A 34-year-old woman is intubated and ventilated following a prolonged generalized tonic-clonic seizure. Initial non-contrast CT brain shows bilateral intracerebral haemorrhages. Arterial blood gases and haematology results post intubation are as follows:

Parameter Patient value Normal range
Arterial Blood Gas    
FiO2 0.5  
pH 7.15 7.35 – 7.45
PaCO2 35 mmHg (4.6 kPa) 35 – 45 (4.6 – 6.0)
PaO2 105 mmHg (14 kPa)
HCO3 12* mmol/l 22 – 26
Haematology    
Haemoglobin 78 g/l 130 – 150
WCC 14.5 l 4.0 – 11.0
Platelets 43 l 150 – 300

Blood picture: Thrombocytopaenia, fragmented cells and reticulocytosis
Coagulation profile: Normal

a) List the abnormalities on the arterial blood gas and give the most likely cause in each case

b) Give three possible diagnoses for her presentation based on the history and investigations

[Click here to toggle visibility of the answers]

College Answer

a) List the abnormalities on the arterial blood gas and give the most likely cause in each case
Metabolic acidosis – lactic acidosis induced by prolonged seizure
Respiratory acidosis / inadequate compensation – inappropriate mechanical ventilation
Increased A-a gradient – aspiration pneumonitis (neurogenic pulmonary oedema)

b) Give three possible diagnoses for her presentation based on the history and investigations
TTP
Eclampsia
HUS
Vasculitis
(Meningo-encephalitis – lower mark)
Evidence of MAHA with low platelets

Discussion

This question assesses ones ability to generate a list of differentials for the causes of seizures, thrombocytopenia and anaemia in a young woman.

The ABG does not give a lactate, but presents us with a severe metabolic acidosis (bicarb 12, pH 7.15). The history of seizures lends itself to the suggestion that lactate is responsible. With this sort of acidosis, respiratory compensation would be maximal - PCO2 in a conscious person would approach the limit of respiratory compensation; but because the woman is ventilated the CO2 is higher, hence the respiratory acidosis.

As for the hypoxia, aspiration and neurogenic pulmonary oedema are good differentials (in the context of seizure) and one may also wish to add pulmonary embolism.

Now, as for reasons why a young lady might become simultaneously anaemic and thrombocytopenic, with normal coags- there are numerous.

Thrombotic thrombocytopenic purpura is a possibility no matter what the presentation.

Eclampsia is a good differential because it incorporates seizures and the intracranial hameoprrhage (implying that it was due to hypertension).

One may also wish to mention HELLP.

Hemolytic-uraemic syndrome certainly results in thrombocytopenia.

Vasculitis is mentioned, but specific vasculitic pathologies are not.

Microangiopathic hemolytic anaemia (MAHA) is called upon, and this certainly results in both anaemia and thrombocytopenia.

DIC is not mentioned because the coags are normal.

References

References

For thrombocytopenia, I turned to UpToDate: Approach to the adult patient with thrombocytopenia.

 

Or if you dont like paying for things, turn to Stasi, Roberto. "How to approach thrombocytopenia." ASH Education Program Book 2012.1 (2012): 191-197.

 

For eclampsia,

American College of Obstetricians and Gynecologists. Diagnosis and management of preeclampsia and eclampsia ACOG practice bulletin, number 33, jan. 2002

 

For HUS,

Noris, Marina, and Giuseppe Remuzzi. "Hemolytic Uremic Syndrome." Journal of the American Society of Nephrology 16.4 (2005): 1035.

 

For MAHA,

chapter 51 in Williams' Hematology, reproduced here.