A variety of intravenous fluid and blood products are administered to children in the perioperative period. Indications include preoperative deficit replacement, ongoing maintenance requirements, fluid loss replacement, and treatment of anemia and hypovolemia. This chapter describes the use of these fluid and blood products in pediatric patients in the perioperative period.
Normal Fluid Requirements
Water Requirements
Water maintenance rates in children are based on studies that demonstrated a direct association between metabolic rate and water requirements. In general, water requirements on a per-kilogram basis increase with decreasing size of the child. This is secondary to the higher metabolic rate with decreasing size and the relatively greater evaporative loss from body surfaces in smaller children because of a higher ratio of body surface area to weight. Prematurely born infants have an even greater rate of evaporative loss because of thinner, more permeable, vascularized skin. In general, the amount of evaporative water loss per kilogram is inversely proportional to the gestational age.
In a very influential paper published in 1957, Holliday and Segar developed an easily remembered formula for calculating caloric requirements of the “average” hospitalized child (>2 weeks of age) based on bodyweight. They also demonstrated that the water requirement in milliliters was equal to the total energy expended (i.e., 1000 mL of water is required for every 1000 kcal expended). Thus the formula for caloric requirements can easily be used to calculate daily water requirements using the “4–2–1 rule” ( Table 14.1 ).
| Bodyweight (kg) | Maintenance Rate |
|---|---|
| 0–10 | 4 mL/kg/h |
| 11–20 | 40 mL+2 mL/kg/h for each kg over 10 kg |
| 21–70 | 60 mL + l mL/kg/h for each kg over 20 kg |
Subsequent studies during pediatric surgery demonstrated that intraoperative caloric and fluid requirements are less than those calculated by Holliday and Segar. Nevertheless, for the vast majority of healthy children undergoing surgery, these formulae will consistently prevent perioperative fluid and electrolyte abnormalities, and thus, are still in use today.
Electrolyte Requirements
For each 100 calories metabolized in 24 hours, the average child requires 3 mEq of sodium, 2 mEq of potassium, and 2 mEq of chloride. These recommendations are based on the approximate electrolyte concentration of human breast and cow’s milk, and the resulting normal urine osmolality after milk ingestion. In most otherwise healthy hospitalized children, these electrolyte requirements will be met by administering a solution of 0.2% sodium chloride with 20 mEq of added KCl per liter at the normal maintenance rate ( Table 14.2 ).
| Electrolyte | Amount |
|---|---|
| Sodium | 130 mEq |
| Potassium | 4 mEq |
| Calcium | 3 mEq |
| Chloride | 109 mEq |
| Lactate | 28 mEq |
In the perioperative period, it is necessary to replace surgical losses in addition to providing maintenance fluids and electrolytes. Therefore we commonly use solutions that contain a greater percentage of sodium. This better approximates the fluid that is associated with losses during surgery and avoids hyponatremia that would result from large infusions of a hypotonic fluid, especially in the face of an increase in antidiuretic hormone release caused by the stress of surgery. Lactated Ringer’s (LR) solution (or similar) meets these needs for the majority of surgical procedures in children. Normal saline contains 154 mEq/L of sodium and is preferred when replacing large amounts of isotonic fluid because LR is somewhat hypotonic.
Intraoperative Fluid Requirements
Intraoperative fluid administration is required to meet the body’s needs for ongoing losses secondary to metabolism and water and electrolyte losses caused by medical and/or surgical conditions. Additional fluid deficits are incurred during preoperative fasting and intraoperative evaporation and third-spacing.
Replacement of Preoperative Deficit
Normally, children presenting for elective surgical procedures have incurred a fluid deficit during the preoperative fasting interval. Although ingestion of clear liquids is often encouraged up to 1 or 2 hours before the scheduled procedure time, depending on institutional guidelines, many children have fasted for a longer time. Many pediatric anesthesiologists feel that this deficit should be replaced with isotonic fluid to compensate for anesthetic-induced vasodilatation and unexpected intraoperative or postoperative fluid and blood loss. Preoperative fasting deficits are calculated by multiplying the hourly maintenance rate by the number of hours the child fasted. Traditionally, 50% of this deficit is replaced in the first hour of intravenous hydration and 25% in each of the next 2 hours. For relatively short, minor surgeries, a volume of 4 mL/kg of isotonic solution has been suggested as an appropriate replacement volume that covers the preoperative deficit and intraoperative maintenance requirements.
