Taken from Anesthesiology News
David Hardman, MD, MBA, FASA
Professor of Anesthesiology
Vice Chair for Professional Affairs
Department of Anesthesiology
University of North Carolina at Chapel Hill School of Medicine
Chapel Hill, North Carolina
Inadequate intraoperative patient positioning is not the only cause of perioperative peripheral nerve injuries. Anesthesiologists should take time to understand the differential diagnosis of these adverse events.
A 57-year-old insurance salesman with a body mass index (BMI) of 23 kg/m2 and a history of hypertension and hepatitis B virus is scheduled to undergo an emergency orthotopic liver transplant. You place a blood pressure cuff on the patient’s right arm along with standard monitors, and place his arms at a 90-degree angle to the sides on a padded arm board in foam cradles. After proceeding with a rapid sequence induction, and placing a right radial arterial line and a 9 Fr central venous sheath in the right internal jugular vein, you proceed with an isoflurane-based balanced anesthetic.
After incision, the surgeon attaches the anchors of a Thompson Retractor (Thompson Surgical) apparatus on the side rails of the operating room table, and asks you to move the arm boards slightly cephalad. Although 2 L of blood loss occurs over the course of the procedure, there are no sustained periods of hypotension during the case, and 9 hours after induction, you transfer the patient to the surgical ICU (SICU), intubated and sedated. During the next 72 hours, the patient remains intubated and sedated in the SICU because of bleeding and periods of hemodynamic instability, before finally being extubated. He remains in the SICU for another day, and is then transferred to the floor, where he remains for another 2 weeks, before discharge home.
One week after discharge, at the time of his first postoperative visit, the patient complains of numbness, weakness, and tingling in the medial aspect of his right hand and fingers. He also claims that he first noticed these symptoms immediately post-op, although a review of the medical records does not corroborate his assertion. Over the next 2 months, his injury does not significantly improve, and he complains that his typing abilities are impaired and interfering with his ability to work. He claims that this is a positioning-related injury that occurred during anesthesia, and plans to file a lawsuit against you.
Questions to consider:
- Whatshould you do?
- Have you ever experienced an ulnar perioperative peripheral nerve injury (PNI) in your practice, or known of a colleague who had one?
- What are the potential causes of this ulnar PNI?
- How common is an ulnar perioperative PNI? When is it usually first noticed after surgery?
- What are the risk factors for developing an ulnar PNI?
- Is there a standard of care for patient positioning? What references are available?
- What type of information should be charted on the anesthesia record to document patient safety with respect to anesthesia and surgical positioning?
- How frequently should this information be updated during the surgical procedure?
- Is the use of a noninvasive blood pressure cuff a risk factor for the development of a PNI?
- Who is responsible for ensuring proper patient positioning?
- Do you think that this is a positioning-related injury? Why or why not? When do you think the injury occurred?
- Are most PNIs preventable?
- Is there a definition for anesthesia standard of care? If so, what is it?
- How would you define negligence on behalf of the anesthesia provider when a suspected positioning-related PNI occurs?
Although uncommon, many anesthesiologists may be aware of a colleague who has experienced a positioning-related PNI in their practice. According to the most recent American Society of Anesthesiologists (ASA) Closed Claims Project analysis of nerve injury associated with anesthesia, nerve injuries account for 16% of all claims in the database, with ulnar nerve injury accounting for 28% of these claims, followed by brachial plexus injury (20%), lumbosacral injury (16%), and spinal cord injury (13%).1 Over time, ulnar nerve injury has decreased from 37% of all nerve injury claims in the 1980-1984 epoch to 17% of nerve injury claims in the 1990-1995 epoch, and is now the third leading cause of nerve injury claims, after spinal cord injury and brachial plexus injury.
The authors of the ASA Closed Claims Project analysis determined that the mechanism of nerve injury was apparent in only 9% of all ulnar nerve claims, despite extensive medical-legal investigation, and that anesthetic care was judged appropriate in 73% of these cases. The prevalence of other PNIs in the database (median, radial, sciatic, femoral) is in the single digits for each, and in all cases less than 6%. Unfortunately, the absence of a mechanism of injury in a majority of these cases limits the potential for prospective injury prevention measures, and calls into question how many of these injuries can be prevented by anesthesia care team members.
