Causes of apnea
1- can be voluntarily achieved 2- drug-induced 3- mechanically induced4- neurological disease 5- trauma
Recommended patients : severe brain injury (large size intracranial hemorrhage,
massive stroke , diffuse brain edema with absent basal fissures and sulci , multiple hemorrhagic contusions )
2- Absence of brain stem reflexes pupils are examined (pupils that are between 4-6 mm in size )
examination of facial sensation and facial motor response , The jaw reflex , The oculocephalic reflex
The bulbar function is best tested by examining cough response to bronchial suctioning.
A catheter should be inserted into the trachea
If these brain stem reflexes are absent, can proceed with the apnea test
Prerequisites
1- Core Temperature 36.5°C or 97°F
Correction of hypothermia facilitates CO2 production and reduces the chances of hypotension
2- Systolic blood pressure 90 mm Hg
3- Positive fluid balance
4- Normal PCO2 (Arterial PCO2 of 35-45 mm Hg)
5- Preoxygenate with 100% O2 for 30 minutes recommend maintenance of a normal PO2 or
preoxygenation to obtain an arterial PO2 ≥ 200
6- medication such as pancuronium
Test : 1- Connect a pulse oximeter and disconnect the
ventilator
techniques for ascertaining that there is sufficient oxygenation during ATinsert a catheter or cannulanot disconnected from the respiratorBIPAPcontinuous flow of 100 % oxygen and low (PEEP)
2- Look closely for respiratory movements (abdominal or chest excursions that produce adequate tidal volumes)
3- Measure PO2, PCO2, and pH after 10
minutes and reconnect the ventilator
Positive or negativebrain death indeterminate result
respiratory movements are absent
arterial PCO2 is 60 mm Hg (option: 20 mm Hg increase in PCO2 over a baseline normal PCO2)
the apnea test is positive
respiratory movements are detected
If the PCO2 is < 60 mm Hg or PCO2 increase is < 20 mm Hg over baseline normal PCO2
the result is indeterminate and an additional confirmatory test can be considered
Duration of the apnea testApnea is concluded when no breathing effort
is observed at a PaCO2 of 60 mm Hg or with a 20 mm Hg increment from baseline
if respiratory movements are detected, the AT is classified as negative (i.e., not supportive of a BD diagnosis)
Duration of the apnea test
arterial pressure drops to < 90 mm Hg
desaturation cardiac arrhythmias recommended that the test be stopped after
10–15 min, even if blood gas levels cannot be determined
Contraindicationhemodynamic instability poor PaO2 inability to achieve target PaCO2 levels Extensive thoracic trauma presence of some pathologic condition significant pulmonary disorders interfering
with ventilation are other conditions that may prevent the use of the AT
Complicationssevere hypotension pneumothorax excessive hypercarbia hypoxia, acidosis cardiac arrhythmia or asystole
ancillary tests cerebral blood flow by transcranial Doppler
studies CT angiography multimodality evoked potential studies atropine test
References 1. Determination of brain death in children: A medical center experience.
[PubMed] 2. SPECT in the diagnosis of brain death in children. [PubMed] 3. Ashwal S. Clinical diagnosis and confirmatory testing of brain death in
children 4. Variability in brain death determination practices in children 5Apnea testing in suspected brain dead children-physiological and
mathematical modelling.. [PubMed] 6. A. Apnea documentation for determination of brain death in Thai
children. J Med. [PubMed]