Page 432 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

422 FLUID THERAPY

81
D-form. It is stated on the bag of LRS that it should little change in blood pressure, but in a patient that is
not be used in patients with a lactic acidosis, but infu- already hypovolemic, dramatic decreases in blood pres-
sion of LRS was not associated with an increase in sure can be seen (Figure 17-2). 158 Acetate-containing
blood lactate concentrations even when there was solutions also are contraindicated in patients with diabetic
considerable impairment of hepatic function. 50,71 ketoacidosis because they tend to increase blood ketone
However, hepatic removal of lactate is a saturable pro- concentrations. 4
cess, and infusion of lactate in patients with severe
hyperlactatemia (>9 mmol/L) may result in an 5% DEXTROSE
increase in blood lactate concentration. 130 However, Five percent dextrose in water contains no electrolytes,
at concentrations of lactate greater than 9 mmol/L, and only water remains when the dextrose is metabolized.
the peripheral tissues remove more lactate than the Five percent dextrose may be the solution of choice for
liver, and peripheral metabolism of lactate is not satu- patients that have suffered from pure water loss, but it
rable. 130 In clinical patients with initial lactate is rarely indicated as the prime replacement solution dur-
concentrations greater than 10 mmol/L, infusion of ing anesthesia and surgery. Apart from the fact that the
LRS and other volume support was always associated volume of distribution of the 5% dextrose is likely to be
with a decrease in blood lactate concentrations. 30 larger than that of a balanced electrolyte solution (which
Some patients with cancer may be hyperlactatemic would result in a diminished ability to maintain
and have increased ability to recycle lactate to glu- circulating volume), the glucose itself may be detrimental
cose. 192 In some patients with cancer cachexia, con- in certain circumstances. 150 In both acute renal and acute
cern has been expressed that the metabolism of cerebral injury, high concentrations of glucose may be
108,115,128
lactate consumes energy and thus lactated solutions detrimental. Concentrations of glucose more
should not be used. It has been shown that dogs with than 200 mg/dL may be of concern in animals with cere-
lymphoma have a transient inability to cope with the bral ischemia. 108,115
lactate load imposed by infusion of LRS. 186 Although
this finding may be valid in unusual cases, the amount 2.5% DEXTROSE IN
of lactate provided with LRS at 10 mL/kg/hr is HALF-STRENGTH IONIC SOLUTION
approximately 36% of the basal production or utiliza- Dextrose (5%) can be mixed with any of the preceding
tion rate, and it is likely that any negative effect is ionic solutions in a 1:1 ratio to halve the ionic strength.
transient. 3 Such solutions may be of use in the management of
The metabolism of lactate is either by gluconeogenesis patients with hypernatremia. These solutions are
or by oxidation, and hydrogen ions are consumed in both designed to increase the free-water content of the body,
instances. It takes approximately 30 minutes for this and it is important to monitor electrolyte concentrations
alkalinizing effect to be accomplished. 81 The alkalinizing to ensure that excessive dilution does not occur.
effect is not as great as that seen with acetate (approxi-
mately 50%).
ACETATED POLYIONIC SOLUTIONS
300
It is thought that acetate is metabolized rapidly through-
out the body, and the alkalinizing effect of this solution is
Acetate solution bolus
more readily available. As with lactate, the effect takes
approximately 30 minutes to be evident. 81 In some com-
mercial solutions, gluconate also is used. There is little Systolic
information on the effects of gluconate, but it does Arterial BP (mm Hg) 150
appear to cause a slight increase in pH. 104 Acetated Mean
Ringer’s solution suffers from the same disadvantage as
LRS in terms of its sodium content, but some of the com-
Diastolic
mercial solutions have higher sodium content and
osmolalities (e.g., Plasmalyte-148, Na ¼ 140 mEq/L
and osmolality ¼ 294 mOsm/L), and these are much 0
5 10 16 20
closer to the reference intervals in dogs and cats. Many
Minutes
of the commercial solutions are calcium-free and can be Figure 17-2 Administration of an acetated solution (Plasma-Lyte
given through the same line as blood products. The main 148) to a 16-kg dog being anesthetized for cataract surgery. The
disadvantage of solutions containing acetate is the vasodi- 50-mL bolus was given before the start of surgery. Hypotension
latation that can occur with rapid administration. 75,92 In occurred, and the dog was given 0.5 mg/kg of epinephrine
a normal healthy patient, a bolus of acetated polyionic intravenously when the mean pressure had leveled off at 33 mm Hg
solution usually results in an increase in heart rate but (approximately 10 minutes).