You’ve heard us several times in the past recommend the surgical “timeout” or any other preoperative “huddle” be used for things other than merely identifying correct patient and surgical site (see our Patient Safety Tips of the Week for April 9, 2007 “Make Your Surgical Timeouts More Useful” and December 9, 2008 “Huddles in Healthcare” and March 10, 2009 “Prolonged Surgical Duration and Time Awareness”). One recommendation is to discuss whether the patient will be at risk for nerve injury and at what point in a procedure would repositioning of the patient be considered. This month’s issue of the journal Anesthesiology contains an article on perioperative peripheral nerve injuries (Welch 2009). They reviewed all perioperative peripheral nerve injuries at one institution over a 10-year period and found a nerve injury rate of 0.03% per anesthetic given, a rate similar to that found in previous literature. That article and the accompanying editorial (Prielipp 2009) both acknowledge that this is probably an underestimate of the true incidence of perioperative nerve injuries because of the methods used to ascertain cases. 65% of those injuries involved the upper extremities. They found three underlying medical conditions to be statistically associated with nerve injuries: diabetes, hypertension, and tobacco use. They found nerve injuries associated with general and epidural anesthesia but none with monitored anesthesia care.
Perioperative nerve injuries are the second or third most common reason for malpractice claims against anesthesiologists and the number of closed claims for perioperative nerve injuries has remained quite consistent over time (Cheney 1999).
Ulnar nerve injuries are the most commonly reported upper extremity nerve injuries (Barner 2003). Almost all series have demonstrated a strong male preponderance for these, though the reason is very unclear. Patients either excessively thin or obese appear to be at greater risk. Often the symptoms and signs are delayed in onset and there appears to be a correlation with lengths of hospitalization greater than 14 days. This, plus the finding that some patients admitted to medical services develop ulnar neuropathy, have suggested that prolonged bedrest in the supine position may be a contributory factor (Warner 2000). Though the mechanism most often speculated about is pressure on the nerve at the elbow, cases have occurred even in circumstances where adequate padding to the elbow has been utilized (Cheney 1999). The nerve appears to be particularly vulnerable at the elbow, where it passes throught the ulnar groove and an aponeurotic band of tissue. Various movements and positions of the elbow may increase compression of the nerve in this area. Flexion of the elbow and pronation of the forearm and internal rotation of the shoulder, in particular, are movements that increase pressure in the ulnar groove. This may be aggravated by subluxation. Anatomical or arthritic changes in the region may also accentuate the pressure. These dynamic factors may help explain why patients lying supine with elbows flexed and forearms pronated may be at risk for developing ulnar neuropathy, regardless of whether they are medical or surgical patients.
Though we know of no solid evidence base for preventive measures, most recommendations include careful padding and intraoperative positioning (eg. keeping forearms supinated), avoiding hard surfaces or edges near the elbow, and not leaning against the patient (Barner 2003).
The same authors (Barner 2002) reviewed perioperative nerve injuries in the lower extremities as well. They discuss the complexities and challenges, both clinical and electrophysiological, involved in differentiating dysfunction of individual peripheral nerves from dysfunction more proximally or at the lumbosacral plexus level. Though they stress the vulnerability of the peroneal nerve to external pressure at the level of the fibular head in procedures done in the lateral decubitus position or in the lithotomy position (particularly when external devices such as stirrups or leg straps are used) but again stress that localization of the site of the compression may be misleading.
And it’s not just the OR that carries the risk for perioperative nerve injuries. A recent report noted peroneal nerve injuries associated with colonoscopy in children (Bong 2009). They found 3 cases of peroneal nerve injury in a cohort of 746 children undergoing colonoscopy, suggesting that such injuries are not uncommon. In addition to risk factors such as weight loss, malnutrition, chronic systemic inflammation, and steroid use, positional factors and relatively long duration of anesthesia were considered to be contributing factors. Duration of anesthesia was 120 minutes in two cases and 70 minutes in the third. All patients were temporarily in the supine position with hips flexed and externally rotated and knees flexed and supported laterally (“frog legs” position) and then in a lateral decubitus position. Pressure on the peroneal nerve may have occurred directly while in the lateral decubitus position or from the lateral knee support in the “frog legs” position.
The risk factors and contributing factors to these perioperative nerve injuries have not been well defined in the literature. Compression of or stretching of the nerve, ischemia, and direct trauma are often mentioned as possible mechanisms of injury but in most cases a mechanism is not clearly demonstrated.
We do know that the existence of some underlying polyneuropathies may render nerves more vulnerable to the effects of pressure or other trauma. It’s well known that entrapment neuropathies are more common in patients with underlying polyneuropathies. So a history of known polyneuropathy, such as a diabetic polyneuropathy, should clearly be considered as a risk factor for perioperative nerve injury. Patients with hypertrophic neuropathies, whether hereditary or acquired, are especially susceptible to the effects of compression.
