Anaesthetics Flashcards
What are the normal ranges for sodium and potassium in the blood and why is there such a difference?
Sodium: 135-145mmol/L
Potassium: 3.5-5.0mmol/L
Sodium mostly exists in the extracellular compartment (ECF and blood), potassium mostly exists in the intracellular compartment
What are the daily requirements of water, sodium and potassium?
WATER: 30-40ml/kg (approx 2-3L for average adult)
SODIUM: 1-2mmol/kg (approx 70-140mmol/L for average adult)
POTASSIUM: 0.5-1/0mmol/kg (approx 35-70mmol/L for average adult)
***these are the sorts of levels we should aim for when prescribing MAINTENANCE FLUIDS
What kinds of things cause FLUID LOSS?
Poor oral intake (elderly, dysphagia, unconsciousness, fasting NBM) Increased requirements (Trauma, burns, post-operative) Increased loss (fever, sweating, bleeding, D&V, renal loss)
How do we classify fluid loss?
As mild, moderate or severe
MILD
- 4% body weight, loss of skin turgor and dry mucus membranes
MODERATE
- 5-8% body weight, oliguria, tachycardia and hypotension
SEVERE
- >8% body weight, profound oliguria and CVS collapse
What are some crystalloids and what are some examples?
They are water soluble substances dissolved in solution. They can be rapidly administered but can cause pulmonary oedema
NaCl 0.9%
Dextrose
Haartmans
What is in NaCl and what are some risks?
(0.9% mean 9g in 100ml) - contains 154mmol/L Na and 154mmol/L Cl
So about the right amount of sodium but there is a risk of hyperchloraemic acidosis
What is in dextrose and when should it be used?
5% = 50g per L water
Good if people have glucose requirements
What is in Haartman’s and what are some benefits of using it?
Na - 131 Cl - 111 K - 5 Ca 2 Lactate 29
this is much more isotonic and the patient is at less risk of becoming hypokalaemia
What are some examples of colloids? Where are they sometimes used?
Gelfusin Voluven Volulyte Albumin Sometimes used in trauma but rarely elsewhere
What is a fluid challenge?
Getting IV access with a wide bore cannula and administering 250-500mL of fluid as quickly as possible (usually 10-15mins) and monitoring for a response (BP, HR, UOP, JVP)
If an unwell patient hasn’t improved after 3 fluid challenges then need senior support
What is an example of a good maintenance fluid regimen in a 70kg man?
0.9% NaCl + 40mmol K over 8 hours
5% dextrose + 20mmol K over 8 hours
5% dextrose + 20mmol K over 8 hours
Why will people need more than just maintenance fluid after surgery?
People loose fluids during surgery (on average 600-900mL) so they will need some extra fluids before they’re placed on a maintenance regime
How do you manage fluid therapy in fever?
Add 10% extra fluids for every degree of fever
What should you ask in the history section of a pre-operative assessment?
Current illness (health in the past 2 weeks, any new problems or infections)
Exercise tolerance
Symptoms of apnoea (snoring, tired throughout day, headache)
ONGOING medical conditions and how well controlled
Anaesthetic history (personal and family)
Drug hx and allergies
What ongoing medical conditions in particular should you ask about during anaesthetic history?
IHD, diabetes, HTN, asthma, COPD, liver or kidney disease. Always ask how well controlled these are
What should you examine in a pre-operative assessment?
Neck movement, jaw opening and dental health (dentures, caps, crowns or loose teeth)
Mallampati
General examination (listen to heart and chest, feel abdomen, feel peripheries, feel calves for swelling or tenderness)
What is the mallampati score?
I - complete visualisation of soft palate
II - Complete visualise of uvula
III - Can only see base of uvula
IV - Cannot see soft palate
What is the ASA-GRADING for surgery?
1 - completely safe no ongoing disease
2 - Chronic disease but with no functional impairment (e.g. well controlled diabetes, HTN or smoker)
3 - Severe chronic disease with functional impairment e.g. angina or COPD
4- Severe angina, ESRD or liver disease
5 - Moribund patient who is unlikely to survive with or without operation
6 - Brainstem dead patient for transplant
What are the surgical grades for the operation?
1 (minor) - skin excision or toenail removal
2 (intermediate) - hernia repair or tonsillectomy
3 (major) - hysterectomy or thyroidectomy
4 (major+) - C/S, joint replacement, thoracic operational or radical dissection
What investigations does EVERYONE get in pre-operative assessment?
FBC, U&E, clotting and and group and save
What are some extra investigations for specific things in pre-operative assessment?
