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Local anesthetics

There are two major groups of local anaesthetics: esters and amines.

  1. Esters : procaine (Novocaine), and tetracaine (Pontocaine)
  2. Amines: lidocaine (Xylocaine) and bupivacaine (Marcaine).

If a past allergy is reported, an anesthetic from another class can be used. Most often, however, the allergy is to the preservative used in the lidocaine multidose vials. Therefore, one option is to use a single-dose lidocaine preparation that does not contain preservatives.

For routine Emergency room use, a mixture of lidocaine 1%, with or without epinephrine 1/100,000 parts, is recommended. For regional nerve blocks, a 2% solution is used. The lidocaine 2% solution can be combined with equal parts of the Marcaine 0.25% solution to obtain relatively quick, yet longer lasting anaesthesia. The anaesthetic effect of lidocaine lasts less than an hour, but as long as two hours if the epinephrine containing preparation is used. Marcaine’s effect lasts from 12-24 hours. This would be important, for example, in the case of a distal digit amputation, where longer-term anaesthesia is desired. Some patients continue to experience considerable pain even after simple suturing, and Marcaine could significantly reduce such pain.

Epinephrine is commonly used as an adjuvant to reduce bleeding and slow anaesthetic absorption systemically. A noticeable decrease in wound bleeding will be noted in about seven minutes. Epinephrine should be avoided in those patients with vasospastic disorders, those with crush or circumferential extremity injuries, or those on beta-blockers. The use of epinephrine in the fingers, toes or penis has classically been contraindicated, because of its supposed propensity to cause vasospasm in these areas.

A toxic dose of Xylocaine (lidocaine) is 3 mg per kg intravenously; 5 mg per kg when injected without epinephrine into the wound margin, and 7 mg per kg when injected with epinephrine into the wound margin. There is evidence that the toxic dose may actually be much higher than usually quoted. The toxicity of Marcaine is one-quarter that of lidocaine, on a weight to weight basis.

Prior to the administration of local anaesthetics, check the sensory and motor nerve response, and for allergy (very rare). The pediatric literature supports the use of a topical anesthetic such as LET (a combination of lidocaine, epinephrine and tetracaine) prior to needle infiltration to reduce the pain. Slow injection by a small needle (such as a 25, 27 or 30 Gauge) will reduce the pain of infiltration.

Adverse reactions to local anaesthetics may take several forms.

Adverse Reactions to Local Anaesthetics
Type
Incidence
Mechanism
Symptoms
Vasovagal Common   nausea, light-headedness
bradycardia
vasodilatation
hypotension
syncope
Epinephrine related Common   “ rash”
tremor, headache
palpitations
abdominal and uterine cramps
Toxic
(>3mg /kg IV, >5 mg/kg without epinephrine,
> 7 mg/kg with epinephrine)
relatively common IV leak (? From regional blocks?) tachycardia
arrhythmia
CNS excitation, depression
seizure, coma
Allergic rare to amides
uncommon to esters
IgE mediated
? methylparaben
preservative
? antioxidants
(sulphites)
angioedema
bronchospasm
tachycardia
hypotension


If there is doubt about allergy, in minor cases, plain normal saline can be injected into the wound margin to stretch the skin, thereby affording some degree of anaesthesia.

Malignant hyperthermia is now considered NOT to be precipitated by the use of lidocaine. Traditionally, in this setting, an ester has been utilised.


Tetanus prophylaxis - Tetanus vaccination
The tetanus disease itself is a serious one but relatively rare in Canada.

An identifiable acute injury occurs in the majority of cases (70%). Puncture wounds and lacerations account for most cases. Interestingly, approximately one-half of these injuries occurred indoors. Only a small percentage of cases occur in previously properly “immunised” patients. The incubation period is from two days to two months.

Tetanus vaccines must be administered intramuscularly. The anterolateral thigh is recommended in infants and the deltoid muscle in older children and adults. These adsorbed vaccines should not be administered subcutaneously as sterile abscess can form.

Since 1982, all school children in Ontario are required by law to be immunised. As of 1987, it is the law in Ontario that physicians inform their patients of the risks and benefits of immunisation. Adverse reactions to primary immunisation with tetanus toxoid are rare. The booster dose, however, can cause local erythema and swelling. Overuse of tetanus vaccines can lead to Arthus type reactions, urticarial reactions, and angioneurotic edema , and rarely, peripheral neuropathy and anaphylaxis.

Tetanus immune globulin (human) is a passive immunising agent containing preformed antibodies. Serum sickness can occasionally occur especially in the past when the globulin was derived from horse sera.

The decision to administer tetanus prophylaxis in the Emergency room depends on the current immunisation status of the patient and the liability of tetanus contamination in a given wound. In this Emergency Department, the order for a “tetanus booster” usually means that tetanus polio (Salk type) inactivated vaccine is administered.

Several protocols for the administration of tetanus prophylaxis are available.
The Canadian Immunization Guide – 6th Edition – 2002 is available at
http://www.hc-sc.gc.ca/pphb-dgspsp/publicat/cig-gci/
.



Prophylactic oral, IM or IV antibiotics in wound care of routine lacerations

There is NO evidence (based on many clinical studies and a meta-analysis) to support the routine use of prophylactic oral, IM or IV antibiotics to prevent wound infections after closure of routine lacerations. Antibiotics do NOT substitute for proper wound cleansing.

Prophylactic antibiotic treatment is, however, proven to be of value in the treatment of animal and human bites in particular. See D. Special Situations in Wound Care / Mammalian bites

``Use of antibiotics should be individualized based on the degree of bacterial contamination, the presence of infection-potentiating factors, such as soil, the mechanism of injury, and the presence or absence of host predisposition to infection. In general, decontamination is far more important than antibiotics. Prophylactic antibiotics should be used in most human, dog, and cat bites, intraoral lacerations, open fractures, and exposed joints or tendons.`` From Management of lacerations in the emergency department. O. Capellan and J. Hollander Emergency Medicine Clinics of North America. Volume 21, Number 1, February 2003



 
©2003 Department of Emergency Medicine, University of Ottawa

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