Intraoperative neurophysiological monitoring during complex spinal deformity cases in pediatric patients: methodology, utility, prognostication, and outcome

Management of unilateral craniofacial microsomia with orthopaedic functional appliances: A systematic literature review

The study aimed to summarize current knowledge regarding the use of orthopaedic functional appliances (OFA) in managing unilateral craniofacial microsomia (UCM). The eligibility criteria for the review were (1) assessing use of OFA as a stand-alone treatment and (2) using OFA in combination during or after MDO. The PICO (population, intervention, comparison and outcome) format formulated clinical questions with defined inclusion and exclusion criteria. No limitations concerning language and publication year were applied. Information sources: A literature search of Medline, Scopus, Embase, Cochrane Central Register of Controlled Trials, Web of Science databases without restrictions up to 30 September 2022. The risk of bias was assessed. According to Cochrane and PRISMA guidelines, two independent authors conducted data extraction. The level of evidence for included articles was evaluated based on the Oxford evidence-based medicine database. Due to the heterogeneity of studies and insufficient data for statistical pooling, meta-analysis was not feasible. Therefore, the results were synthesized narratively. A total of 437 articles were retrieved. Of these, nine met inclusion criteria: five assessing OFA and four assessing OFA during or after MDO. There is limited evidence to suggest that stand-alone and combination treatment with OFA is beneficial for treating mild-to-moderate UCM-related dentofacial deformities in short term. No studies assessed the burden of care. In the management of UCM, there is insufficient evidence supporting the efficacy of OFA as a stand-alone treatment or when combined with MDO. Additionally, there is a lack of evidence regarding treatment protocols and the effect on the condyles and the TMJ. The study was registered at Prospero database number CRD42020204969.

The "state of the art" of intraoperative neurophysiological monitoring: An Italian neurosurgical survey

Introduction

Intraoperative Neurophysiological Monitoring (IOM) is widely used in neurosurgery but specific guidelines are lacking. Therefore, we can assume differences in IOM application between Neurosurgical centers.

Research question

The section of Functional Neurosurgery of the Italian Society of Neurosurgery realized a survey aiming to obtain general data on the current practice of IOM in Italy.

Materials and methods

A 22-item questionnaire was designed focusing on: volume procedures, indications, awake surgery, experience, organization and equipe. The questionnaire has been sent to Italian Neurosurgery centers.

Results

A total of 54 centers completed the survey. The annual volume of surgeries range from 300 to 2000, and IOM is used in 10-20% of the procedures. In 46% of the cases is a neurologist or a neurophysiologist who performs IOM. For supra-tentorial pathology, almost all perform MEPs (94%) SSEPs (89%), direct cortical stimulation (85%). All centers perform IOM in spinal surgery and 95% in posterior fossa surgery. Among the 50% that perform peripheral nerve surgery, all use IOM. Awake surgery is performed by 70% of centers. The neurosurgeon is the only responsible for IOM in 35% of centers. In 83% of cases IOM implementation is adequate to the request.

Discussion and conclusions

The Italian Neurosurgical centers perform IOM with high level of specialization, but differences exist in organization, techniques, and expertise. Our survey provides a snapshot of the state of the art in Italy and it could be a starting point to implement a consensus on the practice of IOM.

The Utility of Intraoperative Neuromonitoring in Pediatric Surgical Oncology

BACKGROUND

Intraoperative nerve monitoring (IONM) is a technique used to decrease the possibility of nerve-associated morbidity and damage to nearby neural structures during complex surgical procedures. The use and potential benefits of IONM in pediatric surgical oncology are not well-described.

METHODS

An overview of the current literature was performed to elucidate the various techniques that may be useful to pediatric surgeons for resection of solid tumors in children.

RESULTS

The physiology and common types of IONM relevant to the pediatric surgeon are described. Important anesthetic considerations are reviewed. Specific applications for IONM that may be useful in pediatric surgical oncology are then summarized, including its use for monitoring the recurrent laryngeal nerve, the facial nerve, the brachial plexus, spinal nerves, and lower extremity nerves. Troubleshooting techniques regarding common pitfalls are then proposed.

CONCLUSION

IONM is a technique that may be beneficial in pediatric surgical oncology to minimize nerve injury during extensive tumor resections. This review aimed to elucidate the various techniques available. IONM should be considered as an adjunct for the safe resection of solid tumors in children in the proper setting with the appropriate level of expertise. A multidisciplinary approach is advised. Additional studies are necessary to further clarify the optimal use and outcomes in this patient population.

