A 69-year-old male has been intubated and ventilated in the Emergency Department for worsening respiratory distress and abdominal pain. He was diagnosed with oesophageal cancer 3 months ago and has received chemotherapy followed by an oesophageal stent. He has non-insulin dependent diabetes.
The following blood results were obtained:
|Parameter||Patient Value||Adult Normal Range|
|pH||7.13*||7.35 - 7.45|
|p02||253 mmHg (33 kPa)|
|pC02||25.0 mmHg (3.3 kPa)*||35.0 - 45.0 (4.6 - 6.0)|
|Bicarbonate||8.0 mmol/L*||22.0 - 26.0|
|Base Excess||-19.0 mmol/L*||-2.0 - +2.0|
|Lactate||10.0 mmol/L* ./||0.5 - 1.6|
|Sodium||136 mmol/L||135 - 145|
|Potassium||4.6 mmol/L||3.5 - 5.0|
|Chloride||103 mmol/L||95 - 105|
|Glucose||15.5 mmol/L*||3.5 - 6.0|
|Urea||54.0 mmol/L*||3.0 - 8.0|
|Creatinine||644 µmol/L*||45 - 90|
|Albumin||20 g/L*||35 - 50|
|Ionised calcium||1.15 mmol/L||1.10 - 1.35|
Interpret the data provided and give likely causes for the abnormalities in this patient. (50% marks)
Interpret the data provided and give likely causes for the abnormalities in this patient
Increased Aa gradient – aspiration, ARDS, fluid overload – any plausible cause
High anion gap metabolic acidosis, elevated lactate – sepsis in immunosuppressed individual, consider oesophageal perforation, cardiac failure, metformin toxicity
Respiratory acidosis – primary lung pathology, inadequate ventilator settings for degree of acidosis
Delta ratio 1.1 (taking into account albumin)
Renal impairment- sepsis, dehydration,
Hyperglycaemia, low albumin – diabetes, stress response, malnutrition.
Guidance to examiners: answers which are more specific to the known patient problems score more
– e.g. oesophageal perforation, metformin toxicity
The history offered here suggests strongly that the gas exchange and metabolic problem is probably related to the oesophageal stent somehow.
A systematic dissection of these results:
- The patient is hyperoxic (PaO2 of 253 mmHg) and the A-a gradient is raised (72.3mmHg)
- There is acidaemia.
- The CO2 is appropriately depressed. The expected CO2 is in fact 21 (by SBE method) or 20 (by using the Boston rules), and so there is also be a mild respiratory acidosis.
- The SBE is -19, suggesting that there is a severe metabolic acidosis
- The anion gap is (136) - (103 + 8) = 25, or 29.6 when calculated with potassium.
The delta ratio, assuming a normal anion gap is 12 and a normal bicarbonate is 24, would therefore be (25 - 12) / (24 - 8) = 0.81. Even though we have been recently instructed not to correct the anion gap for albumin "unless otherwise specified in the question stem", the college examiners here clearly did expect the candidates to do this even though the stem does not mention it. Seeing that the albumin is 20 we would expect an anion gap of 7.0, which means that the delta ratio, assuming a normal anion gap is 12 and a normal bicarbonate is 24, would therefore be (25 - 12) / (24 - 8) = 1.12.
Thus, unless one corrected the anion gap, one would not realise that this is a pure high anion gap metabolic acidosis.
The lactate is 10, which does not completely account for the change in the anion gap. One might interpret the raised glucose and sky-high urea and creatinine as signs that the patient is severely dehydrated and has some contribution from diabetic ketoacidosis (even though NIDDM is stated in the college question). The alternative explanation is uraemia, i.e. the retention of non-volatile acids in renal failure.