Local Anaesthetics.ppt

5/28/2018 Local Anaesthetics.ppt

1/26


2/26

Topical anesthesia(surface) Infiltration

Plexus block

Epidural (extradural) block Spinal anesthesia (subarachnoid block)
http://en.wikipedia.org/wiki/Topical_anesthetichttp://en.wikipedia.org/wiki/Infiltration_(medical)http://en.wikipedia.org/wiki/Local_anesthesiahttp://en.wikipedia.org/wiki/Local_anesthesiahttp://en.wikipedia.org/wiki/Infiltration_(medical)http://en.wikipedia.org/wiki/Topical_anesthetic


3/26

AmidesLidocaine (Xylocaine) Bupivacaine(Marcaine) Mepivacaine (Carbocaine)Prilocaine (Citanest) Etidocaine (Duranest)

EstersProcaine (Novocain) Chloroprocaine(Nesacaine) Tetracaine (Pontocaine)


4/26

The local adverse effects of anesthetic agentsinclude neurovascular manifestations such asprolonged anesthesia(numbness) andparesthesia(tingling, feeling of "pins and

needles", or strange sensations). These aresymptoms of localized nerve impairment ornerve damage.
http://en.wikipedia.org/wiki/Anesthesiahttp://en.wikipedia.org/wiki/Paresthesiahttp://en.wikipedia.org/wiki/Nerve_damagehttp://en.wikipedia.org/wiki/Nerve_damagehttp://en.wikipedia.org/wiki/Paresthesiahttp://en.wikipedia.org/wiki/Anesthesia


5/26

Depending on local tissue concentrations oflocal anesthetics

there may be excitatory or depressant effects

At lower concentrations, a relatively selectivedepression of inhibitory neurons results incerebral excitation, which may lead togeneralized convulsions.
http://en.wikipedia.org/wiki/Convulsionhttp://en.wikipedia.org/wiki/Convulsion


6/26

A profound depression of brain functionsoccurs at higher concentrations which maylead to coma, respiratory arrestand death.

Due to 1.very high plasma levels afterintravenous injection of a large dose.

2. direct exposure of the central nervoussystem through the CSF, i.e. overdose in

spinal anesthesiaor accidental injection intothe subarachnoid spacein epiduralanesthesia.
http://en.wikipedia.org/wiki/Comahttp://en.wikipedia.org/wiki/Respiratory_arresthttp://en.wikipedia.org/wiki/Spinal_anesthesiahttp://en.wikipedia.org/wiki/Subarachnoid_spacehttp://en.wikipedia.org/wiki/Epidural_anesthesiahttp://en.wikipedia.org/wiki/Epidural_anesthesiahttp://en.wikipedia.org/wiki/Epidural_anesthesiahttp://en.wikipedia.org/wiki/Epidural_anesthesiahttp://en.wikipedia.org/wiki/Subarachnoid_spacehttp://en.wikipedia.org/wiki/Spinal_anesthesiahttp://en.wikipedia.org/wiki/Respiratory_arresthttp://en.wikipedia.org/wiki/Coma


7/26

The signs and symptoms of CNS toxicityinduced by local anesthetics resemblevasovagal responses.

Early symptoms, such as a metallic taste,tinnitus, lightheadedness, and confusion, arefollowed by tremors and shivering.


8/26

The conductive system of the heart is quitesensitive to the action of local anesthetics.

Lidocaine is often used as an antiarrhythmic drugand has been studied extensively, but the effects ofother local anesthetics are probably similar tothose of Lidocaine.

Lidocaine acts by blocking sodium channels,leading to slowed conduction of impulses. Thismay obviously result in bradycardia, but

tachyarrhythmiacan also occur. With high plasmalevels of lidocaine there may be higher-degreeatrioventricular block and severe bradycardia,leading to coma and possibly death.
http://en.wikipedia.org/wiki/Bradycardiahttp://en.wikipedia.org/wiki/Tachyarrhythmiahttp://en.wikipedia.org/wiki/Bradycardiahttp://en.wikipedia.org/wiki/Tachyarrhythmiahttp://en.wikipedia.org/wiki/Tachyarrhythmiahttp://en.wikipedia.org/wiki/Bradycardia


9/26


10/26

Recent case reports have been published ofthe successful use of lipid emulsion in thisway (Rosenblatt 2006, Litz 2006, Foxall2007) to save patients who were

unresponsive to the usual resuscitationmethods. All patients recovered completelyshortly after intravenous injections of lipid.


11/26

20 Intralipid: 1.5 mL/kg as an initial bolus, followed by 0.25 mL/kg/min for 30-60 minutes Bolus could be repeated1-2 times forpersistent asystole Infusion rate could be increasedif the BP

declines.


