1. General Anesthesia Part1
Practical conduct of
General Anesthesia Part1
Prepared by
Dr. Mahmoud Abdel-Khalek
Jan 2015

2. General Anesthesia
General Anesthesia is a pharmacologically induced reversible state of unconsciousness which is maintained despite the presence of noxious stimuli

3. General Anesthetics OR
General anesthetics are drugs which produce reversible loss of all sensations and consciousness. OR
General anesthetics are a class of drugs used to depress the CNS to a sufficient degree to permit the performance of surgery and other noxious or unpleasant procedures

4. Anesthetists Role of anesthetists
Preoperative evaluation and patient preparation
Intraoperative management
General anesthesia
Inhalation anesthesia
Total IV anesthesia
Regional Anesthesia& pain management
Spinal, epidural & caudal blocks
Peripheral never blocks
Pain management (acute and chronic pain)
Postanesthesia care (PACU management)
Management of Anesthesia Complications “

5. Goals of Anesthesia
All techniques strive to achieve the following goals, known as the “Four A’s of Anesthesia”:
Lack of Awareness: unconsciousness.
Amnesia: lack of memory of the event
Analgesia: the abolition of the subconscious reactions to pain, including somatic reflexes (movement or withdrawal) and autonomic reflexes (hypertension, tachycardia, sweating and tearing).
Akinesia: lack of overt movement. In some cases, the provision of muscle relaxation may be required.

6. Anesthesia with single or multi agents
In the past, general anesthesia was achieved using a single agent such as ether or chloroform. Because the above-described goals were achieved by a progressive depression of the central nervous system rather than by any direct or specific effect, relatively high concentrations of the gases were required. Consequently the associated side effects were frequent and severe. In current practice, we have many different agents (both intravenous and inhaled) at our disposal. The intravenous agents in particular have specific effects such as analgesia or muscle relaxation and therefore can be used to achieve the desired effect in a dose-related fashion.

7. Balanced Anesthesia
The practice of using combinations of agents, each for a specific purpose, is what is termed “balanced anesthesia”.
An example of a balanced technique would be the use of
Propofol for “induction”
Isoflurane and N2O for “Maintenance”
Fentanyl for “Analgesia”
Rocuronium for “muscle relaxation”

8. Benefits of Balanced Anesthesia
Balanced technique is still the most common technique used for the provision of general Anesthesia
Benefits of balanced technique as compared to “ether anesthesia” of the past include
improved hemodynamic stability
more effective muscle relaxation
More rapid return of respiratory functions, consciousness and airway control following the completion of the procedure
Recently the development of short acting IV agents such as propofol makes total intravenous anesthesia possible (TIVA)

9. Preparation for Anesthesia
The anesthetic machine must be tested before use for leaks, misconnections and proper function
The breathing system to be used should be new for each patient, or a new filter installed
The availability and function of all anesthetic equipment should be checked before starting
The anesthetist should be satisfied that the correct
operation is being performed upon the correct patient and that consent has been given
The patient must be on a tilting bed or trolley
the anesthetist should have a competent, trained assistant.

10. Equipment checking before anesthesia

11. Equipment checking before anesthesia

12. Before Starting What you should do?
Supervise a safe transfer of the patient from his bed to the operating room table
Place anesthetic record on the anesthesia clipboard
Check to make sure that all requested labs at the preoperative visit are there (e.g. Hb, ECG, etc.)
Attach monitors including an ECG, blood pressure cuff, and pulse oximeter to start with
Establish an intravenous line . Prepare your intravenous drugs before the patient arrives
Record the patients initial vital signs on the anesthesia record (Baseline vital signs)

13. Phases of Anesthesia
Preinduction begins with premed administered and ends when anesthesia induction begins in OR
Induction from consciousness to unconsciousness
Maintenance surgery takes place during this requires maintenance of physiological function by anesthetist
Emergence as surgery is completed (start to wake up), restoration of gag reflex, extubation
Recovery time during when patient returns to full consciousness begins in OR and carries into stay in PACU and beginning healing stages

14. Drugs commonly used in anesthesia
Intravenous anesthetic drugs e.g.
Thiopental, Propofol, Ketamine
Inhalational anesthetic drugs e.g.
Nitrous oxide, Isoflurane, Sevoflurane
Neuromuscular blocking drugs e.g.
Succinylcholine, atracurium, rocuronium, pancuronium
NMB reversal drug e.g.
Neostigmine, Atropine, Glycopyrrolate
Opioid drugs e.g.
Morphine, Fentanyl

15. IV Anesthetic Agents

16. IV Anesthetic Agents

19. IV Anesthetics Physical Properties

20. IV Anesthetics Effects on Body

21. Inhalational Anesthetic Agents

22. Inhalational Anesthetic Agents

24. Inhalational Anesthetic Agents

25. Systemic effects of volatile agents

26. How the inhalational agent pass to the brain?

27. Potency of Inhalational Anesthetic Agents
Just as potency of oral or intravenous drugs is measured in milligrams (or micrograms), potency of volatile anesthetics is associated with the term ‘MAC’ (minimum alveolar concentration)

28. Minimum alveolar concentration (MAC)
Definition
is the minimum alveolar concentration of an inhaled anesthetic agent which prevents reflex movement in
response to surgical incision in 50% of subjects
The effects of inhalational anesthetics are additive: thus 1 MAC-equivalent could be achieved by producing an alveolar concentration of 70% nitrous oxide (0.67 MAC) and 0.4% isoflurane (0.33 MAC)

29. Signs of Anesthesia

30. Factors Which Lead to a Reduction in MAC
Sedative drugs such as premedication agents, analgesics
Nitrous oxide
Increasing age
Drugs which affect neurotransmitter release such as methyldopa, pancuronium and clonidine
Higher atmospheric pressureHypotension
Hypothermia
Myxedema
Pregnancy.
Higher atmospheric pressure, as anesthetic potency is related to partial pressure – e.g. MAC for sevoflurane is 2.0% (2.03 kPa) at a pressure of 1 ata, but 1.0% (still 2.03 kPa) at 2 ata

31. Factors Which Increase MAC
Decreasing age
Pyrexia
Induced sympathoadrenal stimulation, e.g. hypercapnia
Drugs: ephedrine, or amphetamine
Thyrotoxicosis
Chronic alcohol ingestion

32. Other Factors affecting MAC of inhalational anesthetics
The rate at which MAC is attained may be increased by
raising the inspired concentration
avoidance of airway obstruction
increasing ventilation
The time taken for equilibration
Low blood/gas solubility coefficient of the agent (It follows, therefore, that the inspired concentration must be considerably higher than MAC to produce an adequate alveolar concentration)
Those with a high blood/gas solubility coefficient (e.g. halothane) do not reach equilibrium for several hours

33. Questions?