Apnea Test During Brain Death Examination, by Dr. Robert Tasker.
At this stage we would now want to do the apnea test.
Under normal circumstances the child would have had their mechanical ventilation altered.
So the carbon dioxide was at around 40 millimeters of mercury.
And we would have pre-oxygenated for at least 10 minutes with 100% oxygen, via the ventilator,
and have a blood gas to show that our carbon dioxide was around 40 millimeters of mercury.
We then proceed to the apnea test.
There are a couple of ways of doing this.
We need to have the child's chest exposed so that we can actually see any breathing
movements.
And then we want to try and maintain oxygenation during the procedure.
After disconnecting the child from the ventilator, we can use a T-piece connected to the ventilator,
with at least 10 liters per minute flow through that.
When we disconnect the child, we're then going to make sure that the oxygen saturation stays
above 85% and the blood pressure stays above the 5th percentile for age.
And in this child we'll take it to be 75 millimeters of mercury.
We need to observe the child for a period of 5 to 10 minutes.
And during that time, we would hope that the carbon dioxide would rise by at least 20 millimeters
of mercury.
Please note, if the oxygen saturation falls below 85%, or the blood pressure falls below
the previously determined lower limit, the test should be discontinued.
Before reconnecting the child to the ventilator, a blood gas should be drawn.
If the results of the blood gas analysis demonstrate a PaCO2 level greater than 60 millimeters
mercury, then the apnea test would be considered positive.
Therefore, this apnea test does not need to be repeated.
But if this was the first apnea test you would still proceed with your second clinical exam
and second apnea test.
In this instance, let's just assumes that we've not seen any breathing for 5 to 10 minutes.
At the termination of the test we would take another blood gas, connect the child up back
to the ventilator, and wait for the result of the gas.
If that showed a 20 millimeter rise and it was above 60 millimeters of mercury then we
can say that the child has not breathed to that stimulus.
Point of Clarification.
Please note, the apnea test should be performed following both brain death examinations.
Clinical Pearl.
Please note, brain death should never be diagnosed at a PaCO2 level less than 60 millimeters
mercury, even if the rise in PaCO2 has been 20 millimeters mercury or more.
There have been case reports in the literature of children breathing at higher PaCO2 levels.
Therefore, some experts have advocated that the threshold should be raised even higher
than a PaCO2 level of 60 millimeters mercury.
You will need to follow the guidelines set forth in your institution.
Please also note, any breathing, no matter how high the PaCO2 level, indicates that the
diagnosis of brain death cannot be made.