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Incidence of hospital-acquired anemia in hospitalized dogs & cats | VETgirl Veterinary CE Podcasts

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In today’s VETgirl online veterinary continuing education podcast, we review the incidence of hospital-acquired anemia in the hospitalized canine and feline patient. In the veterinary patient, the presence of anemia results in decreased oxygen carrying capacity, which directly affects all tissues by diminishing function and impairing tissue healing. It other words, it results in decreased oxygen deliver (DO2).

Despite having easier access to transfusion products for dogs and cats, blood transfusions should never be thought of as “benign” procedures. Transfusion reactions are not uncommon and can potentially be detrimental to your patient’s healing due to known risks [e.g., transfusion related acute lung injury (TRALI), transfusion associated circulatory overload (TACO), etc.]. Also, cost of transfusions can also be quite significant to your patient’s overall medical bill. It’s important to recognize that our medical decisions can profoundly contribute to our patients’ progression or development of anemia while they are in hospital, and to understand how we can minimize this occurrence. Veterinary professionals must be aware that repeated phlebotomy for clinicopathologic testing could be a potential cause for developing hospital-acquired anemia.

It’s important to remember that you should only remove up to a maximum of 20% of a patient’s blood volume in a healthy patient (e.g., for a healthy blood donor). Blood volume equations for dogs and cats will vary slightly depending on your reference, but in dogs their blood volume is roughly 60-90 mL/kg and in cats this is roughly 60 mL/kg.

In the emergency critical care setting, the majority of patients admitted are NOT healthy and cannot handle decreased oxygen delivery. Often times, anemia may already be present due to underlying disease (e.g., anemia of chronic disease, hemoabdomen, IMHA, etc.). For this reason, veterinary professionals should be aware of the dangers of hospital acquired anemia. Again, this may be iatrogenic – due to excessive blood loss secondary to phlebotomy. Other causes for hospital-acquired anemia may include blood loss associated with procedures, hemodilution from IV fluid administration, impaired production or destruction of RBCs, and dyserythropoeisis.

A 2016 study out of Tufts found 32% (272/851) of both cats and dogs combined had anemia on admission to the hospital and this number increased to 56% (479/851) during their hospitalization.1 Presumably due to their small size, cats were found to have a higher risk of developing hospital-acquired anemia than dogs, but their hospital-acquired anemia did not prove to have a negative impact on their overall outcome. They found that repeated phlebotomy in both dogs and cats was associated with an increased risk of developing hospital-acquired anemia.

Hiratzka et al out of Fox Valley Animal Referral Center, in Appleton, WI, wanted to further expound on the findings of this previous study by documenting the incidence of hospital-acquired anemia in a privately-owned small animal veterinary emergency and referral center, and investigate the causes for hospital-acquired anemia in veterinary medicine. This prospective study included 56 total pets (both cats and dogs combined) between August 2014 and March 2015. Inclusion criteria for cats and dogs included a hospitalization stay of at least 48 hours within this facility, a documented PCV within the normal reference range on admission, and at least one PCV <39% for dogs and <28% for cats at any time during their hospitalization. If the patient received a blood transfusion during their hospitalization, they were excluded from the study. PCVs were obtained on admission via direct venipuncture or from central venous catheters according to the three-syringe technique within the first 4 hours after patient admission and before initiation of IV fluid therapy to avoid the affect of hemodilution. PCVs were then obtained once every 24 hours and any additional blood volumes required for testing were recorded or estimated. Intravenous fluid volumes were recorded to assess the affects of hemodilution from intravenous fluids, but this study failed to take into consideration the volumes of IV medications administered (and flushes!), which can potentially be substantial depending on the medication. In total, 43% (20/46) of dogs and 70% (7/10) cats developed hospital-acquired anemia. Surprisingly, this study failed to prove cats more likely than dogs to develop anemia, as was found in the prior JVIM study. Within the first 24 hours of hospitalization, 34% of pets developed anemia. This number increased to 43% within the first 48 hours, and 48% within 72 hours of admission to the hospital. Of all animals that developed hospital-acquired anemia, this study found that 70% of them developed anemia within the first 24 hours. This study did not find age, sex, or body weight to be risk factors associated with developing hospital-acquired anemia. Surgery was found to be a risk factor, as 15 of 24 (62.5%) patients that received surgery became anemic. IV fluid therapy was found to be a risk factor with each additional 1 mL/kg/d of crystalloids administered creating higher odds of developing anemia. The authors state that 38% (11/29) patients receiving ≤ 100mL of crystalloids/kg/day and 59% (16/27) that received > 100mL/kg/day developed hospital-acquired anemia. However, it doesn’t appear that the effects of phlebotomy was considered as an independent factor within this population, so these numbers may be affected if the affect of phlebotomy was standardized across this patient population.

