Monitoring depth of anaesthesia

1. Monitoring Depth of
Anaesthesia
Presentation by :
Dr. Ketaki Didolkar
Guided by :
Dr. Abhay Bodhey

3. AIM OF MONITORING :AIM OF MONITORING :
Guarantee the safety of anaesthesia as well as the Guarantee the safety of anaesthesia as well as the
painlessness of surgery.painlessness of surgery.
Overall incidence of intra-operative awareness- Overall incidence of intra-operative awareness-
0.2-3 % 0.2-3 %
Incidence >40% in patients of cardiac surgery, Incidence >40% in patients of cardiac surgery,
caesarean section, multiple trauma & caesarean section, multiple trauma &
haemodynamically unstable patients.haemodynamically unstable patients.
 A 2001 study reported that 56.3% of a group of
patients who had awakened during surgery met the
diagnostic criteria for ‘post traumatic stress disorder’—
as late as 17 years after their operation.

5. AIM OF MONITORING :AIM OF MONITORING :
Intra-operative awareness is Intra-operative awareness is
a major medicolegal liability a major medicolegal liability
to anaesthetists & it is our to anaesthetists & it is our
prime responsibility to prime responsibility to
diagnose and avoid it at all diagnose and avoid it at all
costs !!!!costs !!!!

6. HISTORICAL BACKGROUND :HISTORICAL BACKGROUND :
DioscoridesDioscorides first used the term ‘anaesthesia’ to first used the term ‘anaesthesia’ to
describe narcotic effect of plant mandragora.describe narcotic effect of plant mandragora.
O.W. Holmes O.W. Holmes coined the term ‘anaesthesia’ to coined the term ‘anaesthesia’ to
describe the new phenomenon that made surgical describe the new phenomenon that made surgical
procedures possible.procedures possible.
Plomley Plomley (1847) first attempted to define depth of (1847) first attempted to define depth of
anaesthesia by describing 3 stages- intoxication, anaesthesia by describing 3 stages- intoxication,
excitement and narcosis.excitement and narcosis.
John Snow John Snow (1847) described ‘five degrees of (1847) described ‘five degrees of
narcotism’ ; the first 3 included induction of narcotism’ ; the first 3 included induction of
anaesthesia by ether & last 2 represented surgical anaesthesia by ether & last 2 represented surgical
anaesthesia.anaesthesia.

7. HISTORICAL BACKGROUND :HISTORICAL BACKGROUND :
Guedel Guedel (1937) gave the classic description of clinical signs of (1937) gave the classic description of clinical signs of
ether anaesthesia. Included 4 stages: analgesia, delirium, ether anaesthesia. Included 4 stages: analgesia, delirium,
surgical anaesthesia & respiratory paralysis.surgical anaesthesia & respiratory paralysis.

8. HISTORICAL BACKGROUND :HISTORICAL BACKGROUND :
ArtusioArtusio (1954) expanded Guedel’s stage 1 into 3 planes : (1954) expanded Guedel’s stage 1 into 3 planes :
1)1)No amnesia & analgesiaNo amnesia & analgesia
2)2)Total amnesia & partial analgesiaTotal amnesia & partial analgesia
3)3)Complete amnesia & analgesia Complete amnesia & analgesia
WoodbridgeWoodbridge (1957) defined 4 components of anaesthesia : (1957) defined 4 components of anaesthesia :
I.I.Sensory blockade of afferent impulsesSensory blockade of afferent impulses
II.II.Motor blockade of efferent impulses Motor blockade of efferent impulses
III.III.Reflex blockade of RS, CVS, GI tractReflex blockade of RS, CVS, GI tract
IV.IV.Mental block or unconsciousnessMental block or unconsciousness
Prys – Roberts Prys – Roberts (1987) defined anaesthesia as a state in (1987) defined anaesthesia as a state in
which the patient neither perceives nor recalls noxious stimuli which the patient neither perceives nor recalls noxious stimuli
as a result of drug induced unconsciousness.as a result of drug induced unconsciousness.

