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