Layered metals as polarized transparent conductors.

The quest to improve transparent conductors balances two key goals: increasing electrical conductivity and increasing optical transparency. To improve both simultaneously is hindered by the physical limitation that good metals with high electrical conductivity have large carrier densities that push the plasma edge into the ultra-violet range. Technological solutions reflect this trade-off, achieving the desired transparencies only by reducing the conductor thickness or carrier density at the expense of a lower conductance. Here we demonstrate that highly anisotropic crystalline conductors offer an alternative solution, avoiding this compromise by separating the directions of conduction and transmission. We demonstrate that slabs of the layered oxides Sr2RuO4 and Tl2Ba2CuO6+δ are optically transparent even at macroscopic thicknesses >2 µm for c-axis polarized light. Underlying this observation is the fabrication of out-of-plane slabs by focused ion beam milling. This work provides a glimpse into future technologies, such as highly polarized and addressable optical screens.

Dynamics and Control of In-Flight Wingtip Docking.

Project Link! is a NASA-led effort to study the feasibility of multi-aircraft aerial docking systems. In these systems, a group of vehicles physically link to each other during flight to form a larger ensemble vehicle with increased aerodynamic performance and mission utility. This paper presents a dynamic model and control architecture for a system of ftxed-wing vehicles with this capability. The dynamic model consists of the 6 degree-of-freedom ftxed-wing aircraft equations of motion, a spring-damper-magnet system to represent the linkage force between constituent vehicles, and the NASA-Burnham-Hallock wingtip vortex model to represent the close-proximity aerodynamic interactions between constituents before the linking occurs. The control architecture consists of a guidance algorithm to autonomously drive the constituents towards their linking partners and an inner-loop angular rate controller. A simulation was constructed from the model, and the flight dynamic modes of the linked system were compared to the individual vehicles. The main contributions of this work are twofold. First is the introduction of close-proximity aerodynamic effects to create a realistic simulation framework for this problem. Second is the application of a sophisticated leader-follower guidance algorithm to achieve in-air wingtip docking. Simulation results for both before and after linking are presented.

Complications of cerebrospinal fluid drainage after thoracic aortic surgery: a review of 504 patients over 5 years.

BACKGROUND: Cerebrospinal fluid drainage, a well-established means of preventing paraplegia after thoracic aortic aneurysm surgery, can result in serious, sometimes lethal complications. In a large group of patients who underwent surgical thoracic aortic aneurysm repair with cerebrospinal fluid drainage, we examined the incidences of and potential risk factors for these outcomes. METHODS: The records were reviewed of 504 patients who underwent surgical thoracic aortic aneurysm repair with cerebrospinal fluid drainage at the Texas Heart Institute at St. Luke's Episcopal Hospital between February 2005 and December 2009. All historical data, inpatient records, and billing data were searched for evidence of complications. RESULTS: Of the 504 patients, 14 (2.8%) had intracranial hemorrhage, of whom 10 (72%) had subdural hematoma. Postdural puncture headache developed in 49 patients (9.7%), of whom 17 (34.6%) required epidural blood patch placement for resolution. Multivariable analysis identified having a connective tissue disorder (odds ratio, 3.08; 95% confidence interval, 1.33-7.13) as an independent predictor of postdural puncture headache, but not age less than 40 years (odds ratio, 0.97; 95% confidence interval, 0.94-0.99). CONCLUSIONS: Cerebrospinal fluid drainage, as performed by our method, seems to be associated with a modest rate of intracranial bleeding in patients who undergo surgical thoracic aortic aneurysm repair. In contrast, postdural puncture headache is not uncommon, particularly in patients with connective tissue disease. Clinicians caring for these patients should consider the likelihood of postdural puncture headache, and any such patient with postoperative headache should be assessed for epidural blood patch placement.

Radiation protection principles.

