✓ Brain damage due to retraction was studied morphologically and physiologically in the dog brain. Two methods of retraction were compared using a retractor with a strain gauge: 1) continuous retraction; and 2) intermittent retraction. Total retraction time was 60 minutes for each method. Brain damage started to appear at a retraction force of 30 gm with continuous retraction, and increased in proportion to the force used. The power spectrum of the electrocorticogram showed full recovery after the release of retraction when the retraction force was less than 40 gm. With intermittent retraction, the damage was morphologically minimal with a retraction force of less than 50 gm, and recovery of the power spectrum of the electrocorticogram was prompt in comparison with continuous retraction. The results indicate the superiority of intermittent over continuous retraction.
An experimental study
Akira Yokoh, Kenichiro Sugita and Shigeaki Kobayashi
An experimental and clinical study
Kazuhiro Hongo, Shigeaki Kobayashi, Akira Yokoh and Kenichiro Sugita
✓ The problem of minimizing tissue damage during brain retraction was studied both experimentally in dogs and clinically with the aid of newly designed strain-gauge retractor. The pressure required to obtain a specific exposure decreased gradually with time. The average time for a 50% reduction in retraction pressure was 6.6 minutes in the earlier trials of repeated retraction. The attenuation rate of retraction pressure gradually decreased when retraction of the same area was repeated. The lower the head position of the dog, the larger was the amplitude of brain retraction pressure. Clinical studies demonstrated that: 1) cerebrospinal fluid drainage was effective in decreasing the retraction pressure required; 2) use of multiple retractors reduced the pressure applied by each retractor; and 3) retraction pressure could be monitored when the strain-gauge retractors were applied to arteries and cranial nerves.