- 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
- 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 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.
Signs of Fluid Loss (Hypovolemia)....
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