 ml/100 g (CBV), and 7.3+/-3.9 s (MTT). Significant differences in CBF and CBV were found between ROI in grey and white matter, with time after the event, between patients with significant and absent or minor vasospasm, and between patients with and without a presumed vasospasm-related infarct.

Cerebral blood volume and blood flow at varying arterial carbon dioxide tension levels in rabbits during propofol anesthesia.

UNLABELLED: There are little data on the effects of propofol on cerebral blood volume (CBV). We studied the effects of changes in PaCO(2) on CBV and cerebral blood flow (CBF) during propofol anesthesia in eight New Zealand white rabbits. We also investigated the effects of propofol over time on CBV and CBF during normocapnia (control group). At normocapnia, the mean (+/- SD) CBV and CBF values were 2.41 +/- 0.68 mL/100 g and 56 +/- 28 mL/100 g/min, respectively,. When PaCO(2) was reduced from 41 to 27 mm Hg, no significant change in either CBV or CBF was observed (P > 0.10). However, increasing PaCO(2) from 41 to 58 mm Hg resulted in a 30% increase in CBV (3.08 +/- 0.86 mL/100 g, P < 0.05) and a 91% increase in CBF (97 +/- 39 mL/100 g/min, P < 0.01). In the control group, there were no significant changes in CBV and CBF (P > 0.10) during 2 h of propofol anesthesia. These results indicate that, during propofol anesthesia, cerebrovascular reactivity of blood flow and blood volume is maintained during hypercapnia but is markedly diminished during hypocapnia. IMPLICATIONS: During propofol anesthesia in rabbits with normal brains, a reduction in the arterial carbon dioxide level may not always be accompanied by a reduction in brain blood flow and blood volume.

A CT method to measure hemodynamics in brain tumors: validation and application of cerebral blood flow maps.

BACKGROUND AND PURPOSE: CT is an imaging technique that is routinely used for evaluating brain tumors. Nonetheless, imaging often cannot show the distinction between radiation necrosis and neoplastic growth among patients with recurrent symptoms after radiation therapy. In such cases, a diagnostic tool that provides perfusion measurements with high anatomic detail would show the separation between necrotic areas, which are characterized by low perfusion, from neoplastic areas, which are characterized by elevated CBF. We attempted to validate a dynamic contrast-enhanced CT method for the measurement of regional CBF in brain tumors, and to apply this method by creating CBF maps. METHODS: We studied nine New Zealand White rabbits with implanted brain tumors. We obtained dynamic CT measurements of CBF, cerebral blood volume (CBV), and permeability surface (PS) from the tumor, peritumor, and contralateral normal tissue regions. In all nine rabbits (two studies per rabbit), we compared CT-derived CBF values with those simultaneously obtained by the standard of reference ex vivo microsphere technique. Using CT, we examined three rabbits to assess the variability of repeated CBF and CBV measurements; we examined the other six to evaluate regional CBF reactivity to arterial carbon dioxide tensions. Finally, CT CBF maps were obtained from a rabbit with a brain tumor during normocapnia and hypocapnia. RESULTS: We found a significant linear correlation (r = 0.847) between the regional CT-and microsphere-derived CBF values, with a slope not significantly different from unity (0.99+/-0.03, P>.01). The mean difference between regional CBF measurements obtained using both methods did not significantly deviate from zero (P>.10). During normocapnia, tumor had significantly higher CBF, CBV, and PS values (P<.05) than did peritumor and normal tissues. The variability in CT-derived CBF and CBV measurements in the repeated studies was 13% and 7%, respectively. CT revealed no significantly different CBF CO2 reactivity from that determined by the microsphere method (P>.10). The CBF map of tumor regions during normocapnia showed much higher flow than normal regions manifested, and this difference was reduced on the hypocapnia CBF map. CONCLUSION: The dynamic CT method presented herein provides absolute CBF measurements in brain tumors that are accurate and precise. Preliminary CBF maps derived with this method demonstrate their potential for depicting areas of different blood flow within tumors and surrounding tissue, indicating its possible use in the clinical setting.

Rate of change of cerebral blood flow velocity with hyperventilation during anesthesia in humans.

