Disorders of Salt and Water Balance After Pituitary Surgery.

Transsphenoidal surgery is the first-line treatment for many clinically significant pituitary tumors and sellar lesions. Although complication rates are low when performed at high-volume centers, disorders of salt and water balance are relatively common postoperatively. Both, or either, central diabetes insipidus (recently renamed arginine vasopressin deficiency - AVP-D), caused by a deficiency in production and/or secretion of arginine vasopressin, and hyponatremia, most commonly secondary to the syndrome of inappropriate antidiuresis, may occur. These conditions can extend hospital stay and increase the risk of readmission. This article discusses common presentations of salt and water balance disorders following pituitary surgery, the pathophysiology of these conditions, and their diagnosis and management.

Evaluation of Multiple Linear Regression-Based Limited Sampling Strategies for Enteric-Coated Mycophenolate Sodium in Adult Kidney Transplant Recipients.

BACKGROUND: Although multiple linear regression-based limited sampling strategies (LSSs) have been published for enteric-coated mycophenolate sodium, none have been evaluated for the prediction of subsequent mycophenolic acid (MPA) exposure. This study aimed to examine the predictive performance of the published LSS for the estimation of future MPA area under the concentration-time curve from 0 to 12 hours (AUC0-12) in renal transplant recipients. METHODS: Total MPA plasma concentrations were measured in 20 adult renal transplant patients on 2 occasions a week apart. All subjects received concomitant tacrolimus and were approximately 1 month after transplant. Samples were taken at 0, 0.33, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 6, and 8 hours and 0, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 2, 3, 4, 6, 9, and 12 hours after dose on the first and second sampling occasion, respectively. Predicted MPA AUC0-12 was calculated using 19 published LSSs and data from the first or second sampling occasion for each patient and compared with the second occasion full MPA AUC0-12 calculated using the linear trapezoidal rule. Bias (median percentage prediction error) and imprecision (median absolute prediction error) were determined. RESULTS: Median percentage prediction error and median absolute prediction error for the prediction of full MPA AUC0-12 were <15% for 4 LSSs, using the data from the same (second) occasion. One equation (1.583C1 + 0.765C2 + 0.369C2.5 + 0.748C3 + 1.518C4 + 2.158C6 + 3.292C8 + 3.6690) showed bias and imprecision <15% for the prediction of future MPA AUC0-12, where the predicted AUC0-12 from the first occasion was compared with the full AUC0-12 from the second. All LSSs with an acceptable predictive performance included concentrations taken at least 6 hours after the dose. CONCLUSIONS: Only one LSS had an acceptable bias and precision for future estimation. Accurate dosage prediction using a multiple linear regression-based LSS was not possible without concentrations up to at least 8 hours after the dose.

Magnesium alloy AZ91 exhibits antimicrobial properties in vitro but not in vivo.

Magnesium alloys hold great promise for developing orthopedic implants that are biocompatible, biodegradable, and mechanically similar to bone tissue. This study evaluated the in vitro and in vivo antimicrobial properties of magnesium-9%aluminum-1%zinc (AZ91) and commercially pure titanium (cpTi) against Acinetobacter baumannii (Ab307). The in vitro results showed that as compared to cpTi, incubation with AZ91 significantly reduced both the planktonic (cpTi = 3.45e8, AZ91 = 8.97e7, p < 0.001) colony forming units (CFU) and biofilm-associated (cpTi = 3.89e8, AZ91 = 1.78e7, p = 0.01) CFU of Ab307. However, in vivo results showed no significant differences in the CFU enumerated from the cpTi and AZ91 implants following a 1-week implantation in an established rodent model of Ab307 implant associated infection (cpTi = 5.23e3, AZ91 = 2.46e3, p = 0.29). It is proposed that the in vitro results were associated with an increased pH in the bacterial culture as a result of the AZ91 corrosion process. The robust in vivo buffering capacity likely diminished this corrosion associated pH antimicrobial effect. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 221-227, 2018.

Bio-Corrosion of Magnesium Alloys for Orthopaedic Applications.

Three Mg alloys, Mg-1.34% Ca-3% Zn (MCZ), Mg-1.34% Ca-3% Zn-0.2% Sr (MCZS), and Mg-2% Sr (MS), were examined to understand their bio-corrosion behavior. Electrochemical impedance spectroscopy and polarization scans were performed after 6 days of immersion in cell culture medium, and ion release and changes in media pH were tracked over a 28 day time period. Scanning electron microscopy (SEM) of alloy microstructure was performed to help interpret the results of the electrochemical testing. Results indicate that corrosion resistance of the alloys is as follows: MCZ > MCZS > MS.

