ANAESTHETICS Flashcards
Broadly, what are the two types of airway management?
Simple airway
Advanced airway
Describe how a simple airway is maintained.
- Airway manoeuvre
- BVM
- OP/NP tube
Name two types of airway manoeuvre. What is the aim of airway manoeuvres?
Head tilt, chin lift
Jaw thrust
To lift the tongue and soft tissues of the pharynx anteriorly to open the airway.
When should you use a jaw thrust manoeuvre instead of head tilt?
Suspected trauma.
What is BMV?
Bag-mask-ventilation.
Facemask is used.
Which two airways can be used to aid BMV?
Oropharyngeal (OP) (guedel)
Nasopharyngeal (NP)
How do you insert an OP airway?
- Measure from the centre of the mouth to the angle of the jaw
- Insert into mouth and twist to advance
DO NOT USE IF GAG REFLEX PRESENT
How do you insert a NP airway?
- Measure from the tip of the nose to the tragus of the ear
- Through the nose
- Advance straight
DO NOT USE IN HEAD INJURY
Name two supraglottic airways?
LMA
iGel
How do you insert an LMA?
Insert blind
Inflate mask once situated
How do you insert an ET tube?
- Visualise with laryngoscope
- Sizing: 7 for women, 8 for men
- Inflate cuff to protect the airway
- 20-24cm markings should lie between the teeth
- Used in theatre and ICU
Elastic bougies can be used to aid ET tube placement.
How do you insert a tracheostomy?
• Needle (emergency) or surgical cricothyroidotomy
• Inserted from front of the neck
• Cuff to protect airway
Used in ITU
Which interventions protect the airway?
ET
Fibreoptic intubation
Cricothyroidotomy
What is a definitive airway?
Cuffed tube below the vocal cords to create a seal and prevent aspiration.
ET tube or tracheostomy.
(NOT LMA as this may not protect the airway and there is still risk of gastric aspiration).
Broadly, what are the two types of ventilation?
Non-invasive airway (NIV)
Invasive airway
When do we use NIV?
When supplemental O2 is failing e.g. respiratory failure.
What are the two types of NIV?
CPAP
BiPAP
How do we decide which type of NIV to use?
Depends on the type of respiratory failure.
Type I = CPAP
Type II = BiPAP
How does CPAP work?
Maintains a minimum airway pressure.
In alveolar collapse (pneumonia) –> keeps alveoli open
In pulmonary oedema (heart failure) –> pushes the fluid out
How does BiPAP work?
During inspiration, BiPAP gives extra IPAP (inspiratory positive pressure).
Increases lung expansion and ventilation.
AND during expiration, maintains minimum airway pressure with EPAP (same as CPAP):
Keeps alveoli open and pushes fluid out.
Give two examples of invasive ventilation.
ET tube.
Tracheostomy.
What two types of ventilation can be achieved with invasive management?
- Volume control - theatres.
2. Pressure control - theatres and ITU, protects lungs from too much pressure (ITU/children).
How does invasive ventilation work in terms of volume-control and pressure-control?
Volume-control:
- Pressure increases
- Target volume reached
- Ventilator stops
- Expiration occurs
Pressure-control:
- Pressure constant
- Target time reached
- Ventilator stops
- Expiration occurs
What is FiO2?
Fraction of inspired O2.
Molar/volumetric content of O2 in an inhaled gas.
What is the FiO2 for patients on air?
How does increasing the flow rate change the FiO2?
21%
Increases - 10L = 60%
Name four different methods of delivery O2?
Nasal cannula
Hudson mask
Reservoir mask (non-rebreather)
Venturi
What are the indications for the following type of O2 mask: Nasal cannulae? Hudson mask? Reservoir mask? Venturi mask?
NC - mild hypoxia.
Hudson mask - mild to moderate hypoxia
Reservoir mask - moderate to severe hypoxia
Venturi mask - COPD
What are some common issues with NC?
Irritate the nasal airway.
Don’t allow close control of FiO2.
What are some common issues with Hudson masks?
Risk of aspiration if the patient vomits whilst wearing the mask.
Don’t allow close control of FiO2.
What do you need to remember to do before fitting a reservoir mask?
Forgetting to fill the reservoir bag before attaching to the patient.
Doesn’t have a fixed seal so some air will leak out - it is not a fixed performance device.
What is humidified O2? Why is it used?
Oxygen is passed through a humidifying device producing a sterile vapour.
Reduces the drying effects of standard O2 and protects the airway mucosa.
What are the 3 components of anaesthesia?
Hypnosis
Muscle relaxation
Analgesia
What are the 3 levels of hypnosis? What class of drugs are used to achieve each level?
- Awake - local
- Sedated - sedatives
- Asleep - general
What types of local anaesthetic are there? What are they used for?
