Local anesthetics, adverse events and dental practice

Local anesthetics (LAs) are indispensable in dental practice, providing effective pain management for many procedures. Their administration is generally safe; however, dentists must remain vigilant regarding potential adverse events, some of which, though rare, can be severe. This article delves into the safe use of local anesthetics in dentistry, emphasizing the importance of preventing and treating LAST (Local Anesthetic Systemic Toxicity) and recognizing other LA associated adverse events.

Adverse events associated with local anesthetics: Systemic toxicity

Local anesthetics can be harmful to patients. Possibly the most lethal adverse event is LAST with an estimated occurrence of 0.27/1000 LA administrations.¹ Local anesthetics are generally safe when restricted to the intended site of treatment. However, high plasma levels of circulating LA can affect a plethora of diverse systemic targets through inhibition of: sodium, calcium and K+ channels, stimulatory kinases, ATP production and mitochondrial metabolism.^1-7 The result is systemic neurologic and cardiac toxicity.^1-7

Prodromal CNS symptoms present initially as dizziness, confusion, dysphoria, tinnitus, perioral numbness, or a metallic taste although, the most common CNS manifestation are seizures (68%–77%).^1-7 As blood plasma levels of the anesthetic increase, the patient may experience respiratory depression and coma.^1-7 Cardiac toxicity often follows CNS toxicity with the first indicators being hypertension and tachycardia followed by hypotension and bradycardia. Progressively, arrhythmias, conduction block, asystole and cardiac arrest can occur.^1-7 Atypical cases can present with cardiac toxicity preceding CNS symptoms, 20% of the time.¹ Extra vigilance is required when local anaesthetic is administered with sedation as the first signs of LAST can be masked.⁷ Often occurring rapidly within 1-5 minutes of LA injection^1,3,6, LAST can have a delayed onset sometimes upto 6 hours later.¹

Prompt intervention is essential to mitigate the clinical course of the condition. Early recognition of LAST and immediate provision of oxygen and ventilation can prevent acidosis and hypoxia thereby averting the progression to seizures and cardiac arrest.^{1-4, 7,8} Practitioners should activate emergency services (alerting the closest cardiopulmonary bypass hospital), be prepared to manage and treat seizures with benzodiazepines (if trained) and provide CPR if required.^1-4,7,8 If initiating ACLS, modifications to standard protocols must be made to prevent exacerbating the effects of LAST. Clinicians should refrain from using lidocaine, beta-blockers, calcium channel blockers and vasopressin. If epinephrine is administered reduce the dose to 1 microgram/kilogram to prevent arrhythmia.^1,4,7,8,9

Since 2010, the definitive treatment for LAST is 20% lipid emulsion IV, known as lipid resuscitation therapy (LRT).^1,7,8,10-12 LRT has multiple effects that improve cardiac perfusion, conduction and contractility. Additionally, it sequesters local anesthetic from its many systemic target receptors thereby facilitating drug elimination.^8-12 In severe refractory cases, cardiopulmonary bypass or ECMO (extracorporeal membrane oxygenation) is required to oxygenate and circulate the patient’s blood until therapeutic intervention can detoxify the cardiovascular system.^4,8,10

Adherence to dosage guidelines

Prevention is the first line of treatment for LAST. Practitioners need to maintain safe plasma levels of LA by staying within the total dose recommended and routinely using the minimum effective dose possible for all patients.^1,7,13-15 A minimum effective dose is the lowest concentration and lowest volume that renders profound anaesthesia for the intended duration of the procedure. Dose reduction may be necessary for patients that are pregnant, have a metabolic condition or pre-existing cardiac, hepatic or renal compromise.^1,2,4,6 Furthermore, clinicians need to be aware that a high dose to weight ratio as can occur in children, the elderly or patients with smaller muscle mass increases their susceptibility to LAST. Muscles act as a depot for circulating LA, thereby reducing systemic LA plasma levels.³

To further ensure safe LA plasma levels, dental practitioners need to remain vigilant and aspirate prior to every injection as an intravascular injection or an injection into a highly vascular area within the recommended dose can often instigate LAST.^1-4,16 Finally, the addition of epinephrine to LA is protective to prevent absorption of LA systemically. However, the maximum allowable amounts of epinephrine must be considered, especially in patients with cardiovascular compromise, as this may limit the number of LA cartridges suitable for use.

Commonly used local anesthetics and their maximum dosages

The following table outlines commonly used local anesthetics in dentistry, their concentrations, maximum dosages, and the corresponding number of cartridges for an average-sized 70 kg or 150 lb adult. See Table 1: Maximum Dosages for Commonly Used Local Anesthetics in Dentistry.

