Anaesthetics Flashcards
What is general anaesthesia?
Produces insensibility in the whole body, usually unconsciousness
Centrally acting drugs
What is regional anaesthesia?
Produces insensibility in an area or region
Local anaesthetics applied to nerves supplying area
What is local anaesthesia?
Produces insensibility in only relevant part of body
Applied directly to tissues
What is the triad of anaesthesia?
Analgesia
Hypnosis
Relaxation
What drugs tend to be used to cause analagesia in surgery?
Opiates
What agents are used to cause hypnosis in surgery?
General anaesthetic agents
Lectures…
What agents are used to cause relaxation in surgery?
Muscle relaxants
What is balanced anaesthesia?
Using different drugs to do different jobs
Titrating each drug separately
Avoids overdose
Gives flexibility
What are the problems with muscle relaxants?
They create the need for:
Artificial ventilation
A means of airway control
Awarness
Incomplete reversal = airway obstruction
How do general anaesthetic agents work?
They interfere in neuronal ion channels
Hyperpolarise neurone cells making it less likely to send impulses
How do inhalational agents work?
They dissolve in membranes
Gives a direct physical effect
How do IV agents give their effect?
Through allosteric (enzyme) binding GABA receptors open choloride channels
What function is lost in general anesthesia? What is retained?
Cerebral function “from top down” lost
Most complex first
More primative lost later
Reflexes relatively spared
As primitive with small number of synapses
What are the downsides of general anaesthesia?
Long drawn out resus Mandates airway management Impact on resp function + control of breathing CVS impact Care of unconcious patient
What are the benefits of IV anaesthesia?
Rapid onset of unconciousness
>arm-brain circulation time
Rapid recovery
>however drug not necessarily out of system, just distributed
What are the inhalational agents?
Halogenated hydrocarbons
Main one sevoflurane (halothane)
What is MAC?
Minimum alveolar concentration
Measure of potency
Low number=high potency
What are the benefits/downsides to inhaled anaesthetics?
Slow induction
However, very flexible duration
And quick to come back round
What is the generic way of adminstering anaesthesia in surger?
Induction with IV
Maintain with inhalation
What is general anaesthesia’s effect on the cardiovascular system?
Depresses central cardiovascular centre
>Reduces sympathetic outflow
>Negative iontropic effect on heart
>reduced vasoconstriction -> vasodilation
Causes decreased peripheral resistance Causes venodilation (Decreased venous return = decreased Cardiac Output)
What is the effect of general anaesthesia on the respiratory system?
Respiratory depressant Reduce hypoxic drive Decreased tidal volume, increases rate Paralyse cilia Causes VQ mismatch, which may be prolonged
What are the indications of muscle relaxants?
Ventillation + incubation
When immobility essential
Body caivty surgery
Why is analgesia used intraoperatively?
To prevent arousal
Opiates contribute to hypnotic effect of GA
Supression of reflexes to painful stimuli (tachycardia, hypertension)
What are the benefits of local/regional analgesia?
The patient retains awareness/consciouness (pregnancy)
Lack of global effects
Derangement of CVS proportional to affected area
Relative sparing of resp function
What are the limitations of local anaesthetics?
Toxicity
High plasma concentration due to IV
Absorption faster than metabolism
They vasoconstrict
Why do local anaesthetics cause a differential cascade?
Due to different penetration of nerve types
Motor fibres are thicker + myelinated so are relatively spared
Whereas pain fibres as thinner and so affected first
Allows for no paralysis but analgesia
What are the main IV anaesthetic drugs?
Propofol
Thiopentone (used less, but still in maternity hospital)
What are the downsides to IV induction?
Easy to overdose
Apnoea very common
Generally rapid loss of airway reflexes
When would you normally use gas induction?
In young children
What are the planes of anaesthesia?
Analgesia/sedation
Excitation
Anaesthesia (light-> deep)
Overdose
What is the light/deep “sleep” of inhaled anaesthesia dependant on?
Responsivness to stimuli
How is conciousness monitored when a patient is under anaesthesia?
Loss of verbal contact Movement Respiratory pattern Processed EEG Stages/planes of anaesthesia
What is the triple airway manoeuvre?
Head tilt
Chin lift
Jaw thrust
What simple apparatus are used for airway maintenance in anaesthesia?
Face mask Oroopharyngeal aiway (guedal) Nasopharyngeal airway (less used)
Why should you wait for a patient to be in deep anaesthesia before using a oropharyngeal/ guedal airway?
As insertion in light patient may cause vomitting or laryngospasm
Only tolerated by unconcious patient
What is the laryngeal mask airway?
A cuffed tube with a mask sitting over glottis
Maintains but does not protect airway (aspiration)
What is a laryngospasm?
Forced reflex adduction of vocal cords
May result in complete airway obstruction
Caused by airway simulation in light planes of anaesthesia
Often not relieved by simple manoeuvres
What can cause obstruction?
Innefective triple airway manoeuvre
Airway device malposition/kink
Laryngospasm
What are the possible complications with the airway
Obstruction
Aspiration
What is endotrachieal intubation?
Placement of cuffed tube in trachea
Laryngeal reflexes must be abolished
>Possible in awake patient using local anaesthetic + fibre optic scope
Why are people intubated?
To protect airway from gastric contents
Need for artificial ventilation after muscle relxants
Shared airway with risk of blood contamination
Need for tight control of blood gases
If restricted access to airway
What are the risks to an unconcious patient?