- Local - minor surgery, lacerations or wound repair.
- Regional - target specific nerves e.g. brachial plexus, usually for post-operative pain relief.
- Neuraxial - subarachnoid block (spinal) or epidural, for intra-operative and post-operative use.
What layers are found between the skin and CSF?
Skin –> fat –> supraspinous ligament –> Intraspinous ligament –> ligamentum flavum –> dura –> CSF
What is the difference between a spinal and epidural?
Spinal (subarachnoid block):
• Needle goes through ligament AND dura.
• Injected as a bolus, lasts about 2 hours.
• Smaller dose.
• Lumbar (below spinal cord) - same target as lumbar puncture.
Epidural: • Needle goes through ligament ONLY. • Catheter is passed. Local anaesthetic can be given as an infusion. • Larger doses can be given. Thoracic or lumbar.
What other drug is commonly mixed with epidural infusions?
Opioids - be careful not to prescribe opioids for these patients via other routes.
Below which dermatome can an incision be made following a spinal/epidural?
T10 - umbilicus (below the highest nerve root affected by the block).
An incision above this level will require general anaesthesia.
How do local anaesthetics work?
Reversibly block Na+ channels and inhibit the generation of action potentials.
Small diameter fibres and unmyelinated neurones are affected first.
Why are some local anaesthetics mixed with adrenaline?
Adrenaline acts as a vasoconstrictor:
• Reduces bleeding
• Prolongs effect by reducing perfusion to other tissues
Do not use adrenaline on end arteries e.g. fingers.
Name two commonly used local anaesthetics. What are they used for?
Lidocaine:
- Immediate onset, 15 mins duration
- Small procedures - laceration, chest drains, big cannulae
Bupivacaine:
- 10 mins onset, 2 hour duration (12-24 hour analgesia)
- Regional, spinal epidural
Why are neuraxial blocks preferred over GA?
Reduced affect on endocrine system
Reduced incidence of DVTs
Name a short-term sedative. What are its uses?
Midazolam IV
Endoscopy, regional anaesthesia
Name a long-term sedative. What are its uses?
IV propofol +/- alfentanil
ITU, intubated patients for theatre or transfer
Name 3 hypnotic drugs that can be inhaled.
- Isoflurane - cheapest
- Desflurane - wears off quickly
- Sevoflurane - used for induction
Name 3 hypnotic drugs that can be used intravenously.
- Propofol - quick onset, also antiemetic, fast redistribution
- Thiopenthal - quick, emergency
- Ketamine - CVS instability and analgesia
Name two ways the airway can be managed once sedation is achieved.
Spontaneous breathing - BVM or laryngeal mask (e.g. iGel)
OR
Controlled ventilation - intubating the trachea (requires muscle relaxant)
Why are muscle relaxants used?
- To aid intubation (relax the glottis)
- Muscles relaxed for surgery
- Patients do not ‘fight’ the ventilator
What are the two types of relaxant? What are they used for?
- Non-depolarising - routine and emergency, 2-3 mins onset
2. Depolarising - emergency, 30 seconds
Name three non-depolarising muscle relaxants.
Atracurium
Rocuronium - rapid onset
Vecuronium
Name one depolarising muscle relaxants.
Suxamethonium (two ACh molecules bound together)
What is the physiology of muscle contraction?
ACh arrives released into NMJ. Binds to (BOTH) ACh receptors. Ca2+ crosses membrane to cause contraction.
How do non-depolarising muscle relaxants work?
Competitively binds to ACh receptors.
Block binding site and prevent depolarisation.
How do depolarising muscle relaxants work?
Block both binding sites simultaneously (non-competitive).
Causes depolarisation and contraction.
Keeps pores open and prevents further contraction.
What can be used to reverse muscle blocks?
Neostigmine - cholinesterase inhibitor (prevents the breakdown of ACh). Facilitates the transmission of impulses across the NMJ.
Describe the WHO pain ladder.
Mild: paracetamol & NSAIDs
Moderate: Codeine & tramadol
Severe: morphine
What opioids might be used pre-operatively?
Codeine - weak
Tramadol - weak
Morphine - strong
Which opioids might be used intraoperatively?
Fentanyl (potent)
Remifentanil (rapid onset)
Name three types of antiemetic. Give an example for each group.
Serotonin receptor antagonist - ondansetron.
Dopamine receptor antagonist - metoclopramide, domperidone
Histamine receptor antagonist - cyclizine, cinnarizine, promethazine
Where is the site of action for 5HT3 antagonists?
CTZ (chemoreceptor trigger zone)
GIT
Where is the site of action for H1 antagonists?
Vomiting centre and vestibular system
Name some causes of nausea that you might come across in surgical patients.
