Local Anesthesia Lec #4 by Mohammad Bader

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Local Anesthesia Lec #4 by Mohammad Bader

Post by Sura on 26/10/2011, 1:00 am

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Today’s lecture talks about clinical aspects of local anesthesia

Indications of local anesthesia:

-When the procedure is simple.

-Not prolonged procedure.

-When the patient is cooperative.

-When general anesthesia is contraindicated.

*Absolute contraindication: this drug should not be used under any circumstances.

When there is documented allergy toward the use of anesthetic, it’s not the anesthetic itself that caused the allergy, but the allergy is in some additives, so the best thing to do is taking history, and if you want to make sure you can take skin test.

Allergic response toward local anesthesia could occur in several circumstances:

1) Latex allergy: the rubber diaphragm that is present in the carpule (use vials instead of carpules).

2) Ester local anesthetics: could have an allergic response in specific types of patients when they have cholinesterase deficiency. The material that is responsible for this allergic reaction is para-aminobenzoic acid.

3) Methylparaben: which is a product that is added to the vials, it is bacteriostatic and it is not used anymore

High doses of Prilocaine, articaine, cocaine can convert normal hemoglobin to methemoglobinemia, which is a disorder characterized by the presence of a higher than normal level of methemoglobin in the blood which is an oxidized form of hemoglobin that has an increased affinity for oxygen, resulting in a reduced ability to release oxygen to tissues.. So the patient will have cyanosis and loss of consciousness... so Prilocaine is RELATIVELY contraindicated (if there is no alternative drugs the dose should be reduced) in patients who have idiopathic or congenital methemoglobinemia.

Liver failure can be acute or chronic; any liver disease that persists more than 3 months is considered as chronic, or if the glomerular filtration rate decreased for more than 3 months, this is considered chronic renal failure. Now mild local anesthetics are metabolized mainly in the liver and excreted in the kidney but ester local anesthetics are metabolized in plasma by pseudocholinesterase enzyme.

Note: you can differentiate the amide groups by the following: the first prefix contains “I” and ends in “Caine” except Articaine which is classified as amide but it consists of ester linkage.

American association of anesthesiologist divided the patients according to their medical conditions to 6 groups:

1) Fit and healthy.

2) Mild systemic disease with significant risk factor (hypertension above 140).

3) Severe systemic disease but does not considered as risk factor (does not threaten lives) (hypertension 160-180).

4) Severe systemic disease which threaten lives (stroke can happen at any time).

5) Patient unable to survive without the operation.

6) Brain death (we just use them as a donor).

Individuals response to the drug (bell shaped curve): some people, the local anesthesia can continue longer than the expected period. If we have 100 patients, 70% of them will have 60 minutes pulpal anesthesia, 15% hyper responders will have 70, 80, 90 minutes of anesthesia, the remaining is hypo responders 40, 15 minutes pulpal anesthesia duration and these who we care about. These variances are not due the rapid metabolism of the drug, but it differs between adults and old and young people.

Simplified description of pregnancy classifications for local anesthetics:

-category A: this drug is safe according to human studies.

-category B: this drug is safe according to animal studies.

-category C: this drug is unsafe according to animal studies.

-category D: there is a benefit of using this drug just for the pregnant but not for the fetus (we just use it in cases of emergency).

-category X: this drug is unsafe according to human and animal studies (it is contraindicated).

Now lets talk about some calculations:

Every 1%=10mg, 2%=20mg, 3%=30mg …..

So there is in 2% 20mg/ml of the solution

Now the carpule has 1.8 à so 20*1.8=36mg of lidocaiene, and epinephrine= 1g:100,000ml=1000mg:100,000ml=1:100=0.01 per ml à in 1.8 ml= 0.01*1.8=0.018mg of epinephrine in one carpule.

Maximum recommended dose for adults (MRD):

Patient 1: 22 year old, healthy, female, 110 LBS, Lidocaine 2%, MRD: 3.0mg/lb: 300mg

How much lidocaine can this patient receive(in carpules)?

Answer: 1) multiply her weight in pounds by MRD: 110*3=330

2) as we said before 1 carpule has 36mg of 2% lidocaine, so 330/36= 9 carpules of lidocaine this patient can receive

Patient 2: 6 year old, healthy, male, 40 LBS, Mepivacaine 3%, MRD: 2.0mg/lb.

How much Mepivacaine can this patient receive (in carpules)?

Answer: - 3% à 30/ml

- The carpule is 1.8 so 30*1.8=54 ml of Mepivacaine in

one carpule

- 40*2=80

- 80/54= 1.5 carpule

Patient 3: 100 LBS female, healthy, Prilocaine 4%, MRD 2.7 mg/lb.: 400mg. patient received 2 carpules, but anesthesia is inadequate. Doctor wishes to change to lidocaine 2% (MRD=2mg/lb.) + epinephrine 1:100,000.

How much lidocaine can this patient receive (in carpules)?

Answer: - 2*100=200mg the MRD for lidocaine

- 40*1.8=72mg per carpule à72*2=144mg per 2


- 200-144=56 mg

- 56/36=1.5 carpule he can use

Done By: Mohammad Bader
Local Anesthesia lec. 4
Dr. Al-shayyab

عدد المساهمات : 484
النشاط : 2
تاريخ التسجيل : 2010-09-29

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