Phlebotomy for clinicopathologic testing was found to be a risk factor for developing anemia. To describe the effects of phlebotomy on the patient, the authors chose to express the blood volumes drawn as a percentage of the patient’s blood volume, using 60mL/kg for cat total blood volume and 90ml/kg for dog total blood volume. This study found that removing >3% of estimated blood volume via phlebotomy was associated with the development of hospital-acquired anemia. Along these lines, we find it surprising that this study did not find body weight to be a risk factor for development of hospital-acquired anemia. Required blood volumes for testing are uniform in accordance to the test so one would assume that the same tests performed in an animal < 10kg would produce a more profound effect on reducing the PCV as compared to this blood volume being removed in an animal > 10kg; the authors did not suggest a proposed cause for this finding, but perhaps the small sample size used in this study lead to the lack of significance when considering the effect of body weight. These authors refer to a prior study to give probable explanation (other than body weight) for why cats are at a higher risk for developing anemia than dogs. Cats have inherent increased RBC fragility and lower blood volumes. Surprisingly, a kitten in this study had an estimated 28.1% of total blood volume removed. It is theorized that neonates have higher total blood volume than adults, and only the adult blood volume formulas were used in this study despite the patient’s age.

There are several limitations to this study including a small sample size (which may influence the significance of body weight), and that the authors used a small window of hospitalization (72 hours) compared to human studies of similar fashion. Also, illness severity scores were not used to standardize the patient population, so medical condition and severity may have played an affect in this study. As noted above, the known effects of phlebotomy were not taken into consideration when evaluating the effects of IV fluid administration on PCV; sicker animals that received higher rates of fluids may have also been skewed to have more tests performed resulting in higher blood volumes drawn.

So, what we can take from this VETgirl podcast? Phlebotomy and surgery were found to be risk factors in developing hospital-acquired anemia. To minimize our phlebotomy volumes, we should pay close attention to prioritizing our tests and/or find other ways of roughly assessing what we need. Ways around submitting for a full chemistry panel might be to run a BUN or AZO strip (in conjunction with urine specific gravity) to provide a rough estimate of kidney function (although hydration and GI bleeding can affect these too). Handheld glucometers and handheld lactate readers use only a drop of blood to provide useful information. Pediatric hematocrit tubes, which are smaller than the commonly used adult hematocrit tubes, are available for obtaining PCV/TS. And finally, a drop of blood is all it takes to make a blood smear that can replace your CBC for assessing red and white blood cell counts, morphology, and platelet estimates. Careful consideration should be given to minimize blood draws by batching tests to make the most out of each sample, and serum should be stored through the patient’s hospitalization as this can be combined to produce enough serum for certain ancillary tests if needed.

Abbreviations:
PCV – packed cell volume
IV – intravenous
RBC – red blood cell

References:
1. Lynch AM, Respess M, Boll AE, et al. Hospital-acquired anemia in critically ill dogs and cats: a multi-institutional study. J Vet Intern Med 2016;30(1):141–146.
2. Hiratzka JL, Licari LG, Peters LK. Incidence of hospital-acquired anemia in hospitalized dogs and cats. JAVMA 2018;252(5):560-564

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