The International Commission on Radiological Protection (ICRP) recommends a system of radiological protection that is in use worldwide. This paper describes the elements of that system, identifying the central assumptions and principles. A key assumption for protection at low doses is that there is a simple proportionate relationship between increments in dose and increments in risk. The system focuses on changes to the level of peoples' exposure, recommending that any change is justified (i.e., the benefit is clear) and protection is then optimised (i.e., improvement in dose reduction is promoted when possible and reasonable). In doing so, the system considers the amenability of the source of exposure to control and the acceptability of the exposure to individuals or society.

Jugular venous oxygenation during hypothermic cardiopulmonary bypass in patients at risk for abnormal cerebral autoregulation: influence of alpha-Stat versus pH-stat blood gas management.

In a prospective, randomized study of cardiac surgical patients at risk for impaired cerebral blood flow autoregulation, we compared alpha-stat and pH-stat blood gas management. The 40 patients enrolled had age >70 yr, diabetes, prior stroke, or uncontrolled hypertension. During hypothermia and early rewarming, jugular oxygen tensions were significantly lower in alpha-stat patients (n = 12) than pH-stat patients (n = 19; P < 0.05). During rewarming, jugular venous desaturation (i.e., SjvO(2) <50%) occurred in 6 of 12 alpha-stat patients, but no pH-stat patients (P = 0.0006). Patients at risk for poor cerebral autoregulation have higher oxygen tensions and saturations if pH-stat blood gas management is used during cardiopulmonary bypass.

Intraoperative anticoagulation management during cardiac transplantation for a patient with heparin-induced thrombocytopenia and a left ventricular assist device.

Heparin-induced thrombocytopenia is an immunologically mediated syndrome that is associated with potentially life-threatening arterial and venous thrombosis. Re-exposing patients who have heparin-induced thrombocytopenia to heparin during cardiopulmonary bypass may be hazardous. We describe the re-exposure to unfractionated heparin of a patient with a left ventricular assist device and evidence of heparin-induced thrombocytopenia who needed cardiac transplantation, which was accomplished without complications.

Contributions of anesthesiology to the surgical treatment of cerebrovascular disease: the role of Arthur S. Keats, M.D.

Increased tolerance to cerebral ischemia produced by general anesthesia during temporary carotid occlusion. By B. A. Wells, A. S. Keats, and D. A. Cooley. Surgery 1963; 54:216-23. Local anesthesia with little or no preoperative sedation is currently recommended as the anesthetic of choice for temporary carotid occlusion during carotid endarterectomy. Purported advantages include minimal circulatory and respiratory changes from the local anesthetic, and constant verbal contact can be maintained with the patient so that neurologic changes are promptly recognized. However, local anesthesia may not be satisfactory in uncooperative or semiconscious patients. We therefore undertook a trial of general anesthesia in 56 consecutive patients undergoing carotid endarterectomy. Patients were induced in standardized fashion using intravenous thiopental (100-400 mg), atropine (0.2 mg), and succinylcholine (40-80 mg). Cyclopropane, along with deliberate hypercapnia and hypertension, was used for anesthesia maintenance. All patients tolerated carotid occlusion for periods of up to 30 min during general anesthesia without shunt, bypass, or hypothermia. Except for one patient, electroencephalogram evidence of cerebral ischemia was not apparent during occlusion, and no patient suffered postoperative neurologic sequela. Twenty percent of patients who had their carotid arteries occluded preoperatively for 30-60 s without general anesthesia suffered convulsions. These data suggest that general anesthesia increased the tolerance to cerebral ischemia. Potential mechanisms involved might include: 1) decreased cerebral metabolic rate for oxygen; 2) increased cerebral blood flow from hypercapnia; 3) increased arterial oxygen tension; and 4) recruitment of new routes of collateral circulation.

Complex liver resection for a large intrahepatic cholangiocarcinoma in a Jehovah's witness: a strategy to avoid transfusion.

