Anaesthetics General Flashcards
Which anti-hypertensives must be stopped before surgery
Stop ACEi and diuretics on day of surgery as they have a risk of prolonged hypotension
Only exception is if the diuretic is being used for heart failure
How do you manage someone’s antiplatelets before surgery
Should stop anti-platelets 7 days before surgery as this allows new platelets to come back into circulation
However, aspirin is a grey area. half life is 24 hours and risk of bleeding is relatively low so now usually continue until the day before then stop.
What surgery MUST aspirin be stopped 7 days before
Intracranial surgery - neurosurgery
Orthopaedics
Bleeds would be very high risk
How should warfarin be managed prior to surgery
Should be stopped 5 days before surgery and then restarted post-op
If on for low risk reason like AF then stop completely with no replacement is fine
If high risk like mechanical valve, recurrent PE they are high clot risk so give bridging therapy (stop warfarin for 5 days, give LMWH on day 4 and 5 then restart)
How should DOACs be managed prior to surgery
These needs stopped 2 days before and can be restarted - easier to manage
How long should someone fast before surgery
Should fast for at least 6 hours pre-op - this is the timing of gastric emptying
Stop drinking 2 hours - can sip till send (sip small amounts of water to reduce dehydration)
How should you manage diabetics prior to surgery
They are at risk of both hyper (due to body stress) and hypos (due to fasting)
Make them 1st on list to minimise risk from fasting (hypo risk)
Monitor glucose regularly
Get them back into usual routine as fast as possible
IV insulin can be used in more complex case
When is jaw thrust preferable to head tilt chin lift
If there suspicion of C-spine pathology
What are the 2 types of airway adjunct
Oro-pharyngeal or Guedel airway
Naso-pharyngeal airway
How do you size a oro-pharyngeal airway
Roughly the distance between the patient’s incisors and the angle of the jaw
Better to be slightly too big than too small
How do you size a naso-pharyngeal airway
Length corresponds to the distance between the tip of the patient’s nose to the tragus/earlobe
If too long it might make them gag
When should you remove an oro-pharyngeal airway
If the patient starts gagging
NP is better tolerated
How much O2 can be delivered via nasal cannula
1-4L/min
Which type of mask is needed for high flow (15L/min) O2 delivery
Non-rebreather
How can reduced consciousness lead to airway obstruction
There is a decrease in muscle tone which results in posterior displacement of the tongue and soft palate which can block the airway
This may be as a result of drugs, neurological conditions, anaesthetics or patients in critical condition
When are naso-pharyngeal airways used
If patient is not deeply unconscious
If they have a clenched jaw trismus or maxillofacial injuries
What is the major contraindication to nasopharyngeal airway use
Base of skull fracture
What are the signs of a clear airway on bag-mask ventilation
Misty, Chesty, Tracey
- mask misting
- smooth respiratory mechanics of the chest
- square wave capnography trace
Where are supraglottic airways positioned
Inserted into the oropharynx
The cuff at the bottom forms a seal around the laryngeal opening - above the epiglottis
What are the absolute contraindications to supraglottic airways
History of gastric reflux or hiatus hernia
Intra-abdominal pathology
Pregnancy
Recent major trauma or administration of opiates
Morbid obesity
Gastroparesis
This is due to aspiration risk
What is the only total contraindication to endotracheal intubation
Total airway obstruction of the upper airway preventing laryngeal access and necessitating a front-of-neck-airway
List some potential complications of endotracheal intubation
Dental damage
Damage to other structures such as trachea or larynx
ETT may go down the wrong hole into the oesophagus
ETT may go too far down into the bronchi
When is a front-of-neck intubation needed
If the patient is not being oxygenated but cannot be intubated
Where is a front-of neck airway placed
In the cricothyroid membrane into the trachea
Called a cricothyroidotomy
Describe the ‘ladder’ of critical care
Ward based
HDU - single organ failure
ICU - multi-organ failure and/or ventilation
What conditions may present post-ICU survival
PTSD, anxiety etc
Muscle weakness
Fatigue
Long term renal and respiratory support needed
When would you use CPAP vs BiPAP
CPAP - gives pressure on expiration. Used for type 1 resp failure and pulmonary oedema.
