Practical conduct
of
General Anesthesia
Part1
Prepared by
Dr. Mahmoud Abdel-Khalek
Jan 2015
General Anesthesia
General Anesthesia is a pharmacologically induced
reversible state of unconsciousness which is maintained
despite the presence of noxious stimuli
General Anesthetics
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
Anesthetists
Role of anesthetists
 Preoperative evaluation and patient preparation
 Intraoperative management
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 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
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.
Anesthesia with single or multi agents
In the past, general anesthesia was achieved using a single
agent such as ether or chloroform. Because the abovedescribed 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.
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”
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)
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.
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Equipment checking before anesthesia
Equipment checking before anesthesia
Before Starting What you should do?
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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)
Phases of Anesthesia
1.
2.
3.
4.
5.
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
Drugs commonly used in anesthesia
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Intravenous anesthetic drugs e.g.
– Thiopental, Propofol, Ketamine
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Inhalational anesthetic drugs e.g.
– Nitrous oxide, Isoflurane, Sevoflurane
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Neuromuscular blocking drugs e.g.
– Succinylcholine, atracurium, rocuronium, pancuronium
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NMB reversal drug e.g.
– Neostigmine, Atropine, Glycopyrrolate
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Opioid drugs e.g.
– Morphine, Fentanyl
IV Anesthetic Agents
IV Anesthetic Agents
IV Anesthetics
Physical Properties
IV Anesthetics
Effects on Body
Inhalational Anesthetic Agents
Inhalational Anesthetic Agents
Inhalational Anesthetic Agents
Systemic effects of volatile agents
How the inhalational agent pass to the
brain?
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)
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
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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)
Signs of Anesthesia
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.
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Factors Which Increase MAC
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Decreasing age
Pyrexia
Induced sympathoadrenal stimulation, e.g. hypercapnia
Drugs: ephedrine, or amphetamine
Thyrotoxicosis
Chronic alcohol ingestion
Other Factors affecting MAC of
inhalational anesthetics
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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)
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Questions?