CNS 5

Report
ANESTHETICS
SAMUEL AGUAZIM ( MD)
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Patient factors
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 Which influence the selection of the anesthetics
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are
Liver & kidney – target organs for toxic effects by
the release of Fluoride, Bromide & other
metabolites by halogenated compounds can
affect this organ.
Respiratory system – if Inhalational anesthetics.
CVS – hypotensive effect by most anesthetic
agents
Nervous system - neurological disorders
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 ANESTHETICS
 A drug that brings about a reversible loss of
consciousness.
 to induce or maintain general anesthesia to
facilitate surgery.
Definition
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Anesthesia: Condition of reversible
unconsciousness and absence of response to
otherwise painful stimuli.
1.
2.
3.
4.
Unconsciousness
Analgesia
Immobility
Amnesia
WHAT ARE THE TWO MAJOR CLASSES
OF ANESTHETIC AGENTS?
 * GENERAL
 * LOCAL
 General anesthetics are given either as inhaled or
intravenous agents.
 They primarily have CNS effects
 Local agents are injected at the operative site to
block nerve conduction
What are the stages of general anesthesia?
 There are four stages:
 Stage 1- analgesia- reduced sensation of pain; the
patient remains conscious and conversational
 Stage 11- excitement- delirium and combative
behaviour ensue; there is an increase in blood
pressure and respiratory rate.
 Stage 111- surgical anesthesia- the patient is
unconscious and regular respiration returns; there is
muscle relaxation and decreased vasomotor response
to painful stimuli
 Stage iv- medullary paralysis- respiratory drive
decreases and vasomotor output diminishes; death
may quickly ensue
APPROACHES FOR TESTING
DEPTH OF ANAESTHESIA
- Blinking of eyelids on striking the eyelashes.
- Swallowing
- Regularity and depth of respiration.
- Increase in respiratory rate and B.P.
- Tightness of jaw muscles.
Above responses fade on deepening of the
anesthesia.
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What is induction of anesthesia?
 The time from administration of a general
anesthetic to the achievement of surgical
anesthesia.
 Induction is dependent on how fast the
anesthetic reaches the CNS
 RECOVERY IS THE REVERSE OF INDUCTION and
it is dependent on how quickly the anesthetic is
removed from the CNS
Factors that influence the rate of
induction for inhaled anesthetics
 Solubility
 Pulmonary ventilation
 Partial pressure of the inhaled agent
 Alveolar blood flow
 Arteriovenous concentration gradients
INHALED AGENTS
 HALOTHANE
 ENFLURANE
 ISOFLURANE
 SEVOFLURANE
 NITROUS OXIDE
 There potency is defined base on the concept of
minimum alveolar concentration ( MAC)
What is MAC?
 Mac is the minimum alveolar concentration of an
anesthetic necessary to eliminate movement among 50%
of patients challenged by a standardized skin incision
 The greater the MAC of an agent, the greater the
concentration needed to provide anesthesia.
Thus an agent with high MAC has low potency (
e.g.. Nitrous oxide)
 MAC of any inhaled agent can be reduced using it in
conjunction with analgesia such as opoid or sedative
hypnotics
Halothane
 The first of the halogenated volatile anesthetics to be
developed.
 Clinical use: it is used in the pediatric population
because of its pleasant odor and lack of
hepatotoxicity.
 MAC: 0.75%
CARDIOVASCULAR EFFECTS OF
HALOTHANE
 It sensitizes the myocardium to the effect of
catecholamines ( thus increasing the risk of
arrhythmia).
 Decrease heart rate and cardiac output and leads to
lowered BP and peripheral resistance.
 Toxicity: halothane hepatitis
 Malignant hyperthermia.
What is malignant hyperthermia?
