Epidemiology, practice of ventilation and outcome for patients at increased risk of postoperative pulmonary complications

BACKGROUND Limited information exists about the epidemiology and outcome of surgical patients at increased risk of postoperative pulmonary complications (PPCs), and how intraoperative ventilation was managed in these patients. OBJECTIVES To determine the incidence of surgical patients at increased risk of PPCs, and to compare the intraoperative ventilation management and postoperative outcomes with patients at low risk of PPCs. DESIGN This was a prospective international 1-week observational study using the ‘Assess Respiratory Risk in Surgical Patients in Catalonia risk score’ (ARISCAT score) for PPC for risk stratification. PATIENTS AND SETTING Adult patients requiring intraoperative ventilation during general anaesthesia for surgery in 146 hospitals across 29 countries. MAIN OUTCOME MEASURES The primary outcome was the incidence of patients at increased risk of PPCs based on the ARISCAT score. Secondary outcomes included intraoperative ventilatory management and clinical outcomes. RESULTS A total of 9864 patients fulfilled the inclusion criteria. The incidence of patients at increased risk was 28.4%. The most frequently chosen tidal volume (VT) size was 500 ml, or 7 to 9 ml kg1 predicted body weight, slightly lower in patients at increased risk of PPCs. Levels of positive end-expiratory pressure (PEEP) were slightly higher in patients at increased risk of PPCs, with 14.3% receiving more than 5 cmH2O PEEP compared with 7.6% in patients at low risk of PPCs (P < 0.001). Patients with a predicted preoperative increased risk of PPCs developed PPCs more frequently: 19 versus 7%, relative risk (RR) 3.16 (95% confidence interval 2.76 to 3.61), P < 0.001) and had longer hospital stays. The only ventilatory factor associated with the occurrence of PPCs was the peak pressure. CONCLUSION The incidence of patients with a predicted increased risk of PPCs is high. A large proportion of patients receive high VT and low PEEP levels. PPCs occur frequently in patients at increased risk, with worse clinical outcome

Epidemiology, practice of ventilation and outcome for patients at increased risk of postoperative pulmonary complications: LAS VEGAS - An observational study in 29 countries

BACKGROUND Limited information exists about the epidemiology and outcome of surgical patients at increased risk of postoperative pulmonary complications (PPCs), and how intraoperative ventilation was managed in these patients. OBJECTIVES To determine the incidence of surgical patients at increased risk of PPCs, and to compare the intraoperative ventilation management and postoperative outcomes with patients at low risk of PPCs. DESIGN This was a prospective international 1-week observational study using the ‘Assess Respiratory Risk in Surgical Patients in Catalonia risk score’ (ARISCAT score) for PPC for risk stratification. PATIENTS AND SETTING Adult patients requiring intraoperative ventilation during general anaesthesia for surgery in 146 hospitals across 29 countries. MAIN OUTCOME MEASURES The primary outcome was the incidence of patients at increased risk of PPCs based on the ARISCAT score. Secondary outcomes included intraoperative ventilatory management and clinical outcomes. RESULTS A total of 9864 patients fulfilled the inclusion criteria. The incidence of patients at increased risk was 28.4%. The most frequently chosen tidal volume (V T) size was 500 ml, or 7 to 9 ml kg−1 predicted body weight, slightly lower in patients at increased risk of PPCs. Levels of positive end-expiratory pressure (PEEP) were slightly higher in patients at increased risk of PPCs, with 14.3% receiving more than 5 cmH2O PEEP compared with 7.6% in patients at low risk of PPCs (P ˂ 0.001). Patients with a predicted preoperative increased risk of PPCs developed PPCs more frequently: 19 versus 7%, relative risk (RR) 3.16 (95% confidence interval 2.76 to 3.61), P ˂ 0.001) and had longer hospital stays. The only ventilatory factor associated with the occurrence of PPCs was the peak pressure. CONCLUSION The incidence of patients with a predicted increased risk of PPCs is high. A large proportion of patients receive high V T and low PEEP levels. PPCs occur frequently in patients at increased risk, with worse clinical outcome.</p

