Hemodynamics and outcome of septic shock

Septic shock is a common killer in intensive care units (ICU). The most crucial issue concerning the outcome is the early and aggressive start of treatment aimed at normalization of hemodynamics and the early start of antibiotics during the very first hours. The optimal targets of hemodynamic treatment, or impact of hemodynamic treatment on survival after first resuscitation period are less known. The objective of this study was to evaluate different aspects of the hemodynamic pattern in septic shock with special attention to prediction of outcome. In particular components of early treatment and monitoring in the ICU were assessed. A total of 401 patients, 218 with septic shock and 192 with severe sepsis or septic shock were included in the study. The patients were treated in 24 Finnish ICUs during 1999-2005. 295 of the patients were included in the Finnish national epidemiologic Finnsepsis study. We found that the most important hemodynamic variables concerning the outcome were the mean arterial pressures (MAP) and lactate during the first six hours in ICU and the MAP and mixed venous oxygen saturation (SvO2) under 70% during first 48 hours. The MAP levels under 65 mmHg and SvO2 below 70% were the best predictive thresholds. Also the high central venous pressure (CVP) correlated to adverse outcome. We assessed the correlation and agreement of SvO2 and mean central venous oxygen saturation (ScvO2) in septic shock during first day in ICU. The mean SvO2 was below ScvO2 during early sepsis. Bias of difference was 4.2% (95% limits of agreement 8.1% to 16.5%) by Bland-Altman analysis. The difference between saturation values correlated significantly to cardiac index and oxygen delivery. Thus, the ScvO2 can not be used as a substitute of SvO2 in hemodynamic monitoring in ICU. Several biomarkers have been investigated for their ability to help in diagnosis or outcome prediction in sepsis. We assessed the predictive value of N-terminal pro brain natriuretic peptide (NT-proBNP) on mortality in severe sepsis or septic shock. The NT-proBNP levels were significantly higher in hospital nonsurvivors. The NT-proBNP 72 hrs after inclusion was independent predictor of hospital mortality. The acute cardiac load contributed to NTproBNP values at admission, but renal failure was the main confounding factor later. The accuracy of NT-proBNP, however, was not sufficient for clinical decision-making concerning the outcome prediction. The delays in start of treatment are associated to poorer prognosis in sepsis. We assessed how the early treatment guidelines were adopted, and what was the impact of early treatment on mortality in septic shock in Finland. We found that the early treatment was not optimal in Finnish hospitals and this reflected to mortality. A delayed initiation of antimicrobial agents was especially associated with unfavorable outcome.Septisessä sokissa määritelmän mukaisesti potilaalla todetaan infektion aiheuttamana yleinen tulehdusreaktio sekä sepsikseen liittyen matala verenpainetaso ja riittämätön verenkierto nestehoidosta huolimatta. Kuolleisuus septiseen sokkiin on suuri, 30 60% ja se on eräs yleisimmistä kuolinsyistä teho-osastoilla. Väitöstutkimuksen tavoiteena oli arvioida eri näkökohtia septisen sokin hemodynamiikkaan, hoitoon ja ennusteeseen liittyen suomalaisilla potilailla. Väitöstutkimus koostuu yhdestä retrospektiivisestä ja kolmesta prospektiivisesta kohorttitutkimuksesta. Kaksi tutkimuksista oli kansallisen sepsistutkimuksen Finnsepsiksen osatöitä. Tutkimuksissa oli yhteensä 401 potilasta 24:ltä suomalaiselta teho-osastolta vuosina 1999-2005. 218:lla potilaista todettiin septinen sokki ja 192:lla vaikea sepsis. Hemodynamiikan hoidon tavoitteista septisessä sokissa on useita erilaisia suosituksia, joiden ennusteellinen merkitys on puutteellisesti tunnettu. Tässä tutkimuksessa arvioitiin yleisesti mitattujen ja monitoroitujen hemodynaamisten muuttujien ennusteellista vaikutusta. Totesimme, että keskiverenpaine (MAP) ja sekoittuneen laskimoveren happisaturaatio (SvO2) ovat ennusteellisesti erittäin merkityksellisiä. Nykyisin yleisesti käytetyt tavoiterajat (MAP>65mHg, SvO2>70%) ovat ennusteen kannalta optimaaliset. Korkea keskuslaskimopaine viittaa potilaan huonontuneeseen ennusteeseen. Kansainvälisessä sepsiksen hoitosuosituksessa keskuslaskimon happisaturaatio (ScvO2) ja SvO2 rinnastetaan vertailukelpoisiksi toisiinsa nähden. Väitöstutkimus selvensi että saturaatioiden rinnastaminen ei kuitenkaan ole suositeltavaa septisessä sokissa näiden huomattavan vaihtelun ja eroavaisuuden vuoksi. Useista biomarkkereista on odotettu diagnostista tai ennusteellista apua sepsiksessä. Me selvitimme sydämen erittämän hormonin, natriureettisen peptidin (NT-proBNP) ennustevaikutusta vaikeassa sepsiksessä ja septisessä sokissa. Havaintomme mukaan NT-proBNP ennustaa merkittävästi mortaliteettia mutta ei ole riittävän luotettava biomarkkeri hoitopäätöksiä ajatellen. Varhainen tehokas ja riittävä antibioottihoito, verenkierron nestehoito sekä infektion kirurginen saneeraus tarvittaessa on oleellisia toimia sepsispotilaiden ennusteen parantamiseksi. Tutkimuksessa selvitimme septisen sokin varhaisen hoidon onnistumista Suomessa. Totesimme, että varhainen hoito ei toteudu optimaalisesti. Puutteellinen alkuhoito ja erityisesti antibioottihoidon viivästyminen lisää kuolleisuutta. Päivystyspoliklinikalla vietetty aika ennen teho-osastolle siirtoa korreloi varhaisen hoidon toteutumiseen sekä antibioottihoidon aloitusviiveeseen. Sepsiksen ennustetta voidaan tulevaisuudessa parantaa tehostamalla sepsiksen tunnistamista, diagnostiikkaa ja kehittämällä paikalliset hoitoketjut toimiviksi potilaan ensikontaktista alkaen

