Transcript 6-General anesthesia..

GENERAL ANESTHESIA
BY
P R O F. D R . Y I E L D E Z B A S S I O U N I
What is meant by general
Anesthesia?
General anesthesia
is a controlled
reversible state of:
1. Loss of sensation
(analgesia)
2. Loss of consciousness
3. Skeletal muscle
relaxation(in some not needed for
all surgery)
AIM OF ANESTHESIA
 Facilitates
surgery
Not therapeutic
or diagnostic
‫غير عالجية أو‬
‫تشخيصية‬
STAGES OF GENERAL
ANESTHESIA
Stage 1: Analgesia ‫فقدان األلم‬
Loss of sensation but patient is still alert and speaking
 Stage 2: Excitement ‫إثارة‬
CNS excitation+  BP (irregular) +  respiratory rate
 Stage 3: Surgical Anesthesia ‫التخدير الجراحي‬
Regular respiration + relaxed skeletal muscles + eye
movement stops and pupil is fixed
 Stage 4: Coma→→→ death
MECHANISM OF ACTION
Anesthetic agents may enhance action
of inhibitory neurotrasmitters such as
GABA and glycine as well as blocking
excitatory NTM actions such as
glutamic acid
It is suggested that incorporation of
the anesthetic drug into cell membrane
phospholipids alters cell
membrane fluidity
Pre-anesthetic medications
These are drugs used to facilitate
smooth induction of anesthesia and
help to lower the dose and side
effects of anesthetic drugs
Reduce postoperative pain
Provide amnesia, decrease anxiety
Decrease secretions(
give antichlinergic due to vagal
stimulation --- bradycardia ----- increase secretions)
Pre-anesthetic medications
1.Sedative hypnotics: BZs or barbiturates
2.Antihistaminics: H1 (anti-allergic) and H2
blockers (to reduce gastric acidity)
3.Anti-emetics: metoclopramide
4.Opioid analgesics: morphine or
pethidine
5.
Anti-cholinergics: scopolamine
Muscle relaxant , drugs to potentiate anesthesia action  adjuvants given
anesthesia
Classification of general
anesthetic agents:
2) IV anesthetic
drugs
1) Inhaled volatile
agents
IV anesthetic
drugs
• The term intravenous anesthetic agents
means inducing anesthesia by drugs
administered intravenously.
 Unbound, lipid soluble, unionized
molecules cross the blood brain barrier the
quickest.
Advantages of IV anesthesia include:
• rapid and smooth induction of anesthesia
• little equipment requirement (syringes,
needles, catheters)
• easy administration of drugs
PROPERTIES OF THE IDEAL INTRAVENOUS ANAESTHETIC AGENT
o quick and smooth induction and recovery
o high therapeutic index
o no toxic metabolites & no emetic effects
o No involuntary movements
No emergence nightmares,
No hang over effect
o potent, so small volume is required for anesthetic
induction/maintenance
o compatible with other dugs ( muscle relaxants)
o no cardiopulmonary depression , no pain on injection
O No histamine release/hypersensitivity reactions
INTRAVENOUS ANESTHETICS
1- Ultra- short acting barbituates
-thiopental (Pentothal)
-methohexital (Brevital)
2- Benzodiazepines (adjuvant )
-diazepam (Valium)
-lorazepam (Ativan)
-midazolam (Versed)
3- Etomidate (Amidate)
4- Propofol (Diprivan)
INTRAVENOUS ANESTHETICS
5- Opioids
-fentanyl (Duragesic, Sublimaze)
-fentanyl- droperidol (neuroleptanalgesia)
-Morphine only with high doses, so not used
6- Dissociative anesthetics
-ketamine (Ketalar)
Sodium thiopental
(pentothal)
 An IV dose of 3-5 mg/kg results in loss of
consciousness ( 30-60 secs after
administration). This is called the “arm
brain” circulation time
 It has a short duration of action 5-10 min
due to its redistribution away from the brain
towards muscle and fat tissue
 If its concentration is low enough in the
brain, consciousness returns
 It does not provide adequate skeletal muscle
relaxation alone used in OB / GYN
Sodium thiopental (pentothal)
Disadvantages:
1- hypotension
2- respiratory depression: dose-dependent respiratory
depression
3- tissue necrosis :
following i.v. infusion
4- it does not provide analgesia
5- no skeletal muscle relaxation
6- laryngeal spasm
7- bronchospasm: unusual but may be
precipitated in asthmatics pts
Propofol (Diprivan® )
Advantages:
*High lipophilicity; rapid and smooth
onset and rapid recovery
*Minimal nausea and vomiting
* Amnestic and anti-emetic effects
Disadvantages:
 Not water soluble-- painful (50%)
 Dose – related Respiratory
depressant
PROPOFOL & CVS
 Myocardial depression
 Propofol causes the most marked fall in
blood pressure of all the induction
drugs. This is mainly due to systemic
vasodilatation.