Weight loss is another predisposing factor to some compressive neuropathies. Peroneal nerve injuries are particularly likely to occur in individuals who have lost the typical subcutaneous fat pad that protects the nerve near the head of the fibula. So it might be expected that cancer patients might be particularly susceptible because of weight loss and the frequent occurrence of polyneuropathy (either as a remote effect of cancer or a result of chemotherapy).
As above, we know of no solid evidence base for preventive measures. But the American Society of Anesthesiologists (ASA) did issue a practice advisory for prevention of perioperative peripheral neuropathies in 2000. They made recommendations on specific positioning to use or to avoid in attempt to prevent various nerve or plexus injuries, plus recommendations about use of protective padding in certain cases and equipment such as automated blood pressure cuffs. The specifics can be found in that document. However, what is most striking is that virtually all of the recommendations are made based upon opinions of consultants, task force members, and a random sampling of ASA members. This practice advisory points out the dearth of scientific literature on interventions to minimize the risk for perioperative nerve injuries.
Strikingly, even the data from the medicolegal databases lacks information about total duration of anesthesia, duration a patient was in a certain position, etc. You don’t have to be a neurologist to know that positional changes may affect nerve function. All of you have experienced your arm or leg “falling asleep” when it is in a certain position too long. What do you do in response? You change position and maybe shake the limb around a little bit and the sensation returns in a few seconds. You can often then return it to the original position. It is amazing that the literature on perioperative nerve injuries does not even comment on the issue of periodic or intermittent repositioning of limbs.
There have been at least a few attempts at better understanding the relationship between positional changes and nerve damage. Kamel et al (Kamel 2006) retrospectively looked at patient undergoing spinal surgery who had intraoperative monitoring of somatosensory evoked potentials (SSEP’s). The amplitudes of SSEP’s are affected by multiple factors, such as mean arterial blood pressure, depth of anesthesia, manipulation of the spine, etc. but they may also be sensitive to ischemia, compression, stretching or other dysfunction of peripheral nerves or plexuses. In their study, they found that about 6% of changes in upper extremity SSEP’s during spine surgery responded to changes in position of the affected upper extremity. They were thus able to determine which body positions were more likely to be associated with such changes during spine surgery. The study did not include assessment of individual nerve function so information cannot be generalized to make recommendations for protection of specific peripheral nerves. But such methodology is promising and needs to be studied prospectively in a variety of surgical settings. Since patients under anesthesia cannot sense symptoms related to peripheral nerve dysfunction, SSEP’s do have promise at uncovering reversible changes during a variety of surgical procedures, not just spinal surgery.
Even though the rate of 0.03% per anesthetic given may sound quite low, the fact is that translated to about one case a month at the medical center where Welch et al. did their retrospective study. We agree with the term used in the Prielipp editorial: “scream”. The problem is really “screaming out” for legitimate scientific investigation into etiological factors related to these nerve injuries and, more importantly, effectiveness of various preventive intervention strategies.
We wish we had some firmer recommendations for you in this significant patient safety issue. However, all we can say at this time is that you should attempt to identify patients at highest risk, try to minimize the total duration of anesthesia or the duration they are in certain positions, and use the ASA recommendations for position, padding, equipment, etc. A lot more needs to be done before we have any definitive recommendations.
Welch MB, Brummett 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
Prielipp RC,Warner MA. Perioperative Nerve Injury: A Silent Scream? Anesthesiology 2009; 111(3): 464-466
Cheney FW, Domino KB, Caplan RA, Posner KL. Nerve Injury Associated with Anesthesia: A Closed Claims Analysis. Anesthesiology 1999; 90(4): 1062-1069 http://journals.lww.com/anesthesiology/Fulltext/1999/04000/Nerve_Injury_Associated_with_Anesthesia__A_Closed.20.aspx
Barner KC, Landau ME, Campbell WW. A Review of Perioperative Nerve Injury to the Upper Extremities. Journal of Clinical Neuromuscular Disease 2003; 4(3): 117-123
Barner KC, Landau ME, Campbell WW. A Review of Perioperative Nerve Injury to the Lower Extremities: Part I. Journal of Clinical Neuromuscular Disease 2002; 4(2):95-99
Warner MA, Warner DO, Harper CM, Schroeder DR, Maxson PM.. Ulnar Neuropathy in Medical Patients. Anesthesiology 2000; 92(2): 613-615
Bong CL, Seefelder C. Peripheral Neuropathy Following Colonoscopy Is Not Uncommon. Anesthesia & Analgesia 2009; 108(1): 384-385
American Society of Anesthesiologists Task Force on Prevention of Perioperative Peripheral Neuropathies. Practice Advisory for the Prevention of Perioperative Peripheral Neuropathies: A Report by the American Society of Anesthesiologists Task Force on Prevention of Perioperative Peripheral Neuropathies. Anesthesiology 2000; 92(4): 1168-1182
Kamel IR, Drum ET, Koch SA, Whitten JA et al. The Use of Somatosensory Evoked Potentials to Determine the Relationship Between Patient Positioning and Impending Upper Extremity Nerve Injury During Spine Surgery: A Retrospective Analysis.
Anesthesia & Analgesia 2006; 102(5): 1538-1542