Page 288 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Metabolic Acid-Base Disorders 279

Renal In another report, hypokalemia was found in only 5% of
Tubular fluid tubular cell Blood dogs with pituitary-dependent hyperadrenocorticism but
in 45% of those with adrenocortical neoplasia. 158 Ahigh
rate of secretion of cortisol and other corticosteroids,
suchasdesoxycorticosterone andcorticosteroneinpatients
Na + with adrenocortical malignancies, could be responsible
for hypernatremia, hypokalemia, and metabolic alkalosis
in adrenal-dependent hyperadrenocorticism.
Cl –
Miscellaneous
Large doses of penicillin, ampicillin, or carbenicillin
administered as a sodium salt can lead to hypokalemia
and metabolic alkalosis in human patients. The drug
may increase lumen electronegativity in the distal neph-
ron by acting as a nonresorbable anion and enhancing
þ
þ
Na + Na -H þ and Na -K þ exchange. “Refeeding” alkalosis
K + can occur in human patients when glucose is administered
after prolonged fasting. The mechanism for this type of
alkalosis is unknown. These types of metabolic alkalosis
Na + have not been reported in the veterinary literature.
H + HCO 3 –
TREATMENT OF METABOLIC
ALKALOSIS
H 2 CO 3
H O + CO
2 2
Acid-basedisturbancesaresecondaryphenomena.Diagno-
sis and definitive treatment of the responsible disease pro-
Approximate filtered loads cess are integral to the successful resolution of acid-base
(10-kg dog with GFR 4 ml/min/kg) disorders. However, it must be remembered that alkalosis
persists until chloride is replaced if vomiting of stomach
Na + 8352 mEq/day contents or diuretic administration is responsible for the
Cl – 6336 mEq/day metabolic alkalosis. The goal of treatment in chloride-
HCO 3 – 1210 mEq/day
K + 230 mEq/day responsive metabolic alkalosis is to replace the chloride def-
Figure 10-13 Effects of chloride and potassium depletion on icit while providing sufficient potassium and sodium to
acid-base balance. See text for explanation. (Drawing by Tim Vojt.) replace existing deficits. Definitive treatment of the under-
lyingdiseaseprocess(e.g.,removalofagastricforeignbody)
prevents recurrence of the metabolic alkalosis.
Hyperadrenocorticism Patients with chronic pulmonary disease that have
Metabolic alkalosis occurs in approximately one third of hypoxemia and hypercapnia are at greater risk from met-
human patients with Cushing’s syndrome. 104 It is more abolic alkalosis than others because superimposition of
common in patients with adrenocortical carcinomas metabolic alkalosis can further reduce ventilation and lead
and in those with ectopic production of ACTH by to worsening of hypoxemia. Thus, metabolic alkalosis
nonadrenal malignancies than in those with pituitary- should be treated appropriately if present and avoided if
dependent hyperadrenocorticism. The frequency of met- not present. Giving oxygen to patients with metabolic
abolic alkalosis and serum electrolyte disturbances in dogs alkalosis should also be avoided if possible because
with hyperadrenocorticism is uncertain. Serum sodium this may impair ventilation and further aggravate
and potassium concentrations often are normal in dogs hypercapnia.
with hyperadrenocorticism. This may reflect the fact Potassium without chloride (e.g., potassium phos-
that 80% to 85% of dogs with hyperadrenocorticism have phate) corrects neither the alkalosis nor the potassium
pituitary-dependent disease. In a large group of dogs with deficit because administered potassium is excreted in
hyperadrenocorticism, 21 of 52 (40%) dogs had increased the urine. A chloride salt must be given for alkalosis to
serum sodium concentrations and 25 of 52 (48%) be resolved and potassium retention to occur. Provision
had decreased serum potassium concentrations. 139 of chloride as either the sodium or potassium salt corrects
The relative frequency of pituitary- and adrenal-depen- chloride-responsive metabolic alkalosis. This therapy
dent disease was not reported in this study. In another allows the kidneys to reabsorb the sodium the body
study,mildhypernatremiaandhypokalemiawereobserved requires with chloride to maintain electroneutrality.
occasionally in dogs with hyperadrenocorticism, and total Thus, a NaCl solution (0.45% or 0.9%) with added KCl
CO 2 content was increased in 33% of affected dogs. 188 is the fluid of choice for dogs and cats with chloride-