PURPOSE: Although it has been suggested that the rate at which the cerebral circulation responds to changes in PaCO2 is different with differing anesthetics, there have been no attempts to measure this. Transcranial Doppler allows the continuous measurement of cerebral blood flow velocity (CBFV) and any changes over time. Our aim was to compare the rate of change of CBFV when end-tidal CO2 (P(ET)CO2) was rapidly altered during halothane or isoflurane anesthesia. METHODS: Twenty-eight unpremedicated healthy patients were randomly assigned to receive air/O2 and either 1-1.5 MAC halothane or isoflurane as the primary anesthetic. After 15 min of steady state, P(ET)CO2 was rapidly reduced from 45 mm Hg to 30 mm Hg. CBFV and P(ET)CO2 were recorded every 30 sec for the next 10 min. RESULTS: The rate of change of normalized CBFV (delta CBFV vs. delta time) was more rapid in the isoflurane group (P <0.0001) especially in the initial few minutes. In all patients anesthetized with isoflurane, and in all but two patients anesthetized with halothane, the reduction in P(ET)CO2 produced a corresponding decrease in CBFV However, there were no differences in the magnitude of cerebrovascular CO2 reactivity (delta CBFV vs. delta P(ET)CO2) between the two groups. CONCLUSIONS: The rate of change of CBFV was faster in the isoflurane than in the halothane group especially in the initial few minutes. Indeed, for two patients in the halothane group Vmca did not change despite a change in P(ET)CO2. This may be of clinical importance when cerebrovascular tone needs to be changed rapidly.

CT assessment of cerebral perfusion: experimental validation and initial clinical experience.

PURPOSE: To validate a dynamic single-section computed tomographic (CT) method to measure cerebral blood volume (CBV) and cerebral blood flow (CBF) by using a noncarotid artery as the input and to demonstrate the feasibility of this method in a pilot series of patients. MATERIALS AND METHODS: Twelve dynamic contrast material-enhanced CT studies were performed in beagles. CBV, CBF, and mean transit time (MTT) values were calculated by using an internal carotid artery (ICA) and a noncarotid artery as the input artery to the brain. Patient studies with use of the radial artery as the input were performed (a) repetitively in two patients after subarachnoid hemorrhage, (b) in a patient with a symptomatic ICA occlusion before and after the intravenous injection of 1 g of acetazolamide, and (c) in a patient with a malignant brain tumor. RESULTS: Linear regression analyses revealed highly significant correlations (P < .001) between CBV (r, 0.98; slope, 0.96), CBF (r, 0.89; slope, 0.87), and MTT (r, 0.80; slope, 0.76) values calculated with the ICA and the noncarotid inputs. The CT-derived patient data correlated well with ancillary clinical and neuroradiologic findings. CONCLUSION: Dynamic single-section CT scanning to measure CBV and CBF on the basis of a noncarotid input is a highly accessible and cost-effective blood flow measurement technique.

The effect of sevoflurane and isoflurane anesthesia on interictal spike activity among patients with refractory epilepsy.

UNLABELLED: The electrophysiologic effects of sevoflurane are not well characterized in humans. Among patients with refractory epilepsy, this study compared 1) electroencephalographic (EEG) interictal spike activity during wakefulness and sevoflurane anesthesia, and 2) electrocorticographically (ECoG) recorded interictal spike activity during sevoflurane and isoflurane anesthesia. We studied 12 patients undergoing insertion of subdural electrodes. Before commencing anesthesia, awake (baseline) EEG recordings were obtained. After inhaled induction, EEG interictal spike activity was evaluated during stable, normocapnic, and hypocapnic (Paco2 = 28-30 mm Hg), sevoflurane anesthesia administered at 1.5 times the minimum alveolar anesthetic concentration (1.5 MAC). Immediately after surgery, ECoG recordings were obtained from subdural electrodes during 1) 1.5 MAC isoflurane, 2) 0.3 MAC isoflurane, and 3) 1.5 MAC sevoflurane anesthesia. EEG spike frequency increased in all patients during sevoflurane anesthesia compared with awake recordings (P = 0.002). Compared with 0.3 MAC isoflurane anesthesia, ECoG interictal spike frequency was higher in all patients during 1.5 MAC sevoflurane anesthesia (P = 0.004) and in 8 of 10 patients during 1.5 MAC isoflurane anesthesia (P = 0.016). Under sufficiently rigorous conditions, both sevoflurane and isoflurane can provoke interictal spike activity at near burst-suppression doses. This property is more prominent with sevoflurane than isoflurane. IMPLICATIONS: The results of this study suggest that the capacity to modulate neuroexcitability is a dose-dependent feature of volatile anesthetics that is manifested most prominently at near burst-suppression doses (i.e., 1.5 times the minimum alveolar anesthetic concentration) and is minimal or absent at low doses.

