White paper d77490-a1


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White paper d77490-a1

  1. 1. PRONE WHITE PAPER POSITIONING OF PATIENTS ON OPERATING ROOMSUPPORT EQUIPMENT:INTRA-OPERATIVE COMPLICATIONSAuthor: Helen M. Manson, MB ChB MRCGP (UK) ABSTRACT: This paper summarizes the complications related to positioning devices used to support patients during prone surgery. The surgical patient’s position must allow the surgeon optimal access to the operative site, but it can unduly influence the patient’s recovery time, morbidity and mortality. The types of complications associated with the prone position include: cardiopulmonary, central nervous system, pressure, ophthalmological, and oropharyngeal. These complications can have serious consequences for the patient, leading to pain, disability, paralysis, visual loss, or even death. The methods used to support the prone patient influences the occurrence and severity of complications. The design and ergonomics of the positioning equipment, in conjunction with staff education on proper techniques for positioning the patient, is vitally important. “The successful outcome of surgery on the thoracic and lum- reflexes. Enforced immobility during surgery, often for a longbar spine is largely dependent on the proper positioning of the duration of time, combined with drug-induced loss of tissuepatient before the operation begins” (Iqbal Singh, M.D, The tone, changes in tissue mass associated with aging,Prone Position: Surgical Aspects, 19871). This fundamental co-existing medical conditions, the physiological consequenc-premise is important: careful positioning not only allows the es of being prone, and inadvertent pressure on the abdomensurgeon optimal access to the operative site, but also influences while prone, can lead to many complications. The patient’s ori-the patient’s recovery time, morbidity and mortality. Numer- entation on the operating table, the type of device used to sup-ous commentators have described the range of complications port the patient in the operating room, and the way in whichresulting from improper prone positioning.1,2,3,4,5 Sengupta and positioning devices are used by staff are also known to poten-Herkowitz write in Complications of Pediatric and Adult Spi- tially influence the occurrence and severity of certain complica-nal Surgery (2004): “Proper positioning of patients is one of tions.2,3,4,5,6 Support devices include operating room tables orthe most challenging tasks in spinal surgery. Air embolism, pe- table frames, kneeling attachments, pads, rolls, blankets, safetyripheral nerve palsy, blindness, quadriplegia, compartment syn- belts, arm supports, mattress overlays and head supports.drome, pressure necrosis of the skin, excessive bleeding, andvenous thrombosis are only some of the complications that This paper summarizes the intra-operative complications relat-may result from improper positioning.”6 ed to positioning devices used to support patients prone, with particular reference to spinal surgery. This summary is basedThe prone position is a natural posture often adopted during on an extensive literature search of Ovid Medline, conductedsleep, when protective involuntary alterations in posture coun- in January 2008. Search terms included combinations of theteract postural atelectasis, ischemia, nerve compression and following terms: “prone”, “position”, chest”, “breast”, “ im-skeletal stress.1 Anesthesia leads to loss of these protective plant”, “rupture”, “spine”, “spine surgery”, spinal surgery”, Copyright 2009, Allen Medical Systems. D-770490-A1 Oct. 22, 2009
  2. 2. “breast pain”, “anesthesia”, “complications”, “pressure ulcers”,“visual loss” and “nerve injury”. The reference lists of those 1. CARDIOPULMONARY EFFECTSpapers found in the initial search provided additional sources OF THE PRONE POSITIONof information, and a library search was also conducted to find Prone positioning during anesthesia is associated with pre-relevant textbooks. dictable changes in cardiopulmonary physiology. The way in which the patient is positioned, the type of support de-Several authoritative sources were found that provided an over- vices used, together with certain characteristics of spinalview of prone complications. Martin has written an evidence- surgery can combine to magnify the impact of these physi-based summary on prone positioning, supplemented by his ological effects on the hemodynamic and respiratory systems.extensive experience as an anesthesiologist, in: Positioning inAnesthesia and Surgery (edited by Martin and Warner, 1997).2 Inferior Vena Cava ObstructionSengupta and Herkowitz describe these complications in detail In the prone posture, pressure on the abdomen compressesin the context of spinal surgery, in Complications of Pediatric the inferior vena cava (IVC) and femoral veins, diverting bloodand Adult Spinal Surgery (edited by Vaccaro, 2004).6 Edgcombe from the distal parts of the body into perivertebral venouset al have recently published a comprehensive review paper plexuses. This makes wound hemostasis difficult and obscuressummarizing the evidence underlying the complications of an- the surgical field. The great vessels and small bowel are at riskesthesia in the prone position (2008).3 The Association of pe- of being pressed against the lumbar spine by raised intra-ab-riOperative Registered Nurses (AORN) has also characterized dominal pressure, increasing the risk of accidental iatrogenicthe complications of prone positioning, producing important injury to these organs during spinal surgery.2,3 IVC obstruc-guidelines to aid prevention.4 These sources describe the range tion from pressure on the abdomen can therefore potentiallyof complications related to techniques used to support patients reduce cardiac output and also contribute to blood loss.in the prone position, summarized in Table 1, and further dis-cussed in this paper. Different positioning devices have been designed to maximize operative access while minimizing pressure on the abdomen. TABLE 1: THE RANGE OF COMPLICATIONS ASSOCIATED WITH PRONE POSITIONING DURING SURGERY COMPLICATION DESCRIPTION Decreased cardiac index, inferior vena cava obstruction, venous gas embolism and non- Hemodynamic effects gaseous embolism. Respiratory effects Decreased respiratory compliance (in the presence of abdominal compression). Ischemic cerebrovascular events (due to occlusion of the carotid or vertebral arteries); neu- Central nervous system injury rological deficits related to venous occlusion, air entrainment, pneumorrhachis, or cervical spine injury; triggering of symptoms from undiagnosed space-occupying lesions. Pressure injury: Skin Pressure ulcers, contact dermatitis, compression of the pinna, viscerostomy damage. Pressure injury: Chest Tracheal compression, mediastinal compression. Hepatic ischemia, pancreatitis, acute mesenteric ischemia; limb compartment syndrome and Pressure injury: Vascular supply rhabdomyolysis; avascular necrosis of the femoral head. Pressure injury: Bone & joints Shoulder injury, bone and joint pain. Pressure injury: Breasts & genitalia Pain, bleeding, implant rupture. Brachial plexus, ulnar, axillary, musculocutaneous and radial nerve compression; lateral Pressure injury: Peripheral nerve femoral cutaneous nerve injury (meralgia paresthetica); facial nerve injury; penile nerve compression; supraorbital neuropraxia. Corneal abrasion, chemosis, ischemic optic neuropathy, central retinal artery occlusion, transient or permanent ophthalmoplegia, cavernous sinus thrombosis, central retinal vein Ophthalmological complications occlusion, orbital hemangioma, orbital compartment syndrome, bilateral angle closure glau- coma, non-traumatic subperiosteal orbital hemorrhage, amaurosis, dislocated intraocular lens, fixed mydriasis, cortical blindness. Oropharyngeal complications Nasopharyngeal congestion, salivary gland swelling, macroglossia, oropharyngeal swelling. Loss of body heat Hypothermia 2 Copyright 2009, Allen Medical Systems. D-770490-A1 Oct. 22, 2009
