Injuries Associated With Nerve and Plexus Blocks

Susan B. McDonald

Brian M. Ilfeld

CASE SUMMARY

A 55-year-old woman with a past medical history significant for type 2 diabetes mellitus, mild obesity, and hypertension presents for right shoulder arthroscopy. Moderate-to-severe postoperative pain is anticipated. Before induction of general anesthesia, an interscalene block is placed using 30 mL of 0.5% ropivacaine with 2.5 µg per mL of epinephrine under sterile technique facilitated by use of a nerve stimulator and minimal intravenous sedation. After local anesthetic infiltration of the skin, a 22-gauge insulated needle is advanced into the interscalene groove at the C6 level until a biceps twitch is elicited with a minimum current of 0.42 mA. During gentle administration of an initial 0.5 mL of the anesthetic solution, the patient reports a painful sensation “shooting” into her elbow. The needle is withdrawn 1 mm. Following negative aspiration and no further reports of paresthesia, the incremental injection of the local anesthetic continues. After completion of the block, general anesthesia is induced, and the surgery commences.

In the postanesthesia care unit (PACU), the patient reports complete motor and sensory block of her right upper extremity and no pain in her shoulder. However, she does complain of difficulty breathing. Room air oxygen saturation is 94%, and no wheezing is heard on auscultation. A chest x-ray reveals an elevated right hemidiaphragm but no other abnormalities. The patient is reassured and discharged home with a sling. On postoperative day 3, the patient complains of persistent numbness down her forearm into her fifth finger.

▪ SINGLE-INJECTION PERIPHERAL NERVE BLOCKS

What Is the Incidence of Complications?

As reflected in the American Society of Anesthesiologists (ASA) Closed Claims Database, serious complications of peripheral nerve blocks are rare. Claims related to peripheral nerve blocks accounted for only 13% of all regional anesthesia claims between 1980 and 1999, with only half being block-related and the majority (72%) only temporary or nondisabling (see Table 62.1).¹ Indeed, studies verify that most neurologic deficits resolve within weeks to a few months.²,³ This conclusion is supported by a French survey in which seven cases of death or permanent neurologic injury were reported out of approximately 44,000 peripheral nerve blocks.⁴ The median time to presentation has been reported as 3 days, with the majority presenting within 3 weeks.¹,²,⁵

In the United States, most peripheral nerve blocks are used for upper extremity surgery. This preferential use helps to explain why the nerves most commonly injured in the ASA Closed Claims Database were, in descending order: Brachial plexus, median, ulnar, and radial nerves, followed by femoral/sciatic nerves.¹ Nerve injury remained the most frequently cited claim in the database (31%) followed by pneumothorax (25%) and eye damage (18%). However, in the 1990s, claims associated with ophthalmic anesthesia surpassed other peripheral nerve blocks with regard to permanent injury or death.⁶

Nerve injury after surgery involving a peripheral nerve block can occur as a result of patient, surgical, or anesthetic factors, or a combination of insults (see Table 62.2).

How Does the Nerve Block Contribute?

▪ NEEDLE TRAUMA

There is broad consensus that injection of any solution into the nerve itself will result in nerve injury. Such intraneural injection can mechanically disrupt the nerve fiber bundles, cause intraneural ischemia resulting in further injury, or both. Intraneural injections can cause significant pain in the awake patient. Therefore, any pain during injection must be considered a potential warning sign.

TABLE 62.1 Peripheral Nerve Blocks Associated with Claims for Nerve Injury as Filed in the Closed Claims Database (1980 to 1999)^a

Block Type	Total (% of 291)		Temporary	Permanent	Death
Axillary	61	(21%)	46	11	4
Interscalene	23	(8%)	17	3	3
Supraclavicular	11	(4%)	10	1	0
Intercostal	28	(10%)	27	1	0
Pain blocks (stellate/trigger)	40	(14%)	38	1	1
Ophthalmic blocks (retrobulbar, peribulbar)	54	(19%)	16	34	4
Intravenous regional	32	(11%)	28	3	1
Other	7	(2%)	—	—	—
^a Of the 6,448 total claims, 291 involved peripheral nerve blocks.
Data from: Lee LA, Domino KB. Complications associated with peripheral nerve blocks: Lessons from the ASA closed claims project. Int Anesthesiol Clin. 2005;43:111-1118.

