Methemoglobin suppression in a 0.3 Tesla magnet: an in vitro and in vivo study.

RATIONALE AND OBJECTIVES: The aim of this study was to design a pulse sequence that suppresses methemoglobin and is applicable in a 0.3-T permanent magnet. MATERIALS AND METHODS: Blood samples were collected from six healthy volunteers. Magnetic resonance imaging was performed with a 0.3-T scanner until the typical signal intensities of methemoglobin were obtained. Each blood sample was then scanned using repetition times of 300, 600, 900, 1200, 1500, and 1800 ms and a constant echo time of 20 ms. All other parameters (field of view, slice thickness, matrix, and number of signal averages) were kept constant for all six sequences. Signal intensities and repetition time data were used to calculate the T1 relaxation time of extracellular methemoglobin. T1 was determined by ordinary least square regression according to the equation S =k(1 - e(-repetition time/T1)), where S is signal intensity and k is the proportional constant. A short tau inversion recovery sequence with an inversion time calculated from the T1 value of methemoglobin was used on fat, water, and methemoglobin blood samples and in 11 patients diagnosed with subacute brain hemorrhages. The inversion time was calculated as ln2 T1 (tissue), where T1 is the relaxation time of extracellular methemoglobin to be suppressed. RESULTS: The T1 relaxation time of extracellular methemoglobin was determined to be 231.24 +/- 9.068 ms, and inversion time was calculated to be 160 +/- 6.67 msec. Application of an inversion time of 160 ms showed complete suppression on extracellular methemoglobin blood samples and all of the 11 subjects. CONCLUSION: A methemoglobin suppression technique using an inversion time of 160 +/- 6.67 ms is applicable in a 0.3-T permanent magnet.

Infections associated with indwelling ventriculostomy catheters in a teaching hospital.

BACKGROUND: Ventriculostomy-associated infections are a serious complication of external ventricular drains. The objective of this study was to analyze the clinical features of and risk factors for such infections. METHODS: We retrospectively collected demographic and clinical data on patients with indwelling ventriculostomy catheters hospitalized in a teaching hospital from July 2001 to June 2006, comparing those with and without ventriculostomy-associated infections. RESULTS: A total of 197 drains (2910 catheter-days) placed in 155 patients were studied. Infections developed in 28 of the 197 (14.2%) drains. The duration from insertion to infection ranged from 7 to 36 days. The cut-off point of duration from insertion to infection was 15.5 days. Re-insertion because of catheter malfunction carried a high risk of infection (p<0.001). Patients with infections had a longer intensive care unit stay (p=0.001), longer duration of catheterization (p=0.002), and a higher incidence of concurrent sepsis (p=0.018), urinary tract infection (p=0.011) and pneumonia (p=0.004). Gram-negative bacilli were the leading pathogens (84%); Pseudomonas aeruginosa was the most common isolate. Polymicrobial infections occurred later than monomicrobial infections (p=0.003). CONCLUSIONS: Repeated insertion and longer duration of drains are major risk factors for ventriculostomy-associated infections.

Clinical practice guidelines in severe traumatic brain injury in Taiwan.

BACKGROUND: Severe TBIs are major causes of disability and death in accidents. The Brain Trauma Foundation supported the first edition of the Guidelines for the Management of Severe Traumatic Brain Injury in 1995 and revised it in 2000. The recommendations in these guidelines are well accepted in the world. There are still some different views on trauma mechanisms, pathogenesis, and managements in different areas. Individualized guidelines for different countries would be necessary, and Taiwan is no exception. METHODS: In November 2005, we organized the severe TBI guidelines committee and selected 9 topics, including ER treatment, ICP monitoring, CPP, fluid therapy, use of sedatives, nutrition, intracranial hypertension, seizure prophylaxis, and second-tier therapy. We have since searched key questions in these topics on Medline. References are classified into 8 levels of evidence: 1++, 1+, 1-, 2++, 2+, 2-, 3, and 4 based on the criteria of the SIGN. RESULTS: Recommendations are formed and graded as A, B, C, and D. Grade A means that at least one piece of evidence is rated as 1++, whereas grade B means inclusion of studies rated as 2++. Grade C means inclusion of references rated as 2+, and grade D means levels of evidence rated as 3 or 4. Overall, 42 recommendations are formed. Three of these are rated as grade A, 13 as grade B, 21 as grade C, and 5 as grade D. CONCLUSIONS: We have completed the first evidence-based, clinical practice guidelines for severe TBIs. It is hoped that the guidelines will provide concepts and recommendations to promote the quality of care for severe TBIs in Taiwan.