PNIs are rare, with reported incidences of 0.14% by Parks; 0.11% by Blitt et al; and, most recently, 0.03% by Welch et al.2-4 A large case series of 7,150 patients undergoing total hip arthroplasty in the lateral position identified only 0.22% with PNIs, the majority of which were ulnar nerve injuries.5 Warner et al, in a large retrospective case series of 1,129,692 patients, calculated an 0.037% incidence of ulnar PNIs. Risk factors included male gender, extremes of BMI, and duration of hospitalization greater than 14 days. Of interest, initial symptoms for most of these ulnar neuropathies were first noticed more than 24 hours after the surgical procedure.6
A follow-up prospective study by Warner et al of 1,502 surgical patients undergoing noncardiac surgery, and having daily neurologic exams until hospital discharge, revealed a 0.5% incidence of ulnar PNIs. The median time for symptom onset occurred on postoperative day 4, with a range of onset between 2 and 7 days postoperatively.7 These injuries were noted primarily in men, ranging between 50 and 75 years of age; some of these patients tended to inaccurately recall the onset time of their surgery when questioned 2 months later, with 20% insisting that the injury occurred immediately postoperatively, in contradiction to their medical records that documented onset of neurologic injury at 4 to 6 days.
A similar prospective study of ulnar nerve injury in a sample of 990 medical patients revealed an 0.2% incidence of ulnar nerve injury, similar to the observed 0.5% incidence in surgical patients.8The authors hypothesized that ulnar nerve injuries are more likely to occur in the postoperative period rather than during intraoperative positioning, and that the mechanism may be a pressure-related compression injury over the olecranon groove, as patients recuperate in the supine position with the head of the bed elevated and with their elbows flexed and hands placed on their chest. Anatomic mechanisms of injury that may explain the higher prevalence of this injury in men include a coronoid tubercle that is 1.5 times larger in men versus women, less adipose tissue over the medial elbow, and a thicker arcuate ligament in the flexor retinaculum of the cubital tunnel that can increase the risk for compression injury.8
It is difficult to determine the cause and timing of the ulnar nerve injury in this case scenario, as it could easily have occurred at a time other than during the 9-hour intraoperative period. The injury could have occurred during the 96-hour time interval in the SICU, while the patient was intubated and exposed to varying degrees of sedation, or possibly after transfer from the SICU to the hospital ward, during the 2-week hospitalization. A positioning-related nerve injury usually involves a single peripheral nerve or plexus element unilaterally,9 which is the presenting symptomatology in this case. Intraoperative mechanisms for a positioning-related ulnar nerve injury could include hyperabduction of the right arm with placement of the Thompson Retractor anchoring apparatus, resulting in a stretch injury to the lower trunk of the brachial plexus manifesting as an ulnar nerve injury; or a hematoma secondary to central line placement, with subsequent compression of the lower trunk.10
Patient positioning during surgery is normally considered a shared responsibility of all health care providers in the operating room, including the surgeon, anesthesiologist, nurse anesthetist or anesthesiology resident, and the circulating nurse.11,12 However, alternative interpretations exist, claiming that the responsibility for surgical positioning other than routine supine positioning clearly belongs to the surgeon, and that when an anesthesiologist or other health care provider assists with positioning, he or she is only acting as an agent on behalf of the surgeon.13
Although there are no standards with respect to intraoperative patient positioning, the ASA Committee on Standards and Practice Parameters has created a practice advisory for the prevention of perioperative peripheral neuropathies.14,15 Note that “practice advisories developed by the ASA are not intended as standards, guidelines, or absolute requirements. Adhering to practice advisories cannot guarantee any specific outcome, and may be adopted, modified, or rejected according to clinical needs and constraints, and are not intended to replace local institutional policies.”14
When the level of scientific evidence is insufficient to formulate an evidence-based guideline, then a practice advisory is published in lieu of a guideline. Practice advisories are a distillation of a combination of opinion-based and scientific evidence.
With respect to the prevention of perioperative PNIs, the following limited recommendations are excerpted from the ASA practice advisory14:
- Advisory for preoperative history and physical assessment:Body habitus, preexisting neurologic symptoms, diabetes, peripheral vascular disease, alcohol dependence, arthritis, and sex are important elements of a preoperative history. When judged appropriately, it would be helpful during a preoperative assessment to ascertain that patients can comfortably tolerate the anticipated operative position.