A paresthesia during block placement is not synonymous with intraneural injection. For decades, many regional anesthetists considered the paresthesia to be a valuable tool in the placement of peripheral nerve blocks.⁷ However, paresthesias have been condemned as an indicator of potential nerve damage.⁵,⁸ In Auroy’s survey of French regional anesthesia, all patients with permanent neurologic injuries reported either a paresthesia or pain on injection during block placement, and the reported paresthesia corresponded to the anatomic location of the injury.⁹ However, the link does not prove causation, and avoiding paresthesia may be impossible.⁸,¹⁰,¹¹

It has been argued that the use of a peripheral nerve stimulator to locate the nerve is “safer” than the paresthesia-seeking technique because the needle approaches the nerve without actually contacting it. This assumption, however, is questionable, especially because it applies to performing blocks under heavily sedated or anesthetized patients. Studies have demonstrated that the expected motor response does not occur in 25% to 70% of patients who experience paresthesias during block placement.¹²,¹³

Ultimately, a reported paresthesia or pain during injection should be considered a warning sign of intraneural injection. Patients should be instructed to report any such painful sensations immediately. Patients do not always protest when feeling discomfort, because some mistakenly believe that either it is a “normal” experience or a complaint might anger their physician.¹⁴ The possibility of intraneural injection also should be suspected if there is any resistance to injection.

TABLE 62.2 Risk Factors for Nerve Injury during Peripheral Anesthetic Blocks

Anesthetic Block Factors	Surgical Factors	Patient Factors
Needle trauma	Mechanical stretch	Diabetes
Catheter trauma	Direct trauma	Multiple sclerosis
Hematoma	Malpositioning	Chemotherapy
Epinephrine	Hematoma	Polyneuropathies
Local anesthetic neurotoxicity	Infection	Obesity
	Tourniquet	Male gender

Recognition of a paresthesia may be difficult in patients with partially anesthetized nerves, as may theoretically occur when a multiple injection technique is used. Two studies demonstrated a higher incidence of deficits in patients who received a repeat injection for an incomplete block.⁸,¹⁵ In contrast, a prospective observational study of approximately 4,000 axillary blocks carried out using a multiple injection technique with a peripheral nerve stimulator and insulated needle did not demonstrate a significantly higher occurrence of neural deficits.¹¹ Nevertheless, caution is warranted whenever reinjection after partial block is employed, because paresthesias may not always provide a warning.

Recently, investigators have suggested that ultrasonographic guidance of peripheral nerve blocks is even safer than the peripheral nerve stimulator because the nerve is directly visualized.¹⁶,¹⁷ However, evidence of any benefit in decreasing the risk of neuropathy will require further research.

Needle configuration may also be a factor. Some evidence suggests that use of short-bevel needles may decrease the risk of intraneural injection. The shorter bevel configuration may cause the nerve to roll away from the needle point, thereby lessening the risk of “impaling” the nerve than might occur with a long-beveled needle.¹⁸ However, one in vitro experiment suggests that, although the incidence of piercing the nerve might be lower with
shorter bevels, the subsequent injury is more severe and of longer duration than with longer bevels.¹⁹

▪ VASCULAR COMPROMISE

Nerve ischemia can result from a variety of vascular injuries. Pressure-induced ischemia of the nerve microcirculation may exacerbate an injury caused by intraneural injection. External compression from a hematoma may also cause deficits that typically are early in onset and temporary in duration.²⁰ Surgical intervention is often required, especially for hematomas resulting from ophthalmic retrobulbar blocks.²¹ Vasospasm, pseudoaneurysm formation, and vascular insufficiency may also result from direct damage to adjacent blood vessels.¹⁵,²²,²³

Another potential aggravation of nerve damage results from the addition of epinephrine to the injectate. In a rat model, the addition of 5 µg per mL of epinephrine dramatically reduced the epineural blood flow to just 22% of its baseline flow.²⁴ The epineural circulation provides half of the nerve’s blood supply. Therefore, such a reduction in blood flow may compromise nerves that already have tenuous microcirculation, such as in patients with diabetes or peripheral vascular disease.²¹,²⁴ Should an intraneural injection of anesthetic solution with epinephrine occur, the nerve’s intrinsic circulation could also be compromised, further increasing the risk of injury. The addition of epinephrine also may result in prolonged nerve exposure to local anesthetic, as could the use of inappropriately high concentrations of the drug, with potential neurotoxicity from both.²¹ In such situations, a combination of mechanical and chemical insult may be required to cause nerve damage.⁸,²¹

Another serious vascular-related morbidity is inadvertent, direct injection of large amounts of local anesthetic into the blood stream. Details regarding this complication are presented later in the text. Systemic local anesthetic toxicity is cited in 3% of closed claims for peripheral nerve blocks.¹

What Patient Factors May Contribute?