BiPAP - also gives inspiratory pressure so better for type 2 resp failure and hypercapnia as helps decrease CO2
Those with end stage lung disease may not be accepted for mechanical ventilation - true or false
True
They would be unlikely to be able to wean off it - will never recover their resp function
Often considered a terminal event and discussed in AD - support until end of life
What is ECMO
A way of oxygenating the blood outwith the body - bypasses heart and lungs
Used for severe respiratory failure
How are vasopressors a used
In vasodilatory, neurogenic or distributive shock
e.g. in sepsis, anaphylaxis etc
How do vasopressors work
Primarily alpha-adrenergic Used in vasodilatory/distributive shock
Causes venoconstriction - increases venous return (and CO etc)
And arterial constriction - increases SVR
How do positive inotropes work
Primarily beta-adrenergic stimulation
Increase cardiac output by increased contractility
How are inotropes used
In states of low CO such as cardiogenic shock
When hypotension is caused by poor contractility and has not responded to fluids
What are the first line fluids in the critically ill
Crystalloids such as Hartmann’s
Balanced solutions like this are better than saline alone
If drug treatment fails, how can you treat cardiogenic shock
Intra-aortic balloon pump
- inflate in diastole to increase pressure and improve coronary filling
- deflates in systole to reduce afterload and myocardial O2 demand
When would you need a central venous catheter
Monitoring of Central Venous Pressure
Venous Access for Haemodialysis
Venous Access for Cardiac Pacing
Administration of Inotropes, cytotoxic agents
List some immediate complications of central venous catheter insertion
Arterial puncture Haemorrhage Pneumothorax / haemothorax Air embolism Cardiac arrhythmia Damage to nearby structures - eg trachea, oesophagus, thoracic duct, nerves
List some late complications of central venous catheter insertion
thrombosis
infection
endocarditis
cardiac or valve rupture
Where should a central venous catheter sit
The tip should be at the entrance to the right atrium
What is a vasopressor
A substance which increases the systemic vascular resistance
What is an inotrope
A substance that affects the force of muscular contraction, either positively or negatively.
When discussing medication we mean positive ones - increase contraction
Inotropes must always be given by infusion through a central venous catheter - true or false
True
List examples of positive inotropes
Adrenaline
Dobutamine
List examples of vasopressors
Nor-adrenaline
Metaraminol
Adrenaline
Ephedrine
What happens to pO2 as air moves through the body
It decreases
Highest in atmospheric gas and gets lower as it moves through the steps of respiration - lowest in mitochondria
How does hypovolaemic shock cause hypotension
It decreases preload - the amount of blood getting back to the heart
How does cardiogenic shock cause hypotension
It decreases myocardial contractility
How does septic/neurogenic shock cause hypotension
It decreases afterload - the resistance the heart is beating against
decreased SVR
List signs of shock
Tachycardia, tachypnoea and vasoconstriction (waiting for BP drop is dangerous)
Decreased urine output
Decreased conscious level
Acid Base Abnormality - Metabolic Acidosis/Respiratory compensation
How is haemorrhagic shock classed
4 classes based on how much blood has been lost.
