You are performing clinical brain death testing on a 63-year-old male. Two arterial blood gas (ABG) results are presented below. ABG 1 was performed immediately prior to testing, and ABG 2 was performed at the end of the apnoea test.

a) Comment on the implication these results have for diagnosing brain death in this patient.  (20% marks)

Parameter

Patient Value

Adult Normal Range

ABG 1

ABG 2

FiO2

0.4

1.0

pH

7.41

7.32*

7.35 – 7.45

pO2  

110 mmHg (14.7 kPa)

148 mmHg (19.7 kPa)

pCO2

49.0 mmHg (6.5 kPa)*

62.0 mmHg (8.3 kPa)*

35.0 – 45.0 (4.6 – 6.0)

SpO2

96%

97%

Bicarbonate 

30.0 mmol/L*

31.0 mmol/L*

22.0 – 26.0 

Base Excess 

5.3 mmol/L*

4.9 mmol/L*

-2.0 – +2.0 

Lactate 

1.8 mmol/L*

1.8 mmol/L*

0.5 – 1.6

Sodium 

151 mmol/L*

152 mmol/L*

135 – 145 

Potassium 

4.2 mmol/L

4.1 mmol/L

3.5 – 5.0

Chloride 

103 mmol/L

102 mmol/L

95 – 105

Glucose 

7.5 mmol/L*

8.1 mmol/L*

3.5 – 6.0

[Click here to toggle visibility of the answers]

College answer

a) 
Although the CO2 has risen to above 60 mmHg, the pH remains above 7.3, and so brain death cannot be diagnosed. The Na of 152 does not preclude the diagnosis of brain death. 
       

Discussion

This question is straight from the CICM ANZICS statement (vesion 3.2) which reads:

"At the end of the period without mechanical ventilation, apnoea must persist in the presence of an adequate stimulus to spontaneous ventilation, i.e. an arterial PaCO2 > 60 mmHg (8 kPa) and an arterial pH < 7.30"

The key point there is an arterial PaCO2 > 60 mmHg (8 kPa) and an arterial pH < 7.30. Both must be demonstrated in order for the clinical diagnosis of brain death to be valid.  As to why and how this was decided, the ANZICS statement is silent. The American guidelines do not contain this rule.

As for the sodium level, the ANZICS statement is not prescriptive; "marked derangements" are disqualifying, but there no mention as to how marked these must be. Other Intensive Care Societies are more informative;  for example the Irish ICSI guidelines recommend 125-155mmol/L as the acceptable range for clinical testing.  

References

References