An Assessment of Earth's Climate Sensitivity Using Multiple Lines of Evidence.

We assess evidence relevant to Earth's equilibrium climate sensitivity per doubling of atmospheric CO2, characterized by an effective sensitivity S. This evidence includes feedback process understanding, the historical climate record, and the paleoclimate record. An S value lower than 2 K is difficult to reconcile with any of the three lines of evidence. The amount of cooling during the Last Glacial Maximum provides strong evidence against values of S greater than 4.5 K. Other lines of evidence in combination also show that this is relatively unlikely. We use a Bayesian approach to produce a probability density function (PDF) for S given all the evidence, including tests of robustness to difficult-to-quantify uncertainties and different priors. The 66% range is 2.6-3.9 K for our Baseline calculation and remains within 2.3-4.5 K under the robustness tests; corresponding 5-95% ranges are 2.3-4.7 K, bounded by 2.0-5.7 K (although such high-confidence ranges should be regarded more cautiously). This indicates a stronger constraint on S than reported in past assessments, by lifting the low end of the range. This narrowing occurs because the three lines of evidence agree and are judged to be largely independent and because of greater confidence in understanding feedback processes and in combining evidence. We identify promising avenues for further narrowing the range in S, in particular using comprehensive models and process understanding to address limitations in the traditional forcing-feedback paradigm for interpreting past changes.

Subtle ocular movements in a patient with brain death.

Introduction and Case Presentation: Brain death can be associated with limb movements that are attributed to spinal reflexes. Although head/face movements have been rarely reported, no case of overt eye movements in brain death has been documented. We report a case of a patient with subtle eye movements whose exam was otherwise consistent with brain death. The presence of eye movements delayed pronouncing the patient as brain dead and delayed organ donation. We agree with American Academy of Neurology Position statement from 2019 that brain death does not mean demise of every neuron. Discussion: This case raises important questions about the types of movements that should be "allowed" during the determination of brain death to avoid delays in diagnosis.

Is ice-rafted sediment in a North Pole marine record evidence for perennial sea-ice cover?

Ice-rafted sediments of Eurasian and North American origin are found consistently in the upper part (13 Ma BP to present) of the Arctic Coring Expedition (ACEX) ocean core from the Lomonosov Ridge, near the North Pole (≈88° N). Based on modern sea-ice drift trajectories and speeds, this has been taken as evidence of the presence of a perennial sea-ice cover in the Arctic Ocean from the middle Miocene onwards (Krylov et al. 2008 Paleoceanography 23, PA1S06. (doi:10.1029/2007PA001497); Darby 2008 Paleoceanography 23, PA1S07. (doi:10.1029/2007PA001479)). However, other high latitude land and marine records indicate a long-term trend towards cooling broken by periods of extensive warming suggestive of a seasonally ice-free Arctic between the Miocene and the present (Polyak et al. 2010 Quaternary Science Reviews 29, 1757-1778. (doi:10.1016/j.quascirev.2010.02.010)). We use a coupled sea-ice slab-ocean model including sediment transport tracers to map the spatial distribution of ice-rafted deposits in the Arctic Ocean. We use 6 hourly wind forcing and surface heat fluxes for two different climates: one with a perennial sea-ice cover similar to that of the present day and one with seasonally ice-free conditions, similar to that simulated in future projections. Model results confirm that in the present-day climate, sea ice takes more than 1 year to transport sediment from all its peripheral seas to the North Pole. However, in a warmer climate, sea-ice speeds are significantly faster (for the same wind forcing) and can deposit sediments of Laptev, East Siberian and perhaps also Beaufort Sea origin at the North Pole. This is primarily because of the fact that sea-ice interactions are much weaker with a thinner ice cover and there is less resistance to drift. We conclude that the presence of ice-rafted sediment of Eurasian and North American origin at the North Pole does not imply a perennial sea-ice cover in the Arctic Ocean, reconciling the ACEX ocean core data with other land and marine records.

Solar forcing of regional climate change during the Maunder Minimum.

We examine the climate response to solar irradiance changes between the late 17th-century Maunder Minimum and the late 18th century. Global average temperature changes are small (about 0.3 degrees to 0.4 degrees C) in both a climate model and empirical reconstructions. However, regional temperature changes are quite large. In the model, these occur primarily through a forced shift toward the low index state of the Arctic Oscillation/North Atlantic Oscillation as solar irradiance decreases. This leads to colder temperatures over the Northern Hemisphere continents, especially in winter (1 degrees to 2 degrees C), in agreement with historical records and proxy data for surface temperatures.

Ultrasound-guided vascular access in critical illness.

