Joseph M. Darby

CBF Measured by Xe-CT: Approach to Analysis and Normal Values

Normal reference values and a practical approach to CBF analysis are needed for routine clinical analysis and interpretation of xenon-enhanced computed tomography (CT) CBF studies. We measured CBF in 67 normal individuals with the GE 9800 CT scanner adapted for CBF imaging with stable Xe. CBF values for vascular territories were systematically analyzed using the clustering of contiguous 2-cm circular regions of interest (ROIs) placed within the cortical mantle and basal ganglia. Mixed cortical flows averaged 51 ± 10 ml · 100 g−1 · min−1. High and low flow compartments, sampled by placing 5-mm circular ROIs in regions containing the highest and lowest flow values in each hemisphere, averaged 84 ± 14 and 20 ± 5 ml · 100 g−1 · min−1, respectively. Mixed cortical flow values as well as values within the high flow compartment demonstrated significant decline with age; however, there were no significant age-related changes in the low flow compartment. The clustering of systematically placed cortical and subcortical ROIs has provided a normative data base for Xe-CT CBF and a flexible and uncomplicated method for the analysis of CBF maps generated by Xe-enhanced CT.

The Effect of Hypothermia on the Incidence of Delayed Traumatic Intracerebral Hemorrhage

Hypothermia has been shown to cause coagulation abnormalities, primarily related to platelet dysfunction. We reviewed coagulation function and the incidence of delayed traumatic intracerebral hemorrhage in a series of 36 patients with severe head injuries (Glasgow Coma Scale 3-7) enrolled in a prospective, randomized, clinical trial of therapeutic moderate hypothermia. Patients were randomized to a normothermic group (n = 16) or to a group cooled to 32 to 33 degrees C within 6 hours of injury (n = 20). Prothrombin times, partial thromboplastin times, and platelet counts were obtained in the emergency room and then again within 24 hours of randomization. Delayed traumatic intracerebral hemorrhage occurred in 6 of 20 (30%) hypothermic patients and 5 of 16 (31%) normothermic patients. In the hypothermic group, 9 of 17 patients had an increased prothrombin time during hypothermic therapy, as opposed to 11 of 16 in the normothermic group during the corresponding time period. The partial thromboplastin time was prolonged in 2 of 17 hypothermic patients and 2 of 16 normothermic patients. Three patients in the hypothermic group and one in the normothermic group developed thrombocytopenia (a platelet count of less than 100,000). There were no significant differences between the two groups in the incidence of delayed traumatic intracerebral hemorrhage, in measured coagulopathy, or in the mean values of measured coagulation parameters. Although the possibility of a hypothermia-induced coagulopathy has not yet been excluded, the short-term use of hypothermia does not appear to increase the risk for intracranial hemorrhagic complications in head injuries.

Levetiracetam versus phenytoin for seizure prophylaxis in severe traumatic brain injury

OBJECT Current standard of care for patients with severe traumatic brain injury (TBI) is prophylactic treatment with phenytoin for 7 days to decrease the risk of early posttraumatic seizures. Phenytoin alters drug metabolism, induces fever, and requires therapeutic-level monitoring. Alternatively, levetiracetam (Keppra) does not require serum monitoring or have significant pharmacokinetic interactions. In the current study, the authors compare the EEG findings in patients receiving phenytoin with those receiving levetiracetam monotherapy for seizure prophylaxis following severe TBI. METHODS Data were prospectively collected in 32 cases in which patients received levetiracetam for the first 7 days after severe TBI and compared with data from a historical cohort of 41 cases in which patients received phenytoin monotherapy. Patients underwent 1-hour electroencephalographic (EEG) monitoring if they displayed persistent coma, decreased mental status, or clinical signs of seizures. The EEG results were grouped into normal and abnormal findings, with abnormal EEG findings further categorized as seizure activity or seizure tendency. RESULTS Fifteen of 32 patients in the levetiracetam group warranted EEG monitoring. In 7 of these 15 cases the results were normal and in 8 abnormal; 1 patient had seizure activity, whereas 7 had seizure tendency. Twelve of 41 patients in the phenytoin group received EEG monitoring, with all results being normal. Patients treated with levetiracetam and phenytoin had equivalent incidence of seizure activity (p = 0.556). Patients receiving levetiracetam had a higher incidence of abnormal EEG findings (p = 0.003). CONCLUSIONS Levetiracetam is as effective as phenytoin in preventing early posttraumatic seizures but is associated with an increased seizure tendency on EEG analysis.