Where is the majority of body fluid stored
As the intracellular fluid - 2/3
Rest is extracellular - interstitial and plasma
List examples of crystalloid fluids
Saline
Hartmann’s
Dextrose
What are the benefits of crystalloid fluids
Easily available
Cheap
What are the cons of crystalloid fluids
Variable volume of distribution (can end up in undesirable spaces) - easily diffuses through a semi-permeable membrane
What are the benefits of colloid fluids
Stays in intravascular space - does not diffuse through membranes due to large protein/carb particles
Expands plasma volume - draw in water from interstiital fluid
Relatively expensive
What are the cons of colloid fluids
Risk of anaphylaxis
No proven benefit over saline in hypovolaemia
List examples of colloid fluids
Gelofusine
What are the benefits of using blood to resus
Well recognised
Good colloid - stays in intravascular space
Replaces ‘like with like’
Carries oxygen well
What are the drawbacks of using blood to resus
Expensive Risk of transfusion reactions Infection risk etc Packed red cells does not contain platelets and clotting factors
What type of pain is usually seen in acute scenarios
Nociceptive
Direct response to injury (physical, chemical), or
other pathology - proportionate
How can under-treated pain affect the cardiovascular system
Tachycardia Hypertension Increased peripheral vascular resistance Increased myocardial oxygen consumption Myocardial ischaemia
How can under-treated pain affect the respiratory system
Decreased lung volumes Atelectasis Decreased cough and sputum retention Infection Hypoxaemia
How can under-treated pain affect the GI system
Decreased gastric and
bowel motility
How can under-treated pain affect the GU system
Urinary retention
How can under-treated pain affect the MSK system
Muscle spasm
Immobility
How can under-treated pain affect the endocrine system
Increased catabolic hormones and decreased anabolic hormones
Insulin resistance
How can under-treated pain affect the patient psychologically
Anxiety and fear
Depression
Sleeplessness
Is it better to use high doses of one drug or lower doses of multiple drugs to treat acute pain
Best done by using a combination of drugs
from different classes -so lower doses of
each drug can be used
If someone with an opiate problem needs analgesia what do you give them
If they are already prescribed Methadone then continue at same dose
If not already in progranne, do not start methadone! Give normal opioids plus extra to control pain but monitor closely
As required pain medication should be avoided in patients with substance abuse issues - true or flase
True
Better to aim for a stable plasma opioid level- e.g. with long acting opioids
Which medications are typically used for chronic pain
Maintained on opioids - regular dose plus breakthrough
Regular paracetamol/NSAID as baseline
May need to consider other adjuvant analgesics
Which analgesic should be avoided in renal failure
NSAIDs
Those with many active metabolites - may accumulate due to decreased renal function
How do you convert oral morphine to IV or IM
Divide by 2-3
IV dose needs to be lower
How does paracetamol work
Inhibits prostaglandin synthesis in the CNS
What is the typical dose of paracetamol
1 gram (2x500mg tabs) 6 hourly - max 4x daily Dose will need reduced if patient is below 50kg
How do NSAIDs work
These drugs inhibit the enzyme cyclo-oxygenase [cox]
1 and 2
What are the contraindications to NSAID use
GI bleeding - old or new Active peptic ulcers Coagulopathy Renal impairment Aspirin or NSAID allergy
When should NSAIDs be used with caution
Elderly Dehydration Asthmatics Certain types of surgery, e.g. - plastic or eye surgery, some orthopaedic surgery Cardiac failure Pregnancy Concurrent medication e.g. anticoagulants
How do you reverse respiratory depression caused by opioids
Give oxygen
Adjust dose or stop delivery of opioid until
situation satisfactory
If necessary give naloxone and titrate to effect
Clinical opioids act on which receptor
μ (mu) opioid receptor.
How is morphine metabolised
Metabolised in the liver to M6G and M3G
M6G is responsible for the analgesic effect.
These have longer half-lives than morphine and are excreted via the kidney
How does tramadol work
Centrally acting synthetic analgesic
Has mu opioid receptor activity and inhibits the uptake of noradrenaline and serotonin
Tramadol should be avoided in which patients
Epileptics
Not suitable as the sole analgesic in
morphine-dependent patient
What are the benefits of tramadol
Doesn’t build tolerance
Lower abuse potential
Less respiratory depression
Less constipation
When is patient controlled analgesia used
Post-op pain
Severe non operative pain e.g. pancreatitis, fractured
ribs
What is used for patient controlled analgesia
The usual prescription is a 1 mg bolus of morphine with a 5 minute lockout-i.e. the patient can receive up to 12 mgs morphine per hour.