Over the past two decades, ultrasound (US) has become widely accepted to guide safe and accurate insertion of vascular devices in critically ill patients. We emphasize central venous catheter insertion, given its broad application in critically ill patients, but also review the use of US for accessing peripheral veins, arteries, the medullary canal, and vessels for institution of extracorporeal life support. To ensure procedural safety and high cannulation success rates we recommend using a systematic protocolized approach for US-guided vascular access in elective clinical situations. A standardized approach minimizes variability in clinical practice, provides a framework for education and training, facilitates implementation, and enables quality analysis. This review will address the state of US-guided vascular access, including current practice and future directions.

Inverse ratio ventilation in ARDS. Improved oxygenation without autoPEEP.

Inverse ratio ventilation and related ventilatory modes (eg, pressure release ventilation) have been applied to patients with the adult respiratory distress syndrome (ARDS) with apparent beneficial effects on arterial oxyhemoglobin saturation. While several mechanisms of improved gas exchange have been postulated, many intensive care physicians believe that the development of occult PEEP (autoPEEP; intrinsic PEEP) leads to the observed rise in oxygen saturation. We report here our findings in a patient whose improved oxygenation on inverse ratio ventilation could not be attributed to autoPEEP.

Cardiac tamponade and contralateral hemothorax after subclavian vein catheterization.

A patient developed life-threatening cardiac tamponade and contralateral hemothorax after insertion of a subclavian catheter in the operating room. Contrast was infused through the catheter, demonstrating its malposition in the pericardial space. Contrast infusion was valuable in evaluating this complication of central line placement.

Fortuitous esophageal intubation.

Esophageal malposition is a potentially disastrous complication of attempted airway intubation. We report an unusual case in which a promptly recognized esophageal intubation aided detection of a perforated gastric ulcer. After the endotracheal tube was repositioned and the ulcer was surgically repaired, our patient had an excellent outcome.

Sodium bicarbonate for the treatment of lactic acidosis.

Lactic acidosis often challenges the intensivist and is associated with a strikingly high mortality. Treatment involves discerning and correcting its underlying cause, ensuring adequate oxygen delivery to tissues, reducing oxygen demand through sedation and mechanical ventilation, and (most controversially) attempting to alkalinize the blood with IV sodium bicarbonate. Here we review the literature to answer the following questions: Is a low pH bad? Can sodium bicarbonate raise the pH in vivo? Does increasing the blood pH with sodium bicarbonate have any salutary effects? Does sodium bicarbonate have negative side effects? We find that the oft-cited rationale for bicarbonate use, that it might ameliorate the hemodynamic depression of metabolic acidemia, has been disproved convincingly. Further, given the lack of evidence supporting its use, we cannot condone bicarbonate administration for patients with lactic acidosis, regardless of the degree of acidemia.

Serendipitous discovery during jugular catheterization. Partial anomalous pulmonary venous connection.

This report describes the identification of a partial anomalous pulmonary venous connection during routine central venous catheterization in a man with pulmonary hypertension. To our knowledge, this is the first report in the English literature to describe this occurrence during central line placement.

Pleural effusion masquerading as myocardial infarction.

The effects of pleural effusions on the ECG have not been well studied. We report herein the case of a patient with extreme QRS axis deviation mimicking acute myocardial infarction. Thoracentesis caused the return of a more normal axis.

Treatment of bronchospasm by metered-dose inhaler albuterol in mechanically ventilated patients.

beta 2-agonist bronchodilators delivered by metered-dose inhalers (MDI) are commonly used in the treatment of bronchospasm in both intubated and nonintubated patients. Substantial data support the effectiveness of MDI delivery systems in nonintubated patients. However, few studies have examined the effectiveness of MDIs in intubated, mechanically ventilated patients. MDIs are often used in conjunction with a spacing device that may enhance delivery of drug to the airways, but few in vivo data have demonstrated efficacy of this delivery method in ventilated patients. We studied ten critically ill patients who had a peak (Ppeak) to pause (Ppause) gradient of more than 15 cm H2O during sedated, quiet breathing on assist control ventilation. We administered 5, 10, and 15 puffs (90 micrograms per puff) of MDI albuterol through a specific spacer (Aerovent) at 30-min intervals, while measuring resistive pressure (defined as Ppeak-Ppause) before and after treatments. Resistive airway pressure after 5 puffs decreased in nine of ten patients, from 25.1 +/- 7.2 to 20.8 +/- 5.6 cm H2O (p < 0.12). The addition of 10 more puffs further reduced resistive pressure in nine of nine patients from 20.8 +/- 5.6 to 19.0 +/- 4.4 (p < 0.01). Fifteen more puffs (30 cumulative puffs) did not result in further improvement (p > 0.5). A toxic reaction occurred in one patient (systolic blood pressure decreased 20 mm Hg) after 5 puffs of albuterol. We conclude that MDI administered through this specific spacer is effective in mechanically ventilated patients in doses up to 15 puffs, and that therapy should be titrated to effectiveness and toxicity.

