Think Outside the Blocks: Creative Uses For Lidocaine

Lidocaine is used routinely in the ED to numb up lacerations before repair and abscesses before I&D, or to perform digital blocks, hematoma blocks, nerve blocks, or intra-articular analgesia. Every medical student is taught how to infiltrate the skin with a thin needle, producing a blanching skin wheal. Lidocaine is also one of the ACLS 2015 antiarrhythmics for VF or pulseless VT. However, there are numerous other ways in which lidocaine can be used. The data supporting them is variable, and many of the uses are off-label. However, given the subjectivity inherent in the experience of pain, and the myriad mechanisms by which pain and noxious stimuli are sensed and transmitted, it is not surprising that there is some variability in the clinical response to lidocaine from patient to patient. Here we will outline a few of the interesting ways that lidocaine can be used. Personally, we have used it successfully basis for NG tube placement, urethral catheterization, in lower cervical muscular injections for headaches, atomized before nasal scope, and nebulized for cough or for ENT procedures.

How it Works
Lidocaine is an amino amide that blocks voltage-dependent sodium channels. It can produce local anesthetic effects but can also provide analgesia for visceral pain, headaches, neuropathic pain, post-op pain, central pain, and post-herpetic neuralgia [^1] (see our recent Rx Pad on the Lidoderm patch for more) [2].

Renal Colic
Lidocaine was first trialed as a paravertebral block [3] and then as a trigger point injection [4] for renal colic. Lidocaine has been used for decades by urologists to assist with pain control during instrumentation, and may help provide urethral dilation as well. Several studies have since then evaluated IV lidocaine for renal colic. In the first, performed in Iran in 2012, patients were given either lidocaine (1.5mg/kg IV) or morphine (0.1mg/kg IV). The group that received lidocaine had statistically significantly lower pain scores than the morphine group after treatment. At 10 minutes after administration, the lidocaine group had scores that had decreased from 9.65 to 1.83, whereas the morphine group’s score had only decreased from 9.74 to 2.89 (p=0.0001) [5]. A more recent randomized double blind controlled trial in 2016 looked at 110 adult patients, comparing morphine plus placebo vs. morphine plus lidocaine and found a trend towards earlier resolution of pain in the lidocaine group (87min vs 100min p=0.71) [6]. More studies are needed to provide greater clarity. However, in patients for whom morphine may not work well, who have high tolerance, or in those for whom it carries a high risk of side effects, lidocaine is a tenable option [7]. NSAIDs are the other mainstay of renal colic pain management, but they also carry risks for the elderly and patients with chronic kidney disease.

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Bottom line: Consider trying lidocaine IV 1-1.5mg/kg IV slow infusion (over 5-20 min.) for renal colic in patients for whom opiates and NSAIDs are high risk. Side effects from lidocaine are rarely serious under the recommended dose levels [8]. 

Painful Mucosal Instrumentation
Sticking things in the nose is painful. However, we regularly have to place NG tubes, perform nasotracheal scopes, remove nasal foreign bodies, or rarely, nasotracheally intubate. Viscous or mucosal atomized lidocaine before a procedure may help reduce discomfort. One option is to use a mucosal atomization device (MAD) on a syringe. Prior to tube placement, a vasoconstrictor such as oxymetazoline can be used to reduce the risk of bleeding. 1.5cc of 4% lidocaine atomized into the nare, and 3cc into the back of the throat, can help reduce discomfort. For NG tube placement, viscous lidocaine (5cc to the nare, and 5cc swallowed) is an option that provides both pain reduction and lubrication.  Nebulized lidocaine can also be used before awake intubation or nasal scopes, with up to 5mL of 4% lidocaine for adults. Viscous lidocaine (in a 5-10cc syringe or in a pre-made urojet) can also help reduce pain and lubricate placement of Foley catheters in men. For a review of use of intranasal topical anesthetics with practical tips, see references online [^17].

Bottom line: Try viscous or atomized lidocaine before your next NGT and viscous lidocaine for Foley placement. Nebulized lidocaine can also be used for nasal scopes or as part of the anesthetic management for awake intubations or nasotracheal intubation.

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Cough
Some patients present with a cough so intractable they can barely tell you their medical history. In these patients, a nebulized lidocaine treatment may help control the cough if other medications are not working. The data to date has been of poor quality and not completely conclusive. However, some studies have found a benefit with doses of 10-20mg (2mL of 1%, or 0.5mL of 4%) [^18].

