Positioning injuries declare themselves after the PACU

Why it matters

The positioning injury is the complication the PACU is asked to rule out and usually cannot. In the Mayo series of 1,129,692 sedated or anesthetized patients, persistent ulnar neuropathy occurred in 414, about 1 in 2,729, and in most of them the initial symptoms were noticed more than 24 h after the procedure warner-1994. Postoperative visual loss after spinal fusion is rarer and worse, and its risk factors are set before the patient reaches the PACU: male sex, obesity, the Wilson frame, the length of the anesthetic and the blood lost povl-study-group-2012.

The consequence of getting this wrong is a normal PACU examination taken as proof that no injury occurred, and a complaint on the ward the next day that nobody documented a baseline for.

Mechanism

The textbook mechanism of ulnar neuropathy is compression or stretch of the nerve at the elbow during surgery. The largest series does not support that story cleanly: neither anesthetic technique nor patient position was associated with the neuropathy, while male sex, a long hospital stay and both very thin and obese habitus were, and symptoms usually appeared after the first day warner-1994. The mechanism is therefore marked contested on this page. What is not contested is that a nerve injury takes time to declare itself, so the absence of a deficit in the PACU is a baseline, not a clearance.

Ischemic optic neuropathy after prone spine surgery has a more coherent mechanism in the risk-factor pattern: venous congestion and raised orbital and optic-nerve pressure from prone positioning with the head dependent, prolonged operating time, large blood loss with crystalloid replacement, and a body habitus that raises venous pressure further. The Wilson frame, which lowers the head relative to the heart, sits at the top of the list povl-study-group-2012.

Evidence

Warner 1994 reviewed Mayo Clinic patients from 1957 to 1991: persistent ulnar neuropathy, lasting more than three months, occurred in 414 of 1,129,692, about 1 per 2,729; 9% were bilateral; initial symptoms in most were noted more than 24 h after the procedure; male gender and hospitalization longer than 14 days were associated (P less than 0.01), as were very thin and obese body habitus; neither anesthetic technique nor patient position was associated; and 53% of the 382 patients alive at one year had recovered fully warner-1994.

The Postoperative Visual Loss Study Group compared 80 cases of ischemic optic neuropathy after spinal fusion with 315 controls: independent risk factors were male sex, OR 2.53 (1.35 to 4.91); obesity, OR 2.83 (1.52 to 5.39); the Wilson frame, OR 4.30 (2.13 to 8.75); anesthesia duration, OR 1.39 per hour (1.22 to 1.58); estimated blood loss, OR 1.34 per liter (1.13 to 1.61); and colloid as a percentage of non-blood replacement, OR 0.67 per 5% (0.52 to 0.82), with a model area under the curve of 0.85 povl-study-group-2012.

The current ASA practice advisories on the prevention of perioperative peripheral neuropathies (2018, superseding 2011 and 2000) and on perioperative visual loss associated with spine surgery (2019, superseding 2012 and 2006) are the society documents for this day asa-neuropathy-2018 asa-povl-2019. The 2018 neuropathy advisory was read in full on 2026-09-06 and four of its positioning recommendations bear directly on what the PACU inherits, verbatim: when possible, limit arm abduction in a supine patient to 90 degrees, while the prone position may allow patients to comfortably tolerate abduction greater than 90 degrees; for a supine patient with the arm on an armboard, position the upper extremity to decrease pressure on the postcondylar groove of the humerus, the ulnar groove, using either supination or the neutral forearm position; for a supine patient with arms tucked at the side, place the forearm in a neutral position; and when possible, avoid flexion of the elbow to decrease the risk of ulnar neuropathy asa-neuropathy-2018. The 2019 visual loss advisory has still not been read.

What this does not show

Both primary sources are observational: a retrospective institutional series and a registry case-control study warner-1994 povl-study-group-2012. They establish incidence, timing and association. They do not show that any positioning practice prevents either injury, and the series that looked for an association with position did not find one warner-1994.

The 2019 visual loss advisory has now been read, and it is open access. Its postoperative recommendation is explicit about where this happens: assess the vision of a high-risk patient when the patient becomes alert, for example in the recovery room, and if there is concern about visual loss obtain an urgent ophthalmologic consultation to determine the cause, with imaging used case by case to exclude intracranial causes and to visualize an abnormal optic nerve, and with additional management directed at hemoglobin, hemodynamic status and arterial oxygenation asa-povl-2019. The advisory grades its own basis for that in the same document: the literature is insufficient to evaluate the effect of assessing a high-risk patient’s vision when the patient becomes alert asa-povl-2019. Brachial plexus injury still has no general rate. The nearest source is a series of 575 consecutive median sternotomy patients examined before and after operation with nerve conduction studies at 7 days, 4 weeks and 6 months, in which 3 patients (0.5%) had a brachial plexus injury, every one of them after harvest of the left internal mammary artery, presenting after extubation within the first three postoperative days, with two of the three resolved by six months unlu-2007. That is cardiac surgery and sternal retraction. A general figure now exists: across 380,680 anesthetics over ten years at one institution, 112 patients met the definition of a perioperative nerve injury, a frequency of 0.03% welch-2009. Read that as a floor rather than a rate. Injury was defined as a new sensory or motor deficit, complications arising from the surgery itself were excluded, and cases were found retrospectively through quality assurance, closed claims and billing records rather than by screening anyone, so it counts injuries that were noticed and recorded welch-2009. The associations it reports are hypertension, tobacco use and diabetes, general and epidural anesthesia, and neurosurgical, cardiac, general and orthopedic surgery welch-2009. The prone-position risk factors for visual loss are specific to spinal fusion in the registry; other prone surgery is not covered by the case-control data povl-study-group-2012.

One general recommendation has been removed rather than relabeled: that a visual complaint after prone spine surgery should reach ophthalmology the same hour rather than be watched overnight. The advisory’s own instruction, to assess vision when the patient becomes alert and to obtain an urgent consultation if there is concern, is cited above; the same-hour corollary is teaching practice with no source here.

At the bedside

Examine and document the arms and the vision of every patient who was prone, whose arms were abducted or tucked for a long case, or who is very thin or obese, before they leave the PACU, and write it as a baseline rather than a clearance, because most ulnar symptoms appear after the first day warner-1994.

One piece of commonly taught positioning practice is worth correcting against the advisory’s own wording. Residents are taught to pad the elbow at the cubital tunnel. The advisory asks instead that the upper extremity be positioned to decrease pressure on the postcondylar groove of the humerus, and it mentions padding only inside a general category of positioning strategies, protective padding and equipment placement asa-neuropathy-2018. Padding is a means; decreasing pressure on the groove is the instruction, and the two come apart when a pad is placed but the arm is still resting on the groove. Tell the patient and the ward what to watch for and when: numbness or weakness in the hand, or any change in vision, in the first days after surgery. A complaint that arrives on day two with a documented normal baseline is a different problem from one with no baseline at all.

For the patient after a long prone spinal fusion with large blood loss, particularly a man with obesity on a Wilson frame, ask about vision explicitly on waking and again before discharge, because the risk factors were all present before the PACU could do anything about them povl-study-group-2012. Local practice differs. whether a formal visual check is part of PACU discharge after spine surgery, and how peripheral nerve findings are documented, differ between institutions.

Check yourself

Three items. Every option carries an explanation. Progress is not saved.