Although morbidity and mortality after liver resection have improved over the last two decades, complex liver resections still require perioperative blood transfusions. In this report, we describe the use of a combined left trisegmentectomy and caudate lobectomy, along with resection of the inferior vena cava, to treat a large intrahepatic cholangiocarcinoma in a Jehovah's Witness. To our knowledge, this is the first report of major liver resection for a large malignant tumor in this patient population. We also discuss the perioperative strategy and surgical technique we used to minimize blood loss and avoid transfusion. This approach could be a safe alternative for use in all patients with complex liver tumor, regardless of their religious beliefs, to reduce the risks and cost associated with blood transfusion.

Fatal pulmonary microthrombi during surgical therapy for end-stage heart failure: possible association with antifibrinolytic therapy.

BACKGROUND: Maintaining hemostasis in patients with end-stage heart failure undergoing cardiac surgery is always challenging. These patients have chronic hepatic insufficiency, resulting in derangement of coagulation. In addition, they are commonly receiving both systemic anticoagulation (warfarin or heparin) and antiplatelet therapy. The introduction of antifibrinolytics has had a significant effect on postoperative coagulopathy. We report fatal pulmonary microthrombi in patients receiving antifibrinolytics who developed suprasystemic pulmonary artery pressures and right heart failure that was impossible to overcome despite insertion of a right ventricular assist device. METHODS: We reviewed the surgical procedure and autopsy reports to identify patients with high pulmonary artery pressures caused by pulmonary microthrombi after a cardiac surgical procedure for end-stage heart failure. Patient demographics and preoperative, intraoperative, and postoperative variables were collected from a retrospective review of the patients' medical records. RESULTS: We identified 9 patients (7 men and 2 women; mean age, 45 +/- 16 years) who died of pulmonary microthrombi after cardiac surgery between January 1997 and January 2004. Surgical procedures included 5 left ventricular assist device implantations, 2 heart transplantations, and 2 left ventricular reconstructions with mitral valve repair or replacement. Eight patients received aprotinin, and 1 patient received epsilon-aminocaproic acid immediately before and during cardiopulmonary bypass. All patients had severe suprasystemic pulmonary artery pressures after protamine administration for heparin reversal, a complication that proved fatal in all cases. Intraoperative wedge biopsy of the lungs revealed multiple microthrombi within capillaries and in the small- and medium-sized pulmonary arterioles. CONCLUSION: We report 9 cases for which fatal pulmonary microthrombi might be associated with the use of prophylactic antifibrinolytic therapy. Mortally ill patients with multiorgan failure who are receiving systemic anticoagulation and undergoing surgical procedures require careful perioperative monitoring to identify potential hazards. Anticoagulation and antifibrinolytic therapy protocols may require adjustment in such patients.

Alterations in alpha adrenoreceptor density and localization after mechanical left ventricular unloading with the Jarvik flowmaker left ventricular assist device.

Cardiac alpha one adrenoreceptors (alpha(1)AR) are known to mediate positive inotropism in human ventricular myocardium. In the early stages of heart failure, ventricular contractility is maintained by adrenergic stimulation, rennin-angiotensin activation, and other neurohormonal and cytokine system responses. As the disease progresses, however, these compensatory mechanisms cease to provide benefit; ventricular dilation and fibrosis occur and cardiac function deteriorates. When ventricular contractility becomes severely depressed and is no longer responsive to inotropic support, insertion of a left ventricular assist device (LVAD) may allow the left ventricle to rest, remodel, and recover some contractile function. Our previous work has demonstrated that the myocardium has the capacity to repair itself during a period of unloading, after which some patients are able to resume a normal lifestyle and no longer need a cardiac transplant.

Clopidogrel and bleeding in patients undergoing elective coronary artery bypass grafting.

