Rivers (on land) and turbidity currents (in the ocean) are the most important sediment transport processes on Earth. Yet how rivers generate turbidity currents as they enter the coastal ocean remains ...poorly understood. The current paradigm, based on laboratory experiments, is that turbidity currents are triggered when river plumes exceed a threshold sediment concentration of ~1 kg/m3. Here we present direct observations of an exceptionally dilute river plume, with sediment concentrations 1 order of magnitude below this threshold (0.07 kg/m3), which generated a fast (1.5 m/s), erosive, short‐lived (6 min) turbidity current. However, no turbidity current occurred during subsequent river plumes. We infer that turbidity currents are generated when fine sediment, accumulating in a tidal turbidity maximum, is released during spring tide. This means that very dilute river plumes can generate turbidity currents more frequently and in a wider range of locations than previously thought.
Key Points
Here we document for the first time how very dilute (up to 0.07 kg/m3) river plumes can generate powerful turbidity currents
Such low sediment concentrations are 20 times lower than those predicted by past theory and experiments
Therefore, turbidity currents are likely to be much more frequent and occur at a far wider range of locations than previously thought
Large-scale (20m to 7km wavelength) bedforms are common on the seafloor, yet there is a lack of consensus on how they form and thus what to call them. We conducted statistical analysis on a dataset ...of 82 seafloor bedforms that span a range of water depths and environments. The data form three distinct groups: 1) small-scale (20–300m wavelength) sediment waves with mixed relief made of medium sand to cobble-sized sediment that form in confined settings, which we call small sediment waves; 2) large-scale (300–7000m wavelength) sediment waves with mixed relief made of fine-grained sediment that form in relatively unconfined settings, which we call large sediment waves; and 3) large-scale fully enclosed depressions in the seafloor, which we call scours. There is a statistically significant data gap in the size of bedforms between small sediment waves and large sediment waves that does not appear to be a sampling artefact. This data gap probably results from the environments in which sediment waves form being either confined (e.g. channel or canyon) or unconfined (e.g. open slope). Bedform migration direction is available for 36% of the data and includes small and large-scale sediment waves; of these examples all are shown to migrate up-current. Up-current migration is indicative of supercritical flow; thus this data suggests that supercritical flows operate in a wide range of environments and can generate both small and large sediment waves. Therefore, we suggest that small and large sediment waves form by similar processes despite the gap in bedform wavelength and sediment size. The migration direction for scours remains unknown. Scours may form from similar processes to small and large sediment waves, or alternatively they may be a completely separate bedform type that form when erosive flows exploit pre-existing defects in the seafloor. This novel statistical analysis of a global database shows that up-current migrating bedforms associated with supercritical flow are unusually widespread, and are recognised at two distinct scales.
•Novel statistical analysis of global seafloor bedform database•Simplification of existing classification bedform schemes•Evidence that supercritical flows are more prevalent than previously appreciated.•Bimodal size of bedforms relates to environmental confinement.
Background:
Emergency laparotomy for abdominal trauma is associated with high rates of surgical site infection (SSI). A protocol for antimicrobial prophylaxis (AMP) for trauma laparotomy was ...implemented to determine whether SSI could be reduced by adhering to established principles of AMP.
Patients and Methods:
A protocol utilizing ertapenem administered immediately before initiation of trauma laparotomy was adopted. Compliance with measures of adequate AMP were determined before and after protocol implementation, as were rates of SSI and other infections related to abdominal trauma. Univariable and multivariable analyses were performed to determine risk factors for development of infection related to trauma laparotomy.
Results:
Over a four-year period, 320 patient operations were reviewed. Ertapenem use for prophylaxis increased to 54% in the post-intervention cohort. Compliance with individual measures of appropriate AMP improved modestly. Overall, infections related to trauma laparotomy decreased by 46% (absolute decrease of 13%) in the post-intervention cohort. Multivariable analysis confirmed that treatment during the post-intervention phase was associated with this decrease, with a separate analysis suggesting that ertapenem use was an important factor in this decrease.
Conclusions:
Development of a standardized protocol for AMP in trauma laparotomy led to decreases in infectious complications after that procedure.
Abstract
After the World War II, fecal diversion became the standard of care for colon injuries, although medical, logistic, and technical advancements have challenged this approach. Damage control ...surgery serves to temporize immediately life-threatening conditions, and definitive management of destructive colon injuries is delayed until after appropriate resuscitation. The bowel can be left in discontinuity for up to 3 days before edema ensues, but the optimal repair window remains within 12 to 48 hours. Delayed anastomosis performed at the take-back operation or stoma formation has been reported with variable results. Studies have revealed good outcomes in those undergoing anastomosis after damage control surgery; however, they point to a subgroup of trauma patients considered to be “high risk” that may benefit from fecal diversion. Risk factors influencing morbidity and mortality rates include hypotension, massive transfusion, the degree of intra-abdominal contamination, associated organ injuries, shock, left-sided colon injury, and multiple comorbid conditions. Patients who are not suitable for anastomosis by 36 hours after damage control may be best managed with a diverting stoma. Failures are more likely related to ongoing instability, and the management strategy of colorectal injury should be based mainly on the patient's overall condition.
