3. Inhalational Agents Flashcards
Sevoflurane
MAC
Metab by
releases
Mac 2.5
By P450 2E1 to hexafluoroisopropanol and the release of inorganic fluoride ions.
Enflurane
B:G
Mol wt
BP
blood:gas partition coefficient - 1.8
Wt - 184
BP 56.5
Isoflurane
B;G
Mol wt
Blood g 1.4
Mol wt 184
Desflurane
B:G coeff
Problems
fluorinated methyl ether
approximately one-fifth the potency of isoflurane.
All volatile anaesthetic agents are weak calcium channel antagonists and therefore potentiate neuromuscular blocking agents.
It has a boiling point of approximately 23°C
The induction of anaesthesia can stimulate the sympathetic system as can change in inspired concentrations.
MAC 4-6%
B:G 0.42
way irritation leading to coughing, apnoea and laryngospasm
Halothane
B:G
BP
B;G 2.4
BP 23.5
Type 1 halothane hepatitis is characterised by a transient derangement of the liver function tests together with an acute hepatitis on histology. It may resolve without treatment and has no long term side effects.
Type 2 halothane hepatitis is thought to have an auto-immune aetiology and has a significant mortality.
Thymol is a preservative added to halothane, which accumulates on the wicks and effects the efficiency of the vapouriser if it is not emptied regularly.
MAC increased by
Hyperthyroidism
hyperthermia
MAC decreased by
Hypotension
Hypothermia
Hypoxia
HPV inhibited by
no effect
Agents that inhibit HPV
Ether
Halothane
Desflurane (>1.6 MAC)
Salbutamol
Agents with minimal or no effect on HPV
Thiopentone Fentanyl Desflurane (1MAC) Isoflurane (<1.5MAC) Sevoflurane (1MAC) Propofol.
Oil gas coeff & mac of Desflurane Isoflurane N2O Sevo Xenon
The physicochemical properties of all drugs influence pharmacokinetic behaviour in vivo.
Oil/gas (MAC) Desflurane 18 6 Isoflurane 90 1.2 Nitrous oxide 1.4 104 Sevoflurane 53.4 2 Xenon 1.9 71
Clinical potency is measured using the minimal alveolar concentration (MAC).
The anaesthetic agent with the highest oil:gas partition coefficient has the lowest MAC.
Halothane hepatitis
Minor derangement in liver function tests to fulminant hepatic failure.
appearance of liver damage within 28 days of halothane exposure
Seventy five per cent of patients with halothane hepatitis
avoided if:
Previous exposure has occurred within three months
There is known adverse reaction to halothane
Family history of adverse reaction
Pre-existing liver disease.
Halothane increases cerebral blood flow but reduces intraocular pressure.
MH & triggers
`Life threatening autosomal dominant condition linked with other myotonic disorders
Intracellular calcium transport is deranged with generalised muscular contraction generating excess heat.
Trigger
Sux
Inhaled agents - Trichloroethylene, cycloprop
Rx Dantrolene
Haloperidol - NLMS -Rx dantrolene also / bromocriptine
MAC is
(MAC) is defined as the alveolar concentration required in order to prevent movement to a standard surgical stimulus in 50% of unpremedicated patients at a pressure of 1 atmosphere.
Meyer-Overton hypothesis
Meyer-Overton hypothesis states that potency (lipid solubility) is proportional to the oil:gas partition co-efficient. The relationship between log oil:gas partition coefficient and MAC is linear with a high oil:gas partition coefficient equating to a low MAC (higher potency).
The blood:gas partition coefficient
The blood:gas partition coefficient is a measure of the solubility of an anaesthetic agent in blood. The lower the solubility, the greater the partial pressure it exerts and the faster the onset.
Nitrous Oxide
affect on cerebral
flow
metab
Affect on NMDA
Affect on CO2 reactivity
Whats the second mssgr
causes direct cerebral stim=
increases cerebral blood flow.
Increased metabolism specifically in the frontal lobes and limbic system =
increases the cerebral metabolic rate of oxygen consumption (CMRO2).
Cerebral autoregulation is impaired
used with propofol maintained.