 May be slight increase in heart rate.
 The fall in blood pressure is dosedependent and is most marked in the elderly
and in shocked patients.
Ketamine (Ketalar)
* Structurally similar to phencyclidine
* Dissociative anesthesia; the patient is
unconscious but appears awake and doesn’t
feel pain night mares + hallucination
* Ketamine causes stimulation of the CVS.
(increase HR, BP, CO)
* Good analgesic
• Ketamine acts by noncompetitive
antagonism at the N-methyl-D aspartate
(NMDA) receptor in the brain and spinal
cord.
Ketamine: advantages
1-Ketamine is a potent bronchodilator
can be used as in asthmatic patients
2- Potent analgesic in sub-anesthetic
doses
3- can be administered i.v., i.m., orally,
nasally, rectally, and epidurally.
4- Suitable for shocked patients??
Ketamine: Disadvantages
1- The onset of action is slower than other induction
drugs
2- ketamine increases cerebral blood flow, and
intracranial pressure. Emergence can produce
hallucination and unpleasant dreams (15 % esp. females &
large dose of ketamine) usually be avoided by
concomitant application of a sedative such as a BZ.
3- Generalized increase in the muscle tone and
purposeful movements
4- It produces central sympathetic stimulation, which
increases: arterial blood pressure, heart rate, and
cardiac output
Thiopental
1. IV barbiturate
2. Rapid induction
3. Short duration
4. Potent anesthetic but
not analgesic
Ketamine
Propofol
1. Slower onset &
1. Rapid induction, rapid
recovery
2. dissociative
anesthesia
pleasant recovery
2. No emesis
3. amnestic effect
3. Good analgesia
4. Bronchodilator
1. No analgesia
2. Little Sk.m. relaxation
1.  sympathetic
outflow
3.  BP & bradycardia
2.  cerebral blood
4. Laryngospasm, apnea,
flow; postoperative
cough, bronchospasm
Hallucination, night
mares
1. No analgesic action
2. Pain at injection site
3. Dose-related respiratory
depression,
4. bradycardia, and
hypotension
Benzodiazepines
They are used as adjuvant IV anesthetic
agents for the following :
1 – amnesia
2 – minimal cardiac & respiratory
depressant effect
3 – anticonvulsant activity
4 – low incidence of tolerance and
dependence
5- availability of antagonist ‘ flumazenil’
Etomidate
 is a short acting iv anaesthetic agent used
for the induction of general anesthesia
 for sedation for short procedures such as
reduction of dislocated joints, tracheal
intubation
 Rapid onset of action, usually within one
minute. Duration of action 3-5 min.
 Etomidate causes the least cardiovascular
depression of the IV anaesthetics
Etomidate: Disadvantages
Adrenal suppression: It supresses corticosteroid synthesis in the adrenal cortex
(Reduced cortisol plasma levels)
Do not use etomidate for critically ill patients
( increased mortality).
Post operative vomiting is more common than
with other induction agents.
