Retraction Pressure Research Articles

Deep Bypasses to the Distal Posterior Circulation

The subtemporal approach for a superficial temporal artery-to-superior cerebellar artery bypass requires significant superior retraction that can injure the temporal lobe, compromise veins, and cause edema postoperatively. In contrast, the pretemporal approach requires posterolateral retraction that seems to be less injurious to the temporal lobe and better tolerated clinically. We hypothesized that the pretemporal approach provides ample exposure, more gentle retraction, and better clinical results than the subtemporal approach. Standard orbitozygomatic-pterional and subtemporal approaches were performed on both sides of 4 formalin-fixed cadaver heads for morphometric measurements. Temporal lobe retraction was quantified for each approach in terms of brain shift and retraction pressure by using both sides of 3 fresh, unfixed cadaver heads. Similar morphometric measurements were made in 14 patients in whom bypasses to the distal posterior circulation were performed. The effect of temporal lobe retraction was assessed with edema volumes on postoperative computed tomography scans. In cadaver heads and in patients, the pretemporal approach optimized exposure of the P2A segment of the posterior cerebral artery (PCA) and the subtemporal approach optimized exposure of the lateral pontomesencephalic segment of the superior cerebellar artery (SCA). Working depths and lengths of exposed artery were similar with these 2 approaches, but the PCA was a larger recipient than the SCA. Brain shift was 42% less with pretemporal than with subtemporal retraction, and retraction pressure was 43% less with pretemporal than with subtemporal retraction. The volume of temporal lobe edema was 56% less in patients with bypasses performed with the pretemporal approach as compared with the subtemporal approach. Pretemporal exposure of the PCA is equivalent to subtemporal exposure of the SCA, but the pretemporal approach is facilitated by a larger recipient artery. Posterolateral temporal lobe retraction associated with the pretemporal approach is gentler than superior retraction with the subtemporal approach. These results validate our preference for the pretemporal approach over the subtemporal approach when performing deep bypasses to the posterior circulation.

Intrusion and Retraction of Fluids in Nanopores: Effect of Morphological Heterogeneity

This paper reports on a molecular simulation study of intrusion and retraction of a nonwetting fluid in silica nanopores without or with morphological defects (constrictions or undulations) to mimic mercury porosimetry in porous materials. All the pores considered in this work are of a finite length and are connected to bulk reservoirs so that they mimic real materials for which the confined fluid is always in contact with the external phase. Our results for pores with constant or variable cross-section are in qualitative agreement with experimental data: (1) the intrusion and retraction pressures are larger than the bulk saturating vapor pressures, (2) the intrusion and retraction pressures are decreasing functions of the pore size, and (3) entrapment of the confined fluid leads to irreversible intrusion/retraction isotherms (except for the smallest pore, for which intrusion is reversible). Our data show that the intrusion pressure varies linearly with the pore diameter when both quantities are plotted on a logarithmic scale; the slope, −1.1 ± 0.1, is close to the theoretical value −1 given by the Washburn−Laplace equation (the contact angle θa is found to be about 102° ± 15°). In contrast, the retraction pressure varies with a larger slope, −1.6 ± 0.1, due to the fact that retraction consists of the nucleation of a gas bubble within the pore. We find that the intrusion chemical potential for the large cavities of the constricted pores corresponds to that for a regular cylindrical nanopore having the same diameter as the constriction, i.e. intrusion in the constricted pores occurs when the nonwetting fluid invades the constrictions that isolate the large cavity from the bulk external phase. On the other hand, the retraction chemical potentials for pores with uneven diameter underestimates the value found for a regular cylindrical pore having the pore diameter of the wider parts of the variable-diameter pore. These results suggest that intrusion and retraction experiments (porosimetry) can be used to assess and characterize morphological defects in nanopores, provided that the pore size is known from other independent measurements. The present work also provides a theoretical frame to explain some discrepancies observed between properties assessed by mercury porosimetry and nitrogen adsorption.