  3. 3. These support devices have varying effects on intra-abdomi- or negative pressure may draw in air intravascularly from a sur-nal pressure. Schonauer et al found, on literature review, that gical wound. Efforts to minimize abdominal compression indifferences in intra-abdominal pressure and the extent of the prone position can result in an increased negative pressureblood loss are linked to the patient’s position, and vary ac- gradient between the right atrium and veins at the operativecording to the table or frame used during spinal surgery in site. The low pressure in the IVC results in a negative pressureprone patients.10 which could then move gas from the operative site to the right atrium. Air embolism has been reported infrequently follow-A rise in intra-abdominal pressure may be caused by factors ing surgery in the prone position, described in the publishedother than the table or frame, such as sandbags, bolsters, pads, literature as case reports.3,9,11,12,13 The precise incidence of airpillows, or the mattress of the operating table. The careful po- embolism during spine surgery is unknown, complicated by thesitioning of patients on operating support surfaces, and the varying sensitivity of detection methods.3 However it is knownuse of support surfaces that minimize intra-abdominal pres- that the risk is dependent upon patient position and operativesure, are recognized as essential in order to reduce the risks of site. In a review of pediatric patients undergoing neurosurgicalIVC obstruction.2,3,10 operations, there were two possible episodes of air embolism in 120 operations, an incidence of 1.7%.14Decreased Cardiac IndexDecreased cardiac index is a consistent physiological effect; an Edgcombe et al describe four case reports of fat embolism inalmost universal finding when a patient is moved from supine patients undergoing spine surgery in the prone position.3 Into prone.3 The specific prone position used influences the ex- one case, involving lumbar decompression and spinal fusiontent of hemodynamic effect. In one study of 21 patients under- with harvesting of the iliac crests for bone grafts, the authorsgoing lumbar surgery (1991), direct pulmonary artery and infe- considered that the prone position had contributed to the em-rior vena cava (IVC) pressures were monitored: the flat prone bolic process, speculating that prolonged venous stasis hadposition did not interfere with circulatory function, but use of played some part in the release of multiple emboli from bonea convex saddle frame decreased the cardiac index and stroke harvesting sites.15volume index, with no effect on IVC pressure.7 This was con-firmed in a 2006 study, which used transesophageal echocar- Respiratory Effectsdiography to compare different prone positioners.8 Cardiac As acknowledged by Edgcombe et al: “There are clear differ-output decreased with the Wilson and Siemens AG frames, ences in respiratory physiology between the supine and pronewhile cardiac index and stroke volume decreased with the An- position, including an increase in functional residual capacitydrews, Wilson, and Siemens systems. Cardiac preload decreased and alterations in the distribution of both ventilation and per-using the Andrews frame. The Jackson spine table and longi- fusion throughout the lungs.”3 Provided that the patient is sup-tudinal bolsters had the least effect on cardiac performance. ported with the abdomen free from pressure, prone positioningThese studies demonstrate that the prone position can have an is known to improve ventilation/perfusion matching and con-important hemodynamic impact, which varies with the type of sequently improve oxygenation in the surgical patient.2,3patient support used. However, if abdominal compression occurs, this can lead toIn certain variants of the prone position, such as the Tuck posi- decreased respiratory compliance. Inadvertent compressiontion, venous drainage can be inadvertently obstructed by knee can happen if the patient is obese or incorrectly positioned onor hip flexion, allowing pooling of blood in the dependent the operating frame. Under these circumstances, very high air-structures and reduced atrial filling and cardiac output. Spinal way pressures may be required to ensure adequate ventilation.surgery is often associated with unexpected blood loss and hy- High airway pressures can in turn impair venous return to thepovolaemia, which may itself cause cardiac arrest in susceptible heart, decreasing cardiac output and increasing systemic venouspatients. The prone position may exacerbate hypovolaemia by pressure. This in turn potentially affects spinal cord perfusionfurther reducing venous return and cardiac output.9 pressure, increasing the patient’s risk for neurological complica- tions.10 According to Martin and Warner: “The necessary highEmbolic Complications airway pressures and large tidal volumes needed to ventilate aAir embolism is one of the most serious complications in spi- patient who is improperly positioned prone can have severalnal surgery. Any open vein in which there is subatmospheric potential side effects that can be harmful, (including): pulmo- 3 Copyright 2009, Allen Medical Systems. D-770490-A1 Oct. 22, 2009
  4. 4. nary interstitial emphysema leading to mediastinal, retroperito- to head rotation during anesthesia in the prone position.3 Forneal or subcutaneous emphysema; an exaggerated rise and fall these reasons, it is generally accepted that careful positioning ofof the patient’s back, potentially affecting the surgical field; and the neck, and head support in a neutral position are essential tohigh venous and cerebrospinal fluid pressures, visible as fluid prevent neurological injury while prone.2,3,4fluxes in the wound.” The authors recommend ensuring a posi-tion that does not compress the abdomen and using the least Venous Occlusionpermissible lung inflation pressures to minimize venous conges- Edgcombe reports nine cases that involve prone patients andtion and cerebrospinal fluid surges in the operative field.2 spinal surgery, in which hemodynamic changes have led to spi- nal cord ischemia.3 In a study by Bhardwaj et al , four patientsChanges in pulmonary mechanics are also dependent on the developed new neurological deficits immediately after a cervicaltype of prone position used, and on the equipment used to sup- laminectomy (two had hemiparesis, one quadriparesis, and oneport the patient prone. For