General anesthesia Flashcards
function of general anesthesia
medically induce a coma
aim is to ensure :
1. analgesia
2. amnesia
3. unconsciousness
4. relaxation of skeletal muscles
5. loss of control of reflexes of autonomic nervous system
stages of GA
- analgesia
- excitement
- surgical anaesthesia
- medullary depression
types of GA
inhaled and intravenous
what affects conc. of inhaled anaesthetic effect
- solubility of gas
- lower solubility in blood = faster / higher onset of action - concentration of anaesthetic in gas
- increased conc = faster transfer from blood to brain - rate and depth of pul. ventilation
- increase rate of ventilation = increase absorption - pulmonary blood flow
- increase blood flow = lesser time to diffuse from air to blood - arteriovenous concentration grdient
- high conc gradient = longer time to achieve equilibrium in brain
how does gaseous anaesthetic enter brain?
air -> lungs -> blood -> brain
how are gaseous GA excreted
mainly via Lungs
- hepatic metab also contributes to clearance
- bacteria in GIT breaks down nitrous oxide !!
long duration of exposure of gaseous GA can lead to…
more soluble anaesthetics accumulating in skin, muscle , fat -> slower rate of elimination
CVS effects
- variable effect on HR
- decrease mean arterial pressure
- decrease CO
- depress myocardial function
respiratory effects
- decrease minute ventilation
- reduced hypercapnia response
- increase apnoic threshold
- depression of mucociliary function
brain effects
increase cerebral blood flow by decreasing cerebral vascular resistance
renal effects
impairs renal autoregulatory function due to reducing renal bloodflow
liver effects
- decrease hepatic blood flow
- repeat exposure of halothane -> liver damage
uterus effects
halogenated anaesthetics are potent uterine muscle relaxants !
Types of intravenous GA
- barbiturates
- benzodiazapine
- propofol
- ketamines
Name a barbiturate
Thiopental
What do barbiturates bind to
GABA receptors + AMPA receptors (to depress glutamate mediated excitation)
Funfacts of barbiturates ig
- commonly used for induction of anaesthesia as it rapidly crosses BBB after intravenous bolus and sufficient doses given
- quick loss of consciousness
- high lipid solubility → hence thiopental distributes out of blood and brain to muscle and fat
- potent respi depressant + decreases arterial BP, SV and CO + decrease cerebral metab , O2 consumption and blood flow
Who are barbiturates recommended for
recommended for patients with raised intracranial pressure as it can decrease cerebral blood flow
Name 3 benzodiazepines
Diazepam, Lorazepam, Midazolam
what is a benzodiazepine antagonist administered for recovery
flumazenil
Why is Propofol favoured
faster rate of onset than barbiturates but also faster recovery rate
how is propofol metabolised
metab rapidly by liver and excreted by kidney
what is propofol used for
induction and maintenance of anaesthesia
special qualities of ketamine
- only intravenous GA with both analgesic and anaesthetic properties
- stimulates cardiovascular system via stimulation of Central sympathetic NS and inhibiting reuptakes of noradrenaline -> useful in poor risk elderly patients / those in cardiogenic / septic shock
neurological effects of ketamine
post op illusions, dreams, disorientation
Alternatives to general anaesthesia
- balanced anaesthesia
- monitored anaesthetic care
- conscious anaesthetic care
balanced vs monitored anaesthetic care
- both involve sedation
balanced = patient is reliant on ventilation to breath
monitored = patient NOT reliant on ventilation to breath
monitored vs conscious sedation
monitored sedation = deeply sedated + anasthesiologist needed
conscious sedation = not as deeply sedated, conscious ! anasthesiologist not needed
if patient wakes up distressed :
- administer supplementary oxygen
- ensure patient’s airway not obstructed + adequate ventilation
- examine patient for signs of volume overload and treat haemodynamic derangements with appropriate drugs to lower bP !!
