The use of brain retractors, unavoidable method in operation of deep intracranial lesions, may lead to focal cerebral ischemia and thereby cause brain infarction. In such operation, the surgical microscope is commonly used to get good surgical field. However, as the time of operation becomes lengthened, it results in longer retraction of the brain and probable greater ischemic infarction. To estimate the risk of ischemic damage, the authors investigated the regional cerebral blood flow(rCBF) and the electroencephalographic(EEG) activity at different forces and durations of the brain retraction in the cat models simulating the frontal approach of the pituitary surgery. Twenty-six adult cats weighing from 2.4 to 4.5 kg were used in this study. The animals were divided into 3 groups : control(n=6), 20g-retraction(n=10), and 30g-retraction groups(n=10) respectively. The brain retraction was produced by applying the lead weight with the stainless steel retractor on the right frontal lobe through a craniectomy over the right frontal bone. The weight(20g or 30g) was supported with the pulley so that its long axis was perpendicular to the cortical surface, The measurements of rCBF activity were carried out in each animal before and immediately after brain retraction at 30 min, 60 min, 90 min, 120 min and 180 min after retraction. The results were as follows ; 1) After brain retraction, there were rise in intracranial pressure, bradycardia, elevation in blood pressure and alteration in respiration at 60 min after brain retraction. 2) Normal control flows(rCBF, ml/100g/min) were 39.7+/-6.1 in the right frontal, 37.8+/-2.6 in the left frontal, 37.5+/-3.6 in the right parietal and 38.8+/-4.1 in the left parietal lobes. 3) A considerable reduction in rCBF was demonstrated at 60 min after brain retraction. A reduction of rCBF to 40% of control flow(19.5+/-7.5ml/100g/min) was found at 60 min after retraction in the right frontal with the 20g-retractor. With the 30g-retractor, rCBF were reduced to 64% of control flow(13.3+/-6.8ml/100g/min) at 60 min and 90% of control flow(4.0+/-2.1 ml/100g/min) at 180 min after retraction in the right frontal lobe. 4) A close correlation was found between EEG activity and rCBF changes, suggesting a threshold relationship. The changes of EEG activity began to be noted at the rCBF value of less than 20.0 ml/100g/min. A 50% suppression of the EEG activity appeared at the rCBF value of 4.0+/-1.2 ml/100g/min. It is concluded that EEG activity is secondarily is secondarily suppressed by reduction in local blood flow which is caused by local compression. It is advisable to retract the brain with the least force necessary and for the shortest time possible. It is also suggested to resect the brain partially before retraction to avoid irreversible ischemic infarction of the brain in consequence of forceful, longtime retraction in exploration of deep intracranial lesions.
Adult ; Animals ; Axis, Cervical Vertebra ; Blood Pressure ; Bradycardia ; Brain Infarction ; Brain Ischemia ; Brain* ; Cats* ; Electroencephalography ; Frontal Bone ; Frontal Lobe ; Humans ; Infarction ; Intracranial Pressure ; Parietal Lobe ; Rabeprazole ; Respiration ; Stainless Steel