2A1-G10 バルーンを用いた手術支援マニピュレータの開発 : バルーンセンサによる圧排圧力の推定(手術支援ロボティクス・メカトロニクス)

2A1-G10 バルーンを用いた手術支援マニピュレータの開発 : バルーンセンサによる圧排圧力の推定(手術支援ロボティクス・メカトロニクス)

A Comparison of Retraction Pressure During Anterior Cervical Plate Surgery and Cervical Disc Replacement

Dysphagia is a well-recognized complication after anterior cervical discectomy and fusion, observed in as high as 50% of cases by videofluoroscopic evaluation postoperatively. Esophageal injury due to surgical retraction is a complication due to which swallowing difficulties may ensue. There are limited published data evaluating the effect of soft tissue retraction on intraesophageal pressures during anterior cervical instrumentation procedures. The purpose of this study was to (a) measure the intraesophageal pressure secondary to retraction during anterior instrumentation, (b) determine whether any pressure differences exist between plating and cervical disc replacement, and (c) determine whether the surgical level or length of the plate influences the magnitude of intraesophageal pressure during retraction. An analysis of soft tissue retraction pressure was performed for anterior single-level and 3-level cervical plating and cervical disc replacement procedures. Using a 4-cm transverse incision, a Smith-Robinson anterior approach to the cervical spine was performed on 7 fresh, frozen cadavers. The correct placement of an esophageal pressure-transducing catheter was confirmed by laryngoscopy, manual palpation of the esophagus, and fluoroscopic imaging. Three surgical instrumentation groups were used for comparisons: (a) single-level plate (b) single-level Porous Coated Motion cervical disc replacement, and (c) 3-level plate. Hand-held appendiceal retractors were used to retract the soft tissues during screw insertion into the plate and during application of the disc prosthesis into the interspace. Care was taken to exert just enough force on the retractors to allow the surgeon to move the desired implant into the correct position. In addition the individual performing the retraction was blinded to the procedure being performed-1-level plating, 3-level plating, or disk replacement. Fluoroscopy confirmed that the pressure sensors were directly behind the retractors during data acquisition. Significantly greater intraesophageal pressures were demonstrated for single-level cervical plating at C5-6 compared to that at C3-4 (P=0.036). Similarly, significantly greater pressures were recorded at C5-6 versus C3-4 for the 3-level plating group (P<0.001). In contrast, there was no statistically significant difference in pressures observed during disk replacement at C5-6 compared to that at C3-4 (P=0.084). Significantly greater pressures were recorded during single-level plating compared to disc replacement at both C3-4 (P=0.016) and C5-6 (P=0.016). Three-level plating demonstrated significantly greater pressures at C5-6 compared to disk replacement (P<0.001) but no statistically significant difference compared to disk replacement at C3-4 (P=0.333). The highest mean pressure, 154.5+/-49.5 mm Hg, was recorded at C5-6 level during insertion of the 3-level plates. On the basis of the data presented here, anterior cervical plating results in significantly greater intraesophageal pressures when performed at C5-6 compared to C3-4. This holds regardless of whether the plate spans the distance from C3 to C6 (3-level plate) or the single C5-6 level. In addition, the insertion of the cervical disc replacement seems to require less esophageal retraction and hence reduced intraesophageal pressures when compared to anterior cervical plating.

Comparison of Minimally Invasive and Conventional Open Posterolateral Lumbar Fusion Using Magnetic Resonance Imaging and Retraction Pressure Studies

To determine whether minimally invasive lumbar spinal fusion results in less paraspinal muscle damage than conventional open posterior fusion. The maximum intramuscular pressure (IMP) generated by a minimally invasive and standard open retractor was compared in cadavers using an ultra-miniature pressure transducer. In a second clinical study, eight patients with either minimally invasive or open posterolateral lumbar spinal fusion underwent magnetic resonance imaging (MRI) scanning approximately 6 months post surgery. MRI was used to estimate edema and atrophy within multifidus, with T2 mapping and diffusion-weighted imaging allowing quantification of differences between the two surgical techniques. IMP measured with the minimally invasive retractor was 1.4 versus 4.7 kPa with the open retractor (P < 0.001). The minimally invasive retractor produced a transient maximal IMP only on initial expansion. Maximum IMP was constant throughout open retractor deployment. Striking visual differences in muscle edema were seen between open and minimally invasive groups on MRI. The mean T2 relaxation time at the level of fusion was 47 milliseconds in the minimally invasive and 90 milliseconds in the open group (P = 0.013). The mean apparent diffusion coefficient was 1357 x 10(-6) mm/s and 1626 x 10(-6) mm(2)/s (P = 0.0184), respectively. The peak IMP generated by the minimally invasive retractor was significantly less than with the open retractor. Postoperatively, less muscle edema was demonstrated after the minimally invasive lumbar spinal fusion, with lower mean T2 and apparent diffusion coefficient measurements supporting the hypothesis that less damage occurs using a minimally invasive approach.