LFTs for liver or billiard op
Sickle cell screen for Afro-Caribbean patients
TFTs if they’re on thyroxine
CXR if ICU care might be required
Echo if they’ve got valve problem or murmur
Spirometry if lung disease
What must you correct before the operation if found to be abnormal?
INR (with vit K or platelets/FPP/cryoprecipitate)
Anaemia
What is the general rule for stopping medications before an operation?
In general omit on the day of operation and resume the day after
What more specific medications must be stopped before operation?
Warfarin - stop 5 days before DOACs - stop 24h before LMWH - stop 48h before Aspirin/clopidogrel - stop 7 days before Insulin - don't have morning dose Oral hypoglycaemic - avoid on day of op Diuretics/ACE-is - avoid on day of Long-term steroids - consider switch to hydrocortisone COCP - stop 4 weeks before
What are the fasting guidelines before an operation?
No food for 6 hours before (have dinner nil else)
No milk for 4 hours before
Only clear fluids until 2 hours before - NBM
How much oxygen can be given through nasal cannulas?
1-6L (most commonly 2L)
24-40% O2
How much oxygen can be given through a simple face mask (hudson)?
5-10L (CO2 can accumulate if the flow is less than 5L)
Not very reliable
What demonisations are there of venturi devices? In whom are they commonly used?
24, 28, 35, 40 and 60%
Good in CO2 retainers (COPD) to control concentration of O2
How much oxygen can be given through a non rebreathe mask?
15L and probably gives up to around 85% - this is about as good as we can get unless we artificially ventilate someone
What options do we have if the patient need assistance with ventilation?
BAG-VALVE MASK
NIV
ET tube or airway adjunct
What are some examples of NIV?
CPAP and BiPAP
CPAP pressure is continuous and BiPAP has different inspiratory and expiratory pressures
How do you measure a Gedell airway?
HARD to HARD
Angle of the mandible to the front incisors
What are the average sizes of NP tubes? When should they not be used
7mm for women
8mm for men
Do not use if any suspicion of basal skull fracture
What are some examples of supraglottic airways?
Laryngeal mask airway (LMA) and iGEL
When are LMAs preferably used and how do you insert an LMA?
Used in shorter surgeries when an ET tube is not required or if you cannot intubate someone (easier to put in)
NOT A DEFINITIVE AIRWAY
Reflexes should be suppressed e.g. with propofol then insert with the curve of the airway (no need to rotate)
What kind if airway is an ET tube? How are the sized
Definitive
Sized by diameter - 7-8mm for women, 8-9mm for men
What is the process of inserting an ET tube?
- preoxygenate the patient
- Wait for the neuromuscular blockage (90-120s)
- Place the patient in the sniffing the morning air position
- Hold laryngoscope in L hand
- Insert the laryngoscope in the R hand corner of the mouth and slide it down between the tongue and the epiglottis
- then lift with your whole arm up and to the left
- Aim to visualise the vocal cord
- Insert the tube to just beyond the vocal cords
- Inflate the cuff of the tube, attach to the bag valve mask and look for signs that it is in the right place
What signs are there that the ET tube is in the right place?
Rising of the chest (symmetrically, if it is not symmetrical it might have gone too far down the R main bronchus)
Misting of the tube
EtCO2 properly traced (5 clear traces)
What are some possible complications of ET tubing?
Breaking teeth with the laryngoscope
Incorrectly positioned tube (into oesophagus) if in doubt take it out
Right lung intubation if put too far down
Laryngospasm - especially if someone has asthma or COPD
What are the three types of anaesthetic?
Local, Regional, General
When putting someone under a general anaesthesia what three things do you need to achieve?
AMNESIA - unconscious and won’t remember
AKINESIA - cannot move
ANALGESIA - won’t be in pain or have a pain response
How do we achieve amnesia in general anaesthesia?
INDUCTION AGENTS INITIALLY (propofol, thiopentone, etomiidate and ketamine)
Then maintained with VOLATILE AGENTS
What dose is propofol used in and what are some risks and benefits?
1.5-2.5mg/kg
Has a very good suppression of airway reflexes and goo at preventing PONV
Causes a marked drop in HR and BP - need to compensate for this. Also can be painful to inject because it is lipid based
What dose is thiopentone used in and what are some risks and benefits?
This is a BARBITUATE that is commonly used in 4-5mg/kg doses
It works much faster than propofol and thus is often used in RSI
It also has anti-epileptic properties and is quite neuroprotective
HOWEVER, it drops BP but INCREASES HR and can cause a rash and bronchospasm, it also needs to be injected intra-arterially meaning it can lead to gangrene and thrombus. AVOID in PORPHYRIA
What effects does ketamine have, what dose is it used in and what are some risks and benefits?
