Trials which randomize practices II: sample size

BACKGROUND: When practices are randomized in a trial and observations are made on the patients to assess the relative effectiveness of the different interventions, sample size calculations need to estimate the number of practices required, not just the total number of patients. OBJECTIVE: Our aims were to introduce the methodology for appropriate sample size calculation and discuss the implications for power. METHOD: A worked example from general practice is used. DISCUSSION: Designs which randomize practices are less powerful than designs which randomize patients to intervention groups, particularly where a large number of patients is recruited from each practice. Studies which randomize few practices should be avoided if possible, as the loss of power is considerable and simple randomization may not ensure comparability of intervention groups.      

外科手术中产生的烟气:仅仅是大量的热空气吗?

外科医生和手术室人员经常接触手术设备产生的烟气,病人也会暴露于烟气中,特别是腹腔镜手术中产生的烟气滞留于腹腔内这一密闭空间并被吸收.这些烟气是一种与香烟烟气相似的毒性物质,然而对这种毒性物质的影响还未引起足够重视.应该采取必要措施尽可能减少手术中烟气的不良影响.     

Advancing the Neurophysiological Understanding of Delirium

Delirium is a common problem associated with substantial morbidity and increased mortality. However, the brain dysfunction that leads some individuals to develop delirium in response to stressors is unclear. In this article, we briefly review the neurophysiologic literature characterizing the changes in brain function that occur in delirium, and in other cognitive disorders such as Alzheimer's disease. Based on this literature, we propose a conceptual model for delirium. We propose that delirium results from a breakdown of brain function in individuals with impairments in brain connectivity and brain plasticity exposed to a stressor. The validity of this conceptual model can be tested using Transcranial Magnetic Stimulation in combination with Electroencephalography, and, if accurate, could lead to the development of biomarkers for delirium risk in individual patients. This model could also be used to guide interventions to decrease the risk of cerebral dysfunction in patients preoperatively, and facilitate recovery in patients during or after an episode of delirium.     

Antimicrobial resistance predicts death in Tanzanian children with bloodstream infections: a prospective cohort study

Background

Bloodstream infection is a common cause of hospitalization, morbidity and death in children. The impact of antimicrobial resistance and HIV infection on outcome is not firmly established.

Methods

We assessed the incidence of bloodstream infection and risk factors for fatal outcome in a prospective cohort study of 1828 consecutive admissions of children aged zero to seven years with signs of systemic infection. Blood was obtained for culture, malaria microscopy, HIV antibody test and, when necessary, HIV PCR. We recorded data on clinical features, underlying diseases, antimicrobial drug use and patients' outcome.

Results

The incidence of laboratory-confirmed bloodstream infection was 13.9% (255/1828) of admissions, despite two thirds of the study population having received antimicrobial therapy prior to blood culture. The most frequent isolates were klebsiella, salmonellae, Escherichia coli, enterococci and Staphylococcus aureus. Furthermore, 21.6% had malaria and 16.8% HIV infection. One third (34.9%) of the children with laboratory-confirmed bloodstream infection died. The mortality rate from Gram-negative bloodstream infection (43.5%) was more than double that of malaria (20.2%) and Gram-positive bloodstream infection (16.7%). Significant risk factors for death by logistic regression modeling were inappropriate treatment due to antimicrobial resistance, HIV infection, other underlying infectious diseases, malnutrition and bloodstream infection caused by Enterobacteriaceae, other Gram-negatives and candida.

Conclusion

Bloodstream infection was less common than malaria, but caused more deaths. The frequent use of antimicrobials prior to blood culture may have hampered the detection of organisms susceptible to commonly used antimicrobials, including pneumococci, and thus the study probably underestimates the incidence of bloodstream infection. The finding that antimicrobial resistance, HIV-infection and malnutrition predict fatal outcome calls for renewed efforts to curb the further emergence of resistance, improve HIV care and nutrition for children.     

STAR procedure becomes SAFER: First-in-man case series of a new antegrade dissection re-entry technique

Introduction

Antegrade dissection and re-entry (ADR) is an integral part of the hybrid algorithm, which has allowed for improved outcomes in chronic total occlusion (CTO) coronary intervention (PCI).

Methods

A new ADR method, Subintimal Antegrade FEnestration and Re-entry (SAFER), is described. The results of a first-in-man series are presented.

Results

SAFER was performed on seven consecutive patients with angiographic and clinical success in all patients.

Conclusions

This first-in-man study has shown that the SAFER technique is feasible and effective with the possibility of improving the antegrade PCI CTO success rate.     

