The Weekend Effect in Hospitalized Patients: A Meta-Analysis.

BACKGROUND: The presence of a "weekend effect" (increased mortality rate during Saturday and/or Sunday admissions) for hospitalized inpatients is uncertain. PURPOSE: We performed a systematic review to examine the presence of a weekend effect on hospital inpatient mortality. DATA SOURCES: PubMed, EMBASE, SCOPUS, and Cochrane databases (January 1966-April 2013) were utilized for our search. STUDY SELECTION: We examined the mortality rate for hospital inpatients admitted during the weekend compared with those admitted during the workweek. To be included, the study had to provide discrete mortality data around the weekends (including holidays) versus weekdays, include patients who were admitted as inpatients over the weekend, and be published in English. DATA EXTRACTION: The primary outcome was all-cause weekend versus weekday mortality with subgroup analysis by personnel staffing levels, rates and times to procedures rates and delays, or illness severity. DATA SYNTHESIS: A total of 97 studies (N = 51,114,109 patients) were examined. Patients admitted on the weekends had a significantly higher overall mortality (relative risk, 1.19; 95% confidence interval, 1.14-1.23). With regard to the subgroup analyses, patients admitted on the weekends consistently had higher mortality than those admitted during the week, regardless of the levels of weekend/weekday differences in staffing, procedure rates and delays, and illness severity. CONCLUSIONS: Hospital inpatients admitted during weekends may have a higher mortality rate compared with inpatients admitted during the weekdays.

High content evaluation of shear dependent platelet function in a microfluidic flow assay.

The high blood volume requirements and low throughput of conventional flow assays for measuring platelet function are unsuitable for drug screening and clinical applications. In this study, we describe a microfluidic flow assay that uses 50 µL of whole blood to measure platelet function on ~300 micropatterned spots of collagen over a range of physiologic shear rates (50-920 s(-1)). Patterning of collagen thin films (CTF) was achieved using a novel hydrated microcontact stamping method. CTF spots of 20, 50, and 100 µm were defined on glass substrates and consisted of a dense mat of nanoscale collagen fibers (3.74 ± 0.75 nm). We found that a spot size of greater than 20 µm was necessary to support platelet adhesion under flow, suggesting a threshold injury size is necessary for stable platelet adhesion. Integrating 50 µm CTF microspots into a multishear microfluidic device yielded a high content assay from which we extracted platelet accumulation metrics (lag time, growth rate, total accumulation) on the spots using Hoffman modulation contrast microscopy. This method has potential broad application in identifying platelet function defects and screening, monitoring, and dosing antiplatelet agents.

Single- and two-phase flow in microfluidic porous media analogs based on Voronoi tessellation.

The objective of this study was to create a microfluidic model of complex porous media for studying single and multiphase flows. Most experimental porous media models consist of periodic geometries that lend themselves to comparison with well-developed theoretical predictions. However, many real porous media such as geological formations and biological tissues contain a degree of randomness and complexity at certain length scales that is not adequately represented in periodic geometries. To design an experimental tool to study these complex geometries, we created microfluidic models of random homogeneous and heterogeneous networks based on Voronoi tessellations. These networks consisted of approximately 600 grains separated by a highly connected network of channels with an overall porosity of 0.11-0.20. We found that introducing heterogeneities in the form of large cavities within the network changed the permeability in a way that cannot be predicted by the classical porosity-permeability relationship known as the Kozeny equation. The values of permeability found in experiments were in excellent agreement with those calculated from three-dimensional lattice Boltzmann simulations. In two-phase flow experiments of oil displacement with water we found that the wettability of channel walls determined the pattern of water invasion, while the network topology determined the residual oil saturation. The presence of cavities increased the microscopic sweeping efficiency in water-oil displacement. These results suggest that complex network topologies lead to fluid flow behavior that is difficult to predict based solely on porosity. The novelty of this approach is a unique geometry generation algorithm coupled with microfabrication techniques to produce pore scale models of stochastic homogeneous and heterogeneous porous media. The ability to perform and visualize multiphase flow experiments within these geometries will be useful in measuring the mechanism(s) of displacement within micro- and nanoscale pores.