Nitrous oxide antagonises NMDA receptors (it is not an NMDA agonist), which may result in neurological damage, but this effect may be limited by the concurrent use of GABA agonists or inhalational anaesthetics.
Carbon dioxide reactivity remains unaffected.
Cyclic guanosine monophosphate (cGMP - 2nd messenger
Xenon
Inert gas
not negatively inotropic
Not cause vasodilatation.
Xenon gives rapid induction and recovery,
low blood/gas solubility coefficient (0.115),
MAC of 71%
boiling point is −108°C
oil/gas solubility coefficient of 1.9.
Its low blood solubility can cause diffusion hypoxia if supplementary oxygen is not provided at the end of anesthesia.
Xenon:
Has a low toxicity
Is not teratogenic
Is not metabolised within the body, and
Is not a trigger for malignant hyperpyrexia.
Several studies have shown that xenon exhibits neuroprotective properties without co-existing neurotoxicity by protecting neural cells against ischaemic injury.
Xenon is produced as a by-product of the fractional distillation of liquid air and is an expensive process and is thus delivered in closed circuit breathing systems.
Xenon-133, unlike elemental xenon, is a radioactive gas produced by fission of uranium-235, which is used in diagnostic inhalational tests.
Ideal volatile agent for an inhalational induction
Pleasant smell and not pungent
Not irritant to the respiratory tract, that is, induces breath-holding, coughing or laryngeal spasm
Rapid onset and offset of action. (e blood:gas partition coefficient)
Blood gas coeff of common inhal
Halothane 2.3 Isoflurane 1.4 Sevoflurane 0.6 Desflurane 0.45 Nitrous oxide 0.47
Penthrox
what the blood gas coeff
mac
svp
properteis
metab
safe upper lim
Methoxyflurane - halogen ether
high blood gas - 16 - slow
Mac .16
SVP 49 @20
Non iritant, min fx systyemic
Neprhotx - lipid solubility
Pehtnrox = .3 mac hours
onset 4-5 min
50% hepatic meatb
Fluoride ion -
Neprhotox - safe lim 2mac hours
Up to 50% of methoxyflurane undergoes hepatic metabolism. The principal metabolites are fluoride ions, dichloroacetic acid and oxalic acid. Recent studies have shown that methoxyflurane also undergoes significant metabolism to fluoride within the kidney itself. The oxalic acid and fluoride are both nephrotoxic. The safe upper limit of exposure to methoxyflurane is 2 MAC-hours, which gives a serum fluoride level of 40 μmol/L, below the threshold for toxicity.
Methoxyflurane (PenthroxTM) is delivered from a self-administered inhaler with a volume of 3 mL that provides 25-30 minutes of analgesia with continuous use (intermittent use extends the duration of action).
The maximum exposure from a single methoxyflurane inhaler device is 0.3 MAC-hours, while the maximum recommended dose for analgesia of five inhalers a week
The onset of analgesic effect is 4-5 minutes.
MAC
Unaffected by
Increased by
Decreased by
Unaffected Gender Acidaemia Alkalaemia Body weight Serum potassium variations and The duration of the anaesthetic.
MAC is increased in:
Infants/children Hyperthermia Hypermetabolic states Sympathetic increase and Chronic alcoholism.
MAC is reduced in:
Hypothermia
Hypoxaemia
Old age
The presence of other depressant drugs,for example, opioids and
When the central nervous system has low levels of catecholamines, for example, alpha methyl dopa.
Carbon dioxide (levels >120 mmHg) has been used an anaesthetic - Hickman, which by an additive effect can be considered as decreasing MAC. On the other hand a markedly elevated CO2 (and even severe acidaemia) can stimulate the sympathetic system/release catecholamines and result in MAC increasing.
N2o manufactured by
What impurities formed
How reomoved
Examples of impurities
problems with the impurities
How do we test for these impurities
Problems with prolonged use of N2O
heating ammonium nitrate (not nitrite) to 240°C.
Ammonia
Nitric acid
Higher oxides of nitrogen),
Removed by passage through scrubbers and washers.
The higher oxides of nitrogen which are formed include:
Nitric oxide (NO) Nitrogen dioxide (NO2) Dinitrogen trioxide (N2O3) which decomposes to NO and NO2.
