Delayed cardioprotection with isoflurane: role of reactive oxygen and nitrogen.

We determined whether isoflurane can confer delayed cardioprotection in the adult rat by triggering increased production of reactive oxygen (ROS) and nitrogen species (RNS). Our objectives were to determine 1) the concentration of isoflurane that confers delayed cardioprotection in the adult rat, 2) the role of ROS and RNS in the induction of delayed cardioprotection, and 3) the cellular sources of ROS and RNS responsible for induction of delayed cardioprotection by isoflurane. Male Sprague-Dawley rats at 8 wk of age (n = 8 rats/group) were exposed to 0.5%, 0.8%, 1%, and 2% (vol/vol) isoflurane-100% oxygen for 2 h. Isoflurane conferred delayed cardioprotection 24 h later at a concentration of 0.8% (vol/vol). Administration of manganese (III) tetrakis (4-benzoic acid)porphyrin chloride (MnTBAP), a superoxide scavenger (15 mg/kg ip), or N(G)-nitro-L-arginine methyl ester (L-NAME), a general nitric oxide synthase inhibitor (15 mg/kg ip), 15 min before isoflurane treatment abolished the delayed cardioprotective effects of isoflurane. MnTBAP and L-NAME had no effect on delayed cardioprotection in untreated hearts. Perfusion of isolated hearts with hydroethidine, a fluorescent probe for superoxide, after isoflurane treatment resulted in a twofold increase in ethidine staining of isoflurane-treated hearts compared with untreated controls, which was attenuated by myxothiazol, an inhibitor of the mitochondrial electron transport chain (0.2 mg/kg ip) and L-NAME (15 mg/kg ip). Nitrite and nitrate content in isoflurane-treated hearts was 1.5-fold higher than in untreated hearts, whereas myocardial reduced glutathione levels were decreased by 13% in 0.8% but not in 1.0% isoflurane-treated hearts. We conclude that isoflurane confers delayed cardioprotection in the adult rat, triggered by ROS and RNS.

The pulse in reflectance pulse oximetry: modeling and experimental studies.

OBJECTIVE: Reflectance pulse oximetry permits the use of alternative monitoring sites such as the face or torso, and is the approach commonly employed in fetal pulse oximetry systems. The purpose of this study is to investigate the impact of assumptions about the nature of arterial pulsatility on the calibration of such systems. METHODS: Monte Carlo simulations of reflectance pulse oximetry were run on a six-layer tissue model, varying depth and magnitude of the arterial pulse. SpO2 readings on and off the femoral artery obtained during desaturation studies in newborn piglets were compared to predictions. Results. Monte Carlo simulation results clarified the difference between deep and shallow pulsatility found with photon diffusion models, agreeing with earlier in vivo observations. Significant overestimation of SpO2 <75% and slight underestimation >75% is expected if a sensor is placed on a highly pulsatile site. The on- and off-artery SpO2 readings recorded during desaturation in the newborn piglet follow the model predictions. CONCLUSIONS: The sensitivity of reflectance pulse oximetry calibration to the depth and magnitude of arterial pulsatility reinforces the observation that monitoring site selection is of importance in optimizing reflectance pulse oximetry performance, particularly fetal pulse oximetry. Sites with palpable pulsatility should be avoided.

Monitoreo contínuo de la saturación fetal de oxígeno: analgaseia obstétrica vs dolor

El presente es un estudio prospectivo que tiene como objetivos, evaluar un nuevo sensor intrauterino de pulso oximetría para monitoreo continuo de la saturación de hemoglobina fetal y estudiar los efectos de la analgesia peridural sobre la misma durante el trabajo de parto, comparando simultáneamente las variaciones de la frecuencia cardíaca fetal. Se incluyeron en el estudio 38 pacientes, embarazadas, en el primer período de trabajo de parto, a las cuales se les hizo monitoreo continuo de frecuencia cardíaca y la saturación de oxígeno fetal, usando un nuevo sensor intrauterino. Diez pacientes fueron sometidas a analgesia obstétrica. A todas las pacientes se les hizo monitoreo en decúbito dorsal con y sin desplazamiento uterino y en decúbito lateral izquierdo; el tiempo de monitoreo varió de 0.1 a 6 horas. Se encontró en la mayoría de los casos una saturación fetal de oxígeno entre el 50-80 por ciento (x=65 por ciento), (SD=3.7). La FCF promedio fue de 144 l/min, con una SD=8.5. El APGAR fue normal en la mayoría de los recien nacidos, excepto en cuatro casos entre los cuales había un embarazo gemelar, una cardiopatía congénita cianosante y dos casos de los cuales se observó tempranamente FSat02 baja con FCF normal. Las pacientes que fueron sometidas a analgesia obstétrica, mostraron mayor estabilidad durante el monitoreo y los recien nacidos presentaron Apgar mayor