- Advisory for positioning strategies to reduce perioperative brachial plexus neuropathy:Arm abduction should be limited to 90 degrees in a supine patient.
- Advisory for positioning strategies to reduce perioperative ulnar neuropathy:In a supine patient with an arm on an arm board, the extremity should be positioned to decrease pressure on the ulnar groove (either with supination or neutral forearm position). In a supine patient with arms tucked at the side, the forearm should be in a neutral position. Flexion of the elbow may increase the risk for ulnar neuropathy, but there is no consensus on an acceptable degree of flexion during the perioperative period.
- Advisory for periodic assessment of the upper extremity:Periodic perioperative assessments may ensure maintenance of the desired position. The literature is insufficient to evaluate the efficacy of periodic assessment of patient positioning.
- Advisory for protective padding:Padded arm boards may decrease the risk for upper extremity neuropathy. The use of chest rolls in the laterally positioned patient may reduce the risk for upper extremity neuropathy. Padding at the elbow may decrease the risk for upper extremity neuropathy.
- Advisory for equipment:The use of properly functioning automated blood pressure cuffs on the arm (above the antecubital fossa) does not change the risk for upper extremity neuropathy. The use of shoulder braces in a steep head-down position may increase the risk for perioperative neuropathies.
- Advisory for postoperative physical assessment: A simple postoperative assessment of extremity nerve function may lead to early recognition of peripheral neuropathies.
- Advisory for documentation:Documentation of specific perioperative positioning actions (overall patient position, position of arms, position of lower extremities, specific padding) may be useful for continuous improvement processes.
These advisory recommendations can be incorporated into a modern template for electronic medical record positioning documentation, which can list in great detail all the actions taken relating to positioning, including surgeon involvement and approval; patient position; position of the arm (supine, neutral); position of the forearm (flexed, etc); padding, including padded arm boards or foam cradles; pressure points checked; head and spine placed in neutral position; and a notation that positioning was checked at regular intervals. Consideration should be given to documenting a brief neurologic exam in the anesthesia record at the time of handoff to PACU staff, and as part of the PACU discharge note.
The medical-legal definition for anesthesia standard of care is a community standard, not a national standard. The standard is defined as what a similarly trained anesthesiologist would do when taking care of a similar type of patient. This standard could potentially vary based on the practice organization model, with anesthesia services being either personally performed, medically directed, or medically supervised. The medical-legal definition of negligence requires that an anesthesiologist had a duty to take care of a patient; that the anesthesiologist practiced below the standard of care; and that the deviation from the standard of care directly resulted in the consequent injury. Based on the natural history of the patient’s ulnar PNI—with its initial onset several days postoperatively, postoperative mechanisms of causation, and limited scientific evidence in the practice advisory to prevent injury—it should be difficult for a plaintiff’s attorney to prove negligence on behalf of the anesthesiologist in this case scenario.
A 52-year-old, obese white man with a BMI of 40 kg/m2 is scheduled to undergo total knee arthroplasty under an adductor canal block and spinal anesthesia. He has a history of tobacco use, hypertension, and type 2 diabetes. After sedation with 2 mg of midazolam, both regional blocks are performed uneventfully, and the patient is positioned in the supine position, with his arms abducted to the side on a padded arm board. You are medically directing a nurse anesthetist, and then leave to start your other rooms without double-checking the patient’s positioning. The case proceeds uneventfully, and 3 hours later, the patient is taken to the PACU. After achieving an Aldrete Score of 10, the patient is sent to the ward, and 5 days later is discharged without incident.
During his 5-day hospitalization, there is no mention in the medical record of any neurologic abnormality in the hands and arm, including the physical therapist’s daily notes. One month after discharge, the patient contacts the orthopedic surgeon’s office nurse, and complains of bilateral numbness in his fourth and fifth digits and decreased grip strength. The surgeon refers him to a neurologist who examines the patient and finds evidence of bilateral ulnar neuropathies based on physical exam findings. The neurologist also diagnoses a left median nerve sensory injury. Three months later, the patient states that his injury is progressing, and that he cannot hold on to objects and keeps dropping them from his hands. He contacts you and claims that this is an anesthesia positioning–related injury and that his arms were “stretched back” when they were placed on the surgical arm boards at the time of surgery, and that they were not adequately padded.