12/26

Adverse reactions to local anesthetics(especially the esters) are not uncommon, buttrue allergyis very rare.

Allergic reactions to the esters is usually dueto a sensitivity to their metabolite, para-aminobenzoic acid(PABA), and does notresult in cross-allergy to amides.

There are also cases of allergy to parabenderivatives, which are often added aspreservatives to local anesthetic solutions.
http://en.wikipedia.org/wiki/Allergyhttp://en.wikipedia.org/wiki/Para-aminobenzoic_acidhttp://en.wikipedia.org/wiki/Para-aminobenzoic_acidhttp://en.wikipedia.org/wiki/Para-aminobenzoic_acidhttp://en.wikipedia.org/wiki/Para-aminobenzoic_acidhttp://en.wikipedia.org/wiki/Para-aminobenzoic_acidhttp://en.wikipedia.org/wiki/Allergy


13/26

The pain of injection is caused by insertion of the needleand infiltration of the anesthetic into the skin. Ideally, the smallest gauge needle, usually 25 to 30,

should be used to inject all anesthetics. Adjunctive techniques using topical anesthetics,

cryotherapy, or distraction may complement the routine

use of lidocaine. Pinching the skin stimulates local sensory nerves, partially

blocking the transmission of other painful stimuli. Injecting slowly and steadily can minimize the pain of the

anesthetic itself. If clinically indicated, injecting into the subcutaneous

tissues is less painful than infiltrating directly into thedermis to raise a wheal.

Physicians should remember that ethyl chloride isflammable and should not be used with electrocautery.


14/26

The addition of epinephrine at 1:100,000 to200,000 (5 to 10 g per mL) is useful to prolongthe duration of anesthesia and provide somedegree of hemostasis. When working on highlyvascular tissues such as the scalp, the physician

may need to wait between injection and surgery.The onset of optimal vasoconstrictive effect fromepinephrine is approximately five minutes. Withthe vasoconstriction and resultant delay inabsorption afforded by epinephrine, the

maximum recommended dose of lidocaineincreases from4 to 7 mg per kg1 (Table 23-5).


15/26

Adrenaline 1:1000 contains 1 gram ofadrenaline per 1000mls solution i.e. 1mg/ml.

To prepare a 1 in 200,000 solution the1:1000 must be diluted 200 times. This isachieved by taking 0.1ml (= 0.1mg) andadding 19.9 mls of local anaesthetic solution.


16/26

Plain Solution With

Adrenalinemg/kg mg/kg

Prilocaine 6 9

Lignocaine 3 7

Bupivacaine 2 2


17/26

Adrenaline containing solutions should neverbe used for infiltration around end-arteriesi.e. penis, ring block of fingers or other areaswith a terminal vascular supply as the intense

vasoconstriction may lead to severeischaemia and necrosis.


18/26

[edit] Hypersensitivity/Allergy Adverse reactions to local anesthetics (especially the

esters) are not uncommon, but true allergyis veryrare. Allergic reactions to the esters is usually due toa sensitivity to their metabolite, para-aminobenzoicacid(PABA), and does not result in cross-allergy toamides. Therefore, amides can be used asalternatives in those patients. Non-allergic reactionsmay resemble allergy in their manifestations. In somecases, skin tests and provocative challenge may benecessary to establish a diagnosis of allergy. There

are also cases of allergy to paraben derivatives, whichare often added as preservatives to local anestheticsolutions
http://en.wikipedia.org/w/index.php?title=Local_anesthetic&action=edit&section=11http://en.wikipedia.org/wiki/Allergyhttp://en.wikipedia.org/wiki/Allergyhttp://en.wikipedia.org/wiki/Para-aminobenzoic_acidhttp://en.wikipedia.org/wiki/Para-aminobenzoic_acidhttp://en.wikipedia.org/wiki/Para-aminobenzoic_acidhttp://en.wikipedia.org/wiki/Para-aminobenzoic_acidhttp://en.wikipedia.org/wiki/Para-aminobenzoic_acidhttp://en.wikipedia.org/wiki/Para-aminobenzoic_acidhttp://en.wikipedia.org/wiki/Para-aminobenzoic_acidhttp://en.wikipedia.org/wiki/Para-aminobenzoic_acidhttp://en.wikipedia.org/wiki/Para-aminobenzoic_acidhttp://en.wikipedia.org/wiki/Allergyhttp://en.wikipedia.org/w/index.php?title=Local_anesthetic&action=edit&section=11