9. MODERN CONCEPT :MODERN CONCEPT :
In modern times, anaesthesia is a complex interaction In modern times, anaesthesia is a complex interaction
of multiple stimuli applied, the diverse responses of multiple stimuli applied, the diverse responses
measured & the drug induced probability of measured & the drug induced probability of
nonresponsiveness to stimuli.nonresponsiveness to stimuli.
The The hypnotic agents hypnotic agents produce such profound CNS produce such profound CNS
depression that the most powerful surgical stimulus depression that the most powerful surgical stimulus
cannot arouse patient from state of cannot arouse patient from state of
nonresponsiveness.nonresponsiveness.
The The analgesicsanalgesics & & LA LA attenuate the surgical stimuli.attenuate the surgical stimuli.
The interaction between analgesics & hypnotics is The interaction between analgesics & hypnotics is
thus fundamental to understanding & defining thus fundamental to understanding & defining
anaesthetic depth.anaesthetic depth.

11. PAIN & ANAESTHETICS PAIN & ANAESTHETICS

12. FACTORS AFFECTING CORRECT DRUG FACTORS AFFECTING CORRECT DRUG
DOSES: DOSES:
The lack of a universally accepted The lack of a universally accepted definition of definition of
"consciousness.”"consciousness.”
The increased use of The increased use of combinations of anaesthetic combinations of anaesthetic
agents rather than single drugs. agents rather than single drugs.
Changes in the patient's response to anaesthesia over Changes in the patient's response to anaesthesia over
the the course of the operation.course of the operation.
AgeAge-related differences in responsiveness to specific -related differences in responsiveness to specific
anaesthetics anaesthetics
SexSex : Women appear to emerge from anaesthesia : Women appear to emerge from anaesthesia
more rapidly than men. more rapidly than men.
Individual variation Individual variation in sensitivity to anaesthesiain sensitivity to anaesthesia

13. MEMORY AND ANAESTHESIA:MEMORY AND ANAESTHESIA:
Anaesthesia , with increasing depth , progressively Anaesthesia , with increasing depth , progressively
decreases the ability of brain to carry out tasks and to decreases the ability of brain to carry out tasks and to
remember them afterwards.remember them afterwards.
Memory is affected much before noticeable autonomic Memory is affected much before noticeable autonomic
responses are seen.responses are seen.
Types of memory :-Types of memory :-
Short -termShort -term
Long –termLong –term

Procedural / Implicit Procedural / Implicit } } effortless effortless
retrievalretrieval
Declarative : 1) Somatic / ImplicitDeclarative : 1) Somatic / Implicit
2) Episodic / Explicit - efforts required 2) Episodic / Explicit - efforts required

14. STAGES OF AwARENESS :STAGES OF AwARENESS :
(GRIFFITH & JONES)(GRIFFITH & JONES)
1.1.Conscious awareness with explicit recallConscious awareness with explicit recall
2.2.Conscious awareness with no explicit recallConscious awareness with no explicit recall
3.3.Unconscious awareness with implicit recallUnconscious awareness with implicit recall
4.4.No awarenessNo awareness

19. Specific drugS & depth of Specific drugS & depth of
anaeStheSia :anaeStheSia :

20. inhalational agentS :inhalational agentS :
Purposeful movement of any part of the body in Purposeful movement of any part of the body in
response to noxious perioperative stimuli is the most response to noxious perioperative stimuli is the most
useful clinical sign of depth of anaesthesiauseful clinical sign of depth of anaesthesia
Eger & Merkel therefore defined MAC as the minimum Eger & Merkel therefore defined MAC as the minimum
alveolar concentration of inhaled anaesthetic required alveolar concentration of inhaled anaesthetic required
to prevent 50% of subjects from responding to painful to prevent 50% of subjects from responding to painful
stimuli with gross purposeful movementstimuli with gross purposeful movement
Tracheal intubation represents stronger noxious
stimulus than all surgical stimuli

