Varianza analitica y aproximada del costo total de un proyecto

La varianza estadística del costo total de un proyecto usualmente se estima por medio de la simulación de Monte Carlo, bajo el supuesto de que los acercamientos analíticos son demasiado complicados. Este artículo analiza este supuesto y muestra que, contrario a lo esperado, la solución analítica es relativamente directa. También se muestra que el coeficiente de variación no se ve afectado por el tamaño (área superficial) del proyecto cuando se usan los costos de los componentes estandarizados. Se provee un caso de estudio en el cual se analizan los costos reales de los componentes para obtener la varianza del costo total requerida. Los resultados confirman trabajos previos al mostrar que la aproximación del segundo momento (varianza) bajo el supuesto de independencia subestima considerablemente el valor exacto. El análisis continua examinando los efectos del juicio profesional y con los datos simulados utilizados, la aproximación resulta razonablemente exacta - el juicio profesional absorbe la mayor parte de las intercorrelaciones involucradas. También se da un ejemplo en el cual las cantidades de los componentes unitarios son valoradas por sus costos unitarios promedios y muestra, una vez más, que la aproximación es cercana al valor real. Finalmente, el trabajo se extiende mostrando cómo obtener, para cada proyecto, las varianzas exactas del costo total.

The clinical effectiveness of interventions to assist perioperative temperature management for women undergoing Cesarean Section : a systematic review

Background Women undergoing Cesarean Section (CS) are vulnerable to the adverse effects associated with perioperative core temperature drop, in part due to the tendency for CS to be performed under neuraxial anesthesia, blood and fluid loss, and vasodilation. Inadvertent perioperative hypothermia (IPH) is a common condition that affects patients undergoing surgery of all specialties and is detrimental to all age groups, including neonates. Previous systematic reviews on IPH prevention largely focus on either adult or all ages populations, and have mainly overlooked pregnant or CS patients as a distinct group. Not all recommendations made by systematic reviews targeting all adult patients may be transferable to CS patients. Alternative, effective methods for preventing or managing hypothermia in this group would be valuable. Objectives To synthesize the best available evidence in relation to preventing and/or treating hypothermia in mothers after CS surgery. Types of participants Adult patients over the age of 18 years, of any ethnic background, with or without co-morbidities, undergoing any mode of anesthesia for any type of CS (emergency or planned) at healthcare facilities who have received interventions to limit or manage perioperative core heat loss were included. Types of intervention(s) Active or passive warming methods versus usual care or placebo, that aim to limit or manage core heat loss as applied to women undergoing CS were included. Types of studies Randomized controlled trials (RCTs) that met the inclusion criteria, with reduction of perioperative hypothermia a primary or secondary outcome were considered. Types of outcomes Primary outcome: maternal core temperature measured during the preoperative, intraoperative and postoperative phases of care Secondary outcomes: newborn core temperature at birth, umbilical pH obtained immediately after birth, Apgar scores, length of Post Anesthetic Care Unit (PACU) stay, maternal thermal comfort. Search strategy A comprehensive search was undertaken of the following databases from their inception until May 2012: ProQuest, Web of Science, Scopus, Dissertation and Theses PQDT (via ProQuest), Current Contents, CENTRAL, Mednar, OpenGrey, Clinical Trials. There were no language restrictions. Methodological quality Retrieved papers were assessed for methodological quality by two independent reviewers prior to inclusion using JBI software. Disagreements were resolved via consultation with the third reviewer. An assessment of quality of the included papers was also made in relation to five key quality factors. Data collection Two independent reviewers extracted data from the included papers using a previously piloted customized data extraction tool. Results 12 studies with a combined total of 719 participants were included. Three broad intervention groups were identified; intravenous (IV) fluid warming, warming devices, leg wrapping. IV fluid warming, whether administered intraoperatively or preoperatively, was found to be effective at maintaining maternal (but not neonatal) temperature and preventing shivering, but does not improve thermal comfort. The effectiveness of IV fluid warming on Apgar scores and umbilical pH remains unclear. Warming devices, including forced air warming and under body carbon polymer mattresses, were effective at preventing hypothermia and reduced shivering, however were most effective if applied preoperatively. The effectiveness of warming devices to improve thermal comfort remains unclear. Preoperative forced air warming appears to aid maintenance of neonatal temperature, while intraoperative forced air warming does not. Forced air warming was not effective at improving Apgar scores and the effects for umbilical pH remain unclear. Conclusions Intravenous fluid warming, by any method, improves maternal temperature and reduces shivering for women undergoing CS. Preoperative body warming devices also improve maternal temperature, in addition to reducing shivering.