Faculty Bibliography

Unfractionated heparin and low-molecular-weight heparins are commonly used as thromboprophylaxis for hospitalized patients. Though generally considered safe at prophylactic doses, cases of catastrophic hemorrhage have been reported. The proposed mechanism involves bioaccumulation of heparin through saturation of the rapid-elimination pathway in its metabolism. We present an unusual case of an average-weight man with metastatic melanoma who suffered hemorrhage with syncope and end-organ damage while on prophylactic three times daily unfractionated heparin. Coagulation studies were consistent with heparin toxicity. Despite administration of protamine, the clearance of heparin was remarkably delayed, as demonstrated by serial coagulation studies. We review the suspected risk factors for heparin bioaccumulation and the emerging understanding of this unusual adverse event involving a nearly ubiquitous medication.

Epidemics of respiratory syncytial virus (RSV) are known to occur in wintertime in temperate countries including the United States, but there is a limited understanding of the importance of climatic drivers in determining the seasonality of RSV. In the United States, RSV activity is highly spatially structured, with seasonal peaks beginning in Florida in November through December and ending in the upper Midwest in February-March, and prolonged disease activity in the southeastern US. Using data on both age-specific hospitalizations and laboratory reports of RSV in the US, and employing a combination of statistical and mechanistic epidemic modeling, we examined the association between environmental variables and state-specific measures of RSV seasonality. Temperature, vapor pressure, precipitation, and potential evapotranspiration (PET) were significantly associated with the timing of RSV activity across states in univariate exploratory analyses. The amplitude and timing of seasonality in the transmission rate was significantly correlated with seasonal fluctuations in PET, and negatively correlated with mean vapor pressure, minimum temperature, and precipitation. States with low mean vapor pressure and the largest seasonal variation in PET tended to experience biennial patterns of RSV activity, with alternating years of "early-big" and "late-small" epidemics. Our model for the transmission dynamics of RSV was able to replicate these biennial transitions at higher amplitudes of seasonality in the transmission rate. This successfully connects environmental drivers to the epidemic dynamics of RSV; however, it does not fully explain why RSV activity begins in Florida, one of the warmest states, when RSV is a winter-seasonal pathogen. Understanding and predicting the seasonality of RSV is essential in determining the optimal timing of immunoprophylaxis.

BACKGROUND:Cardiothoracic surgery places significant demands on blood bank resources. Measures aimed at reducing intraoperative hemodilution were initiated as part of a blood conservation program. STUDY DESIGN AND METHODS/METHODS:We initiated a series of measures aimed at reducing hemodilution volume: 1) reduction of intravenous fluid (IVF) volume, 2) reduction of circuit size, and 3) use of autologous priming techniques. All sources and volumes of IVF were obtained from the medical record. Intraoperative hematocrit (Hct) measurements were performed at the following intervals: first in operating room (OR), lowest on-pump, last on-pump, after protamine reversal, and immediately before discharge from OR. Red blood cell (RBC) transfusions were recorded. Intraoperative IVF, Hct levels, and transfusions were analyzed by cardiopulmonary bypass phase (prepump, on-pump, and off-pump), comparing preimplementation and postimplementation periods. RESULTS:Total intraoperative IVF volume was reduced by 973.7 mL (95% confidence interval, 671.6-1275.9 mL; p < 0.001) leading to a mean on-pump Hct improvement of more than 2% (p < 0.004). This contributed to a reduction in off-pump RBC transfusions by 20.6% (p = 0.014). A significant degree of heterogeneity in transfusion practice was noted between anesthesiologists. CONCLUSIONS:Blood conservation efforts in cardiac surgery should include efforts aimed at reducing hemodilution. Potential improvements are blunted by variation in transfusion practice.