Irritant Respiratory tract -
pulmonary oedema hours
severe fibrotic reaction may occur after several weeks, which destroys the lung tissue.
Tested for contamination
Higher oxides of nitrogen,
Exposing moistened starch-iodide paper - gaseous contents of a cylinder, which turns blue if contaminants are present.
Prolonged use of N2O is associated with many side effects including the inhibition of methionine synthase, which results in bone marrow depression and a megaloblastic anaemia (not microcytic).
GWP100 of the following gases are as follows:
What is GWP100
What is it for Co2 Sevo iso des sevo methane
The inhalation halogenated anaesthetic agents, isoflurane, sevoflurane, and desflurane absorb infra-red radiation within the range of 7-10 µm and have a significant GWP100. The Carbon dioxide 1 Methane 23 Sevoflurane 130 Nitrous oxide 310 Isoflurane 510 Desflurane 2540
The approximate percentage metabolism of the volatile agents is as follows:
Halothane Iso En sevo des
Desflurane 0.02%.
Isoflurane 0.2%
Enflurane 2%
Sevoflurane 3-6%
Halothane 20%
Halothane effect on vasoconstriction cerebral vs iso
BP
SVP
Affect on myocardium
MAC
Halothane causes less cerebral vasoconstriction than isoflurane, which explains why isoflurane is popular in neuroanaesthesia.
Halothane boils at 50°C and has a saturated vapour pressure (SVP) of 32.3 kPa. The SVP is almost identical to isoflurane, and this may allow them be delivered using the same vaporiser, for example, Oxford miniature vaporiser.
All volatile agents inhibit hypoxic pulmonary vasoconstriction and therefore increase shunting.
Halothane sensitises the myocardium to circulating catecholamines and this is one reason why surgeons usually ask the anaesthetist prior to infiltrating epinephrine (adrenaline) containing local anaesthetics.
Drop SVR 18%
barorec reflex decerease
ganlgiong blocking
central vasomot depressant action
The minimum alveolar concentration (MAC) of halothane is 0.7% (not 1.15%).
Halothane absorb Uv + IR -
causes change elsaticity of silicone rubber
can be determ using refractormer
Mol wt 197 vs N2o 44
Convert MAC to PP
The partial pressure of a gas is proportional to its concentration, therefore, by transforming the MAC values for the volatile agents into partial pressures at 1 atmosphere (or 760 mmHg):
MAC (Volume %) = ( partial pressure of volatile agent (x) / 760mmHg )x 100
Halothane for example = 0.75 =( x/760)x100
x=(0.75 x 760)/100 =5.7mmHg
Age related mac partial pressures
Age related MAC for 40-year-old patient population
Halothane (MAC of 0.75%) has a partial pressure of 5.7
Isoflurane (MAC of 1.17%) has a partial pressure of 8.9
Enflurane (MAC of 1.68%) has a partial pressure of 12.8
Sevoflurane (MAC of 1.8%) has a partial pressure of 13.7
Desflurane (MAC of 6.6%) has a partial pressure of 50.2
Properties ideal anaesthetic
Phsyical
- Liquid Room temp
- High SVP - easy vape
- Low latent heat vaporisation
- Low specific heat capacity
- Chemically stable in light & heat
- Inert when in contact w/ metal rubber & soda lime
- Non flammable /explosive
- Long shelf life
- Inexpensive
10 No additives / preservatives - Environmentally friendly
- Non irritant/ nice smell
PK of Ideal inhalational
Low blood : gas coefficientg - fast onset
High oil partiation coeff - low MAC
Minimal metabolism - no Fl- prod
Excretion via lungs
PD Ideal
CNS Smooth rapid indcution Only affect cns Rapidly reversbily No increase CBF/ICP Analgesic Not epileptogenic
CVS
No depression
No sensation of myaocardium
No cor flow decrease
Resp
No breath holding laryngospasm
broncholidation
No resp depression
MSK
