Local Anesthesia

1. LOCAL ANESTHESIA
YUZBASHEVA NIHAL 221B

2. Introduction and History
 Cocaine is a naturally occurring compound
indigenous to the Andes Mountains, West Indies,
and Java.
 It was the first anesthetic to be discovered and is
the only naturally occurring local anesthetic; all
others are synthetically derived.
 Cocaine was introduced into Europe in the 1800s
following its isolation from coca beans. Sigmund
Freud, the noted Austrian psychoanalyst, used
cocaine on his patients and became addicted
through self-experimentation.

3.  In the 1880s, Koller introduced cocaine to the field
of ophthalmology, and Hall introduced it to
dentistry.
 Halsted was the first to report the use of cocaine
for nerve blocks, in the United States in 1885, and
also became addicted to the drug through self-
experimentation.
 Procaine, the first synthetic derivative of cocaine,
was developed in 1904.
 Lofgren later developed lidocaine, the most
widely used cocaine derivative, in 1943, during
World War II.

4. Mechanism of Action
 Local anesthetics produce anesthesia by
inhibiting excitation of nerve endings or by
blocking conduction in peripheral nerves.
 This is achieved by anesthetics reversibly
binding to and inactivating sodium channels.
 The open state of the sodium channel is the
primary target of local anesthetic molecules.

6. Chemical Structure
 All local anesthetics have an intermediate chain
linking an amine on one end to an aromatic ring
on the other.
 The amine end is hydrophilic, and the aromatic
end is lipophilic.
 Variation of the amine or aromatic ends changes
the chemical activity of the drug.

7.  Two basic classes of local anesthetics exist:
-the amino amides
-amino esters.
 Amino amides have an amide link between
the intermediate chain and the aromatic end,
whereas amino esters have an ester link
between the intermediate chain and the
aromatic end.

8.  Amino esters and amino amides differ in
several respects:
- Amino esters are metabolized in the plasma
via pseudocholinesterases, whereas amino
amides are metabolized in the liver
- Amino esters are unstable in solution, but
amino amides are very stable in solution.
- Amino esters are much more likely than amino
amides to cause allergic hypersensitivity
reactions.

9.  Commonly used amino amides
include: lidocaine, mepivacaine, prilocaine, bupi
vacaine, etidocaine, and ropivacaine and
levobupivacaine.
 Commonly used amino esters include: cocaine,
procaine, tetracaine, chloroprocaine,
and benzocaine.
 An easy way to remember which drug belongs
in which category is that all of the amino amides
contain the letter "i" twice, as does the term
"amino amides."

10.  More recently, DepoFoam technology (Pacira
Pharmaceuticals, Inc; San Diego, Calif) has
been utilized to create liposomal bupivacaine
(Exparel), a longer-acting form of bupivacaine
in which the anesthetic is delivered via a
multivesicular liposomal system.

11.  Physiologic activity of local anesthetics is a
function of their:
- lipid solubility
- diffusibility
- affinity for protein binding
- percent ionization at physiologic pH
- and vasodilating properties.

12. Administration of Local
Anesthetics
 For proper administration of local anesthetics,
consider:
- the individual characteristics of the patient
- dose of local anesthetic to be administered,
presence or absence of epinephrine
- speed of administration
- local tissue vascularity
- technique of administration.

13. In each case, physicians should
strive to find the smallest dose
possible administered over the
longest period of time that
achieves adequate anesthesia.
Dosages are presented in the
table below.

14.  The surgeon should calculate the maximum
tolerable dose by giving consideration to the
dose to be used, patient weight, and any history
of heart disease.
 Although the anesthesiologist is a useful person
to consult regarding maximum dose allowable in
a particular patient, ultimately, the responsibility
of deciding what dose is safe and taking care
not to exceed that dose lies with the surgeon.

15.  Dilution of the concentration of local anesthetic
may aid in decreasing the total dose required to
establish adequate anesthesia
 . Commercial preparations of local anesthetics are
typically provided in bottles of 1% or 2%
concentrations.
 These concentrations are higher than those
required to produce the desired effect in most
individuals.
 By diluting the solution with sterile injectable
saline, the surgeon can decrease concentration to
0.25%, 0.5%, or other concentrations.
 This provides additional volume for injection over
a larger operative field without increasing the total
dose administered.

16.  Addition of epinephrine to the local anesthetic
solution may improve safety and allow
administration of lower doses of local
anesthetic.
 Epinephrine induces vasoconstriction,
delaying absorption of the local anesthetic for
longer duration of action at the site of injection.
 By delaying absorption, epinephrine also
increases the safe dose of local anesthetic that
may be administered.

17.  Addition of epinephrine also improves
hemostasis of the operative field, which may
decrease duration of the operation and thus
obviate the need for prolonged local anesthetic
effect.
 This can help avoid the need for subsequent
injection if local anesthetic begins to wear off
as surgery proceeds.

18.  Epinephrine has been demonstrated to cause
effective vasoconstriction at concentrations as
small as 1:1,000,000, although most surgeons
use a concentration of 1:100,000 to 1:400,000,
which is available in commercial preparations.
 Lower concentrations of epinephrine require
longer to achieve maximal effect.
 Thus, when using dilute concentrations of
epinephrine, the surgeon should wait longer
between injection and incision than when using
solutions containing higher concentrations of

19.  Epinephrine has its own toxicities and should be
used with caution in certain patients.
 Cardiac arrhythmias may be produced in patients
with heart disease or with the concomitant use of
halothane anesthesia.
 Hypertension may develop in patients with a
preexisting history of hypertension or with
hyperthyroidism.
 In some cases, hypertension may be severe and
actually trigger a hypertensive crisis.

20.  Speed of administration is also important
because toxicity develops as a result of peak
serum concentration.
 When multiple areas are to be anesthetized with
local anesthetic, inject each site sequentially
rather than all at once at the beginning of the
procedure.
 If an area will not be operated on at the
beginning of the procedure, wait to inject it until
ready to extend the procedure to that site.

21.  Tissue vascularity is another important
consideration. Nasal mucosa, oral mucosa, the
scalp, and the skin of the head and neck have a
tremendous blood supply.
 This leads to rapid absorption of local
anesthetics into the serum, which may
precipitate an adverse reaction.
 When working in these areas, inject the area
more slowly and wait longer between injections.

22.  Technique of injection is important for safety
reasons and for patient comfort.
 Always aspirate before injecting. This prevents
inadvertent direct intravascular injection of the
local anesthetic, which leads to an abrupt rise
in serum levels and may precipitate an
adverse reaction.
 Using the smallest needle possible decreases
the pain of injection.

23. Thanks For
Your
Attention!