Best Practices

Chapter 67


Transfusion Medicine


Best Practices*




The positive and negative aspects of blood product administration, as further understood through recent developments in transfusion medicine, have significantly changed how and why veterinarians use these products. Practitioners have better access to a wider variety of blood products, which allows for more selective component therapy. This improved product availability has enhanced the level of care provided in the fields of surgery, medicine, and critical care. The ability to ensure donor-recipient compatibility, and thus patient safety, because of increased understanding of canine and feline erythrocyte antigens has made transfusion medicine practical. However, the negative effects of blood products on the inflammatory, immune, and coagulation systems also have been further documented. Although blood products are a great resource when required, they also are often a finite resource and require a risk:benefit analysis before use. An understanding of current practices in transfusion medicine can help guide the practitioner to smart, safe, and successful use of blood products in the small animal patient.




Indications for Blood Products


Deciding on a “transfusion trigger” is patient dependent and requires careful review of historical, physical examination, and hematologic parameters. Factors to consider include the cause and chronicity of anemia, quantity and rapidity of blood loss, possibility of additional blood loss, and existing comorbidities. Although critically ill animals tend to tolerate anemia well, those with pulmonary or cardiac disease already may be at risk of hypoxemia. This may change the animal’s ability to tolerate anemia and thus alter the transfusion trigger for that animal. Key points to assess on physical examination include markers of intravascular volume status and peripheral tissue perfusion (e.g., mucous membrane color, capillary refill time, heart rate, pulse quality, arterial blood pressure, respiratory rate, and the presence of weakness or lethargy). Additional markers of impaired oxygen delivery, such as blood lactate concentration or central venous oxygen saturation, also may be helpful in determining a transfusion trigger.


Which blood product to administer depends largely on the aforementioned parameters along with the patient’s packed cell volume (PCV), hemoglobin concentration, total solids concentration, platelet count, and clotting profile. Blood products containing red cells should be considered if the hemoglobin concentration is 7 g/dl or less or the PCV is 20% or less. If surgery with significant blood loss is anticipated, the PCV transfusion trigger may be slightly higher. Products containing clotting factors should be considered if the prothrombin time or partial thromboplastin time is increased by 30% or more. Products containing platelets generally are indicated in animals with life-threatening hemorrhage due to severe thrombocytopenia or thrombocytopathia, in animals requiring massive transfusion, and in those with significantly decreased thrombopoiesis. When these general guidelines are used, it is important to remember that the entire clinical picture must be taken into account and that the decision to transfuse is highly patient dependent.



Types of Blood Products


Numerous blood products are available, and choice is based on the needs of the patient. Making an educated decision regarding which blood components are required helps conserve resources, limit transfusion reactions, and prevent other transfusion-related adverse effects. Categories of products to consider are discussed in the following sections.



Whole Blood


Fresh whole blood (FWB) and whole blood (WB) contain red blood cells (RBCs), white blood cells (WBCs), stable clotting factors, and plasma proteins. FWB also provides labile clotting factors (factor V and factor VIII) and some platelets if administered within a short time of collection. If FWB is not administered within the initial 24-hour time frame, it is termed whole blood. Both products are stored at 1° to 6° C (33.8° to 42.8° F). WB may be stored for up to 35 days but undergoes significant changes during this time. These changes include decreased concentrations of 2,3-diphosphoglycerate, which increases hemoglobin’s affinity for oxygen and thereby decreases offloading of that oxygen to the tissue. Older RBCs also develop other “storage lesions” that alter their biochemical structure and the efficacy of oxygen delivery. With time, storage products (e.g., ammonia, hydrogen ions, proinflammatory cytokines, potassium) also accumulate within the blood unit. Another option for administration of WB is autotransfusion, defined as the collection and subsequent reinfusion of the patient’s own shed blood. This can be a practical, cost-effective way to provide blood without placing a large demand on hospital resources. Autotransfusion should not be considered if the shed blood contains bacteria, urine, bile, or neoplastic cells. The recommended starting dose for WB is 10 to 20 ml/kg, or dose may be determined by using the formula that 2 ml/kg of WB will raise the PCV approximately 1%.


