Resection Of Intradural Spinal Tumors Research Articles

Single-Center Experience of Resection of 120 Cases of Intradural Spinal Tumors

Our study presents a single center experience in resection of intradural spinal tumors either with or without using intraoperative CT (iCT)-based registration and microscope-based augmented reality (AR). Microscope-based AR was recently described for improved orientation in the operative field in spine surgery, using superimposed images of segmented structures of interest in a two- (2D) or three-dimensional (3D) mode. All patients who underwent surgery for resection of intradural spinal tumors at our department were retrospectively included in the study. Clinical outcomes in terms of postoperative neurological deficits and complications were evaluated, as well as neuroradiological outcomes for tumor remnants and recurrence. 112 patients (57 female, 55 male, median age 55.8 ± 17.8 years) who underwent 120 surgeries for resection of intradural spinal tumors with use of intraoperative neuromonitoring were included in the study, with median follow up of 39 ± 34.4 months. Nine patients died during the follow-up to reasons unrelated to surgery. Most common tumors were meningioma (n= 41), schwannoma (n= 37), myopapillary ependymomas (n= 12), ependymomas (n= 10), and others (20). Tumors were in thoracic spine (n= 46), lumbar spine (n= 39), cervical spine (n= 32), lumbosacral spine (n= 1), thoracic and lumbar spine (n= 1) and one tumor in cervical, thoracic, and lumbar spine. Four biopsies were performed, ten partial resections, 13 subtotal resections, and 93 gross total resections. Laminectomy was the common approach. In 79 cases, patients experienced neurological deficits prior to surgery, with ataxia and paraparesis as the most common ones. Following surgery, 67 cases were unchanged, in 49 improved and in 4 worsened. Operative time, extent of resection, clinical outcome and complication rate did not differ between the AR and non-AR group. However, use of AR improved orientation in the operative field by identification of important neurovascular structures. High rates of GTR with favorable neurological outcome in a vast majority of patients as well as low recurrence rate with comparable complication rates was noted in our single center experience. AR improved intraoperative orientation and increased surgeons comfort by enabling early identification of important anatomical structures , however clinical and radiological outcomes did not differ, when AR was not used.

A Retrospective Cohort Study Evaluating the Comparative Effectiveness of Unilateral Hemilaminectomy and Bilateral Laminectomy in the Resection of Spinal Meningiomas.

The primary treatment modality for spinal meningiomas (SM) is surgical resection. In recent years, minimal invasive spine surgery has gained considerable popularity, attributing its growth to advancements in surgical technologies and improved training of surgeons. Nonetheless, the suitability and effectiveness of minimal invasive spine surgery for intradural spinal tumor resection remain a subject of debate. In this cohort study, we aimed to compare the extent of resection of the unilateral hemilaminectomy approach, a less invasive technique, with the more traditional and invasive bilateral laminectomy. We performed a retrospective cohort study including patients with SM who underwent surgery at our department between 1996 and 2020. Cohorts included patients who underwent tumor resection through bilateral laminectomy and patients who underwent a unilateral hemilaminectomy. The primary end point was extent of resection according to the Simpson classification. Of 131 with SM, 36 had a bilateral laminectomy and 95 were operated through a unilateral hemilaminectomy. In both groups, gross total resection, Simpson grades 1 and 2, was achieved in 94.44% and 94.74%, respectively (P = .999). The neurological outcome was also comparable in both cohorts (P = .356). Both length of hospital stay and estimated blood loss were significantly lower in the unilateral cohort (P < .05). The results of this study indicate that the unilateral hemilaminectomy yields comparable results in both oncological and neurological outcome when compared with the bilateral laminectomy. Thus, unilateral hemilaminectomy may serve as a viable and safe alternative for the surgical removal of SM.

Subfascial drains are safe and effective in preventing postoperative cerebrospinal fluid leaks after intradural spine tumor surgery.