21. inhalational agentS :inhalational agentS :
MAC has been expanded as :MAC has been expanded as :
MAC-awake :(Stoelting)minimum alveolar MAC-awake :(Stoelting)minimum alveolar
concentration that would allow opening of eyes on concentration that would allow opening of eyes on
verbal command during emergence from anaesthesiaverbal command during emergence from anaesthesia
MAC-intubation : (Yakaitis)minimum alveolar MAC-intubation : (Yakaitis)minimum alveolar
concentration that would inhibit movement & coughing concentration that would inhibit movement & coughing
during endotracheal intubation.during endotracheal intubation.
MAC-BAR : (Roizen)minimum alveolar concentration
that would prevent adrenergic response to skin incision
as measured by venous concentration of
catecholamines

22. MAC may be modified by use of nitrous oxide,opioids MAC may be modified by use of nitrous oxide,opioids
& other anaesthetics& other anaesthetics
The haemodynamic responses to surgical stimuli do The haemodynamic responses to surgical stimuli do
not correlate well with end tidal concentration of not correlate well with end tidal concentration of
inhaled anaesthetics.inhaled anaesthetics.
inhalational agentS :inhalational agentS :

23. nonopioid intravenouS agentS: nonopioid intravenouS agentS:
induction of anaeStheSia induction of anaeStheSia
Plasma drug concentration peaks in half to one minute Plasma drug concentration peaks in half to one minute
& declines rapidly due to redistribution& declines rapidly due to redistribution
Depth of anaesthesia follows plasma drug Depth of anaesthesia follows plasma drug
concentrationconcentration
Clinical endpoints for assessment-Clinical endpoints for assessment-
1.1.Loss of verbal responsivenessLoss of verbal responsiveness
2.2.Loss of eyelid reflexLoss of eyelid reflex
3.3.Loss of corneal reflexLoss of corneal reflex
Strongest stimulation during induction is laryngoscopy Strongest stimulation during induction is laryngoscopy
& intubation& intubation
Analgesics are needed to maintain haemodynamicsAnalgesics are needed to maintain haemodynamics

24. nonopioid intravenouS agentS: nonopioid intravenouS agentS:
Maintenance of anaeStheSiaMaintenance of anaeStheSia
Plasma levels of anaesthetic agents are accurate Plasma levels of anaesthetic agents are accurate
predictors of brain levels of the drug & good indicators predictors of brain levels of the drug & good indicators
of anaesthetic depthof anaesthetic depth
Clinical endpoints for assessment :Clinical endpoints for assessment :
1.1.Loss of eyelid reflexLoss of eyelid reflex
2.2.Loss of corneal reflexLoss of corneal reflex
3.3.Absence of movement in response to sqeezing Absence of movement in response to sqeezing
trapeziustrapezius
Opioids in large doses need to be added when precise Opioids in large doses need to be added when precise
haemodynamic control is necessary as in CADhaemodynamic control is necessary as in CAD

25. t.i.v.a.t.i.v.a.
‘‘Minimum infusion rate’ is used to compare Minimum infusion rate’ is used to compare
requirements of anaestheticsrequirements of anaesthetics
The 50% effective dose & 95 % effective dose The 50% effective dose & 95 % effective dose
infusion rates are calculated using movement infusion rates are calculated using movement
response to skin incisionresponse to skin incision
IV bolus of anaesthetic combined with maintenance IV bolus of anaesthetic combined with maintenance
infusion can produce steady state plasma infusion can produce steady state plasma
concentration of the drug to maintain anaesthetic concentration of the drug to maintain anaesthetic
depth.depth.