MRI Is Unnecessary to Clear the Cervical Spine in Obtunded/Comatose Trauma Patients: The Four-Year Experience of a Level I Trauma Center

BACKGROUND Cervical (C)-spine clearance protocols exist both to identify traumatic injury and to expedite rigid collar removal. Computed tomography (CT) of the C-spine in trauma patients facilitates the removal of immobilization collars in patients who are neurologically intact, and magnetic resonance imaging (MRI) has become an indispensable adjunct for evaluating trauma patients with neurologic deficits. Yet, the management of patients with impaired mental status who lack neurologic deficits attributable to the spinal cord remains controversial. C-spine MRI has been suggested and employed as an imaging modality to exclude occult C-spine instability in this population of patients. However, currently available data are inconclusive as to the necessity of MRI in the C-spine clearance of obtunded or comatose trauma patients with a normal CT. METHODS The records of patients undergoing contemporaneous CT and MRI of the C-spine in a level I trauma center from January 2003 to December 2006 were retrospectively analyzed. From this group, patients admitted with a Glasgow Coma Scale score </=13 and a normal C-spine CT with sagittal and coronal reconstructions were identified. Patients were excluded if a neurologic deficit potentially referable to the spinal cord was identified. The results of C-spine MRI in this group were tabulated and analyzed. RESULTS A total of 690 patients were identified who had undergone contemporaneous C-spine CT and MRI. Of this group, 180 patients (26.2%) were identified as having a normal CT with sagittal and coronal reconstructions, no neurologic deficit, and Glasgow Coma Scale score </=13. Within this group, the average time interval between CT and MRI was 4.6 days (median, 4 days). Among these 180 patients, C-spine MRI identified 38 patients (21.1%) with acute traumatic findings in the cervical spine. However, none of these patients had a missed unstable injury and no patient required surgery or developed evidence of delayed instability. CONCLUSION Our data suggests that, outside of its appropriate application to patients with a neurologic deficit, MRI is unlikely to uncover unstable C-spine injuries in patients who are obtunded or comatose when C-spine CT using modern imaging protocols is normal.

Utilization and diagnostic yield of blood cultures in a surgical intensive care unit

OBJECTIVE To evaluate the diagnostic yield of blood cultures obtained in a surgical intensive care unit (ICU) and to assess factors potentially influencing yield. DESIGN Retrospective, descriptive study. SETTING Surgical ICU in a university hospital. SUBJECTS All patients who had a blood culture obtained during their admission to the trauma/neurosurgical ICU of Presbyterian University Hospital from January 1, 1993 to December 31, 1993. MEASUREMENTS AND MAIN RESULTS Blood culture isolates were categorized as pathogens or contaminants and overall diagnostic yield was determined. Blood cultures were positive for pathogens in 4.6% of all culture episodes, while contaminants were isolated in 5.5% of all culture episodes. A total of 23 true bacteremias were identified in 21 patients, for an overall rate of bacteremia of 3.6 per 100 admissions (5.9 per 1,000 patient days). Concurrent antibiotics were being used at the time of blood culture in 65.3% of all culture episodes. The yield for pathogens was significantly lower (2.2%) when cultures were obtained on antibiotics compared with culture episodes obtained off antibiotics (6.4%) (p < .05). Single-set blood culture episodes were obtained in approximately 32% of all culturing episodes with the overall yield for pathogens of these culturing episodes lower (2.9%) than that of multiple-set culture episodes (5.3%) (p = NS). CONCLUSIONS Blood culture yield in this surgical ICU was relatively low in comparison with other published studies. The data further suggest that concurrent use of systemic antibiotics and inappropriate or excessive culturing may negatively influence blood culture yield.

Regional Cerebral Blood Flow and CO2 Reactivity in Fulminant Hepatic Failure

Alterations in cerebral hemodynamics are postulated to contribute to brain herniation, a major cause of death in patients with severe hepatic encephalopathy due to fulminant hepatic failure (FHF). In an effort to identify these changes in cerebral hemodynamics, regional and global cerebral blood flow (CBF) and CO2 reactivity were measured using stable xenon-enhanced computed tomography (Xe/CT) in 24 patients within 72 h of onset of severe hepatic encephalopathy. Regional variations in CBF, most notably, a relative decrease in CBF in the anterior circulation and an increase in CBF in the posterior circulation were found. CBF was significantly lower in FHF patients compared with controls, however, these values are well out of the established ischemic range. FHF patients also showed significant impairment in CBF response to hypoventilation, while the CBF response to hyperventilation remained intact. This study suggests that FHF patients demonstrate early changes in both CBF patterns and CO2 reactivity. The relatively “normal” CBF values obtained in FHF patients in severe hepatic encephalopathy coupled with the lack of vasodilatation to hypoventilation suggest a state of uncoupled CBF and metabolism or “luxury perfusion” that could theoretically contribute to vasogenic edema, brain swelling, and cerebral herniation.

