Short-term tissue decomposition alters stable isotope values and C:N ratio, but does not change relationships between lipid content, C:N ratio, and Δδ13C in marine animals.

Measures (e.g. δ15N, δ13C, %C, %N and C:N) derived from animal tissues are commonly used to estimate diets and trophic interactions. Since tissue samples are often exposed to air or kept chilled in ice over a short-term during sample preparation, they may degrade. Herein, we hypothesize that tissue decomposition will cause changes in these measures. In this study, we kept marine fish, crustacean and mollusc tissues in air or ice over 120 h (5 days). We found that tissue decomposition in air enriched δ15N (range 0.6‰ to 1.3‰) and δ13C (0.2‰ to 0.4‰), decreased %N (0.47 to 3.43 percentage points from staring values of ~13%) and %C (4.53 to 8.29 percentage points from starting values of ~43%), and subsequently increased C:N ratio (0.14 to 0.75). In air, while such changes to δ13C were relatively minor and therefore likely tolerable, changes in δ15N, %N, %C and C:N ratio should be interpreted with caution. Ice effectively reduced the extent to which decomposition enriched δ15N (≤ 0.4‰) and δ13C (≤ 0.2‰), and eliminated decomposition in C:N ratio, %N and %C. In our second experiment, for fish tissues in either air or ice over 120 h, we observed no effects of decomposition on relationships between lipid content, C:N ratio, and Δδ13C (change in δ13C after lipid removal), which are employed to correct δ13C for samples containing lipid. We also confirmed that lipid in tissues caused large errors when estimating δ13C (mean ± standard error = -1.8‰ ± 0.1‰, range -0.6‰ to -3.8‰), and showed both lipid extraction and mathematical correction performed equally well to correct for lipids when estimating δ13C. We, therefore, recommend that specimens of marine animals should be kept in ice during sample preparation for a short-term, as it is an effective means for minimizing changes of the stable isotope measures in their tissue.

The hemodynamics of oxytocin and other vasoactive agents during neuraxial anesthesia for cesarean delivery: findings in six cases.

Oxytocin is a commonly used uterotonic that can cause significant and even fatal hypotension, particularly when given as a bolus. The resulting hypotension can be produced by a decrease in systemic vascular resistance or cardiac output through a decrease in venous return. Parturients with normal volume status, heart valves and pulmonary vasculature most often respond to this hypotension with a compensatory increase in heart rate and stroke volume. Oxytocin-induced hypotension at cesarean delivery may be incorrectly attributed to blood loss. Pulse power analysis (also called "pulse contour analysis") of an arterial pressure wave form allows continuous evaluation of systemic vascular resistance and cardiac output in real time, thereby elucidating the causative factors behind changes in blood pressure. Pulse power analysis was conducted in six cases of cesarean delivery performed under neuraxial anesthesia. Hypotension in response to oxytocin was associated with a decrease in systemic vascular resistance and a compensatory increase in stroke volume, heart rate and cardiac output. Pulse power analysis may be helpful in determining the etiology of and treating hypotension during cesarean delivery under neuraxial anesthesia.

Acute normovolemic hemodilution, intraoperative cell salvage and PulseCO hemodynamic monitoring in a Jehovah's Witness with placenta percreta.

A Jehovah's Witness who had had four previous cesarean deliveries was referred to our institution for management of a complete placenta previa at 34 weeks of gestation. A subsequent ultrasound scan was suggestive of placenta percreta with bladder involvement. After erythropoietin and iron supplementation, cesarean hysterectomy was performed. Using PulseCO technology for continuous hemodynamic monitoring, preoperative acute normovolemic hemodilution and intraoperative cell salvage were used resulting in a successful cesarean hysterectomy with a 5500-mL estimated blood loss. The PulseCO system provides continuous, real-time hemodynamic data by applying pulse power analysis to the arterial pressure waveform. A bolus of oxytocin given after delivery produced profound hypotension, the hemodynamics of which were elucidated with the PulseCO system. To our knowledge, the combined use of acute normovolemic hemodilution, intraoperative cell salvage and PulseCO hemodynamic monitoring for cesarean hysterectomy has not been reported previously. These techniques may be particularly useful in managing patients who refuse blood products and/or in whom the baseline hemoglobin is suboptimal.

Susceptibility of populations of Banks grass mites (Acari: Tetranychidae) suspected of developing bifenthrin resistance from three maize fields.

Banks grass mite, Oligonychus pratensis (Banks), from three Texas maize fields were assayed for bifenthrin resistance following poor field control in 1995. Laboratory bioassays showed the field mites to be 3- to 23-fold more tolerant to bifenthrin than the susceptible laboratory culture. Comparison of LC50 values to assays with bifenthrin from 1985 to 1993 indicated no statistically significant changes in mite resistance. However, high LC90 values in 1995 suggest possible resistance development. The percentages of resistant mites from the three fields in 1995 were calculated to be 4.7%, 17.9%, and 30.9%. The Banks grass mite population exhibiting the highest level of tolerance to bifenthrin was further assayed to evaluate tolerance levels to other insecticides alone and in combination with synergists and insecticides. A high level of tolerance existed in the 1995 'bifenthrin-selected' Banks grass mite strain to bifenthrin, dimeothate, and amitraz. The combination of bifenthrin or dimethoate with a synergist indicated changes in the ability of the more resistant 1995 mites to detoxify insecticides. The activity of a dimethoate + bifenthrin mixture and a three way mixture of dimethoate, bifenthrin, and piperonyl butoxide caused 5- and 38-fold increase in toxicity against the more resistant Banks grass mite.

Identifying insecticide-resistant greenbugs (Homoptera: Aphididae) with diagnostic assay tests.

Laboratory bioassays were used to develop a diagnostic assay test for identifying greenburg, Schizaphis graminum (Rondani), populations that are insecticide-resistant. Petri dish assays with chlorpyrifos showed greenbug mortality should be monitored after 2 h of exposure. One-hour exposure did not kill a high percentage of susceptible greenbugs, and a 3-h exposure killed too many resistant greenbugs. Ethanol and methanol were both good solvents for mixing with chlorpyrifos in the petri dish assay. From the laboratory bioassays, four diagnostic concentrations of chlorpyrifos (3, 10, 30, and 100 ppm) were evaluated in the field by Texas A&M University agricultural research and extension entomologists across the Texas High Plains. Results from the diagnostic assay tests were compared with gel-electrophoresis resistance tests to validate resistance detection. The diagnostic assay tests gave the same greenbug resistance identification as the gel-electrophoresis analysis in 21 of 22 field bioassays in 1994 and 35 of 39 field bioassays in 1995. Diagnostic concentrations of 30 and 100 ppm chlorpyrifos killed > or = 85 and > or = 90%, respectively, of greenbugs identified by gel-electrophoresis as susceptible and < 40% and < 55%, respectively, of resistant greenbugs. The diagnostic assay technique is a quick, reliable, and inexpensive method for detecting insecticide resistance in greenbug populations.