A plasma approach to rare-earth based solar spectrum conversion

Solar spectrum conversion concepts are undoubtedly necessary to further enhance the solar cell efficiency. According to this approach, the solar spectrum can be efficiently modified by shifting the photons towards a wavelength range where the solar cell has a higher response. Therefore, by placing a spectrum conversion layer on the front surface (i.e. down convertors) or at the back of the solar cell (i.e. up convertors), the existent optical losses can be quantitatively reduced. One of the light conversion mechanisms, namely the luminescent down shifting (LDS) mechanism, has been implemented for different luminescent materials embedded in different host matrices showing their potential for a wide range of PV technologies. In general, the LDS mechanism can be activated by incorporating specific rare-earth (RE) ions in a host material due to their special optical properties, i.e. UV absorption followed by visible emission. Currently, thin amorphous layers such as silicon nitride or silicon oxide, are extensively applied in c-Si as well as thin film solar cell technologies. In this PhD thesis a plasma-based deposition approach to obtain LDS layers has been applied. In particular, a hybrid method combining two plasma- aided techniques, namely an expanding thermal plasma and a magnetron sputtering unit, has been developed to obtain novel amorphous RE doped materials, i.e. a-SiNx:Eu, a-SiO2:Eu,. The novelty of this approach consists in combining three functionalities in one amorphous layer, i.e. antireflection, bulk/surface passivation of the absorber and spectral conversion properties of the rare earth elements. The goal is to demonstrate whether the LDS mechanism proposed to increase the solar cells efficiency can be achieved. The challenge in achieving this goal is to control the incorporation of RE elements in the amorphous layer through a proper control of the plasma process parameters. In order to determine the ion flux available for the RE target sputtering, ion flux measurements have been carried out. A pulse-shaped capacitive probe has been implemented for the first time in a high rate deposition (2-20 nm/s) ETP system fed with depositing gas mixtures, showing the probe tolerance towards the presence of insulating layers. The method is based on the discharge of an external capacitor, Cp, by changing the slope of the applied bias signal. This method makes the ion probe an accurate and relatively simple tool to determine ion fluxes under harsh conditions. Moreover, for high SiH4 flows (> 1 sccs), an interesting behaviour in the downstream region of the plasma at 5 cm off the axial position of the reactor, has been observed. We have hypothesized on the presence of the local ion flux enhancement: it is suggested that cluster formation occurs in the recirculation volume of the ETP at the boundaries between the plasma jet and the reactor walls. The response of the clusters to pressure, thermophoretic and electrostatic forces, has been investigated. Therefore, the ion probe technique has been proposed as suitable tool to detect the presence of clusters developed in depositing plasmas. Moreover, the ion flux measurements performed in front of the substrate in combination with in situ film growth monitoring by spectroscopic ellipsometry (SE) during the deposition process has been used to understand the influence of ETP plasma on magnetron sputtering rate when the sources are simultaneously operated. The successful incorporation of Eu in both oxide and nitride matrices has been confirmed by Rutherford Backscattering (RBS) measurements whereas the valence state of Eu (i.e. Eu2+and Eu3+) has been identified by X-ray Photoelectron Spectroscopy (XPS). In order to confirm whether the Eu incorporated in the amorphous matrix is optically active, photoluminescence (PL) measurements have been performed. We have observed Eu3+ line emissions corresponding to (J = 1, 2, 3, 4) transitions superimposed on an Eu2+ band emission corresponding to transition from 400 to 800 nm. However, in addition to radiative emission, a contribution of nonradiative emission indicated by the fast decay time values for the doped dielectric layers has been observed. Moreover, Transmission Electron Microscopy (TEM) top view and cross sectional measurements show the presence of Eu clusters with an average diameter of 3 nm, suggesting clustering phenomena occurring in the dielectric layer. In conclusion, by combining the short decay time values we measured and the clusters observed in the TEM images, a hypothesis for the nonradiative decay has been drawn as it follows: the energy transfer between the luminescent active centres within a cluster becomes very efficient, which will then be transferred to a defect in the vicinity of the cluster and therefore lost. Both plasma and material characterization insights obtained through the investigation of RE doped materials are particularly useful to further explore the possibility of using the ETP-PVD hybrid technique in the synthesis of novel materials for solar cell applications

Ion probe detection of clusters in a remotely expanding thermal plasma

The investigation of a remote depositing Ar/NH3/SiH4-fed expanding thermal plasma by means of an ion probe, under high SiH4 flow rate (formula) conditions, is reported here. Given the expanding nature of the plasma in the downstream region, a Gaussian-like ion flux radial profile is observed. A peculiar local off-axis ion peak for high (formula) is also observed nearby. A hypothesis for this phenomenon is proposed, on the basis of the plasma chemistry occurring in the downstream region. The local depletion of electrons, being withdrawn by silicon-containing clusters formed at the boundaries between the plasma beam and the background gas, is responsible for the local enhancement of the ion flux. This hypothesis is corroborated by further studies aiming to evaluate the effects of thermophoretic and electrostatic forces on the above-mentioned clusters. The presented work suggests the application of the capacitive probe technique for cluster detection in specific plasma chemistries

