*5.7.1 Determination of brain death*

The American Academy of Neurology issued guidelines on the determination of brain death in adults, most recently revised in 2010 [48]. Similarly the Society of Critical care Medicine, American Academy of pediatrics and the Child Neurology Society jointly published guidelines for the determination of brain death in children and infants in 2011 [49]. The following general criteria apply to all patients undergoing brain death testing, although the specifics may vary by institutional policies. Patients should be relatively normothermic, and electrolytes and glucose should be within acceptable ranges. Any medications that may interfere with respiratory drive and neurologic function must be discontinued, with drug levels obtained if needed. The patient must demonstrate absence of all motor function and lack of responsiveness to stimuli, except spinal reflexes. Cranial nerve testing should reveal absence of pupillary reflexes, corneal reflexes, oculovestibular and oculocephalic reflexes, absence of cough and gag reflexes and absent brain stem reflexes.

The apnea test is an important component of brain death testing without which ancillary studies such as cerebral angiography, nuclear scanning for cerebral blood flow, electroencephalography, transcranial Doppler etc. are required to demonstrate absence of blood flow to the brain. The apnea test is performed to demonstrate absence of spontaneous respiratory drive in the presence of rising paCO2 levels in the blood. The patient is pre-oxygenated with 100% FiO2 and ventilated to achieve normocarbia, if possible. A baseline blood gas analysis is obtained. The patient is then disconnected from the ventilator and oxygenated via a T-piece or flow-inflating anesthesia bag. The patient is closely observed for signs of spontaneous respiration or chest rise. Serial blood gases are obtained at every few minute intervals. A rise in paCO2 > 60 mmHg and > 20 mmHg above baseline is conclusive of absence of respiratory drive. If the patient were to become hypoxic or hemodynamically unstable the apnea test should be discontinued and ancillary studies obtained.

### *5.7.2 Apnea testing on ECMO*

While clinical criteria of absence of cortical function and brain stem reflexes can be assessed in the usual manner, apnea testing can be difficult on ECMO. A proposed method for apnea testing is oxygenating the patient by use of continuous positive airway pressure (CPAP) or T-piece or by placing the patient on a selfinflating anesthesia bag with a PEEP valve, while watching for spontaneous respirations. The oxygenator on the circuit can then be capped. Alternatively, the sweep

gas is decreased to 0.5 –1 L/minute and oxygen increased to 100% FiO2 through the circuit, without any changes to extracorporeal blood flow [50, 51]. In-line gas monitoring on the ECMO circuit can be used to trend venous paCO2, but serial arterial blood gas analysis should be used to confirm the lack of ventilation secondary to central apnea. For patients on VA ECMO, hemodynamics should be maintained through circuit flows and use of vasoactive medications as needed. Patients found to be brain dead on ECMO can be considered as candidates for organ donation.