Intraoperative measurement of pharynx/esophagus retraction during anterior cervical surgery. Part I: pressure

Temporary dysphagia after anterior cervical discectomy (ACD) is common. However, its mechanism is poorly understood. Pressure induced by retractor blades onto pharynx/esophagus were measured intraoperatively in order to gain more information regarding traumatization of the pharynx/esophagus wall. Thirty-one patients underwent anterior cervical discectomy and fusion (ACDF) for degenerative disc disease. An online pressure transducer was applied to the rear side of the medial retractor blade (epi-esophageal-pressure, epi-P) and a cylindric, inflatable transducer was preoperatively inserted into the pharynx/esophagus under fluoroscopic guidance at the level to be operated on (endo-esophageal-pressure, endo-P). Pressure values were recorded continuously during the operation. Mean arterial pressure (MAP) and endotracheal cuff pressure (ETCP) were recorded additionally. An in vitro model was developed in order to analyze the impact of the retractor blade design onto the epi-esophageal-pressure. Mean epi-P before and following adequate retractor opening for exposure of the disc space was 58.3 and 92.7 mmHg. Thirty, 60 and 90 min later the epi-P decreased to 79, 70 and 66%, respectively. Mean basal endo-P was 9.8 mmHg and increased to 20.6 mmHg after retractor placement. Thirty, 60 and 90 min later the endo-P decreased to 80, 71 and 62%, respectively. The mean MAP was 76 mmHg and the ECTP was adjusted to 25 mmHg during the procedures. In the in vitro model retraction pressure correlated inversely with the contact area between visceral wall and retractor blade. During ACDF the retraction pressure onto the pharyngeal/esophageal wall exceeds MAP and even more the mucosal perfusion pressure of 25 mmHg. Over time the pharynx/esophageal wall adapts to the applied pressure induced by the retractor blade. The contact area between them influences the retraction pressure.

Technical pitfalls in a porcine brain retraction model

We describe technical pitfalls of a porcine brain injury model for identifying primary and secondary pathological sequelae following brain retraction by brain spatula. In 16 anaesthetised male pigs, the right frontal brain was retracted in the interhemispheric fissure by a brain spatulum with varying pressures applied by the gravitational force of weights from 10 to 70 g for a duration of 30 min. The retracted brain tissue was monitored for changes in intracranial pressure and perfusion of the cortex using a Laser Doppler Perfusion Imager (MoorLDI). To evaluate the extent of oedema and cortical contusions, MRI was performed 30 min and 72 h after brain retraction. Following the MR scan, the retracted brain areas were histopathologically assessed using H&E and Fluoro-Jade B staining for neuronal damage. Sinus occlusion occurred in four animals, resulting in bilateral cortical contusions and extensive brain oedema. Retracting the brain with weights of 70 g (n = 4) caused extensive oedema on FLAIR images that correlated clinically with a hemiparesis in three animals. Morphologically, an increased number of Fluoro-Jade B-positive neurons were found. A sequential decrease in weights prevented functional deficits in animals. A retraction pressure applied by 10-g weights (n = 7) caused a mean rise in intracranial pressure to 4.0 +/- 3.1 mm Hg, and a decrement in mean cortical perfusion from 740.8 +/- 41.5 to 693.8 +/- 72.4 PU/cm2 (P < 0.24). A meticulous dissection of the interhemispheric fissure and a reduction of weights to 10 g were found to be mandatory to study the cortical impact caused by brain spatula reproducibly.

P155. Intraesophageal retraction pressure during anterior cervical plating vs. cervical disc replacement

BACKGROUND CONTEXT: Dysphagia is a well-recognized complication following anterior cervical discectomy and fusion, observed as high as 50% by videofluoroscopic evaluation postoperatively. Esophageal injury due to surgical retraction is one mechanism by which swallowing difficulties may ensue. There are limited published data evaluating the effect of soft tissue retraction on intra-esophageal pressures during anterior cervical instrumentation procedures.

