50 year old man with Motor Neuron Disease presents with acute onset of thoracic back pain.
Describe and Interpret the following blood gas:
pH 7.122 Na 145
pCO2 108 K 3.7
pO2 171 Cl 101
HCO3 38 Glu 9.5
BE 3.2 Lactate 0.8
Issues from stem:
MND – need to consider severity, stage of disease, advanced directives, previous established ceilings of care.
Marked hypertension with back pain and altered concious level
? central pathology – SOL, SAH, bleed
? vascular event esp. dissection
? hypertensive crisis
? Myocardial ischaemia +/- pulm odema
pH 7.122 Severe acidaemia – raised pCO2 & raised HCO –> primary resp acidosis
pCO2 108 – significant hypercarbia likely contributing to altered GCS
pO2 171 – hypoxaemia not cause of decreased GCS likely on supplemental oxygen, unable to calculate A-a gradient without FiO2
HCO 38 – alkalosis – expected HCO for pCO2 if acute pCO2 raised expected HCO is ~31 (10:1 rule) if chronic expected HCO ~51 – actual HCO between the two so likely acute on chronic especially given MND and acute deterioration
Hb 183 – elevated – ?haemoconcentration ? polycythaemia
Na 145 – normal with normal glucose (nil further correction required)
K 3.7 – low normal – adjusting for pH actual K is ~2.3 anticipate correction to be required as acidosis resolves
Cl 101 – normal
Glu – normal – not cause of decreased GCS
Anion gap = 6
Critical unwell patient with likely acute on chronic resp failure and hypertensive emergency, DDx as above.
Treat reversible causes of resp depression e.g opiates / benzos.
Ventilatory support may be not be appropriate pending disease severity, advance directives.
If IPPV considered apppropraite avoid depolarising muscle relaxants for RSI.