Diffusion-emission theory of photon enhanced thermionic emission solar energy harvesters

Numerical and semi-analytical models are presented for photon-enhanced-thermionic-emission (PETE) devices. The models take diffusion of electrons, inhomogeneous photogeneration, and bulk and surface recombination into account. The efficiencies of PETE devices with silicon cathodes are calculated. Our model predicts significantly different electron affinity and temperature dependence for the device than the earlier model based on a rate-equation description of the cathode. We show that surface recombination can reduce the efficiency below 10% at the cathode temperature of 800 K and the concentration of 1000 suns, but operating the device at high injection levels can increase the efficiency to 15%.Comment: 5 pages, 4 figure

Thermoelectric bolometers based on ultra-thin heavily doped single-crystal silicon membranes

We present ultra-thin silicon membrane thermocouple bolometers suitable for fast and sensitive detection of low levels of thermal power and infrared radiation at room temperature. The devices are based on 40 nm-thick strain tuned single crystalline silicon membranes shaped into heater/absorber area and narrow n- and p-doped beams, which operate as the thermocouple. The electro-thermal characterization of the devices reveal noise equivalent power of 13 pW/rtHz and thermal time constant of 2.5 ms. The high sensitivity of the devices is due to the high Seebeck coefficient of 0.39 mV/K and reduction of thermal conductivity of the Si beams from the bulk value. The bolometers operate in the Johnson-Nyquist noise limit of the thermocouple, and the performance improvement towards the operation close to the temperature fluctuation limit is discussed.Comment: 11 pages, 3 figure

Magnetostatic field noise near metallic surfaces

We develop an effective low-frequency theory of the electromagnetic field in equilibrium with thermal objects. The aim is to compute thermal magnetic noise spectra close to metallic microstructures. We focus on the limit where the material response is characterized by the electric conductivity. At the boundary between empty space and metallic microstructures, a large jump occurs in the dielectric function which leads to a partial screening of low-frequency magnetic fields generated by thermal current fluctuations. We resolve a discrepancy between two approaches used in the past to compute magnetic field noise spectra close to microstructured materials.Comment: 9 pages, 1 figure, EPJ D style, accepted in Topical Issue on "Atom Chips

Glass Polarization Induced Drift in Microelectromechanical Capacitor

We present a quantitative physical model for glass substrate polarization and study the glasspolarization by measuring the capacitance drift from microelectromechanicalcapacitor test structure. The model consists of mobile and immobile charge species, which are related to alkali metals and non-bridging oxygen in glass. The model explains consistently our results and the previously observed non-homogeneous charging effect in a radio-frequency switch fabricated on a glass substrate. The results indicate that the bulk properties of the glass layer itself can be a significant source of drift. The modeling allows estimation of the drift behavior of the several kinds of device structures.Peer reviewe

Modeling the effect of mobile ion contamination on the stability of a microelectromechanical resonator

We present a theoretical model for mobile ion contamination in a silicon microelectromechanical resonator. In the model both drift and diffusion of the mobile charge in dielectric films are taken into account. The model is verified through a comparison to existing experimental data. We show that the model can describe the frequency drift of resonators in a wide temperature range.Peer reviewe

Time Dependence of Charge Transfer Processes in Diamond Studied with Positrons

We have developed a method called optical transient positron spectroscopy and apply it to study the optically induced carrier trapping and charge transfer processes in natural brown type IIa diamond. By measuring the positron lifetime with continuous and pulsed illumination, we present an estimate of the optical absorption cross section of the vacancy clusters causing the brown color. The vacancy clusters accept electrons from the valence band in the absorption process, giving rise to photoconductivity.Peer reviewe