Subcostal versus transhepatic view to assess the inferior vena cava in critically ill patients.

BACKGROUND: Evaluation of the inferior vena cava (IVC) is not always possible through the subcostal (SC) window. METHODS: Inferior vena cava diameters measured by transhepatic (TH) and SC views were compared by Bland and Altman analysis. RESULTS: 131 patients were enrolled, including 88 (67%) under mechanical ventilation. The echogenicity was statistically poorer through the TH view in comparison with the SC view (P = .002). The correlation between the SC and TH views was good and better for respiratory variation than for end-expiratory or end-inspiratory diameter measurements (r = 0.86). Despite low bias, the limits of agreement were wide (-7.5 and 7.7 mm for end-expiratory diameter, -8.7 and 8.5 mm for end-inspiratory diameter, and -5.3 and 5.8 mm for respiratory variation). Complementary analysis showed that the concordance between the SC and the TH views was better when the IVC was distended. However, the limits of agreement remained broad. CONCLUSIONS: Although feasible in almost all patients, the TH view does not provide better echogenicity in comparison with the SC view. Despite a good correlation with the SC view and a low bias, the limits of agreement were wide, especially when the IVC has an ellipsoidal shape, suggesting caution in the interpretation of data obtained by the TH view.

Transfer and degradation of the common pesticide atrazine through the unsaturated zone of the Chalk aquifer (Northern France).

Groundwater in the Chalk aquifer is an important water resource whose quality has degraded due to fertilizer and pesticide use. Atrazine, classified as a priority substance, has been one of the most applied pesticides and also one of the most frequently detected pesticides in groundwater. The present study investigated the transfer and degradation of atrazine in the unsaturated zone of the Chalk aquifer in Northern France. The study was conducted in an underground quarry (Saint-Martin-le-Noeud), which provides a direct access to the water table and intercepts the unsaturated zone at different depths. The lake and the ceiling percolation of 16 sites throughout the quarry were followed. For 16 sites, the percolating flow rate and lake level were measured and the lake water was sampled for nitrate, atrazine and deethylatrazine (DEA, main degradation product of atrazine) analysis over 2.5 years. High spatial variations in hydrodynamics (percolating flow rate and lake level) and in lake water quality (atrazine between 55±11 and 202±40 ng L-1 and DEA between 269±53 and 1727±345 ng L-1) indicate that the properties of the unsaturated zone influence the transfer and the degradation of atrazine. A counterclockwise hysteresis characterizes the relationship between the lake level and atrazine concentration. Temporal variation shows that the atrazine is transferred through the matrix and fractures with a delay caused by the sorption process that differs in atrazine and DEA. The layer of clay-with-flints is shown to favor the degradation of atrazine near the surface. Preferential pathways may be created below clay-with-flints, through which the transfer of atrazine is quicker.

Water, nitrate and atrazine transfer through the unsaturated zone of the Chalk aquifer in northern France.

The water quality of the Chalk aquifer is degrading due to fertilizers and pesticides use which are classified as toxic to public health. The study aims to provide a better understanding of the transfer processes in the unsaturated zone of the Chalk aquifer using different environmental tracers (nitrate, atrazine and tritium). The study was conducted in an underground quarry in northern France (St. Martin le Noeud). The quarry provides direct access to the lower part of the unsaturated zone of the Chalk at a depth of 18-30 m. Fifteen sites throughout the quarry display percolation directly from the unsaturated zone. Since percolation intensity is heterogeneous at one site, a comparison was made between the variation of geochemical properties of ten samples from one site and the spatial variation of samples from 15 sites throughout the quarry. Using the Siegel-Tukey and Wilcoxon tests, we found that the variation between the sites is higher than the variation within one site. Therefore, one percolation sample can be used to represent one site. The transfer time of nitrate and atrazine is estimated based on its use in the cultivated fields. Pore water with no contamination indicates water infiltrated before the use of contaminants at the surface, and pore water with a high concentration of contaminants indicates water infiltrated during the use of contaminants at the surface. The transfer time of water molecules is estimated using the time series of tritium. Transfer velocities were computed for each environmental tracer (nitrate, atrazine and tritium) by dividing the estimated transfer time by the depth of each site. Two transfer velocity ranges are determined: (1) <0.32 ±â€¯0.02 m/year and (2) between 0.72 ±â€¯0.14 and 2.15 ±â€¯0.43 m/year, showing most water transfer through the matrix but also a mixture of water with different velocities.