LEVELS OF EVIDENCE

Level III.

Knowledge Review of Spinal Deformity and the Need for Fusion and Fixation following Treatment for Spinal Tumors among the Pediatric Age Group

BACKGROUND

Spinal tumors are rare pathology in the pediatric population. The tumors can be classified as extradural, intradural extramedullary, or intramedullary. Any of the spinal tumors can eventually lead to spinal deformity. The progressive spinal deformity can be part of the initial presentation or evolve on long follow-up, even years after the initial intervention and treatment.

SUMMARY

Management of spinal deformity associated with spinal tumors in children is not well defined. Patients with progressive symptoms and even neurological deficits need correction for their deformity when diagnosed. Patients that do not have pain or related neurological deficits should be evaluated for the severity of their deformity and followed long-term. Special consideration is needed for young patients who need multilevel surgery or have deformity at presentation.

KEY MESSAGES

When considering the need for instrumentation and fusion, the surgeon should consider the age of the patient, expected future growth of the spine, neurologic status, extent of initial deformity, and the number of vertebral levels involved by tumor. Providers should also consider how surgery may fix or prevent deformity, especially when instrumentation can affect imaging at follow-up.

Pediatric Intraoperative Neurophysiological Monitoring and Long-Term Outcomes in a Developing Country

PURPOSE

Pediatric intraoperative neurophysiological monitoring (IONM) has been shown to be effective in preventing and reversing postoperative neurological deficits in developed countries. There are currently no published studies from developing countries that describe neurophysiological findings and postoperative outcomes. Our study aims to address these gaps in children undergoing neurosurgical procedures in a single center.

METHODS

We conducted a retrospective study of case series of children who underwent IONM (2014-2020) in the State of Mexico, Mexico. Sociodemographic characteristics, IONM modalities, changes during procedures, and short-term and long-term postoperative results were recorded. Descriptive statistics were used.

RESULTS

We included 35 patients (≤18 years of age), 57% (20/35) boys. A relative increase of up to 5 times in the use of IONM is observed from 2014 (5.7%) to 2020 (25.7%) in our center. The most frequent preoperative pathologies were located at the infratentorial cranium (40%), followed by the spine and spinal cord (37.1%). The IONM modalities were as follows: free-running EMG 94.3%, transcranial electrical stimulation motor-evoked potentials 91.4%, somatosensory-evoked potentials 85.7%, triggered EMG 28.6%, EEG 25.7%, and visual-evoked potentials 5.7%. Only in 8.3%, we did not obtain sufficient evoked potential baseline signals. At 24 hours postoperatively true negatives were 100%. Long-term follow-up was completed in 22/35 (63%) at 3 months, 12/35 (34.2%) at 6 months, and 5/35 (14.3%) at 12 months with progressive motor and sensory improvement.

CONCLUSIONS

Pediatric multimodal IONM in neurosurgeries from a single center in a developing country is mainly used in pathologies of the posterior fossa, spine, and spinal cord, with true negatives in 100% of those monitored, preventing and avoiding postoperative sequelae.

Feasibility of intraoperative motor evoked potential monitoring during tethered cord surgery in infants younger than 12 months

PURPOSE

Feasibility, reliability, and safety assessment of transcranial motor evoked potentials (MEPs) in infants less than 12 months of age.

METHODS

A total of 22 patients with a mean age of 33 (range 13-49) weeks that underwent neurosurgery for tethered cord were investigated. Data from intraoperative MEPs, anesthesia protocols, and clinical records were reviewed. Anesthesia during surgery was maintained by total intravenous anesthesia (TIVA).

RESULTS

MEPs were present in all patients for the upper extremities and in 21 out of 22 infants for the lower extremities. Mean baseline stimulation intensity was 101 ± 20 mA. If MEPs were present at the end of surgery, no new motor deficit occurred. In the only case of MEP loss, preoperative paresis was present, and high baseline intensity thresholds were needed. MEP monitoring did not lead to any complications. TIVA was maintained with an average propofol infusion rate of 123.5 ± 38.2 µg/kg/min and 0.46 ± 0.17 µg/kg/min for remifentanil.

