Anaesthetics Flashcards
What are the 2 main categories of anaesthesia?
General- Unconscious, requires support of ventilator
Regional- Block feeling to isolated area (eg: Limb)
What is the purpose of fasting before a general anaesthetic?
Empties stomach
Reduces risk of reflux stomach contents into oropharynx and being aspirated
What are the risks of aspiration in administering a general anaesthetic?
Can lead to aspiration pneumonitis and pneumonia
What are the fasting guidelines related to general anaesthetic?
6h no food/feeds before operation
2h no clear fluids (nil by mouth)
Outline preoxygenation in general anaesthetic
Several minutes before general anaesthetic breathing 100% oxygen
Gives reserve of oxygen between losing consciousness and successful intubation and ventilation
Outline premedication before general anaesthetic
Given to relax patient, reduce anxiety, reduce pain and make intubation easier
Benzo (midazolam)- Relax muscle, reduce anxiety (also causes amnesia)
Opiate (fentanyl)- Reduce pain and hypertensive response to laryngoscope
Alpha-2-adrenergic agonist (clonidine)- Sedation and pain
What is the purpose of cricoid pressure in an RSI?
Compresses oesophagus and prevents stomach contents refluxing into pharynx
What is the triad of general anaesthesia?
Hypnosis
Muscle relaxation
Analgesia
List IV options for hypnotic agents in general anaesthesia
Propofol (most common)
Ketamine
Thiopental sodium (less common)
Etomidate (rarely used)
List inhaled options for hypnotic agents in general anaesthesia
Sevoflurane (most common)
Desflurane (bad for environment)
Isoflurane (rarely used)
NO- Combined with others- May be used for children
What is a common way to administer hypnotic agents for general anaesthesia?
IV meds for induction agent, inhaled meds for maintenance
What is Total IV anaesthesia?
Uses IV meds for induction and maintenance of GA
Propofol most common
Give nicer recovery than inhaled options
Outline use of muscle relaxants in GA
Block NMJ
ACh released by axon but is blocked from stimulating response from muscle
Relax and paralyse muscles
What are the 2 categories of muscle relaxants used in GA?
Depolarising (eg: Suxamethonium)
Non-depolarising (eg: Rocuronium and atracurium)
What reverses the effects of NMJ blocking meds in GA?
Cholinesterase inhibitors- Neostigmine
Which med is used specifically to reverse effects of non-depolarising muscle relaxants following GA?
Sugammadex
What are the options for analgesia in GA?
Opiates most common:
Fentanyl
Alfentanil
Remifentanil
Morphine
What is given for symptoms control at the end of a procedure requiring GA?
Antiemetics:
Ondansetron
Dexamethasone
Cyclizine
What is the MoA of ondansetron and its CIs?
5HT3 receptor antagonist
Avoid in risk of prolonged QT interval
What is the MoA of cyclizine and which patients is caution given?
H1 receptor antagonist
Caution- HF and elderly
Outline emergence from GA
Before waking:
Muscle relaxant needs to wear off- Use nerve stimulator on ulnar nerve and watch for thumb movement
After waking:
Stop inhaled anaesthetic
Extubate when breathing for themselves
What are the risks of GA?
Sore throat
Post-operative N+V
Accidental awareness
Aspiration
Dental injury
Anaphylaxis
CV events- MI, stroke, arrhythmias
Malignant hyperthermia
Death
What is malignant hyperthermia?
Rare potentially fatal hypermetabolic response to anaesthesia
Certain medications and genetic mutations (autosomal dominant) increase risk
Which medications increase risk of malignant hyperthermia?
Volatile anaesthetics- Isoflurane, sevoflurane, desflurane
Suxamethonium
How does malignant hyperthermia present?
Hyperthermia
Increased CO2 production
Tachycardia
Muscle rigidity
Acidosis
Hyperkalaemia
How is malignant hyperthermia managed?
Dantrolene- Interrupts muscle rigidity and hypermetabolism- Interferes with movement of calcium ions in skeletal muscle
Outline peripheral nerve blocks
Regional anaesthesia
Patient remains awake
Local anaesthesia injected around specific nerves- Area distal anaesthetised
Injection under US guidance with nerve stimulator
When is central neuroaxial anaesthesia used?
C section
Transurethral resection of prostate (TURP)
Hip fracture repair
What is central neuraxial anaesthesia?
Spinal anaesthetic/spinal block
Type of regional anaesthesia
Local anaesthetic injected into CSF within subarachnoid space
Only used in lumbar spine (L3/4 or L4/5)
Takes 1-3h to wear off
What are the adverse effects of epidural?
Headache if dura punctured- Creates hole for CSF to leak from (dural tap)
Hypotension
Motor weakness in legs
Nerve damage (rare)
Infection- Meningitis
Haematoma (may cause spinal cord compression)
When is epidural used?
Labour
Post-op after a laparotomy
Outline epidural anaesthesia
Catheter in epidural space in lower back
Outside dura mater, separate from SC and CSF
Local anaesthetics infused through catheter
Give an example of an epidural
Levobupivacaine with or w/o fentanyl
What are the risks of using an epidural in labour?
Prolonged 2nd stage
Increased probability of instrumental delivery
When do patients need an urgent anaesthetic review with an epidural?
Develop significant motor weakness (unable to straight leg raise)
Catheter may be incorrectly sited in subarachnoid space
What is this us and how can it affect intubation?
Pain and constriction when opening jaw
Makes intubation more difficult- May need awake fibre-optic intubation
What do you use to check the pressure in the cuff of the endotracheal tube?