OBJECTIVE: In an effort to minimize transfusions in patients undergoing elective coronary artery bypass grafting operations after recent clopidogrel exposure, we studied laboratory tests predictive of platelet dysfunction and used a strict algorithm-driven treatment of bleeding. METHODS: Forty-five patients receiving clopidogrel within 6 days of the operation and 45 control subjects were studied. Prothrombin time, activated partial thromboplastin time, platelet count, and platelet function test results were measured before heparinization, after protamine administration, and then every 2 hours. No transfusions were administered unless a patient met both laboratory and clinical criteria. RESULTS: Algorithm-driven treatment of bleeding significantly reduced the mean units of all blood components transfused by about one third, as shown by comparison with current control and historical data. Compared with current control subjects, clopidogrel recipients required significantly more transfusions of platelets (9.0 +/- 1.7 vs 1.2 +/- 0.5 U; P <.0001) and packed red blood cells (4.3 +/- 0.6 vs 2.3 +/- 0.5 U; P =.01) and required longer periods of controlled ventilation (12.4 +/- 1.3 vs 8.6 +/- 0.8 hours; P =.02). Preoperative platelet dysfunction before heparin administration for cardiopulmonary bypass, as measured by using adenosine diphosphate aggregometry (response <40%), predicted all but 1 case of severe coagulopathy requiring multiple transfusions (16.6 +/- 2.8 U of platelets and 5.8 +/- 1.0 U of packed red blood cells). CONCLUSIONS: A strict transfusion algorithm can reduce the transfusion requirement for all blood components. Preheparin testing of platelet function with adenosine diphosphate aggregometry can identify patients at highest risk for perioperative bleeding and transfusions and might further reduce the perioperative transfusion requirement.

Emergency percutaneous tracheostomy after unsuccessful orotracheal intubation in a patient with an acute myocardial infarction.

A 41-year-old woman had acute respiratory failure related to a myocardial infarction. Attempts at orotracheal intubation were unsuccessful; therefore, an emergency percutaneous tracheostomy was performed. The patient was then taken to the cardiac catheterization laboratory for myocardial revascularization. After the tracheostomy cannula was removed, the patient recovered successfully and was discharged from the hospital. The percutaneous tracheostomy technique may be useful in similar patients who need emergency airway access.

Cardiac failure and left ventricular assist devices.

LVADs represent advanced therapy for cardiac failure. The anesthesiologist's contribution to the pre-, intra-, and postoperative management of these challenging patients continues to grow as LVAD technology is refined and as more patients become eligible to receive these life-saving devices.

Anesthetic management for implantation of the Jarvik 2000 left ventricular assist system.

UNLABELLED: The Jarvik 2000 Heart(TM) is a left ventricular assist device that produces continuous nonpulsatile axial flow by means of a single, rotating, vaned impeller. Anesthetic and perioperative considerations of the Jarvik 2000 Heart(TM) differ from those of conventional assist devices. The Jarvik 2000 is implanted within the left ventricle through a left thoracotomy, which is aided by left lung isolation. A brief period of cardiopulmonary bypass and induced ventricular fibrillation facilitate implantation. Transesophageal echocardiography is essential to assure proper intraventricular positioning of the device and aortic outflow, confirmed by observation of aortic valve opening in the presence of adequate left ventricular volume. Because continuous flow devices function best in the presence of lower systemic and pulmonary vascular resistance, milrinone was preferentially used as an inotropic drug. In the first group of 10 patients to receive the Jarvik 2000, the pump provided a cardiac output of up to 8 L/min, depending on preload, afterload, and pump speed. There were no early perioperative deaths. The average support duration was 81.2 days; the range was 13-214 days. Seven of the 10 patients survived to transplantation. Survivors underwent complete physical rehabilitation during pump support. IMPLICATIONS: The Jarvik 2000 is a left ventricular assist device that produces continuous nonpulsatile axial flow by means of a rotating, vaned impeller. Because the anesthetic considerations differ from those of conventional left ventricular assist devices, we report the perioperative management of the first 10 patients who participated in a bridge-to-transplantation feasibility study of the Jarvik 2000.