 A potentially fatal reaction to any of the inhaled
anesthetics, which results in hyperthermia,
metabolic acidosis, tachycardia and accelerated
muscle contraction
 Treatment : dantrolene and stop the offending
agent
Enflurane
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 Rapid induction and recovery, less potent
than halothane
 Fewer arrhythmias
 Greater muscle relaxation
 Proconvulsant
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 Contraindications/Precautions
 CI in renal failure. This anesthetic is not
used in patients with kidney failure.
 malignant hyperthermia susceptibility
 seizure disorder
 intracranial hypertension
Isoflurane
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 Rapid recovery
 Good muscle relaxation
 Stable cardiac output
 Very less effect on heart
 No rise in ICP.
 One of the best Inhalational agent..
 Isoflurane maintains CO and coronary function
better than other agents used in pts with
ischemic heart disease.
Nitrous oxide
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1. odorless and non-explosive gas.
2. Anesthetic action.
Good analgesia
Safe, non irritating
Rapid induction due to low solubility.
Rapid onset and recovery
Negative points:
 No muscle relaxation
 Incomplete anesthesia,
 Must be used in combination ..
Toxicity: bone marrow depression with prolonged
administration.
 High concentrations may cause neuropathies
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INTRAVENOUS AGENTS
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THIOPENTONE
 Potent anesthesia
 High lipid solubility
 Rapid entry into brain
 Decreased cerebral blood flow
 Rapid onset of action
 Short surgical procedures
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Thiopentone
Negative points:
 Poor analgesia
 Little muscle relaxation
 Laryngospasm
Ketamine
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 Good analgesia
 Dissociative anesthetic.
 Cardiovascular stimulant
 Causes disorientation, hallucinations..
 Increases cerebral blood flow.
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 Ketamine affects the senses, and produces a
dissociative anesthesia (catatonia, amnesia,
analgesia) in which the patient may appear
awake and reactive, but cannot respond to
sensory stimuli.
 These properties make it especially useful
during warfare medical treatment.
 Used in Trauma and emergency Surgical
Procedures
 also used in high-risk geriatric patients and in
shock cases, because it also provides cardiac
stimulation.
Fentanyl
 Good analgesia
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 Mostly used with other CNS depressants
during anesthesia
 Because opioids rarely affect the
cardiovascular system, they are particularly
useful for cardiac surgery
 Can cause resp. depression and muscle
rigidity..
Propofol
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 nonbarbiturate hypnotic agent and the most
recently developed intravenous anesthetic.
 Its rapid induction and short duration of
action identical to thiopental.
 Recovery occurs more quickly and with
much less nausea and vomiting
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 Rapidly metabolized in the liver and excreted
in the urine, so it can be used for long
durations of anesthesia, unlike thiopental.
 Hence, propofol is rapidly replacing
thiopental as an intravenous induction agent.
Etomidate
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 Ultra short acting non-barbiturate hypnotic
 No analgesic properties
 Used for induction followed by other agents
 Produces postoperative nausea & vomiting
 Lowers plasma cortisol levels
LOCAL ANESTHETICS
There are two classes determined by their bonding the
lipophilic portion of the molecule with the
hydrophilic components- either an ester or amide
bond.
ANESTHETICS
NAME THE ESTER
ANESTHETICS
NAME THE AMIDE
ANESTHETICS
 COCAINE
 LIDOCAINE
 BENZOCAINE
 MEPIVACAINE
 PROCAINE
 BUPIVACAINE
 TETRACAINE
 PRILOCAINE
Mechanism
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 Block Na channels by binding to specific
receptors on inner portion of the channel.
 First loss of pain, then temp, touch, pressure
at the last.
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 Using epinephrine mixed with local
anesthetics causes vasoconstriction, which
decreases clearance of the agent, increases
duration of action, and decreases the total
required dosage.
USES
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 Short local procedures
 Spinal anesthesia
 Minor surgical procedures
SE
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 Severe CVS toxicity – Bupivacaine
 Hypertension & arrhythmias – cocaine
 CNS excitation
 Seizures

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