Case 10 - Yaffas Flashcards
what is general anaesthesia
this is a medically induced coma and loss of protective reflexes resulting from the administration of one or more general anaesthetic agents
what are the purposes of general anaesthesia
Analgesia – loss of response to pain
Amnesia – loss of memory
Immobility – loss of motor reflexes
Unconsciousness – loss of consciousness
Skeletal Muscle Relaxation
what is the theory of general anaesthetic action
alter neurone function by interacting directly with a small number of ion channels.
upon activation, channels change the electrical excitability of neurones by controlling the flow of depolarising (excitatory) and hyper polarising (inhibitory) ions across the cell membrane via an ion channel that is integral wtith the receptor that senses the initial signal
general anaesthetics primarily act by either enhancing inhibitory signals or by blocking excitatory signals
what is the pre anaesthetic evaluation key factors
patient’s age, body mass index, medical and surgical history, current medications and fasting time.
also an evaluation of the patients airway, involving inspection of the mouth opening and visualisation of the soft tissues of the pharynx is required.
does consent have to be obtained
yes
what is monitored during GA
ECG – this may also help identify early signs of heart ischaemia.
Blood pressure – can be invasive or non-invasive.
Oxygen saturation – pulse oximetry – allows early detection of a fall in a patient’s haemoglobin saturation with oxygen (hypoxaemia).
End tidal CO2 – carbon dioxide measurement (capnography).
Inspired oxygen – low oxygen alarm.
Inspired agent concentration
Neuromuscular blockade
Airway pressures and flows
Temperature – to discern hypothermia or fever.
Depth of anaesthesia
what are the three stages of anaesthesia
induction
maintenance
reversal
what is the excitement stage
there is an excitement stage that occurs after induction and before maintenance. this is marked by excited and delirious activity - there may be an irregular heart rate and breathing rate
what is included in the induction stage
anaesthetic agents may be administered by various routes, including inhalation, injection, oral or rectal.
the stages of intravenous induction
bolus of drug injected
travels to the brain
highly lipid soluble
rapidly enters the brain
onset is in one arm - brain time
initial recovery by redistribution
ultimate recovery by elimination
what happens once drugs are in the circulatory system
they are transported to their biochemical sites of action in the central and autonomic nervous systems, where they exert their pharmacologic effect
what are the stages of inhalation induction
vapour breathed in via lungs
enters the blood
travels to the brain
highly lipid soluble
enters the brain
initial recovery by exhalation
ultimate recovery by exhalation
minimal amounts are metabolised
is the onset of anaesthesia faster with IV or inhalation
faster with IV, taking about 10-20 seconds to induce total unconsciousness
what are commonly used IV induction agents
propofol, sodium thiopentone, etomidate and ketamine.
when may an inhalation induction be chosen
where IV access is difficult to obtain, where difficulty maintaining the airway is anticipated or due to the patient preference e.,g children
what is the duration of action of IV drugs
5-10 minutes, after which time spontaneous recovery of consciousness will occur
how is anaesthesia prolonged
for the reuquired duration, anaesthesia must be maintained.
how is maintenance achievee
allowing the patient to breathe a carefully controlled mixture of:
oxygen
nitrous oxide
isoflurane (volatile anaesthetic agent)
this can also be achieved by having a carefully controlling continuous infusion propofol through an IV catheter
what are inhaled agent usually supplemented by
intravenous anaesthetics, such as opioids (usuallyfentanyl or morphine) and sedative-hypnotics (usually propofol).
when does recovery of consciousness occur
when the concentration of anaesthetic in the brain drops below a certain level (usually within 1 to 30 minutes, depending upon the duration of surgery)
what is an integral part of modern anaesthesia
paralysis or temporary muscle relaxation with a neuromuscular blocker
what does muscular relaxation allow
surgery within major body cavities e.g abdomen and thorax, without the need for very deep anaesthesia, and is also used to facilitate endotracheal intubation
what does acetylcholine do
causes muscle to contract when it is released from nerve endings
what do muscle relaxants do
prevent acetylcholine from attaching to its receptor
examples of muscle relaxants
E.g. atracurium, succinylcholine (suxamethonium), tubocurarine (curare), rocuronium, vecuronium.
what happens when paralysis of the muscles of respiration occurs
requires artificial respiration
how are the airway usually protected
by an endotracheal tube
how are the effects of muscle relaxants revered at the terminations of surgery
by acetylcholinesterase drugs
with the loss of consciousness, what else is there a loss of
Protective airway reflexes (such as coughing)
Airway patency (airway obstruction)
Regular pattern due to the effect of anaesthetics, opioids, or muscle relaxants.
what is used to reverse the muscle relaxants (drugs used)
(neostigmine + glycopyrrolate).
what is spontaneous respiration
normal negative pressure breathing
supine position and V/Q matching
respiratory depression - increase in CO2 - hypercapnia
hypoxic on room air
what is positive pressure ventilation
inspiration is now positive pressure
expiration is passive
needs a tracheal tube
increased indcidence of chest infection
what are the cardiovascular consequences of anaesthesia
Decreased venous return
Decreased cardiac output
Decreased force of contraction
Increase in arrhythmia potential
Vasodilation
Change in regional flow patterns
what are the CNS consequences of anaesthesia
Unconsciousness
Depression of cerebral metabolism
Dreaming
Awareness
Specific EEG changes
Possible long-term effects
what happens with agents with high lipid solubility
they accumulate gradually in body fat and may produce a prolonged hangover. if used for a long operation.
why does this happen
because of the low blood flow to adipose tissue meaning it can take hours for the drug to enter and leave the fat
what is monitored and assessed during post operative recovery
oxygenation
pain control
fluid balance
postoperative nausea and vomiting
cardiovascular stability
conscious level
urine output
what is early postoperative management
‘recovery’
what is late post operative recovery
wound infection
DVT
chest infection
surgical problems
what is the risk due to anaesthesia alone
less than 1 in 500,000
diagram of GA etc. please learn this off as a summary