CONCLUSION

In spinal cord release surgery, the use of intraoperative MEP monitoring is indicated regardless of the patient's age. We could demonstrate the feasibility and safety of MEP monitoring in infants if an adequate anesthetic regimen is applied. More data is needed to verify whether an irreversible loss of robust MEPs leads to motor deficits in this young age group.

Surgical correction of pediatric spinal deformities with coexisting intraspinal pathology: A case report and literature review

Background

Surgical correction of spinal deformities with coexisting intraspinal pathology (SDCIP) requires special consideration to minimize risks of further injury to an already abnormal spinal cord. However, there is a paucity of literature on this topic. Here, the authors present a pediatric patient with a residual pilocytic astrocytoma and syringomyelia who underwent surgical correction of progressive postlaminectomy kyphoscoliosis. Techniques employed are compared to those in the literature to compile a set of guidelines for surgical correction of SDCIP.

Methods

A systematic MEDLINE search was conducted using the following keywords; "pediatric," "spinal tumor resection," "deformity correction," "postlaminectomy," "scoliosis correction," "intraspinal pathology," "tethered cord," "syringomyelia," or "diastematomyelia." Recommendations for surgical technique for pediatric SDCIP correction were reviewed.

Results

The presented case demonstrates recommendations that primarily compressive forces on the convexity of the coronal curve should be used when performing in situ correction of SDCIP. Undercorrection is favored to minimize risks of traction on the abnormal spinal cord. The literature yielded 13 articles describing various intraoperative techniques. Notably, seven articles described use of compressive forces on the convex side of the deformity as the primary mode of correction, while only five articles provided recommendations on how to safely and effectively surgically correct SDCIP.

Conclusion

The authors demonstrated with their case analysis and literature review that there are no clear current guidelines regarding the safe and effective techniques for in situ correction and fusion for the management of pediatric SDCIP.

Intraoperative Neurological Monitoring in Lower Limb Surgery for Patients With Mucopolysaccharidoses

BACKGROUND

There are reports of spinal cord injury (SCI) occurring after lower extremity (LE) surgery in children with mucopolysaccharidoses (MPS). Intraoperative neurological monitoring (IONM) has been adopted in some centers to assess real-time spinal cord function during these procedures. The aim of this investigation was to review 3 specialty centers' experiences with MPS patients undergoing LE surgery. We report how IONM affected care and the details of spinal cord injuries in these patients.

METHODS

All pediatric MPS patients who underwent LE surgery between 2001 and 2018 were reviewed at 3 children's orthopaedic specialty centers. Demographic and surgical details were reviewed. Estimated blood loss (EBL), surgical time, positioning, use of IONM, and changes in management as a result of IONM were recorded. Details of any spinal cord injuries were examined in detail.

RESULTS

During the study period, 92 patients with MPS underwent 252 LE surgeries. IONM was used in 83 of 252 (32.9%) surgeries, and intraoperative care was altered in 17 of 83 (20.5%) cases, including serial repositioning (n=7), aggressive blood pressure management (n=6), and abortion of procedures (n=8). IONM was utilized in cases with larger EBL (279 vs. 130 mL) and longer operative time (274 vs. 175 min) compared with procedures without IONM. Three patients without IONM sustained complete thoracic SCI postoperatively, all from cord infarction in the upper thoracic region. These 3 cases were characterized by long surgical time (328±41 min) and substantial EBL (533±416 mL or 30.5% of total blood volume; range, 11% to 50%). No LE surgeries accompanied by IONM experienced SCI.

CONCLUSIONS

Patients with MPS undergoing LE orthopaedic surgery may be at risk for SCI, particularly if the procedures are long or are expected to have large EBL. One hypothesis for the etiology of SCI in this setting is hypoperfusion of the upper thoracic spinal cord due to prolonged intraoperative or postoperative hypotension. IONM during these procedures may mitigate the risk of SCI by identifying real-time changes in spinal cord function during surgery, inciting a change in the surgical plan.

LEVEL OF EVIDENCE

Level III-retrospective comparative series.

Exploring the utility of neuro-monitoring in neurosurgery: The users' perspective in a single center

Background:

The purpose of intraoperative neuro-monitoring (IONM) is to minimize injury to eloquent neural structures and optimize tumor resection.