Development of multi-DOF brain retract manipulator for minimally invasive neurosurgery

In order to extend applicable area of minimally invasive neurosurgery, multi-DOF brain retract manipulator is developed. By inserting this manipulator deeper into the brain as a conductor and then other micromanipulator [K. Kan, M. Fujie, F. Tajima, K. Nishizawa, T. Kawai, A. Shose, Development of HUMAN system with three micromanipulators and minimally invasive neurosurgery, Proc. on the 15th International Symposium and Exhibition of Computer Assisted Radiology and Surgery (CARS), 2001, pp. 144–149.] afterwards, it will be possible to realize new minimally invasive neurosurgery. The brain retract manipulator system consists of the following mechanisms: 10-DOF polyarticular spatula, brain retraction pressure monitoring system, Tendon-driven unit, which controls lock or free status of each joint of polyarticular spatula, passive-hybrid control system that assures the system a suitable safety, and 6-DOF SCARA type supporting structure. In evaluation test with a hog, insertion of the polyarticular spatula as deep as the cerebral base was realized, and the possibility of securing the space between the temporal lobe and the cerebral base is verified.

Effects of nerve root retraction in lumbar discectomy

The authors studied whether the amount of retraction pressure applied to a compromised nerve root during lumbar discectomy has an impact on intra- or postoperative outcome. The authors conducted a prospective analysis of 20 patients. There were 12 men and 12 women whose mean age (+/- standard deviation [SD]) was 42.25 years +/- 15 years (range 21-65 years). During intraoperative electromyography (EMG) monitoring, measurements were obtained during routine retraction of the affected nerve root by using a specially designed and constructed nerve root retractor connected to a reconfigured personal computer for this specific purpose. Follow-up results were assessed in the immediate postoperative period and at up to 1 year. The maximum measured force applied during random periods of time was 9.85 N/second (mean 6.95 +/- N/second [+/- SD]). The mean retraction time was 39.5 +/- 21 (SD). No intraoperative EMG-detected irritation was noted during or after routine retraction. In four of 20 patients, sensory changes occurred at the ipsilateral nerve root level, which resolved at the time of discharge. The authors found that routine nerve root retraction does not cause nerve root irritation, as demonstrated by EMG monitoring, nor was patient outcome affected in this series.

Physiologic changes of nerve root during posterior lumbar discectomy.

The effects of nerve root retraction in posterior discectomy on pressure, blood flow, and electrophysiologic changes of the nerve root were investigated. This study was performed to assess the effects of nerve root retraction in posterior discectomy on pressure, blood flow, and electrophysiologic changes of the nerve root. The effects of compression on nerve tissue have been clinically studied mainly in peripheral nerves. The potential risk for lumbar nerve root injury has not been evaluated precisely in humans. Among 31 patients with lumbar intervertebral disc herniation, the correlation between retraction pressure and changes in blood flow of the nerve root was evaluated. Retraction pressure was continuously monitored during the discectomy and the length of the discectomy procedure was measured. Threshold and amplitude of compound muscle action potentials were monitored before and after discectomy. The relationship between intraoperative data on nerve root physiology and postoperative neurologic change was analyzed. Nerve root blood flow was decreased to 18-30% of the initial value under the pressure around 70 g/cm2. An abrupt decrease in nerve root blood flow was observed even within 1 or 2 mm of retraction distance. The threshold of the nerve root before retraction was minimal in the nerve root of the asymptomatic side, but increased in the affected root demonstrating sensory loss only, and significantly increased in the root showing sensory/motor deficit. Amplitude of compound muscle action potentials evoked by the stimulation at distal from herniated mass was lowest in the nerve root showing sensory/motor deficit. In 4 of 31 patients, high retraction pressure (> 170 g/cm2) was required and they showed temporary sensory deterioration after surgery. The length of discectomy procedure in these 4 patients was 14.1 +/- 4.1 minutes, but it was 9.9 +/- 2.7 minutes in the remaining 27 patients. In posterior lumbar discectomy, nerve root ischemia usually occurs during retraction. The magnitude of pressure and time of retraction may be potential risk factors for nerve root injury.

Back muscle injury after posterior lumbar spine surgery. Part 2: Histologic and histochemical analyses in humans.