Detailed knowledge of the past history of an active volcano is crucial for the prediction of the timing, frequency and style of future eruptions, and for the identification of potentially at-risk ...areas. Subaerial volcanic stratigraphies are often incomplete, due to a lack of exposure, or burial and erosion from subsequent eruptions. However, many volcanic eruptions produce widely-dispersed explosive products that are frequently deposited as tephra layers in the sea. Cores of marine sediment therefore have the potential to provide more complete volcanic stratigraphies, at least for explosive eruptions. Nevertheless, problems such as bioturbation and dispersal by currents affect the preservation and subsequent detection of marine tephra deposits. Consequently, cryptotephras, in which tephra grains are not sufficiently concentrated to form layers that are visible to the naked eye, may be the only record of many explosive eruptions. Additionally, thin, reworked deposits of volcanic clasts transported by floods and landslides, or during pyroclastic density currents may be incorrectly interpreted as tephra fallout layers, leading to the construction of inaccurate records of volcanism. This work uses samples from the volcanic island of Montserrat as a case study to test different techniques for generating volcanic eruption records from marine sediment cores, with a particular relevance to cores sampled in relatively proximal settings (i.e. tens of kilometres from the volcanic source) where volcaniclastic material may form a pervasive component of the sedimentary sequence. Visible volcaniclastic deposits identified by sedimentological logging were used to test the effectiveness of potential alternative volcaniclastic-deposit detection techniques, including point counting of grain types (component analysis), glass or mineral chemistry, colour spectrophotometry, grain size measurements, XRF core scanning, magnetic susceptibility and X-radiography. This study demonstrates that a set of time-efficient, non-destructive and high-spatial-resolution analyses (e.g. XRF core-scanning and magnetic susceptibility) can be used effectively to detect potential cryptotephra horizons in marine sediment cores. Once these horizons have been sampled, microscope image analysis of volcaniclastic grains can be used successfully to discriminate between tephra fallout deposits and other volcaniclastic deposits, by using specific criteria related to clast morphology and sorting. Standard practice should be employed when analysing marine sediment cores to accurately identify both visible tephra and cryptotephra deposits, and to distinguish fallout deposits from other volcaniclastic deposits.
There are limited data on risk factors for surgical site infection (SSI) after open or laparoscopic cholecystectomy.
A retrospective cohort of commercially insured persons aged 18-64 years was ...assembled using
(ICD-9-CM) procedure or Current Procedural Terminology, 4th edition codes for cholecystectomy from December 31, 2004 to December 31, 2010. Complex procedures and patients (eg, cancer, end-stage renal disease) and procedures with pre-existing infection were excluded. Surgical site infections within 90 days after cholecystectomy were identified by ICD-9-CM diagnosis codes. A Cox proportional hazards model was used to identify independent risk factors for SSI.
Surgical site infections were identified after 472 of 66566 (0.71%) cholecystectomies; incidence was higher after open (n = 51, 4.93%) versus laparoscopic procedures (n = 421, 0.64%;
< .001). Independent risk factors for SSI included male gender, preoperative chronic anemia, diabetes, drug abuse, malnutrition/weight loss, obesity, smoking-related diseases, previous
infection, laparoscopic approach with acute cholecystitis/obstruction (hazards ratio HR, 1.58; 95% confidence interval CI, 1.27-1.96), open approach with (HR, 4.29; 95% CI, 2.45-7.52) or without acute cholecystitis/obstruction (HR, 4.04; 95% CI, 1.96-8.34), conversion to open approach with (HR, 4.71; 95% CI, 2.74-8.10) or without acute cholecystitis/obstruction (HR, 7.11; 95% CI, 3.87-13.08), bile duct exploration, postoperative chronic anemia, and postoperative pneumonia or urinary tract infection.
Acute cholecystitis or obstruction was associated with significantly increased risk of SSI with laparoscopic but not open cholecystectomy. The risk of SSI was similar for planned open and converted procedures. These findings suggest that stratification by operative factors is important when comparing SSI rates between facilities.