Table 1: Maximum Dosages for Commonly Used Local Anesthetics in Dentistry

Anesthetic	Concentration (%)	Maximum Dose (mg/kg)	Maximum Total Dose (mg)	Maximum Cartridges*
2% Lidocaine with Epinephrine 1:100,000	2.0	7.0	500	13*
4% Articaine with Epinephrine 1:100,000	4.0	7.0 5.0 (children)	500	7*
0.5% Bupivacaine with Epinephrine 1:200,000	0.5	2.0	200	10*
3% Mepivacaine	3.0	6.6	400	7
4% Prilocaine	4.0	8.0	500	8

Other common and less severe adverse events

Aside from LAST, which the vast majority of dentists are unlikely to encounter during their careers, several types of adverse events will be more familiar to dentists. These include but are not limited to:

• Psychogenic reactions: Of the adverse reactions, these are the most common, often stemming from patient anxiety or fear of dental procedures and/or the LA injection itself. Symptoms may include dizziness, hyperventilation, nausea, vomiting, alterations in heart rate or blood pressure, and syncope.¹⁸ Validated anxiety assessment tools should always be utilized to comprehensively evaluate patient fears thus enabling clinicians to provide effective non-pharmacologic and pharmacologic interventions as necessary.¹⁹
• Epinephrine reaction: Also known as an “adrenaline rush,” this reaction results from the inadvertent intravascular injection of epinephrine. Symptoms may manifest as apprehension, anxiety, restlessness, tremor, dizziness, sweating, palpitations, pallor and headache. Typically, short-lived lasting the duration of epinephrine’s half-life and self-limiting, dentists should reassure affected patients.^16,18
• Non-surgical paresthesia: A persistent neuropathy exhibited as burning, tingling or numbness, although often transient, can become permanent in rare cases. The exact etiology is unknown. It may be a function of direct trauma to the nerve²⁰ determined by the number and ratio of nerve fascicles affected_²¹ and/or the neurotoxicity of highly concentrated LAs such as 4% articaine and prilocaine.²⁰ Dental clinicians need to assess the risk versus benefit for the type of LA used for different administrative techniques and areas to be anesthetized.
• Allergic reactions: Allergic reactions to amide local anesthetics are rare. A patient may present with a psychogenic reaction that mimics allergic or anaphylactic symptomatology.^18,22,23 An allergist can determine if a true allergy exists to the amide local anesthetic or another agent in the local anesthetic cartridge.^18,22,23 Ester-based topical anesthetics do have a higher propensity for patient allergic and anaphylactic responses.^18,22,23 Dental practitioners should carefully monitor patients for signs and symptoms of allergy when ester based anesthetics are used and be emergency ready to activate anaphylaxis protocols as indicated.

Key recommendations for safe administration

To mitigate the risks associated with local anesthetics, the following practices are recommended:

• Thorough medical history: Assess patients for anxiety, previous reactions to local anesthetics, allergies, conditions that predispose patients to LAST and potential drug interactions.
• Patient communication: Communicate thoroughly and empathetically, including obtaining informed consent, to reduce patient anxiety.
• Aspiration technique: Routinely, employ aspiration before injection to minimize the risk of intravascular administration. Consider frequent aspiration when injecting into highly vascularized tissue.
• Patient monitoring: Observe patients for early signs of toxicity, or other adverse events especially those at higher risk.
• Emergency preparedness: Ensure that emergency protocols are in place, and that resuscitation equipment and medications are readily available.

Patient safety in dental practice hinges on vigilance and proactive management of potential risks associated with local anesthetic use. By adhering to established guidelines and maintaining a high index of suspicion for adverse events, dental professionals can continue to provide safe and effective care. 

Oral Health welcomes this original article.

References

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About the authors

Dr. Sangeeta Patodia is a board-certified Dental Anaesthesiologist having earned her dental and specialty degree from the University of Toronto. She provides anaesthesia to patients of all ages and instructs dentists at the University of Toronto’s Faculty of Dentistry and throughout Canada in medical emergencies, sedation and risk mitigation. 

Julian Perez is Chief Risk and Compliance Officer at dentalcorp, where he oversees legal, regulatory compliance, corporate governance and enterprise risk functions to support practices in the delivery of optimal patient care. He earned his bachelor’s degree from Yale University and a JD from Columbia University’s School of Law. 

Dr. Gary Glassman lectures globally on endodontics, is on staff at the University of Toronto, Faculty of Dentistry in the graduate department of endodontics. He maintains a private practice, Endodontic Specialists in Toronto, Ontario, Canada. His personal/professional website is www.drgaryglassman.com and his office website is www.rootcanals.ca. He can be reached at gary@rootcanals.ca.