Releax
Non MH trigg#
GI
Anti emetic
Reanl haep haem
No effects / flow
not rterato
Onset is determined by
Blood: gas coefficient
Lower = faster
Potency
Oil:gas partition coeff
High - miore potent
Signif blood gas partition coeff
Ratio - amt anaes in blood to gas when equal vol in equil
PParadox a/w speed induction
Poorly soluble - high PP in blood - fast onset
Converse - solube -
rapidly enter blood - exert low PP
Slower onset
Effects related to PP in blood -> brain * not absolute amount present
Blood gas part coeff in order
Xenon .17 Des .42 NO .47 Sevo .68 Iso 1.4 En 1.9 Halo 2.3
Onset influenced
Blood gas coeff
Also - by mac
Alveolar vent /; irritability
Des - profound irritant
Equilibrium reached quicker with high or low blood g partition coeff
Reached more quick;y with those w/ a lower partition coeff
Factors influencing the speed appraoch equilibrium
Phsyiologty patient - factors related agents
High inspire conc - rapid increase PP alveoli - rapid onset
Increased alveolar vent - PP increase faster
FRC large - Inspoire conc dilute - opposite affect
CO - influces - low - more time for equilibration
incres onset
Conc grad mainatianed where COP increase - slower rise alveolar PP
Cocnetration effect & second gas effect
Concentration effect
NO 20x more solube blood vs O2 / N
High conc introduced - rapid upatke
Reduction in volume alveoli - NO extracted fast than N
Fract conc gas left in alveoli incrase = ‘conc effect’
Second gas effect
Inahl coadmi w/ high conc - NO higher alverolar PP of inahlation
Extration alveolar gas - augmented vent, trachael gas w/ onhal drawn in
-INcrease equligibrium of alveolar fraction to inspire rati = increase onset
Oil gas coeff
Neuraonl cell membrane interactopm
Odrect - secondary messnger - lipid solubility
anaesthetic potenct
Meyer overton hypotehsis
Correl liid solublity & potency
Aneaethsia - number inhal agent molecule dissolbe in lipid bilayer -
If true product of oil:gas partici coeff - constant - not case
Many sub w/ high lipid solubilty - no anaestheit effect
Larger moleculew/ high lip solub - less potent
Iso & en - structu iso
sim oil:gas coeff
Mac iso 1.17 70% that enflurane
Isoflurane
Ideal agent?
Liquid room temp
Chemically stable in light
SVP 32kpa
Inert metal Soluble rubber Not flammable No stabilizers Cheap
Pungent
Irritability
Cough
Breath holding
May react soda lime = CO
Bl:g 1.4
Oil g 98
Low mac 1.17
.2% metabolized
Not toxic
Sevoflurane - ideal
svp
reactivty
bl@g
cost
metab
mol wt
oil gas
Liquid room
Stable light
SVP 22 @ 20
Low solubility Rubber & plastic
Non flammable
No additives preservative
Non irritant
Pleasant odour
Bl:G .7
Low mac
Insol - rapid induction & recovery
Expensive
Unstable moist soda lime - compound a
Hepatic metab 3-5% more other inhalation
No renal
mol wt 200
Oil gas 80
achiral
Desflurane ideal?
Liquid room temp
Protected from light
BP 23.5C
SVP 89 @ 20
Volatile unsuitable conventional vaporiser
TEC6 - heats liquid 39C - SVP 200
No additives
Flammable @17%
Oil:G 29
Mac 6.6
Bld:g .47
Rapid alter depth anaes & fast recovery
Pungent breath holding secretions apnoea
CHF2 group - react soda lime = CO
.02 mean- min tox effects
PD of sevo iso des
Resp depression
Decrease TV
Broncho diln
Iso des drop SVR Map & tachy
SVP dose dep drop CV
Red SVR MAP contractility
All decrease cerebral vascular resistance
Cmr
CBF
Intracranial pressure
None epileptigoenic
All dose depend relax uterus
MH trigger
Sevo metab
Metab
3-5% hepatic cyp450 2e1
Hexaflurousoprpanol
Inorg fl
Compund A
Vinyl ester
CH2F-O-C(CF3)=CF2
Dose dep renal hepatic cerebral dng
Rats not nan
Nephrotoxic to animals?
