Concomitant field terms for asymmetric gradient coils: consequences for diffusion, flow, and echo-planar imaging.

As a consequence of the Maxwell equations, linear field gradients are accompanied by additional spatially dependent field components. A description of the Maxwell field terms is presented which explicitly takes into account the asymmetry of the gradient coil. It is shown both theoretically and experimentally that, in contrast to symmetric coils, an asymmetric coil generates concomitant field terms of zeroth and first order in space. Artifacts induced by concomitant fields can be much more pronounced for asymmetric coil designs than for symmetric ones. For the strong gradient amplitudes available on modern MR systems the effect of these concomitant magnetic fields on the evolution of magnetization has to be taken into consideration in a variety of NMR acquisition techniques. The formalism is used experimentally to compensate for artifacts observed in three different imaging methods: an image shift in standard echo planar imaging (EPI), an echo shift in diffusion-weighted EPI, and a phase shift in a flow quantification technique based on phase contrast images.

Effect of ethnicity on denial of authorization for emergency department care by managed care gatekeepers.

OBJECTIVE: After a pilot study suggested that African American patients enrolled in managed care organizations (MCOs) were more likely than whites to be denied authorization for emergency department (ED) care through gatekeeping, the authors sought to determine the association between ethnicity and denial of authorization in a second, larger study at another hospital. METHODS: A retrospective cohort design was used, with adjustment for triage score, age, gender, day and time of arrival at the ED, and type of MCO. RESULTS: African Americans were more likely to be denied authorization for ED visits by the gatekeepers representing their MCOs even after adjusting for confounders, with an odds ratio of 1.52 (95% CI = 1.18 to 1.94). CONCLUSIONS: African Americans were more likely than whites to be denied authorization for ED visits. The observational study design raises the possibility that incomplete control of confounding contributed to or accounted for the association between ethnicity and gatekeeping decisions. Nevertheless, the questions that these findings raise about equity of gatekeeping indicate a need for additional research in this area.

Reliability of performance-based clinical skill assessment of emergency medicine residents.

OBJECTIVE: To test the overall reliability of a performance-based clinical skill assessment for entering emergency medicine (EM) residents. Also, to investigate the reliability of separate reporting of diagnostic and management scores for a standardized patient case, subjective scoring of patient notes, and interstation exercise scores. METHODS: Thirty-four first-year EM residents were tested using a 10-station standardized patient (SP) examination. Following each 10-minute encounter, the residents completed a patient note that included differential diagnosis and management. The residents also were asked to read an ECG or chest x-ray (CXR) associated with each case. History, physical examination, and interpersonal skills were scored by the SPs. The patient note, CXR, and ECG readings were scored by faculty emergency physicians. Intercase reliability was determined for the residents. RESULTS: Global score reliability, Cronbach's alpha = 0.85. Reliabilities for the other components were: history, 0.77; physical examination, 0.83; and interpersonal skills, 0.80. Differential diagnosis and management reliabilities were 0.61 and 0.66, respectively. Subjective scoring of the patient note resulted in acceptable reliability for legibility (0.80), history completeness (0.80), and history organization (0.81). Physical examination completeness and organization reliabilities were 0.74 and 0.73. For ECG and CXR readings, alpha = 0.74 and 0.34, respectively. CONCLUSIONS: SPs can be used to reliably assess bedside clinical skills of EM residents. While component reliability levels are slightly lower than the global clinical skill reliability coefficient, they are still high enough to use for identification of individual strengths and weaknesses.

Phenytoin loading in chronic alcoholic patients.

Controversy exists concerning the appropriate loading dose of phenytoin in chronic alcoholic patients. Chronic alcoholics are frequently assumed to have low albumin levels secondary to malnutrition and liver disease. Phenytoin is bound to albumin, and therefore the usual loading dose of phenytoin might result in a higher percentage of unbound drug and increased toxicity in these patients. Thirty-six chronic alcoholic patients were given a 15-mg/kg loading dose of phenytoin by constant intravenous infusion. After the infusion, patients were evaluated for clinical signs of phenytoin toxicity. At 1 hour after infusion, blood was sent for determination of total phenytoin, free phenytoin, and albumin levels. Fifteen patients were hypoalbuminemic (mean, 3.4 g/dL); 21 patients had albumin levels within the normal range (mean, 4.3 g/dL). In the hypoalbuminemic group, the mean free phenytoin level was 1.1 micrograms/mL, and the mean total phenytoin level was 13.6 micrograms/mL. In patients with normal albumin levels, the mean free phenytoin level was 1.3 micrograms/mL, and the mean total phenytoin level was 15.7 micrograms/mL. There were no statistically significant differences in total phenytoin or free phenytoin levels between either groups. No patient had a postinfusion phenytoin level (either free or total) within the toxic range. Although our sample size was small, our results suggest that a 15-mg/kg loading dose of phenytoin does not produce toxic levels in chronic alcoholics.

Hypermagnesemia and perforated viscus.

Reported is an unusual case of hypermagnesemia secondary to exogenous intake in the presence of a perforated viscus and normal renal function. The patient's neurological and cardiovascular complications resolved with repair of a duodenal ulcer and correction of hypermagnesemia. The presentation of hypermagnesemia can be subtle, but should be considered in patients with gastrointestinal complications who present in shock.