2. Flow of content
History
Ideal anesthetic agents
-property-physical
-pharmacokinatical
-pharmacodynamical.
Classification of anesthetic agents.
Stages of anesthesia.
Individual drugs and properties.`
3. History
During the Middle Ages, attempts were made to use
alcohol fumes as an analgesic during surgery.
Another inhaled technique, the soporific sponge, is
mentioned in numerous manuscripts written in the Middle
Ages.
4. History
The first public demonstration of inhalation
anaesthetic was nitrous oxide used by Professor
Gardner Q. Colton and dentist Horace Wells on 11
December 1844.
On Oct 16th 1846 William Morton successfully
demonstrated Ether anaesthesia at Massachusetts
general hospital.
6. Ideal inhalational anaesthetic
Physical properties
(1) Stable over a range of temperatures
(2) Not be degraded by light
(3) Does not require the presence of a preservative
(4) Non-explosive and does not support combustion
(5) Odourless or has a pleasant smell
(6) Environmentally safe
(7) Does not react with other compounds (e.g. Soda
lime, plastic and metals etc.)
(8) Has a boiling point well above room temperature
7. Pharmacodynamic properties
(1) Predictable dose-related CNS depression
(2) Analgesic, anti-emetic and muscle relaxation properties
(3) Minimal respiratory depression, does not cause
coughing or bronchospasm
(4) Minimal cardiovascular effects.
(5) No increase in cerebral blood flow (and therefore
intracranial pressure).
(6) Not epileptogenic
(7) Does not impair renal or hepatic function
(8) No effect on uterine smooth muscle
(9) Does not trigger of malignant hyperthermia
8. Pharmacokinetic properties
(1) Low blood: gas solubility co-efficient
(2) Low oil: gas solubility co-efficient
(3) Not metabolised or no active metabolites
(4) Is excreted completely by the respiratory system
10. In administering an anesthesia
Signpost
Guides in determination of depth of anesthesia
Guedel describe depth of anaesthesia by dividing it
into stages and planes.
Stages of Anesthesia
11. Guedel’s criteria based on :
Respiration
Eyeball movement
Presence or absence of various reflexes
Gillespie added other criteria
Secretion of tears
Response to skin incision
Evaluation of pharyngeal &
laryngeal reflexes
12. Stages were first described for ether anesthesia
Can be used with modification for all agents
Can be recognized during both induction & recovery
13. Starts from beginning of anaesthetic inhalation and
lasts up to the loss of consciousness.
Pain is progressively abolished.
Patient remains conscious, can hear and see, and feels
a dream like state
Stage I- Stage of Analgesia
14. Reflexes and respiration remain normal.
Some minor operations can be carried out during this
stage
But it is difficult to maintain
Therefore use is limited to short procedures
15. Stage starts from loss of consciousness upto gain of
rhythmical respiration
Respiration – Irregular and large in volume
Heart rate and BP raises
Pupils – Large and divergent
Muscle tone increased – jaw may be tight
Patient may shout or struggle
Involuntary micturation , or defecation
Stage II – Stage of Excitement
16.
17. Extends from onset of regular respiration to cessation of
spontaneous breathing.
This has been divided into 4 planes:
o Plane 1- Roving eyeballs.
o This plane ends when eyes become fixed.
o Plane 2- Loss of corneal and laryngeal reflexes.
o Plane 3- Pupil starts dilating and light reflex is lost.
o Plane 4- Intercostal paralysis
Shallow abdominal respiration
Dilated pupil.
Stage III- Surgical Anaesthesia
18. As anaesthesia passes to deeper planes
Progressively-muscle tone decreases
BP falls
Heart Rate increases with weak pulse
Respiration decreases in depth and later in frequency
19. There is cessation of breathing leading to failure of
circulation and death.
Pupil is widely dilated
Muscles are totally flabby
Pulse is thready or imperceptible
BP is very low.