example, Palmon (1998) showed that paraparesis).19 These patients were prone, supported by chestpulmonary compliance decreased when patients were supported rolls. The authors proposed that the use of chest rolls led to in-on chest rolls or on the Wilson frame, whereas the Jackson table creased venous pressure, which, when combined with mild arte-was not associated with any change in pulmonary function.16 rial hypotension, decreased the perfusion pressure in the spinal cord, causing ischemia. This paper states: “The use of framesSummary that prevent abdominal compression, as well as avoidance ofOverall, it is evident that prone positioning of the patient, the perioperative arterial hypotension, is important in maintainingtype of patient support device used, and how the patient is adequate spinal perfusion during and after decompressive spinalplaced on the support can have a significant impact on cardiac cord surgery.” A similar mechanism is thought to explain an ad-output, intra-abdominal venous pressure, respiratory compli- ditional case of quadriplegia after thoracolumbar decompres-ance, extent of intra-operative blood loss and the risk of air or sion20 and two reports of thoracic level paraplegia after lumbarfat embolism. spine surgery.21 Two cases occurred in patients with abnormal venous anatomy. A patient with achondroplasia, who had stenosis of the jugular 2. CENTRAL NERVOUS SYSTEM foramina (a recognized feature of achondroplasia), developed INJURY bilateral venous infarcts in the cerebellum. This occurred afterThe manner in which the patient is positioned can result in seri- a nine hour thoracolumbar operation, head-down on a Wilsonous injury to the central nervous system. Although an uncom- frame, with high intra-thoracic pressures during positive pres-mon complication, central nervous system injury can occur sec- sure ventilation.22 Another case report describes a patient withondary to arterial or venous occlusion, air entrainment, cervical an occipital meningioma who was placed prone on a horseshoespine compression or from the triggering of symptoms related headrest: it is thought that the headrest caused compression ofto an undiagnosed space-occupying lesion.3,6 the anterior emissary veins, leading to venous stasis and rupture into the frontal extradural space.23Ischemic Cerebrovascular EventsExcessive movement of the patient’s neck during positioning Air Entrainmentcan affect blood flow in the carotid and vertebral arteries. Wang Entrainment of air into the cranial cavity is common after neu-et al describe a patient who had a fatal ischemic stroke after rosurgical procedures and occurs in any operative position.3 Inbeing positioned prone with the head rotated during spinal sur- one study, 16 of 28 patients (57%) undergoing posterior fossagery. This patient had an unrecognized carotid artery stenosis.17 or cervical spine procedures in the prone position experiencedAnother patient was reported as having a dissection of the left pneumocephalus, although this was asymptomatic and did notcarotid artery, resulting in hemiparesis and aphasia, after spinal result in neurological deficit.24 Two cases of tension pneumo-surgery.18 The dissection was thought to be related to extension cephalus have been reported, both in children undergoing in-or rotation of the neck during positioning. tracranial surgery, placed prone.25,26Occlusion or dissection of the vertebral arteries has been re- A single case report of air entrainment into the spinal canalported in at least four cases, linked to hypoperfusion secondary (pneumorrhachis) after posterior fossa exploration, resulting in Copyright 2009, Allen Medical Systems. D-770490-A1 Oct. 22, 2009 4
  5. 5. quadriplegia, was thought to be related to the prone head-downposition.27 The patient’s position was thought to have contrib- 3. PRESSURE INJURIESuted to the tracking of air through the foramen magnum intothe cervical region. Injuries can occur in the prone position as a result of the direct application of pressure, or indirectly, as a result of compressionSpinal Cord Compression of the vascular supply or nerves (Table 2).Prone positioning is known to be a high risk factor for patientswith pre-existing spinal cord dysfunction. Two case reports de- TABLE 2: Pressure Injuries Related To The Prone Positionscribe postoperative paraplegia due to cervical spine injury, at- Injury From Indirect Injury Fromtributed to neck positioning during prone spinal surgery.3 An Direct Pressure Pressure On Vascular Supply or Nerves18 year old patient had an eight hour operation to remove a Pressure ulcers Visceral ischemia: hepaticcerebellar medulloblastoma, placed prone in the “Concorde” ischemia, pancreatitis, acuteposition with hyperextension of the neck: afterwards, he had Contact dermatitis mesenteric ischemia.a complete and permanent C5/6 sensory and motor deficit.28 Compression of the pinna Avascular necrosis of theIt was postulated that the cervical cord was stretched in a nar- femoral head Viscerostomy damagerow spinal canal, with an already-bulging C5/6 disc, resulting Limb compartment syndromesin ischemia. The other case involved a patient placed prone for Tracheal compression and rhabdomyolysistwo hours with head turned to the left side and cushion support, Mediastinal compressionwho developed a prolapsed intervertebral disc at C6/7.29 The Peripheral nerve injury Breast injuryauthors concluded, “Careful neck positioning (is) mandatory forpatients receiving surgery in the prone position”. Injury to the genitalia Joint and bone pain,Undiagnosed space-occupying lesions dislocation or fractureProne positioning can trigger neurological symptoms in patients Source: Compiled from Martin, Edgcombe, Sengupta and Herkowitz, AORN.2,3,4,6with previously asymptomatic space-occupying lesions withinthe spinal canal or cranium. This is rare, reported in four cases.3 Pressure on The Skin and Underlying TissueIn each case, the proposed mechanism involved altered cerebro- Complications related to pressure on the skin and underlyingspinal fluid flow and epidural venous engorgement. One patient tissue have been reported in published articles as contact derma-with neurofibromatosis had a neurofibroma in the posterior fos- titis and pressure ulcers. Experienced clinicians have describedsa fall anteriorly when positioned prone, compressing the me- other injuries related to prone positioning that are not presenteddulla and pons and leading to bradycardia and fatal neurogenic as case reports or in case series in published articles, in particu-pulmonary edema.30 lar, compression of the pinna and viscerostomy damage.2Summary Contact DermatitisPositioning of the patient is of crucial importance to avoid seri- Edgcombe reviewed two case reports that describe contact der-ous or fatal neurological injury. The prone position can cause matitis in patients positioned prone during surgery. One patientneurological deficits through: an increase in abdominal pressure had their head supported in a flexible polyurethane foam posi-leading to a decrease in spinal cord perfusion; provision of the tioner that supports the face during surgery by molding around“right” conditions for the introduction of air into the cranial the eyes, nose and mouth. The other case developed contactcavity or spinal cord; and, by exacerbating a neck position that dermatitis in response to a monitor placed on the forehead. Thecan occlude the arterial supply to the brain or compress the spi- skin reaction was thought to have been exacerbated by the pronenal cord. Patient support devices that minimize abdominal com- position causing pressure against the electrode conductive gel.3pression and maintain the neck and body in a neutral positioncan help prevent these neurological complications. Compression of The Pinna Martin points out that improper positioning can cause all or part of the ear to be folded over. Pressure can result in cartilaginous damage that is potentially disfiguring.2 5 Copyright 2009, Allen Medical Systems. D-770490-A1 Oct. 22, 2009