Investigation of Rare Earth - Doped Silicon Nitride Layers for Solar Cell Applications

Nowadays the application of thin SiNx layers as bulk passivating and antireflection coatings for Si-based solar cells applications is considered to be a successful solution for the increase in efficiency1. A new concept to further increase the efficiency of the solar cell is based on the light conversion mechanism: according to this approach the solar spectrum can be efficiently modified by shifting the photons towards a wavelength range where the solar cell has a better or higher response2. Recently, a novel class of rare earth (RE)- doped SiNx layers has been demonstrated to be a highly promising red-emitting conversion phosphor for white-LED applications. These materials have allowed the shifting of the emission wavelength by tuning the concentration of a specific RE element in a SiNx based crystalline matrix3. The investigation of RE-doped amorphous silicon nitride (SiNx) compounds, where the electronic properties of Si are combined with the optical properties of RE3+ ions, have been shown already potential in optoelectronics4. Therefore, parallel studies on the incorporation of a RE material in amorphous SiNx host lattices, which could be implemented in solar cells to increase the efficiency, are considered to be presently a challenge. In this contribution the properties of europium- and samarium- doped amorphous SiNx layers are investigated. The RE-doped SiNx layers are deposited using a remote PECVD expanding thermal plasma fed with Ar/SiH4/NH3 mixtures in combination with a RE magnetron sputtering source implemented in the proximity of the substrate holder. Growth rates of the RE doped layers obtained from Spectroscopic Ellipsometry (SE) measurements were in the range 0.6-2.2 nm/s. The successful incorporation of RE in the SiNx matrix has been demonstrated by means of Rutherford Back Scattering (RBS) and X-ray Photoelectron Spectroscopy (XPS) analysis, i.e. up to 2%. Preliminary photoluminescence results point out a broad band emission in the region of 500-800 nm when excitation wavelengths of 270 nm and 320 nm have been used. The emission band observed can be attributed to Sm2+. [1] J. Hong et al., J. Vac. Sci. Technol. B. 21 (5). [2] C. Strümpel et al., Sol. Energ. Mat. Sol. C. 91 (2007) 238 – 249. [3] Y. Q. Li et al., J. Alloys. and Comp. 417, 273 – 279. [4] A. R. Zanatta, et al., J. Phys.:Condens. Matter 19 (2007) 436230

Surface Hydride Composition of Plasma-Synthesized Si Nanoparticles

We have determined the surface hydride composition of amorphous and crystalline Si nanoparticles (NPs) (3-5 nm) synthesized in a low-temperature SiH(4)/Ar plasma using in situ attenuated total reflection Fourier-transform infrared spectroscopy and H(2) thermal effusion measurements. With increasing power to the plasma source, the particles transition from amorphous to crystalline with a corresponding increase in the fraction of SiH species on the surface. The surface hydride composition indicates that Si NPs synthesized at higher plasma powers crystallin in the gas-phase due to a greater degree of plasma-induced heating, which enhances the desorption rates for SiH(2) and SiH(3). Furthermore, these Si NPs do not contain any detectable H in the bulk

A capacitive probe with shaped probe bias for ion flux measurements in depositing plasmas

The application of a pulse shaped biasing method implemented to a capacitive probe is described. This approach delivers an accurate and simple way to determine ion fluxes in diverse plasma mixtures. To prove the reliability of the method, the ion probe was used in a different configuration, namely, a planar Langmuir probe. In this configuration, the ion current was directly determined from the I-V characteristic and compared with the ion current measured with the pulse shaped ion probe. The results from both measurements are in excellent agreement. It is demonstrated that the capacitive probe is able to perform spatially resolved ion flux measurements under high deposition rate conditions (2-20 nm/s) in a remote expanding thermal plasma in Ar/ NH3 / SiH4 mixture

A capacitive probe with shaped probe bias for ion flux measurements in depositing plasmas

The application of a pulse shaped biasing method implemented to a capacitive probe is described. This approach delivers an accurate and simple way to determine ion fluxes in diverse plasma mixtures. To prove the reliability of the method, the ion probe was used in a different configuration, namely, a planar Langmuir probe. In this configuration, the ion current was directly determined from the I-V characteristic and compared with the ion current measured with the pulse shaped ion probe. The results from both measurements are in excellent agreement. It is demonstrated that the capacitive probe is able to perform spatially resolved ion flux measurements under high deposition rate conditions (2-20 nm/s) in a remote expanding thermal plasma in Ar/ NH3 / SiH4 mixture