RESUMO
The objective of this study was to evaluate microwave heating enhancements offered by iron/iron oxide nanoparticles dispersed within tissue-mimicking media for improving efficacy of microwave thermal therapy. The following dopamine-coated magnetic nanoparticles (MNPs) were considered: 10 and 20 nm diameter spherical core/shell Fe/Fe3O4, 20 nm edge-length cubic Fe3O4, and 45 nm edge-length/10 nm height hexagonal Fe3O4. Microwave heating enhancements were experimentally measured with MNPs dissolved in an agar phantom, placed within a rectangular waveguide. Effects of MNP concentration (2.5-20 mg/mL) and microwave frequency (2.0, 2.45 and 2.6 GHz) were evaluated. Further tests with 10 and 20 nm diameter spherical MNPs dispersed within a two-compartment tissue-mimicking phantom were performed with an interstitial dipole antenna radiating 15 W power at 2.45 GHz. Microwave heating of 5 mg/mL MNP-agar phantom mixtures with 10 and 20 nm spherical, and hexagonal MNPs in a waveguide yielded heating rates of 0.78 ± 0.02 °C/s, 0.72 ± 0.01 °C/s and 0.51 ± 0.03 °C/s, respectively, compared to 0.5 ± 0.1 °C/s for control. Greater heating enhancements were observed at 2.0 GHz compared to 2.45 and 2.6 GHz. Heating experiments in two-compartment phantoms with an interstitial dipole antenna demonstrated potential for extending the radial extent of therapeutic heating with 10 and 20 nm diameter spherical MNPs, compared to homogeneous phantoms (i.e., without MNPs). Of the MNPs considered in this study, spherical Fe/Fe3O4 nanoparticles offer the greatest heating enhancement when exposed to microwave radiation. These nanoparticles show strong potential for enhancing the rate of heating and radial extent of heating during microwave hyperthermia and ablation procedures.
RESUMO
BACKGROUND: Multiple studies suggest tranexamic acid reduces blood loss and red cell transfusions in patients undergoing THA or TKA. However, many of the dosing schedules in these studies are not ideally suited for routine application. QUESTIONS/PURPOSES: We asked whether one 20-mg per kg intraoperative dose of tranexamic acid in patients having primary THA or TKA would (1) decrease perioperative blood loss and red cell transfusion rates and (2) be a cost-effective protocol. PATIENTS AND METHODS: We retrospectively reviewed the records of 234 patients operated on from April 1 to June 30, 2007 (before our study protocol) and 259 patients from April 1 to June 30, 2008 with the single-dose protocol. We then compared change in hemoglobin, transfusion rates, hemoglobin at discharge, hospital length of stay, and complications between the two groups. No other routine patient care practices or blood conservation program strategies were altered during this time. RESULTS: We found a reduction in the decrease in hemoglobin in 2008 compared with 2007 for THA and TKA (39 from 46 g/L and 36 from 45 g/L, respectively),which led to a reduction in transfusion rates (3.6% from 13.5% and 2.0% from 13.4%, respectively) and higher hemoglobin levels at discharge [corrected].There were no recorded major adverse events associated with the introduction of this protocol. CONCLUSIONS: One 20-mg per kg intraoperative dose of tranexamic acid reduced the perioperative decrease in hemoglobin and red blood cell transfusion rates in patients having TKA and THA compared with those of a similar cohort of patients in whom the protocol was not used. This weight increment dosing facilitated pharmacy drug preparation, led to minimal dose variability and wastage, and resulted in a substantial estimated cost savings. LEVEL OF EVIDENCE: Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