Bottom line: The data is limited, but 10-20mg of nebulized lidocaine may help for cough resistant to other medications.

Headaches
Pain from headaches can be remarkably resistant to treatment. However, patients with chronic daily headaches or with status migranosus may benefit from lidocaine. One theory is that it may block the sodium channels until other pain treatments can kick in. The research in this area has been limited to date. A case report of lidocaine for severe trigeminal neuralgia at a rate of 1mg/min for four hours resulted in resolution of the pain after one hour, though it later relapsed [9]. IV lidocaine for chronic daily headaches has been used and reduced the pain over 8.5 days of use [^10]. This, despite nationwide increasing boarding times and lengths of stay, is not a tenable ED treatment. A 2014 study from Iran among 90 adults found that pain scores after treatment with atomized intranasal 0.1mL 10% (10mg) lidocaine to each nare had significantly improved pain scores compared to saline atomization [^11]. Another study of 162 patients randomized to intranasal lidocaine vs. saline found no difference in the pain reduction with lidocaine [^12]. There are case reports of the use of lidocaine intranasally for cluster headaches, but no studies large enough to draw conclusions [^13,14].

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Another way to use lidocaine with bupivacaine, or bupivacaine alone for headaches is as a lower cervical intramuscular injection. In this technique, 1.5mL of bupivicaine is injected into the muscles bilaterally at the base of the C spine at the level of C6-C7 and in one study of 417 patients provided complete relief in 65% of patients. Treatment of headaches in the ED with lower cervical intramuscular bupivacaine injections: a 1-year retrospective review of 417 patients.

It remains to be seen whether larger studies will show a significant advantage. However, the side effects are low, and it is possible that lidocaine in conjunction with other medications may prove even more effective. A very small study of 13 patients comparing 1mg/kg IV lidocaine to IV saline for migraine found no difference in pain intensity at 20 min [^15]. The 2015 Canadian Headache Society guidelines weakly recommended for intranasal lidocaine and against IV lidocaine based on a low level of evidence. The dose they suggest is intranasal 40-80mg, which would be 1-2mL of 4%, or 0.4-0.8mL of 10% IN [^16].

Bottom line: Intranasal lidocaine (10-80mg by mucosal drops or mucosal atomization device) may help in migraines and cluster headaches, but the data is poor. The jury is out on IV lidocaine.

I.O. Line Pain
IO lines are painful when placed, but extremely painful when first flushed to clear the space. IO lidocaine flushed right after placement can help reduce the pain of the IO line flow. The typical dose is 40mg (4mL of 1%) over 1-2 min which should be allowed to sit for about 1 minute before flushing with 10cc of saline. It can be followed by a second dose of 20mg (2mL of 1%) lidocaine, if needed.

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Bottom line: Flush the IO with 40mg of lidocaine before pushing the saline flush to reduce pain.

Dosing and Toxicity
While lidocaine is safe at the correct doses, remember that it is a class I antiarrhythmic agent, and if inadvertently injected IV at high doses, it can cause CNS symptoms, such as tremor, somnolence, dysarthria, ataxia, agitation, hallucinations, confusion, and seizures. Cardiac side effects include bradycardia and asystole, which are associated with more rapid infusions.

Cutaneous Infiltration Dosing
The dosing and labeling of lidocaine can be confusing. For cutaneous infiltration, the maximum dose is 4.5mg/kg within two hours (max 300mg), or 7mg/kg if a vasoconstrictor such as epinephrine is used concomitantly. But what does this mean for how much you draw up in a syringe, and how do you convert % lidocaine into mg/mL?

• 1% is 1g per 100mL, or 10mg/mL
• 2% is 2g per 100mL, or 20mg/mL
• 4% is 4g per 100mL, or 40mg/mL

Bottom line: For a 70kg individual, the max dose for cutaneous infiltration is 31.5mL of 1%, or 15.75mL of 2%, which is far more than we would ever typically use for most lacerations.

IV Dosing
IV dosing of lidocaine is typically at 1-1.5mg/kg given over 5-20min for most purposes. The max dose is generally considered 3mg/kg IV.

Bottom line: For a 70kg individual, the IV dose of lidocaine would be 70-105mg, which is 7-10.5mL of 1% or 3.5-5.25mL of 2%.

Cost
Lidocaine is among the cheaper medications we give in the ED. The 1% solution is about $4 for 30mL.

Disclaimer: The Rx Pad authors have no financial affiliations with the makers of any of the medications that we feature in our column.

REFERENCES

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