26. opioidS :opioidS :
CpCp
50 50 is steady state plasma concentration of opioid is steady state plasma concentration of opioid
which will prevent purposeful movement to noxious which will prevent purposeful movement to noxious
stimuli in 50% populationstimuli in 50% population
Clinical events which indicate inadequate infusion Clinical events which indicate inadequate infusion
rates-rates-
1)1)Increase in systolic BP more than 15 mmHg above Increase in systolic BP more than 15 mmHg above
normal for the patientnormal for the patient
2)2)Heart rate > 90/m in absence of hypovolemiaHeart rate > 90/m in absence of hypovolemia
3)3)Somatic : movement, swallowing, coughing or opening Somatic : movement, swallowing, coughing or opening
eyeseyes
4)4)Autonomic : lacrimation, sweating, flushingAutonomic : lacrimation, sweating, flushing

27. aSSeSSMent of depth aSSeSSMent of depth
of anaeStheSia :of anaeStheSia :

28. Subjective methodsSubjective methods ::
–Autonomic changesAutonomic changes
–Changes in pupil diameterChanges in pupil diameter
–Isolated forearm techniqueIsolated forearm technique
Objective methodsObjective methods ::
–E.E.G. & derived indicesE.E.G. & derived indices
–Spontaneous surface electromyogramSpontaneous surface electromyogram
–Lower oesophageal contractilityLower oesophageal contractility
–Heart rate variabilityHeart rate variability
–Evoked potentialsEvoked potentials
claSSification of MethodS :claSSification of MethodS :

29. SuBJective MethodS :SuBJective MethodS :

30. 1. autonoMic changeS :1. autonoMic changeS :
Include sudden hypertension, tachycardia, sweating, Include sudden hypertension, tachycardia, sweating,
tearing or mydriasistearing or mydriasis
Commonly used as clinical indicators of lightening of Commonly used as clinical indicators of lightening of
depth of anaesthesiadepth of anaesthesia
Patient response to surgical stimulus (PRST) score Patient response to surgical stimulus (PRST) score
includes 4 haemodynamic parameters : Pressure includes 4 haemodynamic parameters : Pressure
(BP), Rate (pulse rate), Sweating & Tearing (BP), Rate (pulse rate), Sweating & Tearing

31. p.r.S.t. Scorep.r.S.t. Score
INDEX :CONDITION : SCORE :
Pressure <control + 15
<control + 30
>control + 30
0
1
2
Pulse Rate<control + 15
<control + 30
>control + 30
0
1
2
Sweating Nil
Skin moist
Visible beads of sweat
0
1
2
Tears No excess tears in open eyes
Excess tears in open eyes
Tears over flowing

0
1
2

32. diSadvantageS :diSadvantageS :
These changes are also seen with intra-operative These changes are also seen with intra-operative
events like hypotension, dehydration, hypoxia, events like hypotension, dehydration, hypoxia,
hypothermia, hyperthermia or sudden blood loss.hypothermia, hyperthermia or sudden blood loss.
Patient factors like built & baseline tone also affectPatient factors like built & baseline tone also affect
Drugs like beta blockers , inotropes, vasodilators, anti-Drugs like beta blockers , inotropes, vasodilators, anti-
hypertensives also lead to such haemodynamic hypertensives also lead to such haemodynamic
changes while opioids & muscle relaxants suppress changes while opioids & muscle relaxants suppress
them.them.
Haemodynamic response to noxious stimuli does not Haemodynamic response to noxious stimuli does not
necessarily signify awareness nor does lack of necessarily signify awareness nor does lack of
haemodynamic changes guarantee unconsciousnesshaemodynamic changes guarantee unconsciousness

33. 2. changeS in pupil diaMeter :2. changeS in pupil diaMeter :
Guedel’s stages of ether anaesthesia describe initial Guedel’s stages of ether anaesthesia describe initial
pupillary constriction followed by dilatation as pupillary constriction followed by dilatation as
anaesthesia deepens.anaesthesia deepens.
These changes are affected by circulating These changes are affected by circulating
catecholamines, atropine & opioids.catecholamines, atropine & opioids.
Pupillary light reflex is also affected by opioids & Pupillary light reflex is also affected by opioids &
anoxia .anoxia .

