Blood Product Dosages
The aim of transfusion in the anemic patient is not to return the packed cell volume to normal values but to correct the clinical signs. The appropriate volume of blood must be administered to each patient. Specific component therapy should be utilized to treat each disorder and the patient’s cardiovascular status should always be assessed prior to determining the required volume and administration rate. The volume of blood administered is dependent on the presence of active bleeding, onset and degree of anemia, clinical status of the patient and body weight. For practical purposes, feline patients initially receive one unit of whole blood (40–50 mL) or one unit of PRBC (20–25 mL) or one unit of fresh-frozen plasma (20–25 mL). The following dosages are used to determine the required blood component volume in dogs:
- 10-20 ml/kg = ml WB needed,
- 6-10 ml/kg = ml PRBC needed,
- 6-10 ml/kg = ml plasma needed.
Because blood is a colloid solution, vascular overload is a potential complication. Clinical signs include coughing (as a result of pulmonary edema), dyspnea, cyanosis, tachycardia and vomiting. If volume overload is of concern, blood administration should, at the very least, be temporarily discontinued and supportive care instituted.
Blood Product Preparation
Refrigerated blood may be gently warmed by allowing it to sit at room temperature for approximately 30 minutes. Properly administered cold blood will not increase the chance of a transfusion reaction, but large amounts of cold blood given at a rapid rate can induce hypothermia and cardiac arrhythmias. Routine warming of red cell products is not recommended except in neonates, hypothermic patients and with massive transfusion. Several types of blood warmers are commercially available. In an emergency situation, the tubing of the administration set can be placed in a warm water bath, not to exceed 37°C, so that warming can occur as blood passes through the tubing. The entire unit should not be immersed in the bath. Frozen products should also be thawed in a 37°C warm water bath. Once thawed, products should remain at 37°C for no longer than 15 minutes to minimize the degradation of certain coagulation factors. No blood product should be exposed to temperatures exceeding 42°C as it will result in damage to red blood cells and denaturation of blood proteins. Once refrigerated or frozen products are brought to room temperature, they should not be rechilled. Warming red cell products or thawing plasma products in a microwave oven is not recommended.
Blood and blood components can be administered via the intravenous or intraosseous route. Intravenous is obviously the most effective route in that the infused red blood cells or plasma products are immediately available to the general circulation. The intraosseous route is utilized in puppies or kittens when vascular access is difficult or unsuccessful. When delivering blood products intraosseously, infused cells and proteins are available to the general circulation within minutes. The most common sites for intraosseous catheter placement are the trochanteric fossa of the femur, the wing of the ilium and the shaft of the humerus. Care should be taken in the placement of these catheters due to the increased risk of osteomyelitis.
Blood product administration rates are variable. The desirable rate of infusion depends upon the patient’s blood volume, cardiac status and hemodynamic condition. For example, a patient with massive hemorrhage may require a more rapid transfusion than a normovolemic patient with a chronic anemia. The maximum rate of transfusion for a normovolemic patient (where circulatory overload is a potential problem) is 11–22 ml/kg/hr, while hypovolemic patients can tolerate rates of 22–66 ml/kg/hr. If rapid transfusion is needed, blood can be infused as rapidly as the patient’s circulatory system will tolerate, within a few minutes, if the rate does not cause the red cells to hemolyze. Cardiovascularly compromised animals cannot tolerate infusion rates that exceed 4ml/kg/hr. In general, a blood transfusion should be completed within four hours to ensure administration of functional blood components and to prevent growth of bacteria in the event of contamination. Maximum time should not be confused with recommended time; most transfusions are completed within two hours. Most feline transfusions may be safely completed in one hour, with the exception of cats with heart failure.
It is recommended for all patients that blood components be infused slowly (e.g., 1 ml/kg) for the first 10 to 15 minutes while closely observing for signs of an acute transfusion reaction. The blood product should then be infused as quickly as will be tolerated, but should not take longer than four hours. Before infusion, baseline values of attitude, rectal temperature, pulse rate and quality, respiratory rate and character, mucous membrane color, capillary refill time, hematocrit, total plasma protein and plasma and urine color should be monitored. The majority of these parameters should be checked every 30 minutes during transfusion and evaluated routinely post-transfusion to ensure the desired effect has been achieved.
All blood products should be filtered to help prevent thromboembolic complications. Standard blood infusion sets have in-line filters with a pore size of approximately 170–260 microns. A filter of this size will trap cells, cellular debris and coagulated protein. Trapped debris combined with room temperature conditions may promote proliferation of any bacteria that may be present; therefore, blood infusion sets may be used for several units of blood products or for a maximum time of four hours. Micoraggregate filter systems with a pore size of 20–40 microns may be used for low-volume transfusion (i.e., < 50 ml whole blood, < 25 ml pRBC or plasma).