General Local Inhalation Intravenous Anesthetics Definition General anesthesia is a reversible state of CNS depression where the patient is in amnestic state resulting in loss of response to ID: 908805
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Slide1
Anesthetics
Slide22
Anesthesia
General
Local
Inhalation
Intravenous
Anesthetics
Slide3Definition
General anesthesia
is a reversible state of CNS depression, where the patient is in
amnestic
state
resulting in loss of response to
external stimuli and pain.
Anesthesia provides these five important benefits: Sedation and reduction of anxietyLack of awareness and amnesia
Skeletal muscle relaxationSuppression of undesirable reflexes
Analgesia
General Anesthetics
Slide4The concept of a ‘
triad of anaesthesia’ describes general anaesthesia
as a combination of relaxation, hypnosis and analgesia
4
Definition
General Anesthetics
Slide51. Multiple adjunct agents:
These agents facilitate smooth induction of anesthesia
and, when administered concurrently, also lower the dose of anesthetic required to maintain the desired level
of surgical
anesthesia
.
However, such
coadministration can also enhance undesirable anesthetic effects
5
Slide6STAGES AND DEPTH OF ANESTHESIA
Induction
is the period of time from the onset of administration of the potent anesthetic to the development
of effective
surgical
anesthesia.
Maintenance
provides a sustained surgical anesthesia. Recovery
is the time from discontinuation of administration of anesthesia until consciousness and protective physiologic reflexes are regained.
6
Anesthetics
Slide7Induction
Normally induced with an IV
anesthetic like propofol, which produces unconsciousness within 30–40 seconds after injection.
(WHY IV ? )
For
children
without IV access,
inhalation induction is used with nonpungent agents, such as halothane or
sevoflurane, to induce general anesthesia7
STAGES AND DEPTH OF ANESTHESIA
Slide8Maintenance of anesthesia
Anesthesia is commonly maintained by the administration of volatile
anesthetics, which offer good control over the depth of anesthesia.
In addition, the IV anesthetics which used in induction have short duration of action >>
can
not maintain the anesthetic activity for long time.
8
STAGES AND DEPTH OF ANESTHESIA
Slide9Recovery
Redistribution (it plays a major role) from the site of action (rather than metabolism of the anesthetic)
underlies recovery.
STAGES AND DEPTH OF ANESTHESIA
Slide10Depth of anesthesia
10
Stage I—Analgesia:
Loss of pain sensation results from
interferencewith
sensory transmission in the
spinothalamic
conscious
Amnesia Reduced awareness.Stage II —Excitement:
Delirium combative behaviorRise and irregularity in blood pressure and respiration
To shorten this stage,a rapid acting agent, such as propofol ,is given intravenously before inhalation anesthesia is administered.
Slide113. Stage III— Surgical anesthesia:
Gradual loss of muscle tone (Relaxation) and reflexes as the CNS is further depressed.
Regular respirationThis is the ideal stage of anesthesiafor
surgery
.
Continuous careful monitoring is required to prevent Stage IV.
4. Stage IV —
Medullary paralysis: Severe depression of the respiratory and vasom motor centers >>> coma >>Death.
11
Depth of anesthesia
Slide1212
Anesthetics
Slide13INHALATION ANESTHETICS
Used mainly for the maintenane
of anesthesia after indution of anesthesia by IV agent.Include:
Gas anesthetic
(nitrous oxide)
liquid volatile anesthetics
(halothane,
sevoflurane, desflurane and isoflurane).
Have a very narrow therapeutic index (generally from 2 to 4)>>> should be monitored carefully.
No antagonists exist.
Slide14Mechanism
No specific receptor has been identified as the locus of general anesthetic action.
The main targets for the inhalation anesthetic are:Increase
the sensitivity of the
GABA receptors
to the neurotransmitter,
GABA.
The activity of the inhibitory glycine receptors in the spinal motor neurons is increased.
Blocking the excitatory postsynaptic current of the nicotinic receptors.
