Contamination-free Ge-based graphene as revealed by graphene enhanced secondary ion mass spectrometry (GESIMS).

In this study, we demonstrate that graphene grown on Ge does not contain any copper contamination, and identify some of the errors affecting the accuracy of commonly used measurement methods. Indeed, one of these, the secondary ion mass spectrometry (SIMS) technique, reveals copper contamination in Ge-based graphene but does not take into account the effect of the presence of the graphene layer. We have shown that this layer increases negative ionization significantly, and thus yields false results, but also that the graphene enhances, by an order of two, the magnitude of the intensity of SIMS signals when compared with a similar graphene-free sample, enabling much better detection limits. This forms the basis of a new measurement procedure, graphene enhanced SIMS (GESIMS) (pending European patent application no. EP 16461554.4), which allows for the precise estimation of the realistic distribution of dopants and contamination in graphene. In addition, we present evidence that the GESIMS effect leads to unexpected mass interferences with double-ionized species, and that these interferences are negligible in samples without graphene. The GESIMS method also shows that graphene transferred from Cu results in increased copper contamination.

Long-duration low-flow sevoflurane and isoflurane effects on postoperative renal and hepatic function.

UNLABELLED: Sevoflurane degradation by carbon dioxide absorbents during low-flow anesthesia forms the haloalkene Compound A, which causes nephrotoxicity in rats. Numerous studies have shown no effects of Compound A formation on postoperative renal function after moderate-duration (3-4 h) low-flow sevoflurane; however, effects of longer exposures remain unresolved. We compared renal function after long-duration low-flow (<1 L/min) sevoflurane and isoflurane anesthesia in consenting surgical patients with normal renal function. To maximize degradant exposure, Baralyme was used, and anesthetic concentrations were maximized (no nitrous oxide and minimal opioids). Inspired and expired Compound A concentrations were quantified. Blood and urine were obtained for laboratory evaluation. Sevoflurane (n = 28) and isoflurane (n = 27) groups were similar with respect to age, sex, weight, ASA status, and anesthetic duration (9.1 +/- 3.0 and 8.2 +/- 3.0 h, mean +/- SD) and exposure (9.2 +/- 3.6 and 9.1 +/- 3.7 minimum alveolar anesthetic concentration hours). Maximum inspired Compound A was 25 +/- 9 ppm (range, 6-49 ppm), and exposure (area under the concentration-time curve) was 165 +/- 95 (35-428) ppm. h. There was no significant difference between anesthetic groups in 24- or 72-h serum creatinine, blood urea nitrogen, creatinine clearance, or 0- to 24-h or 48- to 72-h urinary protein or glucose excretion. Proteinuria and glucosuria were common in both groups. There was no correlation between Compound A exposure and any renal function measure. There was no difference between anesthetic groups in 24- or 72-h aspartate aminotransferase or alanine aminotransferase. These results show that the renal and hepatic effects of long-duration low-flow sevoflurane and isoflurane were similar. No evidence for low-flow sevoflurane nephrotoxicity was observed, even at high Compound A exposures as long as 17 h. Proteinuria and glucosuria were common and nonspecific postoperative findings. Long-duration low-flow sevoflurane seems as safe as long-duration low-flow isoflurane anesthesia. IMPLICATIONS: Postoperative renal function after long-duration low-flow sevoflurane (with Compound A exposures greater than those typically reported) and isoflurane anesthesia were not different, as assessed by serum creatinine, blood urea nitrogen, and urinary excretion of protein and glucose. This suggests that low-flow sevoflurane is as safe as low-flow isoflurane, even at long exposures.

Screen-based anesthesia simulation with debriefing improves performance in a mannequin-based anesthesia simulator.

BACKGROUND: Previous investigations have established the need for improved training for management of anesthetic emergencies. Training with inexpensive screen-based anesthesia simulators may prove to be helpful. PURPOSES: We measured the effectiveness of screen-based simulator training with debriefing on the response to simulated anesthetic critical incidents. METHODS: Thirty-one 1st-year clinical anesthesia residents were randomized into 2 groups. The intervention group handled 10 anesthetic emergencies using the screen-based anesthesia simulator program and received written feedback on their management, whereas the traditional (control) group was asked to study a handout covering the same 10 emergencies. All residents then were evaluated on their management of 4 standardized scenarios in a mannequin-based simulator using a quantitative scoring system. RESULTS: The average point score for the simulator-with-debriefing group was 52.6 +/- 9.9 out of 95 possible points. The traditional group average point score was 43.4 +/- 5.9, p = .004. CONCLUSIONS: Residents who managed anesthetic problems using a screen-based anesthesia simulator handled the emergencies in a mannequin-based anesthesia simulator better than residents who were asked to study a handout covering the same problems. Computer simulations with feedback are effective as a supplement to traditional residency training methods for the management of medical emergencies.

Recertification of respiratory therapists' intubation skills one year after initial training: an analysis of skill retention and retraining.

