[Part 2: 6 minutes 48 seconds]
The examination of the brainstem focuses on the presence or absence of the cranial nerve reflexes. First, the pupillary reflex is tested, and there should be absolutely no responsiveness of the pupils to light. Second, the corneal response, a fifth nerve reflex is tested and there should be no blinking in response to touching the cornea. Third, the oculocephalic reflex should be tested, and there should be no response to the so-called dolls eye maneuver with rotating the head from side to side. Fourth, the occulovestibular reflex must be evaluated, and there should be no deviation of the eyes from midline despite irrigation of the ears with a cold saline solution. Fifth, an assessment of the lower brainstem should be performed, and there should be no gag or cough. And finally, determining if apnea is present.
At the very bottom of the brainstem, that is in the medulla, are the centers that drive respiratory function and in the brain dead individual there will be no respiratory drive and no breathing. And it’s important to prove that. In most instances where one is determining brain death, the patient is already on a ventilator, and one doesn’t know whether some minor ventilation drive may be present or not. So it’s important to test for that and determine reliably if the patient shows any ventilatory effort or not. And it’s done simply by a thing called apnea testing.
The following procedure is recommended. The patient should be ventilated with pure oxygen or an oxygen and carbon dioxide mixture for ten minutes. A baseline blood gas should be measured and in most cases the PaCO2 will be in the range of 35 to 40 millimeters. The ventilator is then turned off and oxygen is allowed to flow passively through an endotracheal catheter. The patient should be watched for any efforts to breathe or any indications of cardiac instability such as bradycardia or cardiac arrhythmias, in which case ventilator support should be reinstated immediately.
It’s kind of the last test that you do testing for brain death. The reason for that is that it’s the bottom of the brainstem it does require stopping the ventilator, gearing up a little bit to do it. So it’s slightly harder to do than just checking the pupil response. And probably the most important reason for saving it for last is that if one plans to terminate the care of the patient at that point then you would just not put them back on the ventilator and the heart would stop within a matter of minutes.
After 10 minutes blood gases should again be measured and the ventilator reconnected. If the PaCO2 has risen to 60 millimeters or above and the patient has not made efforts to breathe apnea has been established. In certain cases, brain death cannot be determined on the basis of a neurological examination alone. In these cases, confirmatory tests may be used.
Once in a while it is helpful to have technical confirmation of brain death. The best example I can think of is when a patient has been placed in a barbiturate coma by the physicians as a treatment for elevated intracranial pressure–being the most common use. When that occurs you cannot use the neurologic examination because you have put the exam to sleep basically with a barbiturate. You may still strongly believe at some point that a patient is brain dead, persistently high intracranial pressure. If ICP is as high as arterial pressure then no blood is flowing to the brain and the brain cannot live in that circumstance. One way to prove there is no blood flow to the brain is to do specific blood flow tests; there are a variety of ones can that can be done. One that is easiest to do is a radionucleide study where an isotype is injected in a vein and a gamma camera is placed over the head and when one can show no radioisotope going into the brain then there is no evidence of blood flow. Another form of blood flow is the old style angiogram where contrast material is injected into the carotid artery, and if it doesn’t flow into the brain then blood is not flowing into the brain and the brain cannot live without oxygen and nutrients being delivered by the bloodstream. So, absence of blood flow is indeed brain death.
The EEG test may be useful when there is substantial physician uncertainty about the diagnosis of brain death. For instance, if a stroke perhaps has occurred, the magnitude of the stroke or the exact importance of the stroke is a little hard to determine say from a CT scan which would take perhaps days to evolve to the point where you would see overwhelming brain injury. There is no requirement for an EEG in the determination of brain death. There is a requirement that you be as sure as you can be that irreversible damage has occurred and so if the physician feels unclear and wants the extra information then one EEG or, if the physician is particularly uncertain, EEG’s separated in time, perhaps six or twelve hours might be useful. But the EEG is not invariably reliable; there are times when very low level signals appear to be brain activity, but subsequently turn out to be artifact or some other technical problem, and in fact the patient is brain dead. If bonafide EEG traces are available, and one can be certain about that then, by definition, brain death is not present and one would negate the tentative diagnosis of brain death with a truly positive EEG.
Peter McL. Black:
Even the Harvard group did not say the EEG was absolutely necessary; it was recommended and subsequently we’ve moved back even from that kind of approach to say that the EEG is a good idea as an ancillary test, but there are other ancillary tests. And in fact, none of those is necessary. In fact, it’s enough looking at the clinical state of the patient in the appropriate setting to be able to make the diagnosis without any EEG, without blood flow tests, without anything else.