Effect of asphyxia on the pupils of brain dead subjects

The pupils dilate following cardiac arrest but the mechanism is unknown. If pupillary dilation represents inadequate blood supply to the midbrain, pupil size might be a rough guide to the adequacy of the resuscitation effort. The brain dead organ harvest patient presents a unique opportunity to study pupillary activity in the absence of an intact midbrain and to examine the effects of asphyxia on the pupil. Because the midbrain is dead in these subjects, the pupil has no supraspinal autonomic control and following aortic cross clamp, no blood can be delivered to the orbit. Ten brain dead patients scheduled for organ harvest were studied. Pupil size was measured from the right eye every minute for 9 min before and every minute for 10 min following aortic cross-clamp. Dapiprazole eye drops were instilled into the left eye at least 1 h before cross clamp in five cases and pupillary measurements were intermittently taken before and after cross clamp. Pupil size was stable before cross clamp. Following cross clamp, the pupil dilated in all cases, reaching 10.6 mm in one case. Mean dilation was 1.8+/-0.9 mm. Time to peak dilation was 4.3+/-1.4 min and latency of dilation was 1.4+/-1.2 min. Dapiprazole eye drops prevented the pupillary dilation in contralateral eye of the five cases in which it was used. The cause of this sympathetic activity is either a short burst of neuronal activity in the peripheral sympathetic system innervating the dilator muscle, or release of stored norepinephine from the presynaptic terminals, as asphyxia intervenes.