Anaesthetics and Critical Care Flashcards
What is a Biers block good for?
Regional anaesthesia for upper limb procedures - e.g. distal radius fractures
What are the pre-requisites for performing a Biers block?
2 doctors Fully serviced tourniquet system free from leaks and with integral pressure monitoring system Exsanguination bandage
What pressure would you inflate the tourniquet to in Biers block for normal adult male?
100mmHg above SBP
What LA can’t you use in Biers block? Why?
Bupivacaine - cardiotoxic - in case tourniquet fails
What LA would you choose in Biers block?
Lidocaine or prilocaine
Describe how to do a Biers block?
What may happen in incarcerated hernia surgery with bowel involvement once anaesthetic (muscle relaxant) given?
SIRS response as bowel reperfuses and causes toxic metabolites to circulate
What is the classical cause of malignant hyperthermia? When does it present?
Suxamethonium
Usually almost immediately, rarely post-op
What happens in malignant hyperthermia?
Catabolic state - hyperthermia, tachycardia, muscle rigidity, rhabdomyolysis, acidosis, increase in end tidal CO2
What happens in malignant hyperthermia on a cellular level?
Calcium channel abnormalities leading to uncontrolled influx of calcium into sarcoplasmic reticulum and sustained, uncontrolled muscle contraction
What is the inheritance of malignant hyperthermia?
AD inherited, Ch19 gene defect encoding for ryanodine receptor
Less common cause of trigger malignant hyperthermia?
Halothane
Treatment for malignant hyperthermia? How does it work?
Muscle relaxant, works directly on cellular receptors to prevent release of calcium
What general kinds of muscle relaxants are safe in possible malignant hyperthermia?
Non-depolarising
Define brain death?
Complete and irreversible cessation of all functions of the entire brain including the brain stem
What are the preconditions to brain death testing?
Patient in deep and irreversible coma of known aetiology
Absent reflexes
Exclusion of reversible causes - stop narcotics, hypnotics, tranquilisers, muscle relaxants etc, metabolic and endocrine causes excluded
Normothermia over 34 degrees
Apnoeic requiring mechanical ventilation not secondary to sedatives or neuromuscular disorder
Who and when does brain death testing? At what intervals?
2 appropriately trained senior doctors on 2 separate occasions
No specific interval between but must have normal physiological parameters before commencement of second test
Outline brain death testing?
Fixed pupils, non-reactive to light
No corneal reflex
Absent oculo-vestibular reflexes (caloric testing - 50ml ice cold water into each ear in turn)
No response to supraorpital pressure
No cough on bronchial stimulation, or gag on pharyngeal stimulation
No observed respiratory effort in response to disconnection of ventilator for 5 minutes, to allow PaCO2 over 6 (or 6.5 in chronic CO2 retainers) - with pre-oxygenation to ensure adequate PO2
What is the pattern of BP during routine GA?
Falls at induction of anaesthetic
Goes up during intial phase due to pressor response
Stabilises during main part of procedure
Rises during extubation process
What would you do with poorly controlled hypertension for elective surgical patients?
Get GP to manage and delay until under control
Check for end organ dysfunction - urine dip, ECG, U+E etc.
4 surgical factors which can impact peri-operative BP?
Hypovolaemia - third spacing or haemorrhage
Cross-clamping, unclamping of major vessels e.g. vascular
Laparoscopic techinques esp air insufflation
Manipulation of structures such as adrenals, vagus nerve
4 anaesthetic/medical factors that can impact on peri-operative BP?
Antihpertensives
Anaesthetic agents
Epidural/spinal anaesthetic
Inotropes
How can pneumoperitoneum affect BP in surgery - both during establishment and when established? What would you do if it dropped?
Can cause vagal response via peritoneal stretching - leading to bradycardia and fall in cardiac output
Then once fully established if pressure high can impede venous return to reduce preload, fall in CO
Stop - make sure pressure isnt too high. If at normal pressure still low BP consider possibility of vascular injury and conversion to open
2 reasons to use muscle relaxants?
Facilitate surgical procedures
Permit safe ET intubation
What is the difference between depolarising and non-depolarising muscle relaxants?
Depolarising e.g. suxamethonium - bind to post-synpatic ACh receptor at muscle end plate, activating and causing brief period of fasciculation - then rapidly hydrolysed once withdrawn by plasma acetylcholinesterase to facilitate normal function
Non-depolarising e.g. rocuronium, vecuronium - compete with ACh at post-synpatic receptor and do not cause depolarisation, so have slower onset and longer duration
What are depolarising muscle relaxants good for? Risks?
E.g. suxamethonium, risk of MH but good for rapid and complete muscle relaxation e.g. RSI
What are the advantages and disadvantages of non-depolarising muscle relaxants? Reversibility?
e.g. rocuronium, vecuronium
Advantages are longer duration of action (if desired), no risk of MH
Disadvantages - slower onset, need specific reversal by increasing ACh conc at synpatic cleft e.g. with rivastigmine, a cholinesterase inhibitor
If reversing non-depolarising muscle relaxant actively, what should you consider giving alongside and why?
Consider antimuscarinic e.g. atropine or glycopyrrolate to avoid bradycardia, hypersalivation
3 complications of suxamethonium?
Immediate - due to end plate depolarisation prior to paralysis, widespread fasciculation e.g. in severe burns or crush injuries can cause potassium release and arrhythmias, arrest
Malignant hyperthermia
Pseudocholinesterase deficiency - prolonged recovery following withdrawal (couple of hours)