34. 3.iSolated forearM techniQue :3.iSolated forearM techniQue :
Tourniquet inflated on an arm of patient prior to Tourniquet inflated on an arm of patient prior to
administering intravenous muscle relaxant isolates administering intravenous muscle relaxant isolates
forearm & allows it to remain free to move in response forearm & allows it to remain free to move in response
to verbal command in light plane of anaesthesia.to verbal command in light plane of anaesthesia.
Limitations :Limitations :
Nonspecific startle response may be wrongly Nonspecific startle response may be wrongly
interpreted as consciousnessinterpreted as consciousness
Higher dose of muscle relaxant required in IFT to Higher dose of muscle relaxant required in IFT to
prevent movementprevent movement
Inability to move arm despite consciousness is Inability to move arm despite consciousness is
complained by some patientscomplained by some patients

35. oBJective MethodS :oBJective MethodS :

36. 1.electroencephalograM :1.electroencephalograM :
EEG is a low voltage (1-50 µv) deflection recorded EEG is a low voltage (1-50 µv) deflection recorded
from surface of scalp by electrodes.from surface of scalp by electrodes.
Noninvasive indicator of cerebral functionNoninvasive indicator of cerebral function
Represents cortical electrical activity derived from Represents cortical electrical activity derived from
excitatory & inhibitory postsynaptic activityexcitatory & inhibitory postsynaptic activity
This electrical activity has physiologic correlates This electrical activity has physiologic correlates
relevant to depth of anaesthesiarelevant to depth of anaesthesia
Cerebral physiology & metabolism both affect the EEG Cerebral physiology & metabolism both affect the EEG
& anaesthetic drugs affect both cerebral physiology & & anaesthetic drugs affect both cerebral physiology &
EEGEEG

37. 1.ELECTROENCEPHALOGRAM :1.ELECTROENCEPHALOGRAM :
 Effects of noxious stimulus on EEG :Effects of noxious stimulus on EEG :
Desynchronization with appearance of fast rhythmsDesynchronization with appearance of fast rhythms
Appearance of 6 -10 Hz spindlesAppearance of 6 -10 Hz spindles
Bursts of 1-3 Hz slow wavesBursts of 1-3 Hz slow waves
Anaesthetic drugs result in low frequency EEG & burst Anaesthetic drugs result in low frequency EEG & burst
suppression at high concentration suppression at high concentration

39. EEG INDICES :EEG INDICES :
1) Compressed spectral array (CSA): 1) Compressed spectral array (CSA):
The individual frequency distributions of EEG can be The individual frequency distributions of EEG can be
considered as time slices and joined together into a considered as time slices and joined together into a
3D plot is called CSA3D plot is called CSA
During peaks of anaesthesia, CSA shows low During peaks of anaesthesia, CSA shows low
frequency activityfrequency activity
At recovery and lighter planes CSA shows high At recovery and lighter planes CSA shows high
frequency activity with decreased low frequency frequency activity with decreased low frequency
waveswaves
Disadvantages include difficulty to comprehend the Disadvantages include difficulty to comprehend the
changes & to quantify themchanges & to quantify them

41. EEG INDICES :EEG INDICES :
2) Spectral edge frequency (SEF) : Defined as 2) Spectral edge frequency (SEF) : Defined as
frequency below which 95 % of EEG power is frequency below which 95 % of EEG power is
contained.contained.
3) Median frequency (MF) : Defined as frequency above 3) Median frequency (MF) : Defined as frequency above
& below which 50% of EEG power spectrum is & below which 50% of EEG power spectrum is
distributed.distributed.
4) Bispectral index (BIS) 4) Bispectral index (BIS)

42. BISPECTRAL BISPECTRAL
INDEXINDEX

43. BISPECTRAL INDEX :BISPECTRAL INDEX :
Developed in 1987, by Aspect Medical Systems in Developed in 1987, by Aspect Medical Systems in
Massachusetts Massachusetts




It is a numerical index ranging from 100 (awake) to 0 It is a numerical index ranging from 100 (awake) to 0
(no detectable EEG activity) (no detectable EEG activity)
The BIS correlates with level of responsiveness & The BIS correlates with level of responsiveness &
provides an excellent prediction of the level of provides an excellent prediction of the level of
consciousness with propofol, midazolam & isoflurane consciousness with propofol, midazolam & isoflurane
anaesthesia anaesthesia



 The bispectral index itself is a complex mathematical
algorithm that allows a computer inside the BIS
monitor to analyze data from a patient's
electroencephalogram (EEG) during surgery.

