Page 320 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Mixed Acid-Base Disorders 311

metabolic acidosis and metabolic alkalosis are shown in additive effect lowering the pH because the normal com-
Box 12-6. The pH usually is normal in these settings, pensation for metabolic acidosis is impaired because of

and treatment of stable patients should be directed at pulmonary disease. The [HCO 3 ] is low; PCO 2 is normal
resolving the underlying disease processes. Patients with or high; and the resultant pH can be dangerously low.
lactic acidosis and severe volume depletion need more Dogs, cats, and human patients with cardiopulmonary
aggressive therapy. arrest typically develop lactic acidosis as a result of low car-
diac output and hypoventilation. 32,39,58 During resusci-
DISORDERS WITH ADDITIVE EFFECTS tation, however, arterial blood gases may indicate a
ON pH normal pH with mixed metabolic acidosis and respiratory

Mixed disorders composed of primary problems with an alkalosis and not reflect the ongoing marked reduction in
additive effect on pH always have abnormal pH. mixed venous and tissue pH. Mixed venous blood should
Depending on the combination of primary problems, be used for analysis in this setting. 58 In addition to being
the pH can be dangerously high or low and requires better for assessing global tissue perfusion and cardiac
immediate attention. Box 12-7 shows examples of poten- output, venous pH and PCO 2 will change earlier and to
tial causes of additive mixed acid-base disorders. a greater extent than arterial values during periods of cir-
culatory insufficiency. 44 Patients with pulmonary edema
Respiratory Acidosis and Metabolic Acidosis may develop hypoxemia and lactic acidosis. 57 The situa-
This combination of acid-base disturbances may occur in tion is worse in patients in which pulmonary edema is sec-
a variety of settings usually in patients with acute severe ondary to heart failure. Low cardiac output compromises
respiratory compromise (e.g., thoracic trauma, pulmo- tissue perfusion, worsening the lactic acidosis. 40 Dogs in
nary edema, cardiopulmonary arrest, acute neuromuscu- septic shock usually demonstrate respiratory alkalosis and
lar junctional disruption such as with toxic or metabolic metabolic acidosis. Later in the course of the disease pro-
or junctionopathies) that also have lactic acidosis as cess, however, patients may develop respiratory acidosis
a result of hypoxemia, shock, or poor cardiac output because of ventilation-perfusion (V/Q) mismatch. 23,26
(see Box 12-7). Thus metabolic acidosis usually is caused Dogs with gastric dilation-volvulus complex also can
by an increase in unmeasured strong ions. There is an present with metabolic acidosis caused by lactic acidosis

BOX 12-7 Examples of Potential Causes of Additive Mixed
Acid-Base Disorders

Mixed Respiratory and Metabolic Disorders Severe canine babesiosis caused by Babesia canis rossi
Parvovirus gastroenteritis and sepsis
Respiratory Acidosis and Metabolic Acidosis
Hypoadrenocorticism-like syndrome in dogs with Mixed Metabolic Disorders
gastrointestinal disease
Cardiopulmonary arrest Hyperchloremic and High-Anion Gap Metabolic
Severe pulmonary edema Acidoses
Thoracic trauma with hypovolemic shock Renal failure
Low cardiac output heart failure with pulmonary edema Resolving diabetic ketoacidosis
Advanced septic shock (V/Q mismatch) Diarrhea complicating high-anion gap acidosis
Gastric dilatation-volvulus Severe canine babesiosis caused by Babesia canis rossi
Acute tumor lysis syndrome Mixed High-Anion Gap Acidoses
Gastrointestinal endoscopy*
Diabetic ketoacidosis and renal failure
Venom of the scorpion Leiurus quinquestriatus
Diabetic ketoacidosis and lactic acidosis
Neurotoxic poisons and metabolic conditions disrupting
Ethylene glycol intoxication with lactic acidosis
neuromuscular junction function
Uremic acidosis and other high-anion gap acidosis
Respiratory Alkalosis and Metabolic Alkalosis Mixed Normal-Anion Gap Metabolic Acidosis
Gastric dilatation-volvulus
Fluid therapy with fluids rich in chloride (e.g., lactated
Hyperadrenocorticism with pulmonary thromboembolism Ringer’s solution, 0.9% NaCl) in a patient with
Respirator-induced mixed alkalosis (correction of PCO 2 too hyperchloremic acidosis
rapidly) Diarrhea and parenteral nutrition
Congestive heart failure and diuretics
Hepatic disease and diuretics, vomiting, or hypoproteinemia

*pH is usually only slightly acidemic, and most patients do not require therapy. 28