Pharmacology Of Anaestheisa Flashcards
Advantages and disadvantages of IV induction
Pleasant for patients
Rapid loss of consciousness under control of the anaesthetists
Loss and recovery of consciousness dependent on passive pharmacokinetic processes so relatively predictable
May be adverse CVS and RS effects esp in elderly those in pain or shocked
Easy to OD if cardiac output low and there is slow arm to brain circulation time
Need to inject the agent slowly t prevent relative OD
What is propofol
2,6 di-isopropyl phenol
Commonest IV anaesthetic in the developed world
It is lipohilic and insoluble in water so is suspended in a soybean oil, egg phosphatide emulsion
Rapid recovery
Fast acting it’s offset of action is due to rapid redistribution rather than and not metabolism
Induction and maintenance - TIVA, TCI
Problems - can be pain on injection
antiemetic effect
Who is prop for CI in
Egg or soybean allergy
<17 years for sedation
Extremes of age
Compromise airway
What is etomidate
Ester Carboxylated imidazole No accumulation - rapid recovery Little CVS effect Used as a induction agent only
Why is etomidate used in induction only
Prolonged us - can lead to lethal adrenal suppression
Side effects etomidate
- adrenal suppression
- local thrombophlebitis at the site of injection
- can cause involuntary muscle spasms
What is thiopentone sodium
Barbiturate powder Rapid onset Cheap Effects last 3-8 min Long terminal half life Hangover effect
SE/CI thiopentone
Mycocardial depressent
CI Airway obstruction Barbiturate allergy Fixed cardiac output Hypovolamia /dec BP Porphyria Compromised airway
What is ketamine
Phencyclidine derivative
Acts on NMDA receptor
Can be given IM or IV
IM - useful for being an in the field agent producing analgesia without shock
Effects of ketamine
Useful in positioning patients in order to facilitate spinal anaesthesia in the setting of features esp FNOF
Used in children as anaesthesia ad sedation in adults
CO is unchanged or increased - so doesn’t produce shock
Also bronchodilators properties so an be considered in the intubation of status asthmaticus
Problems with ketamine
Hypertonus and salivation Slow recovery Lirum Hallucinations Nighmares All made worse if the patient is disturbed during recovery Avoid in hypertensive Inc ICP Inc IOP Avoid in psych patients
Pros and cons of inhalation induction
Ad
Slower and greater onset on ‘sleep’effects
More control over unwanted side effects
If problems arise the patient can be allowed to waken
Good in peads if diff to cannulate
Adults who are diff to cannulate or have difficult airways and fear of needles
Dis
Requires skill and attention to technique to do it well
Needs skilled assistant\
Needs good patient cooperation
Speed of action depends on drug solubility, resp rate and depth and CO
What are Guedels stages of anaesthesia
Stage 1 - amnesia and analgesia
Stage 2 - excitement or delirium
Stage 3 - surgical anaesthesia
Stage 4 - anaesthetic overdoses
What is the ideal inhalation agent (there is none that exist which have all these properties)
Non flamm, non exposure at room temp
Stable in light
Liquid an vaporisable at room temp - low latent heat of vaporisation
Stable at RTP with long shelf life
Stable with soda lime and plastic and metals
Environmentally friendly - no ozone depletion
Cheap an easy to manufacture
Have low solubility in blood and tissue to allow for quick induction and recovery
No injuries effects on tissues
Be administrable in reliable and known concentration
Please to inhale non irritant
Minimal effects on other systems
Excreted by lungs ideally
Non toxic to theatre personnel
Ideal IV agent
Act rapidly with arm within one arm brain circulation
Recovery quick with no hangover effect
Analgesic properties
Resp and CVS effects minimal
Not interact with other anaesthetic agents
No hypersensitivity reactions
There should be no post-op phenomena N/V hallucinations
Ideal muscle relaxant
Non-depolarising mode of action Rapid onset Short duration of action with high potency Spontaneous predictable reversal No CV effects Pharmacologically inactive metabolites Unaffected by renal or hepatic failure
What is MAC
The concentration that prevents movement in response to skin incision in 50% of unpremeditated animals
Do not move during surgery due to the anaesthetic
Advantages of MAC
Alveolar concentration can be easily measured
Near equilibrium, alveolar and brain tensions are virtually equal
The high cerebral blood flow produces the rapid equilibrium
Factor which support the use of the measure are:
- MAC is invariant with a variety of noxious stimuli
- individual variability is small
- sex, height and weight and anaesthetic duration do not alter MAC
Doses of anaesthetic in MACS are additive
N2O as a anaesthetic agent
Odourless odourless gas
Ineffective as a sole agent
MAC is 105% so therefore if this was a sole agent you’d die cos there would be no oxygen
It has analgesic properties
How is N2O usually given to patients
As entonox
50:50 mix of N2O and O2
Used in labour, trauma, children
What is halothane
It is a halogenated hydrocarbon
No longer used in the UK
It is pleasant smelling with a small analgesic affect had a MAC of 0.75%
Problems with halothane
Chemically unstable in light Increases Vagal tone - bradycardia Halothane hepatitis - rare but ha a high mortality Immune mechanism
What are enflurane and isoflurane
They are fluorinated ethers
Optical isomers of each other
MAC enflurane - 1.68%
MAC isoflurane - 1.15%
Problems with enflurane and isoflurane
Irritant - so produce coughing but this can be reduced with opioids
Although should be quick onset can take longer due to the time it takes for the agent to be inhaled
Enflurane no longer used due to renal damage