  6. 6. Viscerostomy Damage the patient can decrease the pressure-reducing effect of a mat-Viscerocutaneous stomas can be compressed by prone supports, tress or overlay33, and the use of a warming blanket under theresulting in leakage of contents and operative contamination. patient during surgery has been shown to increase risk of pres-Compression of the stoma can also potentially lead to ischemia sure ulcers.38 Although there is a need for additional studies toof the stoma margins and a need for surgical revision.2 compare the pressure-reducing effects of various commercially- available support surfaces, it is clear that patient positioning, andPressure Ulcers the support device used, are important factors in the preventionIt is widely recognized that surgery itself is a risk factor for the of intraoperative pressure ulcers.development of pressure ulcers because of prolonged immobil-ity, unrelenting pressure on dependent parts of the body, and use This is emphasized in the guidelines provided by the AORNof anesthetic agents. Therefore, all surgical patients are regarded and others4,31,33 which recommend: the tailoring of positioningas being at risk of damage to skin integrity, regardless of their devices to the surgical position used, and to the body habitus ofbody position during surgery. The incidence of intraoperatively- the individual patient; the requirement for firm and stable de-acquired pressure ulcers has been reported in studies to range vices to minimize shearing; the use of support surfaces resistantfrom 8.5% to as much as 45%.31, 32,33,34 Since pressure ulcers to moisture; and, the design of support equipment to distributethat are initiated by surgery often do not appear until one to four pressure evenly, over a large surface area.days after an operation, these can be mislabeled, for example asa burn. This means that these are often not directly attributed There are few studies assessing the incidence of pressure ulcersto the surgical procedure and therefore the incidence of intra- in patients positioned prone and no studies so far that evaluateoperative pressure ulcers may be under-reported.32,34 the efficacy (in terms of ulcer prevention), of different support devices used for patients placed in the prone position. DespiteThe elderly, and patients with co-morbidity (such as diabetes, the lack of specific data, it is evident that prone patients arepreoperative hypertension, respiratory disease or vascular dis- at risk of pressure ulcer development, related to the increasedease), and sub-optimal nutritional status or small body size, are risk inherent in undergoing a surgical procedure, the prolongedknown to be at increased risk of developing an intra-operative nature of spinal surgery, and the vigorous manipulation oftenpressure ulcer.31,33,34 Perioperative exposure of the skin to required in this type of surgery (increasing the likelihood ofwetness (such as preparation solutions) and shearing, tearing shearing forces). As stated by Aronovitch: “All surgical patientsor friction forces are recognized as contributory factors.4,31,33 undergoing prolonged procedures should be considered at riskDuration of anesthesia has also been implicated as a risk factor for intraoperative ulceration.”35 Many authors advise close at-for skin ischemia in some studies. Aronovitch (1999) surveyed tention in prone patients to pressure points at the forehead,1128 patients undergoing a procedure of at least three hours’ chin, tip of the nose, ears, breasts, genitalia, anterior superiorduration and reported an incidence of 5.8% for surgery lasting iliac spines, knees and feet.2,4,6 Sengupta and Herkowitz pointthree to four hours, increasing to 13.2% for surgical procedures out that pressure on the face is especially high during posteriorlasting over seven hours.35 However, as noted by Price et al, this surgery of the cervical spine and cranio-cervical junction, andrelationship between risk and duration of surgery has not been recommend that Mayfield tongs are used, to reduce the effecta consistent finding.34 Hoshowsky and Schramm describe the of pressure on the face.6 Case reports in prone patients describe“interactive effects of patient risk factors”, referring to the in- intraoperative pressure sores on the malar regions of the face,creased risk from a combination of contributory factors.36 chin, eyelids, nose, tongue and iliac crests.3How the patient is positioned, and the characteristics of the op- Pressure ulcers are associated with significant costs, summed uperating room support device used can exacerbate these macerat- by Schultz: “Pressure ulcers, regardless of their origin, representing or tearing forces, or increase pressure on bony areas, result- negative outcomes for patients, including pain, additional treat-ing in damage to skin integrity.31,32,33,34 For example, the use ments, and surgery, longer hospital stays, disfigurement or scar-of a standard operating mattress is known to increase capillary ring, increased morbidity, and increased costs.”33 Beckrich andinterface pressures over bony prominences beyond the capillary Aronovitch calculated that, each year, approximately 1.6 millionclosing pressure, making ischemia more likely.35 Foam caused patients developed hospital-acquired pressure ulcers, at a costsignificantly more ulcers than a standard operating table in one of $2.2 to $3.6 billion (1998 figures).39 23% of these ulcers oc-study.37 Layering of materials such as blankets or padding under curred in surgical patients undergoing procedures lasting more 6 Copyright 2009, Allen Medical Systems. D-770490-A1 Oct. 22, 2009