Method:

We explored the utility of IONM using a qualitative approach in a single center. Eight experienced users of its use in spinal and cranial surgery in adults and children were the informants. Using a constant comparative method, the findings were collated by thematic analysis.

Results:

The user perspective is that of caution to minimize adverse effects whilst empowering the need for formal training to enhance its efficacy. The process of IONM needs standardization as practices vary amongst users. Most users expressed limited trust on its current capabilities but hoped for its advancement to achieve higher sensitivity and specificity. None were however prepared to abandon its use.

Conclusion:

IONM needs optimization. Its utility depends on user vigilance, multi-disciplinary validation, and individual expertise. This study draws out key issues from the user perspective that need to be addressed in order to enhance the utility of IONM.

Anesthesia management during meningomyelocele repair alongside motor-evoked potentials in a newborn and a small infant

Intraoperative neuromonitoring has become an increasingly commonly applied practice during surgical operations for preventing formation of neurological damage. Although it has been used on adults for a long time, the benefits and techniques of applying it in small children are not clear. We applied two different anesthesia protocols during meningomyelocele repair alongside motor-evoked potentials in a newborn and a small infant. We discussed our anesthesia management method and the effects of anesthesia on intraoperative neuromonitoring in our two very young cases in only one of which we obtained significant records.

What Is the Frequency of Intraoperative Alerts During Pediatric Spinal Deformity Surgery Using Current Neuromonitoring Methodology? A Retrospective Study of 218 Surgical Procedures

INTRODUCTION

There is variability in intraoperative neuromonitoring (IONM), anesthetic and surgical techniques for the treatment of pediatric spinal deformity. This study evaluates a series of patients treated at multiple centers utilizing transcranial motor and somatosensory evoked potentials (TcMEP and SSEP) and electromyography (EMG). The frequency of alerts and the intraoperative follow-up is reported.

METHODS

Standard patient demographics and IONM data were collected from a two-month cohort of pediatric spine deformity cases.

RESULTS

Data from 218 scoliosis patients were included from 46 facilities and 72 surgeons. Baseline upper and lower extremity TcMEP data were present in 96.7% and 93.9% patients respectively. Baseline upper and lower SSEPs were present in 99.5% and 95.4% respectively Surgical TCMEP alerts occurred in 19 (8.7%) patients during deformity correction (n = 11), placement of instrumentation (n = 5), decompression (n = 2), and closing (n = 1) with concurrent SSEP alerts occurring in five patients. Nine had TCMEP recovery, eight showed partial recovery and two did not recover. Additional alerts occurred due to: positioning (n = 16), inhalational agent change (n = 4), global physiological change (n = 4) and technical reasons (n = 2). A total of 2164 pedicle screws were tested. Of 197 (9.1%) screws that tested from 6-9 mA, 171 (65.4%) were left unchanged, 10 (51%) removed, eight (4.1%) repositioned with improved threshold, and eight (4.1%) without improvement. Of 26 screws that tested ≤ 5 milliamperes (mA), 17 (65.4%) were left unchanged, five (19.2%) removed, two (7.7%) repositioned with improved threshold, and two (7.7%) without improvement.

CONCLUSIONS

IONM provides data that causes re-evaluation in about 10% of pediatric spinal deformity cases.

Spinal Cord Injury After Extremity Surgery in Children With Thoracic Kyphosis

BACKGROUND

Spinal cord injury is a rare complication after lower extremity surgery in children with skeletal dysplasia and thoracic kyphosis. We encountered two patients who had this complication, from among 51 (39 from Nemours/Alfred I. duPont Hospital for Children and 12 from Seattle Children's Hospital) who underwent lower extremity surgery during an 8.5-year period (June 2004 to December 2012). Because spinal cord injury is a devastating complication likely not known to most physicians treating patients with skeletal dysplasias, we sought to examine factors that may contribute to this rare complication.

CASE DESCRIPTION

We performed a retrospective review of two patients with skeletal dysplasia who had paraplegia develop after extremity surgery. Outcome measures included operative time, vital signs, and postsurgery recovery of neurologic deficit. MR images were reviewed. Two patients were found-an 8.5-year-old boy with spondyloepiphyseal dysplasia congenita with a 76°-thoracic kyphosis apex at T4 and a 6.5-year-old boy with mucopolysaccharidosis type 1-H with an 80°-thoracic kyphosis apex at T2. Bilateral proximal femoral osteotomies or bilateral innominate and proximal femoral osteotomies had been performed. The spinal cord injuries occurred at the apex of the kyphosis as determined by clinical examination and MRI assessment. In both patients, the mean arterial blood pressure decreased below 50 mm Hg and might be a factor in the etiology of the paralysis. The first patient recovered motor function in 5 months; the second had no recovery.

