Early postoperative cognitive recovery and gas exchange patterns after balanced anesthesia with sevoflurane or desflurane in overweight and obese patients undergoing craniotomy.

Abstract: Overweight and obese patients are at especially high risk for delayed awakening after general surgery. Whether this risk also applies to cerebral neurosurgical procedures remains unclear. This study evaluated early postoperative cognitive recovery and gas exchange patterns, after balanced anesthesia with sevoflurane or desflurane, in overweight and obese patients undergoing craniotomy for supratentorial expanding lesions. Fifty-six patients were consecutively enrolled, and randomly assigned to 1 of 2 study groups to receive balanced anesthesia with sevoflurane or desflurane. Cognitive function was evaluated with the Short Orientation Memory Concentration Test and the Rancho Los Amigos Scale and gas exchange patterns (pH, PaO2, and PaCO2) were recorded in all patients at 5 time-points: preoperatively and postoperatively, after patients reached an Aldrete score Z9, at 15, 30, 45, and 60 minutes. Preoperative cognitive status was similar in the 2 treatment groups. Early postoperative cognitive recovery was more delayed and Short Orientation Memory Concentration Test scores at 15 and 30 minutes postanesthesia were lower in patients receiving sevoflurane- based anesthesia than in those receiving desfluranebased anesthesia (21.5±3.5 vs. 14.9±3.5) (P<0.005) and (26.9±0.7 vs. 21.5±1.4) (P<0.005), and the postoperative Rancho Los Amigos Scalegrade 8 showed a similar trend (25/28 patients 89% vs. 8/28 patients 28% (P<0.005) and 28/28 patients (100% vs. 13/28 patients 46%) (P<0.005). Similarly, gas-exchange analysis showed higher PaCO2 at 15 and 30 minutes and lower pH up to 45 minutes postextubation in patients receiving sevoflurane-based anesthesia. In overweight and obese patients undergoing craniotomy desflurane-based anesthesia allows earlier postoperative cognitive recovery and reversal to normocapnia and normal pH. Key Words: neuroanesthesia, postoperativ

New perspectives on ice forcing in continental arc magma plumbing systems

Determining how and why eruptive outputs are modulated by the loading and unloading of ice is key to understanding whether ongoing and accelerating deglaciation across mid- to high-latitudes will impact future activity at many volcanoes. Here, we address two central questions. First, does decompression of the upper crust during rapid thinning of ice sheets propel increases in eruption rates? Second, does surface loading during ice sheet growth, followed by rapid unloading during deglaciation, promote changes in magma storage conditions and compositions within the underlying magma plumbing systems? To provide new perspectives on these questions, we address the mechanics and dynamics of ice sheet-arc magma plumbing system interactions at a regional-to-local scale within the Andean Southern Volcanic Zone. Here, piedmont glacier lobes, forming the northernmost extension of the Patagonian ice sheet, have enveloped dozens of large, active, composite volcanoes as these glaciers reached local thicknesses of nearly 2 km during the local Last Glacial Maximum (LGM) between similar to 35 and 18 ka, before retreating rapidly between 18 and 15 ka. Our multi-faceted review features a synthesis of existing and new field observations, laboratory measurements, and numerical simulations. Advances in Ar-40/Ar-39 radioisotopic and He-3 surface exposure geochronology, in conjunction with geologic mapping, facilitate reconstructions of volcanic eruptive histories spanning the last glacial-deglacial cycle and in places provide constraints on the thickness of ice at specific time slices. The magnitude and geometry of the glacial loading and unloading is captured in a climate model-driven numerical simulation that reveals spatial and temporal heterogeneities in the configuration of the northernmost Patagonian ice sheet retreat. Geological observations including dated moraine complexes, dated lava-ice contact features, and glacial erratic boulders at high altitude on volcano slopes, are consistent with this model. Deep valleys imply intense localized erosion on volcano flanks, and deposited sediment in nearby floodplains implies narrow regions of rapid sediment deposition. These observations, in conjunction with dated lava flows, provide constraints on rates and patterns of crustal loading and unloading by sediment redistribution.The ice loading model, cone growth, and a sediment redistribution history inform numerical simulations of intra-crustal stress changes below the volcanic arc in response to the ice-driven and sediment-driven changes. In turn, the modeled surface loading is central to designing numerical simulations of magma reservoir responses to intra-crustal stress changes beneath the volcanoes. Following periods of subdued volcanic output, upticks in eruptive rates are found at three volcanoes during, or shortly after, the LGM. A numerical magma chamber model suggests that this behavior could be the result of a delicate balance between the timescales of magma cooling, the rate of magma recharge from depth, and viscous relaxation of surrounding crustal rocks. Depressurization of the crust increases eruptive mass flux to the surface only if: (1) the rate of recharge just outcompetes the rate of cooling, (2) the rate of recharge is barely large enough before loading to overcome viscous relaxation of overpressure by creep around the chamber, and (3) magmas are volatile undersaturated, and exsolve volatiles via second boiling during the long repose associated with the high ice loads that precede rapid deglaciation. Existing and newly developed thermobarometers that constrain magma crystallization and storage depths can be applied to eruptive products spanning a glacial-deglacial transition, such that not only secular changes in rates of volcanic eruption, but also changes in the depths of pre-eruptive magma storage and in magma composition can each be interpreted in the light of intra-crustal stress changes associated with glacial loading and unloading.National Science Foundation from the Frontier Research in Earth Science progra