Questions to consider:
- IsASA physical status a predictor of this PNI?
- Can a PNI related to positioning occur in a patient who is not under general anesthesia? Why or why not?
- Which part of the brachial plexus is at risk with hyperabduction of the arm?
- Under the rules of medical direction, you are expected to be present for induction, emergence, and at critical points, and be immediately available. Should you be present for positioning, or can you delegate that task to a nurse anesthetist?
- Do you believe that this is an intraoperative positioning injury? If not, when did it occur? What are the potential etiologies of the patient’s neurologic injuries?
- What would you do next to establish a diagnosis?
- How would you interpret the results of clinical neurophysiologic testing, and what specifically would you be looking for to establish a diagnosis and prognosis for eventual recovery? Which extremity would you test?
PNIs can occur in patients even without having had general anesthesia or regional nerve blocks. In this case scenario, the patient sustained bilateral upper extremity ulnar nerve injuries, even though he was awake with minimal sedation, and the nerve blocks were administered for the lower extremities. The ASA Closed Claims Project database includes 8 claims for ulnar nerve injury in patients who were awake with spinal anesthesia.1 Although one might expect that an awake or minimally sedated patient experiencing compression or stretch of the ulnar nerve would be symptomatic and complain or attempt to reposition his or her arms, there is evidence, especially in men, that only 50% of awake, unmedicated volunteers, with pressure on their ulnar nerve resulting in abnormal evoked potential readings, were able to notice paresthesias or abnormal sensations.16 This study highlights the difficulty in preventing intraoperative ulnar nerve injury and suggests particular vigilance with respect to positioning and padding of the arms and forearms in male patients.
In the Welch et al retrospective case series of 380,680 patients, ASA physical status was not an independent risk factor for predicting the development of a PNI, although diabetes mellitus, hypertension, and tobacco use were identified as patient-related risk factors.4 Length of surgery was not analyzed as a risk factor in this study.
Hyperabduction related stretch injury to the brachial plexus typically involves the lower trunk, formed by the C8-T1 roots, manifested by abnormalities in all ulnar muscles of the hand (first dorsal interosseous, abductor digiti minimi, flexor digitorum profundus), as well as median nerve C8-T1 innervated muscles (flexor digitorum profundus, flexor pollicis longus, abductor pollicisbrevis).10 On clinical exam, this type of injury would demonstrate decreased sensation to the fourth and fifth digits and medial aspect of the palm and the hand, along with decreased grip strength.
Under the rules of medical direction, any procedure or task that the anesthesiologist does not perform him- or herself must be delegated to a qualified provider that the anesthesiologist deems capable of performing the task. A certified registered nurse anesthetist or anesthesiology assistant is qualified and capable of performing anesthesia and surgical positioning, without necessitating the presence of an anesthesiologist.17,18
Although possible, it is unlikely that this case scenario represents an intraoperative positioning-related injury due to the time course of onset (1 month post-surgery) and the bilateral nature of the ulnar injuries. In the large retrospective case series conducted by Warner et al, only 9% of ulnar injuries were bilateral, and in the prospective study by Warner et al, 14% were bilateral.6,7The ASA Closed Claims Project database lends further support to these figures, with a 14% prevalence of bilateral ulnar nerve injuries.1
A more likely explanation for neurologic injuries in this case would be attributed to a diabetic polyneuropathy, involving both extremities and multiple nerves (radial, median and ulnar nerves). Additional patient risk factors for the development of a PNI in this case include the use of tobacco and the presence of hypertension.
