A 70-year-old male presents to the ED with a 2-week history of increasing dyspnoea, cough with altered sputum and fever. Past history includes chronic obstructive airways disease (COPD), lung cancer seven years ago treated with chemotherapy and radiation therapy with no sign of recurrence since.
Examination findings included RR 30 breaths/min, BP 110/70mmHg, HR 145 bpm, Temp 37.4ºC, anxious and distress but tired and peripherally cold and cyanosed.
CXR shows findings consistent with COPD and right lower lobe infiltrate.
The following arterial blood gas is taken one hour after receiving 2 litres of fluid resuscitation, antibiotics and bi-level non-invasive ventilation (NIV), at FiO2 = 1.0.
Parameter |
Patient Value |
Normal Adult Range |
|||
FiO2 |
1.0 |
||||
pH |
7.16* |
7.35 |
– 7.45 |
||
PCO2 |
33 mmHg* (4.3 kPa)* |
35 |
– |
45 (4.6 – 6.0) |
|
PO2 |
272 mmHg (38.5 kPa) |
||||
Bicarbonate |
11 mmol/L* |
22 |
– |
30 |
|
Base Excess |
-17 mmol/L* |
-3 – +3 |
|||
Sodium |
138 mmol/L |
135 – 145 |
|||
Potassium |
4.3 mmol/L |
3.5 – 5.0 |
|||
Chloride |
121 mmol/L* |
95 |
– |
110 |
|
Glucose |
13.1 mmol/L* |
3.5 – 7.8 |
|||
Lactate |
6.4 mmol/L* |
0.6 – 2.4 |
|||
Haemoglobin |
131 g/L* |
135 – 175 |
|||
Creatinine |
150 micromol/L* |
70 |
– |
120 |
a) Give your interpretation of the arterial blood gas and outline potential causes.
(40% marks)
a)
ABG:
Metabolic acidosis, normal anion gap however mixed cause (hyperchloremic predominant), high lactate and renal impairment.
Respiratory compensation but less than expected (superimposed respiratory acidosis). Impaired oxygenation with moderate shunt PaO2:FiO2 272 – A-a DO2 400.
Hyperglycemia (stress response).
Dx.
Type 1 respiratory impairment secondary to pneumonia on background of COAD.
Inadequate respiratory compensation due to fatigue and reduced respiratory reserve (COAD).
Metabolic acidosis due to:
Let us dissect these results systematically.
In summary: