1. General Anesthesia
Dr. Israa

2. General anesthesia
General anesthesia was not known until the mid-1800’s
Diethylether was the first general anesthetic used for surgery
General Anesthetics are divided into two classes:
Inhaled anesthetics (usually halogenated compounds)
Intravenous anesthetics or induction agents

3. Modern Anesthesia It combines the following: Analgesia
Sleep (loss of consciousness)
Skeletal Muscle relaxation
Amnesia
Abolition sensory & autonomic reflexes
No single drug can produce all these effects

4. (No single drug can produce all these effects)
Ideal anesthesia
Ideal anesthesia is:
Induce loss of consciousness smoothly and rapidly
Allow for prompt recovery of cognitive function after its administration is discontinued
Possess wide margin of safety
Have no side effects
(No single drug can produce all these effects)

5. Stages of anesthesia Stage 1:analgesia
Decreased pain awareness, sometimes with amnesia, conscious may be impaired but not lost
Stage 2:disinhibition
Delirium, excitation, amnesia, enhanced reflexes, irregular respiration and incontinence

6. Stages of anesthesia Stage 3: surgical anesthesia
Unconsciousness, no pain reflex, regular respiration and maintained blood pressure
Stage 4:medullary depression
Severe CVS and respiratory depression and the patient require pharmacological and ventilatory support

7. Anesthesia protocols
For minor procedure, conscious sedation techniques that combine IV agent with local anesthetics are often used; these can provide profound analgesia, with retention of the patient ability to maintain a patent airway and response to verbal commands
For extensive surgical procedure protocol commonly includes IV drug for induction, inhaled agent (with or without IV) for maintenance and neuromuscular junction blockers to cause muscle relaxation

8. General Anesthetics
Absence of sensation associated with a reversible loss of consciousness, skeletal muscle relaxation, and loss of reflexes.
Drugs used for anesthesia are CNS depressants with action that can be induced and terminated more rabidly than conventional sedative and hypnotics

9. General Anesthetics
Most sensitive site of action for general anesthetics is the reticular activating system of the brainstem (RAS)
Anesthetic dose: does not cause depression of cardiac, vasomotor or respiratory centers
Has a small margin of safety

10. 1. Inhaled Anesthetics Include: Nitrous oxide Halothane Enflurane
Isoflurane
Desflurane

11. 2. Intravenous Anesthetics
Include:
Barbiturates
Thiopental & Methohexital
Opioids
Alfentanil, Meperidine, Fentanyl, Sufentanil (agonists)
Naloxone (antagonist)
Benzodiazepines
Diazepam, Midazolam
Flumazenil (antagonist)

12. Intravenous Anesthetics
Miscellaneous Agents
Etomidate: non-barbiturate hypnotic agent without analgesic properties
Droperidol: Neuroleptic (similar to Haloperidol) combined with Fentanyl and is used for neuroleptanalgesia (state of analgesia and amnesia)
Ketamine: dissociative anesthetic
Propofol

13. Intravenous agents Mechanism of action: Act at cell surface receptors:
Barbiturates and benzodiazepine act at GABA-A receptors to increase Cl- influx
Opioids act on μ and other subtypes
Ketamine antagonizes PCP site on NMDA receptors (prevent excitation)

14. Intravenous agents Pharmacokinetics Rapid induction = shorter acting
Duration of effect proportional to redistribution from brain to other tissue

15. A. Barbiturates: Thiopentone
Ultra-short acting hypnotic with no analgesic action
High lipid solubility promotes rapid entry to the brain
Eliminated by the liver
Has rapid onset of action and recovery
Mechanism of action:
Potentiates GABA, decrease glutamate activity, increase chloride ion conductance
Adverse reactions:
Decreased myocardial and respiratory activity

16. B.OPIOIDS Morphine and fentanyl are used in anesthesia regimens.
Respiratory depression due to these drugs may be reversed by naloxone.

17. C. Benzodiazepines
Midazolam is widely used adjunctive with inhaled anesthetics and IV opioids
It has slow onset and longer duration of action if compared to thiopental.
Flumazenil is an antidote if respiratory depression occur.

18. D. Miscellaneous Agents
1. Etomidate
Imidazole derivative that provide induction with minimal change in cardiac function and respiratory rate and has short duration of action
It is not analgesic , and its primary advantage is in anesthesia for patient with limited respiratory and cardiac reserve
Activates GABA receptors
Side effects
Myoclonus
Post-operative nausea and vomiting
Adrenal suppression if prolonged use.

19. 2. Ketamine
This drug produce dissociative state in which the patient is patient remains conscious but has marked catatonia, analgesia, and amnesia
It is a chemical congener of the psychotomimetic agent, phencyclidine (PCP)
It is a cardiovascular stimulant drug
Can cause increase intracranial pressure
Emergency reactions include disorientation, excitation and hallucination which can be reduced by preoperative administration of benzodiazepines

20. Uses
Induction of anesthesia
in children
in severely hypovolemic patients
Contraindications
Increased intracranial pressure
Ischemic heart disease
Psychological disorders

21. 3.Propofol
Effects
Hypnosis , Antiemetic
Fast acting, short duration.
Fewer peripheral side effects compared to barbiturates
Uses
Induction and maintenance of anesthesia
As anesthetic agent at outpatient surgery
Also effective in producing prolong sedation in patient in critical care setting
Contraindications
Cardiovascular instability due to marked reduction in the peripheral resistance

22. Preanaesthetic Medication

23. GOOD LUCK