Delayed cerebrospinal fluid (CSF) leaks are a known complication following intradural spinal tumor surgery. The placement of subfascial drains in these patients undergoing requisite intradural surgery is controversial. Here, we demonstrated that placing a subfascial drain on partial suction for 48 h, with early ambulation, proved to be safe and effective in preventing early/delayed recurrent CSF fistulas. Medical records of 17 patients undergoing surgery for intradural spinal tumors over a 30-month were reviewed. All patients underwent intradural tumor resection followed by primary dural closure, placement of Gelfoam in a non-compressive fashion, application of fibrin sealant, and utilization of a subfascial drain placed on partial suction for 48 h postoperatively. Patients are mobilized the morning following surgery. We tracked the incidence of postoperative recurrent CSF leaks, over drainage, infection, wound dehiscence, pseudo meningocele formation, and the reoperation rate. For the 17 patients, our programmed average utilization of subfascial drains was 48 h. Moreover, the average drain output was 165 mL. Over the 1-year follow-up period, no patient developed a recurrent early/ delayed CSF leak, there were no wound complications, nor need for revision surgery. Utilizing subfascial drains on partial suction following the resection of intradural spinal tumors with primary dural closure proved to be safe and effective.

Fluorescence-guided resection of intradural spinal tumors: a systematic review and meta-analysis

Fluorescence-guided resection of intradural spinal tumors: a systematic review and meta-analysis

Prediction of Discharge Status and Readmissions after Resection of Intradural Spinal Tumors.

ObjectiveIntradural spinal tumors are uncommon and while associations between clinical characteristics and surgical outcomes have been explored, there remains a paucity of literature unifying diverse predictors into an integrated risk model. To predict postresection outcomes for patients with spinal tumors. MethodsIBM MarketScan Claims Database was queried for adult patients receiving surgery for intradural tumors between 2007 and 2016. Primary outcomes-of-interest were nonhome discharge and 90-day postdischarge readmissions. Secondary outcomes included hospitalization duration and postoperative complications. Risk modeling was developed using a regularized logistic regression framework (LASSO, least absolute shrinkage and selection operator) and validated in a withheld subset. ResultsA total of 5,060 adult patients were included. Most surgeries utilized a posterior approach (n=5,023, 99.3%) and tumors were most commonly found in the thoracic region (n=1,941, 38.4%), followed by the lumbar (n=1,781, 35.2%) and cervical (n=1,294, 25.6%) regions. Compared to models using only tumor-specific or patient-specific features, our integrated models demonstrated better discrimination (area under the curve [AUC] [nonhome discharge] = 0.786; AUC [90-day readmissions] = 0.693) and accuracy (Brier score [nonhome discharge] = 0.155; Brier score [90-day readmissions] = 0.093). Compared to those predicted to be lowest risk, patients predicted to be highest-risk for nonhome discharge required continued care 16.3 times more frequently (64.5% vs. 3.9%). Similarly, patients predicted to be at highest risk for postdischarge readmissions were readmitted 7.3 times as often as those predicted to be at lowest risk (32.6% vs. 4.4%). ConclusionUsing a diverse set of clinical characteristics spanning tumor-, patient-, and hospitalization-derived data, we developed and validated risk models integrating diverse clinical data for predicting nonhome discharge and postdischarge readmissions.

Microsurgical Resection of Giant Thoraco-Lumbo-Sacral Ependymoma With Hybrid Spinal Reconstruction Using Multilevel Laminoplasty and Up-Front Thoracolumbar Posterior Fixation: 2-Dimensional Operative Video.

Extensive multifocal intradural lesions in children present a formidable challenge. This surgical video illustrates our management of a 14-yr=old boy with two intradural mass lesions on magnetic resonance imaging (MRI): one at T2-5 and the other from T12 through the sacral cul-de-sac. In a single procedure, we performed a T2-5 laminectomy and laminoplasty and T12-sacrum laminectomy for tumor resection. For reconstruction, we performed complete laminoplasty at all levels with supplementation at the thoracolumbar junction via T11-L2 posterior spinal fixation and allograft placement for fusion. In this video, we illustrate the microsurgical challenges of intradural tumor resection in both the thoracic cord and amidst the cauda equina. In young patients, prevention of postsurgical spinal deformity is of paramount concern. We discuss considerations for long-segment spinal stabilization in an adolescent and describe our decision-making to perform stabilization at the thoracolumbar junction to supplement laminoplasty while preserving function. The patient and their family consented to the procedure. Image of the article at 0:51 is from McGirt et al, Short-term progressive spinal deformity following laminoplasty versus laminectomy for resection of intradural spinal tumors: analysis of 239 patients, Neurosurgery, 2010, 66(5), 1005-1012, by permission of the Congress of Neurological Surgeons.

