Neuronal pattern separation of motion-relevant input in LIP activity.

In various regions of the brain, neurons discriminate sensory stimuli by decreasing the similarity between ambiguous input patterns. Here, we examine whether this process of pattern separation may drive the rapid discrimination of visual motion stimuli in the lateral intraparietal area (LIP). Starting with a simple mean-rate population model that captures neuronal activity in LIP, we show that overlapping input patterns can be reformatted dynamically to give rise to separated patterns of neuronal activity. The population model predicts that a key ingredient of pattern separation is the presence of heterogeneity in the response of individual units. Furthermore, the model proposes that pattern separation relies on heterogeneity in the temporal dynamics of neural activity and not merely in the mean firing rates of individual neurons over time. We confirm these predictions in recordings of macaque LIP neurons and show that the accuracy of pattern separation is a strong predictor of behavioral performance. Overall, results propose that LIP relies on neuronal pattern separation to facilitate decision-relevant discrimination of sensory stimuli.NEW & NOTEWORTHY A new hypothesis is proposed on the role of the lateral intraparietal (LIP) region of cortex during rapid decision making. This hypothesis suggests that LIP alters the representation of ambiguous inputs to reduce their overlap, thus improving sensory discrimination. A combination of computational modeling, theoretical analysis, and electrophysiological data shows that the pattern separation hypothesis links neural activity to behavior and offers novel predictions on the role of LIP during sensory discrimination.

External validation of the YEARS diagnostic algorithm for suspected pulmonary embolism.

BACKGROUND: Validated diagnostic algorithms are used to manage patients with suspected pulmonary embolism (PE). The recently published YEARS study proposed a simplified diagnostic strategy to reduce the use of computed tomography pulmonary angiography. OBJECTIVES: To externally validate this strategy in an independent cohort. METHODS: We analyzed data from three previous prospective cohort studies of outpatients with suspected PE. We retrospectively applied the YEARS algorithm. The three YEARS clinical criteria are: clinical signs of deep vein thrombosis, hemoptysis, and PE as the most likely diagnosis. If zero YEARS criteria are met, a D-dimer < 1000 ng/mL will rule out PE. If ≥1 YEARS criteria are met, a D-dimer < 500 ng/mL will rule out PE. RESULTS: Of the 3314 patients, 731 (22.1%) had PE. Applying the YEARS diagnostic algorithm, 1423 (42.9%) patients could have had PE ruled out without imaging. Of these patients, 17 (1.2%; 95% confidence interval 0.8-1.9) were diagnosed with PE at initial testing. All 17 had no YEARS item and a D-dimer < 1000 ng/mL. All 17 had a D-dimer level above their age-adjusted cutoff. Among the 272 patients with no YEARS criteria and a D-dimer < 1000 ng/mL but above their age-adjusted D-dimer cutoff, PE was diagnosed in 6.3% (17/272; 95% confidence interval 3.9-9.8). CONCLUSION: We provide external validation of the YEARS diagnostic algorithm in an independent cohort. The rule appears to safely exclude PE. However, caution is required in patients with no YEARS item and a D-dimer < 1000 ng/mL but above their age-adjusted D-dimer cutoff.

Is intrathecal morphine of benefit to patients undergoing cardiac surgery.

A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed is whether intrathecal morphine is of benefit to patients undergoing cardiac surgery? Using the reported search 850 papers were identified. Ten papers represented the best evidence on the subject. The author, journal, date and country of publication, patient group studied, study type, relevant outcomes, results and study comments and weaknesses were tabulated. The ten papers demonstrated that intrathecal morphine reduces postoperative pain scores, increases time to first IV morphine dose and reduces the overall postoperative IV morphine dose required, indicating its analgesic effect. Opioid-related complications remained comparable to controls, however, other benefits of reduced time to extubation, reduced ICU stay and improved postoperative lung function are variably reported with significant results found only in small retrospective studies. No spinal haematomas were reported, however, high-risk patients were excluded. We conclude that intrathecal morphine is an alternative method of pre-induction analgesia that benefits patients as less postoperative IV morphine is required, however, other benefits are less well reported.

Is steroid therapy ever of benefit to patients in the intensive care unit going into septic shock.