Lethal conc 300-400ppm sevp 3hrs
Threshold humans 150-200ppm inferred
Conc human less than toxic conc in animals
Max conc <30ppm after 5h even low flow
Not a/w deranged renals
Compounds form CO w. Dry soda lime & why
Inhaled w. CHF2 Passed dry warm soda lime / baralyme Iso En Des
Which form CO w. Dry soda lime
Inhaled w. CHF2 Passed dry warm soda lime / baralyme Iso En Desh
Halothane hepatits
Type 1
Mild
Self limiting hepatotox
25-30%
Trans rise enzymes & altered metabolism
Reductive metab halothane
D/t hepatic hypoxia
Others metab lesser extent other mechanised
Type 2 Uncommon Centrilonular liver necrosis Fulminanr failure Jaundice fever v elevated transaminase
High mortality 30-70%
Immune mediated
Oxidative metabolism -> TFA
Hapten bind covalent protein= antibody fomation
Type 2
Susceptible
Repeated exposure
RF obesity, hypoxaemia, female, middle age
Dx exclusion
Avoid if
Hx adverse reaction
Previous exposure 3/12
Hx unexpl jaund/ pyrexia after exposure
Xenon
Inert odorless noble
Fract distillation air
No occupation / enviro hazards
Makes 0.000087% atm
Non flam
Not combustible
Mac 71%
Low bl:g .14
Extreme rapid
Non irritant
Compat soda
Not metab
Red RR increase TV = Same MV
Higher density/ viscosity
Doesnt appear = diffusion hypoxia
PONV
Cardiostable. No sense to catechol, unalt contractilty
Unconciousness, Significant analgesic,
Muyscle relax >60%
Not MH trigger
Increases CBF - not neuroanest
Used enhanced CTB
Radio labelled xenon - organ blood flow v/q scan
Massive cost - X2000 more NO
No designed machine - use
Difficulty monitoring conc - lack experience use
Helium
Light, inert
Present air & natural gas
Supply 100% - brown cylinders 137 bar
Heliox w 21% O2
brown white / quart shoulder
not support ocombustion
Lower density o2, n & air Upper auirway obstruction - reduce wob Increase alverolar o2 supply less usefl - lower airway Flow is laminar depnding on viscoisty -
Deep sea diving - avoid nitrogen narcosis
Lower denisty - high vocal cord frequency sounds
Lung volumes measure - Low Solublitiy
MAC
Min alveolar conc - inhalation agent Sea level 1 atm & 100% o2 50% un premedicated usbject - fail repsopnd standard midline incision
ED 50 - 50% subjects
other 50 will be higher or lower
MAC 95
I
MAC is related to
Inversely to potency
High MAC - low potency
Plt oil g coeff - using log sacle -linear
Measured usign etconc
Rapid cerebral bloow flow - equil occurs rapidly
Reach - conc alveoli & brain ~equal
Guide clinical dosage
Used simulatneosy additive
0.5 Sev & 0.5 N2O = 1MAC
Prevention of movment - not awareness
Awareness is less than that to prevent movemnet
MAC BAR
Block adrenergic response
Increase in HR BP response to stimulus prevent in 50%
MAC Awake
MAC - 50% not respond to commands
when conc gradully increase from awake state
Alv conc - response aprpro emergncing
What factors decrease MAC
Increase age - 10% per 10 years
Hypo: Volaemia Thermia Oxia Capnia Natraemia Thyroidism
Anaem
Prgenancy
Acute alcohol
CNS depress - opioo bzd
Other drugs
clonidine, lidocaine, NO
Increased
Unaffected by
Decrease age
Hyperthermia
Hypercapnia
Hypernatraemia
Thyrotox
Chronic alcohol & opiod
Severe anxiety
Sympathadrenal stim
Ambient pressure
Unaffected gender, weight, height druation anaes
Mac of Halothane iso en sevo des xeno no
Halo 0.75 iso 1.15 en 1.68 sevo 2 des 6.6 xenon 71 N2O 105
Oil gas patition coeff halo Iso En Seco des xenon N2o
halo 224 Iso 98 En 98 Seco 53 des 19 xenon 1.9 N2o 1.4
N2O
What is it
Who invented it
Inorganic gas
number uses
GA adjunct
Anaglesic labour
painful procedures
Cryotherapy
Priestly
Chemist - prouce 1772
Humphrey 0 invx further 1799 0
Wells 1844 Dental extractions
Not much use again til 1863 - Colton
Manufactured
heat ammonum nitrate to 250C
NH4NO3 -> N2o & 2h20
Temp carefully controlled Or will result in contaminants\; Ammonia Nitrogen N2o Nitro diox Hno3
If inhaled - irrtant
Pulmonary oedmany
Destructive pulonary fibrosis 2-2 week
Actively removed in maufacture of N2o
Scurbbers water & caustic soda
How is N20 stored
