A 60-year-old male was admitted after an argument with his partner who found him, 2 hours later, unconscious in his workshop, having likely ingested an unknown substance with empty liquid bottles around him.

 a) Describe the significant abnormalities in the results below.                                                         (20% marks)

Parameter

Patient Value

Adult Normal Range

FiO2

1.0

pH

7.04*

7.35 – 7.45

pO2  

452 mmHg (60.3 kPa)

pCO2

38.0 mmHg (5.07 kPa)

35.0 – 45.0 (4.60 – 6.00)

SpO2

95%

Bicarbonate 

10.0 mmol/L*

22.0 – 26.0 

Base Excess 

-18.0 mmol/L*

-2.0 – +2.0 

Lactate 

15.0 mmol/L*

0.5 – 1.6

Sodium 

141 mmol/L

135 – 145

Potassium  

2.9 mmol/L*

3.5 – 5.0

Chloride 

99 mmol/L

95 – 105

Bicarbonate 

10.0 mmol/L*

22.0 – 26.0 

Glucose 

22.4 mmol/L*

3.5 – 6.0

Urea 

4.7 mmol/L

3.0 – 8.0

Creatinine  

97 μmol/L*

45 – 90 

Magnesium

1.10 mmol/L*

0.75 – 0.95

Albumin 

44 g/L

35 – 50 

Protein 

66 g/L

60 – 80

Total bilirubin 

7 μmol/L

< 26

Aspartate aminotransferase (AST)

98 U/L*

< 35

Alanine aminotransferase (ALT)

20 U/L

< 35

Alkaline phosphatase (ALP)

65 U/L

30 – 110

γ-Glutamyl transferase (GGT)

113 U/L*

< 40

Calcium corrected 

2.08 mmol/L*

2.12 – 2.62

Phosphate 

1.78 mmol/L*

0.80 – 1.50

Creatinine Kinase 

66 U/L

55 – 170 

Osmolality

382 mOsm/kg*

275 – 295

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College answer

a) Describe the significant abnormalities in the results. (2 marks) 
(a)    Elevated A-a Gradient (214mmHg) 
(b)    HAGMA 
(c)    Respiratory acidosis (or incomplete compensation) 
(d)    Delta ratio 1.4 (uncomplicated HAGMA) 
(e)    Lactic Acidosis 
(f)    High Osmolar Gap (65) 
(g)    Hyperglycaemia 
(h)    Hypokalemia 
 

Examiners Comments: 
 
Generally, these questions were answered well. Those candidates that failed, missed all or part of the question or misinterpreted what was being asked, reiterating how important it is to read the question and understand what is required before starting to answer. 

 

Discussion

This is another one of the dying breed of CICM PArt II SAQs which ask the trainees to detect a list of abnormalities, which are easy to mark but which unfortunately do not test any sort of higher order analytic skills.

Let us dissect these results systematically:

1) There is an elevated A-a gradient: (1.0  × 713) - (38 / 0.8) - 452 = 213.5 mmHg. The patient is generally hyperoxic (i.e. it is not clear that they need all of that FiO2

2) There is profound acidaemia

3) There is a metabolic acidosis - the SBE is -18

4) There is no respiratory compensation; the expected PaCO2 is (1.5 × 10) + 8 = 23 mmHg, or 22 mmHg by using the Copenhagen SBE-based method of assessing compensation. The upshot of this is that there is a co-existing respiratory acidosis

5) The anion gap is raised (34.9 if you include potassium, 32 if you don't) -  the raised lactate of 15 mmol/L does not explain all of  this gap.

6) The delta ratio is 1.4, which suggests that there is a pure high anion gap acidosis

7) The osmolar gap is raised: calculated osmolality is  (2 × 141 + 22.4 + 4.7) = 309.1, whereas the measured osmolality is 382. The osmolar gap is therefore 73.9 cOsm/kg. The college quote a slightly different value, perhaps because of using a different formula for calculated osmolality. If one includes potassium, the value is closer to the college answer (67.1). Nitpicking aside, it's raised. 

8) Notable abnormalities include:

  • Hypokalemia
  • Hyperglycaemia
  • High albumin (suggesting dehydration)
  • Trivial LFT derangement (GGT)
  • Hypocalcemia
  • Hyperphosphataemia

9) Notable "normalities" include normal renal function, normal CK and essentially normal LFTs.

A nice way to continue this question into the direction of actually testing something meaningful would have been to then ask the trainees, "what three possible causes could have given rise to this biochemical pattern".

References

References