Page 97 - Basic Monitoring in Canine and Feline Emergency Patients

–
+
UA (keytones,
+
UC (Ca, Mg) AG lactate, Alb, Phos) UC (Ca, Mg) AG UA (keytones,
–
VetBooks.ir K HCO – 3 K lactate, Alb, Phos)
+
+
–
HCO
3
Addition of an
exogenous
Na + – Na +
Cl ‘strong anion’ –
or increased Cl
alb/phos

Fig. 5.1. Gamblegram of a high-gap metabolic acidosis. The left-hand paired boxes represent the normal
Gamblegram in health with the positive cations on the left and negative anions on the right. Due to electroneutrality,
the columns must always be the same height. Therefore, any change in the size of one box must be adjusted for by
−
an equal change in the buffer (bicarbonate; HCO ) box to compensate. Changes that result in an increase in size of
3
−
−
the HCO represent metabolic alkalosis, and decreases in the HCO box size represent metabolic acidosis. This
3
3
−
figure shows how an increase of an ‘unmeasured’ anion such as lactate will force a decrease the HCO box,
3
representing an acidosis. The anion gap is visually represented as an increased difference in height between the UC
and UA boxes. The right side of this figure displays a high-gap metabolic acidosis; common differentials can be found
in Table 5.2. Alb, albumin; Cl, chloride; Ca, calcium; K, potassium; Mg, magnesium; Na, sodium; Phos, phosphorus;
UA, unmeasured anions; UC, unmeasured cations.
to the development of alternative methods of acid– the effect of total body water on acid–base status.
base assessment. While there are many versions Intuitively, it makes sense that changes in body
of these methods, for simplicity this chapter will water would affect pH. The pH of the body is 7.4,
group discussion of them all (e.g. Stewart-Fencl- while the pH of water is ‘neutral’ on the pH scale
Figge, semi-quantitative) under the heading of the at 7.0. Therefore, the body is slightly alkaline as
‘nontraditional’ approach. compared to water. The addition of more water to
In the nontraditional approach, bicarbonate is the system is acidifying, and removal of more
considered a dependent variable whose level is influ- water is alkalinizing. Using sodium levels as a sur-
enced by buffering other acids or bases. This is dif- rogate for total body water (see Chapter 8), the
ferent than the traditional approach, which considers non-traditional approach allows the clinician to
the absolute amount of bicarbonate relative to CO parse out the metabolic side of the analysis,
2
as a primary independent variable. For example, in including the impact of water, in much more
the traditional approach, a normal-gap (hyperchlo- detail.
remic) metabolic acidosis is defined by a low HCO Therefore, to perform non-traditional acid–base
−
3
level. In the nontraditional approach, the primary analysis, one must measure additional analytes
−
cause of the acidosis would be attributed to an above and beyond the PCO and HCO . These
3
2
excess of chloride (the independent variable), and include sodium, chloride, albumin, phosphorus,
−
−
the drop in HCO as a secondary effect as HCO and lactate. Mathematical equations (Table 5.5)
3
3
is being ‘used up’ as a dependent buffer. Taking it are then used to calculate the impact of each vari-
one step further, the non-traditional approach can able on acid–base status, with negative values indi-
independently calculate the impacts of multiple cating an acidifying effect, and positive values an
analytes such as electrolytes on the overall pH. This alkalinizing effect. The sum of these values can then
is advantageous because it allows the clinician to be subtracted from the BE. Any ‘left over’ BE unex-
see when competing metabolic processes are mask- plained by these five analytes implies an ‘unmeas-
ing each other. ured’ acid or base in the system (e.g. ketones). Case
Another advantage of the non-traditional studies 1 and 2 contrast the use of the traditional
approach is that it allows the clinician to assess approach to the non-traditional approach of
Venous and Arterial Blood Gas Analysis 89