Bolus dose and lock-out period can both be varied
What are the contraindications to patient controlled analgesia
Patient inability to comprehend the technique e.g. extremes of age Patients inability to press the button e.g. severe rheumatoid Patient rejection Ward staff must be trained appropriately
What are the complications of epidural anaesthesia
Spinal haematoma
Abscess
Cannot be used if patient is anti-coagulated
Cyclizine is which type of anti-emetic
Antihistamine - H1 antagonist
Ondasentron is which type of anti-emetic
5HT3 antagonists
Prochlorperazine and metoclopramide are which type of anti-emetic
Antidopaminergic
Hyoscine is which type of anti-emetic
Anticholinergic
Good for motion sickness
What is the definition of chronic pain
Lasting > 3 months
Typically after normal healing has occurred
List primary causes of circulatory/cardiac inadequacy
Ischaemia Myocardial infarction Hypertensive heart disease Valve disease Drugs Electrolyte abnormalities
List secondary causes of circulatory/cardiac inadequacy
Asphyxia Hypoxaemia Blood loss Septic shock Any Shock
what is nociceptive pain and describe how it feels
Also called physiological or inflammatory pain
Pain occurring after obvious tissue injury or illness - protective
Typically sharp and well localised - may have associated ache
what is neuropathic pain and describe how it feels
Pain due to nervous system damage or abnormality
May not have obvious injury
Typically burning/shooting pain with numbness, pin and needles etc.
Not well localised
Chronic pain is typically a complex mix of nociceptive and neuropathic pain - true or false
True
What is nociception
How signals get from the site of injury to the brain
Describe the peripheral section of the nociceptive pathway
Get the initial tissue injury Triggers release of chemicals This stimulates the nociceptors - pain receptors Signal travels in Aδ or C nerve to spinal cord
Describe the spinal section of the nociceptive pathway
Dorsal horn is the first relay station Aδ or C nerve synapses with second nerve here Second nerve crosses and travels up opposite side of spinal cord in the spinothalamic tract
Describe the brain section of the nociceptive pathway
The thalamus is the
second relay station - nerve connects here
This has connections to many other parts of the brain - cortex, stem etc
Pain perception
occurs in the cortex
Describe how the nociceptive pathway is modulated
Descending pathway from brain to dorsal horn Usually decreases pain signal
Give examples of pain caused by nervous system damage
Nerve trauma
Diabetic pain/neuropathy
Give examples of pain caused by nervous system dysfunction
Fibromyalgia
Chronic tension headache
List pathological mechanisms through which pain sensation can be increased
Increased receptor numbers
Abnormal sensitisation of nerves
Chemical changes in the dorsal horn
Loss of normal inhibitory modulation
Which treatments are good for peripheral pain
RICE
Anti-inflammatories
Local anaesthetic
Which treatments are good for pain arising from the spinal cord
Locals
Opioids
Ket
What are the main adverse effects of codeine
Constipation
Also not great for chronic pain
In which type of pain is addiction most likely
Chronic, non-cancer pain
What is the main adverse effect of tramadol
Nausea and vomiting
Which drugs are good for neuropathic pain
Amitriptyline
Anti-convulsants - gabapentin, sodium valproate and carbamazepine
What is the main adverse effect of amitriptyline
Anti-cholinergic side effects
e.g. glaucoma, urinary retention
How does amitriptyline treat pain
Increases descending inhibitory signals
Helps modulate pain
How do anti-convulsants treat pain
Reduce abnormal firing of nerves
Also called membrane stabilisers
What are the treatable/reversible causes of cardiac arrest
4 H's 4 T's Hypoxia Hyovolaemia Hyper/hypokalaemia Hypothermia Toxins Tamponade - cardiac Tension pneumothorax Thrombosis - coronary or pulmonary
How often should adrenaline be administered during ALS
every 3-5 mins
How often should amiodarone be administered during ALS
After the 3rd shock
How do you treat a SVT
Vagal manoeuvres
If ineffective give adenosine
If that doesn’t work give verapamil or a beta-blocker
How do you treat acute AF
Beta-blocker - rate control
Consider digoxin or amiodarone if evidence of heart failure
2nd line is DC shock
Anticoagulate if duration > 48hrs
How do you treat acute bradycardia
Atropine - 500mcg IV
If not enough repeat dose up to 3mg max and consider adrenaline, isoprenaline or TC pacing
What dose of glucose is given in acute hypoglycaemia
100mI of 10% Glucose
What should the HbA1c be before elective surgery is considered
<69mmol/mol (8.5%)
Otherwise discuss with the diabetes team (especially if over 12%
What post-op complications can be caused by hyperglycaemia
Wound infection and cardiac problems
What post-op complications can be caused by hypoglycaemia
Hypoglycaemia can be masked by sedation or general anaesthesia. In extreme cases this may cause irreversible brain damage
Patient’s become more prone to hypos post-op - why is this
They will have been fasted prior to their procedure
Paradoxically the surgical stress response may mean that patients become more prone to hyperglycaemia and insulin resistance after major surgery
There is an association between asthmatics with nasal polyps and sensitivity to NSAlDs - true or false
True
In general cardiac medication should be given over the peri-operative period - true or false
True - most are cardioprotective
Exceptions - ACEi, diuretics, anti-coag and anti-plat
Typically you are aiming for an INR of 1.5 for surgery - true or false
True
Exceptions- dental work or urological ops
Patients who have had a venous thrombo-embolic event 9 months ago are considered high risk of another thrombo-embolic event - true or false
False
Once 3 months has passed, these patients are not considered high risk.
