Transcript /local anesthesia

LOCAL ANESTHETIC AGENTS
History of local anesthesia
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1500’s Accounts referring to Peruvian Indians chewing on
leaves of the coco plant are found
1884 Cark Koller demonstrated the usefulness of the
extract from these leaves[cocaine]as a topical anesthetic
for the eyes, and earned distinction as the “father of local
anesthesia
1884 Willium Halsted used cocaine in the first nerve
block [ Inferior alveolar nerve block]. The use of cocaine
for anesthesia produced several unwanted side effects
including cardiac problem and addiction
1885 James Corning demonstrated the use of a tourniquet
to slow absorption of cocaine
History of local anesthesia
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1901 Heinrich Braun demonstrated the use of epinephrine
to retard local anesthetic absorption from the site of
injection
1904 Alfred Einhorn introduced procaine . Epinephrine
was needed to constrict the vessels in the area of
administration to lengthen the duration of anesthesia. It
was common to see a 1:50,000 concentration for many
years
1943 Nils Lofgren introduced lidocaine
1947 Novocol company made the dental aspirating
syringe available
1959 Disposable sterile needles made available by CookWaite, Roehr Company
Physiology of nerve conduction
Sodium-potassium Pump
Channel Entry
Local anesthetics:
amides vs. esters
Classification of local anesthetics
Amides
Ester
Bupivacaine
Benzocaine
Lidocaine
Cocaine
Mepivacaine
Procaine
Prilocaine
Absorption
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Site of injection
The dose of local anesthetic
Physicochemical properties of local
anesthetic
The addition of epinephrine
Distribution
Site of injection
Systemic absorption
heart
brain
Skeletal muscle
Biotransformation and Elimination
Aminoester
Aminoamide
Plasma esterase
Hepatic enzyme
Renal excretion
สภาพของผูป้ ่ วยกับการขับถ่ายยา
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อายุ – ผูป้ ่ วยสูงอายุขบั ถ่ายยาได้ชา้ ลง
โรคตับ – ทาให้ half life ของยานานขึ้น
cardiac output –ถ้ามี cardiac output ต่า จะขับถ่าย
ยาได้ชา้ ลง
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Potency: lipid solubility
Onset : pKa, concentration of local
anesthetic
What is pKa?
pKa = pH + log[ RNH+ ]
[RN]
(modified Henderson- Hasselbalch equation)
pKa is the dissociation constant, represents the
pH at which the concentration of the
ionized base(RNH+) and the non-ionized
base (RN) are equal.
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RNH+
RN +
H+
Outside membrane
Inside membrane
•RNH+
RN
+
H+
Anesthetic
pKa %RN at pH 7.4
Onset [min]
Mepivacaine
7.6
40
2-4
Etidocaine
7.7
33
2-4
Articaine
7.8
29
2-4
Lidocaine
7.9
25
2-4
Prilocaine
7.9
25
2-4
Bupivacaine
8.1
18
5-8
Procaine
9.1
2
14-18
Example at physiologic pH (7.4)
pKa
onset
Lidocaine
Procaine
7.9
3:1 ionized to
non-ionized
2 to 3 minutes
8.9
32:1, ionized to
non-ionized
6 to 12 minutes
if lidocaine (pKa 7.9) is administered into an area of
infection (pH 4.9) resulting 1,000:1 ionized to nonionized indicates a poorer penetration into the nerve
tissue and therefore a less effective nerve block
Quinn and Malamed (1990) and Haegerstam
(1990) suggested of administer L.A.
AWAY from the area of inflammation
(nerve block) especially in the area of
EXTENSIVE CELLULITIS
Malamed. Handbook of LOCAL ANESTHESIA 1990.
Haegerstam, Introduction to Dental Local anesthesia
1990.
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Duration of action
Differential sensory/ motor blockade
Adverse reaction
Clinical use of local anesthesia
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Topical anesthesia
Infiltration
Peripheral nerve block
Epidural block
Spinal block
Intravenous regional anesthesia
Clinical sign
and symptom
LA toxicity
CNS toxicity
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Potency
The rate of intravenus administration
Acid base status and PaCO2
Cardiovascular toxicity
CC/CNS Ratio
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i.e. the ratio of the LA dosage required
for irreversible cardiovascular collapse
and the dosage that produces CNS
toxicity (convulsions)
the higher the CC/CNS ratio the better
the safety margin
Prevention
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Aspiration before injection
Inject slowly
Use smallest quantity of solution and
lowest concentration of vasoconstrictor
Observe the patient after injection
Choose another anesthetic if the patient has
tendency for allergic reaction
The signs and symptoms of allergic
reaction include:
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generalized body rash or skin redness
itching, urticaria (hives)
bronchospasm (difficulty breathing)
swelling of the throat
asthma
abdominal cramping
irregular heartbeat
hypotension (low blood pressure)
swelling of the face and lips
(angioneurotic edema)
Adverse reactions of commonly used
local anesthetics
 Methemoglobinemia
associated with prilocaine, articaine,
benzocaine
 Local tissue toxicity
Receptor
Alpha stimulation
Beta 1 stimulation
Response
Vasoconstriction
Peripheral resistance
Heart rate
Force of cardiac
contraction
Beta 2 stimulation
Cardiac output
Vasodilatation
Bronchodilation
Coronary blood flow
Adverse reactions of vasopressor
drugs
Signs
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Elevated BP, HR
Symptoms
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Fear
Anxiety
Restlessness
Throbbing headache
Tremor
Dizziness
Pallor
Respiratory difficulty
Palpitations
Contraindication for Epinephrine
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Blood pressure over 200 torr systolic or 115 torr diastolic
Uncontrolled hypertension
Severe cardiovascular disease including less than 6
months after a myocardial infarction or cerebrovascular
accident
Daily episodes of angina pectoris or unstable angina
Cardiac dysrhythmias despite appropriate therapy
Medicated with beta blocker,monoamine oxidase inhibitor
, or tricyclic antidepressant; or general anesthesia with a
halogenated anesthetic like halothane
New York Heart Association :
แนะนำว่ ำควรใช้ epinephrine ในขนำด 3 ug. / kg. Body
weight แต่ ไม่ ควรเกิน 0.2 mg. (200 µg)
หำกผู้ป่วยมีปัญหำเกีย่ วกับ โรคควำมดันโลหิตสู ง
โรคหัวใจ ให้ ใช้ Epinephrine ในขนำด 40 ug และสู งสุ ด ไม่ ควร
เกิน 54 µg ต่ อกำรฉีดยำครั้งหนึ่ง
วิธีคานวณปริ มาณของ Epinephrine
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Epinephrine ขนาด 1 : 200,000
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1 gm / 200,000 ml
1,000 mg / 200,000 ml
1 mg / 200 ml
0.005 mg / 1 ml
ผูป้ ่ วยเด็กอายุ 2 ปี หนัก 12 กิโลกรัม
หกล้มมีแผลฉีกขาดที่นิ้ว
ต้องเย็บแผล ควรใช้ยาชาชนิดใด
ปริ มาณและความเข้มข้นเท่าไร
ผูป้ ่ วยชายอายุ 25 ปี น้ าหนัก 60 กิโลกรัม
ไม่มีโรคประจาตัว
บอกวิธีการให้ยาชาและปริ มาณยาที่ใช้กบั
ผูป้ ่ วย