General Anaethetics Flashcards
what is anaethesia?
“loss of sensation/ consciousness”
What is included in the anaesthesia triangle?
anaesthetic agents (to produce unconsciousness)
neuromuscular blocking agents (muscle relaxation)
analgesics (pain relief)
What are the 4 stages of anaethesia?
1) analgesia - conscious, drowsy
2) Excitement - loss of consciousness but delirium, irregular cardio respiration
3) Anaesthesia - regular respiration, loss of reflux and muscle tone
4) Medullary paralysis
What are the types of anaesthetic agents?
general - loss of sensation throughout the body, often used during major surgical procedures
regional - loss of sensation to specific region of body, spinal, epidural and peripheral
local - small area of body is numbered fully conscious, used during minor procedures
General anaesthetics -how it should work?
1) Loss of conscious awareness
2) Loss of response to noxious stimuli
3) Reversibility
Goals of General Anaesthetics
Induction of sleep
Maintenance of sleep
Waking up from sleep
Inhalational anaesthetics
gasses or vapours (administered via vaporizers)
(usually, halogenated ethers or hydrocarbons e.g. halothane, isoflurane)
Controllable, rapid blood-gas exchange
types of inhalational anaethetics?
N2O
halothane
enflurance
isoflurane
How GAs work?
Potency of GA: Minimum Alveolar Concentration (MAC) – The concentration required to prevent 50 % of patients moving when subjected to surgical midline incision
what is the lipid theory?
critical volume hypothesis & perturbation theory
potency proportional to lipid solubility
Disruption of ion channel functions and disruption of annular lipids associations with ionic channels
what reletionship between inhaled anaethetics potency and lipid solubility?
linear
receptors that work on GAs:
GABA - inhibitory, glycine(enhance more)
nAch, NMDA - exictatory (inhibit less)
All volatile anaesthetics _______ the respiration rate
increase
What are the characteristics of IV anaethetics?
very rapid (onset, brain circulation time 30s)
short-acting
intro and maintenance of anaesthesia
IV
thiopental
etomidate
propofol
ketamine
midazolam and other benzodiazepines
Thiopental (+ive allosteric modulator of GABA)
anion channel (Cl-); GABAa Icl»_space; hyperpolarisation»_space; inhibitory
thiopental pharmacological effect:
potentiates endogenous GABA responses
increase the frequency of channel opening
generalised increase in GABA inhibition
Hypnosis!!!
thiopental adverse effects:
Respiratory depression, apnoea
CVS: myocardial depression, decrease cardiac output
Sneezing, coughing and bronchospasm
thiopental problems
Extremely painful during intra-arterial administration
Hypersensitive reactions (1: 15000)
Propofol (Positive allosteric modulator of GABA)
Pharmacological effect
potentiates endogenous GABA responses
increase the frequency of channel opening
generalised increase in GABA inhibition
Hypnosis!!!
contraindicates in children under 3
Adverse effects
CVS: myocardial depression, decreased peripheral vascular resistance, decreased CO
Respiratory depression
Hypersensitivity 1 : 100 000
Etomidate (Positive allosteric modulator of GABA)
Pharmacological effect
Hypnosis
Contraindications
Phorphyria
Adverse effects
CVS: very little effect on HR, CO, PVR
Minimal respiratory depression
Hypersensitive reactions (1: 75000)
ketamine (NMDA receptor antagonist- competitive)
ligand gated cation channels
depolarisation
AP
excitatroy action
What type of action does ketamine have?
competitively antagonise glutamic acid-mediated NMDA activation: inhibition of AP
what does ketamine interact with?
opioid receptors, monoaminergic receptors, muscarinic receptors and voltage-sensitive Ca ion channels.
Which receptor does ketamine NOT REACT with?
GABA
pharmalogical and side effects of ket?
Pharmacological effect
Hypnosis (used mainly in paediatrics)
Analgesic in emergency medicine
effects
– Increase HR, BP, CO, O2 consumption
– Increase RR, preserved laryngeal reflexes
dissociative anaesthesia, analgesia, amnesia
Problems of use with ketamine:
Slow recovery
High extraneous muscle movement
Hallucinations, nightmares and transient psychotic drugs
Criteria for selection induction agent
1) absolute contraindication - hypersensitivity porpohyria
2) patient realted fctors - CV health, resp health and CNS health (epilepsy)
3) drug related factors - drug-food, drug-drug or other interactions