The PB3300 intraarterial blood gas monitoring system

Continuous intraarterial blood gas (IABG) monitoring is in clinical use both in the operating room and intensive care unit. This technology uses miniature, optically-based sensors that can be placed into a patient's artery. The arterial blood gas values are transduced into an optical signal that is measured by a bedside monitor on which the values are displayed. In this paper, we describe the operating principles of the PB3300 Intra-Arterial Blood Gas Monitoring System (Puritan-Bennett Corporation, FOxS Division, Carlsbad, CA). Topics include the principles of fluorescent determinations of pH,PCo ₂, andPO ₂; the optical path of the PB3300; system calibration; dye layer geometry; and clinical operation. The accuracy, precision, and drift of the system measuring tonometered aqueous standards are reported. The following values were noted for eight sensors sending data to eight monitors: system bias and precisions of 0.00±0.02 pH at a pH of 7.40, –2.5±1.5 mm HgPCo ₂ at aPCo ₂ of 40 mm Hg, and 3.3±1.3 mm HgPO ₂ at aPO ₂ of 80 mm Hg.

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Abstrakt Die kontinuierliche intraarterielle Blutgasüberwachung (IABG) wird klinisch sowohl im OP als auch auf der Intensivstation eingesetzt. Hierbei werden miniaturisierte, optische Sensoren angewandt, die sich direkt in der Arterie des Patienten plazieren lassen. Die Blutgaswerte werden in optische Signale umgesetzt und von einem bettseitigen Monitor gemessen und angezeigt. In dieser Arbeit beschreiben wir das Funktionsprinzip des Intra-Arteriellen Blutgasanalysesystems PB3300 (Puritan-Bennett Corporation, FOxS Division, Carlsbad, CA). Themen sind die Grundlagen der Bestimmung von pH, PCO2 und PO2 mittels Fluoreszenz; die optische Übertragung des PB3300; die Kalibrierung des Systems; die Geometrie der Farbschichten und der Einsatz in der Klinik. Die Genauigkeit, Auflösung und Drift des Systems bei der Messung von tonometrischen wässrigen Standards wird beschrieben. Die folgenden Werte ergaben sich aus einer Meßreihe mit 8 Sensoren, die an 8 Monitore angeschlossen waren (jeweils Bias, Streuung und Sollwert): 0.00±0.02 pH bei 7.40 pH, –2.5±1.5 mmHg PCO2 bei 40 mmHg PCO2 und 3.3±1.3 mmHg PO2 bei 80 mmHg PO2.

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Resumen La monitorizaciòn continua de gases intraarteriales tiene uso clinico, tanto en el pabellòn de operaciones como en la unidad de cuidados intensivos. Esta tecnologia utiliza sensores miniatura de tipo òptico que pueden ser introducidos en una arteria del paciente. Los valores de gases arteriales son transducidos en forma de señal òptica que es medida al lado de la cama del paciente por un monitor que presenta los valores numéricos. En este trabajo, describimos los principios de operaciòn del PB3300 Intra-Arterial Blood Gas Monitoring System (Puritan-Bennett Corporation, FOxS Division, Carlsbad, CA). Los temas incluyen los principios de determinaciones fluorescentes de pH, PCO₂, and PO₂; la via òptica del PB3300; calibraciòn del sistema; geometria de la capa de colorante; y la operaciòn clinica. Se presentan la exactitud, precisiòn, y deriva (drift) del sistema, midiendo soluciones acuosas de tonometrìa estàndar. Los siguientes valores fueron registrados para ocho sensores enviando informaciòn a ocho monitores: los sesgos del sistema y las precisiones fueron de 0.00±0.02 pH a pH 7.40, –2.5±1.5 mmHg PCO₂ a PCO₂ 40 mmHg, y 3.3±1.3 mmHg PO₂ a PO₂ 80 mmHg.

     

Red cell loss following orthopedic surgery: the case against postoperative blood salvage

BACKGROUND: Expensive devices have been developed for the collection and transfusion of blood salvaged after hip or knee arthroplasty. STUDY DESIGN AND METHODS: The volume of salvaged red cells was measured for the first 6 hours after operation. This volume was compared to total red cell loss during hospitalization and to the volume of allogeneic red cells transfused. RESULTS: Mean postoperative red cell loss in 31 patients following hip replacement was 55 +/− 29 mL and that in 20 patients following knee replacement was 121 +/− 50 mL. The 6-hour wound drainage represented 8.7 and 16.8 percent of overall red cell loss during hospitalization for hip and knee replacement, respectively. The transfusion of postoperatively salvaged red cells would have supplanted transfusion of less than one-third of a unit of allogenic blood after hip replacement and two-thirds of a unit after knee replacement. Only three patients (5.9%) lost red cell volume in the drainage equivalent to or in excess of 1 unit of red cells (180 mL). The volume of red cells salvaged postoperatively bore no relationship to perioperative red cell losses as a whole. CONCLUSION: The relatively small red cell loss in the postoperative period in most arthroplasty patients does not appear to justify the routine use of this technique for the recovery of autologous blood.