Frenchblue cylidner as a liquid - w vapour on top
Kept large cylinder in 2 manifold
Gauge pressure 4400kpa - repesents content untill all in gaseosu phase
Liquid less compressible gas - patially filled
Physical propetries
N2O
Colouless gas - sweet smell
Non flammble
Does support comubstion
Mol tw 44
BP -88
Crit temp 36.5
MAc 105%
Oil: gas sol coeff 1.4
Blood gas sol ceff - 0.47
Advantages N2o
Potent analgesic - better anglesia than pethdine
Weak anaes - >:80% - render unconc
MAC 105% - comb w/ other - redcues mac
Usfeul carier -
Rapid onset - ow blood g coeff
Incrase alveolar conc other agent - due to rapid uptake from alveolar
Accel induction ‘second gas effect’
Disadvantages
High diffsuing capactiy x25 N
Non compliant - air filled vaity - middle ear
Increase rapidly - diffusing into cavity
Compliant air fill cavity - pnuemothorax / owel -diffuse in and increase volume
Emtic effect:
Opiod receptor
Sympathtmietic effect
Bowel distension
Toxic effect
BM suppresion
Neurotox
Second gas - duffsion hypoxia - doesnt present signif - resolve w/ supp O2
Resp depress - mcrase rate - red TV
neg ino - exacrb IHD
Pollution
explain analgesic effects of N20
Several ways
- Opiod receptor
potency of morhine - short time - Modulation of endorphin & encphalins
-stim effect on dopaminergic neurones -
release endog op pep
-explains can antag w/ nalox - Supra spinal descending pain ihin system - release encephalins
Entonox
50:50 Mix N2O & O2
Analgesia - labour / procedure
Store french blue - blue white shoulder
13700 kpa
Crti temp 36.5 = n2o
Mixture - -5.5
‘Pseudocritical temp’
Below temp = liquefaction -& seperation = mix N2o /w 20% dissolved O2 & high conc o2 above liquid
O2 drawn first - reamin dissovled comes out solution = hypoxic mix ~ cloose 100% N2O
Sep = 117 bar
Delivery via pipleine 4 bar = pseudocrit
Poynting effect
Bubbling of O2 thru liq N2O
Vaporisnation of liquid - form gaseous mix entonox -
2 gas dissolve into each
behave diff as mix vs indicudal
NOT what causes them to seperate
Explain the concentration effect
Conc effect - greater rate increase in alveolar conc when compared to inspire conc N2o
High conc inspired
N2O only = only n2o gets used in high conc demonstrate
Large gradient generated by high concentration of N2o
Ability to diffuse so rapidly
Fills alveoli - large amount diffuse into pulmonary capillary - drawing gas from conducting airway into alveoli -> keep volume constant
Ventilation increased to supply extra volume
causes alveolar conc change more rapidly when conc are higher
Second gas efffect
D/T concnetration effect
another gas - eg oxygen / volatile
Use alongisde high conc n2o
Conc alveoli x2 reasons
1 - rapid uptake of N20
2 - Increased ventilation
Result 0- indction time shorted - increased conc volatile & increase O2 level
Explain diffusion hypxoia
Reverse second gas effect
End anes - cease inhal N20 & gases turn off
Volume diffuse blood into alveolus - great than gas diffuse alvoley to blood
Dilution of o2 in alveolus & pooss hypxia
Patient switch to 100% O2 - end of anaesthetic - no impact -clincally relevant if not oxygnated at end
Toxic effects of N2O
Inhibits mehtionine synthease
Responsible for synthesis of Methionine, thymidine & tetrahydrolfate
Oxise cobalt atom in b12 & b12 is cofactor
Show occurs 40m N2o
mewthionine prcuirese for myelin
Low level - suiabacte degen cord in b12 defic
Dorsal column impairment accutely
Tetrahydrolfoate
Important nucoletide in dna synth
- N2o - Megaloblstic anaemi b12 & folate defic
Terato gen - provne rat
Meth synt - alpha adregno agonism
A/w develop disorder
situs inversus
Toxic effects reverse folinic acid - another source tetrahydrolfate
Boliling points of the follow
triethyylne enflurane cholorform sevo des iso halothane cycolproane
The approximate boiling points of the different volatile agents are as follows:
Trichloroethylene 87°C Enflurane 56°C Chloroform 61°C Sevoflurane 58°C Halothane 50°C Isoflurane 48°C Desflurane 24 °C. Cyclopropane has a boiling point of −33°C.
