Prone Spine Surgery Research Articles

P49. Monitoring for Ischemic Optic Neuropathy During Prone Spine Surgery? Pupillometry and Retinal Imaging

P49. Monitoring for Ischemic Optic Neuropathy During Prone Spine Surgery? Pupillometry and Retinal Imaging

Visual Loss after Spinal Surgery

Visual Loss after Spinal Surgery

Effect of Head Position on Postoperative Chemosis After Prone Spinal Surgery

Conjunctival swelling is a common finding in patients positioned prone. The purpose of this study was to evaluate the effect of head position on postoperative chemosis after prone spinal surgery. On the basis of the head position, 108 patients scheduled for prone lumbar surgery were randomly allocated to 1 of 2 groups: head neutral group (n=54) versus head down (HD) group (n=54). Head position was defined as neutral when the imaginary line from the occipital protuberance to the top of C7 spine process is parallel to the operating table. HD position was maintained by adjusting the height of the prone headrest 5 cm lower than neutral position. Chemosis was evaluated after surgery. The severity of chemosis, which was graded as none, mild, moderate, and severe, showed statistically significant difference between the head neutral group [24 (44%), 25 (46%), 3 (6%), 2 (4%), respectively] and HD group [10 (19%), 23 (43%), 17 (31%), 4 (7%), respectively, P<0.01]. Positive fluid balance and duration of surgery were risk factors for the development of postoperative chemosis. This result suggested that neutral head position, smaller fluid administration, and shorter duration of surgery were useful in decreasing the development of postoperative chemosis after prone spinal surgery.

Postoperative blindness – a rare but devastating complication

EDITOR: Postoperative visual loss (POVL) is one of the most unexpected complications after surgery with an estimated incidence varying from 0.01 to 1% depending on the type of surgery [1-4]. Although POVL is observed after almost any type of surgery 67% and 10% of all reported cases occur after prone spine procedures and cardiopulmonary bypass cases, respectively [2,4]. The most common cause associated with POVL (81%) is ischaemic optic neuropathy (ION) of the anterior (AION) or posterior (PION) part of the optic nerve [3,5]; only 6% of POVL cases were diagnosed as central retinal artery occlusion (CRAO). ION results from an ischaemic insult of the optic nerve characterized by oedema or pallor around the optic nerve and is often associated with a decrease in pupillary response [1,6]. Clinically ION is manifested by an unilateral or bilateral acute/subacute loss of vision or visual acuity hours to days after surgery. The descriptions of the visual deficits range from transient blurred vision to total blindness on one or both eyes [3]. Although various therapy strategies or interventions including high-dose steroids, mannitol, hyperbaric oxygen and furosemide were attempted no treatment has proven efficacy [5]. Prognosis for complete recovery from ION is poor and patients are frequently left with extensive visual impairment. Because of the lack of a beneficial treatment for ION and the poor prognosis prevention of POVL is important. Suggested preoperative risk factors include hypertension, diabetes, polycythaemia, smoking, renal failure, narrow-angle glaucoma, atherosclerotic vascular disease, collagen vascular disorders and variations in ocular anatomy or physiology. Furthermore, numerous intraoperative risk factors include prolonged prone positioning, hypotension, large blood loss, anaemia, extensive fluid administration and vasoactive drugs [1,2,5,6]. However, there is no experimental or clinical evidence that the proposed risk factors are causally linked to the occurrence of POVL. Thus, there exist currently no evidence based prevention strategies. This treatment dilemma, the incomplete knowledge about the etiology of ION and an increased incidence of POVL has led the American Society of Anesthesiologists (ASA) Committee on Professional Liability to develop the ‘ASA Postoperative Visual Loss Registry’ in July 1999. Aim of the ASA registry is to collect detailed information about POVL cases, determine possible risk factors for POVL and improve our understanding about the etiology of POVL. Currently 129 (June 2005) cases of POVL have been submitted to the ASA Registry [3]. In a preliminary evaluation of 113 POVL cases reported to the ASA Registry 71 occurred in middle-aged patients (median 50 yr) undergoing spine surgery and were caused by ION [3]. In more than 90% anaesthetic duration was <6 h and in 85% the estimated blood loss was >1 L. 9 cases of CRAO had significantly lower mean anaesthetic duration and estimated blood loss compared to ION cases. Importantly 14 patients with ION had their heads placed in Mayfield pins with their eyes free from external pressure indicating that isolated ION is not caused by pressure on the globe [3]. Recently, the American Society of Anesthesiologists Task Force on Perioperative Blindness issued a practice advisory for perioperative visual loss associated with spine surgery [7]. In summary, POVL is a rare and disastrous complication particularly associated with spine and cardiac surgery. Several suggested but not proven risk factors include intraoperative hypotension, anaemia and large blood losses or prolonged prone position indicating a multifactorial etiology of POVL. Until now, there are no evidence-based treatment or prevention strategies available. What can we do as an anesthesiologist about POVL? Apparently there is an urgent need for all anaesthesiologists to closely follow literature and gain knowledge about POVL; the brief booklet about POVL for anaesthesiologists available on the ASA closed claims webpage offers a good summary of this phenomenon [8]. We should be aware that patients undergoing prolonged prone spinal surgery and cardiopulmonary bypass surgery with hypotension and anaemia may have an increased risk of postoperative visual loss secondary to ischaemic optic neuropathy. Patients with POVL should be evaluated by an ophthalmologist as quickly as possible; a gross exam (e.g., reading letter or counting fingers) does certainly not rule out scotoma or delicate visual field deficits as it occurs in ION. Finally, every anaesthesiologist is highly encouraged to report any case of POVL following non-ophthalmic surgery to the ASA POVL Registry (www.asaclosedclaims.org). Further research is needed to improve our understanding about the etiology of POVL, to determine risk factors and to clarify the mechanisms of ION. Recently developed animal models for ION may hopefully improve our knowledge about the mechanisms of ION and offer the possibility to develop appropriate treatment strategies [9].