14
INHALATION ANESTHETICS
Slide15Halothane
PrototypeRapid induction, quick recovery
(low blood solubility) and non explosiveTherapeutic uses
:
Halothane is a potent anesthetic but a
relatively weak analgesic
coadministered with nitrous oxide, opioids, or local anesthetics.
Causes uterine and skeletal muscle relaxation used in obstetric when uterine relaxation is indicatedSuitable for children
(WHY?) low hepatotoxicity in pediatrics and pleasant odor
15
INHALATION ANESTHETICS
Slide16PharmacokineticsIs metabolized
in the body to tissue-toxic hydrocarbons (for example,
trifluoroethanol) and bromide ion >> hepatic necrosis
Anorexia, nausea
, and vomiting, and patients may exhibit signs of
hepatitis.
to avoid it; halothane is given in interval of 2-3 weeks
16
Halothane
INHALATION ANESTHETICS
Slide17Isoflurane
Rapid induction and recovery
(low blood solubility) and has low MAC (high LIPID solubility)
Not used for inhalation induction
(WHY?)
causes severe cough reflex and has pungent smell.
It has a good effect on the cardiovascular system:
Does not induce cardiac arrhythmias and does not
sensitize the heart to the action of catecholamines.It dilates the
coronery artery may be beneficial in patient with ischemia heart disease
Produces dose-dependent hypotension due to peripheral
vasodilation.Produces halogenated metabolites hepatotoxi
city
17
INHALATION ANESTHETICS
Slide18Sevoflurane
Has
low pungency
Rapid induction
(rapid onset and recovery due to low blood solubility)
without
irritating the
airway>>> making it suitable for inhalation induction in
pediatric patients. It is the first choice used for inhalation induction. Sevoflurane is metabolized by the liver >> nephrotoxic
18
INHALATION ANESTHETICS
Slide19Nitrous oxide
Laughing gas
Potent analgesic
weak anesthetic >>> Is combined with another anesthetic to produce pain-free anesthesia.
Nitrous oxide is poorly soluble in blood and other tissues, allowing it to move very rapidly in and out of the body.
Non-irritating
Does
not depress respiration (bronchodilator), Does not produce muscle
relaxation.19
INHALATION ANESTHETICS
Slide20Diffusion hypoxia >>
beause diffuses rapidly from blood back to alveoli faster than oxygen> dilute oxygen> Must be combined with at least 20% oxygen.
Moderate to no effect on the cardiovascular system or on increasing cerebral blood flowIt is the least hepatotoxic
of the inhalation anesthetics.
Contraindicated in pregnancy as it causes hematologic complications including
aplastic
anemia.
Nitrous oxide
INHALATION ANESTHETICS
Slide2121
Slide22INTRAVENOUS ANESTHETICS
22
Slide23INTRAVENOUS ANESTHETICS
Cause the rapid induction of anesthesia.
IV anesthetics may be administered as infusions to help maintain anesthesia during longer procedures.
In
lower
doses, they may be used to provide
sedation
.23
Slide24Barbiturates
High lipid solubility >>
Quickly enter the CNS and depress function Might cause
laryngospasm
,
bronchospasm
if used for anesthesia >>> contraindicated in asthmainduction because they have a fast onset of action.May produce hypotension
INTRAVENOUS ANESTHETICS
Slide25Propofol
IV sedative/hypnotic used in the induction
or maintenance of anesthesiaOnset: The induction is very rapid (30–40 seconds).
Plasma levels
decline rapidly (rapid recovery)
as a result of redistribution.
25
INTRAVENOUS ANESTHETICS
Slide26Ketamine
Short-acting, non
barbiturate anesthetic.Good analgesicInduces a
dissociated state ??!!
in which the patient is 1) remains conscious 2)but may appear to be awake) and 3)does not feel pain.
Stimulates
the central
sympathetic outflow >> causes stimulation of the heart with increased blood pressure and Cardic Output >>> Beneficial in patients with either 1)hypovolemic or 2)cardiogenic shock as well as in patients with 3)asthma 4) when Cardiac depression is undesirable
26
INTRAVENOUS ANESTHETICS
Slide27Metabolized in the liver, but small amounts can be excreted unchanged >>> reduce dose in liver impairment.
