Most people would not question the benefit of a blood transfusion in certain clinical situations, for example the young dog that is presented after being hit by a car with a severe traumatic hemoabdomen, hypovolemic shock, and a packed cell volume (PCV) of 18%. But there are other circumstances when the risk–benefit ratio of administering a transfusion is somewhat less clear, for example the cat with chronic anemia and the same PCV of 18% that is hemodynamically stable and relatively bright. In both of these situations, veterinarians are required to make a decision as to whether or not to recommend a blood transfusion, while considering what is in the best interests of the patient. The decision whether or not to transfuse patients like the cat that are relatively stable and chronically anemic is difficult for many veterinarians due to the fear of transfusion-related complications, lack of readily available blood products, or an absence of resources needed to ensure that the transfusion is safe, such as pre-transfusion screening. Regardless of these factors, given the increasing evidence in veterinary medicine documenting transfusion-related complications and the concern regarding the risks associated with unnecessary or liberal transfusions, veterinarians should continue to question the necessity of transfusions in their patients and consider strategies to limit or avoid allogenic blood transfusions.

There has been a paradigm shift in the field of human transfusion medicine during recent years, which has moved clinicians towards more conservative transfusion triggers, using blood alternatives, and reducing blood loss as ways to limit or avoid allogenic blood transfusions. This shift has arisen from the expanding knowledge within the human transfusion literature documenting that unnecessary transfusions occur and that there are inherent risks involved with any transfusion (Shander et al. 2011). While risks such as infection transmission and transfusion reactions are mostly mitigated by appropriate blood donor and recipient screening, other transfusion-related complications (e.g., transfusion-related immunomodulation) are less clear with regards to how they might be prevented, aside from avoiding transfusions altogether. There are several studies that have demonstrated that transfused human patients have increased morbidity and mortality compared to their non-transfused cohort, but whether it is the underlying disease that necessitates the transfusion or the transfusion itself that worsens the outcome remains unclear (Isbister et al. 2011).

In human medicine, patient blood management (PBM) is a relatively new concept initially proposed to provide treatment for patients who were unwilling or unable to receive transfusions. However, recently it has adopted a broader application with the goal of restricting or eliminating the administration of blood products in order to conserve the blood supply and avoid unnecessary transfusions that might put patients at risk of transfusion-related complications. PBM is employed to maintain hemoglobin concentrations, optimize hemostasis, and minimize blood loss to reduce the need for allogenic transfusions and with the ultimate aim to improve patient outcome (Goodnough and Shander 2012).

More than one-third of human surgery patients demonstrate a pre-operative anemia, which is the most important risk factor for transfusion in people (Musallam et al. 2011). As such, the detection, assessment, and treatment of pre-operative anemia are required in order to minimize the administration of allogenic blood products (Goodnough et al. 2011). Accordingly, PBM was originally intended for the care of elective surgery patients, but the same concepts can be applied to all patients with the potential to require a blood transfusion during their care including non-elective surgery patients, trauma patients, oncology patients, and patients experiencing non-surgical bleeding (Shander and Goodnough 2013).

The approach to PBM relies on input from a multidisciplinary team, including the surgical, medical, anesthetic, and nursing care teams. The main focus of PBM is to identify and manage the risk factors predisposing patients to receiving a blood transfusion, which are typically the existence of anemia, degree of blood loss, and the lack of reliance on evidence-based guidelines to determine when a blood transfusion should be given (Gombotz et al. 2007). PBM uses three main strategies to manage these risk factors: (1) optimizing hematopoiesis, (2) minimizing blood loss and bleeding, and (3) optimizing physiologic adaptation to anemia while implementing appropriate therapies (Shander and Goodnough 2013). When used in combination, these strategies are intended to mitigate or avoid the administration of allogenic blood products to anemic patients.

Transfusion algorithms have been designed to ensure that allogenic transfusions are only administered to patients under certain circumstances, such as moderate to severe anemia or blood loss, so that unnecessary transfusions can be avoided (Enriquez and Shore-Lesserson 2009). However, some controversy exists regarding the hemoglobin concentration that should be minimally acceptable in patients prior to giving a RBC transfusion or what degree of blood loss is considered acceptable during surgical procedures. For patients that are actively bleeding, a transfusion is usually not required if blood loss is <15% of blood volume, but it could be considered if the blood loss were to increase to 15–30%. In patients with blood loss 30–40% of blood volume, a transfusion is usually necessary and in patients whose blood loss exceeds 40%, a transfusion is absolutely indicated (Thomas et al. 2013).

The “critical hemoglobin” or hemoglobin concentration below which oxygen delivery is insufficient to meet oxygen demand varies among species and patients. In people, it is approximately and in anesthetized dogs it is (Cain 1977). This is considered the lowest acceptable hemoglobin concentration to meet tissue oxygen demands and if not treated could lead to death within hours (Pape and Habler 2007). In the past, RBC transfusions were given according to the 10/30 rule (hemoglobin and hematocrit [HCT] 30%). However, this has largely been abandoned in favor of more restrictive transfusion strategies. In general, it is advised to transfuse people whose hemoglobin is , whereas transfusions are rarely recommended in patients with a hemoglobin (Thomas et al. 2013).

The shift in mindset amongst veterinarians towards more conservative use of blood products is less widespread, but has started in recent years. This could be due to increasing concerns regarding storage lesions (Obrador et al. 2015) and the association between administration of older RBC products to canine patients and increased complications, including coagulopathies and thromboembolic disease (Hann et al. 2014). Occasionally, veterinary studies have documented an association between administration of blood products and increased morbidity risk, such as postoperative pulmonary complications (Alwood et al. 2006) or surgical site dehiscence (Ralphs et al. 2003). Likewise, a retrospective study investigating transfusion-related complication in dogs receiving allogenic transfusions found that administration of larger doses of PRBCs and a higher pre-transfusion PCV were risk factors for non-survival (Holowaychuk et al. 2014). Restrictive transfusion strategies therefore might also have the same beneficial effects in veterinary patients as in people.

Regardless of these findings, the concept of PBM has not yet been proposed officially in the veterinary literature. Despite that, several of the PBM concepts have been or could easily be applied to veterinary patients, such as optimizing hematopoiesis by treating the underlying cause of the anemia, as well as optimizing physiologic adaptation to anemia as is done in people. A study investigating the incidence of iatrogenic anemia in 45 critically ill cats hospitalized for more than 48 hours recorded that 74% of non-anemic cats developed anemia during their hospitalization. The number of phlebotomies ranged from one to six per day and a higher number of phlebotomy procedures was associated with a higher need for transfusions, which was associated with a longer duration of hospitalization. Cats that were given a transfusion also had a higher volume of blood drawn (3.3 mL/kg per intensive care unit stay) compared to cats that did not receive a transfusion (1.1 mL/kg per intensive care unit stay) during their hospitalization. More than 80% of cats included in the study had sampling catheters to facilitate phlebotomy procedures (Balakrishnan et al. 2016).