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Anesthetics 2 Anesthesia Anesthetics 2 Anesthesia

Anesthetics 2 Anesthesia - PowerPoint Presentation

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Anesthetics 2 Anesthesia - PPT Presentation

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

anesthesia anesthetics local anesthetic anesthetics anesthesia anesthetic local inhalation induction action blood intravenous rapid recovery depth stage general onset

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Slide1

Anesthetics

Slide2

2

Anesthesia

General

Local

Inhalation

Intravenous

Anesthetics

Slide3

Definition

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

Slide4

The concept of a ‘

triad of anaesthesia’ describes general anaesthesia

as a combination of relaxation, hypnosis and analgesia

4

Definition

General Anesthetics

Slide5

1. 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

Slide6

STAGES 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

Slide7

Induction

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

Slide8

Maintenance 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

Slide9

Recovery

Redistribution (it plays a major role) from the site of action (rather than metabolism of the anesthetic)

underlies recovery.

STAGES AND DEPTH OF ANESTHESIA

Slide10

Depth 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.

Slide11

3. 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

Slide12

12

Anesthetics

Slide13

INHALATION 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.

Slide14

Mechanism

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

Slide15

Halothane

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

Slide16

PharmacokineticsIs 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

Slide17

Isoflurane

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

Slide18

Sevoflurane

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

Slide19

Nitrous 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

Slide20

Diffusion 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

Slide21

21

Slide22

INTRAVENOUS ANESTHETICS

22

Slide23

INTRAVENOUS 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

Slide24

Barbiturates

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

Slide25

Propofol

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

Slide26

Ketamine

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

Slide27

Metabolized 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

Slide28

Benzodiazepines

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

Slide29

Opioids

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

Slide30

PARALYTICS / 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

Slide31

LOCAL ANESTHETICS

Slide32

LOCAL 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

Slide33

The 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

Slide34

Metabolism 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

Slide35

Onset 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

Slide36

Actions

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

Slide37

Allergic 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

Slide38

Allergic reactions

LOCAL ANESTHETICS