If there is no excessive bleeding post-operatively then warfarin should be restarted at the patient’s usual dose on the day of the procedure - true or false
True
Recheck INR 48 hours after restarting
Raised urea and creatinine can indicate dehydration - true or false
True
Even pre-renal failure due to hypovolaemia
What is the minimal acceptable urine output
0.5ml/kg/hr
What is the risk of large, rapid NaCl infusion
Hypernatraemia and acidosis
The influx of negative Cl- ions causes H+ to rise to balance it out
Which fluid department is depleted in pure dehydration
All
Plasma, interstitial and ICF
Which fluid department is depleted in hypovolaemia
Just the plasma
Which fluid department is depleted in
The ECF
Plasma + Interstitial fluid
Should PPIs be continued on day of surgery
Yes
How do benzodiazepines work
They bind to the GABA receptor in the CNS and increase the receptor affinity for GABA
Ion movement across the cell membrane is increased which hyperpolarises the cell membrane and reduces firing of neurons.
Leads to CNS depression
List anesthetic induction agents
Propofol Thiopentone Etomidate Midazolam Ket
Most anaesthetic agents work on which receptor
Majority are GABA mediated
Which drugs can be used for inhalational anaesthesia
Nitrous oxide and sevoflurane
Used in kids or if difficult IV access
Which drugs can be used for maintained anaesthesia
Nitrous oxide
Sevoflurane
Desflurane
Isoflurane
How are neuromuscular blocking agents used in anaesthetics
Given to relax or paralyse muscles
Facilitate intubation
Improve surgical conditions (ie. relax abdominal wall)
List examples of neuromuscular blocking agents
Non-depolarising - atracurium and rocuronium
Depolarising - Suxamethonium
Patient will twitch for a short time with this one
How do local anaesthetics work
Reversible blockade of sodium channels, inhibiting transmission of action potentials in nerve cells.
What is the max dose of 1% lidocaine used
4mg/kg
Why is adrenaline sometimes given alongside local anaesthetci
It prolongs the duration of action by causing local vasoconstriction
therefore dont give to end artery regions!
Why should metoclopramide be avoided in women under 60
Can cause oliguric crisis
Which bloods can be used to help diagnose dehydration
Urea and Electrolytes
Creatinine
What are the normal daily potassium requirements
1 mmol/kg
What are the normal daily sodium requirements
2mmol/kg
What are the normal daily water requirements
25-30ml/kg
2 litres for a 70kg man
How should naloxone be administered
40 microgram increments titrated to effect and reassess the patient
Poor control of blood glucose in the peri-operative period is associated with which complications
An increased risk of wound infection
Increased cardiovascular complications
Irreversible brain damage
What is the correct dose and route of adrenaline for administration during cardiac arrest
1mg IV
What is the correct dose and route of adrenaline for administration during anaphylactic shock
0.5mg IM
Delayed (up to 12 hours) respiratory depression can occur in patients with spinal or epidural opioid administration - true or false
True
What are the common side effects of using opioids in the epidural space
Itch
What are the common side effects of using local anaesthetic alone as a block in the epidural space
Hypotension
Partial block
Post dural puncture headache
Nausea