Disadvantages:
It increases cerebral blood flow
I
nduces
postoperative
hallucinations
(“nightmares”), particularly in adults and potential of abuse.27
Ketamine
INTRAVENOUS ANESTHETICS
Slide28Benzodiazepines
Used in conjunction with anesthetics
(Why?!) to sedate the patientThe most commonly used is midazolam
Diazepam and
lorazepam
alternative.
All three
facilitate amnesia while causing sedation, enhancing the inhibitory effects of various neurotransmitters, particularly GABAMinimal
cardiovascular and respiratory depressant28
INTRAVENOUS ANESTHETICS
Slide29Opioids
Are commonly used with
anesthetics >> Because of their analgesic propertyThe
most commonly
used opioids are
fentanyl
and its congeners,
sufentanil and remifentanil, (WHY?!) because they induce analgesia more rapidly than morphine does it is 100 times the analgesic activity
.They are administrated either intravenously , epidurally and intrathecally.
Are not good amnesicsCause hypotensionRespiratory depressionMuscle rigidity
Postanesthetic nausea and vomiting.
29
INTRAVENOUS ANESTHETICS
Slide30PARALYTICS / NEUROMUSCULAR BLOCKERS
Neuromuscular blockers are used to:
Abolish reflexes to facilitate tracheal intubationTo provide muscle relaxation as needed for certain types of surgery.Their mechanism of action is
blockade of the nicotinic acetylcholine
receptors in the neuromuscular junction.
Include
cisatracurium
, pancuronium, rocuronium, succinylcholine
(Do you remember?), and vecuronium30
Slide31LOCAL ANESTHETICS
Slide32LOCAL ANESTHETICS
Doesn’t cause uncausiousness.
Applied or injected to block nerve conduction of sensory impulses
from the periphery to the CNS
.
Local anesthesia
prevents action potentials (
by blocking sodium ion channels >> prevent the transient increase in permeability of the nerve membrane to sodium that is required for an action potential)>> so sensation cannot be transmitted from the source of stimulation to the brain.
32
Slide33The most widely used of the local anesthetic compounds are: bupi
vacaine, lido
caine, mepivacaine,
pro
caine,
ropi
vacaine
and tetracaine. Of these,
lidocaine is probably the most commonly usedSome of them cannot be used systemically because of poor absorption
BUT lidocaine is used systemally as antiarrythmatic
33
LOCAL ANESTHETICS
Slide34Metabolism of LOCAL ANESTHETICS
Prilo
caine is also metabolized in the plasma and kidney, and one of its metabolites may lead to
methemoglobinemia
.
????
(the presence of a higher than normal level of methemoglobin
(ferric [Fe3+] rather than ferrous [Fe2+] haemoglobin)>> decreased ability to bind oxygen
Toxicity to neonateMepivacaine should NOT be used in obstetric anesthesia due to its toxicity to neonate
34
Slide35Onset and duration of action
Onset and duration of action of local anesthetics are influenced by
several factors.
The
most important
are
pH
of the tissue and pKa of the drug.At physiologic pH, these compounds are charged ionized
(active) >> interacts with sodium channel to inhibit its function. The pH may drop in sites of infection, which causes onset to be delayed or even prevented.
35
LOCAL ANESTHETICS
Slide36Actions
Local anesthetics cause
vasodilation >> leads to rapid diffusion of the drug away from the site of
application (
rapid absorption by the blood
)>>>
short duration of action
when these drugs are administered alone. By adding the
vasoconstrictor epinephrine to the local anesthetic, the rate of local anesthetic diffusion and absorption is decreased. >>> minimizes systemic toxicity and increases the duration of action
36
LOCAL ANESTHETICS
Slide37Allergic reactions
An allergy to one
ester rules out use of another ester,
because
the allergenic component is the
breakdown product
para-aminobenzoic acid, and
metabolism of all esters yields this compound. In contrast, an allergy to one amide
does not rule out use of another amide. A patient may be allergic to other compounds in the local anesthetic, such as preservatives
in vials.37
LOCAL ANESTHETICS
Slide38Allergic reactions
LOCAL ANESTHETICS