Allied health personnel and nonanesthesiologist physicians often undergo training in tracheal intubation but then may actually use the skill relatively infrequently. This study assessed retention of skills one year after initial training and identified specific areas of knowledge critical to successful performance of intubation. Eleven respiratory therapists on the staff of a 253-bed hospital, each of whom had been trained one year previously in airway management, were evaluated. Prior to returning to the operating room for skills assessment and recertification, each respiratory therapist took a 21-question written exam. Therapists then went to the operating room and a trained observer (anesthesiologist) monitored the intubations performed to see whether critical steps were followed, while a second observer monitored a checklist of skills performed. The attending anesthesiologist recertified the therapist only when all steps were correctly performed and the intubation was successful. There was a poor correlation (r = -0.25, p > 0.1) between the number of intubations performed by the therapists for emergencies in the previous year and the number of intubations needed to be recertified. There was a negative correlation (r = -0.8, p < 0.05) between the score on the written test and the number of intubations required for recertification-a higher score meant fewer intubations were needed to achieve recertification. First-pass success occurred significantly more frequently if all skills tested were performed correctly (50/75 first-pass successes had all skills performed correctly vs 10/28 for failed first-pass, p < 0.01). The most common errors were levering the blade on the upper teeth (12/91) and tube not inserted from the right side of the mouth (28/104). When the blade was levered, 8 of 10 intubations failed. When the tube was not inserted from the right side of the face, 6 of 12 failed. The useful findings of this study are: (1) occasional performance of intubation did not ensure skill maintenance; (2) cognitive and procedural abilities correlated, suggesting benefits to study as well as to practical training; and (3) two specific mistakes were associated with a high incidence of failure.

Pharmacokinetics and pharmacodynamics of remifentanil in persons with renal failure compared with healthy volunteers.

BACKGROUND: Remifentanil is an opioid analgesic for use in anesthesia. An ester linkage renders it susceptible to rapid metabolism by blood and tissue esterases. Thus it was hypothesized that remifentanil elimination would be independent of renal function. Because its principal metabolite (GR90291) is eliminated renally, it would depend on renal function. This study was designed to evaluate the pharmacokinetics and pharmacodynamics of remifentanil and its metabolite in persons with and without renal failure. METHODS: Two groups of volunteers received two-stage infusions of remifentanil: low dose with 0.0125 microg x kg(-1) x min(-1) for 1 h followed by 0.025 microg x kg(-1) x min(-1) for 3 h; and high dose with 0.025 microg x kg(-1) x min(-1) for 1 h followed by 0.05 microg x kg(-1) x min(-1) for 3 h. Blood samples were collected for analysis of remifentanil and GR90291 concentrations. The pharmacokinetics of remifentanil were fit using a one-compartment pharmacokinetic model. Remifentanil's effect was determined intermittently using minute ventilation during a hypercapnic (7.5% CO2) challenge. RESULTS: Fifteen patients with renal failure and eight control participants were enrolled. The clearance and volume of distribution of remifentanil were not different between those with renal failure and the controls. Patients with renal failure showed a marked reduction in the elimination of GR90291; the half-life of the metabolite increased from 1.5 h in the controls to more than 26 h in patients with renal failure. The steady-state concentration of GR90291 is likely to be more than 25 times higher in persons with renal failure. There were no obvious differences in opioid effects on minute ventilation in the controls and in patients with renal failure. CONCLUSIONS: The pharmacokinetics and pharmacodynamics of remifentanil were not altered in patients with renal disease, but the elimination of its principal metabolite, GR90291, was markedly reduced. Based on simulations, the concentration of GR90291 at the end of a 12-h remifentanil infusion of 2 microg x kg(-1) x min(-1) is not likely to produce significant opioid effects.

Pharmacokinetics and pharmacodynamics of remifentanil in volunteer subjects with severe liver disease.

BACKGROUND: Remifentanil, a new mu-opioid agonist with an extremely short duration of action, is metabolized by circulating and tissue esterases; therefore, its clearance should be relatively unaffected by changes in hepatic or renal function. This study was designed to determine whether severe hepatic disease affects the pharmacokinetics or pharmacodynamics of remifentanil. METHODS: Ten volunteers with chronic, stable, severe hepatic disease and awaiting liver transplantation and ten matched controls were enrolled. Each subject was given a 4-h infusion of remifentanil. The first five pairs received 0.0125 microgram x kg(-1) x min(-1) for 1 h followed by 0.025 microgram x kg(-1) x min(-1) for 3 h; the second five pairs received double these infusion rates. During and after the infusion, arterial blood was obtained for pharmacokinetic analyses, and the ventilatory response to a hypercarbic challenge was assessed. Simultaneous pharmacokinetic and pharmacodynamic analyses were performed. The pharmacokinetics were described using a one-compartment intravenous infusion model, and ventilatory depression was modelled using the inhibitory E(max) model. The pharmacokinetics of the metabolite GR90291 were determined using noncompartmental methods. RESULTS: There were no differences in any of the pharmacokinetic parameters for remifentanil or GR90291 between the two groups. The subjects with liver disease were more sensitive to the ventilatory depressant effects of remifentanil. The EC(50) values (the remifentanil concentrations determined from simultaneous pharmacokinetic/pharmacodynamic analyses to depress carbon dioxide-stimulated minute ventilation by 50%) in the control and hepatic disease groups were 2.52 ng/ml (95% confidence interval 2.07-2.97 ng/ml) and 1.56 ng/ml (95% confidence interval 1.37-1.76 ng/ml), respectively. CONCLUSIONS: The pharmacokinetics of remifentanil and GR90291 are unchanged in persons with severe, chronic liver disease. Such patients may be more sensitive to the ventilatory depressant effects of remifentanil, a finding of uncertain clinical significance, considering the extremely short duration of action of the drug.

Perioperative drug interactions.

The various classes of IV and inhalation anesthetics all appear to potentiate one another. Many of these interactions are clinically useful in outpatient anesthesia, and many are quite predictable. True synergy is most likely to occur when two drugs produce similar actions by slightly different mechanisms. These principles are particularly well demonstrated by the interactions of hypnotic drugs at the locus ceruleus. It is possible that the reduced anesthetic requirements seen in some disease states may involve similar mechanisms.