Local anesthetic toxicity

While generally safe, local anesthetic agents can be toxic if used in excessive doses or administered improperly. Even when administered properly, patients may still experience unintended reactions to local anesthetics. [Zamanian, R., Toxicity, Local Anesthetics (2005)]

Excessive doses may be unintentionally administered in several ways.
# Repetitive (small) doses of local anesthetic to achieve an adequate level of anesthesia may lead to eventual adminitration of toxic doses.
# Injection of anesthesia in a confined space may result in excesive fluid pressure that may damage nerves.
# Doses intended for epidural or intra-support-tissue administration may be accidentally delivered as intravascular injection resulting in accelerated systematic absorption. [Zamanian, R., Toxicity, Local Anesthetics (2005)]

The toxic effects of local anesthetics can be classified by localized and systemic effects.

Localized toxicity

A cause of local toxicity is allergic reaction to para-aminobenzoic acid (PABA). These reactions range from urticaria to anaphylaxis.

PABA is a metabolic product of the degradation of Ester class of local anesthetics, such as Procaine (Novocaine), Benzocaine, and, to a lesser degree, amide class anesthetics such asLidocaine, and Prilocaine. It is also a metabolic by-product of Methylparaben, a preservative in multi-dose vials of Lidocane. When allergic response to injected anesthetics does occur, it is most likely due to the ester class local anesthetics. The amide class of local anesthetics is far less likely to produce allergic reaction. [Dolan, R., ed. (2004), Facial Plastic, Reconstruction, and Trauma Surgery] . [Univ. of Wisconsin, Local Anesthesia and Regional Anesthetics]

ystemic toxicity

Systemic toxicity of anesthetics involves the central nervous system (CNS), the cardiovascular system, and the immune system.

It can be described by the direct effects on the immune system, blood (hematologic), and cardiovascular system.

Immune system effects

As noted previously, allergic reaction to metabolic break-down of anesthetic agents and preservatives (PABA) can cause anaphylaxis.

Hematologic effects

Methemoglobinemia is a process where iron in hemoglobin is altered, reducing its oxygen-carrying capability, which produces cyanosis and symptoms of hypoxia. Benzocaine, Lidocaine, and Prilocaine all produce this effect, especially Benzocaine. [Dolan, R., ed. (2004), Facial Plastic, Reconstruction, and Trauma Surgery]

Cardiovascular effects

Cardiovascular effects are primarily those of direct myocardial depression and bradycardia, which may lead to cardiovascular collapse. [Zamanian, R., Toxicity, Local Anesthetics (2005)] .

Systemic toxic reactions to locally administered anesthetics are progressive as the level of the anesthetic agent in the blood rises. Initial symptoms suggest some form of central nervous system excitation such as a ringing in the ears (tinnitus), a metallic taste in the mouth, or tingling or numbness of the mouth. advanced symptoms include motor twitching in the periphery followed by grand mal seizures, coma, and eventually respiratory arrest. At extremely high levels, cardiac arrhythmia or hypotension and cardiovascular collapse occur. [Mulroy, M., Systemic Toxicity and Cardiotoxicity From Local Anesthetics (2002)]

See also

* Local anesthetic

References

citation
last=Zamanian |first=Roham T.
author-link=http://www.emedicine.com/cgi-bin/foxweb.exe/screen@/em/ga?book=emerg&authorid=4647&topicid=761
Coauthors=Roham T Zamanian, MD, Fellow in Pulmonary Vascular Disease, Vera Moulton Wall Center for Pulmonary Vascular Disease, Stanford University Medical Center; Julie K Olsson, MD, MS, Fellow, Division of Pulmonary and Critical Care Medicine, Stanford University Medical Center; Bret Ginther, MD, Assistant Program Director, Assistant Clinical Professor, Department of Emergency Medicine, University of California at Irvine Medical Center
title=Toxicity, Local Anesthetics
date=June 20, 2005
year=2005
editor-first=Lance W Kreplick, MD, MMM, Medical Director, Department of Emergency Medicine, Regional Medical Center - Bayonet Point; John T VanDeVoort, PharmD, Clinical Assistant Professor, College of Pharmacy, University of Minnesota; John G Benitez, MD, MPH, FACMT, FACPM, FAAEM, Associate Professor, Department of Emergency Medicine, Pediatrics, and Environmental Medicine, University of Rochester; Managing Director, Associate Medical Director, Ruth A Lawrence Poison and Drug Information Center; John Halamka, MD, Chief Information Officer, CareGroup Healthcare System, Assistant Professor of Medicine, Department of Emergency Medicine, Beth Israel Deaconess Medical Center; Assistant Professor of Medicine, Harvard Medical School; and Raymond J Roberge, MD, MPH, FAAEM, FACMT, Clinical Associate Professor of Emergency Medicine, University of Pittsburgh School of Medicine; Consulting Staff, Department of Emergency Medicine, Magee-Women's Hospital of the University of Pittsburgh Medical Center
publisher=eMedicine by WebMD
url=http://www.emedicine.com/emerg/topic761.htm
accessdate=2007-10-10

citation
title=Local Anesthesia and Regional Anesthetics
publisher=University of Wisconsin at Madison
url=http://www.anesthesia.wisc.edu/med3/localanes/localhandout.html
accessdate=2007-10-10

citation
last=Drasner |first=Kenneth
title=Local Anesthetic Neurotoxicity: Clinical Injury and Strategies That May Minimize Risk
journal=Regional Anesthesia and Pain Medicine
volume=Vol 27
issue=No 6 (November–December)
year=2002
pages=pp 576–580
publisher=American Society of Regional Anesthesia and Pain Medicine
url=http://asra.com/consensus-statements/Drasner.pdf
accessdate=2007-10-10

citation
journal=Risks associated with your anaesthetic,
title=Nerve damage associated with peripheral nerve block
volume=Section 12
publisher=The Royal College of Anaesthetists
date=January 2006
url=http://www.rcoa.ac.uk/docs/nerve-peripheral.pdf
accessdate=2007-10-10

citation
last=Mulroy
first=Michael F.
title=Systemic Toxicity and Cardiotoxicity From Local Anesthetics: Incidence and Preventive Measures
journal=Regional Anesthesia and Pain Medicine
volume=Vol. 27
issue=No 6 (November–December)
year=2002
pages=pp 556–561
publisher=Department of Anesthesiology, VirginiaMason Medical Center, Seattle, Washington
url=http://asra.com/consensus-statements/Mulroy.pdf
accessdate=2007-10-10

citation
editor-last=Dolan
editor-first=Robert W.
title=Facial Plastic, Reconstruction, and Trauma Surgery
publisher=Informa Health Care
year=2004
pages=pp 30-31
isbn=0-8247-4595-7
url=http://books.google.com/books?id=uBB_vaBNyXIC&pg=PA30&lpg=PA30&dq=paba+provokes+allergic+reaction&source=web&ots=gKHqScNptQ&sig=RdrkgUF4V0gpCgim8leFoE8TWtk#PPA30,M1
accessdate=2007-10-10