Nerve conduction studies and needle electromyography (EMG) should be done on both limbs, including the lower extremity, to confirm the suspected diagnosis of a polyneuropathy. Needle EMG in the C8-T1 ulnar and median nerve distribution muscles (abductor pollicus brevis, flexor pollicis longus, flexor digitorum profundus, first dorsal interosseous and abductor digiti minimi) could potentially show the presence of positive sharp waves, abnormal spontaneous activity, and fibrillation potentials, all of which would be pathognomonic for axonal injury. Additionally, ulnar nerve motor and sensory compound motor action potentials and sensory nerve action potentials, at measurement sites above to below the elbow and below the elbow to the wrist, can localize the site of a demyelinating or axonal compression-related injury due to either insufficient padding at the elbow or secondary to other etiologies.10
A 45-year-old woman with a BMI of 22 kg/m2 and a history of breast cancer and subsequent right modified radical mastectomy is scheduled to undergo a reconstructive procedure involving a latissimus flap. After an uneventful induction of general anesthesia, you assist the nurse anesthetist with positioning by placing an axillary roll on the dependent thorax in the left lateral decubitus position, and abduct the nondependent right arm on a padded arm board, with the arm abducted 90 degrees or less. The anesthetic proceeds uneventfully, for a total operative time of 210 minutes. She is extubated after surgery and taken to the PACU, and is discharged to the step-down unit 2 hours later with an Aldrete Score of 10, without any evidence of neurologic abnormalities.
On the first postoperative day, she notices throbbing right shoulder pain and is unable to elevate her right arm. She is also aware of weakness in her left arm and now believes that all of these abnormalities were present immediately after surgery. The patient is seen by the surgeon 1 week after discharge, and is still complaining of weakness, primarily in her right arm, and is having difficulty abducting her right shoulder above 45 degrees. She is referred to a neurologist, who examines her 1 week later and finds significant right deltoid weakness, right infraspinatus weakness, normal right supraspinatus function, and scapular winging on her right side. Significantly, biceps strength and function are normal in both the left and right extremities. The neurologist also finds evidence of mild arm weakness on her left side, involving the deltoid, supraspinatus, and infraspinatus muscles, and diagnoses her with bilateral asymmetrical brachial plexopathies.
Questions to consider:
- Isthe length of surgery and anesthesia an independent risk factor for the development of a PNI?
- Does this appear to be a positioning-related nerve injury?
- What is the purpose of the axillary roll, and where should it be placed?
- Which part of the brachial plexus seems to be affected?
- What further studies would you recommend?
- What is the significance of scapular winging in this case?
- What other etiologies couldexplain these nerve deficits?
- What therapeutic options are available if no further improvement in neurologic function occurs after 6 months?
Although length of surgery and anesthesia would logically seem to be a risk factor for developing a PNI, there is limited evidence to substantiate this notion. The large retrospective case series of Welch et al4 examining the incidence of PNI and associated risk factors did not screen for lengthof anesthesia and surgery as a potential risk factor. However, some data have shown that length of surgery in excess of 2 hours—at least in patients undergoing surgery in the lithotomy position—is associated with an increased risk for developing a PNI.19
This is a very unusual presentation of an asymmetrical bilateral brachial plexus injury that calls into question a positioning-related diagnosis, as positioning injuries are normally unilateral and confined to a single nerve or plexus element.9 Additionally, most PNIs of the brachial plexus related to malpositioning present as painless injuries.9 An approach to the diagnosis and management of PNIs has been published,20 emphasizing the multifactorial causes of nerve injury, including stretch; compression; ischemia; mass lesions; metabolic; hereditary or acquired neuropathies; and postsurgical inflammatory neuropathy, of which the latter is probably frequently underdiagnosed.21
The term “axillary roll” is a misnomer, as it is properly a chest roll, and placed approximately 10 cm away from the axilla in order to prevent compression at the axillary level. Hyperabduction of the dependent arm would be expected to cause ulnar nerve–related symptoms.10 Alternatively, and more consistent with this presentation, injury to the upper trunk of the brachial plexus has been described in the nondependent arm in the lateral position, due to compression of the upper trunk of the brachial plexus (axillary nerve, suprascapular nerve) when the shoulder is elevated and abducted.22
Additional studies could include MRI of the brachial plexus to rule out a hematoma or mass effect, and MRI of the cervical spine to screen for spinal stenosis, a herniated disk, or intervertebral foramen stenosis, potentially compromising the C5-C6 nerve roots. Furthermore, MRI or CT of the neck could rule out the presence of thoracic outlet syndrome secondary to a cervical rib, although this anatomic variant normally causes injury to the lower trunk of the brachial plexus, and would affect the ulnar nerve.10
The presence of scapular winging on exam is significant because it implies injury to the serratus anterior muscle, which is innervated by the long thoracic nerve (C5-C7 nerve roots).10 The muscle injury pattern in this case scenario is distinctive in that the brachial plexus is not affected at a discrete site, but rather at multiple diffuse locations, and muscles with similar nerve root innervations are seemingly spared. The long thoracic nerve (C5-C7) leaves the nerve roots proximal to the formation of the brachial plexus, while the axillary nerve (C5-C6) is affected, but more distally at the level of the posterior cord. The supraspinatus muscle is normal, and is supplied by the C5-C6 nerve roots of the suprascapular nerve, which is the first branch of the superior trunk, and yet the distal muscle supplied by the same nerve, the infraspinatus muscle, is abnormal. At the same time, the biceps muscle, which is supplied by the C5-C6 nerve roots, is completely normal. All of these clinical findings should be verified through needle EMG testing, to look for the presence of fibrillation potentials in affected muscles, along with impairment of motor unit recruitment patterns.