Pain on injection is common and there is a
high rate of thrombophlebitis
Etomidate has no analgesic activity
Inhalational
Anesthetics
Inhalational Anesthetics
Inhalational anesthesia refers to delivery
of gases or vapors via the respiratory
system to produce anesthesia
1- Gases like :Nitrous Oxide (N2O)
prohibitedcyclopropane flammable and xenonexpensive by
flowmeters
2-Volatile liquids are vaporized in a carrier
gas (vaporizers). e.g. halothane,
isoflurane, desflurane and sevoflurane
O2 is
bubbled in
volatile
Anesth.
agnet
blood
Mixture
vapor
Diffuse across
alveolar
capillary
membrane
Anesthetic
machine
Lungs
Brain
Ideal Characteristics
1. pleasant to inhale, permitting a smooth induction
and recovery
2. potent to allow the concomitant administration of
high oxygen
3. Rapid induction and recovery (low solubility)
4. easily and cheaply prepared in a pure form
5. No CV or respiratory effects, non-toxic to organ
systems
6. safe for exposure to operating room staff
7. not flammable, not metabolized. And nvironmentally
safe
8. being liquid at room temperature, but evaporating
easily for administration by inhalation
Rate of induction and recovery
Depends on
Blood/Gas partition coefficient
is the ratio of anesthetic concentration
in blood compared to gas phase.
Solubility in blood:
•More soluble = slower induction (slow
onset) e.g. Halothane slower recovery
•Less soluble = faster induction faster
recovery
e.g. Nitrous oxide
If drug is slow induction
Means good solubility in
blood
MINIMUM ALVEOLAR
CONCENTRATION (MAC)
Anesthetic potency is measured
in MAC. It allows us to compare
the potency of the various
inhalational agents
MAC is defined as the
concentration of anesthetic
that is required to produce
immobility in 50% of patients
exposed to a noxious stimulus
(surgical incision)
MAC VALUE
Halothane = 0.75%
Isoflurane = 1.16%
Euflurane = 1.68%
Sevoflurane = 2%
N2O = 105% fastest onset & recovery because
not soluble
# Halothane is the most potent
# N2O alone is unable to produce
adequate anesthesia ( require high
conc. ) weak  low potency
NITROUS OXIDE
Physical property:
*Colorless, odorless, and nonflammable,
laughing gas
Pharmacology
-Good analgesic
-Low solubility (fast on/off)
-Minimal effects on heart rate and BP
- Weak anesthetic- MAC = 105% (Low potency)
- it must be used as an adjunct anaesthetic,
along with other agents
HALOTHANE
Halogenated hydrocarbon
# Most potent inhalational anesthetic
(MAC=0.75%)
# has a pleasant, non-irritant smell
# bronchodilator
# drug of choice in children
# Slow induction & slow recovery
# Hepatotoxicity
# Myocardial depressant
# Sensitizes myocardium to effects of exogenous
catecholamines ( ventricular arrhythmias)
ISOFLURANE
Advantages
- Rapid induction and recovery
- Little risk of hepatic or renal
toxicity
- Cardiovascular stability
- Muscle relaxation
- Few side effects
Disadvantages
- Pungent odor  ‫ الذع‬cough, breath
holding
Halothane
Isoflurane
Nitrous oxide
1956
1984
1799
Potency
High
High
weak
Induction&
Slow
Rapid
Very rapid
1.  risk
No risk
No risk
No risk
No risk
-drug of choice
1. Good muscle
1. Rapid onset &
in
relaxation.
recovery
2. Rapid recovery
2. Good
recovery
Arrhythmia
2. sensitivity to
catecholamines
Hepatotoxicity
 risk
( not in children)
Therapeutic
advantages
children
- Good for
asthmatic
bronchodilataion
3. No
sensitization to
catecholamines
analgesia
SEVOFLURANE
Advantages
1. Well tolerated (non-irritant, sweet odor),
even at high concentrations, making this the
agent of choice for inhalational induction
2. Rapid induction and recovery
3. Does not sensitize the myocardium to
catecholamines as much as halothane
4. Bronchodilator
SEVOFLURANE
Disadvantages
1. Less potent than similar halogenated
agents
2. Risk of renal toxicity ( about 5% is
metabolized and serum fluoride level is
elevated)
Thank You