It is a DISSOCIATIVE ANAESTHETIC and is also profoundly analgesic
DOSE: 1-1.5mg/kg - it is quite slow to act (90s)
It increases HR and BP and causes bronchodilation which is good
Can causes PONV and EMERGENCE PHENOMENON (vivid dreams and hallucinations)
What dose is etomiidate used in? In whom is it most suitable and what are some risks and benefits?
Used in 0.3mg/kg dose
It confers good haemodynamic stability and so is good in people with cardiovascular conditions
However it is painful on injection, can cause spontaneous movements and adrenocorticoid suppression (cortisol is suppressed for up to 72 hours suggesting it should not be used in very unwell who need the stress response), high PONV
What agents are used to maintain anaesthesia?
Volatile agents (desflurane, isoflurane, enflurane, sevoflurane and NO)
What is minimum alveolar concentration?
MAC - this is the minimum concentration of gas required to eliminate a reaction to a standard stimulus
What are the MACs of sevoflurane, desflurane, NO, enflurane and isoflurane?
Sevo - 2% Isoflurane - 1.15% Desflurane - 6% Enfluane - 1.6% NO - 104%
How does pain affect people under anaesthesia?
They don’t FEEL pain because this is a conscious interpretation. However, they do have nociceptors stimulated which can cause the physiological response of increased HR and BP. That’s why it’s important to give someone analgesics
What are some examples of short acting analgesics?
Fentanyl, ramifentanil, alfentanyl
What are some examples of long acting analgesics?
Morphine and oxycodone
Where do the anti-kinetic agents act?
At the neuromuscular junction - NICOTINIC FIBRES lead to muscular contraction
Ach
What are the two types of akinesis agents and how do their actions differ?
DEPOLARISING - These act in a similar way to the Act NT but they are broken down very slowly so they go into the receptors but then block them
NON-DEPOLARISING - these block the nicotinic receptor without activating them
What is an example of a depolarising akinesis agent? What dose is it used in and what are some adverse effects?
SUXAMETHONIUM - 1-1.5mg/kg OFTEN USED IN RSI
Can cause muscle pains, fasciculations, hyperkalameia, malignant hyperthermia, rise in ICP, IOP and gastric pressures
What are some examples of short-acting non-depolarising agents?
Atracurium and mivacurium
What are some examples of intermediate acting akinesis agents?
vecuronium and rocuronium
What is an example of a long acting akinesis agent?
pancuironium
What is the main advantage of non-depolarising agents and the main reason they are used?
THEY ARE REVERSIBLE
How do we reverse non-depolarising agents?
With neostigmine - an anti-cholinesterase that prevents breakdown of ACh increasing its conc so that it can outcompete akinesis agent?
What is the problem with neostigmine and how can we prevent this?
It is NON-SELECTIVE for nicotinic and also works on muscarinic receptors leading to bradycardia and dry mouth etc.
We can give GLYCOPYRROLATE to prevent this
What other drugs are often prescribed peri-operatively?
Anti-emetics and vaso-active drugs
What class of drug is ondansetron?
5HT3 blocker - anti emetic
What class of drug is cyclizine?
Anti-histamine anti-emetic
What class of drug is metaclopramide?
Anti dopaminergic anti emetic
What other anti-emetics are there and what classes are they?
Dexamethasone (steroid)
Prochlorperazine
What vaso-active drug should you consider if someone’s HR and BP are low?
Ephedrine (rise in rate and contractility of heart)
What vaso-active drug should you consider if someones BP is low but their HR is high?
Phenylephrine - is more alpha selective and just causes vasoconstriction OR Metaraminol (another vasoconstrictor)
If someones hypotension is severe and non-responsive what drugs should you consider?
Adrenaline, Noradrenaline or dobutamine
What is the sequence of events when putting someone under a GA?
- Oxygenate them
- Give them opioid (need to have painkiller before being tubed) - opioids take a little while to work
- INDUCTION AGENT (e.g. propofol to send them to sleep)
- Turn on volatile agent - keep them asleep
- Bag valve mask ventilate them to maintain oxygenation
- Insert the airway and ventilate them
READY FOR SURGERY
What things should you consider prescribing for post-operative patient?
Analgesics - most patients will need some analgesic cover
Fluids - most patients will lose fluids during surgery so will need some element of replacement and then maintenance
Antibiotics - internal surgeries sometimes require prophylactic abx
How do we manage pain post-operatively?
Following guidelines from essential pain management (EPM) RAT system of pain management - Recognise - Assess - Treat
How do we recognise pain?
If the patient is conscious they will tell you - pain is what the patient says it is
Pain response might be dulled in trauma when sympathetic surges of adrenaline dull the response
How do we assess the pain?
