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Development of anemia, phlebotomy practices & blood transfusion requirements in cats | VETgirl Veterinary CE Podcasts

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In today’s VETgirl online veterinary CE podcast, we review a recent study titled Development of anemia, phlebotomy practices, and blood transfusion requirements in 45 critically ill cats. This study hypothesized that iatrogenic anemia occurs in hospitalized cats undergoing repeated venipuncture. This has been observed in people, especially critically ill children, and has been associated with the need for blood transfusions. Unfortunately, we know that transfusions can increase hospital cost to clients, risk of transfusion reactions, and risks of complications such as transfusion-associated circulatory overload (TACO) or transfusion-related acute lung injury (TRALI). Given that less is known about iatrogenic anemia in cats, the objectives of this study were to describe the incidence and development of anemia, to document phlebotomy practices and transfusion requirements in these cats, and to evaluate the association between these factors and duration of hospitalization and outcome in critically ill cats.

This was a retrospective study performed at the University of Pennsylvania between January 2009 and 2011 and included information from 45 cats hospitalized in the ICU for more than 48 hours. That meant that the cats were critical enough to require advanced care and monitoring and that cats hospitalized briefly for post-operative care or those that died or were euthanized soon after presentation were not included. Cats diagnosed with anemia secondary to chronic kidney disease were excluded from this study. The data recorded included signalment, presenting complaint, any comorbidities, final diagnosis, PCV and total protein upon admission to the hospital and upon admission to the ICU, the lowest PCV and total protein during the ICU stay, and the last PCV and TP during the ICU stay. Anemia was defined as a PCV less than 30% and all instances when the PCV of a patient was less than 30% during the ICU stay were recorded. Other data recorded included total duration of hospitalization, average number of blood draws per day, blood work performed during ICU stay, incidence of blood loss (if it was known), presence of a sampling or central venous catheter, any blood transfusions and outcome, which was defined as survival to discharge, death, or euthanasia. The volume of blood drawn was estimated based on the minimum amount needed by the lab to run each test that was recorded in the record.

In this study, the average cat was 8 years old and weighed an average of 4.8 kg. The top five most common final diagnoses in these cats included respiratory disease, congestive heart failure, neoplasia, sepsis, and diabetic ketoacidosis. Twelve cats had surgery during their hospitalization and 1/3 of those cats had moderate to severe intra-operative bleeding. More than 80% of the cats in this study had a sampling or jugular catheter in place. At admission, 22% of cats were anemic and 40% of cats that were not initially anemic developed anemia in the ER prior to being transferred into ICU. Of the non-anemic cats that were admitted to ICU, 74% of them developed anemia during their ICU stay. The development of anemia in the ICU was associated with a longer hospitalization of 5 days versus 4 days in cats that did not develop anemia. However, the development of anemia was not associated with survival. Also, approximately 1/3 of the cats included in this study needed a blood transfusion. 1/3! Those cats had a median PCV of 16% prior to transfusion and were transfused an average of 6 mL/kg of packed RBCs. Cats that received a transfusion also had a longer hospitalization of 7.5 days, compared to 4 days in the cats that did not receive a transfusion. However, the requirement for a transfusion was not associated with survival.

Altogether, the cats in this study had a median of 3 blood draws per day during their ICU stay, which varied from 1 to 6. Cats that developed anemia had a median of 3 blood draws per day versus 1 blood draw per day in the cats that did not. Likewise, cats that received a transfusion had a median of 3 blood draws per day versus 2 blood draws per day in the cats that did not. Similarly, an estimated blood volume sampled during the entire ICU stay was 3.3 mL/kg in the cats that required a transfusion, compared to 1.1 mL/kg in the cats that did not need a transfusion. The most common test that was performed in these cats was a venous blood gas with a median of 12 performed per cat per ICU stay. This was in comparison to 1 CBC and 3 chemistry profiles performed per cat per ICU stay.

Overall, 84% of the cats included in this study survived to hospital discharge and all cats that did not survive were euthanized.
So, what are the take-home messages and interesting discussion points that we can learn from this study? Well…almost half of the cats that were presented to this busy teaching hospital in Philadelphia were anemic or developed anemia during their time in the ER, whereas more than half of the cats developed anemia during their stay in ICU. Reasons for development of anemia in these critical cats include hemodilution secondary to IV fluids, poor regeneration (which cats are notorious for), oxidative damage (which cats are also prone to because of the extra sulfhydryl groups on feline hemoglobin), blood loss (especially since the blood volume of cats is smaller than dogs), and finally, multiple blood draws (which we are all guilty of!). On average, the cats had 3 blood draws per day with approximately 3 mL/kg drawn during their entire ICU stay. Some of the cats in this study had substantial blood draws up to 8.5 mL/kg, which is equivalent to 15-18% of a cat’s blood volume! So, it’s no wonder that so many of the cats developed anemia and ultimately required a blood transfusion. Limitations of this study are that it is retrospective and includes a relatively small number of cats, some of which were euthanized and none of which had illness scores recorded. This makes associations between the study findings and survival difficult and left the study underpowered to draw more significant conclusions regarding the effect of anemia and transfusions on outcome.

So, what do we take away from this VETgirl podcast? This study shows us the importance of blood conservation. As veterinarians and technicians, we must be mindful of the number of daily diagnostic tests we are performing in our patients, and whenever possible, we should use small volume tubes and point-of-care or microanalysis tests to limit the volume of blood drawn. Likewise, waste samples from sampling catheters should be minimized and catheters removed once frequent blood draws are no longer required. Finally, consider using lower transfusion thresholds, especially in cats with more chronic anemias and no clinical signs of anemia. Let’s not allow our own actions as veterinary care professionals lead to unnecessary blood transfusions and longer hospital stays!

References:
1. Balakrishnan A, Drobatz KJ, Reineke, EL. Development of anemia, phlebotomy practices, and blood transfusion requirements in 45 critically ill cats (2009–2011). J Vet Emerg Crit Care 2015; early online release.

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