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GENERAL GENERAL ANESTHESIA ANESTHESIA
BYBY
PROF. DR. YIELDEZ BASSIOUNIPROF. DR. YIELDEZ BASSIOUNI
What is meant by What is meant by generalgeneral
Anesthesia? Anesthesia?
General General anesthesiaanesthesia is a controlled is a controlled reversible state reversible state of: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
أو عالجية غيرتشخيصية
STAGES OF GENERAL ANESTHESIA
Stage 1: Analgesia األلم فقدان
Loss of sensation but patient is still alert and speaking
Stage 2: Excitement إثارة
CNS excitation+ BP (irregular) + respiratory rate
Stage 3: Surgical Anesthesia الجراحي التخدير
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 painProvide amnesia, decrease anxietyDecrease 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: scopolamineMuscle relaxant , drugs to potentiate anesthesia action adjuvants given
anesthesia
Classification of general anesthetic agents:
2) IV 2) IV anesthetic anesthetic drugsdrugs
1)1)Inhaled Inhaled volatile volatile agentsagents
IV anesthetic IV anesthetic drugsdrugs
• 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 INTRA- VENOUS 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)
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
Sodium thiopental (pentothal)
Advantages:*High lipophilicity; rapid and
smooth onset and rapid recovery*Minimal nausea and vomiting* Amnestic and anti-emetic effectsDisadvantages:Not water soluble-- painful
(50%)Dose – related Respiratory
depressant
Propofol (Diprivan® )
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 dose-dependent and is most marked in the elderly and
in shocked patients.
* 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 (Ketalar)
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: advantages
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
Ketamine: Disadvantages
Thiopental Ketamine Propofol1. IV barbiturate
2. Rapid induction
3. Short duration
4. Potent anesthetic
but not analgesic
1. Slower onset &
recovery
2. dissociative
anesthesia
3. Good analgesia
4. Bronchodilator
1. Rapid induction,
rapid pleasant
recovery
2. No emesis
3. amnestic effect
1. No analgesia
2. Little Sk.m.
relaxation
3. BP & bradycardia
4. Laryngospasm,
apnea, cough,
bronchospasm
1. sympathetic
outflow
2. cerebral blood
flow;
postoperative
Hallucination,
night mares
1. No analgesic action
2. Pain at injection site
3. Dose-related
respiratory
depression,
4. bradycardia, and
hypotension
They are used as adjuvant IV anesthetic agents for the following :
1 – amnesia2 – minimal cardiac & respiratory depressant effect3 – anticonvulsant activity4 – low incidence of tolerance and dependence5- availability of antagonist ‘ flumazenil’
Benzodiazepines
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
Adrenal suppression: It supresses cortico- steroid 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
Etomidate: Disadvantages
Inhalational Anesthetics
Inhalational Anesthetics
Inhalational anesthesia refers to delivery of gases or vapors via the respiratory system to
produce anesthesia1- 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
Ideal Characteristics 1. pleasant to inhale, permitting a smooth induction and
recovery2. potent to allow the concomitant administration of high
oxygen3. Rapid induction and recovery (low solubility)4. easily and cheaply prepared in a pure form5. No CV or respiratory effects, non-toxic to organ systems6. safe for exposure to operating room staff7. not flammable, not metabolized. And nvironmentally
safe8. being liquid at room temperature, but evaporating
easily for administration by inhalation
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
Blood/Gas partition coefficient
Rate of induction and Rate of induction and recovery recovery
Depends onDepends on
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)
Advantages- Rapid induction and recovery- Little risk of hepatic or renal toxicity- Cardiovascular stability - Muscle relaxation- Few side effects
Disadvantages-Pungent odor الذع cough, breath holding
ISOFLURANE
Halothane
1956
Isoflurane
1984
Nitrous oxide
1799
Potency High High weak
Induction&
recovery
Slow Rapid Very rapid
Arrhythmia 1 . risk
2 .sensitivity to
catecholamines
No risk No risk
Hepatotoxicity risk
)not in children(
No risk No risk
Therapeutic
advantages
-drug of choice
in children
- Good for
asthmatic
bronchodilataion
1. Good muscle
relaxation.
2. Rapid recovery
3. No
sensitization to
catecholamines
1. Rapid onset &
recovery
2. Good
analgesia
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 recovery3. 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)
SEVOFLURANE
Thank You