Search

An overview of different approaches to modeling of hot tungsten filament performance in the Los Alamos Neutron Science Center (LANSCE) H- surface converter ion source is presented. The most critical components in this negative ion source are two specially shaped wire filaments heated up to the working temperature range of 2600 K-2700 K during normal beam production. In order to prevent catastrophic filament failures (creation of hot spots, wire breaking, excessive filament deflection towards source body, etc.) and to improve understanding of the material erosion processes, we have simulated the filament performance using three different models: a semi-empirical model, a thermal finite-element analysis model, and an analytical model. Results of all three models were compared with data taken during LANSCE beam production. The models were used to support the recent successful transition from the beam pulse repetition rate of 60 Hz-120 Hz. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Anaesthesia / Journal Canadien d'Anesthésie is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We have measured the interaction between closely spaced bilayer split ring resonators (SRRs) by varying separation layer and orientation. Terahertz time domain measurements match closely to simulations for arrays separated by a thin micron-scale polyimide layer. Experimental results indicate that bilayer SRRs resonances strongly depend on interlayer coupling tunable by separation and orientation. Simulation shows a relatively high Q resonance (Q≈30) is associated with the 'antialigned' SRR pair at separations of λ/500. Metamaterials tuned through interlayer coupling allows resonances at frequencies lower than the natural resonance of individual SRRs which has implications for electrically small antenna design. [ABSTRACT FROM AUTHOR]

A possible path for fabricating three-dimensional metamaterials with curved geometries at optical and infrared frequencies is to stack flexible metamaterial layers. We have fabricated highly uniform metamaterials at terahertz frequencies on large-area, low-stress, free-standing 1 μm thick silicon nitride membranes. Their response remains comparable to that of similar structures on thick substrates as measured by the quality factor of the resonances. Transmission measurements with a Fourier transform infrared spectrometer highlight the advantage of fabricating high frequency metamaterials on thin membranes as etalon effects are eliminated. Releasing the membranes enables layering schemes and placement onto curved surfaces in order to create three-dimensional structures. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Anaesthesia / Journal Canadien d'Anesthésie is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

An overview of different approaches to modeling of hot tungsten filament performance in the Los Alamos Neutron Science Center (LANSCE) H(-) surface converter ion source is presented. The most critical components in this negative ion source are two specially shaped wire filaments heated up to the working temperature range of 2600 K-2700 K during normal beam production. In order to prevent catastrophic filament failures (creation of hot spots, wire breaking, excessive filament deflection towards source body, etc.) and to improve understanding of the material erosion processes, we have simulated the filament performance using three different models: a semi-empirical model, a thermal finite-element analysis model, and an analytical model. Results of all three models were compared with data taken during LANSCE beam production. The models were used to support the recent successful transition from the beam pulse repetition rate of 60 Hz-120 Hz.

Unlabelled: Diaspirin cross-linked hemoglobin (DCLHb) solution is a purified human hemoglobin product chemically stabilized to deliver oxygen to tissues. We determined the peak plasma hemoglobin concentration and assessed changes in methemoglobin concentration after the infusion of 1 g/kg DCLHb in large blood loss surgical patients. This prospective, randomized study included 26 surgical patients who were either infused with up to three 250-mL units of 10% DCLHb or transfused with up to three units of packed red blood cells during the study infusion period. Serial plasma hemoglobin, plasma methemoglobin, and whole blood methemoglobin levels were measured before and at intervals up to 48 h after the study infusion period. Plasma hemoglobin and blood methemoglobin concentrations increased during the infusion of DCLHb. The plasma hemoglobin values in the DCLHb group continued to increase during each of the infusion periods to reach a peak plasma concentration of 1450 +/- 176 mg/dL. The fraction of whole blood methemoglobin increased from 0.84 +/- 0.77% at baseline to 4.08 +/- 1.36%. With a median DCLHb dose of 936 mg/kg (range 658-1500 mg/kg), the harmonic mean half-life was 10 h, and the increased whole blood methemoglobin reached a range not associated with complications., Implications: The dose of diaspirin cross-linked hemoglobin (DCLHb) (936 +/- 276 mg/kg) used in this study was one of the largest reported in humans to date. The DCLHb mean half-life was 10 h. The half-life observed was 2-4 times that found at smaller doses in previous studies. Whole blood methemoglobin fraction increased during DCLHb infusion but did not reach a range associated with complications.