Manometer
What is the Murphy’s eye?
Extra hole on side tip that gas can flow through in case main opening tip of ETT becomes occluded
What is a McGrath laryngoscope?
High tech version of standard laryngoscope- Camera and screen attached to visualise vocal cords
Outline awake fibre-optic intubation
ETT inserted under guidance of endoscope (camera) through nose
What is a CI for nasopharyngeal airway?
Basal skull fracture
List indications for tracheostomy
Respiratory failure where long term ventilation may be required
Prolonged weaning from mechanical ventilation
Upper airway obstruction
Management of respiratory secretions (eg: Paralysis)
Reducing risk of aspiration- Unsafe swallow, absent cough reflex
Outline the stages of a difficult airway
Plan A- Laryngoscopy with tracheal intubation
Plan B- Supraglottic airway device
Plan C- Face mask ventilation and wake patient up
Plan D- Cricothyroidotomy
Outline arterial lines
Cannula in artery
Accurate BP recording
Arterial blood samples
NEVER give meds through line
Outline central lines
Central venous catheter
Inserted into large vein with tip in vena cava
Have separate lumens- Can be used for giving meds/taking blood
Last longer and more reliable than cannulas
What are common locations for insertion of a central line?
Internal jugular
Subclavian vein
Femoral vein
Which meds would be too irritating to give through a peripheral cannula?
Give through central venous line instead
Inotropes
Amiodarone
Fluids with high potassium conc.
What is a Vas Cath?
Central venous catheter inserted on temporary basis
Usually in internal jugular vein or femoral vein
Has 2 or 3 lumens
Used short term for haemodialysis
Outline Portacath
Type of central venous catheter
Small port under skin on top of chest used to access device- Connected to catheter that travels through SC tissue and into SC vein, with tip in SVC or RA
When catheter needed to be accessed- Needle inserted through skin into port
Used long term- Chemotherapy
Outline Pulmonary Artery Catheter
Swan-Ganz catheter
Pulmonary artery catheter inserted into IJV through central venous system/RA/RV into pulmonary artery
Inflate balloon- Gives pulmonary artery wedge pressure- Gives indication of pressures in LA
Rarely used- Mostly cardiac
What is a PICC line?
Peripherally inserted central catheter
Type of central venous catheter
Long, thin tube inserted into peripheral vein and fed into central vein
Contain 1 or 2 lumens
Narrower than standard central line
Low risk of infection- Stay in for longer
Outline Tunnelled Central Venous Catheter
Hickman line
Long, thin catheter- Enters skin on chest, travels through SC tissue and enters subclavian or jugular vein with tip that sits in SVC
Stay in long term
Used for regular IV treatment (eg: Chemotherapy or haemodialysis)
What is the definition of chronic pain?
Pain present >3mths
What are the 2 aspects to the experience of pain?
Sensory- Signal transmitted from pain receptor
Affective- Unpleasant emotional reaction to pain
What is pain threshold?
The point at which sensory input is reported as painful
What is allodynia?
Pain experienced with sensory inputs that don’t normally cause pain (eg: Light touch)
What is pain tolerance?
Person’s individual response to pain
Outline the basic pathway of pain signals
Nociceptors detect damage/potential damage- Along afferent nerves- Spinal cord- Up spinothalamic tract and spine reticular tract- Brain- Interpreted as pain in thalamus and cortex
Outline afferent sensory nerves associated with pain
Transmit pain signals
Peripheral nervous system
Called primary afferent nociceptors
What are C fibres?
Unmyelinated and small diameter
Transmit signals slowly and produce dull and diffuse pain sensations
What are A-delta fibres?
Myelinated and larger diameter
Transmit signals fast
Produce sharp and localised pain sensations
What are the main sensory inputs that generate a pain signal?
Mechanical (eg: pressure)
Heat
Chemical (eg: prostaglandins)
Outline referred pain
Pain in location away from site of tissue damage
Nerves may share innervation of multiple parts of body
Pain in one area amplifies sensitivity in SC to signals coming from other areas
Activation from SNS in response to pain results in pain in other areas
What are the typical features of neuropathic pain?
Burning
Tingling
Pins and needles
Electric shocks
Loss of sensation to touch of affected area
Outline neuropathic pain
Abnormal functioning or damage of sensory nerves, resulting in pain signals transmitted to brain
Outline the steps of the analgesic ladder
Step 1: Paracetamol and NSAIDs
Step 2: Weak opioids- Codeine and tramadol
Step 3: Strong opioids- Morphine, oxycodone, fentanyl, buprenorphine
List drugs used to manage neuropathic pain
Amitriptyline- TCA
Duloxetine- SNRI
Gabapentin- Anticonvulsant
Pregabalin- Anticonvulsant
Capsaicin cream- Chilli
What is a common SE of long term use of analgesic meds?
Medication overuse headache
What are the SEs of NSAIDs?
Gastritis with dyspepsia
Stomach ulcers
Exacerbation of asthma
HTN
Renal impairment
CAD, HF and strokes
What are NSAIDs CI in?
Asthma
Renal impairment
Heart disease
Uncontrolled HTN
Stomach ulcers
What are the SEs of opioids?
Constipation
Skin itching (pruritis)
Nausea
Altered mental state (sedation/cognitive impairment/confusion)
Respiratory depression
What is often co-prescribed with NSAIDs?
PPI (omeprazole or lansoprazole)
Reduce risk of GI SEs (acid reflux, gastritis and stomach ulcers)
What is the antidote to opioids?
Naloxone
