Priniciples and Pharmacology Flashcards
Common problems with anaesthesia
-Polypharmacy (drug interactions/allergies)
-Muscle relaxation
Requirement for artificial ventilation
Means of airway control
-Separation of relaxation & hypnosis (?awareness)
3 parts of the triad of anaesthesia
- Analgesia
- Hypnosis
- Relaxation
What parts of the triad does general anaesthesia act on
- Hypnosis
- Relaxation
Effect of general anaesthesia
-Interferes with neuronal ion channels
-Hyperpolarising neurones = less likely to fire
-Cerebral function “lost from top down”
More complex processes interrupted 1st
More primitive processes lost later
LOC early, hearing later
-Reflexes relatively spared
2 types of general anaesthesia and how they work
- Inhalation agents, Dissolver in membranes (direct physical effect)
- Intravenous agents, Allosteric binding (GABA receptors, open chloride channels
Drug used in IV general anaesthesia and its effect
- Propofol or etomidate or ketamine (“in-field anaesthetic”) +/- benzodiazepines (methohexital lowers seizure threshold )
- Rapid onset of unconsciousness (1 arm-brain time)
- Rapid recovery (due to disappearance of drug from circulation)
Drug used in inhaled anaesthesia and its effect
- Halogenated hydrocarbons (e.g. desflurane +/- nitrous oxide)
- Uptake and excretion by lungs
- Concentration gradient, lung>blood>brain
- Cross alveolar BM easily
- Arterial conc equates closely to alveolar partial pressure
- Slow induction
What is meant by minimum alveolar concentration (MAC)
- The concentration of a vapour in the lungs required prevent movement (motor response) in 50% of subjects in response to surgical (pain)
- Measure of potency
- Low no. = high potency
How to awaken a patient after inhaled anaesthesia
- Stop inhalational administration of anaesthetic
- Washout (reversal of concentration gradient)
Effect of general anaesthesia on CVS
Central -Depresses cardiovascular centre: Reduced sympathetic outflow -ve inotropic effect on heart Reduced vasoconstrictor tone leading to vasodilation
Direct -vely inotropic -Vasodilation (decreased peripheral resistance) -Venodilation Decreased venous return Decreased cardiac output
Effect of general anaesthesia on resp. system
- All anaesthetics are resp. depressants
- Reduce hypoxic + hypercapnic drive
- Decreased tidal volume + increased rate
- Paralyse cilia
- Decrease FRC
- Lower lung volumes
- VQ mismatch
Indications for use of muscle relaxants
- Ventilation + intubation
- Immobility is essential (e.g. neurosurgery or microscopic surgery)
- Body cavity surgery
Problems with muscle relaxants
-Awareness
-Incomplete reversal
Airway obstruction, ventilatory insufficiency in immediate post-op period
Apnoea = dependence on airway & ventilatory support
Define the 3 types of anaesthesia
- General, Produces insensibility to whole body, usually causing unconsciousness/coma
- Local, Applied directly to the target tissue, producing insensibility in only the relevant part of the body
- Regional, Local anaesthetic applied to nerves supplying the relevant part of the body, produces insensibility in that area/region of the body
Why give intraoperative analgesia
- Prevention of arousal
- Opiates contribute to hypnotic effect of general anaesthetic
- Suppression of reflex responses to painful stimuli (e.g. tachycardia, hypertension
