Fluid therapy during the operative procedure is a joint responsibility of the surgeon and the anesthesiologist. Except in unusual circumstances, anemia, hemorrhage, and shock should be treated preoperatively. During the operation transfusions should be used with caution as there can be significant risks associated with transfusions. Most patients can withstand up to 500 mL of blood loss without difficulty. However, in operative procedures known to require several units of blood, the blood should be replaced as lost as estimated from the quantity of blood within the operative field, the operative drapes, and the measured sponges and suction bottles. The intravascular volume can be expanded by cross matched packed red blood cells, specifically indicated for their oxygen-carrying capacity, when the hematocrit (Hct) is ≤23 to 25 percent or the hemoglobin (Hb) is ≤7 g/dL. In emergency situations when blood is not available, synthetic colloids (dextran or hydroxyethyl starch solutions), albumin, or plasma may be administered to maintain an adequate expansion of blood volume. All blood products are used with caution because of the possibility of transmitting homologous viral diseases. Infusions of Ringer's lactate (a balanced electrolyte solution), via a secure and accessible intravenous catheter, should be used during all operative procedures, including those in pediatrics. Such an arrangement allows the anesthesiologist to have ready access to the cardiovascular system, and thereby a means of administering drugs or treating hypotension promptly. Additionally, large centrally placed catheters may be used to monitor central venous pressure or even cardiac performance if a pulmonary artery catheter is placed into the pulmonary vasculature. As many modern anesthetic agents may produce vasodilation or depression of myocardial contractility, anesthesiologists may volume load patients with crystalloid solutions. This maintains normal hemodynamic parameters and a good urine output. However, this fluid loading may have serious after effects in some patients; thus the anesthesiologist must monitor the type and volume of fluids given to the patient during the operation and communicate this to the surgeon.