Utility of Augmented Reality and Virtual Reality in Spine Surgery: A Systematic Review of the Literature

Augmented reality (AR), virtual reality (VR), and mixed reality (MR) are emerging technologies that are starting to be translated into clinical practice. Limited data are available regarding these tools in use during live surgery of the spine. Our objective was to systematically collect, analyze, and interpret the existing data regarding AR, VR, and MR use in spine surgery on living people. A systematic review was conducted using the PRISMA (preferred reporting items for systematic reviews and meta-analyses) guidelines. The PubMed, PubMed Central, Cochrane Reviews, and Embase databases were searched. Combinations and variations of the phrases "augmented reality," "virtual reality," and spine surgery using both "AND" and "OR" configurations were used to find relevant studies. The references of the included reports from the systematic review were also screened for possible inclusion as a part of a manual review. The included studies were full-text publications written in English that had included any spine surgery on live persons with the use of VR or AR. A total of 1566 unique reports were found, and 15 full-text publications met the criteria for the present study. The total number of patients from all studies was 241, with a weighted average age of 50.37 years. Surgical procedures using AR, VR, and/or MR were diverse and spanned from simple discectomy to intradural spinal tumor resection. All patients experienced improvement in their symptoms present at clinical presentation. The highest complication rate reported in the studies was 6.1% and was for suboptimal pedicle screw placement. No complications led to clinical sequelae. The systematically collected, analyzed, and interpreted data of existing peer-reviewed full-text articles showed favorable metrics regarding surgical efficacy, pedicle screw target accuracy, radiation exposure, clinical outcomes, and disability and pain for patients with spinal pathology treated with the help of AR, VR, and/or MR.

A refined method of en bloc open-door laminoplasty for resection of intradural spinal tumors in the thoracic and lumbar spine

BackgroundThe open-door laminoplasty has been used to treat cervical spondylotic myelopathy. This technique has been applied to the surgical treatment of thoracic and lumbar spinal canal tumors instead of simple laminectomy or hemilaminectomy. However, previously reported laminoplasty methods did not keep posterior supporting elements intact such as the laminae and the spinous processes with supraspinous and interspinous ligaments, and almost all of them needed instruments for the fixation of reconstructed laminae. The purpose of this paper is to introduce our open-door laminoplasty method, which keep all posterior supporting elements intact and reconstruct the laminae without instrument. MethodsEight patients (mean age 61 years) underwent en bloc open-door laminoplasty in the thoracic and lumbar spine for resection of intradural spinal tumors. Two grooves are made bilaterally on the laminae just medial side of the facet joints. One-half of each spinous process of the adjacent vertebrae above and below the laminoplasty is cracked diagonally to create a green stick fracture and bent to the hinged side for sufficient elevation of the laminar flap. After tumor resection, the laminar flap is restored to its original site, resulting in the complete preservation of the posterior supporting elements. ResultsOperative exposure was good and permitted complete resection. No complications such as postoperative spinal canal stenosis or kyphosis were observed. Computed tomography(CT) indicated that bony fusion occurred in all cases. ConclusionThe supraspinous and interspinous ligaments above and below laminoplasty were kept intact during surgery in our method. Therefore, the continuity of posterior supporting elements (laminae and spinous processes connected by supraspinous and interspinous ligaments) were completely preserved.

Instrumentation following intradural tumor resection: A case analyses and literature review.

Background: Resection of intradural spinal tumors typically utilizes a posterior approach and often contributes to significant biomechanical instability and sagittal deformity.Methods: We searched PubMed for studies regarding pre- and postoperative spine biomechanics/alignment in patients with intradural tumors undergoing posterior decompressions.Results: Three patients underwent posterior decompressions with instrumented fusions to preserve good sagittal alignment postoperatively. Variables analyzed in this study included the extent of preoperative and postoperative deformity, the number of surgical levels decompressed and fused, the different frequencies of instability following the resection of cervical versus thoracic versus lumbar lesions, and whether pediatric patients were most likely to develop instability.Conclusion: Simultaneously performing instrumented fusions following posterior spinal decompressions for tumor removal proved optimal in preventing postoperative spinal deformity. Further, “open” surgical procedures offered more optimal/definitive tumor removal versus minimally invasive approaches, and the greater operative exposure and resultant increased risk for instability were remediated by performing simultaneous fusion.

