Anaesthetics Flashcards
What is suxamethonium?
Depolarising muscle relaxant
How do you recover from suxamethonium?
Spontaneous, following metabolism by plasma cholinesterase which is synthesised in the liver
Why do pesticides prolong the activity of suxamethonium?
Inhibit cholinesterase activity so not broken down as rapidly
In what conditions should use of suxamethonium be with caution? Why?
Liver disease
Malnutrition
Pregnancy
Reduced levels of plasma cholinesterase
What is neostigmine?
Anticholinesterase
What is the American society of anaesthesiologists physical status classification system (ASA)?
ASA1: normal healthy patient
ASA2: mild systemic disease
ASA3: severe systemic disease
ASA4: severe systemic disease that is a constant threat to life
ASA5: moribund patient who is not expected to survive without the operation
ASA6: declared brain dead, organ removal for donor purposes
What is halothane hepatitis?
Appearance of liver damage within 28 days of halothane exposure when other known causes have been excluded
What antibodies do patients with halothane hepatitis have?
Antibodies against halothane altered antigens
When should halothane be avoided?
Previous exposure within 3 months
Known adverse reaction
Family history of adverse reaction
Pre existing liver disease
Why is a rapid sequence induction used?
In a patient who has not fasted to reduce the risk of GORD
A 22-year-old female is extubated following an uncomplicated laparoscopic appendicectomy. However, no respiratory effort is made and she is re-intubated and ventilated. She is monitored in the intensive care unit and all observations are normal. She is weaned from the ventilator 24 hours later successfully. What complication has occurred? Why?
Suxamethonium apnoea
Small subset of population has autosomal dominant mutation, lack of acetylcholinesterase in plasma which breaks down suxamethonium, terminating its muscle relaxant effect. So effects of suxamethonium are prolonged and patient needs to be mechanically ventilated and observed in ITU until the effects of suxamethonium wear off
What are some adverse effects of suxamethonium?
Hyperkalaemia, malignant hyperthermia and lack of acetylcholinesterase
What is the reversal agent of atracurium?
Neostigmine
What does a litre of Hartmanns contain?
Sodium 131 Chloride 111 Potassium 5 Calcium 2 Lactate 29
How does pulse oximetry work?
Spectrophotometry - absorbance of light by haemoglobin
What factors may influence the reading of your pulse oximetry?
Excessive movement Dark pigmentation Vasoconstriction Oedema Poor arterial circulation Low body temperature
What biochemical changes may make pulse oximetry levels inaccurate?
Severe anaemia
Elevated bilirubin levels
Elevated carboxyhaemoglobin levels
Elevated methylhaemoglobin levels
What regions are involved in the control of ventilation?
Senses: chemoreceptors, lung
Central: pons and medulla
Effectors: respiratory muscles
What regions are involved in the central control of ventilation (central controller)? What does each area do?
Medullary respiratory centre: inspiration and expiration. Sets inherent rhythmicity of breathing. When all afferent stimuli have been abolished, rhythm becomes irregular
Apneustic centre in lower pons: inspiratory gasps occur if sectioned above this level
Pneumotaxic centre in upper pons: inhibits inspiration after a certain point, regulating respiratory rate
Cortex: allows voluntary hypoventilation and breath holding
What do central chemoreceptors respond to?
Changes in hydrogen ion concentration
Rise in H+ stimulates ventilation
Where are peripheral chemoreceptors located?
Carotid bodies at bifurcation of common carotid arteries
Aortic bodies above and below aortic arch
What type of cells are located in peripheral chemoreceptors? What neurohormone do they contain?
Glomus cells
Contain dopamine
What do peripheral chemoreceptors respond to?
Decreases in arterial PO2 and pH and increases in arterial PCO2
What post op problems might you encounter in a patient with muscular dystrophy?
Plasma creatinine kinase raised Chest infections Sensitive to opioid and other resp depressant drugs Hyperkalaemia Myoglobulinuria
A 24 year old previously well male gives a hx of right iliac fossa pain associated with anorexia and vomiting. Acute appendicitis is suspected and he is booked for an appendectomy. What type of anaesthesia should be used?
Rapid sequence induction with cricoid pressure - risk of regurgitation and aspiration
Why is cricoid pressure applied during a rapid sequence induction?
Occlude the oesophagus to reduce risk of gastric contents being aspirated
What is a Biers block?
Intravenous regional anaesthesia - can provide anaesthesia for minor surgery to distal ends of both upper and lower limbs
Tourniquet and local anaesthesia used
Why is a subclavian perivasicular block contraindicated in day case surgery?
Risk of pneumothorax
A 28 year old female is scheduled for knee arthroscopy and anterior cruciate ligament reconstruction. She smokes 20 cigarettes per day and has asthma. She never uses her inhalers. What type of anaesthesia should be used?
Spontaneous ventilation through LMA - risk of coughing and bronchospasm reduced
What is the safest approach to anaesthesia in a patient with a fractured mandible with restricted mouth opening?
Awake fibre optic intubation via the nose
A 52 year old male in post op ICU with a central line catheter develops spikes of fever. What is the likely causative organism?
Coagulase negative staphylococci - staph epidermidis
Why does post op atelectasis occur?
Patient not breathing properly due to postoperative pain
Small plugs of mucus block small airways
Alveoli collapse due to inadequate ventilation
Normally patient is able to cough to expectorate small plugs
Which are the shortest and longest acting muscle relaxants out of atracurium, suxamethonium, pancuronium? How long does each last?
Suxamethonium: 10 mins
Atracurium: 15 to 35 mins
Pancuronium: 100 mins
When should suxamethonium be used for muscle relaxation in anaesthesia?
Rapid sequence induction
If patient has not fasted or is high risk of aspiration - hiatus hernia
What is thiopentone and when should it be used?
Barbiturate
Has anticonvulsant properties
Can be used as IV induction agent in patients with epilepsy
What is suxamethonium apnoea?
Pseudocholinesterase deficiency
Abnormality in production of plasma cholinesterases leading to increased duration of action of muscle relaxants in anaesthesia
Respiratory arrest is inevitable unless patient can be mechanically ventilated while waiting for muscle relaxants to degrade
When does warfarin need to be stopped pre op?
At least 72 hours before and replaced with LMWH
What needs to happen with oral steroids pre operatively?
Hydrocortisone dose needs to be escalated prior to surgery with a bolus IV of 50-100mg at induction
When should clopidogrel be stopped pre op?
One week before surgery
What is malignant hyperthermia?
Autosomal dominant condition where intracellular calcium transport is deranged and generalised muscular contractions generating heat are precipitated by anaesthetic agents
How is malignant hyperthermia treated?
Dantrolene
Which commonly used anaesthetic agent cannot be used in myasthenia gravis?
Suxamethonium - depolarising neuromuscular blocker
Will be resistant to its effects and would need significantly higher doses
To which anaesthetic agents would patients with myasthenia gravis be more susceptible?
Non depolarising neuromuscular blockers eg rocuronium