Quantitative assessment of cerebral hemodynamics using CT: stability, accuracy, and precision studies in dogs.

PURPOSE: The limited clinical availability of currently used methods to measure regional cerebral blood volume (CBV) and cerebral blood flow (CBF) represents an important restriction. We undertook this study to evaluate a new dynamic CT method to measure CBV and CBF in normal and ischemic tissue. METHOD: A total of 21 dynamic CT studies were performed in seven male beagles. The contrast enhancement curves of the carotid arteries and of various brain regions were deconvolved to obtain CBV and CBF. The stability of the deconvolution method employed was assessed by comparing three data sets obtained by analyses of one, two, and four regions of interest (ROIs), all covering the entire brain area. The accuracy of CT-derived CBF was analyzed for normal (n = 5 studies) and ischemic (n = 7 studies) brain tissue using fluorescent microspheres. Repetitive CT studies were performed to evaluate the precision of the CT measurements. RESULTS: The stability of the deconvolution method was high with variabilities of 2.3% (CBV), 5.9% (CBF), and 8.9% (mean transit time), respectively. The correlation between the CT and the microsphere measurements was good for both normal and ischemia studies (r > 0.78, slope > 0.9). The variability of the CT CBF (30.6%) was higher than that of the CT CBV (12.3%) measurements. CONCLUSION: Our novel dynamic CT method is stable with respect to the sizes of ROIs used, allowing for accurate measurements of CBV and CBF in both normal and ischemic tissue. Further studies are necessary to evaluate the variability of this method under controlled physiologic conditions.

Cerebral blood volume measurements using dynamic contrast-enhanced x-ray computed tomography: application to isoflurane anaesthetic studies.

A convenient and simple method of measuring cerebral blood volume (CBV) will aid in the clinical management of patients with cerebrovascular diseases and head trauma. Using a two-compartment model to characterize the distribution of x-ray contrast agent in the brain, we have developed a non-equilibrium (dynamic) x-ray CT method to measure CBV and have applied this method to study the effects of isoflurane. CBV and cerebral blood flow (CBF, ex vivo) measurements were made in two groups of New Zealand White rabbits at varying (study group) and constant (control group) arterial CO2 concentration. ANOVA for repeated measures was used on the control data to determine the precision of our two-compartment CT-CBV method. The results showed that the precision of our CT-CBV measurement was 9.8%. In addition a paired t-test analysis of the control data revealed that the duration of isoflurane anaesthesia had no effect on the repeated measurements of CBV or CBF. The rate of change in CBV (0.049 ml/100 g/mmHg) and CBF (6.2 ml/min/100 g/mmHg) with respect to changes in arterial CO2 concentration under the influence of isoflurane anaesthesia was similar to those reported in previous studies, thus validating our experimental CT-CBV and CBF measurements. Our CT-CBV method will lead to more information on the relationship between CBV and CBF under different pharmacological interventions in both normal and disease conditions.

Dynamic CT measurement of cerebral blood flow: a validation study.

