Justify your alpha

Benjamin et al. proposed changing the conventional “statistical significance” threshold (i.e.,the alpha level) from p ≤ .05 to p ≤ .005 for all novel claims with relatively low prior odds. They provided two arguments for why lowering the significance threshold would “immediately improve the reproducibility of scientific research.” First, a p-value near .05provides weak evidence for the alternative hypothesis. Second, under certain assumptions, an alpha of .05 leads to high false positive report probabilities (FPRP2 ; the probability that a significant finding is a false positive

Justify your alpha

In response to recommendations to redefine statistical significance to p ≤ .005, we propose that researchers should transparently report and justify all choices they make when designing a study, including the alpha level

Blood Anion Gaps and Venoarterial Carbon Dioxide Gradients as Risk Factors in Long-Term Extra corporeal Support

Increases in the blood anion gap (AG) and venoarterial carbon dioxide gradients [p(VA) CO2 ] may indicate changes in intracellular acid concentration not demonstrated by blood gas measurements. This prospective study examines these two physiologic markers to determine their relationship to extracorporeal membrane oxygenation (ECMO) survival and duration in 100 patients. Serum electrolytes were drawn every 6 hours and the AG calculated. Simultaneous arterial blood gases and venous blood gases were drawn every 4 hours and the p(V-A)CO2 calculated. Cumulative averages were then calculated from all the AG and p(V-A)CO2 values during each ECMO treatment. The average AG was 11 mEq/L. The average p(V-A)CO2 was 9 mm of mercury (mmHg). Patients with an AG of 11 mEq/L or less had a 12% mortality and those with a higher AG had a 43% mortality (p=0.0005). Patients with a p(V-A)CO2 of less than 9 mmHg had a 13% mortality and those with a 9 mmHg or higher gradient had a 35% mortality (p=0.0126). Patients with both a low AG and a low p(V-A)CO2 had a 7% mortality and survivors were on ECMO 100 (± 37) hours. Patients with both a high AG and a high p(V-A)CO2 had a 56% mortality and survivors were on ECMO 190 (± 1 05) hours. Both mortality and survivors’ ECMO time increase as one or both risk factors increase. Patients with increases in both risk factors have a mortality rate 8 times greater and survivors remain on ECMO almost twice as long as those without increased risk factors. Patients may benefit from a perfusion strategy that seeks to minimize the AG and p(V-A)CO2

Oxygen Pressure field Theory, The Krogh Cylinder and Long-Term Extra corporeal Perfusion: An Old Concept Provides New Insight

This article describes oxygen pressure field theory and its relevance to the application of long-term perfusion support. Prolonged applications of extracorporeal support for cardiac or pulmonary failure require a more perceptive understanding of perfusion and how it works over a period of days or weeks. The key to this understanding lies in the concepts of the Krogh tissue cylinder, the lethal corner and perfused capillary density. The interrelationships of these concepts define the microvascular redistribution system and its need to remain in balance in order to maintain homeostasis. An imbalance in any of the aspects described could result in tissue damage and eventual death. Perfusionists attempting to perform long-term extracorporeal support can improve the odds for patient survival with a clear understanding of oxygen pressure field theory and its associated concepts. By maintaining a balance in the microvascular redistribution system, the perfusionist not only keeps the patient alive, but creates an environment where healing can occur over a period of days or weeks

Defining the Late Implementation of Extracorporeal Membrane Oxygenation (ECMO) by Identifying Increased Mortality Risk Using Specific Physiologic Cut-Points in Neonatal and Pediatric Respiratory Patients

There is no reliable clinical indicator showing how long extracorporeal membrane oxygenation (ECMO) implementation can be delayed before the risk of death becomes unacceptably high in neonatal and pediatric respiratory patients. However, the late use of ECMO may be defined by the elevation of specific physiologic markers separate from pulmonary function and hemodynamic assessments that indicate when the optimal time for implementation of ECMO has past, resulting in a higher than normal mortality, possibly due to reperfusion injury. Neonatal patients were reviewed retrospectively to determine if later implementation of ECMO correlated to increased mortality. Neonatal and pediatric respiratory patients placed on ECMO were reviewed retrospectively to determine if the first adjusted anion gap (AGc), the first venoarterial CO2 gradient (p[v-a] CO2), or the first Viability Index (AGc + p[v-a]CO2 = INDEX) on ECMO could be used to identify a cut-point for increased mortality. Expired neonates (n = 31) were placed on ECMO an average of 2 days later than neonatal survivors (n = 163). The review of 210 respiratory neonatal and pediatric ECMO patients with an overall survival of 82% showed that all three markers were elevated in the expired patients (n = 38, p < .05). Cut-points were an AGc ≥ 23 mEq/L, the p[v-a]CO2 ≥ 16 mmHg, and the INDEX ? 28. These values correlated with a significantly higher risk of mortality (p < .05); survival to discharge being 43% or less. Patients under the cut-points had survival rates of 84% or higher. Starting ECMO too late may cause reperfusion injury that reduces survival. This study describes specific physiologic markers taken soon after ECMO initiation that correlate with mortality. These markers, if assessed earlier, may allow for a more timely ECMO implementation and higher survival

The Correlation of Fluid Balance Changes During Cardiopulmonary Bypass to Mortality in Pediatric and Congenital Heart Surgery Patients

Edema acquired during the perioperative period has long been associated with increased mortality. Edema acquired during cardiopulmonary bypass (CPB) may contribute to this mortality. The intent of this retrospective study was to test the premise that edema in the form of a positive fluid balance change (FBC) acquired during CPB correlated to mortality. If so, FBC from the beginning of CPB (baseline; FBC = 0) to the end of CPB may need to be monitored, measured, and controlled on CPB with the same ardor as blood pressure and pH. This retrospective analysis reviewed the FBC of 1540 pediatric and congenital heart surgery patients at the end of CPB. Additions and subtractions of fluid to the combined patient/CPB circuit were routinely quantified during CPB procedures and during periods of modified ultrafiltration (MUF). The primary outcome assessed was mortality during hospitalization. The overall mortality of the 1540 patients was 5.65%from all causes. Eighty percent (n = 1226, mortality = 4.65%) of the patients had a zero or negative FBC immediately after CPB/MUF. Twenty percent (n = 314, mortality = 9.55%) had a positive FBC. Positive FBC patients tended to be in higher risk categories, weighed more, and had longer pump times (p < .05) with an adjusted odds ratio for mortality of 1.73 (1.01–2.96, 95% confidence interval). There is a correlation between edema acquired during CPB and increased mortality in pediatric and congenital heart surgery patients. The potential exists for the perfusionist to optimize the fluid balance changes while on CPB to reduce mortality rates