Question 29.3

A 25-year-old female with a 5-day history of anorexia, nausea and vomiting presents to hospital after a convulsion and is transferred immediately to your ICU. She is G3P2 and 30/40 gestation. The following blood results are obtained:

Parameter	Patient Value	Adult Normal Range
FiO2	0.28
pH	7.54*	7.35 – 7.45
PO2	87 mmHg (11.6 kPa)
PCO2	33.0 mmHg (4.4 kPa)*	35.0 – 45.0 (4.6 – 6.0)
SpO2	94%
Bicarbonate	28.0 mmol/L*	22.0 – 26.0
Base Excess	4.5 mmol/L*	-2.0 – +2.0

Sodium	127 mmol/L*	135 – 145
Potassium	2.3 mmol/L*	3.5 – 5.0
Chloride	84 mmol/L*	95 – 105
Glucose	4.8 mmol/L	3.5 – 6.0
Creatinine	354 µmol/L*	45 – 90
Urea	29.0 mmol/L*	3.0 – 8.0

Haemoglobin	177 g/L*	120 – 160
White Cell Count	25.4 x 109/L*	4.0 – 11.0
Platelet count	29 x 109/L*	150 – 350

Prothrombin time	15.0 sec	12.0 – 16.5
International normalised ratio (INR)	1.1	0.9 – 1.3
Activated partial thromboplastin time (APTT)	28.0 sec	27.0 – 38.5
Fibrinogen	5.7 g/L*	2.0 – 4.0
D-Dimer	16.8 mg/L*	< 0.5

a) Describe the important metabolic abnormalities and give one explanation for each.

(40% marks)

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College answer

Not available.

Discussion

This question is identical to Question 20.1 from the second paper of 2017, except this time the examiners added the word "important" to "abnormalities", presumably because the last bunch of answers were filled with pointless trivial abnormalities. The reader is left to decide, which of the following list of problems fits that description, and invited to pick whichever ones seem important enough to write in the span of four minutes.

Systematically:

The patient is alkalaemic. This pH is in excess of what would normally be expected in pregnancy
There is normoxia (PaO₂ is satisfactory) but the A-a gradient is raised.
The CO₂is within normal limits for this stage in pregnancy
Oxygen saturation is lower than would be expected for this level of alkalosis (i.e. there is an unexplained right-shift of the oxyhaemoglobin dissociation curve).
Base excess and bicarbonate present a metabolic alkalosis. In pregnancy, one would conventionally expect to normally have a lower bicarbonate level because of the chronic respiratory alkalosis. Ergo, in this scenario, the metabolic alkalosis from vomiting and dehydration is even worse than it seems.
The patient is hyponatremic, though it is not so severe as to produce the seizures. One possible explanation for this is the fluid overload and water retention related to the renal failure.
Potassium is severely depleted, which is likely related to the nausea and vomiting
The low chloride is due to the vomiting
The creatinine and urea are raised, indicating acute kidney injury
The haemoglobin is significantly higher than would be expected at this stage of pregnancy, which suggests significant dehydration
The white cell count is elevated, which may be a combination of haemoconcentration and infection
There is thrombocytopenia, consistent with HELLP - but it could also be consumptive, eg. in the context of thrombosis or something like TTP/HUS.
The coags are normal, which virtually excludes hepatic involvement
The D-dimer is elevated, which might represent thrombosis and consumption (of particular interest would be cerebral venous sinus thrombosis).

References

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