Stage IV- Stage of Medullary
Paralysis
20. Ether
MAC 1.92
,B:G partition coefficient 12
Guedel’s 4 stages of anaesthesia based on ether
Good Analgesic
Good Muscle Relaxant
21. Pungent smell
Inflammable and explosive
Irritant
Slow Induction and Recovery
High incidence of Nausea and Vomitting
22. ether
High CVS stability ; no myocardial depression.
sympathetic stimulation and preservation of
baroreceptor reflex.
No respiratory depression and no blunting of Hypoxic
drive.
Bronchodilatation and Preserves cilliary activity
23. Nitrous oxide
Physical Property
• Not flammable but support combustion.
• Odorless
• Colorless
• Tasteless
• Prepared by heating NH4NO3 at 245-270°C
24. NH4NO3 --> N2O + 2H2O
Small amounts of NH3 and HNO3 produced recombine to
NH4NO3 on cooling.
Small amounts of NO and NO2 are also produced-
- Can cause methaemoglobinaemia, pulmonary edema
if inspired.
- N2O must be purified to remove these contaminants
25. Nitrous oxide
Colour of cylinder = blue.
MAC - 104%
Blood gas partition coefficient -0.46.
Pin index - 3;5
26. Nitrous oxide
Unlike the potent volatile agents, nitrous oxide is a gas at
room temperature and ambient pressure.
It can be kept as a liquid under pressure because its critical
temperature lies above room temperature
With a MAC value of 104%, nitrous oxide, by itself is not
suitable as a sole anaesthetic agent.
Nitrous oxide is an effective analgesic but poor muscle relaxant
It undergoes minimal metabolism.
27. Nitrous Oxide
C.V.S EFFECTS-
The circulatory effects of nitrous oxide are explained
by its tendency to stimulate the sympathetic nervous
system.
Even though nitrous oxide directly depresses
myocardial contractility in vitro, arterial blood
pressure, cardiac output, and heart rate are essentially
unchanged or slightly elevated in vivo because of its
stimulation of catecholamine
28. Nitrous oxide
CEREBRAL
By increasing CBF and cerebral blood volume, nitrous
oxide produces a mild elevation of intracranial
pressure.
Nitrous oxide also increases cerebral oxygen
consumption (CMRO2).
29. The second gas effect
The second gas effect usually refers to nitrous oxide
combined with an inhalational agent. Because nitrous
oxide is not soluble in blood, its' rapid absorption from
alveoli causes an abrupt rise in the alveolar
concentration of the other inhalational anaesthetic
agent.
30. Diffusion Hypoxia
•At the end of anesthesia after discontinuation of N2O,
N2O diffuses from blood into the alveoli much faster
than N2 diffuses from alveoli into the blood.
• Total volume of gas in the alveolus → fractional
concentration of gases in the alveoli is diluted by N2O
→ ↓ PaO2 & PaCO2 → hypoxia.
•This occurs in the first 5-10 mins of recovery. Therefore
it is advised to use 100% O2 after discontinuation of
N2O.
31.
32.
33. Toxicities – Nitrous Oxide
Hematologic:
N2O antagonizes B12 metabolism
inhibition of methionine-synthetase
Decreased DNA production
RBC production depressed (megaloblastic anaemia)
Neurologic
Long term exposure to N2O is hypothesized to result in
neurologic disease similar to B12 deficiency
34. 35 times more soluble in blood than nitrogen, N2 so fills and expands
any air-containing cavities:
air embolism
pneumothorax
intracranial air
lung cysts
intraocular air bubbles
tympanoplasty
may exacerbate pulmonary hypertension
35. Entonox
50% N2O + 50% O2
Colour coding = blue body with blue &white quarters.
Pin index = 7
Poyinting effect: normally N2O is liquid at 2400 psig.
But If N2O is mixed with O2 it remains in gaseous
state called poyinting efect.
Use: 1)labour analgesia.
2)field analgesia(wars)
37. HALOTHANE
Volatile- kept in sealed bottles
Colorless,
Pleasant odor-suitable in pediatrics for inhalation
induction (although sevoflurane is now the agent
of choice )
Non-irritant
Non-explosive, Non-inflammable
Light-sensitive
Corrosive-Interaction – rubber and plastic tubing
38. metabolism
20% metabolized in liver by oxidative pathways.
