The following results were obtained from a 23-year-old female admitted with severe asthma.
Parameter |
Patient Value |
Adult Normal Range |
Fi02 |
0.4 |
|
pH |
6.92* |
7.35 -7 45 |
P02 |
81 mmHg 10.8 kPa) |
|
PC02 |
71.0 mmHg (9.5 |
350- . 45 0 . 4.6 — 6 0) |
sp02 |
95% |
|
Bicarbonate |
14.0 mmol/L* |
22.0 - 26.0 |
Base Excess |
-16.0 mmol/L* |
_2.0 _ +2.0 |
Lactate |
9.0 mmol/L* |
0.5 - 1.6 |
Sodium |
139 mmol/L |
135 - 145 |
Potassium |
4.2 mmol/L |
3.5-5 0 |
Chloride |
108 mmol/L* |
95 - 105 |
Glucose |
19.2 mmol/L* |
3.5 - 6.0 |
a) Describe the abnormalities and give a potential reason for each. (30% marks)
Primary respiratory acidosis – likely secondary to asthma,
Secondary high anion gap metabolic acidosis – shock, sepsis
Concomitant non-anion gap metabolic acidosis – fluid resuscitation, (delta ratio 0.5)
Increased Aa gradient – pulmonary sepsis
Elevated lactate – sepsis, B2 agonist use
Elevated glucose – pre-existing diabetes, stress, B2 agonist, steroids
The abnormalities addressed systematically are as follows:
1) There is no hypoxia per se, but the A-a gradient is widened (114)
2) There is profound acidaemia.
3) The CO2 is a major contributor to the acid-base disturbance.
4) There is a metabolic acidosis; the SBE is -16. As such, the expected CO2 is 28. To use the Boston rules, the expected CO2 = (14 ×1.5) + 8 = 29, close enough for government work. Regardless of which acid-base church you follow, we should all be convinced that there is a combination of a severe metabolic acidosis with a severe respiratory acidosis.
5) The anion gap is (139 + 4.2) - (108 + 14) = 21.2, or 17 if you omit the potassium as the college frequently do.
6) The delta ratio is therefore either 0.92 or 0.5; depending on whether or not you included the potassium you could come to the conclusion that either there is a minor contribution from NAGMA, or that the contribution is substantial. Either way, the delta ratio points to a mixed acidosis. The lactate on its own certainly does not explain all of the base deficit.
Thus:
Explanations? "Potential reasons for each"?
Dawson, K. P., A. C. Penna, and P. Manglick. "Acute asthma, salbutamol and hyperglycaemia." Acta Paediatrica 84.3 (1995): 305-307.
Westen, Edward A., and Henry D. Prange. "A reexamination of the mechanisms underlying the arteriovenous chloride shift." Physiological and Biochemical Zoology 76.5 (2003): 603-614.