PHOTO BY GREGORY KINDRED
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Few people would argue that perioperative fluid therapy is an integral part of anesthesia and surgery; however, perioperative
fluid therapy in dogs and cats is in dire need of focused investigation and reappraisal. Dehydration, oliguria, and hypotension
prompt bolus fluid administration (fluid challenge) in surgical candidates to improve cardiac output and tissue perfusion
and to promote diuresis. Yet very little, if any, data on the safety and efficacy of this fluid challenge have been generated
from awake or anesthetized animals with naturally occurring disease.
Perioperative fluid therapy in people is known to have a direct bearing on outcome measures, including length of hospitalization,
morbidity, and mortality.1-4 Errors in fluid management (usually fluid excess, or overload) in human surgical candidates have been identified as the
most common cause of perioperative morbidity and mortality.1-4 Studies conducted in people concluded that a gain of 5% to 10% body weight from fluid therapy is associated with worsening
organ function in critically ill ICU patients and worse postoperative outcomes after routine surgery, with no evidence of
beneficial effects on renal function.4 These conclusions have important implications for current fluid replacement procedures and are likely to be equally important
in animals.
Traditional approach
Most contemporary authors recommend administering a "balanced" electrolyte solution (lactated Ringer's solution) or a 0.9%
sodium chloride solution at rates ranging from 10 to 15 ml/kg/hr for the duration of a surgical procedure in anesthetized
dogs and cats.5-9 Interestingly, the term balanced is never defined, and the rationale for administering fluids at 10 to 15 ml/kg/hr is never justified or defended. Furthermore,
specific details are often not included about how to administer fluids to treat perioperative blood loss and hypotension (systolic
pressure < 80 to 90 mm Hg; mean pressure < 60 mm Hg), even though blood loss is integral to surgery, and hypotension occurs
in more than 25% of anesthetized dogs and more than 30% of anesthetized cats.6-9-14
This traditional "recipe-based" approach to perioperative fluid therapy is outdated. Although arguably founded on a concern
for maintaining physiologic functions and replacing insensible fluid losses, it does not consider hemoglobin concentration,
the duration of surgery, fluid loss from fasting or into traumatized tissues or surgical wounds, and, most important, anesthetic-imposed
problems associated with monitoring and treating intravascular volume deficits.
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