The histologic and histochemical changes in back muscle were studied in virgin surgery patients with lumbar spine disorders and in patients who underwent repeat posterior lumbar surgery. The results were correlated to provide the evidences of histologic changes of back muscle after posterior lumbar surgery. Back muscles were examined histologically and histochemically after posterior lumbar surgery. No previous study has assessed these changes. Back muscles were obtained before and after retraction from 18 virgin surgery cases with lumbar spine disorders. In four patients, the retraction pressure was monitored and the retraction pressure-time products ([P][T]) were calculated. In 21 repeat lumbar surgery cases, muscle samples were obtained before muscle retraction. Samples were evaluated by histologic and histochemical methods. Abnormal findings were slight in virgin surgery cases. Early back muscle injury tended to depend on operation time and [P][T] products. Late back muscle injury in reoperated patients was marked. Various types of neurogenic changes were observed more than 10 months after the first operation. Histologic damages of back muscle due to previous surgical intervention were long-lasting. To avoid permanent muscle injury, the retraction time and pressure should be shortened or the pressure on the back muscle should be monitored during posterior surgery.

A review of brain retraction and recommendations for minimizing intraoperative brain injury.

Brain retraction is required for adequate exposure during many intracranial procedures. The incidence of contusion or infarction from overzealous brain retraction is probably 10% in cranial base procedures and 5% in intracranial aneurysm procedures. The literature on brain retraction injury is reviewed, with particular attention to the use of intermittent retraction. Intraoperative monitoring techniques--brain electrical activity, cerebral blood flow, and brain retraction pressure--are evaluated. Various intraoperative interventions--anesthetic agents, positioning, cerebrospinal fluid drainage, operative approaches involving bone resection or osteotomy, hyperventilation, induced hypotension, induced hypertension, mannitol, and nimodipine--are assessed with regard to their effects on brain retraction. Because brain retraction injury, like other forms of focal cerebral ischemia, is multifactorial in its origins, a multifaceted approach probably will be most advantageous in minimizing retraction injury. Recommendations for operative management of cases involving significant brain retraction are made. These recommendations optimize the following goals: anesthesia and metabolic depression, improvement in cerebral blood flow and calcium channel blockade, intraoperative monitoring, and operative exposure and retraction efficacy. Through a combination of judicious retraction, appropriate anesthetic and pharmacological management, and aggressive intraoperative monitoring, brain retraction should become a much less common source of morbidity in the future.

Subtemporal Amygdalohippocampectomy for Treating Medically Intractable Temporal Lobe Epilepsy

A SUBTEMPORAL AMYGDALOHIPPOCAMPECTOMY technique has been developed for mesial temporal lobe epilepsy. The conventional subtemporal approach has been modified to diminish temporal lobe retraction and the risk of damage to the temporal lobe. In the new technique, the surgeons' position has moved from above to below and the approach has been changed from anterolateral to posterolateral, thereby avoiding the voluminous and steeply inclined anterior temporal lobe. By this modified approach, it was unnecessary to remove the roof of the external auditory meatus and it was estimated that both the retraction pressure and the extent of temporal lobe retraction were reduced. To date, surgeons using this approach have operated on four patients with temporal lobe epilepsy whose epileptic foci were in the mesial temporal structure; the inferior temporal gyrus, the temporal tip, the vein of Labbé, and the ventral bridging veins were preserved. After surgery, two patients became completely free of seizures and the other two showed over 90% reduction in seizure frequency without neurological sequelae. Postoperative visual field examination revealed full visual fields without quadrantanopsia. This approach can preserve the temporal stem and lateral temporal lobe, it can be used to remove as much of the posterior hippocampus as necessary, and it can be extended to conventional lobectomy if it is indicated.

Retraction brain ischaemia: cerebral blood flow, evoked potentials, hypotension and hyperventilation in a new animal model.

Undue intraoperative brain retraction can cause significant neurosurgical morbidity. By combining brain retractor blade pressure measurement with monitoring of brain electrical activity, one can determine the limits of safe brain retraction and then test systematically various therapeutic interventions. Cortical evoked potential (EP) mapping and laser-Doppler cerebral blood flow (CBF) measurement were undertaken during brain retraction in the miniature swine (Sus scrofa). Forelimb somatosensory EP recording during subtemporal retraction simulated the pterional and subtemporal approaches, respectively. Retraction pressure of 30 mmHg usually resulted in a 50% decrement in EP amplitude after 10 to 20 minutes in normotensive, normocapnic adult animals. Recovery of EP occurred within 5 to 10 minutes of retraction release. The effects of animal age, induced hypotension (nitroprusside, MAP approximately 40), and induced hypocapnia (hyperventilation, PaCO2 approximately 28) on EP preservation during retraction were then investigated, with data reported here from 23 animals (8 to 35 kg). By Spearman rank correlation coefficients, early loss of EP was associated with the following: lower MAP (p approximately 0.0001), lower CBF (p approximately 0.0005), lower PaCO2 (p less than 0.001), and older age (p approximately 0.01). These results indicate (1) retractors should be relaxed every 10-15 minutes whenever possible (for at least 5 minutes), and (2) hypotension, in particular, but also hypocapnia (hyperventilation) should not be used indiscriminately. Details of this new model of retraction ischaemia are presented.