44. Multiple clinically relevant measures like movement, Multiple clinically relevant measures like movement,
haemodynamics, drug concentrations, consciousness, haemodynamics, drug concentrations, consciousness,
recall are considered alongwith concurrent EEG data.recall are considered alongwith concurrent EEG data.
Advanced multivariate statistical analysis is used to Advanced multivariate statistical analysis is used to
correlate components of the multiple EEG signal correlate components of the multiple EEG signal
processing approaches with the clinical data to create processing approaches with the clinical data to create
the univariate BIS indexthe univariate BIS index
The BIS index measures hypnotic components of the The BIS index measures hypnotic components of the
anaesthetic & is insensitive to analgesic components.anaesthetic & is insensitive to analgesic components.
BIS is useful monitor to adjust anaesthetic dosages & BIS is useful monitor to adjust anaesthetic dosages &
decreases incidence of haemodynamic disturbances & decreases incidence of haemodynamic disturbances &
leads to improved recoveryleads to improved recovery
BISPECTRAL INDEX :BISPECTRAL INDEX :

45. DESCRIPTION :DESCRIPTION :
The BIS system is integrated into patient The BIS system is integrated into patient
monitoring devices . monitoring devices .
The BIS system displays both raw data from The BIS system displays both raw data from
the EEG and a single number between 100 the EEG and a single number between 100
(indicating an awake patient) and 0 (indicating (indicating an awake patient) and 0 (indicating
the absence of brain activity) that represents the absence of brain activity) that represents
the patient's degree of sedation.the patient's degree of sedation.
The target number for most anesthetized The target number for most anesthetized
patients is between 40 and 60.patients is between 40 and 60.

46. BIS ELECTRODESBIS ELECTRODES::

49. DEvELOPING THE BIS INDEX :DEvELOPING THE BIS INDEX :

50. BIS & DOSAGE TITRATION BIS & DOSAGE TITRATION
Physical signs Clinical
picture
BIS
value
Management
1.Hypertension Light HighConsider hypnotic / analgesic doses
Tachycardia 40-60 Analgesic dose / antihypertensive
Movement LowDecrease hypnotic dose / start
antihypertensive
Autonomic response
2.Stable vitals Adequate HighConsider hypnotic / analgesic doses
40-60Observe
LowConsider decrease in both drug doses
3.Hypotension Deep HighConsider hypnotic / analgesic doses
Arrhythmias Rule out other etiologies
BP support
40-60Rule out other etiologies
BP support
LowDecrease both drug doses
BP support

51. LIMITATIONS Of BIS :LIMITATIONS Of BIS :
BIS values are affected by the choice of anesthetic BIS values are affected by the choice of anesthetic
agent. A patient with a BIS score of 60 agent. A patient with a BIS score of 60
anesthetized with one combination of agents may anesthetized with one combination of agents may
be more deeply sedated than another patient with be more deeply sedated than another patient with
the same score but anesthetized with a different the same score but anesthetized with a different
combination of drugs. combination of drugs.
The BIS monitor appears unable to accurately The BIS monitor appears unable to accurately
track changes in consciousness produced by track changes in consciousness produced by
certain anaesthetics, specifically ketamine and certain anaesthetics, specifically ketamine and
nitrous oxide. nitrous oxide.
The changes in the BIS algorithm resulting from The changes in the BIS algorithm resulting from
updating and refinement of the producer’supdating and refinement of the producer’s

52. LIMITATIONS Of BIS :LIMITATIONS Of BIS :
database make it difficult to compare results database make it difficult to compare results
obtained by different investigators using different obtained by different investigators using different
versions of the BIS monitor. versions of the BIS monitor.
BIS values are difficult to correlate with other BIS values are difficult to correlate with other
measurements of anaesthetic depth or altered measurements of anaesthetic depth or altered
consciousness like serum concentrations of consciousness like serum concentrations of
anesthetic agents. anesthetic agents.
Standard BIS scores are not useful in monitoring Standard BIS scores are not useful in monitoring
special patient populations, particularly critically ill special patient populations, particularly critically ill
patients with unstable body temperatures and patients with unstable body temperatures and
patients with dementia. patients with dementia.