The Optimal Surgical Approach to Intradural Spinal Tumors: Laminectomy or Hemilaminectomy?

ObjectiveTraditionally, laminectomy has been the preferred surgical approach for the resection of intradural spinal tumors. Recent trends towards minimally invasive techniques have generated interest in hemilaminectomy as an effective alternative surgical approach to resect spinal tumors. However, it remains unclear if the potential benefits of hemilaminectomies, used in other routine spinal procedures, apply to intradural spinal tumors. This report presents a six-year single institutional analysis of open resection of intradural tumors using laminectomies as compared to hemilaminectomies.MethodsA single institution, multisurgeon, retrospective review of 52 patients undergoing resection of intradural spinal tumors over a six-year period was performed. Estimated blood loss, operative time, post-operative complications, length of stay, and post-operative clinical spinal instability were analyzed and compared between the two surgical techniques.ResultsThe mean follow-up was 34 and 20 months for the laminectomy and hemilaminectomy groups, respectively. There was no statistically significant difference in operative times between the two groups (hemilaminectomy: 250.13±76.44 minutes, laminectomy: 244.49±92.85 minutes; p=0.43). Similarly, there was no difference in overall estimated blood loss (hemilaminectomy: 125±74 cc, laminectomy: 256.05±320.8 cc; p=0.27) or mean hospital length of stay (hemilaminectomy: 4.00±2.12 days, laminectomy: 5.26±3.0 days; p=0.60). No patient in either surgical group had post-operative evidence of clinical spinal instability.ConclusionHemilaminectomy is a viable approach for the resection of intradural spinal tumors, with similar rates of post-operative complications to laminectomy when using an open surgical approach. The laminectomy allows for bilateral exposure of the entire spinal canal and neural foramina; and continues to be the preferred method for resection of large tumors with complex morphology.

Dural Repair by Direct Continuous Locking Sutures and Concomitant Insertion of Subfascial Tube in Planned Intradural Spinal Cord Tumor Surgery

Background: Durotomy induced cerebrospinal fluid (CSF) leakage is a terrible complication in spine surgery that could be occurred even with expertise. The estimated rate of CSF leakage in intentional durotomies varies from 5 to 13% in intradural spinal tumor resection to even higher rate for surgeries for tethered cord syndrome or Chiari I malformation. Different treatment modalities are utilized as conservative measures, direct sutures, autograft, dural substitutes and sealant agents to overcome this complication. Patient and method: This is a retrospective descriptive study of thirty patients were operated upon at neurosurgery department of Elsahil teaching hospital from November 2014 to November 2019. They were operated for intradural spinal cord tumor excision followed by primary direct sutural repair of the durotomy site augmented with autograft and concomitant insertion of subfascial tube as a drainage tube for seven to ten days. Aim: To evaluate the results of primary direct dural repair with continuous locking sutures and on lay gel foam layer augmented with autograft (fat or muscle) without sealant agents. With concomitant insertion of subfascial tube closed system as drainage in planned intradural surgery. Results: After subfascial tube removal three cases (10%) show persistent leakage that managed conservatively with tapering cessation within three weeks till complete cessation of the CSF leakage occur. One of the three cases developed pseudomeningocele (3.3%) after complete wound closure and cessation of the leakage. Conclusion: Direct sutural repair of the durotomy site with continuous locking sutural closure and on lay gel foam layer and fat or muscle graft without any sealant agents, and concomitant insertion of subfascial tube closed system as a drainage tube for seven to ten days, is effective and safe economic method for dural repair.