The most likely explanation for this phenomenon is a postsurgical inflammatory neuropathy, with classic diffuse, patchy neuropathy.20,21,23-26 Many similar entities fall under this classification, including brachial neuritis, neuralgic amyotrophy, and Parsonage-Turner syndrome. The triggers are poorly understood, but the condition has been described after surgery, heavy exercise, recent viral illness, recent immunization, and during pregnancy. The symptoms initially present with pain in the shoulder girdle, followed by muscle weakness of the arm, with the most commonly affected nerves including the long thoracic nerve, axillary nerve, suprascapular nerve, phrenic nerve, and anterior interosseous nerve.
This is an immune-related process characterized by lymphocytic infiltration in the neural structure, associated with a microvasculitis. The diagnosis can only be made with nerve biopsy and immunofluorescence staining techniques, and is thought to be frequently underdiagnosed, with an incidence of 1.6 per 100,000 reported in the literature.21 Treatment is primarily palliative, although high-dose steroids have been used with varying degrees of success. Although 90% of patients eventually recover full or partial function, in cases where weakness persists after 6 months, surgical nerve transfer of the accessory nerve to the suprascapular nerve can be considered to improve shoulder function, along with a transfer of the radial nerve fascicle supplying the medial head of the triceps to the axillary nerve.27
These 3 selected cases illustrate why it is important for anesthesiologists to understand the differential diagnosis of perioperative PNIs, and be aware of alternative causation other than inadequate intraoperative patient positioning.
In the first case, a unilateral ulnar PNI was diagnosed, and may well have been a positioning-related injury, but this injury was more likely to have occurred during the postoperative phase: either in the ICU or during recuperation on the ward.
In the second case, the presence of a bilateral ulnar nerve injury, in combination with other PNIs, revealed that a polyneuropathy was to blame, rather than intraoperative malpositioning.
The final case illustrates the confusing presentation associated with postsurgical inflammatory neuropathy, which is most likely underdiagnosed in the general medical community.
Rather than short-circuiting the differential diagnosis of PNIs by immediately attributing causation to intraoperative malpositioning, it is important to refrain from making a diagnosis until expert consultation and electrodiagnostic testing have transpired. Physicians and their patients would probably be better served by describing the problem (eg, PNI) rather than rushing to judgment with a limited differential diagnosis entered into the medical record. Anesthesiologists and other members of the anesthesia care team can protect themselves and their patients by becoming familiar with the most recent ASA practice advisory for the prevention of perioperative peripheral neuropathies, and employ the capabilities of the electronic anesthesia record to enhance the level of detail in the documentation process.
- Cheney FW, Domino KB, Caplan RA, et al. Nerve injury associated with anesthesia: a closed claims analysis. Anesthesiology. 1999;90(4):1062-1069.
- Parks BJ. Postoperative peripheral neuropathies. Surgery. 1973;74(3):348-357.
- Blitt CD, Kaufer-Bratt C, Ashby J, et al. QA program reveals safety issues, promotes development of guidelines: Arizona practice is model. J Clin Monit.1995;11(1):76-79.
- Welch MB, Brumett CM, Welch TD, et al. Perioperative peripheral nerve injuries: a retrospective study of 380,680 cases during a 10-year period at a single institution. Anesthesiology. 2009;111(3):490-497.
