Chapter 29

• Although the intravascular half-life of a crystalloid solution is 20–30 min, most colloid solutions have intravascular half-lives between 3 and 6 h.
• Patients with a normal hematocrit should generally be transfused only after losses greater than 10–20% of their blood volume. The exact point is based on the patient’s medical condition and the surgical procedure.
• The most severe transfusion reactions are due to ABO incompatibility; naturally acquired antibodies can react against the transfused (foreign) antigens, activate complement, and result in intravascular hemolysis.
• In anesthetized patients, an acute hemolytic reaction is manifested by a rise in temperature, unexplained tachycardia, hypotension, hemoglobinuria, and diffuse oozing in the surgical field.
• Transfusion of leukocyte-containing blood products appears to be immunosuppressive.
• Immunocompromised and immunosuppressed patients (eg, premature infants and organ transplant recipients) are particularly susceptible to severe cytomegalovirus (CMV) infections through transfusions. Such patients should receive only CMV-negative units.
• The most common cause of bleeding following massive blood transfusion is dilutional thrombocytopenia.
• Clinically significant hypocalcemia, causing cardiac depression, does not occur in most normal patients unless the transfusion rate exceeds 1 U every 5 min.
• The most consistent acid–base abnormality after massive blood transfusion is postoperative metabolic alkalosis.

All patients except those undergoing the most minor surgical procedures require venous access and intravenous fluid therapy. Some patients may require transfusion of blood or blood components. Maintenance of a normal intravascular volume is highly desirable in the perioperative period. The anesthesiologist should be able to assess intravascular volume accurately and to replace any fluid or electrolyte deficits and ongoing losses. Errors in fluid replacement or transfusion may result in considerable morbidity or even death.

Clinical evaluation and assessment of intravascular volume must generally be relied upon, because measurements of fluid compartment volumes are not readily available. Intravascular volume can be assessed using physical or laboratory examinations or with the aid of sophisticated hemodynamic monitoring techniques. Regardless of the method employed, serial evaluations are necessary to confirm initial impressions and guide fluid therapy. Moreover, modalities should complement one another, because all parameters are indirect, nonspecific measures of volume; reliance on any one parameter may be erroneous and, therefore, hazardous.

### Physical Examination

Physical examination is most reliable preoperatively. Invaluable clues to hypovolemia (Table 29–1) include skin turgor, the hydration of mucous membranes, fullness of a peripheral pulse, the resting heart rate and blood pressure and the (orthostatic) changes from the supine to sitting or standing positions, and urinary flow rate. Unfortunately, many drugs used during anesthesia, as well as the physiological effects of surgical stress, alter these signs and render them unreliable in the immediate postoperative period. Intraoperatively, the fullness of a peripheral pulse (radial or dorsalis pedis), urinary flow rate, and indirect signs, such as the response of blood pressure to positive-pressure ventilation and the vasodilating or negative inotropic effects of anesthetics, are most often used.

Table 29–1. Signs of Fluid Loss (Hypovolemia)....

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