Time course of vasovagal syncope with whole blood donation

Abstract

Background Improving the safety of the donation experience will reduce donor injuries and increase donations, donation frequency and donor satisfaction. Understanding the physiology of donor reactions supports selection of effective interventions to reduce risk. Aims The examination of the time course of donor vasovagal syncopal reactions (VVS) to determine when most reactions occur supports the development of appropriate theories about cause of the majority of the reactions and the application of interventions to reduce the risk of a significant number of reactions. Materials and Methods A database of more than 900 000 donor registrations and more than 500 000 whole blood donation events was examined for the time course of VVS reactions by reviewing the onset time of the reactions. The donor experience was divided into three periods based on the theory that the risk of reaction depends on different factors in each of the periods. The time course was analyzed using frequency distribution counts stratified by donation status and separately by gender. Results There were 956 766 registrations, 554 513 attempted whole blood donations, 536 907 complete donations and 17 606 incomplete donations. The mean draw time of a complete donation was 8.21 (95% CI, 8.2–8.21) min and for an incomplete donation was 8.91 (95% CI, 8.8–9.01) min. The reaction rate for Period 1 (before venipuncture) was 0.045/1000 registrations; for Period 2 (venipuncture to 4 min post‐venipuncture) and Period 3 (4 min post venipuncture to last reported VVS reaction ‐265 min), the reaction rate was 3.5/1000 for women and 1.5/1000 for men. There was a steady increase in the reaction rate during phlebotomy and the rate peaked at the time of needle removal. After needle removal there were peaks in the VVS rate at 5 and 9 min. The reaction rate declined steadily thereafter. Discussion The peak reaction rates occur within a time period of 10 min beginning 1 min before needle removal. The reactions which have the most significant risk of donor injury occur later than this and often occur after the donor leaves the donation site. Approximately 10% of VVS reactions in male donors and 25% of VVS reactions in female donors occur more than 15 min after the needle is removed. The latest VVS reaction was reported to have begun at about 4.5 h after needle withdrawal. Conclusion It is our thought that preventive interventions for reactions which occur during phlebotomy might be slightly different from the preventive measure aimed at reducing risk to donors after assuming upright posture. Once the donor stands up, relative hypovolemia plays a greater role and interventions should be aimed at preventing changes in blood pressure due to hypovolemia during this period.

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