Features and risk factors for recurrence of intradural spinal tumors

Spinal cord tumors include a variety of nosological units and are classified according to their localization and histological type. The search for literature sources in the Pubmed, EMBASE and eLibrary databases demonstrated the absence of studies devoted to study of the features and risk factors for the recurrence of intradural spinal tumors. the purpose of this study was to reveal features and risk factors of recurrence of intradural spinal tumors after microneurosurgical resection. material and methods. The study included medical records of 196 patients with intradural extramedullary and intramedullary spinal tumors. The extent of microneurosurgical tumor resection, clinical efficacy of surgery, and risk factors for recurrence of intradural spinal cord tumors were been analyzed. results. Improvement in neurologic deficit after surgery was noted in 116 (59.1 %) cases, neurologic status remained the same in 47 (24.0 %) patients, and worsening of neurological deficit was observed in 33 (16.8 %) cases. Total microneurosurgical resection of intradural spinal tumors was performed in 140 (71.4 %) patients, subtotal resection in 22 (11.2 %) patients, partial resection in 25 (12.7 %) patients and spinal cord decompression or biopsy and/or its roots were performed in 9 (4.6 %) of patients. The likelihood of recurrence-free survival of patients with benign intradural spinal cord tumors was significantly higher than that of patients with malignant tumors (p&lt;0.001). Benign tumors (χ2=34.7, p&lt;0.05), thoracic and lumbosacral tumors (χ2=10.3, p&lt;0.05), low degree of neurological deficit (χ2=31.5, p&lt;0.05), absence of syringomyelia/syringobulbia signs (χ2=13,2, p&lt;0,05), as well as extramedullary tumors (χ2=12,6, p&lt;0.05) allowed us to perform total degree microneurosurgical resection. Malignant tumors (χ2=34.8, p&lt;0.05), cervical and thoracic tumors (χ2=8,4, p&lt;0,05), high degree of neurological deficit (χ2=12,9, p&lt;0.05), partial resection, biopsy or decompression of neural structures (χ2=9.7, p&lt;0.05) and intramedullary tumors statistically significantly increased the risk of their recurrence. conclusion. Histological pattern, tumor localization, preoperative clinical and neurological deficit according to the McCormick classification and the extent of surgery are significant risk factors for recurrence of intradural spinal tumors.

Descriptive analysis of unplanned readmission and reoperation rates after intradural spinal tumor resection

IntroductionSpinal cord tumors (SCT) are relatively uncommon and usually require surgical treatment. Readmission within 30days after discharge is an important indicator of health care quality. The aim of this study was to investigate the rates and causes of unplanned readmissions and reoperations after SCT surgery. MethodsA retrospective analysis of patients’ charts at a single center from May 2007 to September 2015 was completed. Inclusion criteria: history of laminectomy with excision of neoplasm in the spinal cord. Exclusion criteria: (1) surgery outside the timeframe; (2) less than 19years old; (3) non-neoplastic intramural pathologies; (4) previous resection at the same location; (5) metastatic lesions. ResultsWe found 131 patients that met criteria. Six patients (4.5%) were readmitted within 30days and two within 90days (1.5%). Four underwent reoperation: one for a cerebrospinal fluid leak, two for pseudomenigoceles, and one for repeat laminectomy. Resection of intramedullary tumors resulted in twice the risk of having one or more complications compared to extramedullary tumors (RR 2.0; 95% CI: 1.0–4.2; p=0.057), and nearly four times the risk of having a neurological complication (RR 3.8; 95% CI 1.5–9.5; p=0.005). ConclusionThis study analyzes readmission, reoperation and complication rates for the surgical care of SCT highlighting how SCT surgery is still involved with morbidity in experienced and specialized centers. This information is useful both for health care enhancement projects and for evidence-based patient counseling.

Short-term Progressive Spinal Deformity Following Laminoplasty Versus Laminectomy for Resection of Intradural Spinal Tumors

Gross total resection of intradural spinal tumors can be achieved in the majority of cases with preservation of long-term neurological function. However, postoperative progressive spinal deformity complicates outcome in a subset of patients after surgery. We set out to determine whether the use of laminoplasty (LP) vs laminectomy (LM) has reduced the incidence of subsequent spinal deformity following intradural tumor resection at our institution. We retrospectively reviewed the records of 238 consecutive patients undergoing resection of intradural tumor at a single institution. The incidence of subsequent progressive kyphosis or scoliosis, perioperative morbidity, and neurological outcome were compared between the LP and LM cohorts. One hundred eighty patients underwent LM and 58 underwent LP. Patients were 46 +/- 19 years old with median modified McCormick score of 2. Tumors were intramedullary in 102 (43%) and extramedullary in 102 (43%). All baseline clinical, radiographic, and operative variables were similar between the LP and LM cohorts. LP was associated with a decreased mean length of hospitalization (5 vs 7 days; P = .002) and trend of decreased incisional cerebrospinal fluid leak (3% vs 9%; P = .14). Following LP vs LM, 5 (9%) vs 21 (12%) patients developed progressive deformity (P = .728) a mean of 14 months after surgery. The incidence of progressive deformity was also similar between LP vs LM in pediatric patients < 18 years of age (43% vs 36%), with preoperative scoliosis or loss of cervical/lumbar lordosis (28% vs 22%), or with intramedullary tumors (11% vs 11%). LP for the resection of intradural spinal tumors was not associated with a decreased incidence of short-term progressive spinal deformity or improved neurological function. However, LP may be associated with a reduction in incisional cerebrospinal fluid leak. Longer-term follow-up is warranted to definitively assess the long-term effect of LP and the risk of deformity over time.

