A 63-year-old female presented with high fever and abdominal pain. She has gram- negative bacteraemia and septic shock. The following data are from an arterial blood gas analysis:
Parameter |
Patient Value |
Normal Range |
FiO2 |
0.3 |
|
pH |
7.43 |
7.35 – 7.45 |
PaCO2 |
23* mmHg (3.0 kPa) |
35 – 45 (4.6 – 6.0) |
PaO2 |
107 mmHg (14 kPa) |
|
HCO3 |
15* mmHg |
22 – 26 |
Standard base excess |
-8.6* mmol/l |
-2 – +2 |
Sodium |
147* mmol/l |
135 – 145 |
Potassium |
6.7* mmol/l |
3.2 – 4.5 |
Chloride |
95* mmol/l |
100 – 110 |
Lactate |
23.0* mmol/l |
< 2 |
a) Describe the abnormalities on the above arterial blood gas profile
b) List three causes of a raised lactate in sepsis
a) Describe the abnormalities on the above arterial blood gas profile
b) List three causes of a raised lactate in sepsis
This is a straighforward question about ABG interpretation; it presents the candidate with a triple disorder.
This question is frequently repeated. The chapter on the causes of lactic acidosis in sepsis contains a list of past SAQs which are either identical or very similar.
Yes, the A-a gradient is raised: (0.3 x 713) - 28.8 = 185.1, thus the A-a difference is 195.5-107 = 78.1.
The anion gap is (147) - (95 + 15) = 37, or 43.7 when calculated with potassium.
The delta ratio, assuming a normal anion gap is 12 and a normal bicarbonate is 24, would therefore be (37 - 12) / (24 - 15) = 2.77. This suggests there is also a metabolic alkalosis.
The PaCO2 expected for this sort of bicarbonate level is 30.3 (15 x 1.5 + 8) which suggests that there is also a respiratory alkalosis.
As for the causes of raised lactate in sepsis... The question asks for 3 causes. In the past, the examiners have been firm in saying that if you produce more than the [requested number] of answers, you will only be marked on the first [requested number] answers.
In any case one can usually come up with a few reasons a septic patient might have a raised lactate. The topic of pyruvate dehydrogenase being inhibited by inflammatory mediators is explored in this article.
D C Gore, F Jahoor, J M Hibbert, and E J DeMaria Lactic acidosis during sepsis is related to increased pyruvate production, not deficits in tissue oxygen availability. Ann Surg. 1996 July; 224(1): 97–102.