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Winter's formula for metabolic acidosis:

Expected PaCO2=[(1.5 x bicarbonate) + 8 ± 2] x 0.133

Substituting the patient's values:

Expected PaCO2=[(1.5 x 11.1) + 8 ± 2] x 0.133

Expected PaCO2= 3.01245 to 3.54445

Therefore there is no concomitant respiratory component to the acid-base disturbance.

What is the likely diagnosis?

To remind you of the history, examination and investigations

86 year old woman presents with decreased consciousness (GCS 10). She has no history of trauma.

On examination:

  • Heart rate 90/min
  • Blood pressure 110/70
  • Clinically dehydrated
  • No focal neurological signs
  • No neck stiffness

Preliminary investigations reveal:

  • Capillary blood sugar: >33 mmol/l
  • Haemoglobin 14.6 g/dl
  • Arterial blood sample on 10l/min oxygen via non-rebreathing mask:
    • pH 7.246
    • PaCO2 3.5 kPa
    • PaO2 27.13 kPa
    • Actual bicarbonate 11.1
    • Base excess -14.3
    • Sodium 145 mmol/l
    • Potassium 3.28 mmol/l
  • Urine ketones: +++

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©Charles Gomersall, October, 2009 unless otherwise stated. The author, editor and The Chinese University of Hong Kong take no responsibility for any adverse event resulting from the use of this webpage.
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