171. Progressive Spinal Deformity Following Laminoplasty vs. Laminectomy for Resection of Intradural Spinal Tumors: Analysis of 238 Patients

BACKGROUND CONTEXT: Gross total resection of intradural spinal cord tumors can be achieved in the majority of cases with preservation of long-term neurological function. However, post-operative progressive spinal deformity complicates outcome in a subset of patients after surgery.

Intraoperative sonography of intra- and extramedullary tumors

Intraoperative ultrasound (IOUS) was used in planning the operative resection of intradural spinal tumors, to define its diagnostic potential and limitations. Since 1997, 78 patients diagnosed with an ependymoma ( n = 24), astrocytoma ( n = 7), hemangioblastoma ( n = 7), neurinoma ( n = 15), meningioma ( n = 17) and filum terminale ependymoma ( n = 8) were examined using intraoperative transdural sonography. Intramedullary tumors turned out to show a heterogeneous image with occasional cystic alterations and an indistinct demarcation to the myelon of comparable echogenicity. Intramedullary tumors are easily distinguishable from their extramedullary counterparts, which display a homogeneous signal intensity and sharp demarcation on IOUS. In conclusion, IOUS allows a reliable diagnosis of intraspinal tumors, allowing the distinction between intra- and extramedullary tumors through their respective signal characteristics. Using IOUS, the extension of the neurosurgical approach can be adopted to the true extent of the tumor; thus, avoiding further bone work while the dura is already opened and the frequently edematous spinal cord protrudes through the opening. Our experiences have shown that IOUS may reduce the procedure-related morbidity and should, therefore, be used as a standard intraoperative tool in these high-risk surgical entities. (E-mail: j.regelsberger@uke.uni-hamburg.de)

The development of techniques for resection of spinal cord tumors by Harvey W. Cushing

Harvey Cushing's refinement of Halsted's meticulous surgical techniques facilitated safe resection of intradural spinal tumors. Although Cushing focused his attention on brain tumors at the Peter Bent Brigham Hospital, his numerous contributions to the treatment of intradural spinal tumors include the description of these tumors' natural histories and their histological classifications. The application of his experienced intracranial techniques to the resection of spinal tumors improved outcomes. The authors review selected operative notes and sketches to demonstrate his technique in the excision of the spinal cord tumors.

P-4-481 - Lumbar intradural schwannoma: A case report

Intraoperative ultrasound (IOUS) was used in planning the operative resection of intradural spinal tumors, to define its diagnostic potential and limitations. Since 1997, 78 patients diagnosed with an ependymoma (n = 24), astrocytoma (n = 7), hemangioblastoma (n = 7), neurinoma (n = 15), meningioma (n = 17) and filum terminale ependymoma (n = 8) were examined using intraoperative transdural sonography. Intramedullary tumors turned out to show a heterogeneous image with occasional cystic alterations and an indistinct demarcation to the myelon of comparable echogenicity. Intramedullary tumors are easily distinguishable from their extramedullary counterparts, which display a homogeneous signal intensity and sharp demarcation on IOUS. In conclusion, IOUS allows a reliable diagnosis of intraspinal tumors, allowing the distinction between intra- and extramedullary tumors through their respective signal characteristics. Using IOUS, the extension of the neurosurgical approach can be adopted to the true extent of the tumor; thus, avoiding further bone work while the dura is already opened and the frequently edematous spinal cord protrudes through the opening. Our experiences have shown that IOUS may reduce the procedure-related morbidity and should, therefore, be used as a standard intraoperative tool in these high-risk surgical entities. (E-mail: [email protected])

Cerebral blood flow and cerebral oxygen consumption during hypothermia.

Cerebral blood flow and cerebral oxygen consumption during hypothermia.