Thursday, August 4, 2016

#Brainstem Testing for diagnosis of #BrainDeath

➖The brain stem often fails from the rostral to caudal direction and therefore it is logical to undertake testing in the same manner.


➖The pupillary light reflex involves cranial nerves II and III and localizes to midbrain. The pupils should be nonreactive to both direct and consensual light reflex. 


➖Pinpoint pupils are indicative of damage to descending sympathetic fibers as a result of damage to pons. 

➖The size of the pupils only provides an indication of the site of brainstem involvement and is not crucial for testing brain stem death.


➖It involves cranial nerves III, VI, and VIII and interneurons within the midbrain and pons. On head movement toward right or left, the eyes remain “fixed” on a point in an intact patient. In the brain-dead patient, the eyes move with the head, hence the name “dolls eye” reflex.


➖Before performing this test the physician must rule out cervical fracture or instability. 


➖The reflex tests the V, VII, and III cranial nerves and localizes entirely to the pons. In the intact patient, touching the cornea with a cotton swab causes eyelid closure. 

➖The eye rotates upward, demonstrating the cranial nerve III component, known as “bell’s phenomenon.”


 ➖The oculovestibular reflex tests cranial nerves III, VI, VIII, and IV. It involves the entire pons and midbrain. 


➖Elevate the head 30°C. Irrigate tympanic membrane with 50-cc iced water or saline. Wait 1 min for response. Repeat test on the other side after waiting 5 min. If the oculovestibular reflex is intact using cold water as stimulus, the eyes tonically deviate toward the side of the stimulus immediately followed by a fast recoil toward the contralateral side (apparent nystagmus). In the brain stem dead patient this response is absent.


 ➖They require a functioning medulla and test cranial nerves IX and X. Both reflexes should be absent in brain stem death. 

➖The cough reflex is easily tested by stimulation of carina by suction through the endotracheal tube. The gag reflex can be elicited by stimulating the posterior pharynx with a tongue blade. 


➖This final test aims to demonstrate the failure of medullary centers to drive ventilation. Apnea test should be the last brain stem reflex to be tested. 


➖is to stimulate the medulla while avoiding hypoxia and hemodynamic compromise associated with acidosis secondary to hypercarbia. 


➖After ensuring preoxygenation for 10 min a blood gas is performed to confirm baseline PaCO2 and SaO2 . 

➖With oxygen saturation greater than 95% the ventilatior is disconnected inducing apnea for a period of time to achieve ETCO2 above 6 KPa (=45 mmHg). A repeat arterial blood gases is used to confirm that the PaCO2 is at least 6 KPa and the pH is less than 7.40. 

➖An oxygen flow rate of 2–5 L/min via an endotracheal catheter or in difficult cases CPAP may be used to maintain oxygenation till this state is attained. 

➖Apnea is continued for a further 5 min after a PaCO2 of 6 KPa (=45 mmHg) has been achieved. 

➖If there is no spontaneous respiratory response, a presumption of absence of respiratory activity is made. 

➖A further blood gas can be done to confirm that the PaCO2 has risen by 0.5 KPa (=4 mmHg) from the initial 45 mmHg baseline.

Reference: Brain Death in Neurosurgical Critical Care Amit Prakash,  Basil Matta , Essentials of Neurosurgical Anesthesia & Critical Care 2012

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