Loss of functional small bowel surface area following surgical resection for disorders such as Crohn's disease, intestinal ischemic injury, radiation enteritis, and in children, necrotizing ...enterocolitis, atresia, and gastroschisis, may result in short bowel syndrome, with attendant high morbidity, mortality, and health care costs in the United States. Following resection, the remaining small bowel epithelium mounts an adaptive response, resulting in increased crypt cell proliferation, increased villus height, increased crypt depth, and enhanced nutrient and electrolyte absorption. Although these morphologic and functional changes are well described in animal models, the adaptive response in humans is less well understood. Clinically the response is unpredictable and often inadequate. Here we address the hypotheses that human intestinal stem cell populations are expanded and that the stem cell niche is regulated following massive gut resection in short bowel syndrome (SBS). We use intestinal enteroid cultures from patients with SBS to show that the magnitude and phenotype of the adaptive stem cell response are both regulated by stromal niche cells, including intestinal subepithelial myofibroblasts, which are activated by intestinal resection to enhance epithelial stem and proliferative cell responses. Our data suggest that myofibroblast regulation of bone morphogenetic protein signaling pathways plays a role in the gut adaptive response after resection.
Submerged flanks of volcanic islands are prone to hazards including submarine landslides that may trigger damaging tsunamis and sediment-laden seafloor flows (called “turbidity currents”). These ...hazards can break seafloor infrastructure which is critical for global communications and energy transmission. Small Island Developing States are particularly vulnerable to these hazards due to their remote and isolated nature, small size, high population densities, and weak economies. Despite their vulnerability, few detailed offshore surveys exist for such islands, resulting in a geohazard “blindspot,” particularly in the South Pacific. Understanding how these hazards are triggered is important; however, pin-pointing specific triggers is challenging as most studies have been unable to link continuously between onshore and offshore environments, and focus primarily on large-scale eruptions with sudden production of massive volumes of sediment. We address these issues by integrating the first detailed (2 × 2 m) bathymetry data acquired from Tanna Island, Vanuatu with a combination of terrestrial remote sensing data, onshore and offshore sediment sampling, and documented historical events. Mount Yasur on Tanna has experienced low-magnitude Strombolian activity for at least the last 600 years. We find clear evidence for submarine landslides and turbidity currents, yet none of the identified triggers are related to major volcanic eruptions, in contrast to conclusions from several previous studies. Instead we find that cascades of non-volcanic events (including outburst floods with discharges of >1,000 m3/s, and tropical cyclones), that may be separated by decades, are more important for preconditioning and triggering of landslides and turbidity currents in oversupplied sedimentary regimes such as at Tanna. We conclude with a general model for how submarine landslides and turbidity currents are triggered at volcanic and other heavily eroding mountainous islands. Our model highlights the often-ignored importance of outburst floods, non-linear responses to land-use and climatic changes, and the complex interactions between a range of coastal and tectonic processes that may overshadow volcanic regimes.
Patients with intra-abdominal sepsis and associated bacteremia have a high mortality rate. However, outcomes studies in this population are limited, in part because of the small numbers of such ...patients. The objective of this study was to describe characteristics of critically ill patients with secondary blood stream infection (BSI) of intra-abdominal origin and identify predictors of mortality.
This retrospective, single-center study evaluated patients admitted between January 2005 and January 2011 with bacteremia because of an intra-abdominal source. Patients were included if they met criteria for severe sepsis based on International Classification of Diseases, 9th Revision (ICD 9) codes for acute organ dysfunction, had a positive blood culture, had at least one ICD 9 code indicative of an intra-abdominal process, and had a confirmed or clinically suspected intra-abdominal infection (IAI) within 72 h of the blood culture. Chart review was performed to confirm the presence of these criteria and also the absence of any other potential source of bacteremia. Data were collected on patient demographics, BSI source, source control procedure details, microorganisms isolated, and antibiotics administered. Multivariable logistic regression analysis was performed to identify independent predictors of mortality.
Three hundred six patients with BSI were identified, of which 108 episodes were deemed to be of intra-abdominal origin. Gram-negative organisms comprised 43% of blood isolates, followed by gram-positives (33%), anaerobes (14%), and yeast (9%). Appropriate antimicrobial therapy was administered in 71% of patients. The overall mortality rate was 27.8%. As compared with survivors, non-survivors were older, more likely to have underlying COPD or asthma, and have renal or metabolic failure (p<0.05 for all). Among non-survivors, adequate source control was obtained less frequently (64% vs. 91%, p=0.002) and median time to appropriate antibiotics was longer (23 h vs. 4 h, p=0.004). Logistic regression analysis revealed inadequate source control (p=0.002) and inappropriate antibiotics (p=0.016) to be independently associated with mortality.
Critically ill patients with a BSI of abdominal origin are at high risk for mortality. Failure to achieve adequate source control and administration of inappropriate antibiotics were independent predictors of mortality. Thus, these represent potential opportunities to impact outcomes in patients with complicated IAI.
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