A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was, is steroid therapy ever of benefit to patients in the intensive care unit going into septic shock? Using the reported search 1505 papers were identified. Fourteen papers represented the best evidence on the subject. The author, journal, date and country of publication, patient group studied, study type, relevant outcomes, results and study comments and weaknesses were tabulated. Recent guidelines from the Surviving Sepsis Campaign recommend using stress doses of corticosteroids for septic shock regardless of adrenal function. All patients undergoing cardiothoracic surgery are at risk of developing septic shock. The 14 papers demonstrated that 28-day mortality is unaffected by hydrocortisone, however, the time to shock reversal is significantly reduced. Steroids reduced inflammatory mediators (IL-6, IL-8 and CRP) and neutrophil activation whilst maintaining neutrophil phagocytic functions. Haemodynamically, they increased systemic vascular resistance (SVR) and mean arterial pressure (MAP) and reduced heart rate (HR) and glomerular permeability. We conclude that steroids have no effect on mortality but shorten time to shock reversal, therefore they have a limited capacity in septic shock patients. Their immunological and haemodynamic effects cannot be discounted and could benefit patients in severe septic shock with adrenal insufficiency.

Is a port-access mitral valve repair superior to the sternotomy approach in accelerating postoperative recovery?

A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was whether port-access mitral valve repair reduces the recovery period of patients compared to the conventional sternotomy approach. Using the reported search, 778 papers were identified. Thirteen papers represented the best evidence on the subject and the author, journal, date and country of publication, patient group studied, study type, relevant outcomes, results and study comments and weaknesses were tabulated. The 13 papers demonstrated that patients who undergo minimally invasive mitral valve repair have a shorter ICU and total hospital stay than those who undergo the sternotomy approach. Results vary but mean hospital stays range from 5.6 to 13 days in port-access groups compared to 6.25-15 days in sternotomy groups. Other advantages over the sternotomy approach were reduced postoperative bleeding and pain, shorter time to extubation and a quicker return to daily activities. However, it is consistently reported that operative time is longer, with the increase in bypass time being around 30 min. We conclude that in several cohort studies minimally invasive mitral valve repair is reported to result in a shorter ICU and hospital stay, reduced postoperative bleeding and pain and a shorter time to resuming normal activities. This is at the expense of longer bypass and operative times.

What cardioversion protocol for ventricular fibrillation should be followed for patients who arrest shortly post-cardiac surgery?

A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was how many cardioversion attempts should be performed for patients who have gone into ventricular fibrillation post-cardiac surgery prior to performing chest reopening. Using the reported search, 1183 papers were identified. Fifteen papers represented the best evidence on the subject. The author, journal, date and country of publication, patient group studied, study type, relevant outcomes, results and study comments and weaknesses were tabulated. The quality and level of evidence was assessed using the International Liaison Committee of Resuscitation guideline recommendations. The most recent European Resuscitation Council guidelines suggest single attempts at cardioversion, spaced at 2-min intervals, for all patients going into ventricular fibrillation or pulseless ventricular tachycardia. Cardiac surgery presents a unique challenge for these guidelines in that emergency re-sternotomy may provide additional lifesaving interventions once it is deemed that external cardioversion is unlikely to succeed. The 15 papers identified demonstrated that the success of the first attempt at cardioversion for VF/VT was around 78%. The chance of the second shock succeeding was around 35%. The chance of a third shock succeeding was 14%. Very little data were found on the chance of further shocks succeeding. Of note none of these papers were in patients on the intensive care after cardiac surgery. We conclude that, due to the importance of minimising the delay to chest reopening, three shocks should be quickly delivered. If these do not succeed the chance of a 4th shock succeeding is likely to be <10% and, thus, immediate chest reopening should be performed. (This is a Class-IIa recommendation using ILCOR guideline recommendations.).

What is the evidence on the practice of mucous fistula refeeding in neonates with short bowel syndrome?

A systematic review of literature was performed on the practice of mucous fistula refeeding in neonates with short bowel syndrome. No randomised controlled studies were identified. Case series reports of 30 infants showed improved weight gain (from -2.36 +/- 1.24 to 21.06 +/- 3.02 g/d) and reduced need for total parenteral nutrition. Randomised controlled trials are required to establish the benefits of mucous fistula refeeding in this condition.