Major metabolites : bromin, chlorine, Trifloroacetic
acid, Trifloroacetylethanl amide
39. Systemic effects of Halothane
CNS:
Generalized CNS depression
cerebrovascular dilation causes increased ICP
Autoregulation is blunted
Cardiovascular:
• A dose-dependent reduction of arterial blood pressure is due to direct
myocardial depression
• blunts baroreceptor reflex
40. •Although halothane is a coronary artery vasodilator,
coronary blood flow decreases, due to the drop in systemic
arterial pressure.
• Adequate myocardial perfusion is usually maintained, as
oxygen demand also drops- maybe advantages In pts with
CAD
•Halothane sensitizes the heart to the arrhythmogenic
effects of catecholamine
◦To minimize effects :
Avoid hypoxemia and hypercapnia
Avoid conc. Of adrenaline higher than 1 in 10000
41. Pulmonary:
best bronchodilator among the currently available volatile
anesthetics.
attenuates airway reflexes and relaxes bronchial smooth muscle
by inhibiting intracellular calcium mobilization.
depresses clearance of mucus from the respiratory tract
(mucociliary function), promoting postoperative hypoxia and
atelectasis.
42. Renal:
-Both GFR and renal blood flow is decreased-because of
decrease cardiac output.
- associated with reversible reduction in GFR.
Gastro intestinal tract:-
Inhibition of gastrointestinal motility.
Cause sever post. Operative nausea & vomiting.
Uterus:
Halothane relaxes uterine muscle, may cause postpartum
hemorrhage .
Concentration of less than 0.5 % associated with increase
blood loss during therapeutic abortion.
43. Skeletal muscle:
Its cause skeletal muscle relaxation .
Postoperatively, shivering is common , this increase
oxygen requirement>>> which cause hypoxemia.
Post operative shivering (halothane shakes) and
hypothermia is maximum with halothane among
inhalational agents.
44. Halothane - Hepatic Toxicity
All inhaled AA can cause hepatic injury in animal
studies
All inhaled AA have immunohistochemical
evidence of binding to hepatocytes
Thought that Trifluoroacetic acid metabolites are
root cause
Another theory is due to Hypoxia as halothane causes
Hepatic arterial constriction
45. Halothane Hepatitis
The incidence of fulminant hepatic necrosis terminating
in death associated with halothane was found to be 1 per
35,000.
Demographic factors ; It’s a idiosyncratic reaction,
susceptible population include Mexican Americans,Obese
women, , Age >50 yrs, , Familial predisposition, Severe
hepatic dysfunction while Children are resistant.
Prior exposure to halothane is a important risk factor &
multiple exposure increases the chance of hepatitis.
46. Mechanism of Toxicity
There are various proposed mechanisms:
• Metabolite-mediated direct toxicity
• Immunologically-mediated damage to liver cells
a proportion is biotransformed by hepatic microsomal enzyme CYP 2E1
to a trifluoroacetic acid which can be detected in the urine, but which
also can trifluoroacetylate hepatic proteins, some of which may be
immunogenic and induce cytotoxic reactions.
• Hypoxia alone
47.
48. Hepatic dysfunction:
Two type of dysfunction:
1- Type I hepatotoxicity:-mild, associated with
derangement in liver function test , this result from
metabolic of Halothane in liver. results from reductive
(anaerobic) biotransformation of halothane rather than the
normal oxidative pathway.
2- Type II hepatotoxicity: fulminate (uncommon); sever
jaundice ,fever, progressing to fulminating hepatic
necrosis,
Its increased by repeated exposure of the drugs.
high mortality 30-70%
49. 1- A careful anesthetic history .
2- repeated exposure of halothane within 3 months should be
avoided.
3- History of unexplained jaundice or pyrexia after previous
exposure of halothane.
Recommendation for Halothane anesthesia:
50. Drug Interactions
1. Beta blockers and calcium channel blockers can
produce severe depression of cardiac function with
halothane
2. Aminophylline can produce serious ventricular
arrhythmias with halothane.