LITERATURE REVIEW

Paraplegia is extremely rare after nonspine operations. Many factors contribute to the risk for a spinal cord event: low mean arterial pressure, duration of the surgery, position on the operating table, the kyphotic spine deformity, or unappreciated vascular disease. Motor-evoked potentials and somatosensory-evoked potentials together potentially provide high sensitivity and specificity for predicting a postoperative neurologic deficit.

CLINICAL RELEVANCE

Based on our two patients with skeletal dysplasia and a literature review of patients with hyperkyphosis undergoing extremity surgery, the surgeon must be aware of the risk of spinal cord injury. Careful preoperative assessment possibly including MRI of the spine is recommended. Mean arterial pressure should be maintained at a safe level; neuromonitoring should be considered.

Diagnostic evaluation, monitoring, and perioperative management of spinal cord compression in patients with Morquio syndrome

Mucopolysaccharidosis IVA is an autosomal recessive condition caused by mutations in the GALNS gene, which encodes N-acetylgalactosamine-6-sulfatase, also called galactosamine-6-sulfatase (GALNS). A reduction in or absence of effective GALNS leads to faulty catabolism of keratan sulfate and chondroitin-6-sulfate within the lysosome; their accumulation causes cell, tissue, and organ dysfunction. The connective tissue, cartilage, ligaments, and bone of patients with Morquio A syndrome are particularly affected. Patients with Morquio A syndrome are at high risk of neurological complications because of their skeletal abnormalities; many patients are in danger of cervical myelopathy due to odontoid hypoplasia and ligamentous laxity leading to atlantoaxial subluxation. The multisystemic involvement of patients with Morquio A syndrome requires treatment by multidisciplinary teams; not all members of these teams may be aware of the potential for subluxation and quadriparesis. A multinational, multidisciplinary panel of 10 skeletal dysplasia or Morquio A syndrome specialists convened in Miami, FL on December 7 and 8, 2012 to develop consensus recommendations for early identification and effective management of spinal cord compression, for anesthesia and surgical best practices, and for effectual cardiac and respiratory management in patients with Morquio A syndrome. The target audience for these recommendations includes any physician who may encounter a patient with Morquio A syndrome, however doctors who do not have access to the full spectrum of specialists and resources needed to support patients with Morquio A syndrome should attempt to refer patients to a center that does. Physicians who manage Morquio A syndrome or comorbid conditions within specialty centers should review these expert panel recommendations and fully understand the implications of spinal cord instability for their own practices.

Intraoperative changes in transcranial motor evoked potentials and somatosensory evoked potentials predicting outcome in children with intramedullary spinal cord tumors

OBJECT

Intraoperative dorsal column mapping, transcranial motor evoked potentials (TcMEPs), and somatosensory evoked potentials (SSEPs) have been used in adults to assist with the resection of intramedullary spinal cord tumors (IMSCTs) and to predict postoperative motor deficits. The authors sought to determine whether changes in MEP and SSEP waveforms would similarly predict postoperative motor deficits in children.

METHODS

The authors reviewed charts and intraoperative records for children who had undergone resection for IMSCTs as well as dorsal column mapping and TcMEP and SSEP monitoring. Motor evoked potential data were supplemented with electromyography data obtained using a Kartush microstimulator (Medtronic Inc.). Motor strength was graded using the Medical Research Council (MRC) scale during the preoperative, immediate postoperative, and follow-up periods. Reductions in SSEPs were documented after mechanical traction, in response to maneuvers with the cavitational ultrasonic surgical aspirator (CUSA), or both.