Brainstem death with persistent EEG activity: evaluation by xenon-enhanced computed tomography.

A patient with brainstem infarction met the clinical criteria for brain death but had persistent EEG activity, complicating our decision to withdraw life support. We evaluated cerebral blood flow with xenon-enhanced computed tomography (Xe/CT), which documented the absence of posterior circulation flow and persistent, low, anterior circulation flow. This information led us to withdraw life support, despite the presence of EEG activity. The Xe/CT method noninvasively measures local cerebral blood flow and may enhance diagnostic certainty in complicated brain-death evaluations.

Intracranial pressure response to stable xenon inhalation in patients with head injury

Cerebral blood flow measured by xenon-enhanced computed tomography may provide useful information in victims of severe head injury. To assess the effect of stable xenon inhalation on intracranial pressure, intracranial pressure was measured in 17 mechanically ventilated patients with severe head injury undergoing cerebral blood flow studies with xenon-enhanced computed tomography. Under hypocapnic conditions, mean intracranial pressure increased by less than 1 mm Hg (p less than 0.05) late in the inhalation period only in patients whose baseline intracranial pressure was less than 20 mm Hg. It was concluded that under hypocapnic conditions, the magnitude of this increase in intracranial pressure does not prohibit the safe evaluation of cerebral blood flow in victims of head injury using xenon-enhanced computed tomography.

Effects of dobutamine and dopamine on whole brain blood flow and metabolism in unanesthetized monkeys.

Dobutamine (DO) and dopamine (DA) are positive inotropic agents used clinically to improve cardiac output in patients in acute or chronic heart failure or to counteract intracranial vasospasm. These patients are also at risk for cerebrovascular disease, but studies on the effects of DA on cerebral blood flow (CBF) and metabolism are few and for DO nonexistent. We evaluated the effects on DO and DA on whole brain CBF and cerebral metabolic rates of oxygen (CMRO2) and glucose (CMRglc) in unanesthetized rhesus monkeys. Microelectrodes and catheters inserted in the superior sagittal sinus monitored H2 clearance and sampled cerebral venous blood. Studies were done at low and high doses with control measurements between doses. At 5.10, and 15 microg/kg/min (n = 6), neither systemic nor cerebral variables were affected by either drug. At doses of 50 and 100 microg/kg/min (n = 4), DO and DA increased arterial blood pressure and heart rate by 15 to 30%. Whereas CBF, CMRO2, and CMRglc were clearly unaffected by DO at high doses, they increased by 20-30% with DA, 100 microg/kg/min and although not significant (p >0.05), the consistency and magnitude of the increase along with the likelihood of a type II error led us to conclude that (a) both DO and DA are less effective in monkeys than in humans and (b) whereas DO at all doses tested showed no indication of affecting CBF and CMR, DA increased CBF and CMR by 20 to 30% at a dose of 100 microg/kg/min.

Medication errors during medical emergencies in a large, tertiary care, academic medical center.

PURPOSE Evaluate the rate, type and severity of medication errors occurring during Medical Emergency Team (MET) care at a large, tertiary-care, academic medical center. METHODS A prospective, observational evaluation of 50 patients that required MET care was conducted. Data on medication use were collected using a direct-observation method whereby an observer documented drug information such as drug, dose, frequency, rate of administration and administration technique. Subsequently, a team of three clinicians assessed rate, type and severity of medication errors using definitions consistent with United States Pharmacopeia MEDMARX system. Severity was assessed on a scale of minor, moderate and severe. RESULTS One hundred eighty six doses were observed for 36 different medications. A total of 296 errors were identified; of these 196 errors (66%) were inappropriate aseptic technique. Of the remaining 100 errors, 46% were prescribing errors, 28% administration technique errors, 14% mislabeling errors, 10% drug preparation errors and 2% improper dose prescribing. Examples included: (1) prescribing errors, (2) administering wrong doses, (3) mislabeling, and (4) wrong administration technique such as not flushing intravenous medication through intravenous access. The rate of medication administration errors was 1.6 errors/dose including aseptic technique and 0.5 errors/dose excluding aseptic technique. A notable portion (14%) of errors was considered at least moderate in severity. CONCLUSIONS One out of 2 doses was administered in error after errors of using inappropriate aseptic technique were excluded. There is a need for education and systematic changes to prevent medication errors during medical emergencies as an effort to avoid harm.