Page 315 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice
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306 ACID-BASE DISORDERS
BOX 12-3 Guidelines for BOX 12-5 Potential Problems
Adequate Use of That May Lead to
Compensatory Rules Misdiagnosing a Mixed
from Table 12-2 Acid-Base Disorder
Time Use of venous blood
Sufficient time must elapse for compensation to reach a Local metabolism may affect PCO 2
Normal values for compensation were established
steady state:
using arterial blood
Acute respiratory disorders: 15 min
Too much heparin (>10% of total volume)
Chronic respiratory disorders: 7 days
Long-standing respiratory acidosis: 30 days Decreases [HCO 3 ] and PCO 2
Storage of sample for more than 20 min
Metabolic disorders: 24 hr
Increases PCO 2 and decreases pH
pH Errors in calculation of [HCO 3 ]
Compensation does not return the pH to normal*
Overcompensation does not occur
Values in the Expected Compensatory hyperphosphatemia. See Chapter 13 for further discus-
Range sion of the role of albumin and phosphate in acid-base
Do not prove that there is only one disturbance disorders.
Provide support for a simple acid-base disturbance, if
consistent with the remaining clinical data Chloride Changes
Chloride is the most important extracellular strong
*Exceptions: chronic respiratory alkalosis (>14 days), and anion. Increases in chloride lead to metabolic acidosis
potentially long-standing respiratory acidosis (>30 days). by decreasing SID, whereas decreases in chloride cause
metabolic alkalosis by increasing SID. Therefore plasma
[Cl ]and[HCO 3 ]haveatendencytochangeinopposite
directions in hypochloremic alkalosis and hyperchloremic
acidosis. The contribution of [Cl ] to changes in base
BOX 12-4 Guidelines for Quickly excess (BE) and [HCO 3 ] can be estimated by calculating
Detecting a Mixed the chloride gap, the chloride/sodium ratio, and
Process the sodium-chloride difference (Table 12-3).
Chloride gap is calculated as:
Quick Diagnosis of Mixed Disorders ½Cl gap ¼½Cl normal ½Cl corrected
PCO 2 and [HCO 3 ] changing in opposite directions
Presence of a normal pH (with abnormal PCO 2 and/or or
[HCO 3 ])*
A pH change in a direction opposite to that predicted for ½Cl gap ¼½Cl normal ½Cl patient
the known primary disorder
½Na normal=½Na patient
þ
þ
*Exceptions: chronic respiratory alkalosis (>14 days), and Normal values may vary among laboratories, but using
potentially long-standing respiratory acidosis (>30 days).
midpoint values from Chapter 4, chloride gap can be
estimated for dogs as:
EVALUATION OF THE METABOLIC ½Cl gap ¼ 110 ½Cl patient 146=½Na patient
þ
COMPONENT OF THE ACID-BASE
DISORDER
and for cats as:
Metabolic alkalosis can result from an increase in the
strong ion difference (SID) caused by hypochloremia
½Cl gap ¼ 120 ½Cl patient 156=½Na patient
þ
or by decrease in the concentration of total plasma weak
acids [A tot ] caused by hypoalbuminemia. Metabolic aci-
dosis can be caused by a decrease in SID as a result of Values greater than 4 mEq/L are associated with
hyperchloremia or increased concentration of other hypochloremic alkalosis, whereas values less than
strong anions (e.g., lactate, sulfate, b-hydroxybutyrate), 4 mEq/L are associated with hyperchloremic acidosis.
or by an increase in [A tot ] as a result of A shorter way to evaluate chloride contribution is to