Organ viability associated with renal transplantation is a product of the managing of the donor patient, the allograft, and the recipient patient. Short- and long-term outcome is influenced by perioperative fluid and drug treatment, and the function and viability of the transplanted kidney seem to be optimized if graft perfusion is maximized through mild hypervolemia. At the same time, careful balancing of intraoperative fluids is necessary against cardiovascular problems frequently encountered in patients with uremia. Close intraoperative monitoring, optimization of intravascular fluid volume status to maximize kidney perfusion, and prompt correction of electrolyte disturbances (especially potassium) are key to short- and long-term success of renal transplants.

Low dose renal dopamine continues to be infused in patients at risk for renal dysfunction or as a therapy after acute renal failure has been established. This article reviews the impact of acute renal failure on patients and reviews the history and use of dopamine therapy for patients. A discussion of the rationale, positive and equivocal evidence, side effects, and possible clinical indications for low-dose renal dopamine therapy is included.

Objectives: To compare the anesthetic aspects and intraoperative hemodynamic data and immediate postoperative outcomes in patients whose pheochromocytoma resection was performed either laparoscopically or by traditional open surgery., Methods: Fourteen consecutive patients who underwent laparoscopic procedures (a single surgeon) were compared with 20 patients who underwent open surgery. The patients' records were reviewed for demographic information, preoperative medical history and therapy, intraoperative hemodynamic data, fluid balance, and immediate postoperative course., Results: No differences between the highest intraoperative blood pressures and number of hypertensive episodes between the two groups were found. However, in laparoscopic patients, the intraoperative hypotension was less severe (mean lowest blood pressure 98/57 mm Hg versus 88/50 mm Hg, P = 0.05), and the hypotensive episodes were less frequent (median 0 versus 2, P = 0.005) and required fewer interventions with vasopressors (P = 0.02). Extreme high and extreme low heart rates did not differ between the two groups. The estimated blood loss was lower in the laparoscopic group (P = 0.0001), but the total intraoperative fluid requirement and operative times were similar in the two groups. Patients in the laparoscopic group resumed walking earlier (median 1.5 versus 4 days, P = 0.002) and resumed oral food intake sooner (median 1 versus 3.5 days, P = 0.0001). The median duration of hospitalization in patients who underwent laparoscopic and open adrenalectomy was 3 and 7.5 days, respectively (P = 0.001)., Conclusions: Intraoperative hemodynamic values during laparoscopic adrenalectomy for pheochromocytoma were comparable to those of traditional open surgery, but the patients who underwent the laparoscopic procedure had a faster postoperative recovery.

Objectives: To evaluate the appropriateness of autologous blood (AB) transfusion during radical retropubic prostatectomy in relation to the cardiopulmonary risk of the patient., Methods: We reviewed the medical records of 100 patients with American Society of Anesthesiologists status I, II, or III who underwent radical retropubic prostatectomy under general or combined general and epidural anesthesia. All patients had donated 2 units (U) of autologous blood, received 0, 1, or 2 U of autologous blood perioperatively, and received no allogeneic blood. Patients were placed in three cardiopulmonary risk groups on the basis of risk factors or documented cardiopulmonary disease. The low-risk group was assigned a target discharge hematocrit of 24% or less; moderate-risk, 25% to 28%; and high-risk, 29% or greater. The appropriateness of transfusion was determined by whether patients' hematocrit was in their group's preassigned range at discharge., Results: On the basis of discharge hematocrit, significantly more low-risk patients underwent inappropriate transfusion than moderate-risk (64% versus 26%, P = 0.006) or high-risk (64% versus 13%, P = 0.001) patients. Seventy-five AB units were discarded and at least 53 U were inappropriately transfused. We found an increase in the number of units of autologous blood transfused when a larger estimated blood loss was reported (P < 0.001). The estimated charge for the units discarded and inappropriately transfused exceeded $12,000., Conclusions: Sixty-four percent of autologous blood units were discarded or inappropriately transfused during radical retropubic prostatectomy. Transfusion of autologous blood was not governed by cardiopulmonary risk stratification. If the decision to transfuse had been based on cardiopulmonary risk factors instead of estimated blood loss, fewer patients would have received autologous blood.