- Posta AG, Allen AA, Nercessian OA. Neurologic injury in the upper extremity after total hip arthroplasty. Clin Orthop Relat Res. 1997;(345):181-186.
- Warner MA, Warner ME, Martin JT. Ulnar neuropathy: incidence, outcome, and risk factors in sedated or anesthetized patients. Anesthesiology. 1994;81(6):1332-1340.
- Warner MA, Warner DO, Matsumoto JY, et al. Ulnar neuropathy in surgical patients. Anesthesiology. 1999;90(1):54-59.
- Warner MA, Warner DO, Harper CM, et al. Ulnar neuropathy in medical patients. Anesthesiology. 2000;92(2):613-615.
- Winfree CJ, Kline DG. Intraoperative positioning nerve injuries. Surg Neurol. 2005;63(1):5-18.
- Preston DC, Shapiro BE. Electromyography and Neuromuscular Disorders: Clinical-Electrophysiologic Correlations (Expert Consult – Online and Print), 3rd Edition. New York, NY: Elsevier Saunders; 2013.
- Washington SJ, Smurthwaite GJ. Positioning the surgical patient. Anaesth Intensive Care Med.2009;10(10):476-479.
- Bonnaig N, Dailey S, Archdeacon M. Proper patient positioning and complication prevention in orthopaedicJ Bone Joint Surg Am. 2014;96(3):1135-1140.
- Kumar MM, Harrison BA, Burkle CM. Assigning liability in positioning injuries. ASA Newsletter. 2010;74(6):24-26.
- Practice advisory for the prevention of perioperative peripheral neuropathies: an updated report by the American Society of Anesthesiologists Task Force on prevention of perioperative peripheral neuropathies. Anesthesiology. 2011;114(4):741-754.
- Apfelbaum JL, Connis RT, Nikinovitch 2012 Emery A. Rovenstine Memorial Lecture: the genesis, developmentand future of the American Society of Anesthesiologists evidence-based practice parameters. Anesthesiology. 2013;118(4):767-768.
- Prielipp RC, Morell RC, Walker FO, et al. Ulnar nerve pressure: influence of arm position and relationship to somatosensory evoked potentials. Anesthesiology. 1999;91(2):345-354.
- CMS Manual System; Pub 100-04 Medicare Claims Processing. cms.gov/ Regulations-and-Guidance/ Guidance/ Transmittals/ downloads/ R1859CP.pdf. Accessed July 10, 2017.
- Statement on the Anesthesia Care Team. asahq.org/ Site website/Database web/sitecore/media library/Sites/ASAHQ/Files/Public/Resources/standards-guidelines/statement-on-the-anesthesia-care-team/en/2. Accessed July 10, 2017.
- Warner MA, Martin JT, Schroeder DR, et al. Lower-extremity motor neuropathy associated with surgery performed on patients in a lithotomy position. Anesthesiology. 1994;81(1):6-12.
- Watson JC, Huntoon MA. Neurologic evaluation and management of perioperative nerve injury. Reg Anesth Pain Med.2015;40(5):491-501.
- Staff NP, Engelstad J, Klein CJ, et al. Post-surgical inflammatory neuropathy. Brain. 2010;133(10):2866-2880.
- Logan AM, Black MJ. Injury to the brachial plexus resulting from shoulder positioning during latissimus dorsi flap pedicle dissection. Br J Plast Surg. 1985;38(3):380-382.
- Malamut RI, Marques W, England J, et al. Postsurgical idiopathic brachial neuritis. Muscle Nerve. 1994;17(3):320-324.
- Rubin DI. Neuralgic amyotrophy: clinical features and diagnostic evaluation. Neurologist. 2001;7(6):350-356.
- Hussey AJ, O’Brien CP, Regan PJ. Parsonage-Turner syndrome—case report and literature review. Hand (N Y).2007;2(4):218-221.
- Feinberg JH, Radecki J. Parsonage-Turner syndrome. HSS J.2010;6(2):199-205.
- MacKinnon SE, Colbert SH. Nerve transfers in the hand and upper extremity surgery. Tech Hand Up Extrem Surg. 2008;12(1):20-33.