RESULTS

Data from 12 patients were analyzed. Three lesions were encountered in the cervical and 7 in the thoracic spinal cord. Two patients had lesions of the cervicomedullary junction and upper spinal cord. Intraoperative MEP changes were noted in half of the patients. In these cases, normal polyphasic signals converted to biphasic signals, and these changes correlated with a loss of 1-2 grades in motor strength. One patient lost MEP signals completely and recovered strength to MRC Grade 4/5. The 2 patients with high cervical lesions showed neither intraoperative MEP changes nor motor deficits postoperatively. Dorsal columns were mapped in 7 patients, and the midline was determined accurately in all 7. Somatosensory evoked potentials were decreased in 7 patients. Two patients each had 2 SSEP decreases in response to traction intraoperatively but had no new sensory findings postoperatively. Another 2 patients had 3 traction-related SSEP decreases intraoperatively, and both had new postoperative sensory deficits that resolved. One additional patient had a CUSA-related SSEP decrease intraoperatively, which resolved postoperatively, and the last patient had 3 traction-related sensory deficits and a CUSA-related sensory deficit postoperatively, none of which resolved.

CONCLUSIONS

Intraoperative TcMEPs and SSEPs can predict the degree of postoperative motor deficit in pediatric patients undergoing IMSCT resection. This technique, combined with dorsal column mapping, is particularly useful in resecting lesions of the upper cervical cord, which are generally considered to be high risk in this population. Furthermore, the spinal cord appears to be less tolerant of repeated intraoperative SSEP decreases, with 3 successive insults most likely to yield postoperative sensory deficits. Changes in TcMEPs and SSEP waveforms can signal the need to guard against excessive manipulation thereby increasing the safety of tumor resection.

Intraoperative neurophysiologic monitoring in spine surgery. Developments and state of the art in France in 2011

Intraoperative spinal cord monitoring consists in a subcontinuous evaluation of spinal cord sensory-motor functions and allows the reduction the incidence of neurological complications resulting from spinal surgery. A combination of techniques is used: somatosensory evoked potentials (SSEP), motor evoked potentials (MEP), neurogenic motor evoked potentials (NMEP), D waves, and pedicular screw testing. In absence of intraoperative neurophysiological testing, the intraoperative wake-up test is a true form of monitoring even if its latency long and its precision variable. A 2011 survey of 117 French spinal surgeons showed that only 36% had neurophysiological monitoring available (public healthcare facilities, 42%; private facilities, 27%). Monitoring can be performed by a neurophysiologist in the operating room, remotely using a network, or directly by the surgeon. Intraoperative alerts allow real-time diagnosis of impending neurological injury. Use of spinal electrodes, moved along the medullary canal, can determine the lesion level (NMEP, D waves). The response to a monitoring alert should take into account the phase of the surgical intervention and does not systematically lead to interruption of the intervention. Multimodal intraoperative monitoring, in presence of a neurophysiologist, in collaboration with the anesthesiologist, is the most reliable technique available. However, no monitoring technique can predict a delayed-onset paraplegia that appears after the end of surgery. In cases of preexisting neurological deficit, monitoring contributes little. Monitoring of the L1-L4 spinal roots also shows low reliability. Therefore, monitoring has no indication in discal and degenerative surgery of the spinal surgery. However, testing pedicular screws can be useful. All in all, thoracic and thoracolumbar vertebral deviations, with normal preoperative neurological examination are currently the essential indication for spinal cord monitoring. Its absence in this indication is a lost opportunity for the patient. If neurophysiological means are not available, intraoperative wake-up test is a minimal obligation.

Spinal cord infarction remote from maximal compression in a patient with Morquio syndrome

Morquio syndrome, or mucopolysaccharidosis type IV, is a rare enzyme deficiency disorder and results in skeletal dysplasia. Odontoid dysplasia is common among affected patients, resulting in atlantoaxial instability and spinal cord compression. Surgical treatments include decompression and prophylactic fusion, during which intraoperative neuromonitoring is important to alert the surgical team to changes in cord function so that they can prevent or mitigate spinal cord injury. This report describes a 16-year-old girl with Morquio syndrome who developed paraplegia due to thoracic spinal cord infarction during foramen magnum and atlantal decompression. This tragic event demonstrates the following: 1) that patients with Morquio syndrome are at risk for ischemic spinal cord injury at levels remote from areas of maximal anatomical compression while under anesthesia in the prone position, possibly due to impaired cardiac output; 2) the significance of absent motor evoked potential responses in the lower limbs with preserved upper-limb responses in an ambulatory patient; 3) the importance of establishing intraoperative neuromonitoring baseline assessments prior to turning patients to the prone position following induction of anesthesia; and 4) the importance of monitoring cardiac output during prone positioning in patients with chest wall deformity.