Study Objective: To evaluate heart rate (HR) variability in the prone position with power spectral heart rate (PSHR) analysis during spinal and general anesthesia., Design: Prospective, clinical evaluation of HR variability in the prone position., Setting: Tertiary care teaching hospital., Patients: 20 healthy, ASA physical status I and II patients scheduled for elective lumbar spine surgery in the prone position., Interventions: Anesthetic technique was either a standard general anesthetic or spinal anesthetic, based on the preference of the patient. Power spectral heart rate, HR, and blood pressure (BP) readings were determined prior to anesthetic intervention and as soon as a stable PSHR reading was available in the prone position., Measurements and Main Results: Heart rate and BP were recorded at baseline prior to anesthesia and at the time of stable PSHR data in the prone position. Power spectral heart rate data included low-frequency activity (LFa), high-frequency activity (HFa), and the ratio (LFa/HFa). Spinal anesthesia level was recorded by thoracic dermatome at complete onset. Data were collected from 20 patients; 12 patients chose spinal anesthesia and 8 chose general anesthesia. The prone position resulted in significant increase in HR in the spinal group and significant decrease in BP in the general anesthesia group. Low-frequency activity and LFa/HFa ratio were unchanged in the spinal anesthesia group and were significantly decreased in the general anesthesia group. Spinal level was T8.7., Conclusions: The association of less change in LFa activity and preservation of BP on assumption of the prone position in patients during low spinal anesthesia suggests better preservation of autonomic nervous system compensatory mechanisms during low spinal anesthesia than with general anesthesia.

Purpose: We report a case of ischaemic optic neuropathy which occurred after prolonged spine surgery in the prone position in an obese, diabetic patient., Clinical Features: The patient was a 44-yr-old, 123 kg, 183 cm man for decompressive laminectomy and instrumented fusion of the lumbar spine. Anaesthesia was induced with thiopentone, fentanyl and succinylcholine and maintained with nitrous oxide, oxygen, isoflurane and a fentanyl infusion. He was positioned prone on the Relton-Hall frame and had an uneventful intraoperative course. Estimated blood loss was 3,000 ml. He was taken to the surgical intensive care unit (SICU) and the trachea was extubated 3.5 hr later. He had no pulmonary or haemodynamic problems and went to a regular nursing floor in the morning. He was discharged home on postoperative day #5. He telephoned his surgeon on postoperative day #7 to say that his vision had been blurry since surgery. His visual acuity was decreased, and on examination, he had a bilateral papillary defect, optic swelling and a splinter haemorrhage in the right eye. Magnetic resonance imaging (MRI) scan of the head and orbits detected no other abnormality. Based on this examination, he was felt to have bilateral ischaemic optic neuropathy and treated conservatively. By postoperative day #47, his visual acuity was greatly improved and near normal. Careful review of possible contributing factors suggests that the cause of the ischaemic optic neuropathy was venous engorgement., Conclusion: This patient developed ischaemic optic neuropathy from a prolonged interval in the prone position of the Relton-Hall frame, which may be related to venous engorgement.

Objectives: To determine the effect of shortened hospital stay after radical retropubic prostatectomy on costs, adverse surgical outcomes, and patient satisfaction., Methods: The effect of changes in preoperative counseling, perioperative care, and analgesic management on hospital length of stay; mean cost per case and cost per hospital day; and 30-day complication, hospital readmission, and mortality rates were analyzed for a consecutive sample of 374 patients undergoing radical prostatectomy between July 1989 and November 1995. Satisfaction with length of stay, analgesic regimen, and surgical outcome was assessed in a random subset of 150 patients by anonymous questionnaire., Results: Length of stay (LOS) was shortened from a median 7 to 2 nights after surgery during the study (P < 0.0001), whereas the acute complication, 30-day readmission, and 30-day mortality rates remained constant. Reducing LOS resulted in a 43% decrease in mean cost per case while mean cost per day increased by 22% to 35%. Overall patient satisfaction was high, with 83.5% of patients rating LOS as "just right" and 89.2% reporting they were "satisfied" or "very satisfied" with their pain control after surgery., Conclusions: Shortened LOS after radical retropubic prostatectomy can be accomplished safely and can meet with high levels of patient satisfaction while significantly reducing hospital-related costs. The potential for further incremental reductions in cost with reductions in LOS to less than 2 nights appears to be small, and future efforts at cost reduction for this procedure should center on decreasing the intensity of care during hospitalization.