Children presenting for emergency surgery may have increased fluid losses secondary to fever, vomiting, edema, and blood loss. Therefore these children should receive earlier and more aggressive volume replacement, until establishment of normal urine production (1–2 mL/kg/h). Keep in mind that aggressive fluid deficit replacement is associated with a decrease in core body temperature.
Glucose Administration
Because of the normal hyperglycemic response to surgery, healthy infants over about 1 month of age do not require addition of glucose to intraoperative maintenance fluids. Children at risk for intraoperative hypoglycemia include those less than a month of age, weight for age <5th percentile, ASA status ≥III, having a gastric or jejunal tube, poor feeding, and abdominal surgery. These children should have intermittent glucose checks during anesthesia. A 2% dextrose solution appears to provide the best balance between the risk for hypoglycemia and hyperglycemia, which may cause an osmotic diuresis.
The careful reader will note that the text recommends that a 2% glucose solution might be a good compromise for children at risk for hypoglycemia. But who has that readily available? It probably isn’t available commercially. Let’s take a deeper dive into how easy it is to create this solution in the OR by adding two grams of dextrose to 100 mL of LR or NS solution. This is a good time to digress and let you know that when you see the term “D5” on intravenous (IV) solutions, it means 5% dextrose in water, which means 5 grams per deciliter (100 mL). It also means 50 mg per mL. So, let’s say you want to make a 2% dextrose solution for a small infant, and you have a 50 mL vial of D50 in your anesthesia cart. Because D50 contains 25 grams of dextrose per 50 mL, you should add 4 mL (2 grams) to 96 mL LR (or NS) in the buretrol, which gives you D2. To digress even further, in general, we use the IV administration set with a buretrol for children below 9 years of age to prevent accidental administration of too much IV fluid at one time.
Hospitalized neonates, especially those born prematurely, will often be receiving increased amounts of glucose to compensate for limited glycogen reserves. Because most of these patients will demonstrate a hyperglycemic response to the stress of surgery, this author’s practice is to initially administer the same solution at half its original rate, check blood glucose values at least hourly, and readjust the rate if necessary. Normal saline or LR solution is then used to replace any deficit or intraoperative isotonic fluid loss.
Children who received clonidine premedication or neuraxial blockade before the surgical incision may not develop the intraoperative hyperglycemic stress response. These patients should receive a maintenance fluid that contains dextrose or should undergo intraoperative blood glucose monitoring at regular intervals.
Replacement of Intraoperative Fluid Losses
In addition to insensible losses and ongoing metabolic needs, fluid is lost intraoperatively as a result of evaporation from exposed tissues, “third-spacing,” and surgical blood loss. Third-spacing is the transfer of relatively isotonic fluid from the extracellular volume space to a nonfunctional interstitial compartment, and is triggered by surgical trauma, infection, burns, and other mechanisms of tissue injury. The amount of volume lost to the third space can be estimated based on experience with the particular type of surgery, observation of the surgical field, and the clinical response to volume replacement.
Insensible fluid losses during minor procedures will average less than 3 mL/kg/h. This value will increase based on the location and extent of the surgical injury. For example, a neonate undergoing an exploratory laparotomy for necrotizing enterocolitis and gangrenous bowel may require 50 to 100 mL/kg/h to maintain euvolemia. Most thoracic and neurosurgical procedures require 5 to 10 mL/kg/h.
Intraoperative fluid losses are replaced with an isotonic, nonglucose-containing solution such as LR, NS, or Plasmalyte. When using crystalloid to replace surgical blood loss, three times as much crystalloid solution should be administered as the amount of estimated blood lost. End points of intraoperative volume replacement include an appropriate blood pressure and heart rate, and adequate tissue perfusion as evidenced by a urine output near or above 1 mL/kg/h.
Massive amounts of replacement with each solution carry unique disadvantages. Because of its slightly hypotonic nature, large amounts of administered LR solution are associated with a decreased serum osmolality and development of edema. Large amounts of administered NS are associated with development of dilutional or hyperchloremic acidosis.
Postoperative Intravenous Fluids
In the 1980s it was recognized that some healthy children developed life-threatening hyponatremia after otherwise uncomplicated surgery. Much has been written on this topic with ample warnings about use of hypotonic solutions when not indicated. Unless specifically indicated, hypotonic solutions should not be used for maintenance fluids in children after surgery.
