Question 3.1

Last updated 25/07/2019 - 23:40
 Topic: Acid-Base Disorders
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For each set of the following biochemical and arterial blood gas parameters:

  • Describe the abnormalities.
  • Give one example of an associated clinical scenario.

Any reasonable scenario accepted that was both biochemically correct AND clinically likely.

Test

Value

Normal Adult Range

Sodium

135 mmol/L

135 – 145

Potassium

4.0 mmol/L

3.2 – 4.5

Chloride

110 mmol/L

100 – 110

Bicarbonate*

3 mmol/L

24 – 32

pH*

7.10

7.35 – 7.45

pCO2*

10 mmHg (1.3 kPa)

35 – 45 (4.6 – 5.9)

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College Answer

Increased anion gap and normal anion gap metabolic acidosis with appropriate respiratory compensation.

Clinical scenario – diabetic ketoacidosis with ketonuria or DKA with N saline resuscitation.

Discussion

Let us dissect these results systematically.

  1. The bits to calculate the A-a gradient are not supplied
  2. There is acidaemia
  3. The PaCO2 is compensatory
  4. The SBE is not reported, but the bicarbonate is 3, suggesting a severe metabolic acidosis
  5. The respiratory compensation is roughly adequate - the expected PaCO2(3 × 1.5) + 8 = 12.5mmHg.
  6. The anion gap is raised:
    (135) - (110 + 3 ) = 22, or 26 when calculated with potassium
    The delta ratio, assuming a normal anion gap is 12 and a normal bicarbonate is 24, would therefore be (22 - 12) / (24 - 3 ) = 0.47
    This delta ratio suggests that there is mixed high anion gap and normal anion gap metabolic acidosis here.
     

Situations which might give rise to such findings include

  • Lactic acidosis with concomitant overinfusion of normal saline
  • DKA in the process of therapy
  • Uremic renal failure

One of the below-listed references is from a journal which refers to some sort of small animal clinics. However, given that we share so many enzyme pathways, even in the setting of random mammal outpatients the basics of acid-base metabolism should be preserved.

References

Adams, L. G., and D. J. Polzin. "Mixed acid-base disorders." The Veterinary clinics of North America. Small animal practice 19.2 (1989): 307-326.

Walmsley, R. N., and G. H. White. "Mixed acid-base disorders." Clinical chemistry 31.2 (1985): 321-325.

Reddi, Alluru S. "Mixed Acid–Base Disorders." Fluid, Electrolyte and Acid-Base Disorders. Springer New York, 2014. 429-442

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