We report a case in which sufentanil was given to a patient who was already taking both a monoamine oxidase (MAO) inhibitor and a tricyclic antidepressant. Anecdotal reports have recommended discontinuing MAO inhibitors 2 to 3 weeks prior to elective surgery. However, current anesthesia literature suggests this practice may be unnecessary. This case report involved a patient who refused to stop her antidepressant medications. She was given an uneventful elective anesthetic with measures to minimize the risk of an adverse drug reaction involving the antidepressants she was taking. Our experience suggests that the use of an opioid other than meperidine may allow the anesthetist to proceed cautiously to provide an anesthetic for an elective surgery patient who is also currently receiving MAO inhibitor therapy.

Background: Lactic acidosis, generally defined as a plasma lactate concentration in excess of 5 mmol/L with a concomitant blood pH less than 7.25, is reported to have a direct association with mortality., Objective: To report a case of unexplained perioperative lactic acidosis and to discuss the etiology, recognition, treatment, and importance of a transient rise in plasma lactate concentration., Summary: Severe lactic acidosis developed in a 40-year-old man with Crohn's disease during major abdominal surgery. The plasma lactate concentration reached 16.9 mmol/L (normal range 1.5 to 2.2 mmol/L). This condition resolved within 14 hours without harm to the patient., Conclusions: When lactate accumulates in the perioperative period, the responsible condition is most often self-limiting. Reversible, subacute, marked lactic acidosis should not be assumed to predict mortality as it does in patients whose plasma lactate concentrations remain chronically elevated during severe systemic diseases such as sepsis.

The purpose of this case report is to describe the events, intervention, and aetiology which led to acute airway obstruction in an adult patient after the placement of a Hickman catheter. Airway obstruction secondary to superior vena cava obstruction occurred after placement of a subclavian vein Hickman catheter. This was felt to occur, in part, to a narrowed superior vena cava as evident by subclavian venography. It resulted in emergency oral tracheal intubation to relieve airway obstruction. Shortly after removal of the Hickman catheter, the signs of superior vena cava obstruction syndrome resolved and the patient was extubated without incidence. It is concluded that, although rare, the serious complication of acute airway obstruction can occur after placement of a Hickman catheter.

Potassium is the principle intracellular ion, and its concentration and gradients greatly influence the electrical activity of excitable membranes. Because anaesthesia is so intimately involved with electrically active cells, potassium concentrations in surgical patients have received considerable attention in diagnostic and therapeutic applications. With the ongoing evolution in the indications for potassium, it is important to review the role of potassium in cellular activity, in storage and regulation, in diseases that alter potassium homeostasis, and in the therapeutic implications of perioperative alterations of potassium concentration. A rational approach to abnormal potassium values and the use of potassium in the operating room is sought, based on a physiological understanding of risks and benefits.

Objective: To describe the management of patients in an ICU during failure of both primary and backup electrical systems, resulting in nonfunctioning monitors, mechanical ventilators, and other life-support equipment., Design: Case report of power outage and discussion., Setting: A 45-bed cardiothoracic surgical ICU in a tertiary-care teaching hospital., Patients: Postoperative cardiothoracic surgical patients receiving i.v. infusions of vasoactive medications and mechanical ventilatory support., Main Results: Support measures included the use of pneumatically powered mechanical ventilators, battery-operated transport monitors and infusion pumps, and recruitment of non-ICU personnel to assist with manual ventilation and patient care. Problems identified included communication difficulties caused by failure of electronic telephones, and physical access limitation due to failure of electrical door openers and security locks., Conclusions: Total electrical power failure can occur even when an emergency power system is in place. Although the occurrence of such failure is unlikely, provisions must be made for its occurrence in order to avoid catastrophic patient injury. Such provisions include a mental plan of action, provision of emergency support equipment, physical plant changes, and the provision of power-independent communication systems. Power demands and battery backup capability of equipment should be considered in future equipment purchases. The ICU staff should be aware of the structure and operation of backup electrical power sources.