Gut infection Radiotherapy Opioids Diabetic gastroparesis Motion sickness Vertigo
What are the most appropriate antiemetic to use for post-operative nausea and vomiting (PONV)? What is the best medication to use for prophylaxis of PONV?
Ondansetron OR Cyclizine.
Domperidone.
What are the most appropriate antiemetic to use for motion sickness?
Cyclizine
What are the most appropriate antiemetic to use for vomiting associated with long-term opioid use?
Metoclopramide (long-term opioid use causes gastric stasis which can be treated with a pro-kinetic).
What are the most appropriate antiemetic to use for vertigo?
Prochlorperazine
What is the formula for cardiac output?
CO = HR x SV
Name two types of drug that can increase the heart rate?
Anticholinergics (muscarinic antagonists)
Beta-agonists (adrenergic agonist)
How do anticholinergics lead to an increased heart rate?
Block ACh receptors
Inhibit the vagus nerve
Vagus nerve (X) is parasympathetic (slows the heart rate)
Heart rate increases
How do beta-agonists lead to an increased heart rate? How else to they affect the heart?
Stimulate B-receptors on myocardial cells
Increased heart rate
AND increased contractility.
Give two examples of anticholinergics. How are they used in anaesthetics?
Atropine
Glycopyrrolate
Used to treat bradycardia, common under anaesthetic.
How do atropine and glycopyrrolate differ in their effects?
Atropine = crosses the BBB, faster acting. Glycopyrrolate = does not cross BBB, slower acting.
What is the formula for blood pressure?
BP = CO x peripheral resistance
similar to voltage = current x resistance
Name two types of vasoconstrictor. What drug group do they come under?
Peripheral (via cannula) OR central (via central line).
Alpha agonists.
How do alpha-agonists work on blood vessels?
Stimulate alpha receptors which are found on peripheral vessels
Cause vasoconstriction
Increases blood pressure (BP = CO x peripheral resistance)
However, they can lead to bradycardia as the body compensates to reduce CO (HR x SV).
Give an example of a peripheral vasoconstrictor.
Phenylephrine
Metaraminol
Give an example of a central vasoconstrictor.
Adrenaline (has combined alpha and beta effects but is very potent and should only be used in ITU).
What actions/drugs can reduce heart rate/BP during surgery?
• Low resting heart rate
• Regular medications e.g. propranolol
• Vagal stimulation - especially laparoscopic surgery
Drugs - propofol & opioids
What actions/drugs can increase heart rate/BP during surgery?
• Anxiety
• Pain
Drugs - alpha/beta agonists, anticholinergics
What should be given if heart rate AND blood pressure are low?
Give a combined alpha and beta agonist e.g. ephedrine.
What can you use to check if a low blood pressure reading is accurate?
Perfusion trace (SATS monitor) - in hypoperfusion the trace will be flat, but sats can initially be normal. CO2 - CO2 will be retained due to hypoperfusion of the lungs.
How would you manage the cardiovascular status of a patient with aortic regurgitation?
Most important thing is to maintain cardiac output (prevent shock).
^HR and decrease peripheral resistance.
How would you manage the cardiovascular status of a patient with aortic stenosis?
Most important thing is to maintain coronary perfusion (prevent cardiac arrest).
Reduce HR (don’t want the heart to be working too fast) and increase peripheral resistance.
At what point in the cardiac cycle does blood flow into the coronary arteries?
Diastole - when the ventricles are relaxed.
How does a spinal anaesthetic affect the patient’s blood pressure and heart rate?
Anaesthetic blocks sympathetic nerve roots which leads to vasodilation below the level of the spinal. Blood pressure will drop and heart rate will decrease.
What percentage of total body weight is water?
60%
In a 70kg adult, what is the total body water (in litres)?
42L
How is total body water divided?
2/3 = intracellular fluid 1/3 = extracellular fluid
How is extracellular fluid divided?
2/3 = interstitial 1/3 = intravascular
Describe the sodium and potassium distribution in extracellular and intracellular fluid? Why is this maintained?
ECF - ^Na, low K (140 mmol/L Na+, 4 mmol/L - K+)
ICF - low Na, ^K (8 mmol/L - Na+, 151 mmol/L - K+)
Maintains electrochemical gradient across the membrane - allows nerves to work (for excitable membranes).
What are the two main types of fluid?
Crystalloid
Colloid
Describe the composition of crystalloid fluids and give some examples.
Water + electrolytes.
Can be hyper/hypotonic.
0.9% Saline, Hartmann’s, Plasmalyte, dextrose-saline, dextrose (5, 10, 50%).
Describe the composition of colloid fluids and give some examples.
Contains large insoluble molecules.
Stays in the intravascular space.
Blood products, human albumin, gelatins and starch.
What is the goal of fluid replacement?
To maintain adequate perfusion of the tissues.
