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; their identifiers and currency have been verified but their recommendation text has not been read, so no positioning recommendation is quoted here asa-neuropathy-2018 asa-povl-2019.

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 advisories that would carry prevention recommendations have not been read: [TODO_VERIFY: the recommendation text of the 2018 ASA neuropathy advisory and the 2019 ASA visual loss advisory, from the PMC copy of the latter and the journal text of the former.] Brachial plexus injury is on the director’s content list and has no primary row: [NUMBER NEEDED: incidence, mechanism and timing of perioperative brachial plexus injury]. 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.

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.

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. [PRACTICE VARIES: 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.