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DIFFERENCE BETWEEN GENERAL
ANAESTHESIA & LOCAL ANAESTHESIA
FEATURES Gen.Anaesthsia Local Anaesthsia
Site of action CNS Peripheral nerves
Area of body involved Whole body Restricted area
Consciousness Lost Unaltered
Care of vital functions Essential Usually not needed
Poor health patients Risky Safer
Use in non cooperative
Possible Not possible
Major surgery Preferred Cannot be preferred
Minor surgery Not preferred preferred
DEFINITION: are drugs which, when
applied directly to peripheral nervous
tissue, block the nerve conduction and
abolish all sensations in the part supplied
by the nerve without loss of consciousness.
500’s B.C Coca leaves first used by Peruvians
for psychotropic properties
Cocaine –first discovered in 19 th century-
local anasthetic action
Andean natives –chewed extract of leaves-
stimulatory &euphoric action
1850’s Cocaine isolated, hypodermic needle
Albert niemann-isolated -1860
1884 Sigmund Freud studies the effects of
cocaine it was used as ocular anasthetic
1884 Carl Koller introduces cocaine into
1884 Local anesthesia- used in dentistry by
Halsted and Hall
1905 Procaine synthesized by Einhorn
FEATURES OF LOCAL
Should have quick onset of action
Should not be irritating to skin & mucous membranes
Duration of action must be long enough to allow desired
surgery to be completed
Should be effective on both injection & local application
Should have low Systemic toxicity
Should not cause any permanent damage on any
Should be relatively free from producing allergic
Should be stable in solution and readily undergo
No LA in use today satisfy all of these criteria ,
however all anesthetics do meet a majority of
All local anesthetics are weak bases, they have
Consist of hydrophilic secondary or tertiary amine on
Lipophilic aromatic residue on other side
Two are joined by an alkyl chain through an ester or
cocaine, procaine, tetracaine, and chloroprocaine.
hydrolyzed in plasma by pseudo-cholinesterase.
lidocaine, mepivicaine, prilocaine, bupivacaine, and
metabolized in the liver to inactive agents.
True allergic reactions are rare (especially with
ADVANTAGE OF AMIDE LAs OVER
Produce more intense and longer lasting
Bind to α1 acid glycoprotein in plasma.
Not hydrolysed by plasma esterases.
Rarely causes hypersensitivity reaction.
1. INJECTABLE ANAESTHETIC:
LOW POTENCY, SHORT DURATION
INTERMEDIATE POTENCY AND DURATION
HIGH POTENCY, LONG DURATION
MECHANISM OF ACTION OF LAs
LA blocks the nerve conduction by reducing entry
of Na+ through the voltage gated channels
Due to this, they block the initiation & propagation
of nerve impulse.
At higher doses it also blocks
1. Voltage gated Ca2+
Vasoconstrictor used – adrenaline (1:50,000 to
prolongs duration of action of LAs by decreasing rate of
removal from local site into circulation
Enhances intensity of nerve block
Reduces systemic toxicity of LAs
Provides more bloodless field for surgery
Order of sensory function block
5. deep pressure
If applied to the tongue, bitter taste is lost
first followed by sweet & sour and salty taste
last of all
Recovery in reverse order
CNS: All LAs are capable of producing a sequence
of stimulation followed by depression
CVS: LAs are cardiac depressants, but no
significant effects are observed at conventional
doses. But at high doses they decrease
automaticity, excitability, contractility,
BLOOD VESSELS: LAs tend to produce fall in BP.
This is primarily due to sympathetic blockade, but
higher doses cause direct relaxation of arteriolar
SYSTEMIC TOXICITIES OF LOCAL
Central Nervous System Toxicities:
- Excitement: Tremors, shivering, and convulsions
characterize the CNS excitement.
- Depression: respiratory depression at higher doses
CVS derangement— High plasma titers may depress
the cardiovascular system directly.
Blood pressure may fall because of arteriolar dilation,
myocardial depression, and/or cardiac conduction
Treatment includes patient positioning, IV fluids, and
Haemotological: large dose of prilocaine->10mg/Kg-
Acumalation of it’s metabolite- o toludine-oxidises
haemoglobin to methehaemoglobin Patient –
cyanosed , blood –choclate colouerd –decompensate
in patients with preexisting cardiac /res. Disease
Treatment: I.V methylene blue /ascorbic acid-a
reducing agent – convert methhemoglobin to Hb
Hypersensitivity: Some patients are
hypersensitive (allergic) to some local anesthetics.