Liberation from mechanical ventilation: a decade of progress.

Multiple complications associated with mechanical ventilation mandate that clinicians expeditiously define and reverse the pathophysiologic processes that precipitate respiratory failure and then, detect the earliest point that a patient can breathe without the ventilator. Over the past decade, numerous laboratory and clinical studies have been reported that may inform transformation of the "art of weaning" to the science of liberation. We review these studies and use them to formulate a systematic approach to assure early, safe, and successful liberation of patients from mechanical ventilation.

Computerized smoking cessation program for the worksite: treatment outcome and feasibility.

This study demonstrated the effectiveness of a computer-delivered smoking cessation program for the worksite. 58 VA Medical Center employees were randomly assigned to a computer group (computerized nicotine fading and stop-smoking contest) or a contest-only group. In comparison with the contest-only group, the computer group had nonsignificantly higher abstinence rates across follow-up, had marginally lower CO levels at the 3- and 6-month follow-ups, and smoked cigarettes with lower nicotine levels at the 10-day and 6-month follow-ups.

Absence of supply dependence of oxygen consumption in patients with septic shock.

We tested whether oxygen consumption (VO2) was dependent on oxygen delivery (QO2) in 10 patients with septic shock when QO2 was changed by the use of the inotropic agent, dobutamine. The mean acute physiology and chronic health evaluation (APACHE) II score of the patients was 27.3 +/- 8.1 with a mean blood pressure on entry of 66.8 +/- 12.4 mm Hg, and all had been volume resuscitated to a pulmonary artery occlusion pressure of greater than 10 mm Hg. We measured VO2 by analysis of respiratory gases (VO2G) while calculating VO2 by the Fick equation (VO2F) at three different O2 deliveries. When the dobutamine infusion rate was increased from 2.5 +/- 4.0 to 12.3 +/- 6.0 micrograms/kg/min, thermodilution cardiac output increased from 7.7 +/- 2.6 to 10.1 +/- 2.7 L/min (P < .01). Accordingly, dobutamine increased QO2 from 13.5 +/- 3.8 to 18.2 +/- 4.3 mL/min per kg (increase of 36.4% +/- 19.7%; P < .01), but VO2G did not increase (3.2 +/- 0.5 to 3.2 +/- 0.6 mL/min per kg). During these same interventions, the VO2F tended to increase (2.9 +/- 0.7 to 3.4 +/- 0.8 mL/min per kg, P < .06), presumably a spurious correlation because of measurement errors shared by the calculation of VO2F and QO2. Neither lactic acidosis nor acute respiratory distress syndrome (ARDS) conferred supply dependence of VO2G, but the presence of ARDS was predictive of death in this cohort. It is concluded that VO2 is independent of QO2 in patients with septic shock and lactic acidosis. These data confirm that maximizing QO2 beyond values achieved by initial fluid and vasoactive drug resuscitation of septic shock does not improve tissue oxygenation as determined by respiratory gas measurement of VO2.

Consistent simulations of multiple proxy responses to an abrupt climate change event.

Isotope, aerosol, and methane records document an abrupt cooling event across the Northern Hemisphere at 8.2 kiloyears before present (kyr), while separate geologic lines of evidence document the catastrophic drainage of the glacial Lakes Agassiz and Ojibway into the Hudson Bay at approximately the same time. This melt water pulse may have been the catalyst for a decrease in North Atlantic Deep Water formation and subsequent cooling around the Northern Hemisphere. However, lack of direct evidence for ocean cooling has lead to speculation that this abrupt event was purely local to Greenland and called into question this proposed mechanism. We simulate the response to this melt water pulse using a coupled general circulation model that explicitly tracks water isotopes and with atmosphere-only experiments that calculate changes in atmospheric aerosol deposition (specifically (10)Be and dust) and wetland methane emissions. The simulations produce a short period of significantly diminished North Atlantic Deep Water and are able to quantitatively match paleoclimate observations, including the lack of isotopic signal in the North Atlantic. This direct comparison with multiple proxy records provides compelling evidence that changes in ocean circulation played a major role in this abrupt climate change event.

Amplification of surface temperature trends and variability in the tropical atmosphere.

The month-to-month variability of tropical temperatures is larger in the troposphere than at Earth's surface. This amplification behavior is similar in a range of observations and climate model simulations and is consistent with basic theory. On multidecadal time scales, tropospheric amplification of surface warming is a robust feature of model simulations, but it occurs in only one observational data set. Other observations show weak, or even negative, amplification. These results suggest either that different physical mechanisms control amplification processes on monthly and decadal time scales, and models fail to capture such behavior; or (more plausibly) that residual errors in several observational data sets used here affect their representation of long-term trends.