Question 6.1

Last updated 25/07/2019 - 22:47
 Topic: Acid-Base Disorders
Pass rate
97%
Other SAQs in this topic:
Other SAQs in this paper:

16 year old male has been treated all night for diabetic ketoacidosis. In the morning the blood gas printout is as follows:

Barometric pressure

760mm Hg

FiO2

0.21

pH

7.32

pO2

100mm Hg (13.2 kPa)

pCO2

30mm Hg    (4kPa)

HCO3-

15.2mmol/L

Standard base excess

-11.4mmol/L

Sodium

136mmol/L

(135 – 145)

Chloride

105mmol/L

(100 -110)

Potassium

3.5mmol/L

(3.2 - 4.5)

Lactate

1.3mmol/L

(0.2 - 2.5)

Glucose

5.3mmol/L

(3.6 – 7.7)

a) Describe the acid-base status.

b) Does he need continuation of insulin therapy over the next 6 hours? Give your reasoning.

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College Answer

a) Describe the acid-base status.
Raised anion gap metabolic acidosis with appropriate respiratory compensation

b) Does he need continuation of insulin therapy over the next 6 hours? Give your reasoning.

The patient will require insulin therapy for the next few hours as the anion gap is raised, indicating ongoing ketoacidosis.

Discussion

Let us dissect these results systematically.
 

  1. The A-a gradient is normal.
    PAO2 = (0.21 × 713) - (30 × 1.25) = 112.2
    Thus, A-a = ( 112.2 - 100) = 12.2mmHg.
  2. There is acidaemia
  3. The PaCO2 is compensatory
  4. The SBE is -9.9, suggesting a metabolic acidosis
  5. The respiratory compensation is adequate - the expected PaCO2(15.2 × 1.5) + 8 = 30.8mmHg
  6. The anion gap is (136) - (105 + 15) = 16, or 19.5 when calculated with potassium
    The delta ratio, assuming a normal anion gap is 12 and a normal bicarbonate is 24, would therefore be (16 - 12) / (24 - 15) = 0.44. This delta ratio suggests that there is a mixed high anion gap and normal anion gap metabolic acidosis

This questions would seem identical to Question 7.1 from the first paper of 2009, but the examiners have changed the chloride and glucose. In 2009, this 16 year old patient has a normal anion gap and slightly raised glucose, forcing us to conclude that the ketoacidosis has resolved. No mention is made of insulin.

This time, the ketoacidosis persists. One would be tempted to continue the insulin/dextrose infusion until the anion gap is normal, and only the NAGMA remains.

References

UpToDate has a nice summary of this topic for the paying customer.

Oh's Intensive Care manual: Chapter 58  (pp. 629) Diabetic  emergencies  by Richard  Keays

Umpierrez, Guillermo E., Mary Beth Murphy, and Abbas E. Kitabchi. "Diabetic ketoacidosis and hyperglycemic hyperosmolar syndrome." Diabetes Spectrum15.1 (2002): 28-36.

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