3. Balanced anaesthesia-
• All these modalities achieved
• Using combination of anaesthetic drugs
• So that the dose of individual drugs can
be reduced along with their side effects
9. HISTORY
John Snow
• Calculated dosages for the use
of ether and chloroform as
surgical anaesthetics
• Designed the apparatus to
administer ether & mask to
administer chloroform
• 1853
• administered chloroform
to Queen Victoria during her
8th delivery
11. STAGE 1-Stage of analgesia
From inhalation –LOC
Pain progressively abolished
Dream like state
STAGE 2-Stage of delirium
From LOC -beginning of regular respiration
Apparent excitement
STAGE 3-Surgical anaesthesia
From regular respiration-loss of
spontaneous respiration
Divided into 4 planes
STAGE 4-Medullary paralysis
Loss of spontaneous respiration – failure
of circulation & death
15. Two important characteristics of
Inhalational anaesthetics which
govern the anaesthesia are :
1. Solubility in the fat
(oil : gas partition
coefficient)
2. Solubility in the blood
(blood : gas partition
coefficient)
16. OIL-GAS PARTITION COEFFICIENTS
• It is a measure of lipid solubility of the
anaesthetic
• Measure of anaesthetic potency
• solubility of general anaesthetics in
lipid is the potency
17. BLOOD-GAS PARTITION COEFFICIENT
• Ratio conc. in blood
conc. in gas
• Lower the Blood-gas partition coefficient
faster the induction & faster the recovery.
20. EFFECT OF ION CHANNELS
Potentiation of GABA at GABAA
receptors-
almost all anaesthetics (except
cyclopropane,ketamine,Xenon,N2O)
21. EFFECT OF ION CHANNELS
Activation of Two – pore
Domain potassium channels-
can be directly activated by low conc. of
volatile & gaseous anaesthetics, thus reducing
memb. excitability
22. EFFECT OF ION CHANNELS
Inhibition of excitatory NMDA
receptors-
• Competitive antagonist for glycine - Xenon
• Noncompetitive antagonist of glutamate-
Ketamine
• NMDA channel blocker-N2O
23. EFFECT OF ION CHANNELS
• Other ion channels-ligand-gated channels
including glycine,nicotinic & 5HTreceptors as
well as at cyclic nucleotide –gated K+ channels
• Inhibition of presynaptic Na channels
inhibition of NT release at excitatory synapses
32. FACTORS AFFECTING THE PP OF
ANAESTHETIC ATTAINED IN THE
BRAIN
1. PP of anaesthetic in inspired gas
2. Pulmonary ventilation
3. Alveolar exchange
4. Solubility in blood
5. Solubility of anaesthetic in tissues
6. Cerebral blood flow
33. ELIMINATION
• Same factors which govern induction also
govern recovery.
• Most GA eliminated unchanged
• Halothane >20% metabolised in liver
34. SECOND GAS EFFECT
• Occurs when another inhalational anaesthetic
is used with N2O
• Rapid uptake of N2O produces a vaccum in
the alveoli
• Second gas also undergoes rapid uptake along
with N2O
35. DIFFUSION HYPOXIA
• Reverse of second gas effect occurs when N2O is
discontinued after prolonged anaesthesia
• N2O rapidly diffuses out the alveoli & dilutes the
alveolar air.
PP of O2 reduced in alveoli
Diffusion Hypoxia
36. Anaesthetic MA
C
Oil:Gas
Partition
Coeff.
Blood:Gas
Partition
Coeff.
Induction
Muscle
Relaxation
Remarks
Ether 1.9 65 12.1 Slow V.Good Irritating,inflammable & explosive
Potent,Good analgesia,pungent
Safe ininexperienced hands-no need for
special equipment
Halothane 0.75 224 2.3 Interm Fair Nonirritant,Potent,preferred for
asthmatics
Malignant hyperthermia,hepatotoxic
Isoflurane 1.2 99 1.4 Interm Good Safe in MI, Preferred in neurosurgery
Desflurane 6 19 0.42 Fast Good Out patient surgery,irritant
Sevoflurane 2 50 0.68 Fast Good Pleasant,can be used in paediatric
patients
N2O 105 1.4 0.47 fast Poor Least potent
Good analgesic,breathing & respiration
better maintained
Expand pneumothorax
38. INDUCING AGENTS
• Drugs on IV injection produce LOC in one arm-
brain circulation time, 11 sec
• Thiopentone sod.
• Methohexitone sod.
• Propofol
• Etomidate
39. DRUG INDUCTI
ON
MAJOR
UNWANTED
EFFECTS
REMARKS
PROPOFOL Fast CVS & R.S
depression
Propofol infusion
syndrome
Used for total IV anaesthesia along
with fentanyl
Preferred for OP surgeries
DOC for sedating intubated pts. In
ICU,preferred in asthmatics
THIOPENTAL Fast
hangover
CVS & R.S
Depression, can
precipitate AIP
Necrosis on
extravasation
Other uses – to control convulsions,
Narcoanalysis
ETOMIDATE Fast Excitatory effects
During induction
& recovery
Adrenocortical
suppression
Aneurysm surgeries & cardiac
disease
40. KETAMINE Slow Psychomimetic effects
Postop nausea,
vomiting
Salivation
Raised ICT
Dissociative anaesthesia
Muscle tone ↑
HR,CO,BP,ICT ↑
Preferredfor head & neck
surgeries,hypovolaemic
pts,Asthmatics
MIDAZOLAM slow
Preferred for endoscopies
fracture settings
angiographies,
ECT
FENTANYL Anaesthetic
awareness with
dreadful recall
Opioid analgesic
To supplement balanced anaesthesia
Nerolept analgesia –along with
Droperidol
41. CONSCIOUS SEDATION
• Monitored state of altered consciousness that
can be employed to carryout diagnostic/short
therapeutic/dental procedures in
apprehensive subjects or medically
compromised patients
– Diazepam
– Propofol
– N2O
– Fentanyl
