anaesthetics and perioperative care Flashcards
complications of aspiration of gastric contents during anaesthesia?
aspiration pneumonitis
aspiration pneumonia
what does fasting for an operation typically involve?
- 6hrs of no non-clear fluids/food or feeds before the operation
- 2hrs of no clear fluids as well,ie, fully nil by mouth
what is preoxygenation
Before being put under a general anaesthetic, the patient will have a period of several minutes where they breathe 100% oxygen. This gives them a reserve of oxygen for the period between when they lose consciousness and are successfully intubated and ventilated (in case the anaesthetist has difficulty establishing the airway)`
what are premedication?
Medications are given before the patient is put under a general anaesthetic to relax them, reduce anxiety, reduce pain and make intubation easier. These may include:
Benzodiazepines (e.g., midazolam) to relax the muscles and reduce anxiety (also causes amnesia)
Opiates (e.g., fentanyl or alfentanyl) to reduce pain and reduce the hypertensive response to the laryngoscope
Alpha-2-adrenergic agonists (e.g., clonidine), which can help with sedation and pain
what is rapid sequence induction
Rapid sequence induction/intubation (RSI) is used to gain control over the airway as quickly and safely as possible where a patient is intubated in an emergency scenario and detailed pre-planning is not possible. It is also used in non-emergency situations where the airway needs to be secured quickly to avoid aspiration, such as in patients with gastro-oesophageal reflux or pregnancy.
The biggest concern during RSI is the aspiration of stomach contents into the lungs. The bed can be positioned so the patient is more upright to reduce the reflux of contents up the oesophagus. Cricoid pressure (pressing down on the cricoid cartilage in the neck) may be used to compress the oesophagus and prevent the stomach contents from refluxing into the pharynx (this is somewhat controversial and should only be done by someone trained and experienced).
triad of general anaesthesia
hypnosis
analgesia
muscle relaxation
what are hypnotic agents?
hypnotic agents are used to make the patient unconscious and can be given either IV or INH
IV options for GA
Propofol (the most commonly used)
Ketamine
Thiopental sodium (less common)
Etomidate (rarely used)
INH options for GA
Sevoflurane (the most commonly used)
Desflurane (less favourable as bad for the environment)
Isoflurane (very rarely used)
Nitrous oxide (combined with other anaesthetic medications – may be used for gas induction in children)
what are the 2 ways of giving someone GA?
in GA, there is induction and maintenance.
- Commonly, an intravenous medication will be used as an induction agent (to induce unconsciousness), and inhaled medications will be used to maintain the general anaesthetic during the operation.
- Total intravenous anaesthesia (TIVA) involves using an intravenous medication for induction and maintenance of the general anaesthetic. Propofol is the most commonly used. This can give a nicer recovery compared with inhaled options.
muscle relaxants mechanism of action and purpose?
muscle relaxants block the neuromuscular junction from working. Ach is blocked from stimulating a response on the muscle.
muscle relaxants are given to relax and paralyse the muscles which makes intubation and surgery easier.
give types and examples of muscle relaxants
depolarizing - suxamethonium
non-depolarizing - rocuronium and atracurium
what medications are used to reverse the effects of muscle relaxants?
cholinesterase inhibitors like neostigmine can reverse the effects of NMJ blocking medications
Sugammadex is used specifically to reverse the effects of certain non-depolarizing muscle relaxants
what analgesics are used commonly in anaesthesia?
opiates. - fentanyl, alfentanil, remifentanil, morphine
what additional medication is given at the end of the procedure to prevent post-op N/V. give eg
antiemetics.
ondansetron (5Ht3 antagonist) - avoided in pts at risk of prolonged QT interval
dexamethasone (corticosteroid) - caution in pts with diabetes or immunocompromised pts
cyclizine (H1 receptor antagonist)- caution in elderly pts and pts with heart failure
what is a train of four stimulation?
before waking, the muscle relaxant needs to have worn off.
train-of-four (TOF) stimulation is used where the nerve is stimulated four times using a nerve stimulator (usually ulnar nerve watching for thumb movements or facial nerve watching for movement in the orbicularis oculi) to see if the muscle responses remain strong (indicating it has worn off) or whether they get weaker with additional stimulation (indicating it has not fully worn off).
when are pts extubated
Once the muscle relaxant has worn off, the inhaled anaesthetic is stopped. The concentration of the anaesthetic in the body will fall, and the patient will regain consciousness. They are extubated at the point where they are breathing for themselves.
risks of GA?
sore throat and post op N and V are the most common adverse effects
some significant risks of GA include - accidental awareness aspiration pnuemonitis and pneumonia dental injury anaphylaxis malignant hyperthermia CV events eg MI, arrhythmias, strokes death
what is malignant hyperthermia
rare but potentially fatal hypermetabolic response to anaesthesia. the risk is mainly with volatile anaesthetic agents (sevodlurane, desflurane etc) and suxamethonium.
there are genetic mutations which inc risk of malignant hyperthermia which are inherited in an autosomal dominant pattern
what does malignant hyperthermia cause incl signs and symptoms
hyperthermia muscle rigidity tachycardia acidosis increased CO2 exhalation hyperkalaemia
treatment for malignant hyperthermia?
ABCDE aproach
datrolene - muscle relaxant which interferes with movement of Ca2+ ions in skeletal muscle
in general what tests would you perform pre-op in an elective case?
FBC, U&Es, LFTs, clotting, group and save urine analysis pregnancy test sickle cell test ECG/CXR plan DVT risk management
potential complications of poorly managed diabetes during surgery
undetected hypoglycaemia whilst under GA
increased risk of wound and resp infections
inc risk of post op AKI
inc length of stay in hospital
in general, for an elective surgery, how shd blood glucose be controlled in patients on insulin
- pts on insulin with good glycaemic control (hba1c <69 mmol/mol) and undergoing minor surgery can be managed during the operative period by adjustment of their usual insulin regimen
- pts on insulin with surgery requiring long fasting period of more than 1 missed meal or whose diabetes is poorly controlled will usually require variable rate insulin infusion (VRII)