BACKGROUND AND PURPOSE: Our objective was to develop a method to correct for the effect of partial volume averaging (PVA) in the CT measurement of contrast enhancement in small arteries, and to validate a dynamic contrast-enhanced CT method for the measurement of regional cerebral blood flow (rCBF). METHODS: Contrast-enhanced CT scans of tubes of known inner diameters were obtained to estimate the size-dependent scaling factors (PVSF) due to PVA. The background-subtracted image profiles of the contrast-filled tubes were fitted to gaussian curves, and the standard deviations (SDs) of these curves were correlated with the PVSF of each tube. In the second part of this investigation, 13 studies were performed in six New Zealand white rabbits under normal conditions. Dynamic CT measurements of rCBF, regional cerebral blood volume (rCBV), and regional mean transit time (rMTT) were calculated in the left and right parietal lobes and the basal ganglia. The CT rCBF values were compared with those obtained by the microsphere method, which is the standard of reference. RESULTS: We found strong correlations for the SDs of the gaussian curves to the known inner diameters of the tubes and to their size-related PVSF. These correlations demonstrated that the error from PVA in the measurement of arterial enhancement can be corrected without knowledge of the actual size of the artery. The animal studies revealed a mean (+/- SD) rCBF of 73.3 +/- 31.5 mL/100 g per minute, a mean rCBV of 1.93 +/- 0.74 mL/100 g, and a mean rMTT of 1.81 +/- 1.02 seconds. A strong correlation was found between rCBF values derived by the CT and the microsphere methods. CONCLUSION: We have validated a new dynamic CT method for measuring rCBF. The accuracy of this technique suggests that it can be used as an alternative diagnostic tool to assess the cerebral hemodynamics in experimental and clinical situations.

Mild hypothermia as a protective therapy during intracranial aneurysm surgery: a randomized prospective pilot trial.

OBJECTIVE: To conduct a pilot trial of mild intraoperative hypothermia during cerebral aneurysm surgery. METHODS: One hundred fourteen patients undergoing cerebral aneurysm clipping with (n = 52) (World Federation of Neurological Surgeons score < or =III) and without (n = 62) acute aneurysmal subarachnoid hemorrhage (SAH) were randomized to normothermic (target esophageal temperature at clip application of 36.5 degrees C) and hypothermic (target temperature of 33.5 degrees C) groups. Neurological status was prospectively evaluated before surgery, 24 and 72 hours postoperatively (National Institutes of Health Stroke Scale), and 3 to 6 months after surgery (Glasgow Outcome Scale). Secondary outcomes included postoperative critical care requirements, respiratory and cardiovascular complications, duration of hospitalization, and discharge disposition. RESULTS: Seven hypothermic patients (12%) could not be cooled to within 1 degrees C of target temperature; three of the seven were obese. Patients randomized to the hypothermic group more frequently required intubation and rewarming for the first 2 hours after surgery. Although not achieving statistical significance, patients with SAH randomized to the hypothermic group, when compared with patients in the normothermic group, had the following: 1) a lower frequency of neurological deterioration at 24 and 72 hours after surgery (21 versus 37-41%), 2) a greater frequency of discharge to home (75 versus 57%), and 3) a greater incidence of good long-term outcomes (71 versus 57%). For patients without acute SAH, there were no outcome differences between the temperature groups. There was no suggestion that hypothermia was associated with excess morbidity or mortality. CONCLUSION: Mild hypothermia during cerebral aneurysm surgery is feasible in nonobese patients and is well tolerated. Our results indicate that a multicenter trial enrolling 300 to 900 patients with acute aneurysmal SAH will be required to demonstrate a statistically significant benefit with mild intraoperative hypothermia.

Anaesthesia preadmission assessment: a new approach through use of a screening questionnaire.

PURPOSE: The preadmission assessment of patients one to two weeks preoperatively has become the standard across North America. We have devised a new approach that utilises a preoperative screening questionnaire, and this study attempted to determine the effectiveness of this technique. METHODS: Over six weeks, the attending anaesthetist for each patient undergoing non-cardiac surgery processed through the preadmission clinic (PAC) completed a study survey. This survey questioned if the assessment was appropriate with reasons, the consequences of no assessment, and if time was saved/lost on the day of surgery. RESULTS: Three hundred and seventy patients were processed (243 same-day (SD), 111 outpatient (O/P), and 16 inpatients (I/P)). Of these, 224 were assessed in the PAC (101 by medicine, 84 by anaesthesia and 39 by both): 42% (94) based on the questionnaire, 12% (26) due to consultation, and 46% (104) due to positive questionnaires and consultation. The physician assessments were appropriate 184/219 (84%) times, inappropriate in 35 (16%), while there was no answer for five. Assessments were inappropriate because 25/35 (71%) were unnecessary, while in nine (26%) the patient was not optimised. Of the patients not assessed in the PAC only 9/145 (6%) should have been assessed. CONCLUSION: The use of our screening tool in combination with direct referrals appropriately determines assessment needs of patients and allows for more efficient use of medical personnel in the PAC.

