BackgroundFrailty is an important prognostic factor for adverse outcomes and increased resource use in the growing population of older surgical patients. We identified and appraised studies that tested interventions in populations of frail surgical patients to improve perioperative outcomes.MethodsWe systematically searched Cochrane, CINAHL, EMBASE and Medline to identify studies that tested interventions in populations of frail patients having surgery. All phases of study selection, data extraction, and risk of bias assessment were done in duplicate. Results were synthesized qualitatively per a prespecified protocol (CRD42016039909).ResultsWe identified 2 593 titles; 11 were included for final analysis, representing 1 668 participants in orthopedic, general, cardiac, and mixed surgical populations. Only one study was multicenter and risk of bias was moderate to high in all studies. Interventions were applied pre- and postoperatively, and included exercise therapy (n = 4), multicomponent geriatric care protocols (n = 5), and blood transfusion triggers (n = 1); no specific surgical techniques were compared. Exercise therapy, applied pre-, or post-operatively, was associated with significant improvements in functional outcomes and improved quality of life. Multicomponent protocols suffered from poor compliance and difficulties in implementation. Transfusion triggers had no significant impact on mortality or other outcomes.ConclusionsDespite a growing literature that demonstrates strong independent associations between frailty and adverse outcomes, few interventions have been tested to improve the outcomes of frail surgical patients, and most available studies are at substantial risk of bias. Multicenter, low risk of bias, studies of perioperative exercise are needed, while substantial efforts are required to develop and test other interventions to improve the outcomes of frail people having surgery.

We report on the influence of surface reconstruction on silicon dopant incorporation and transport properties during molecular-beam epitaxy of GaAs(Bi) alloys. GaAs(Bi) growth with an (n × 3) reconstruction leads to n-type conductivity, while growth with a (2 × 1) reconstruction leads to p-type conductivity. We hypothesize that the presence or absence of surface arsenic dimers prevents or enables dopant incorporation into arsenic lattice sites. We consider the influence of bismuth anions on arsenic-dimer mediated dopant incorporation and the resulting electronic transport properties, demonstrating the applicability of this mechanism to mixed anion semiconductor alloys.

Significant composition-dependent incorporation of N into non-substitutional sites is often reported for dilute GaAsN alloys. To distinguish (N-N)As, (N-As)As, and (AsGa-NAs) complexes, we compare Rutherford backscattering spectrometry and nuclear reaction analysis (NRA) spectra with Monte Carlo-Molecular Dynamics simulations along the [100], [110], and [111] directions. For the Monte Carlo simulation, we assume that (N-N)As is aligned along the [111] direction, while (N-As)As is aligned along the [010] direction. The measured channeling NRA spectra exhibit the highest (lowest) yield in the [111] ([100]) directions. Similar trends are observed for simulations of (N-As)As, suggesting that (N-As)As is the dominant interstitial complex in dilute GaAsN.

We have examined the alloy composition dependence of the energy bandgap and electronic states in GaAsNBi alloys. Using direct measurements of N and Bi mole fractions, via ion beam analysis, in conjunction with direct measurements of the out-of-plane misfit via x-ray rocking curves, we determine the “magic ratio” for lattice-matching of GaAsNBi alloys with GaAs substrates. In addition, using a combination of photoreflectance and photoluminescence spectroscopy, we map the composition- and misfit-dependence of the energy bandgaps, along with revealing the energetic position of Bi-related states at approximately 0.18 eV above the valence band maximum.

We have examined the influence of bismuth (Bi) and nitrogen (N) fluxes on N and Bi incorporation during molecular-beam epitaxy of GaAs1-x-yNxBiy alloys. The incorporation of Bi is found to be independent of N flux, while the total N incorporation and the fraction of N atoms occupying non-substitutional lattice sites increase with increasing Bi flux. A comparison of channeling nuclear reaction analysis along the [100], [110], and [111] directions with Monte Carlo-Molecular Dynamics simulations indicates that the non-substitutional N primarily incorporate as (N-As)As interstitial complexes. We discuss the influence of Bi adatoms on the formation of arsenic-terminated [110]-oriented step-edges and the resulting enhancement in total N incorporation via the formation of additional (N-As)As.