Blood Products
The most commonly administered blood products in the perioperative setting are packed red blood cells (RBCs), fresh frozen plasma (FFP), platelets, and cryoprecipitate. Fresh whole blood may also be used in special circumstances such as children less than 2 years old undergoing complex cardiothoracic surgery and children undergoing craniofacial surgery. For each blood product, a standard 150 to 260-micron blood filter is used for administration.
Pretransfusion Testing
Before a surgical procedure where blood loss is anticipated, a type-and-crossmatch will ensure compatible blood is available for the patient. Once a patient’s ABO (Rh) type is confirmed, an antibody screen will detect clinically significant antibodies that are likely to cause hemolysis. In the event that one of these antibodies (e.g., Rh, Duffy, Kell, Kidd) is confirmed, a donor red blood cell unit is prepared that is negative for that particular antigen. RBCs and platelets require specific ABO and Rh compatible blood ( Table 14.3 ). FFP requires ABO type compatible blood ( Table 14.4 ). In situations where a patient does not have a current or previous red blood cell antibody, an electronic or computer crossmatch can be used to detect ABO incompatibility.
| Blood Group | ABO Antigen on RBC | ABO Antibody in Plasma |
|---|---|---|
| A | A | Anti-B |
| B | B | Anti-A |
| O | None | Anti-A, Anti-B, Anti-AB |
| AB | A,B | None |
| Recipient ABO | First Choice | Second Choice |
|---|---|---|
| A | A | AB |
| B | B | AB |
| AB | AB | None |
| O | O | A, B, AB |
Cryoprecipitate and platelets may be given out of type, but platelet transfusions require special precautions for smaller volume patients where hemolysis because of incompatible anti-A or anti-B is more likely. In these cases, blood banks may volume-reduce or wash platelets when ABO type-specific or type-compatible platelets are unavailable or they may identify donors with low-titer anti-A and anti-B antibodies when minor ABO-incompatible platelets must be used. Also, platelets should be Rh-type compatible especially for Rh-negative females of childbearing age to prevent anti-D formation. The universal donor for red blood cells is O and the universal donor for plasma is AB. Platelets are considered a plasma product.
Fresh Whole Blood
Fresh whole blood (FWB) is available on a limited basis depending on the blood center. The definition of “freshness” is undetermined, but one study showed that whole blood <48 hours old may provide improved hemostasis and donor limitation for pediatric cardiothoracic patients compared with separate blood components. One recent study examined the use of O low titer anti-A and anti-B uncrossmatched FWB in injured children with hemorrhagic shock. Similar to other blood products, FWB must undergo standard infectious disease testing before administration. FWB may be manufactured as a leuko-reduced product, but if not, CMV-seronegative FWB should be considered for low birth weight premature infants.
Red Blood Cells
Because whole blood is transfused only under special circumstances, RBC concentrates are almost exclusively administered to correct anemia in pediatric surgical patients. In general, there are few differences between children and adults with regard to the indications for perioperative red blood cell (RBC) administration ( Table 14.5 ).
|
The primary objective of red cell administration is to enhance oxygen delivery to the peripheral circulation. A secondary objective is to maintain the circulating blood volume. Preoperative red cell transfusion before an elective surgical procedure is rarely justified, unless the patient is anemic and symptomatic. Although the incidence of postoperative apnea in premature infants is decreased when the hemoglobin level is >10 g/dL, red cell transfusion is not indicated with mild anemia (7–10 g/dL), provided adequate postoperative monitoring in an intensive care setting is available.
In children without preoperative anemia, intraoperative red cell administration is often based on attainment of the maximum allowable blood loss (MABL) ( Table 14.6 ):
MABL=Weight(kg)×EstimatedBloodVolume(EBV)×(Ho−H1)/HAV
| Age | EBV (mL/kg) |
|---|---|
| Premature infant | 90–100 |
| Full-term newborn | 80–90 |
| Infant 3 months to 1 year | 70–80 |
| Child >1 year of age | 70 |
The lowest acceptable hematocrit, H 1 , is determined before the onset of the surgical procedure and is based on the health of the child and the clinical situation. The estimated blood volume is calculated based on the patient’s age and size (see Table 14.6 ).