Preexisting disease states also may contribute to complications related to peripheral nerve blocks. Diabetic patients, for example, have a predisposition to neurovascular injury or underlying peripheral neuropathy before any insult caused by the block itself. Chemotherapy, multiple sclerosis, and other neuropathies may predispose patients to a lower threshold to injury and prolonged recovery.²⁵ This concept has been termed the double crush phenomenon: A mild preexisting lesion may be compromised beyond what is normal or expected when faced with a second insult, such as needle, surgical trauma, or local anesthetic toxicity.²⁵

Ulnar mononeuropathy presents a unique situation, because it is the most common nerve injury reported regardless of the anesthetic technique.⁵ Recent studies suggest that preexisting mononeuropathy may not predispose a patient to neurologic injury after peripheral nerve block to the same degree as a polyneuropathy, and that regional blocks need not be avoided in these patients.²⁶

Some patients may have a predisposition (e.g., obese or male) to ulnar nerve damage from positioning or other intraoperative surgical factors that have no relation with a peripheral nerve block.⁵ As an example, a patient with a long-acting brachial plexus block who is discharged home with an improperly placed sling would be unable to detect further pressure injury caused by the sling. This example is not used to suggest that long-acting anesthetics should be avoided in the ambulatory environment, because there is strong evidence that they may be used safely in outpatients.²⁷ Proper care and instructions, however, must be emphasized before patient discharge.

How Can Surgery Complicate the Picture?

Contrary to the belief of many patients and some surgical colleagues, nerve injury is not always a result of an improperly performed block. Indeed, 37% of the closed claims on peripheral nerve blocks were not block-related.¹ As with the ulnar nerve issue discussed previously, other trauma may occur perioperatively. Surgical trauma, including direct injury or mechanical stretching of the nerve, pressure from a surgically related hematoma, or ischemia from surgically induced vascular compromise can produce such injury. One retrospective review of 1,614 patients who received axillary blocks for upper extremity surgery found that 89% of nerve injuries resulted from the surgical procedure.²⁸ Patients may have an insensate limb that is improperly positioned or a cast that may place pressure on nerves. Tourniquet-induced ischemia and/or nerve compression also has been shown to produce neurologic damage.¹¹

What Should Be Done for the Patient with a Reported Nerve Injury?

If a patient reports residual numbness or weakness postoperatively, the first thing to do is to offer reassurance. Most of these deficits resolve within weeks to months. A physical examination and history should be thoroughly documented. If the symptoms are minor, observation may be sufficient. However, if the deficit is disabling or persists for more than a few weeks, a neurology consultation should be obtained. Keep in mind that the injury may not be block-related; therefore do not accept blame until the matter has been investigated.

▪ RESPIRATORY CONSEQUENCES OF UPPER EXTREMITY BLOCKS

Upper extremity blocks carry a risk of respiratory complications. Second only to nerve damage in the closed claims database (at 25% of claims), pneumothorax can occur with varying incidence, depending on the location of the block.¹ Infraclavicular, intersternocleidomastoid, and axillary blocks have the theoretic advantage of avoiding this risk, and supraclavicular blocks have the highest reported incidence (as high as 6%, second only to intercostal blocks).²¹,²⁹,³⁰,³¹ Most patients who develop pneumothorax can be observed without treatment but may require chest tube placement if >25% lung involvement is present. The patient may remain asymptomatic for up to 12 hours, so ambulatory patients should receive counseling before discharge.²²

Ipsilateral phrenic nerve paresis leading to diaphragm dysfunction occurs in 100% of patients receiving interscalene blocks³⁰,³²,³³ whether the block is performed from a classic lateral or a posterior approach.³⁴ Even supraclavicular blocks can cause at least a 50% incidence of phrenic nerve block.³² Other manipulations, such as proximal digital pressure or reducing the anesthetic volume, do not prevent phrenic nerve involvement.³⁵,³⁶,³⁷

