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Does the size of the syringe and blood filter affect survival of RBCs in cats? | VETgirl Veterinary Continuing Education Podcasts

Do you give a lot of blood transfusions in your veterinary clinic? Ever wonder if your protocol for blood transfusion administration is correct? In today’s VETgirl online veterinary continuing education podcast, we review whether or not the size of the syringe and blood filter affect survival of RBCs in cats. BTW, check out some of our transfusion videos here and here.

In the veterinary literature, reports of canine RBC injury have been reported when dogs were transfused by syringe, aggregate filters, or via certain mechanical pump mechanisms. So, Heikes et al wanted to assess whether or not damage to RBCs occurred with different routes of administration in cats that were transfused autologous RBCs. They conducted an academic-based (e.g., university setting), prospective controlled observational study, where they evaluated the effects of two different transfusion administration methods on RBC survival and half -life after RBC transfusion. They looked at 6 privately owned, neutered male cats with an age range between 3-9 years (with a median age of 5 years of age). To avoid the immune-related injury to the transfused RBC, autologous transfusions were used. Anti-coagulated blood was collected from cats (35 mls/cat) and separated into red blood cells and plasma. The red blood cells were then washed and labeled using biotinylation methods (biotin densities), after which it was then combined with its previously separated plasma component. This whole blood combination was then placed in a 50 mL bag or a 20 mL syringe, and refrigerated overnight so it could be transfused the next day. Next, the cats were randomly separated to receive the transfusion through either a blood administration set (by gravity flow) or with a syringe pump and 18 μm microaggregate filter (The specific filter that was used in this study was a Hemo-Nate filter, which is designed to remove microparticles of 18 microns or larger). For the blood transfusions that were given by syringe pump, a rate of administration of 2 ml/kg/hr was used with a 20 mL syringe. Now, if you’ve ever given a blood transfusion (especially in a small dog or cat), you know how difficult it is to control or regulate the rate of administration when using a gravity-assisted standard blood administration set. For this reason, the approximate rate of administration in this cat group was higher at 4 ml/kg/hr (with most of the blood being given over 1 hour).

HemoNate blood transfusion filter

So, what’d they find? First, no transfusion reactions were reported by the authors. After the transfusion, blood was collected via jugular venipuncture at the end of the transfusion and every 2 hours until a total of 6 samples were collected. Venipuncture also occurred once a week for 6 weeks, thereafter. Using flow cytometry, the labeled RBCs were then identified; these were present in all samples from all cats over the 6-week testing period. Both groups had an average of 10.6% of the labeled RBCs detected in all cats in the first blood sample after transfusion. This is similar to what the authors were expecting based on the total blood volume of a cat. The authors gave the example that if 17.5 mL of blood was collected in each study population, that represented approximately 8.3–9.7% of the blood volume in a 4-5 kg cat, based on a blood volume of 40-60 ml/kg blood volume. Regardless of how the feline RBCs were transfused, there was “no significant effect of transfusion method on short-term or long-term survival of transfused cells.” This is great news, as this is in stark contrast to previous reports in canine RBCs. The authors also found that the average half-life of transfused RBCs was 23 days, with a steady decline of the transfused RBCs over time. This was a slightly shorter half-life as compared to previous studies by Geiger et al, which reported an average half-life for autologous red blood cells in cats between 29-39 days.

Regardless, this study found that there was no difference in the transfused red blood cell viability between the 2 methods of administration – so it is fine to use a gravity flow method or a syringe pump with a microaggregate blood filter! (VETgirl prefers a syringe pump, since we’re control freaks and know it’s going in at the rate that we want!). Regardless, the use of syringe and Hemo-Nate filters or a standard commercial blood administration set for whole blood transfusion in cats are reliable transfusion methods with no significant effects on RBC survival. This is a good, relatively simple study evaluating the safety and efficacy of a procedure commonly performed in the critical care unit. Despite being a prospective study, however, its limitations were the small sample of patients. Another limitation was that the RBCs were exposed to multiple washing and procedures that could have directly affected survival of the RBCs.

Side note: We all use these microaggregate blood filters post-syringe on the RBC transfusion, right? I mean, that’s what we’ve been clinically trained to do. The weird thing is that the manufacturers recommendations are actually opposite of this – you’re suppose to aspirate the blood through the filter into a syringe, and then administer the transfusion once the filter is removed. Regardless, the good news is that this study shows that despite our veterinary community using this filter incorrectly, it doesn’t seem to affect the RBC survival! So, rest assured…the use of a syringe pump and aggregate filter or blood administration set for whole blood transfusions in cats is an effective method with no clinically important detrimental effects on RBC survival.

References:
1. Heikes BW, Ruaux, CG. Effect of syringe and aggregate filter administration on survival of transfused autologous fresh feline red blood cells. J Vet Emerg Crit Care 2014:24(2):162–167.
2. Giger U, Bucheler J. Transfusion of type-A and type-B blood to cats. J Am Vet Med Assoc 1991; 198(3):411–418.

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