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Variability in Surgical Blood Transfusion Practices and Cardiovascular Outcome
Wen-Chih Hank Wu, MD
Providence VA Medical Center, Providence, RI
Funding Period: July 2005 - December 2007
Anemia is common in the elderly undergoing surgery and has been associated with an increased morbidity and mortality. Specific hematocrit ranges for blood transfusion have been related to improved outcomes in critically ill patients with and without cardiac disease, but similar evidence is lacking for the surgical population who utilizes more than 60% of all red blood cells. Despite the awareness of variable transfusion practices among different practitioners and institutions, it is unknown how this variability may impact the outcome of elderly veterans undergoing non-cardiac surgery.
The objectives of our study were:
(1) to study in elderly veterans undergoing non-cardiac surgery, the associations among preoperative anemia, operative blood transfusion status, and the risk of 30-day adverse cardiac or neurologic events (death, myocardial infarction, cardiac arrest, coma or stroke; and
(2) to study in the same population, the variability in the adherence to American Society of Anesthesiologists' blood transfusion guidelines between different VA hospitals, and its relationship with the hospital's 30-day perioperative adverse cardiac or neurologic event rates.
This is a cohort study using the clinical and administrative information from the NSQIP database merged with prior cardiac care data obtained from the PTF, OPC and VA-Medicare datasets. We included all veteran patients age >65 years in the NSQIP data who underwent major non-cardiac surgery in VA hospitals nationwide during 1997-2004. The primary outcome was 30-day perioperative cardiac or neurologic events (death, myocardial infarction, stroke, cardiac arrest, or coma).
A total of 310,311 surgical cases met the study inclusion criteria. We found a 1.6 percent (95 percent confidence interval, 1.1 to 2.2 percent) increase in 30-day postoperative mortality associated with every percent increase or decrease in the hematocrit value from the normal range (defined as a hematocrit value between 39 to 53.9%). Additional analyses suggested that the adjusted risk of 30-day postoperative mortality and cardiac morbidity begin to rise when hematocrit levels exceed 51%.
Interhospital variability in operative transfusion rates was large. It was greatest for the preoperative hematocrit levels of 18 to 29.9%, with an interquartile range of 17 to 36%; followed by the hematocrit levels of 30 to 35.9%, with an interquartile range of 7%-17%; and the smallest in the hematocrit levels of 36%, with an interquartile range of 3-7%. Only 58% of patients with a preoperative hematocrit <18% received an operative blood transfusion, whereas 8% of patients with preoperative and postoperative hematocrit values 30% were transfused.
Using propensity match analysis, we found that intraoperative blood transfusion is associated with a decreased risk of 30-day postoperative mortality in patients with a preoperative hematocrit of 24% or less, no change in risk for patients with preoperative hematocrit levels of 24 to 30%, and an increased risk in patients with preoperative hematocrit levels of greater than 30%.
Our results identified high risk subgroups of veterans undergoing major non-cardiac surgery who may be vulnerable to the effects of anemia. We provided a scientific rationale to the adherence of blood transfusion guidelines and expect to reduce the surgical mortality of patients in the VA hospitals by identifying high risk surgical subgroups that may require further management prior to or during surgery. We also believe that our study results may improve adherence to blood transfusion guidelines. We also identified areas in need of improvement regarding institutional adherence to current surgical blood transfusion guidelines.
Further studies are needed to understand institutional factors and quantifiy the amount of institutional influence in the variability of blood transfusion practices in major non-cardiac surgery. Our data provided important evidence for the future design of randomized-controlled studies in blood transfusion.
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DRA: Aging, Older Veterans' Health and Care, Health Systems
DRE: Epidemiology, Treatment - Observational
Keywords: Cardiovasc’r disease, Quality assessment, Surgery
MeSH Terms: Practice Guidelines, Quality