Need to get an idea of WHERE it is
Need to get an idea of what the CHARACTER of the pain is like?
Get an idea of associated symptoms
Scale of 1-10: this gives idea of baseline
What are the three classification strategies for pain?
Is it acute or chronic?
Is it cancerous or non-cancerous?
Is it neuropathic or nociceptive?
What is nociceptive pain?
Sometimes called inflammatory or physiological pain this is pain that is in response to illness or injury
It has a protective function - is usually well localised
What is neuropathic pain?
Nerve damage e.g. sciatica or CES
Does not have a protective function
Might be burning, shocking or feel hot/cold
What is the difference between pain and nociception?
Pain is the cerebral input into nociception
What is the nociceptive pathway?
Tissue injury - nociceptors are activated by cytokines such as PGs, histamine and leukotrienes
THEN EITHER TRAVELS in A-delta (fast response) or C pathway (later throbbing pain)
Signal carried to dorsal root ganglion in dorsal horn
Fibers decussate into contralateral spinothalamic tract
Run up into thalamus and pain is perceived
Stimulus is moderated by sending signal back down the descending pathway
How does pain impact the surgical recovery process?
Physical immobility - e.g. chest pain limits breathing leading to infections
If someone has had lots of pain from one procedure might be less willing to have another
Longer stay in hospital and more time off work
How does the body respond to pain?
Tachycardia and hypertension
GI N&V
RESP reduced VC and FRC
DVT and PE
What are the three levels of the analgesic ladder?
0 - Paracetamol 1g PRN max 4g daily
1 - Paracetamol + NSAID (400mg) OR weak opioid e.g. codeine (30-60mg)
2 - Paracetamol + NSAID (400mg) + regular weak opioid e.g. codeine + strong opioid e.g. oromorph
How does paracetamol work?
Inhibits PG production
Selective inhibitor of COX-3
Good anti-pyretic
Poor anti-inflammatory
How do NSAIDs work?
COX-inhibitors
Block production of PGs and thromboxane which potentiate the action of cytokines on nociceptors
What is the difference between COX-1 and COX-2?
COX-1 is a constitutive isoenzyme responsible for lots of homeostatic measures thus is the reason for lots of the side effects (bronchospasm, GI effects, renal, platelets)
COX-2 is a INDUCIBLE enzyme - responsible for inflammation
Which NSAIDs are most COX-2 specific?
PARECOXIB and Celocoxib
In whom are NSAIDs contraindicated?
Those prone to bleeding
Those with peptic ulcers
Caution with asthma
CI’d in renal failure - really excreted
What are some examples of weak opioids and how do they work? Common doses?
Codeine and tramadol Work by unregulated the signal from the descending pathway moderating pain (activate mu-opioid receptors) Codeine: 30-60mg Tramadol: 50-100mg Dihydrocodeine: 30-60mg
What are some examples of strong opioids, how do they work and what kind of pain are they useful in?
Morphine, oxycodone and diamorphine
Strong OP3 receptor agonists
Work well on longer term C fibre pain and less for A-delta pain
What are some examples of short acting opioids?
Fentanyl
Ramifentanil
Alfentanyl
What are some side effects of opioids?
Drowsy, constipated, N&V, tolerance and dependence, hypotension
Respiratory depression - infrequent gulping breaths
What methods of administration are there for post-operative morphine?
oromorph - works very quickly and is very effective - 20mg/hr PRN
IV morphine - common. Can given 10-20mg diluted into 1mg/mL IV dose is 1/3 oral dose
PCAS - patient gives themselves 1mg every 5mins - idea is that this stops spikes of analgesia - keeps constant level
How do you dose paracetamol and ibuprofen?
Paracetamol you can have 1g (2 tablets) every 4 hours no more than 4 times a day (max 8 tablet per day)
Ibuprofen can take 400mg every 6-8 hours up to 3 times a day.
What doses are appropriate for codeine, tramadol and morphine?
Codeine - 30-60mg every 4 hours up to 240mg every 24h
Tramadol - 50-100mg every 4 hours up to 400mg every 24h
Morphine - give them a 10mg dose titrated in over 10mins (they might not need all 10mg)
What can you give for a patient who has had an overdose of opioids?
Naloxone
Other than oral analgesics what other options do we have for managing pain post-operatively?
Local anaesthetic injections
Very often after surgery local anaesthetics are injected around the surgical site to numb it and block the pain
BUPIVACAINE IS OFTEN GIVEN
What drugs are more often given for chronic pain and why?
Amitriptyline, Pregablin and gabapentin, Clonidine, corticosteroids, capsaicin
Different types of drugs are needed because chronic pain is more likely to be neuropathic in nature