What three factors determine oxygen delivery to the tissues?
• CO
• Hb concentration
Oxygen saturation
What is maintenance fluid?
30ml/kg/day
What is the best fluid to use for volume replacement?
Saline OR Hartmann’s (anaesthetists like this).
What is the best fluid to use for blood loss?
Blood
What is the specific danger of giving too much saline in resuscitation?
Hyperchloremic alkalosis - if someone needs a large amount of resuscitation fluid, then you need to be careful about giving exclusively saline.
If a patient is on maintenance fluids, how often should U&Es be taken?
Daily
How can you establish the risk of major complications preoperatively?
Need to assess the degree of impairment from cardiovascular, cerebrovascular and renovascular impairment.
• U&Es • Exercise testing • ECHO - cardiac ischaemic may be silent due to autonomic neuropathy Carotid duplex doppler
Where should diabetic patients be placed on the theatre list? Why?
First - to shorten fasting time and prevent the risk of hypoglycaemia and ketoacidosis.
Why can diabetic patients be difficult to intubate?
Glycosylation of collagen in the cervical vertebrae and temporomandibular joints.
Why might diabetic patients require intubation?
Gastroparesis can lead to delayed gastric emptying due to autonomic neuropathy.
Why are the associated risks with regional vs general anaesthetics in diabetic patients?
Regional - quicker return to normal diet, but may compensate poorly to sympathetic blockade and infection risk is increased.
Why might patients with NIDDM require insulin for major surgery?
Insulin resistance and stress response.
How should diabetic medication be managed for minor surgery (expected to eat/drink <4 hours)?
Oral hypoglycaemics should be omitted on the day of surgery.
Half dose of soluble insulin given if blood glucose >10mmol/L.
No insulin given if blood glucose <10mmol/L.
Resume normal diet and medication as soon as possible post-operatively.
How should medication be managed for major surgery?
Omit oral hypoglycaemics and SC insulin.
VRII with 5% dextrose and KCl 20mmol in 1L at 100mL/h.
Which patients will require VRII?
• Surgery requiring a long fasting period (missing more than one meal)
• Poorly controlled diabetes
High risk of AKI e.g. low eGFR
How should metformin be adjusted in surgery?
Take as normal
When can oral diabetic medications be started again post surgery?
When the patient is eating normally again.
Metformin should only be started if eGFR >60.
Name 3 complications of poor diabetic control during surgery.
• Wound/respiratory infection
• Postoperative AKI
Long stay in hospital
What is the most common classification system used to determine the urgency of a surgery?
NCEPOD (National Classification Enquiry into Patient Outcome and Death).
What is the most common scoring system used to assess general risk before surgery?
ASA grading (American Society of Anaesthesiologists).
What is the purpose of preoperative assessment clinic?
• Assess risk - conduct tests
• Manage risk factors/control chronic disease
Reduce cancellations
What are the important aspects of a preoperative history?
1. Anaesthetic history: • Previous anaesthetic • Airway - previous difficulties with the airway, spinal surgery, previous trauma or infection, scarring of the head/neck 2. Systems review: • Cardiac disease • Respiratory disease • GI disease • Renal disease • CNS disease • MSK disease 3. Medications: • Current • Allergies 4. Lifestyle: • Smoking • Alcohol • Recreational drugs 5. Family history: ask specifically about malignant hyperthermia Any preoperative concerns
Which three classes of drugs are likely to be changed preoperatively?
• Anti-hypertensives
• Hypoglycaemics
Anti-coagulants
List some procedures that require special preparation.
• Thyroid surgery; vocal cord check.
• Parathyroid surgery; consider methylene blue to identify gland.
• Sentinel node biopsy; radioactive marker/ patent blue dye.
• Surgery involving the thoracic duct; consider administration of cream.
• Pheochromocytoma surgery; will need alpha and beta blockade.
• Surgery for carcinoid tumours; will need covering with octreotide.
• Colorectal cases; bowel preparation (especially left sided surgery)
Thyrotoxicosis; lugols iodine/ medical therapy.
How and why should patients fast before anaesthesia?
To prevent gastric juices entering the tracheobronchial tree and causing aspiration pneumonia. Food particulates can also cause airway obstruction.
For elective surgery:
• > 2 hours since clear fluids
• > 4 hours since milk
> 6 hours since food
Which patients are at risk of gastric aspiration even after fasting? How should they be managed?
- Opioid use
- Hiatus hernia
- Acute abdomen
- GI obstruction
- Pregnancy (2nd and 3rd trimester)
- Severe trauma
Early endotracheal intubation.
What is the WHO checklist? When is it used? What does it check?
Checks the patient, procedure and specific concerns such as blood loss, glycaemia control and antibiotic prophylaxis.
Check that everyone is happy with their responsibilities.