When clotting factors are not required and the total solids concentration is normal, packed red blood cells (pRBCs) may be considered in place of WB. Anemia is common in the critically ill due to decreased erythropoietin synthesis, resistance to erythropoietin, reduced RBC life span, blood loss, frequent blood sampling, and oxidative damage. Use of pRBCs should be considered in animals with normal total solids and clotting times (e.g., the critically ill, those with chronic anemia, those with hyperglobulinemia). Advantages of pRBCs include administration of less volume (6 to 10 ml/kg) without the unnecessary WBC and plasma proteins. pRBCs also tend to have a higher PCV than WB. Administration of lactated Ringer’s solution through the same line as the blood product should be avoided because calcium within the fluid precipitates with anticoagulants present in WB and pRBCs (acid citrate dextrose or citrate phosphate dextrose adenine).



Plasma


Fresh frozen plasma (FFP) is frozen at −18° C (−0.4° F) or colder within 6 hours of collection and contains all clotting factors, albumin, antiproteases, and immunoglobulins. If it is frozen for a year or longer, the labile clotting factors are no longer present and the product is termed frozen plasma (FP). Either FFP or FP can be used in cases of rodenticide intoxication, other vitamin K deficiencies, and hemophilia B (factor IX deficiency). FFP is preferred for liver disease–associated coagulopathy, hemophilia A (factor VIII deficiency), von Willebrand’s disease, and active hemorrhage associated with disseminated intravascular coagulation. To raise albumin levels significantly, plasma must be administered in large quantities (approximately 40 ml/kg to raise serum albumin 1 g/dl). The starting dose for plasma is 6 to 10 ml/kg; the product must be rewarmed slowly but temperature should not exceed 37° C (98.6° F).


FFP may be processed further to create cryoprecipitate, then stored at −18° C (−0.4° F) for up to 1 year. Cryoprecipitate contains von Willebrand’s factor, factor VIII, factor XIII, fibrinogen, and fibronectin. Indications for cryoprecipitate include von Willebrand’s disease, hemophilia A, and hypofibrinogenemia or dysfibrinogenemia. The dose is 1 unit per 10 kg. The portion of slowly thawed FFP that is not cryoprecipitate is termed cryo-poor plasma and contains factors II, VII, IX, and X. Cryo-poor plasma may be used for rodenticide intoxication, and the dose is 1 unit/10 kg.



Platelets


Although newer and rarely used in clinical practice, platelet-rich products are gaining attention and becoming available commercially. Clinical studies showing efficacy are in their infancy (Davidow et al, 2012), and therefore platelet component therapy should be considered clinically unproven in veterinary patients. As discussed previously, FWB contains a small number of platelets if administered shortly after collection. Platelet-rich plasma (PRP) is prepared from one unit of FWB and may be administered as PRP or further processed to obtain platelet concentrate (PC). PRP and fresh PC must be stored at room temperature with continuous gentle agitation and remain viable for up to 5 days, which makes their use cumbersome in clinical practice. Refrigeration quickly decreases platelet viability and results in rapid clearance from the circulation, and thus is not recommended.


A more practical alternative is cryopreserved platelets, which commonly are preserved in DMSO (dimethyl sulfoxide) at −80° C (−112° F) and have a shelf life of 6 months. Cryopreserved platelets are available commercially but demonstrate decreased viability and function compared with fresh PC. The dose is 1 to 2.5 units/10 kg, which may raise the platelet count as much as 20,000 to 40,000/µl. Due to the short platelet life span (5 to 7 days), repeat transfusions may be required and platelet alloantibodies may develop. Lyophilized platelets are freeze-dried in paraformaldehyde and can be stored at −80°  C (−112° F) for several years. Unfortunately, they must be resuspended before use and have an extremely short half-life, so that their use is limited strictly to control of active hemorrhage.

< div class='tao-gold-member'>

Related posts:

  1. Ventilator Therapy for the Critical Patient
  2. Lawn and Garden Product Safety
  3. ASPCA Animal Poison Control Center Toxin Exposures for Pets
  4. Diabetic Monitoring

Stay updated, free articles. Join our Telegram channel
Tags:
Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on Best Practices

Full access? Get Clinical Tree
Get Clinical Tree app for offline access