3 .Halothane sensitizes the heart to the
arrhythmogenic effects of epinephrine, so that doses
of epinephrine above 1.5 g/kg should be avoided.
51. Contraindication
Malignant hyperthermia.
susceptibility unexplained liver dysfunction after
previous halothane exposure
intracranial mass lesion
hypovolemia
aortic stenosis
pheochromocytoma
with aminophylline has been associated with severe
ventricular dysrhythmias
52. Isoflurane
2-chloro 1-trifluro methyl-
ethyl ether.
MAC is 1.17 % B:G p co-ef is 1.17.
Isoflurane is characterized by extreme physical
stability, undergoing no detectable deterioration during 5 years of
storage or on exposure to carbondioxide absorbents or sunlight.
The stability of isoflurane obviates the need to add preservatives such
as thymol to the commercial preparation.
53. RESPIRATORY SYSTEM
Initially, until deeper levels of anesthesia are reached,
isoflurane stimulates airway reflexes with:
increases in secretions
coughing
laryngospasm.
54. Isoflurane
CNS:
low concentration Vs High concentration.
Low : no change on the flow.
High : increase blood flow by vasodilatation of the cerebral
arteries.
Generalized CNS depression; Rapid emergence
Increased ICP reversed by Hyperventilation
Agent of choice for neuro-anaesthesia.
55. Cardiovascular:
myocardial depression, decreased vascular assistance &
decreased MAP
Preserves baroreceptor reflex . So that reflex tachycardia
occurs in response to decrease B.P maintaining cardiac
output.
Agent of choice for cardiac anaesthesia.
56. Coronary steal phenomenon
Isoflurane induced coronary artery vasodilatation can lead to
redistribution of coronary blood flow away from diseased areas
where arterioles are maximally dilated to areas with normal
responsive coronary arteries. This phenomenon is called
the coronary steal syndrome
57. Sevoflurane
Florinated Methyl –
isopropyl ether.
MAC -1.80.
Low blood:gas partition coefficient -0.69 (Rapid induction and
recovery.
Compared with isoflurane, recovery from sevoflurane anesthesia
is 3 to 4 minutes faster and the difference is magnified in longer
duration surgical procedures (>3 hours)
58. Pleasant smell , non irritant,bronchodilatation and least airway irritation
among current volatile agents makes it acceptable for inhalation induction
of anesthesia.
• agent of choice for paediatric anesthesia.
• 2nd agent of choice for
• Neuro anesthesia.
• Cardiac anesthesia .
• Asthmatics
Does not sensitize the myocardium to catecholamines as much as
halothane.
Does not result in carbon monoxide production with dry soda lime.
Sevoflurane
59. Sevoflurane may be 100-fold more vulnerable to metabolism
than desflurane -estimated 3% to 5% of the dose undergoing
biodegradation.
metabolites - inorganic fluoride
hexafluoroisopropanol.
cannot undergo metabolism to an acyl halide.
does not result in the formation of trifluoroacetylated liver
proteins.
Therefore cannot stimulate the formation of
antitrifluoroacetylated protein antibodies.
So devoid of the potential to produce hepatotoxicity as well
as cross-sensitivity between drugs.
60. Sevoflurane and Compound A
Sevoflurane forms a degradation product, compound
A [fluoromethyl-2,2-difluoro-1-(trifluoromethyl)vinyl
ether] on contact with the soda lime in a rebreathing
apparatus.
Compound A is a dose-dependent nephrotoxin in rats.
A proposed mechanism for nephrotoxicity is the metabolism of
compound A to a reactive thiol via the β-lyase pathway.
Because humans have less than one-tenth of the enzymatic
activity for this pathway compared to rats, it is possible that
humans should be less vulnerable to injury by this mechanism.
61. Sevoflurane can also be degraded into hydrogen fluoride by
metal and environmental impurities present in manufacturing
equipment, glass bottle packaging, and anesthesia equipment.
Hydrogen fluoride can produce an acid burn on contact with
respiratory mucosa.