Phrenic nerve paresis can reduce forced vital capacity by 25% to 40%.³³,³⁵,³⁶,³⁷ In most patients, this functional alteration is either asymptomatic or mildly bothersome, with the sensation of dyspnea or inability to take a deep breath. Oxygen saturation usually does not decrease below normal levels while the patient breathes room air. Again, reassurance is usually all that is required. Some patients, such as those with significant chronic obstructive pulmonary disease (COPD) or contralateral diaphragm dysfunction, may have significant respiratory compromise until the anesthesia subsides.³⁵,³⁸ No evidence has been found that infraclavicular blocks influence pulmonary function to a clinically relevant degree.²⁹,³⁹

▪ MISCELLANEOUS COMPLICATIONS

Some adverse effects are bothersome, but not clinically significant. For example, in one study evaluating patient perceptions of complications from axillary block, patients reported soreness (40%), bruising (19%), temporarily persistent numbness (11%), or nausea (11%). Yet, 93% said they would elect to have the block repeated for future surgeries.⁴⁰ For interscalene and supraclavicular blocks, up to 90% of patients develop Horner’s syndrome for the duration of the anesthetic, and some may have temporary paralysis of the recurrent laryngeal nerve, causing temporary hoarseness.³,²¹,²² Temporary auditory disturbances have been described with these blocks.⁴¹ Inadvertent block of the femoral nerve has been reported with ilioinguinal nerve blocks, resulting in loss of quadriceps muscle strength and an increased risk of falling. For these complications, reassurance and instruction should be given to the patient.

Other adverse events may be serious if not immediately recognized. Intrathecal, subdural, or epidural spread of anesthetics has been described with both upper and lower extremity blocks.⁴²,⁴³,⁴⁴,⁴⁵ Such spread can result in serious cardiovascular and respiratory compromise that, if not properly treated, can lead to permanent damage or patient death. Although rare, such instances require immediate access to resuscitative equipment and further support the recommendation that peripheral nerve blocks should not be performed under general anesthesia.

▪ CONTINUOUS PERIPHERAL NERVE BLOCKS

Postoperative analgesia may be improved with a continuous peripheral nerve block—also called a perineural local anesthetic infusion. This technique involves the percutaneous insertion of a catheter directly adjacent to the peripheral nerve(s) supplying the surgical site. Potent, site-specific analgesia may subsequently be provided by infusing local anesthetic through the catheter. The following section will review possible continuous block-related complications, steps to minimize complications, and appropriate management techniques when complications occur.

What Is the Incidence of Complications?

Evaluating the incidence of complications associated with continuous peripheral nerve blocks is somewhat difficult because of the relatively recent, widespread use of this technique and lack of large clinical studies. The two largest prospective studies, with more than 1,400 combined patients with perineural catheters in various locations, suggest that the complication incidence is very low—at least as low as, if not lower than, single-injection techniques.⁴⁶,⁴⁷ Many of the complications related to continuous peripheral nerve blocks result from the needle used to place the catheter, and therefore are similar—or identical—to complications of single-injection blocks. Only issues specifically related to continuous blocks will be discussed further.

What Complications Are Inherent to Nerve Blocks?

▪ INACCURATE CATHETER PLACEMENT

Unfortunately, the percentage of inaccurate catheter placements is not trivial. Catheter insertion may be
achieved using a variety of equipment and techniques. Most commonly, an insulated needle is used first to inject the local anesthetic for the initial surgical block and then to pass the perineural catheter.⁴⁸ A successful surgical block may be provided, but an undetected, inaccurate catheter placement is possible using this technique.⁴⁹,⁵⁰,⁵¹ Hours after placement, when the surgical block has resolved, the inadequate perineural infusion will be discovered. Many factors influence the incidence of this complication, including the technique and equipment used, practitioner expertise, and patient factors such as body habitus.⁵²,⁵³ This “secondary block failure” occurs in 0% to 40% of cases.⁴⁶,⁵⁰,⁵⁴ To potentially decrease the chances of secondary block failure, practitioners first insert the catheter and then inject the initial local anesthetic through it.⁴⁷,⁵⁵,⁵⁶,⁵⁷,⁵⁸ In this manner, the catheter may be replaced if a surgical block does not develop.

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