RBCs should be transfused with an end-point of achieving an improvement of clinical symptoms. Most preparations of red cell concentrates have a hematocrit between 55% and 75%, depending on the storage solution. Washed or plasma-reduced RBCs will have a hematocrit of <80%. On average, 10 mL/kg of packed RBCs will increase the hemoglobin by 2 to 3 g/dL. Most pediatric transfusions range between 10 and 15 mL/kg. Larger volumes may be required during periods of hypovolemic shock, or when acute blood loss is >15% total blood volume.
There are several types of preservative solutions that will prolong the shelf life of RBCs to 42 days. Each contains a variable amount of adenine, citrate, dextrose, and phosphate. Some contain mannitol. As the duration of blood storage increases, the amount of extracellular potassium increases, the pH decreases, and red cell levels of 2, 3-diphosphoglycerate decrease. Prior concerns for hepatic toxicity with adenine and renal toxicity with mannitol are based on animal studies. The literature is inconclusive for the adverse effects of additive solutions with regard to large volume transfusions in humans, and many hospitals report safe blood transfusions with additive solutions for large volume transfusions including ECMO patients. For most children with simple small volume transfusions (<15 mL/kg), many hospitals are routinely using additive solutions without the need for additional washing. In cases where more massive transfusion is anticipated or rapid transfusion is administered through a central line, fresh RBC concentrates are often used to mitigate the risk for a hyperkalemic reaction. Institutional protocols for “freshness” vary from 5 to 21 days old. Because blood banking procedures differ between institutions, anesthesiologists should be familiar with their hospital’s specific storage procedures for children ( Table 14.7 ).
| Component | Storage Temperature | Shelf Life |
|---|---|---|
| Whole blood | 1–6° C | 35 days |
| RBCs | 1–6° C | 35–42 days |
| Platelets | 20–24° C | 5 days |
| FFP | < –18° C | 1 year |
| Cryoprecipitate | < –18° C | 1 year |
Massive Transfusion
Massive transfusion is defined as the acute administration of one or more blood volumes. Complications of massive transfusion in pediatric patients include dilutional thrombocytopenia, disseminated intravascular coagulation (DIC), hypothermia, metabolic acidosis, hyperkalemia, hyperglycemia, hypocalcemia, and volume overload.
In the emergency transfusion situation, uncrossmatched type O red blood cells may be administered before a completed type-and-crossmatch. Because O red blood cells are a scarce resource, patients may be safely switched back to their own blood type providing there is no evidence of donor antibodies in the patient’s plasma or on the patient’s red blood cells. A direct antiglobulin test (DAT) will help determine whether antibody is present on the patient’s cells. Although type-specific blood is preferred, because of ABO shortages or preference for direct donation with a compatible but not type specific donor, O red blood cells may be used. Also, O red blood cells may be used for neonates with evidence of hemolytic disease of the newborn or with maternal anti-A, anti-B, or anti-A,B antibodies present. Even with residual plasma in anticoagulated blood with preservatives, washing is often not indicated when O red blood cells are used, especially in emergent situations. This is because of the very low residual titer of any anti-A and anti-B in the plasma when red blood cells are stored in additive solutions.
Fresh Frozen Plasma
Fresh frozen plasma (FFP) is administered to correct bleeding secondary to a documented or presumed coagulation factor deficiency. A prothrombin test (PT) or activated partial thromboplastin time (aPTT) may indicate the need for FFP, but often the turnaround time for these tests is inadequate for decision making in the OR. Some hospitals have implemented thromboelastography (TEG) testing as a more rapid point-of-care test to determine coagulopathy in the surgical patient. TEG may be particularly useful for cardiothoracic or liver transplant cases to predict bleeding. In the absence of TEG, the anesthesiologist relies on clinical evidence of bleeding and estimated blood loss as a high probability of a coagulopathy. The most common perioperative cause of coagulation factor deficiency is dilutional, as a result of massive transfusion of crystalloid or RBCs, especially in neonates. FFP is not indicated for volume expansion without coagulation abnormalities. References values for TEG in pediatric patients have been published.
The dose of FFP will depend on the desired correction of coagulation factor activity. In general, the minimum blood activity level of coagulation factors for physiologic hemostatic effects is approximately 25% of the normal level. The appropriate dose of FFP that will raise the level of coagulation factors to 25% can be determined by first calculating the plasma volume:
PlasmaVolume(mlkg)=[Totalbloodvolume(mlkg)×(1−hematocrit)]
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