19/26

Methemoglobinemia The systemic toxicity of prilocaineis

comparatively low, however its metabolite, o-toluidine, is known to cause

methemoglobinemia. As methemoglobinemiareduces the amount of hemoglobinthat isavailable for oxygen transport, this side effectis potentially life-threatening. Therefore dose

limits for prilocaine should be strictlyobserved. Prilocaine is not recommended foruse in infants.
http://en.wikipedia.org/wiki/Prilocainehttp://en.wikipedia.org/wiki/Methemoglobinemiahttp://en.wikipedia.org/wiki/Methemoglobinemiahttp://en.wikipedia.org/wiki/Hemoglobinhttp://en.wikipedia.org/wiki/Hemoglobinhttp://en.wikipedia.org/wiki/Hemoglobinhttp://en.wikipedia.org/wiki/Methemoglobinemiahttp://en.wikipedia.org/wiki/Prilocaine


20/26

There are few absolute contraindications for local injection anesthetics.Allergy to amide anesthetics such as lidocaine is rare, and when it doesoccur, it is usually caused by the preservative methylparaben.1One wayto circumvent a potential allergic reaction is to use preservative-freelidocaine, which is available in single-dose vials. History of an allergy toan ester anesthetic such as procaine (Novocain) is not a contraindicationto the use of lidocaine,1because they are chemically different, andcross-reaction is rare (Table 1). Another approach includes using 1

percent diphenhydramine (Benadryl), which has proved effective inrandomized studies.2

The addition of epinephrine, a potent vasoconstrictor, is contraindicatedwhen it may compromise blood flow in a confined space. Epinephrineshould never be used in digital and penile blocks or in skin flaps withmarginal viability. The use of epinephrine in the nasal tip and ear isrelatively contraindicated for the same reasons, but it has been used in

studies in which the treated areas are kept warm to prevent additionalvasoconstriction.3The clinician should exercise caution whencontemplating the use of vasoconstrictors in dirty wounds because ofthe increased risk of infection. In addition, certain patients withdiabetes, hypertension, heart block, or cerebrovascular disease may beparticularly sensitive to epinephrine


21/26

Local anaesthetics applied to the skin, the eye, the ear,the nose and the mouth as well as other mucousmembranes.

In general, cocaine, amethocaine, lignocaine andprilocaine are the most useful and effective local

anaesthetics for this purpose. When used to produce topical anaesthesia, they usually

have a rapid onset of action (5-10mins) and a moderateduration of action (30-60 mins).

Cocaine is a potent vasoconstrictor and is useful in the

reduction of bleeding as well as topical anaesthesia.Absorption of local anaesthetics through intact skin isusually slow and unreliable and high concentrations(e.g. 20% benzocaine or 40% lignocaine) are required


22/26

Amide anaesthetics with a moderate duration ofaction are commonly used (lignocaine, prilocaineand mepivacaine).

The site of action is at unmyelinated nerve endingsand onset is almost immediate.

The duration of local anaesthesia is variable.Procaine has a short duration of action (15-30min), while lignocaine, mepivacaine and prilocainehave a moderate duration of action (70-140 min).

Bupivacaine has the longest duration of action(approximately 200 min). The addition ofadrenaline (1 in 200,000) will increase the qualityand prolong the duration of anaesthesia.


23/26

Most pure anesthetic agents exist as solids. Eutectic mixtures are liquids and melt at lower

temperatures than any of their components,permitting higher concentrations of anesthetics.

Eutectic mixture of local anesthetics (EMLA)represents the first major breakthrough fordermal anesthesia on intact skin.

It consists of 25 mg per mL of lidocaine, 25 mg

per mL of prilocaine, a thickener, an emulsifier,and distilled water adjusted to a pH level of 9.4.3


24/26


25/26

EMLA is applied in a thick layer (1 to 2 g per 10cm2, up to a maximal dose of 10 g) to intactskin.8After application, the area is covered with apatch of Tegaderm or clear plastic wrap tofacilitate penetration through the stratum

corneum (Figure 1). Depth of anesthesia dependson contact time with EMLA. Anesthetic effect hasbeen shown to reach a maximal depth of 3 mmafter a 60-minute application, and 5 mm after a120-minute application.9It was also found thatdermal analgesia continues and may evenincrease for 30 to 60 minutes after the cream isremoved.9EMLA should not be applied to thepalms and soles because of variable penetration.


26/26

EMLA has been associated with occasional adversereactions, including blanching and redness at theapplication site.8,12Perhaps the most seriouscomplication is methemoglobinemia. Cases ofmethemoglobinemia have occurred in infants

younger than three months of age who were exposedto high doses of EMLA for prolonged periods.8Sincethen, other studies have demonstrated that 1 g ofEMLA applied to the penis for one hour is safe to usein healthy, full-term neonates before

circumcision.13,14

Although using EMLA is better thanusing no anesthesia at all, the dorsal penile nerveblock still offers superior analgesia beforecircumcision, and the methods may be combined.13

Local Anaesthetics.ppt

Documents

Transcript of Local Anaesthetics.ppt