Substantial reservoirs of molecular hydrogen in the debris disks around young stars.

Circumstellar accretion disks transfer matter from molecular clouds to young stars and to the sites of planet formation. The disks observed around pre-main-sequence stars have properties consistent with those expected for the pre-solar nebula from which our own Solar System formed 4.5 Gyr ago. But the 'debris' disks that encircle more than 15% of nearby main-sequence stars appear to have very small amounts of gas, based on observations of the tracer molecule carbon monoxide: these observations have yielded gas/dust ratios much less than 0.1, whereas the interstellar value is about 100 (ref. 9). Here we report observations of the lowest rotational transitions of molecular hydrogen (H2) that reveal large quantities of gas in the debris disks around the stars beta Pictoris, 49 Ceti and HD135344. The gas masses calculated from the data are several hundreds to a thousand times greater than those estimated from the CO observations, and yield gas/dust ratios of the same order as the interstellar value.

A rotating disk of gas and dust around a young counterpart to beta Pictoris.

beta Pictoris is the best known example of a main-sequence star encircled by a tenuous disk. Optical and infrared images of beta Pic suggest that the disk is composed of dust grains which have been interpreted as the debris generated by the disruption of the asteroid-sized remnants of planet-formation processes. The star itself is relatively old, with an age in excess of 100 Myr. Here we present high-resolution millimetre-wave images of continuum and molecular-line emission from dust and gas surrounding a much younger star, MWC480: the stellar properties of MWC480 are similar to those of beta Pic, but its age is just 6Myr. The morphology of the circumstellar material and a comparison with the predictions of kinematic modelling indicate the presence of a rotating disk, gravitationally bound to the star. Moreover, the mass of the disk is greater than the minimum required to form a planetary system like our own. We therefore suggest that the disk around the young star MWC480 could be a progenitor of debris disks of the type associated with older stars such as beta Pic, and so holds much promise for the study of both the origin of debris disks and the early stages of the formation of planetary systems.

Circumstellar disks and the search for neighbouring planetary systems.

The recent discoveries of planets orbiting several 'mature' stars bring new life to the question of just how common other planetary systems might be. Observations of very young stars provide a way to address this question and suggest that a significant number of such stars harbour conditions appropriate for the formation of planetary systems like our own.

Intravenous lorazepam as an amnestic and anxiolytic agent in the intensive care unit: a prospective study.

OBJECTIVE: To assess the efficacy and hemodynamic safety of intravenous lorazepam as an amnestic and anxiolytic agent in patients undergoing critical care procedures. DESIGN: Prospective study. SETTING: Trauma/intensive care unit and coronary care unit of a 524-bed, tertiary, teaching community hospital. SUBJECTS: Ten patients undergoing critical care procedures. INTERVENTIONS: Intravenous lorazepam was administered at an initial dose of 2 mg, 15 to 20 mins before the critical care procedure (procedures included both invasive and noninvasive techniques) was performed. Anxiety level and memory assessment were evaluated at baseline and at various points following lorazepam administration. Changes in hemodynamic status were evaluated regularly throughout the study. MEASUREMENTS AND MAIN RESULTS: No significant changes in hemodynamic measurements were observed after administration of intravenous lorazepam. Significant differences were seen in anxiety scores and amnestic effects from preprocedure/pre-lorazepam to post-lorazepam evaluations (all p values were < .03). CONCLUSIONS: This study confirms the beneficial anxiolytic and amnestic effects of lorazepam in a subgroup of patients undergoing critical care procedures. The study also substantiates the safety of this drug in this patient population.

Octreotide-induced hyperkalemia.

A 68-year-old woman was admitted with numerous injuries after being hit by an automobile. On day 16 of hospitalization octreotide was started for treatment of a pancreatic fistula, and within 2 days the patient's serum potassium increased. By the third and fourth days of octreotide therapy the level had increased to the point at which it required treatment. The patient was asymptomatic, however, and had normal renal function. Octreotide was discontinued on the fifth day of the course, with a subsequent decrease in serum potassium. Two days later, one dose of the drug was given; serial serum potassium levels were measured before and after the dose, and increased after the rechallenge. Octreotide was not administered for the remainder of the patient's hospitalization, and hyperkalemia did not recur.

Use of ondansetron for control of projectile vomiting in patients with neurosurgical trauma: two case reports.

OBJECTIVE: To describe two cases of projectile vomiting that were treated successfully with ondansetron in patients with neurosurgical trauma. Causes and pharmacologic treatments for nausea and emesis are also discussed. DATA SOURCES: Patient data and literature citations from published case reports, review articles, and clinical research reports as identified by MEDLINE. DATA SYNTHESIS: Ondansetron, a potent and highly selective antagonist of serotonin at the 5-HT3 (subtype 3)-receptor, possesses potent antiemetic effects. It has not been associated with the extrapyramidal adverse effects seen with traditional antiemetics. The occurrence of extrapyramidal reactions may limit the usefulness of conventional antiemetics in neurosurgical patients because such agents interfere with serial mental status examinations and lower the seizure threshold. Therefore, ondansetron may be preferable in this patient population. Two patients with head trauma and projectile vomiting were treated successfully with ondansetron following treatment failure with prochlorperazine. These represent the first reported cases of efficacious treatment with ondansetron in neurosurgical trauma patients. CONCLUSIONS: Ondansetron may be the preferred agent for controlling nausea and vomiting in patients with neurosurgical trauma. Controlled clinical trials are needed to evaluate its safety and efficacy in this patient population.