The American Society of Anesthesiologists Postoperative Visual Loss Registry

Postoperative visual loss after prone spine surgery is increasingly reported in association with ischemic optic neuropathy, but its etiology is unknown. To describe the clinical characteristics of these patients, the authors analyzed a retrospectively collected series of 93 spine surgery cases voluntarily submitted to the American Society of Anesthesiologists Postoperative Visual Loss Registry on standardized data forms. Ischemic optic neuropathy was associated with 83 of 93 spine surgery cases. The mean age of the patients was 50 +/- 14 yr, and most patients were relatively healthy. Mayfield pins supported the head in 16 of 83 cases. The mean anesthetic duration was 9.8 +/- 3.1 h, and the median estimated blood loss was 2.0 l (range, 0.1-25 l). Bilateral disease was present in 55 patients, with complete visual loss in the affected eye(s) in 47. Ischemic optic neuropathy cases had significantly higher anesthetic duration, blood loss, percentage of patients in Mayfield pins, and percentage of patients with bilateral disease compared with the remaining 10 cases of visual loss diagnosed with central retinal artery occlusion (P < 0.05), suggesting they are of different etiology. Ischemic optic neuropathy was the most common cause of visual loss after spine surgery in the Registry, and most patients were relatively healthy. Blood loss of 1,000 ml or greater or anesthetic duration of 6 h or longer was present in 96% of these cases. For patients undergoing lengthy spine surgery in the prone position, the risk of visual loss should be considered in the preoperative discussion with patients.

Use of the Proneview ™ Helmet System with a Modified Table Platform for Open Access to the Eyes During Prone Spine Surgery

Permanent, perioperative visual loss (POVL) is a rare but devastating complication of surgery. The majority of reported POVL cases are associated with spine surgery conducted in the prone position (67%) (1). POVL appeared to be related to a change in a patient’s retinal and/or optic nerve perfusion (1–3). Our goal was to provide a clinically practical method for measuring intraocular pressure, ocular perfusion pressure, and ocular perfusion (using digital retinal vessel/optic disk imaging), so that clinicians may be guided in preventing POVL. Limited access to a prone surgical patient’s eyes makes it challenging to obtain safe, physiologic ocular measurements.

Postoperative visual loss following prone spinal surgery

Postoperative visual loss is a rare but disastrous complication that has an estimated incidence of 0.01-1% after non-ocular surgery. We report a patient who underwent a prolonged spinal operation in the prone position and complained of blindness in one eye postoperatively. We consider the potential aetiological factors contributing to this unilateral postoperative visual loss and suggest strategies to reduce the incidence of this complication in spinal surgery.

Causes of Elevated Intraocular Pressure during Prone Spine Surgery

We read with attention the letter by Lee et al. regarding our study, “The Effect of Prone Positioning on Intraocular Pressure in Anesthetized Patients.” There are several points in their letter that we would like to address. First, we would like to point out that we titled our study “The Effect …,” rather than “The Causes of Elevated IOP…” since the sole purpose of our study was to observe the effects of prone positioning on intraocular pressure (IOP) in anesthetized patients.Second, while we agree that our IOPs in the prone position might be considered strikingly high by some, we found that the fact that the results were reproducible in 20 patients seems to indicate that they may indeed be real. For the authors of the letter to suggest that the results are too high because none of our patients had visual deficits despite a lowered perfusion pressure is ludicrous, as it is plainly known that perioperative visual loss is extremely rare and of as yet unknown cause(s).Third, the authors of the letter also attempt to justify their claim that our results are flawed by comparing the data from a previous study of awake volunteers 1with those we obtained in anesthetized patients. Extrapolating data from awake volunteers for comparison to anesthetized patients is denying any effects of anesthetics on physiology.Fourth, the authors question our methods in terms of how the IOP was measured. Using a pinned head holder prevents all of the obstacles they delineate in their letter (i.e. , eyelid retraction, and approach to the eye with tonometer).Fifth, it is difficult for us to take at “face value” the authors’ reference to their unpublished data.We appreciate the commentaries and criticisms of our study. This study is just the a piece of the puzzle that is perioperative visual loss. We look forward to seeing further data in this area of research.