Arch Otorhinolaryngol (1989) 246 : 190-194 , o ,. Oto-Rhino- Laryngology 9 Springer-Verlag 1989 Controlled hypotension during anesthesia for otologic operations An ultrastructural study of the brain in an experimental animal model L. S. Manolidis 1 , S.J. Baloyannis 2, M. Giala 3, and S. L. Manolidis 1 Departments of 10torhinolaryngology, 2Neurology-Laboratory of Neuropathology, and 3Anesthesiology, AristotelianUniversityof Thessaloniki,Thessaloniki,Greece Summary. We have studied the fine structure of the cerebral cortex, the cerebellar cortex, the thalamus, the caudate nucleus, the amygdala, the putamen, the vestibular nuclei, the substantia nigra, the hippocam- pus and the centrum semiovale in a canine model fol- lowing 20 min controlled hypotension by the adminis- tration of sodium nitroprusside. The neurons and the astrocytes of all structures were intact morphologi- cally. The synapses in the cerebral and cerebellar cor- tex were all unremarkable. Sensitive areas such as the molecular layer of the cerebellum did not demonstrate any ultrastructural alterations. We believe that care- fully controlled sodium-nitroprusside-induced hypo- tension might be applied in middle ear microsurgery in otherwise healthy patients as an effective and innocu- ous method without causing any anoxic insult to sensi- tive areas of the central nervous system. Key words: Sodium nitroprusside - Hypotension - Central nervous system Introduction Operations in the middle ear, especially those which are performed in order to restore hearing, have a spe- cial necessity for hemostasis to allow for a dear, blood- less surgical field. The special demands of microsurgery of the middle ear include an immobile operational field, minimalization of hemorrhage, mild and rapid resuscitation of the patient and the avoidance of cough- ing and hypertonia. The requirements of such surgery impose the need for a special way of administering Offprint requests to: L. S. Manolidis,Department of Otorhino- laryngology,AHEPA Hospital, Thessaloniki54636, Greece anesthesia. In the past, anesthesiologists have tried to obtain a bloodless surgical field by applying various techniques, such as ventilation with positive pressure and controlled hypotension, local anesthesias using injections of local anesthetics containing adrenalin, placement of the patient in a recumbent position, and others. Unfortunately, these procedures have been proved quite ineffective in securing a bloodless surgi- cal field at all times. Methods of controlled hypotension that have been used in the last 20 years have included controlled ar- teriotomies, partial phlebotomies, high epidural anes- thesia and the use of the ganglion-blocking agents. Sodium nitroprusside was first used as a hypotensive agent in 1962 [6]. Although several controversies en- sued concerning the value of this method, strong argu- ments in its favor make it an effective technique in microsurgery of the middle ear. Reasons favoring this method can be summarized as follows: (a) an almost bloodless surgical field, (b) minimalization of hemor- rhage, (c) decrease in the number of vessel ligations required, (d) reduction in the operative time, and (e) decrease in the incidence of inflammation and post- operative edema. For all these reasons, rapid post- operative healing of the middle ear can be obtained, resulting in an almost intact mucosa in spite of the sur- gical manipulations performed. Needless to say, this method also allows the surgeon to distinguish clearly the borders between healthy and pathological tissues as well as the blood vessels present. The major pharmacological property of sodium nitroprusside is to induce direct vasodilatation of blood vessels, quite independent from its action of the cen- tral or autonomic nervous system. Its effectiveness as a hypotensive agent has been clearly established in clinical practice [3-5], so that it can be used safely whenever it is administered by an experienced anes-