53. USES Of BIS :USES Of BIS :
Reduces cost by decreasing anaesthetic use & stay in Reduces cost by decreasing anaesthetic use & stay in
PACUPACU
Provides a useful guide for titration of anaesthetic Provides a useful guide for titration of anaesthetic
agents in cardiac surgery, elderly & paediatric patientsagents in cardiac surgery, elderly & paediatric patients
Reduces the incidence of intraoperative awarenessReduces the incidence of intraoperative awareness

54. SPONTANEOUS SURfACE SPONTANEOUS SURfACE
ELECTROMyOGRAMELECTROMyOGRAM

55. SpontaneouS Surface SpontaneouS Surface
electromyogramelectromyogram
In patients who are not completely paralyzed, In patients who are not completely paralyzed,
spontaneous surface electromyogram (SEMG) can be spontaneous surface electromyogram (SEMG) can be
recorded from various muscle groups, especially recorded from various muscle groups, especially
facial, abdominal and neck muscles.facial, abdominal and neck muscles.
The level of SEMG has been observed to fall during The level of SEMG has been observed to fall during
anaesthesia and to rise to pre-anaesthetic levels just anaesthesia and to rise to pre-anaesthetic levels just
before awakening.before awakening.

56. lower oeSophageal lower oeSophageal
contractilitycontractility

57. lower oeSophageal lower oeSophageal
contractilitycontractility
The non-striated muscles in the lower half of The non-striated muscles in the lower half of
oesophagus retain their potential activity even after full oesophagus retain their potential activity even after full
skeletal muscle paralysis.skeletal muscle paralysis.
Provide two prime derivativesProvide two prime derivatives
1] Spontaneous lower oesophageal 1] Spontaneous lower oesophageal
contractions(SLOG)contractions(SLOG)
These are non-propulsive spontaneous contractions These are non-propulsive spontaneous contractions
mediated via vagal motor nuclei and reticular mediated via vagal motor nuclei and reticular
activating system in the brain stem. The frequency of activating system in the brain stem. The frequency of
these movements is increased as the dose of the these movements is increased as the dose of the
anaesthetic is reduced.anaesthetic is reduced.

58. lower oeSophageal lower oeSophageal
contractilitycontractility
2] Provoked lower oesophageal contractions(PLO)2] Provoked lower oesophageal contractions(PLO)
These are obtained by inflation of a small balloon in These are obtained by inflation of a small balloon in
the lower oesophagus. The brief inflation of small the lower oesophagus. The brief inflation of small
balloon provokes a secondary pulsatile response, balloon provokes a secondary pulsatile response,
which increases in amplitude as anaesthetic depth which increases in amplitude as anaesthetic depth
decreases.decreases.

59. heart rate heart rate
variabilityvariability

60. heart rate variabilityheart rate variability
Normally heart rate increases during inspiration and Normally heart rate increases during inspiration and
decreases during expiration, through a predominantly decreases during expiration, through a predominantly
parasympathetic reflex connecting stretch receptors in parasympathetic reflex connecting stretch receptors in
the lungs and aorta to vagal motor neurons the lungs and aorta to vagal motor neurons
innervating the heart. This is called innervating the heart. This is called respiratory sinus respiratory sinus
arrhythmia(RSA).arrhythmia(RSA).
It is typically characterized by greater than 10% It is typically characterized by greater than 10%
variation in the ECG P-wave interval over 5 minutesvariation in the ECG P-wave interval over 5 minutes
There is reduction in RSA during anaesthesia together There is reduction in RSA during anaesthesia together
with increase in RSA during recovery or light planes.with increase in RSA during recovery or light planes.