  7. 7. than three hours, representing up to 42% of costs of ulcers de- between the spine and sternum while positioned prone. In threeveloping in hospital and an annual direct cost of $750 million to of the four cases, the problem was exacerbated by an underly-$925 million (1998 figures).39 ing connective tissue defect, either Marfan’s Syndrome,47,48 or tracheomalacia.49Since pressure ulcers are considered preventable (according tothe National Pressure Ulcer Advisory Panel Statement on Pres- Sternal or Mediastinal Compressionsure Ulcer Prevention, 1992), damage to skin integrity during Compression of the heart or great vessels has occurred in pa-surgery is considered indicative of deficient quality of care.40 tients positioned prone during spinal surgery, in cases whereThat skin integrity is a hallmark of quality nursing and a Quality there is an anatomical abnormality, such as scoliosis50 or pectusof Care indicator is endorsed by many professional, federal and excavatum51,52, and after cardiac surgery.53,54 Alexianu et al de-private health care organizations, such as the American Nursing scribed severe hypotension in a child with pectus excavatum,Association41, the Agency for Health Care Policy and Research scoliosis and neurofibromatosis around the great vessels, when(AHCPR)42, American Medical Directors Association43, the placed in a prone position on transverse bolsters for posteriorJoint Commission on Accreditation of Healthcare Organiza- spine surgery: sternal pressure was relieved when bolsters weretions44 and the ECRI Institute.32 placed longitudinally.51It is widely-recognized that intra-operatively-acquired pressure Pressure On The Vascular Supplyulcers expose nurses, surgeons, anesthesiologists and institutions Indirect pressure effects on the vascular supply during proneto significant litigation risk.32, 39, 45, 46 According to the ECRI In- surgery have been reported in the published literature as casesstitute (2006): “The mere existence of a pressure ulcer is often involving ischemia of the liver and bowel, compartment syn-viewed as physical evidence of medical negligence.”32 drome and rhabdomyolysis, and avascular necrosis of the femoral head.SummaryProne patients are at risk from intra-operatively-acquired skin Visceral Ischemiadamage because of the effects of anesthesia and the prolonged Compression on the abdomen when prone under anesthesia cannature and physical forces required in surgical procedures that result in ischemia of abdominal organs. Hepatic ischemia andrequire prone positioning (such as spinal surgery). The conse- hepatic infarction have been described after prolonged surgeryquences of pressure effects on the skin, in terms of morbidity in the prone position.50,55,56 The authors of these case reportsand health care costs, are substantial. Intra-operative positioning attributed the cause to the patient’s position and the possibil-and patient support surfaces that mitigate these pressure effects ity of hypo-perfusion and ischemia of intra-abdominal organs.are important factors in the prevention of skin complications. Edgcombe suggests that this complication may be more com-This is recognized by professional and federal organizations mon than is realized: at least five other cases have been identi-such as the AORN and AHCPR, which call for active preven- fied in a recent investigation by the United Kingdom Nationaltive measures, including adequate patient support surfaces, in Patient Safety Agency.3 Mofredj et al describe a case of acutepublished guidelines.4,42 mesenteric ischemia following spinal surgery: prone position and hypotension were thought to have led to venous stasis and mesenteric vein occlusion in a patient with an inherited hyper- coagulable state.57 Prone positioning has also been proposed as 4. PRESSURE EFFECTS a cause of pancreatitis after spondylolisthesis surgery.58 ON THE CHESTTracheal Compression Limb Compartment SyndromePressure on the trachea can result in serious consequences, since and Rhabdomyolysisairway problems are difficult to manage in the prone patient and Flexion of the hips and knees whilst prone can lead to isch-can result in cardiac arrest secondary to hypoxaemia.9 Four cas- emia of the muscles in the lower limbs, especially if surgery ises of tracheal compression have been reported during surgery prolonged. Rhabdomyolysis is caused by muscle ischemia andin patients positioned prone.3 All of these patients had thoracic re-perfusion, and is characterized by dark urine, muscle pain andscoliosis, which is thought to have reduced the anterior-posteri- generalized weakness. Severe hypoperfusion can lead to lacti-or diameter of the chest, causing the trachea to be compressed cacidosis and sometimes hyperkalemia, and acute renal failure. 7 Copyright 2009, Allen Medical Systems. D-770490-A1 Oct. 22, 2009
  8. 8. There is evidence that the knee-chest and “Tuck” positions de- Pressure on breasts and genitaliacrease blood flow in the posterior tibial artery, increase intra- Positioning devices can compress the scrotum and penis, andmuscular pressure in the anterior compartment of the leg and straps and seats to hold the female body in the kneeling pronerelease biochemical markers of muscle damage.3 In one study, position place pressure on the female perineum.215 patients undergoing surgery for spondylolisthesis in the knee-chest position all showed a significant increase in plasma creatine The prone position may inadvertently damage breast tissue, re-phosphokinase levels, and six patients also had myoglobinemia sulting in chest wall pain, breast tenderness or bleeding of theand myoglobinuria.59 nipples. Longitudinal positioning frames or rolls can damage breast tissue by direct compression.2 Prolonged pressure onEight cases of compartment syndrome have been reported in a breast implant has the potential to result in implant rupture.patients undergoing spinal surgery in various prone positions Martin has also noted that extensive breast tissue can potentiallythat involved flexion of the hips and knees.3 In six of these cas- threaten positioning, by forming an unstable and shifting plat-es, surgery lasted longer than three hours. Six patients required form when the patient is placed prone.2fasciotomy and three cases were complicated by acute renal fail-ure, which was fatal for one patient. Pressure on peripheral nerves Peripheral nerve injury is one of the most frequent causes ofRhabdomyolysis in the absence of compartment syndrome has morbidity resulting from improper positioning intraoperative-been identified in four cases.3 Three of the patients had been ly.6 In one study, neurological injury related to positioning wasplaced prone in Jackson frames for prolonged spinal surgery. found in 72 out of 50000 general surgery operations (0.14%),It was thought that muscle ischemia could have resulted either of which 38% were brachial plexus injuries.65 A review based onfrom compression of the large vessels in the abdomen (exac- the American Society of Anesthesiologists closed claims data-erbated by obesity), or from direct compression of the thigh base found an association between prone positioning and claimsmuscles against the support device. for nerve injury,66 however, reliable data on the incidence of peripheral nerve injury specifically in the prone positionAvascular necrosis of the femoral head is lacking.Orpen et al describe three patients with pre-operative radio-logical signs of osteoarthritis, who developed collapse of the Intra-operative injury to peripheral nerves occurs throughfemoral head within two to eight weeks after decompression of stretching or compression of the nerve, or due to nerve isch-spinal stenosis.60 These patients had been positioned prone on emia. This is usually associated with prolonged surgery, althougha Montreal mattress. The authors postulated that the combina- has been noted to occur in procedures lasting 45 minutes.67 Pa-tion of deliberate hypotension and prone positioning led to in- tients with diseased nerves (diabetes, peripheral vascular disease,traosseous venous