The following results are from the arterial blood gas analysis of a 46-year-old male ventilated in ICU for three weeks with severe community-acquired pneumonia and ARDS:
Parameter |
Patient Value |
Normal Adult Range |
FiO2 |
0.6 |
|
pH |
7.5* |
7.35 – 7.45 |
PO2 |
79.0 mmHg (10.5 kPa) |
|
PCO2 |
45.0 mmHg (6.0 kPa) |
35 – 45 (4.6 – 6.0) |
Bicarbonate |
36 mmol/L* |
22 – 27 |
Base Excess |
12 mmol/L* |
-2.0 – +2.0 |
Sodium |
138 mmol/L |
135 – 145 |
Potassium |
5.0 mmol/L |
3.5 – 5.0 |
Chloride |
97 mmol/L |
95 – 105 |
a) Describe the abnormalities.
b) Give one likely cause.
a)
Metabolic alkalosis (PCO2 appropriate using 0.7 x [HCO3] + 20 +/- 5) A-a DO2 = 295 (P/F 130 “moderate” ARDS)
b)
Let us dissect these results systematically.
Thus, this patient has a metabolic alkalosis with respiratory compensation.
This is either a recovery from chronic respiratory acidosis, or the evidence of loop diuretic treatment.
Either is equally likely given this ARDS story.
Khanna, Apurv, and Neil A. Kurtzman. "Metabolic alkalosis." J NEPHROL 2006; 19 (suppl 9): S86-S96