The American Academy of Neurology included directions for apnea testing in the evaluation of a patient for brain death.


Requirements before testing:

(1) core body temperature >= 36.5°C (97°F)

(2) systolic blood pressure >= 90 mm Hg

(3) euvolemia

(4) normal PaCO2 (typically 35-45 mm Hg)

(5) normal PaO2



(1) pulse oximeter

(2) oxygen source

(3) tracheal oxygen cannula

(4) blood pressure monitoring

(5) arterial blood gas requirements



(1) The monitoring equipment is connected to the patient. Collect a baseline arterial blood gas sample.

(2) The patient is disconnected from the ventilator.

(3) The oxygen cannula is placed in the trachea and set to deliver 6 liters per minute.

(4) Observe the patient for respiratory movements (chest wall or abdominal excursions) during the 8 minute observation period.

(5) The test may need to be discontinued early (< 8 minutes) if hypotension, cardiac arrhythmias or a significant oxygen desaturation develop.

(6) Arterial blood gases are collected upon completion of the test.

(7) Reconnect the patient to the ventilator.


If the baseline PaCO2 was normal, then calculate the change in PaCO2 during the test.


change in PaCO2 during the test =

= (PaCO2 in mm Hg at end of test) - (PaCO2 at baseline)

Time Completed

Respiratory Movement

Final PaCO2

Change in PaCO2


8 minutes


>= 60 mm Hg

>= 20 mm Hg

positive (favors brain death)

< 8 minutes


>= 60 mm Hg

>= 20 mm Hg

positive (favors brain death)

< 8 minutes


< 60 mm Hg and change

< 20 mm Hg


8 minutes


< 60 mm Hg

< 20 mm Hg

negative (favors not brain dead)



• Either the final PaCO2 OR the change in PaCO2 may be used for the interpretation.

• According to JAMA 1981: (1) the passive flow of oxygen prevents hypoxia while permitting development of hypercarbia; (2) respirations are stimulation within 30 seconds by a PaCO2 > 60 mm Hg; (3) 10 minutes is sufficient to achieve this level of hypercarbia.


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