Centennial-scale Holocene climate variations amplified by Antarctic Ice Sheet discharge

Proxy-based indicators of past climate change show that current global climate models systematically underestimate Holocene-epoch climate variability on centennial to multi-millennial timescales, with the mismatch increasing for longer periods1,2,3,4,5. Proposed explanations for the discrepancy include ocean–atmosphere coupling that is too weak in models6, insufficient energy cascades from smaller to larger spatial and temporal scales7, or that global climate models do not consider slow climate feedbacks related to the carbon cycle or interactions between ice sheets and climate4. Such interactions, however, are known to have strongly affected centennial- to orbital-scale climate variability during past glaciations8,9,10,11, and are likely to be important in future climate change12,13,14. Here we show that fluctuations in Antarctic Ice Sheet discharge caused by relatively small changes in subsurface ocean temperature can amplify multi-centennial climate variability regionally and globally, suggesting that a dynamic Antarctic Ice Sheet may have driven climate fluctuations during the Holocene. We analysed high-temporal-resolution records of iceberg-rafted debris derived from the Antarctic Ice Sheet, and performed both high-spatial-resolution ice-sheet modelling of the Antarctic Ice Sheet and multi-millennial global climate model simulations. Ice-sheet responses to decadal-scale ocean forcing appear to be less important, possibly indicating that the future response of the Antarctic Ice Sheet will be governed more by long-term anthropogenic warming combined with multi-centennial natural variability than by annual or decadal climate oscillations

Future sea level change under Coupled Model Intercomparison Project Phase 5 and Phase 6 scenarios from the Greenland and Antarctic ice sheets

Projections of the sea level contribution from the Greenland and Antarctic ice sheets (GrIS and AIS) rely on atmospheric and oceanic drivers obtained from climate models. The Earth System Models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6) generally project greater future warming compared with the previous Coupled Model Intercomparison Project phase 5 (CMIP5) effort. Here we use four CMIP6 models and a selection of CMIP5 models to force multiple ice sheet models as part of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). We find that the projected sea level contribution at 2100 from the ice sheet model ensemble under the CMIP6 scenarios falls within the CMIP5 range for the Antarctic ice sheet but is significantly increased for Greenland. Warmer atmosphere in CMIP6 models results in higher Greenland mass loss due to surface melt. For Antarctica, CMIP6 forcing is similar to CMIP5 and mass gain from increased snowfall counteracts increased loss due to ocean warming