congestion and ischemia of a compromised alcohol dependency, pre-existing neuropathy) and anatomicalfemoral head, leading to avascular necrosis. abnormalities that change the pressure point distribution (such as scoliosis) have an increased risk of intra-operative peripheralPressure on bone and joints nerve damage.3,68 Although there are other recognized causesMartin, Ray, and Sengupta and Herkowitz express concern over of intra-operative nerve damage (i.e., retraction injury or brachi-patients placed prone who have pre-existing joint or bone prob- al plexitis), there is no doubt that malpositioning of the patientlems, such as arthritis, osteoporosis and stiff joints (as in anky- and external compression from table surfaces, table edges andlosing spondylitis), or total joint replacements.2,6,61 The process restraining straps are important causative factors.3,68of placing such patients prone, or the application of prolongedpressure on joints while prone can lead to joint or bone pain, or Upper limb nerve injurybone fractures. Brachial plexus injury is reported by Sengupta and Herkowitz as more common in the prone position than in the supine orSutterlin and Rechtine reported shoulder pain in one patient lateral position.6 At least four cases of brachial plexus injury,supported prone during spinal surgery.62 Two case reports de- and other cases involving ulnar, axillary, musculocutaneous andscribe shoulder dislocation occurring during in prone surgical radial nerve injury, have been summarized as published case re-patients.63,64 ports, related to intra-operative prone positioning.3 8 Copyright 2009, Allen Medical Systems. D-770490-A1 Oct. 22, 2009
  9. 9. Lateral femoral cutaneous nerve injury SummaryCompression of the lateral femoral cutaneous nerve (meral- It is widely-acknowledged that positioning of the patient is angia paresthetica) is a common complication of the prone po- important causative factor in the occurrence of peripheral nervesition during spine surgery.65,69,70 Posts supporting the pelvis, damage, and that correct positioning, as well as the use of sup-or pillows under the patient can compress the nerve at the exit port devices that minimize pressure effects, are key to the pre-below the anterior superior iliac spine.69,71 The risk of nerve vention of these injuries. Although complete recovery can beinjury increases with higher Body Mass Index, longer surgical expected in the majority of cases, some patients do experience atime and if the patient has a degenerative spinal disorder.70 In permanent loss of nerve function.one prospective study, 23.8% of 252 patients on a Relton-Hallframe developed evidence of meralgia paresthetica after poste-rior spine surgery.70 Mirovsky and Neuwirth reported that mer- 5. OPHTHALMOLOGICALalgia paresthetica affected 20% of patients after posterior spine COMPLICATIONSsurgery on a Relton-Hall frame: in six of 105 patients, the injury There is no doubt that eye complications are associated with thewas bilateral.71 prone position during anesthesia, and the use of head support equipment.3,79 Compared with supine and lateral positioning,This condition is usually associated with hypoesthesia in the an- there is a ten-fold increase in eye injury associated with surgeryterolateral aspect of the thigh, and occasionally burning pain, while prone.79 Ophthalmological complications related to pronehypersensitivity and dysesthesia.69 Although symptoms usually positioning during surgery range from keratoconjunctival injury,resolve within six months of surgery, meralgia paresthetica can such as corneal abrasion and chemosis, to irreversible blindness.rarely be associated with severe pain and restriction of activity.72 The review paper by Edgcombe et al provides a recent sum-In the study by Mirovsky and Neuwirth, in 89% of patients, mary of the available evidence on visual loss following surgerysymptoms resolved within three months of surgery, but two pa- in the prone position, concluding that: “Ophthalmic complica-tients still had pain and hypoesthesia of the anterolateral thigh tions are well recognized in patients who have been prone underone year after surgery.71 anesthesia, and can be devastating.”3 This is acknowledged by organizations such as the AORN and the American Society ofFacial Nerve Injury Anesthesiologists: these organizations have published guidelinesSeveral case reports relating to nerve injury of the head and for the prevention of postoperative visual loss (POVL).80, 81 Pa-neck have been described in Edgcombe’s review, all attributed by tients undergoing spinal surgery are known to have an elevatedthe authors to nerve compression related to the prone position: risk: a study of cases registered with the Scoliosis Research Soci- One case of injury to the lingual and buccal nerves during ety (1997) estimated that one eye complication occurs for every lumbar laminectomy;73 100 spinal procedures.82 Three patients with supra-orbital nerve compression;74,75 One phrenic nerve injury in a diabetic patient, due to over- Corneal abrasion extension or rotation of the neck;76 Corneal abrasion is a well-recognized, usually self-limiting, com- Recurrent laryngeal nerve damage due to the compres- plication of anesthesia, regardless of patient position during sion of the vocal cord and recurrent laryngeal nerve by the surgery, resulting from incomplete closure of the eye, drying tracheal tube, and traction of the recurrent laryngeal nerve of the eyes, foreign bodies or other unintended materials con- by rotation of the neck.77 tacting the eye during surgery.2,79 Rarely, abrasion can cause a corneal ulcer and partial or complete visual loss in the affectedPenile Nerve Injury eye. Biswas et al found an incidence of 55% for conjunctivalInjury to the dorsal nerve of the penis is described in two pa- abrasions in prone patients undergoing cranial or spinal surgerytients positioned prone on a fracture table.78 Operative posi- in the prone position.83 According to Stambough: “The pronetioning compressed the dorsal nerve of the penis between the position is particularly implicated (in corneal abrasion) becausepubic symphysis and the perineal post of the fracture table. As direct or indirect eye pressure is more likely to occur.”79 Thea consequence, both patients experienced difficulty in obtaining AORN also notes that there is an increased risk for cornealcomplete erections, which appeared to be permanent. abrasion when the patient is in the prone position.81 9 Copyright 2009, Allen Medical Systems. D-770490-A1 Oct. 22, 2009