There are two basic types of local anesthetics
(the amide type and the ester type). A patient who
is allergic to one type may or may not be allergic
to the other type.
Local anesthetics are absorbed when ingested.
Some local anesthetics may be absorbed in
toxic amounts after topical use.
Absorption after an injection depends on drug
solubility in lipid and in water, tissue vascularity
and local anesthetic and vasoconstrictor
effects on local circulation.
Distribution: amides-wide distribution –I.V-lipophilics
taken up by highly perfused organs-then moderately
Ester type- short plasma half life
Metabolism and excretion
Esters are hydrolyzed by plasma and liver esterases.
Longer-acting esters are often metabolized more
slowly.. Patients with altered pseudo-cholinesterase
activity may be highly sensitive to these drugs.
Amides are metabolized in the liver by cyp450.-N-
dealkylation then hydrolysis except prilocaine-
hydrolysis first-o toludine-can cause
Patients with severe hepatic damage or advanced
congestive heart failure may be unusually sensitive to
Some amides are partially excreted unchanged in the
Acidification can enhance excretion
PK properties of amide LAs :
PRECAUTIONS AND INTERACTIONS
Aspirate lightly to avoid intravascular injection.
Inject the LA slowly &take care not to exceed the
maximum safe dose, especially in children.
Propranolol may reduce metabolism of lidocaine and
other amide LAs by reducing hepatic blood flow.
Vasoconstrictor (Adr) containing LA should be
avoided for patients with ischemic heart disease,
cardiac arrhythmia, uncontrolled hypertension those
receiving β-blockers or tricyclic antidepressants
Application of a local anesthetic to nose, mouth, throat,
tracheobronchial tree, esophagus.
Onset & duration depends on the site, the drug, its
concentration and form.
Absorption of soluble LAs from mucous membrane is
Except for eutectic lidocaineprilocaine , no other
LA is capable of anaesthetizing intact skin.
used to relieve itching, burning, and surface pain
(for example, as seen in minor sunburns).
Injection of LA directly into tissue under the skin.
used primarily for surgical procedures.
LAs most frequently used are lidocaine (1%), bupivacaine
(0.25%), etidocaine(0.5-1%), ropivacaine(0.5-1%),
mepivacaine(1-3%) and prilocaine(1-4%).
mix with adrenaline (1:20000) to prolong the action.
Injected around nerve trunks so that area distal to
injection is anaesthetised and paralyzed.
- Choice of LA and concentration is mainly determined
by the required duration of action.
- Lidocaine for intermediate duration of action
- longer lasting anesthesia bupivacaine may be
- produced by injecting the LA subcutaneously in the
surrounding area of nerve so that all nerves coming
to particular field are blocked.
- herniorrhaphy, appendicectomy, dental procedures,
scalp stitching, operations on forearms and legs etc.
- Larger area can be anaesthetized with lesser drug
compared to infiltration.
local anesthetic is injected around a nerve that leads to
the operative site.
Usually more concentrated forms of local anesthetic
solutions are used
eg: radial nerve block, ulner nerve block so on.
Nerve block lasts than field block or infiltration
Lidocaine (1.5%), mepivacaine(1.5%), bupivacaine (0.25-
0.35%) can be used.
spinal dural space is filled with semi liquid fat through
which nerve root travel.
Injected in this space- acts primarily on nerve roots
and small amounts permeates through intravertebral
foramina to produce multiple paravertebral blocks.
used to produce analgesia or anaesthesia in surgical
Divided into 3 categories depending on site of action:
Injected into the subarachnoid space between L2-3 or
L3-4 of the spinal cord .
Suitable LA like lidocaine (3-5%), bupivacaine (0.5-
Primary site of action is cauda equina rather than
Used to anaesthetize lower abdomen and hind limbs.
Use of hyperbaric(in7.5-10% glucose) or hypobaric (in
distilled water) solution of LA .
proper positioning of the patient is also limiting the
block to the desired level.
Advantages over general anaesthesia are:
Produces good analgesia and muscle relaxation without
loss of consciousness.
Cardiac, pulmonary, renal disease and diabetic pose
complication of spinal anaesthesia:
Cauda equina syndrome
Hypotension & hypovolemia
Infant & childrens- control of level is difficult
Vertebral abnormalities - kyphosis
Also referred as Bier’s block & used for upper limb and
Regional analgesia produced within 2-5min and last till 5-
Only ¼ of the injected drug enters systemic circulation
when tourniquet is removed.
Bradycardia can occur and bupivacaine should not be
used because of higher cardio toxicity.