MAC
Eger merkel = 1963
Conc anes prevent movement 50% to stim
Index potencty inhaled
product - oil gas coeff
cant be determind by probit anaylsis
SVP is
whats it dietyhl ether
halothane
constant
boiling point =?
is the PP of vapour above liquid in closed container at equilibrium
indicator of volatility
varies with te`mp (increase)
diethyl ether 59kpa
halothane 32
at bp svp = atm pressure
Desflurance formula
CHF2 OCHFCF3
Sevo formula
CH2FOCHCF3(cf3)
Halothane
mol wt
bp
svp
oil gas
macc
blgas
metab
mol wt 197 Da
Bp 50
SCV 32 kpa
O:G 224
Mac .75
B:G 2.4
20%
Isoflurane
mol wt
bp
svp
oil gas
macc
blgas
metab
Mol 184
BP 48
SVP 33
Oil:G 98
Mac 1.17
B G 1.4
Metab 0.2
Sevo
mol wt
bp
svp
oil gas
macc
blgas
metab
Sevo
200
48
33
80
- 8 2.2
- 7
- 5
Des
mol wt
bp
svp
oil gas
macc
blgas
metab
Des
168da
23.5
89
29
7.3
b;G .45
.02
N20
mol wt
bp
svp
oil gas
macc
blgas
metab
44
-88C
5200kPa
1.4
150
.47
0.01
Enflurane
mol wt
bp
svp
oil gas
macc
blgas
metab
Enflurane
- 5
- 5C
- 3
Oil@G 120
1.68 mac
B:G 1.91
2%
Xenon
mol wt
bp
svp
oil gas
macc
blgas
metab
131
-108
n/A
1.9
71mac
.14 bl g
na metab
N2o can be contam with
which of these can prod pulm oedma
and what afte rhow long
How is it manufcat
Nictric oxide
NO2 (nitrogen dioxide)
Higher oxides = pulm oedema
pulmonary fibrosis 2-3 weeks later
Also prod methaem
Heat ammon nitrate 240
Ammonia produces may contam
also causes pul oed
Max PPM of subs
10
50
100
10- halothane
50
max - Iso + Enflurane
100 nitrous oxide
Which agent at steady state does amt deliver most closely match amount removed via lungs
Nitrous - as least metab .01%
Iso .2% metab
steady sate - pp agent alveoli ==== arterial blood == brain
- difference delivered + removed equal meatb
agent min metab - sml diff amount deliver remove
des .02% metab
Iso and enflurane
what about eeg
structual isomers
.2% iso metab
2% enflurane
3hz spike eeg - a/w high conc enflurane in hypocapnic
Partition coeff -
ratio sub present 1 phase vs other
2 phases - equal vol in equil
Otswald solubil -
is nitrous more soluble in oil or blood
indicates slubility in blood
Oil
37 -1.4 will dissolbe in oil vs .47 im b;ppd
malignant hyperpyrexia
Autosomal dominant
p may be more complex
1:5000 / 1:10000
Ryanodine rec chr 19
increase intra cell Ca
Reduction tendnecy with increasing age
(most seem to have had 3 prev uneventful GA)
Mortalilty ~ 70% without
flush machine 100% for 20-30 mins
Dantrolene
Skeletal muscle relaxant
directly affects excitation contraction cpupling ibn skel muscle
reducing amt ca rel from SR
No effect NMTmission/memb potent/excitability
Effective in Rx mH do 1-10mg
May reduce sux pains if given preop
Mol wts
Des 164
Iso
En 184
Halo
197
Sevo 200