虚血性脳血管障害に合併する無症候性脳動脈瘤に対する治療方針

This study is based on eighty-five cases of unruptured asymptomatic aneurysms associated with ischemic cerebrovascular disease. Sixty-one cases (73 aneurysms) were treated surgically and 24 cases were treated non-surgically. The post-operative course was uneventful in 50 out of 61 cases (82%) and unsatisfactory in 11 cases (18%). There was no significant relation of the surgical results to site of aneurysm, type of stroke, or pre-operative CT and angiographical findings. The results appeared to correlate with patients' age and surgical technique. In the 11 unsatisfactory cases, symptoms worsened due to an intracerebral hematoma (ICH), an enlargement of the infarcted area or a subarachnoid hemorrhage (SAH). The cause of death in five cases, three of which were patients over 70, was attributed to acute myocardial infarction in 2 cases, large post-operative ICH in 2 cases and SAH in 1 case.In the 24 cases without surgery, only one aneurysm ruptured during 1-7 years follow-up.Based on these results, surgery might be indicated for cases with complicated lesions to prevent future SAH due to rupture of aneurysm and stroke following TIA. However, surgery is associated with a high rate of post-operative complications, because ischemic brain tissue is very vulnerable to retraction pressure. Patients over 70 with these complicated lesions should be excluded from surgical indication.

EFFECT OF PROPOFOL ON BRAIN RETRACTION PRESSURE AND CEREBRAL PERFUSION PRESSURE

We have studied the effect of propofol, at a rate of 30 mg kg-1 h-1 for 5 min reducing to 6 mg kg-1 h-1 for a further 5 min, on brain retraction pressure (BRP) in 15 patients undergoing craniotomy. The response of BRP showed two distinct patterns. BRP was reduced by an average of 3.3 mm Hg (P = 0.005). Mean arterial pressure was reduced in all patients by an average maximum of 28.3 mm Hg (P = less than 0.001), which caused a significant reduction in cerebral perfusion pressure (CPP) by 22.9 mm Hg (P less than 0.001). It is concluded that, by reducing BRP, propofol provided suitable conditions for intracranial surgery, but care should be taken to avoid excessive reduction in CPP.

A prototype retractor system designed to minimize ischemic brain retractor injury: Initial observations

The authors have developed and patented a neurosurgical retractor system incorporating an infrared emitter and detector that allows detection of cerebral pulsations. Gentle contact with the surface of cat brains shows cerebral pulsations that correlate with arterial pulse as well as mechanical ventilation. The amplitude of cerebral pulsations decreases with higher retraction pressure and disappears at approximately 20 mmHg. The pressure on the surface of the brain decreased 50% in 5 minutes even though the position of the retractor was maintained constant. The authors postulate that monitoring cerebral pulsation may prove useful in clinical neurosurgery with respect to avoiding excessive retraction, which causes brain damage.

Monitoring retraction pressure on the brain. An experimental and clinical study.

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.

Reduction of regional cerebral blood flow during brain retraction pressure in the rat.

The use of brain retractors in intracranial operations may lead to focal cerebral ischemia and thereby cause brain infarction. To estimate the risk of ischemic damages, the authors investigated the regional cerebral blood flow (rCBF) in rats by means of autoradiography with 14C-iodoantipyrine at different brain retractor pressures (BRP). A reduction in rCBF to between 10 and 75 ml/100 gm/min with 20 mm Hg of BRP for 30 minutes was found in brain cortex lying under the retractor (normal 55 to 150 ml/100 gm/ min). With a BRP of 30 mm Hg for 30 minutes, rCBF was reduced to between 0 and 40 ml/100 gm/min, and with a BRP of 40 mm Hg for 15 minutes rCBF was 0 to 15 ml/100 gm/min. The rCBF in the basal ganglia remained unchanged. Even with a BRP of 20 mm Hg for 30 minutes, there seemed to be a risk of focal ischemic damage.