The risk of patient injury has been substantially reduced by
inhibition of the degradation process by adding water to
sevoflurane during the manufacturing process and packaging it
in a special plastic container.
Postoperative agitation may be more common in children then
seen with halothane.
62. Desflurane
2-fluro,1-trifluro methyl ethyl ether.
MAC =6.6 %
differs from isoflurane only by substitution of a fluorine atom for
the chlorine atom found on the alpha-ethyl component of
isoflurane.
Fluorination rather than chlorination increases vapor pressure
(decreases intermolecular attraction), enhances
molecular stability, and decreases potency.
63. desflurane would boil at normal operating room temperatures
A new vaporizer technology addressed this property, producing
a regulated concentration by converting desflurane to a gas
(heated and pressurized vaporizer that requires electrical
power),which is then blended with diluent fresh gas flow
Solubility characteristics (blood:gas partition coefficient 0.45)
and potency (MAC 6.6%) permit rapid achievement of an
alveolar partial pressure necessary for anesthesia followed by
prompt awakening when desflurane is discontinued.
64. Desflurane
Pungent odor --desflurane less likely to be used for
inhalation induction compared to halothane or
sevoflurane.
Airway irritation, breath-holding, coughing,
laryngospasm,significant salivation, when >6%
desflurane administered to an awake patient.
Produces the highest carbon monoxide
concentrations, followed by enflurane and isoflurane
66. Dual-circuit gas–vapour blender
It was created specifically for the agent desflurane.
Desflurane boils at 23.5 ºC, which is very close to room
temperature.
This means that at normal operating temperatures, the saturated
vapour pressure of desflurane changes greatly with only small
fluctuations in temperature.
A desflurane vaporiser (e.g. the TEC 6 produced by Datex-
Ohmeda) is heated to 39C and pressurised to 200kPa
.
67.
68. Agent of choice for day care (fastest induction)
Agent of choice for geriatric (old) patients.
Agent of choice for hepatic failure
Agent of choice for renal failure
69. Anesthetic B:G PC MAC Features Notes
Halothane 2.3 0.74% PLEASANT Arrhythmia
Hepatitis
Hyperthermia
Enflurane 1.9 1.69% PUNGENT Seizures
Hyperthermia
Isoflurane 1.4 1.17% PUNGENT Widely used
Sevoflurane 0.62 1.92% PLEASANT Ideal
Desflurane 0.42 6.1% IRRITANT Cough
Nitrous 0.47 104% PLEASANT Anemia
70. XENON
Most ideal inhalational agent.
Blood gas partition co-efficient is 0.14. least of all .least
soluble. so fastest induction and fastest recovery.
MAC is 70% so can be given with 30%O2.
Most cardiostable.
No metabolism in body –least side effects non terratogenic.
Non inflamble,does not deplete ozone layer.
Disadvantages = costly, needs special equipment for
delivary, bronchospasm.
Acts on NMDA receptor
72. : CNS-
• increased ICP secondary to increased cerebral blood flow (CBF)
• produce fast frequency and high voltage on the EEG.
• Decrease the threshold for seizure-Epileptogenic inhalational
agent.
• It is primarily used for procedure in which a low threshold for
seizure generation is required like ECT.
Cardiovascular:
• myocardial depressant
• decreased vascular resistance; decreased mean arterial pressure
(MAP), tachycardia
74. Trichloroethylene (trilene)
Most potent analgesic agent - trielene
Reaction with sodalime :-
dichloroacetylene – neurotoxic- V, VII.
phosgene - pulmonary toxicity(ARDS)
CHLOROFORM
1st agent used for labour analgesia.
Cardiotoxic- death due to ventricular fibrillation.
Hepatotoxic.
Profound hyperglycemia.
75. Methoxy-flurane
Most potent inhalational agent (mac-0.16%).
Slowest induction and recovery(b:g – 15).
Most nephro-toxic agent –high output renal failure
Reacts with rubber tubing of closed circuit
76. Cyclopropane
Most inflamable & explosive agent
Liquid gas-Orange cylinder.
Increases sympathetic tone and B.P.
Agent Of Choice in Shock
Cyclopropane shock.