The risk of ischaemic brain damage during the use of self-retaining brain retractors

Self-retaining brain retractors (SRBR) are commonly used during intracranial surgery and they are indispensable during microneurosurgery. To evaluate limitations in the employment of SRBR, as well animal as human studies have been performed. In the animal studies, male Wistar rats were used for measurements of regional cerebral blood flow (rCBF) changes during brain retractor pressure (BRP) provided by lead weights. These weights, corresponding to different levels of mm Hg, were applicated for different periods of time on the parietal cortex after craniotomy. In one part of the animal studies different profiles of the application surface of the weights were evaluated. For measurement of the rCBF (n = 41) autoradiography with carbon-14(14C)iodoantipyrine was used as described by Gjedde et al (1980). A neuropathological method (n = 30) was used to reveal possible brain damage after graded BRP. In the rats the thresholds of rCBF, regional cerebral perfusion pressure (rCPP) and time were 20-25 ml/100 g/min, 20 mm Hg and 7-10 minutes respectively. In the human studies only alert patients without neurological deficits (except defects of the visual fields) and in whom preoperative CT-scans did not disclose any sign of infarction were included. BRP beneath as well the tip as the centre of the SRBR and the MABP were recorded continuously. Patients with peroperative complications were excluded. During the operations induced hypotension (n = 20) and mannitol (n = 6) were administrated. The patients (n = 23) had a 3-month follow-up examination. In man the thresholds of rCPP and time were found to be 10 mm Hg and 6-8 minutes, respectively. Other authors have found a rCBF threshold of 10-13 ml/100 g/min (Astrup 1982, Iannotti & Hoff 1983). It is concluded that the results obtained in the rat studies are comparable to the human situation if reservations are made concerning the differences in the thresholds of rCBF and rCPP. The time threshold of cerebral ischaemia seems to be rather equal in rat and in man. If these thresholds are reached, intermittent BRP is absolutely recommendable. It was also found that the most easily-handled retractors, those with a flat profile, did not decrease the rCBF further than other types of retractors.