  10. 10. ChemosisPostoperative conjunctival edema (chemosis) is noted by Martin Support devices can also affect IOP. One study found intraoc-to be more likely to occur: “when the head of the prone patient ular higher pressures for patients with heads placed in pillows,is below the level of the atrium, or when the infusion volume compared with head stabilization with Mayfield pins, althoughof crystalloids is large.”2 This adverse event may be asymp- the study sample was small. Direct external pressure on thetomatic or lead to conjunctival or corneal infection. Chemo- globes and periorbital structures, caused by a headrest or othersis is a common postoperative finding in patients undergoing support, is known to increase intraocular pressure, potentiallylumbar spine surgery in the prone position. Jeon et al reported resulting in central retinal artery occlusion and POVL (de-an incidence of moderate and severe chemosis at 6% and 4%, scribed as the “Hollenhorst Syndrome”).3 Ironically, devicesrespectively, for patients positioned prone in a Wilson frame used to protect the eye can exert inadvertent pressure on theduring spinal surgery, with their head in a neutral position.84 In eye. Roth et al reported irreversible POVL in a 53 year old manthe head-down position, the incidence of moderate and severe secondary to use of protective goggles whilst in a prone posi-chemosis increased to 31% and 7%, respectively. Positive fluid tion during spinal surgery.95 The authors of this study searchedbalance and duration of surgery increased the risk. the Medwatch MAUDE database and found additional cases of patient injury from use of the goggles, all in patients placedPostoperative visual loss prone in a foam headrest (including keloid scarring on theIt is known that postoperative visual loss (POVL) is associated nose, skin abrasions, eyelid abrasions and neuropraxia of thewith spinal surgery and with prone positioning, although the supraorbital nerve).pathophysiology, etiology, incidence, risk factors and preven-tion of POVL are still being characterized. Stambough and Ischemic optic neuropathyEdgcombe provide informative reviews of the latest research An increase in intraocular pressure or venous pressure, or a de-on POVL and the association of POVL with prone positioning crease in arterial pressure can diminish oxygenation of the op-and spinal surgery.3,79 Buono and Foroozan (2005) compre- tic nerve, leading to ischemic optic neuropathy (ION).3 IONhensively describe the research on ischemic optic neuropathy can occur in the absence of external pressure from headrests,and the relationship of this condition to spinal surgery.86 when the head is supported in pins, for example. As stated by Edgcombe, “A variety of factors influence intraocular pressure67% of all cases of post-operative visual loss registered on and some of these are clearly altered by prone positioning.”the American Society of Anesthesiologists Postoperative Vi- Prone positioning and spinal surgery potentially raise intraocu-sual Loss Registry occurred after prone surgery.85 A retrospec- lar pressure by: 1) increasing venous pressure and peak inspira-tive review of 3450 spinal operations in 1997 found that 0.2% tory pressure, thereby increasing intraocular pressure79; 2) in-of patients developed visual loss after spinal surgery.90 The creasing the risk of abdominal compression, reducing cardiacincidence of visual loss after spinal surgery in the prone po- output and mean arterial pressure; 3) the use of a deliberatesition at one institution91 was 1 in 1100, compared with the anesthetic technique that reduces arterial pressure to minimizeincidence in the general surgical population of 1 in 61000.92 In blood loss. Other factors apart from hypotension that increasethe prone, anesthetized patient, central retinal artery occlusion the risk of ION following spinal surgery include blood loss ofand ischemic optic neuropathy are the most common reasons 1000ml or greater, anesthetic duration of six hours or longer,for POVL.3 complex instrumentation during scoliosis surgery, administra- tion of large volumes of clear fluids, and pre-existing hyper-Central retinal artery occlusion tension or vascular disease (such as atherosclerosis and dia-Factors that increase intraocular pressure can lead to central betes).79,85 Buono and Foroozan describe the well-recognizedretinal artery occlusion, retinal ischemia and POVL. The prone phenomenon that a head-down and prone position can resultposition itself has been associated with raised intraocular pres- in increased venous pressure, with facial and orbital edema,sure (IOP).93,94 Cheng et al measured IOP in 20 patients sched- especially after prolonged surgery and large volumes of intra-uled for spine surgery in the prone position. IOP was noted to operative fluid replacement.86increase in prone patients, and during anesthesia.93 Hunt con-firmed these results in patients undergoing spinal surgery and Occipital cortical infarctconcluded that: “IOP increases when anesthetized patients are Cortical blindness is caused by an isolated stroke that selec-placed in the prone position.”94 tively affects the visual cortex.79 Hypo-perfusion or embolism 10 Copyright 2009, Allen Medical Systems. D-770490-A1 Oct. 22, 2009
  11. 11. are the underlying factors, leading to occipital cortical infarct or cortical blindness. Stambough discusses this complication in hisreview article: Ophthalmic Complications Associated with Prone Positioning in Spine Surgery (2007).79Other causes of visual lossCase reports have been published describing other visual complications after surgery in the prone position. These cases include:supraorbital neuropraxia (three patients), transient or permanent ophthalmoplegia (nine patients), and single case reports of cav-ernous sinus thrombosis, central retinal vein occlusion, orbital hemangioma, orbital compartment syndrome, bilateral angle closureglaucoma, non-traumatic subperiosteal orbital hemorrhage, amaurosis, dislocated intraocular lens; and fixed mydriasis.3,79 Some ofthese cases are described below: CASE EXAMPLE: A 76 year-old patient had surgery for cervical spine stenosis, five hours’ prone un- der anesthesia, with head supported on a Mayfield head clamp. On awakening, he reported unilateral visual loss. On examination, he had mild left proptosis with lid swelling and conjunctival chemosis. Pupil was mid-dilated and non-reactive. Fundoscopy showed retinal edema with a cherry-red foveal spot. A cerebral angiogram two weeks later showed a left cavernous sinus thrombosis. The authors attributed this complication, which resulted in irreversible long-term visual loss, to pressure from the headrest. Anand and Mushin, 2004.87 CASE EXAMPLE: An 80-year old man underwent an eight hour lumbar laminectomy for lumbar spinal stenosis. A silicone head rest was used. The patient experienced facial edema, corneal edema with an extensive corneal abrasion, a nonreactive pupil, advanced cataract and complete ophthal- moplegia, leading to complete and irreversible visual loss in the eye. The authors suggested that: “The progressive orbital edema secondary to the prone position, and possible unilateral direct pres- sure from the headrest device on periorbital structures resulted in congestion at the orbital apex, with a subsequent compartment syndrome and ischemic orbit.” Leibovitch et al, 2005.88 CASE EXAMPLE: A 16 year old girl had scoliosis surgery in the prone position, her face resting on a padded, gel-filled horseshoe rest and eyes taped shut and padded with gauze. After surgery, she complained of visual loss in the right eye. Computed tomography showed a swollen medial rectus muscle with no other orbital pathology. The authors attributed the permanent visual loss to ocular compression against the headrest, caused by repositioning of the patient during surgery. Kumar et al, 2004.89SummaryOphthalmological complications related to prone positioning range from common, self-limiting and mildly symptomatic cornealabrasions or chemosis, to rare, permanent and potentially devastating visual loss. Prone positioning on head support devices plays animportant part in the causation and prevention of all of these ophthalmological complications. 11 Copyright 2009, Allen Medical Systems. D-770490-A1 Oct. 22, 2009