Propofol sedation during awake craniotomy for seizures: electrocorticographic and epileptogenic effects.

This prospective study evaluated the effects of propofol sedation on the incidence of intraoperative seizures and the adequacy of electrocorticographic (ECoG) recordings during awake craniotomy performed for the management of refractory epilepsy. Thirty patients scheduled for temporal or frontal lobectomy for epilepsy under bupivacaine scalp block were randomized to receive patient-controlled propofol sedation (PCS) combined with a basal infusion of propofol (n = 15) or neurolept analgesia using an initial bolus dose of fentanyl (0.7 microg/kg) and droperidol (0.04 mg/kg) followed by a fentanyl infusion (n = 15). Propofol administration was suspended 15 min before ECoG recording in the PCS group. The occurrence of inappropriate intraoperative seizures was noted and, based on blind review, the adequacy of ECoG recordings was compared. A higher incidence of intraoperative seizures was noted among the neurolept patients (6 vs 0, P = 0.008). Intraoperatively, ECoG recordings were adequate to proceed with resection in both groups. Evidence of low spike activity on ECoG did not correlate with the type of sedation administered. Higher frequency background ECoG activity was noted among patients who received propofol, but this did not interfere with ECoG interpretation. The use of propofol sedation does not appear to interfere with ECoG during epilepsy surgery, provided administration is suspended at least 15 min before recording.

Propofol sedation during awake craniotomy for seizures: patient-controlled administration versus neurolept analgesia.

This prospective study evaluated the safety and efficacy of patient-controlled sedation (PCS) using propofol during awake seizure surgery performed under bupivacaine scalp blocks. Thirty-seven patients were randomized to receive either propofol PCS combined with a basal infusion of propofol (n = 20) or neurolept analgesia using an initial bolus dose of fentanyl and droperidol followed by a fentanyl infusion (n = 17). Both groups received supplemental fentanyl and dimenhydrinate for intraoperative pain and nausea, respectively. Comparisons were made between groups for sedation, memory, and cognitive function, patient satisfaction, and incidence of complications. Levels of intraoperative sedation and patient satisfaction were similar between groups. Memory and cognitive function were well preserved in both groups. The incidence of transient episodes of ventilatory rate depression (<8 bpm) was more frequent among the propofol patients (5 vs 0, P = 0.04), particularly after supplemental doses of opioid. Intraoperative seizures were more common among the neurolept patients (7 vs 0, P = 0.002). PCS using propofol represents an effective alternative to neurolept analgesia during awake seizure surgery performed in a monitored care environment.

Patient attitudes regarding pca and associated costs.

PURPOSE: To determine patients' knowledge and attitudes towards patient-controlled analgesia (PCA) costs through the use of our acute pain service quality assurance (QA) programme. METHODS: Quality Assurance questionnaires were distributed to all patients receiving PCA opioids for > 12 hr. Patients were asked to note the presence of side effects (nausea/vomiting, pruritus, urinary retention), to indicate their satisfaction with regard to their pain relief, follow-up assessments, treatment of side effects, and to recall the previous method of pain relief and their satisfaction with it. Patients were also asked to estimate the total cost of PCA (0-$50, $50-100, $100-200, > $200), and what amount if any they would be willing to pay (0-$50, $50-100, $100-200, > $200). Results obtained over a recent four month period were reviewed. RESULTS: One hundred and thirty-three questionnaires were distributed and 103 (77%) were returned. The percentage of patients rating their satisfaction as very good or excellent was 86% for pain relief, 96% for follow-up, 71% for side effect treatment, but only 43% for their previous surgical pain relief (P < 0.001). The distribution of cost estimates was 10% $50-100, 37% $100-200 and 53% > $200 with 60% willing to pay a portion of this cost. Those willing to pay were more likely to have had very good or excellent pain relief (94% vs 71%, P < 0.05) and treatment of side effects (71% vs 48%, P < 0.05) than those not willing to pay. CONCLUSIONS: Patients continue to be highly satisfied with PCA therapy and are aware of the costs involved. A majority of patients were willing to pay to obtain this service if necessary. Patients who had poorer pain relief and less efficacious treatment of their side effects were less willing to pay.