61. heart rate variabilityheart rate variability
In addition, surgical stimulation during light In addition, surgical stimulation during light
anaesthesia elicits a greater increase on RSA than anaesthesia elicits a greater increase on RSA than
seen during lightening anaesthesia alone.seen during lightening anaesthesia alone.

62. evoked potentialSevoked potentialS

63. evoked potentialS (ep)evoked potentialS (ep)
Show the response of more localized areas of the Show the response of more localized areas of the
brainstem, midbrain and cerebral cortex to specific brainstem, midbrain and cerebral cortex to specific
areas.areas.
Recording of EPs consisting of recording EEG epochs Recording of EPs consisting of recording EEG epochs
and time-referencing them to sensory stimuli that have and time-referencing them to sensory stimuli that have
been applied in a repeated fashion.been applied in a repeated fashion.
For intra-operative monitoring, 3 types of EPs are For intra-operative monitoring, 3 types of EPs are
commonly used:commonly used:
1}SEP (somatosensory EP) is recorded over the 1}SEP (somatosensory EP) is recorded over the
somatosensory cortex in response to tibial, peronial or somatosensory cortex in response to tibial, peronial or
median nerve stimulation.median nerve stimulation.
2}VEP (Visual EP)is recorded over occipital cortex in 2}VEP (Visual EP)is recorded over occipital cortex in
response to photic stimulation of the eyes. response to photic stimulation of the eyes.

64. evoked potentialS (ep)evoked potentialS (ep)
3}AEP (auditory EP) is recorded at primary auditory 3}AEP (auditory EP) is recorded at primary auditory
cortex in response to auditory canal stimulation by cortex in response to auditory canal stimulation by
audible clicks.audible clicks.It is most commonly used for the It is most commonly used for the
assessment of anaesthetic drug effect. assessment of anaesthetic drug effect.
•As the concentration of potent inhaled anaesthetic As the concentration of potent inhaled anaesthetic
increases, the latencies of SEP, VEP and AEP increases, the latencies of SEP, VEP and AEP
increase and amplitudes decrease.increase and amplitudes decrease.
•In contrast, NIn contrast, N
22O produces a dose-related decrease in O produces a dose-related decrease in
the amplitude of VEP and SEP, but no effect on the amplitude of VEP and SEP, but no effect on
latency.latency.

65. auditory evoked potential auditory evoked potential
indexindex
Derived from auditory evoked potential and represents Derived from auditory evoked potential and represents
a single numerical variable for monitoring depth of a single numerical variable for monitoring depth of
anaesthesia.anaesthesia.
Calculated from the amplitude difference between Calculated from the amplitude difference between
successive segments of the AEP curve.successive segments of the AEP curve.
AEP index of 37 is 100% specific and 52% sensitive AEP index of 37 is 100% specific and 52% sensitive
for unconsciousness.for unconsciousness.
AEP index is highly sensitive for distinguishing the AEP index is highly sensitive for distinguishing the
transition from unconsciousness to consciousness. transition from unconsciousness to consciousness.

66. futurefuture

67. futurefuture
The only reliable way of determining The only reliable way of determining
depth of anaesthesia will require a depth of anaesthesia will require a
measure of cerebral activity and measure of cerebral activity and
localization of the activity to specific localization of the activity to specific
cortical regions and areas in cortical regions and areas in
brainstem, in real time.brainstem, in real time.

68. poSition emiSSion tomography (pet)poSition emiSSion tomography (pet)
 PET scanning studies have PET scanning studies have
revealed that propofol anaesthesia revealed that propofol anaesthesia
has a widespread suppressive effect has a widespread suppressive effect
on cerebral metabolism. on cerebral metabolism.

69. ultra SenSitive Super conducting ultra SenSitive Super conducting
quantum interference device (SquidS)quantum interference device (SquidS)
Non invasive method, which measures Non invasive method, which measures
functional activity of brain.functional activity of brain.
 Although expensive at present this may Although expensive at present this may
provide the ultimate monitor to the provide the ultimate monitor to the
anaesthesiologists. anaesthesiologists.

70. thank you ….