Anaesthetics and Critical Care

Question 1

What is a Biers block good for?

Answer 1

Regional anaesthesia for upper limb procedures - e.g. distal radius fractures

Question 2

What are the pre-requisites for performing a Biers block?

Answer 2

2 doctors Fully serviced tourniquet system free from leaks and with integral pressure monitoring system Exsanguination bandage

Question 3

What pressure would you inflate the tourniquet to in Biers block for normal adult male?

Answer 3

100mmHg above SBP

Question 4

What LA can’t you use in Biers block? Why?

Answer 4

Bupivacaine - cardiotoxic - in case tourniquet fails

Question 5

What LA would you choose in Biers block?

Answer 5

Lidocaine or prilocaine

Question 6

Describe how to do a Biers block?

Answer 6

Question 7

What may happen in incarcerated hernia surgery with bowel involvement once anaesthetic (muscle relaxant) given?

Answer 7

SIRS response as bowel reperfuses and causes toxic metabolites to circulate

Question 8

What is the classical cause of malignant hyperthermia? When does it present?

Answer 8

Suxamethonium

Usually almost immediately, rarely post-op

Question 9

What happens in malignant hyperthermia?

Answer 9

Catabolic state - hyperthermia, tachycardia, muscle rigidity, rhabdomyolysis, acidosis, increase in end tidal CO2

Question 10

What happens in malignant hyperthermia on a cellular level?

Answer 10

Calcium channel abnormalities leading to uncontrolled influx of calcium into sarcoplasmic reticulum and sustained, uncontrolled muscle contraction

Question 11

What is the inheritance of malignant hyperthermia?

Answer 11

AD inherited, Ch19 gene defect encoding for ryanodine receptor

Question 12

Less common cause of trigger malignant hyperthermia?

Answer 12

Halothane

Question 13

Treatment for malignant hyperthermia? How does it work?

Answer 13

Muscle relaxant, works directly on cellular receptors to prevent release of calcium

Question 14

What general kinds of muscle relaxants are safe in possible malignant hyperthermia?

Answer 14

Non-depolarising

Question 15

Define brain death?

Answer 15

Complete and irreversible cessation of all functions of the entire brain including the brain stem

Question 16

What are the preconditions to brain death testing?

Answer 16

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

Question 17

Who and when does brain death testing? At what intervals?

Answer 17

2 appropriately trained senior doctors on 2 separate occasions

No specific interval between but must have normal physiological parameters before commencement of second test

Question 18

Outline brain death testing?

Answer 18

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

Question 19

What is the pattern of BP during routine GA?

Answer 19

Falls at induction of anaesthetic

Goes up during intial phase due to pressor response

Stabilises during main part of procedure

Rises during extubation process

Question 20

What would you do with poorly controlled hypertension for elective surgical patients?

Answer 20

Get GP to manage and delay until under control

Check for end organ dysfunction - urine dip, ECG, U+E etc.

Question 21

4 surgical factors which can impact peri-operative BP?

Answer 21

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

Question 22

4 anaesthetic/medical factors that can impact on peri-operative BP?

Answer 22

Antihpertensives

Anaesthetic agents

Epidural/spinal anaesthetic

Inotropes

Question 23

How can pneumoperitoneum affect BP in surgery - both during establishment and when established? What would you do if it dropped?

Answer 23

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

Question 24

2 reasons to use muscle relaxants?

Answer 24

Facilitate surgical procedures

Permit safe ET intubation

Question 25

What is the difference between depolarising and non-depolarising muscle relaxants?

Answer 25

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

Question 26

What are depolarising muscle relaxants good for? Risks?

Answer 26

E.g. suxamethonium, risk of MH but good for rapid and complete muscle relaxation e.g. RSI

Question 27

What are the advantages and disadvantages of non-depolarising muscle relaxants? Reversibility?

Answer 27

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

Question 28

If reversing non-depolarising muscle relaxant actively, what should you consider giving alongside and why?

Answer 28

Consider antimuscarinic e.g. atropine or glycopyrrolate to avoid bradycardia, hypersalivation

Question 29

3 complications of suxamethonium?

Answer 29

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)