Effects of simulated inflammation on the corrosion of 316L stainless steel.

Stainless steel alloys, including 316L, find use in orthopaedics, commonly as fracture fixation devices. Invasive procedures involved in the placement of these devices will provoke a local inflammatory response that produces hydrogen peroxide (H2O2) and an acidic environment surrounding the implant. This study assessed the influence of a simulated inflammatory response on the corrosion of 316L stainless steel. Samples were immersed in an electrolyte representing either normal or inflammatory physiological conditions. After 24h of exposure, electrochemical impedance spectroscopy (EIS) and inductively coupled plasma mass spectroscopy (ICPMS) were used to evaluate differences in corrosion behavior and ion release induced by the inflammatory conditions. Scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDX) were used to evaluate surface morphology and corrosion products formed on the sample surface. Inflammatory conditions, involving the presence of H2O2 and an acidic pH, significantly alter the corrosion processes of 316L stainless steel, promoting aggressive and localized corrosion. It is demonstrated that particular consideration should be given to 316L stainless steel implants with crevice susceptible areas (ex. screw-head/plate interface), as those areas may have an increased probability of rapid and aggressive corrosion when exposed to inflammatory conditions.

Influence of MC3T3-E1 preosteoblast culture on the corrosion of a T6-treated AZ91 alloy.

This study investigated the corrosion of artificially aged T6 heat-treated Mg-9%Al-1%Zn (AZ91) for biomedical applications. Corrosion tests and surface analysis were completed both with and without a monolayer of mouse preosteoblast MC3T3-E1 cells cultured on the sample. Electrochemical impedance spectroscopy (EIS) and inductively coupled plasma mass spectroscopy (ICPMS) were used to explore the corrosion processes after either 3 or 21 days of AZ91 incubation in cell culture medium (CCM). The EIS showed both the inner layer resistance (Rin ) and outer layer resistance (Rout ) were lower for samples without cells cultured on the surface at 3 days (Rin = 2.64 e4 Ω/cm(2) , Rout = 140 Ω/cm(2) ) compared to 21 days (Rin = 3.60 e4 Ω/cm(2) , Rout = 287 Ω/cm(2) ) due to precipitation of magnesium and calcium phosphates over time. Samples with preosteoblasts cultured on the surface had a slower initial corrosion (3 day, Rin = 1.88 e5 Ω/cm(2) , Rout = 1060 Ω/cm(2) ) which was observed to increase over time (21 day, Rin = 2.99 e4 Ω/cm(2) , Rout = 287 Ω/cm(2) ). Changes in the corrosion processes were thought to be related to changes in the coverage provided by the cell layer. Our results reveal that the presence of cells and biological processes are able to significantly influence the corrosion rate of AZ91.

Corrosion and mechanical performance of AZ91 exposed to simulated inflammatory conditions.

Magnesium (Mg) and its alloys, including Mg-9%Al-1%Zn (AZ91), are biodegradable metals with potential use as temporary orthopedic implants. Invasive orthopedic procedures can provoke an inflammatory response that produces hydrogen peroxide (H2O2) and an acidic environment near the implant. This study assessed the influence of inflammation on both the corrosion and mechanical properties of AZ91. The AZ91 samples in the inflammatory protocol were immersed for three days in a complex biologically relevant electrolyte (AMEM culture media) that contained serum proteins (FBS), 150 mM of H2O2, and was titrated to a pH of 5. The control protocol immersed AZ91 samples in the same biologically relevant electrolyte (AMEM & FBS) but without H2O2 and the acid titration. After 3 days all samples were switched into fresh AMEM & FBS for an additional 3-day immersion. During the initial immersion, inflammatory protocol samples showed increased corrosion rate determined by mass loss testing, increased Mg and Al ion released to solution, and a completely corroded surface morphology as compared to the control protocol. Although corrosion in both protocols slowed once the test electrolyte solution was replaced at 3 days, the samples originally exposed to the simulated inflammatory conditions continued to display enhanced corrosion rates as compared to the control protocol. These lingering effects may indicate the initial inflammatory corrosion processes modified components of the surface oxide and corrosion film or initiated aggressive localized processes that subsequently left the interface more vulnerable to continued enhanced corrosion. The electrochemical properties of the interfaces were also evaluated by EIS, which found that the corrosion characteristics of the AZ91 samples were potentially influenced by the role of intermediate adsorption layer processes. The increased corrosion observed for the inflammatory protocol did not affect the flexural mechanical properties of the AZ91 at any time point assessed.