A previously fit and well 41 -year-old male underwent an anterior resection under general anaesthesia with regional blockade. In recovery he required additional analgesia for escalating pain and treatment for nausea, following which he had an apparent seizure.
The following arterial blood gas sample was taken during resuscitation:
Parameter |
Patient Value |
Normal Adult Range |
|
FiO2 |
0.6 |
||
6.91* |
7.35 - 7.45 |
||
PCO2 |
64 mmH 8.5 kPa * |
35 —45 (4.6 —6.0 |
|
PO2 |
158 mmH 21 kPa * |
75-98 (10- 13) |
|
SaO2 |
96% |
||
Bicarbonate |
12 mmol/L* |
22 - 26 |
|
Base Excess |
-18 mmol/L* |
||
Sodium |
145 mmol/L |
135 - 145 |
|
Potassium |
4.1 mmol/L |
3.5 - 5.2 |
|
Chloride |
110 mmol/L |
95- 110 |
|
Lactate |
16 mmol/L* |
||
Haemoglobin |
166 g/L* |
115- 160 |
|
Glucose |
9.0 mmol/L* |
3.6 - 7.7 |
Describe the acid-base abnormality. (20% marks)
Give six possible causes for this clinical and biochemical scenario. (30% marks)
a)
b)
a)
Let us dissect these results systematically.
Thus, this is an almost completely pure HAGMA and a respiratory acidosis.
b) The key features of history are abdominal surgery, worsening pain, analgesia, and antiemetics. Then, the patient had an "apparent seizure". The college wanted explanations of this "clinical and biochemical" picture. The following differentials were constructed without the benefit of the college model answer, before the official paper was released, and they differ from the college answer. The college had the LA toxicity, but they also threw in a dystonic drug reaction, intra-abdominal catastrophe, myocardial infarction, anaphylaxis and subarachnoid haemorrhage. It is unclear whether the differentials offered below would have scored any marks.
Generic causes of a lactic acidosis are also offered below, for completeness
Type A lactic acidosis: impaired tissue oxygenation
Type B1 lactic acidosis, due to a disease state
|
Type B2 drug-induced lactic acidosis
Type B3 : inborn errors of metabolism
|