محاسبه حجم خون ازدست رفته در اطفال Pourfarokh m. MD, Anesthesiologist, fellowship in pain management

Packed Red Blood Cells Historically, the use of blood products in pediatric surgical patients has greatly diminished because of the fear of transmission of disease—particularly human immunodeficiency virus (HIV). Because HIV, hepatitis B virus (HBV),hepatitis C virus (HCV), and a number of other disease causing viruses can be transmitted with as little as 10 mL of packed red blood cells (PRBCs), the administration of any blood product requires clear, medically defensible clinical indications that are preferably recorded on the anesthetic record When caring for children, the emphasis should be on blood volumes and portions of blood volumes lost, rather than units, because a unit of blood may constitute several blood volumes in a preterm infant but only a fraction of the blood volume of a robust teenager.

Maximal allowable blood loss (MABL) MABL takes into account the effect of patient age, weight, and starting hematocrit on blood volume. In general, blood volume is approximately 100 to 120 mL/kg for a preterm infant, 90 mL/kg for a fullterm infant, 70 to 80 mL/kg for a child 3 to 12 months old, and 70 mL/kg for a child older than 1 year of age. estimated blood volume (EBV) MABL = EBV × (Starting hematocrit ‐ Target hematocrit)/Starting hematocrit MABL = (15 × 70) × [(38 − 25) ÷ 38] = 1050 ÷ 38 = ∼ 360mL

The MABL would be replaced with 3 mL of lactated Ringer solution per milliliter of blood loss; If blood loss is less than or equal to the MABL and no further significant blood loss occurs or is anticipated in the postoperative period, then there is no need for transfusion of PRBCs. There is sufficient time to make the decision to transfuse by observing postoperative urinary output, heart rate, respiratory rate, and overall cardiovascular stability. The development of lactic acidosis is a late sign of inadequate oxygen-carrying capacity.

Hematocrit values in the low 20% range are generally well tolerated by most children, the exception being preterm infants, term newborns, and children with cyanotic congenital heart disease or those with respiratory failure in need of high oxygen-carrying capacity. Because the incidence of apnea is high in neonates and preterm infants who have hematocrit values less than 30%, the minimal target hematocrit should be discussed with the surgeon and neonatologist. Older children with a history of sickle cell disease may require preoperative transfusion and should be managed in conjunction with their attending hematologist.

As an example, the following simple formula may be used for intraoperative or postoperative estimation of the volume of PRBCs needed in a 15-kg child with a hematocrit (Hct) of 20%: Volume of PRBCs to be transfused = [Desired Hct (35) − Present Hct (20) × EBV (70mL/kg × 15kg)]/Hct of PRBCs( ∼ 60%) (35 − 20) × (70 × 15)/60 = ∼ 262 mL PRBCs

Fresh Frozen Plasma Fresh frozen plasma (FFP) is administered to replenish clotting factors lost during massive blood transfusion (usually defined as blood loss exceeding 1 blood volume), for disseminated intravascular coagulopathy, or for congenital clotting factor deficit. Children with known clotting factor deficits, such as those with massive thermal injury or coagulopathy, may require transfusion of FFP before blood loss exceeds 1 blood volume. Despite the loss of 1 blood volume, prolongation of the prothrombin time (PT) and the partial thromboplastin time (PTT) will only be minor. This generalization applies to children given PRBCs; children given whole blood will not need FFP, even when blood loss exceeds several blood volumes.

Blood loss exceeding 1 to 1 Blood loss exceeding 1 to 1.5 blood volumes (replaced entirely with PRBCs and crystalloid, albumin, or other non–blood-related products) often necessitates a transfusion of FFP. However, the decision to administer FFP should be based on observed coagulopathy or documented prolongation of the PT and PTT values. However, if the clotting factor deficit is associated with abnormal oozing, then a PT exceeding 15 seconds (international normalized ratio [INR] >1.4) or a PTT greater than 60 seconds (>1.5 times baseline) warrants close observation. Usually an INR <2 does not warrant correction.

If these abnormalities exist but oozing does not occur and the surgical field is relatively safe from the complications of hematoma formation, as in orthopedic surgery versus neurosurgery, then it seems appropriate to observe the child and withhold the transfusion of FFP. The volume of FFP required to correct prolongation of the PT and PTT values depends on the severity of the clotting factor deficit and the presence or absence of consumptive coagulopathy. In general, FFP therapy may require replacement of 30% or more of the child’s blood volume.

Transfusion of FFP at rates exceeding 1 mL/kg/min is sometimes followed by severe ionized hypocalcemia and cardiac depression with hypotension, especially if FFP is administered during anesthesia with a potent inhaled anesthetic. Therefore exogenous calcium chloride (2.5 to 5 mg/kg) or calcium gluconate (7.5 to 15 mg/kg) should be administered, preferably through a separate IV, during rapid transfusion of FFP. Ionized hypocalcemia occurs very frequently in neonates given FFP, possibly because of their decreased ability to mobilize calcium and metabolize citrate. Children undergoing liver transplantation or those with compromised hepatic function or perfusion may also be at increased risk because of a decreased ability to metabolize citrate.

Platelets Thrombocytopenia may occur as a result of disease processes (e.g., idiopathic thrombocytopenic purpura, chemotherapy, infection, disseminated intravascular coagulopathy) or dilution during massive blood loss. Children whose platelet count has decreased because of idiopathic thrombocytopenic purpura or chemotherapy generally tolerate platelet counts as low as 15,000/ mm3 without a need for platelet transfusion. In contrast, children whose platelet count has decreased because of dilution (massive blood loss) generally require platelet transfusion when the count is ∼50,000/mm3

However, in the author’s experience, the preoperative platelet count has been extremely valuable in predicting intraoperative platelet requirements. Children who begin surgery with a normal platelet count (150,000 to 350,000/mm3) usually do not require platelet transfusion until two blood volumes or more are lost. Clinical oozing is the typical indication for platelet transfusion, unless the potential for bleeding would be critical to survival, such as during neurosurgery, cardiac surgery, or major organ transplantation.

The initial volume of platelets transfused is approximately 0. 1 to 0 The initial volume of platelets transfused is approximately 0.1 to 0.3 U/kg; the increase in platelet count achieved with this amount of transfusion varies considerably and depends on the presence or absence of platelet antibodies and the rate of platelet consumption.