  12. 12. Humphreys et al described complications in a series of 107 pe- 6. OROPHARYNGEAL diatric patients undergoing upper cervical spine and posterior COMPLICATIONS cranial fossa surgery in the prone position.99 A Relton frameHans et al describe a case of bilateral painful swelling of the with Mayfield or Gardner head holder was used. The authorssubmandibular glands occurring after neurosurgery in the reported the following as complications related to the position-prone position, with the patient’s head supported in a Mayfield ing of the patient: a drop in temperature (in all 24 infants, andholder.96 The authors determined that stretching of the salivary reduction of greater than 3oC in three of these patients), ob-ducts, leading to stasis and acute swelling, explained the underly- structed endotracheal tube, possible air embolus (two patients)ing etiology. Another paper describes six cases of bilateral pa- and blood loss. However, the authors concluded that the pronerotid gland enlargement occurring after general anesthesia (“an- position was safer than supine and sitting positions for pediatricesthesia mumps”), five of which occurred after prone surgery.97 patients who needed this kind of surgical treatment, since theVascular congestion resulting from the patient’s position during risk of air embolism was less.surgery was thought to have contributed to this complication. TABLE 3: Pediatric complications of the prone positionThree reports document macroglossia after surgery in the prone Pediatric Complicationsposition, complicating a suboccipital craniotomy, a posterior Unintentional extubationcervical spine decompression and posterior fossa surgery.3 The Eye complications: corneal abrasions, conjunctival and perior-authors identified obstruction to venous drainage, excessive bital edema of the dependent eye, retinal ischemia, post-oper-flexion of the head, and/or the tracheal tube obstructing venous ative visual loss due to ischemic optic neuropathy.drainage from the lingual and pharyngeal veins as underlying Entangling of cables.mechanisms. Abdominal compression (leading to impaired ventilation, in- creased bleeding, and decreased cardiac output). Improper head and neck positioning (leading to venous and lymphatic obstruction). 7. COMPLICATIONS OF THE PRONE POSITION IN PEDIATRIC PATIENTS Macroglossia.In children, complications linked to prone positioning are similar Possibility of venous air embolism.to those described for adults. However, there are particular risks Source: Soundararajan and Cunliffe98in children related to: the hemodynamic consequences of posi-tioning, blood loss, and the potential for vascular compromise Being positioned prone on a support involving four pillars, suchof the spinal cord; underlying pathology (such as spinal defor- as the Relton-Hall table, increases the potential for heat loss inmity, or genetic syndromes with “hidden” organ structure, dys- children, since the ventral surface of the patient is exposed tofunction or location); and, age-related anesthetic considerations, room air. LeBard100 and Soundararajan98 point out that hypo-particularly hypothermia in neonates and small children.98,99 thermia prolongs recovery from neuromuscular block, impairsThese complications are summarized in Table 3. Soundararajan platelet function, and leads to a higher incidence of wound in-and Cunliffe describe these challenges in their paper, Anesthesia fections.for Spinal Surgery in Children (2007).98 The authors emphasizethe importance of: “Careful positioning of the patient to pre- Meralgia paresthetica has also been noted after posterior spinevent compression of the abdomen,” especially with the aim of fusion in pediatric patients Tejwani et al found that, of 56 chil-minimizing both spinal cord ischemia and compression on the dren undergoing spine fusion for scoliosis (on a Jackson tablespinal cord, whilst maintaining a bloodless surgical field. They with either the lower leg support table and thigh supports, oralso caution that: “Anesthetic management requires a meticu- lower leg suspension sling), 10 (18%) developed meralgia par-lous approach to safety, positioning, and spinal cord perfusion, esthetica.101 This manifested as anterolateral thigh numbnesswith maintenance of normothermia and normovolemia.” without pain or weakness. Symptoms in all affected patients re- solved in less than 6 weeks. Patients with meralgia parestheticaMeridy et al reviewed pediatric patients undergoing neurosurgi- more often had idiopathic scoliosis, were positioned with thecal operations and reported two possible episodes of air embo- lower leg sling instead of the flat table support and tended tolism in 120 operations, an incidence of 1.7%.14 have longer surgery times. 12 Copyright 2009, Allen Medical Systems. D-770490-A1 Oct. 22, 2009
  13. 13. SUMMARYThe most common complications associated with the prone position include: ischemia of the skin at pressure points, peripheralnerve compression, and mild ocular injuries. These surgical outcomes can lead to prolonged hospital stays and increased healthcare costs, and have a significant impact on the patient’s recovery time and quality of life. Many additional complications of pronepositioning occur less frequently, but can have serious consequences for the patient, leading to pain, disability, paralysis, visual loss,or even death.Complications of prone positioning during anesthesia are related to the following factors, or to a combination of these factors: the physiological effects of being prone; the consequences of compression on the abdomen while prone; the nature of spinal surgery (such as prolonged duration, the need for a clear surgical field, manipulation and movement of the patient to allow instrumentation); pressure effects on different parts of the body from the equipment used to support the prone patient.The evidence presented in this summary illustrates the importance of the equipment used to support the patient. The review byEdgcombe et al concluded: “It is clear that the specific prone position and support system used influences not only the incidenceof complications but also the alterations in cardiovascular and respiratory physiology which occur when a patient is moved from asupine to prone position in the operating theater.”3 The way in which the patient is supported whilst prone influences the occurrenceand severity of complications. The design of support equipment to minimize these complications, together with appropriate educa-tion of staff in how to optimize the preventive qualities of support devices, is vitally important. There is also a need for research thatprovides an evidence base demonstrating the efficacy and safety of different types of operating room support equipment. 13 Copyright 2009, Allen Medical Systems. D-770490-A1 Oct. 22, 2009
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