Airway Temperature Loss of other protective reflexes - conreal, joint position VTE risk Concsent/identification Pressure areas
What is the process to emergence
Muscle relaxation reversed Turn off anaesthetic agents Resumption of spontaneous respiration Return of airway reflexes/control Extubation
Can be quick or slow
What are the signs in someone who is euvolaemic (has the right amount of fluid in body)
Not thirsty Veins well filled Warm extermities Mild sweat Normal BP/HR Normal urine
What are the signs of someone who is hypovolaemic?
Feels nauseous/thirsty Flat veins Cool peripheries No sweat Low/postural BP High HR Concentrated urine Response to SLR
What are the needs of someone who is hypovolaemic?
Resuscitation fluids (If low BP)
Rehydration fluids
Find the cause and stop it
What are the signs of hypervolaemia?
Breathless, not thirsty Distended veins Warm /oedematous extermities Sweaty High BP/HR Dilute urine
How do you manage someone who is hypervolaemic?
Stop any fluids
Possibly diuretics
Haemofiltration if anuric
What is resuscitation fluid?
IV fluids to restore circulation with hypovolaemia
>Reassess after! (BP)
In shock!
What is routine maintenance fluid?
IV fluids if cannot take orally ot enterally to meet patient maintenance requirements
If cannot eat
>Limited as if cannot eat not getting any nutrients
Reassess after (fluid balance every day)
What are the 5 Rs of fluid?
Resus Routine maintenance Replacement Redistribution reassessment
What is replacement resuscitation?
Don't need urgent IV resuscitation but do need additional IV to maintenance to correct existing deficit or ongoing abnormal external losses Reassess after (bloods - did it work?)
What is redistribution resuscitation?
Patients with abnormal internal fluid redistribution/abnormal fluid handling
Particularly with sepsis/major illness, cardiac, liver or renal disease etc
When is dextrose useful?
Chronic dehydration
Hypernatreamia
When is dextrose not useful?
Resuscitation
Or low albumin
What are the properties of dextrose fluid?
Moves through all compartments
>Not useful for blood volume expansion
No sodium so depletes sodium, isotonic
When are crystalloids useful?
acute dehydration
AKI
Resuscitation
When is crystalloids not useful?
Long term maintainence
Hypernatraemic patient
When are plasma expanders useful?
Liver patients
Select intraopertative
How do you work out how much fluid they need?
Work out fluid balance (input/output charts)
What are the properties of crystalloids?
Remain in ECF
High sodium load, which can cause problems over time
Lots of different types
What are colloid expanders?
Colloids
>Examples such as Blood and TPN, Albumin
What are teh ASA grades?
ASA1: healthy patient ASA2: Mild-moderate systemic disturbance ASA3: severe systemic disturbance ASA4: Life threatening disease ASA5: Moribund patient ASA6: organ retrieval
What are some potenital anaesthetic problems?
Airway
Spine
Reflux
Obesity
What are METs?
A measure of exercise tolerance
What are the classifications of pain?
Duration >Acute/chronic/ Acute on chronic Cause >Cancer/non cancer Mechanism >Nociceptive >Neuropathic
What is chronic pain?
Pain lasting more than 3 months
Pain lasting after normal healing
Often no identifiable cause
What is cancer pain?
Progressive pain
Mix of acute and chronic
What is nociceptive pain?
Obvious tissue injury/illness
“Physiological”/”inflammatory” pain
Protective function
Sharp +/- dull pain
>Often well localised
What is neuropathic pain?
Nervous system damage/abnormality
Injury may not be obvious
No protective function
Burning, shooting +/- numbness/parasthesia
>Not well localised
What fibres carry nerve pain?
A delta
C nerve fibres
What pathway carries nerve pain?
Spinothalamic tract
>Dorsal root synapse
>Thalamus synapse
>Cortex destination
What are the pathological mechanisms causing neuropathic pain?
Increased receptor numbers
Abnormal sensations of nerves
Chemical changes in dorsal horn
Loss of normal inhibitory modulation
What are the advantages for paracetamol?
Cheap and safe
Oral, rectal or IV administrations
Good for mild pain by itself, and moderate-severe pain with others
What are the advantages of NSAIDs?
Cheap and gernally safe (GI/renal side effects)
Good for nociceptive pain
What are teh advantages/disadvantages of codein?
Cheap/safe
Good for mild-moderate acute nociceptive pain
However, constipation and not good in chronic pain
What does tramadol do?
Weak opoid effect + inhibition of serotonin/noradrenaline uptake
What are the advantages/disadvantages of tramadol?
Less respiratory depression than with other opoids
Can be used with opoids/other analgesics
Not a controlled drug
However, can cause nasuea/vomitting
What are teh advantages of morphine?
Cheap + generally safe Oral, IV, IM + Subcut administration Effective if regular Good for mod-severe acute nociceptive pain Chronic cancer pain
What are the disadvantages of morphine?
Constipation
Respiratory depression in high dose
Misunderstandings about addiction
Controlled drug
Oral dose 2-3 x IV/IM/SC
What is amitriptyline?
Trycyclic antidepressant
Increases descending inhibitory signals
What are the advantages of Amitriptyline?
Cheap, safe in low dose
Good for neuropathic pain
Also treats depression, poor sleep
However, anticholinergic side effects
What are some examples of anticonvulsant drugs?
Carbamazepine (Tegretol)
Sodium valproate (Epilim)
Gabapentin (Neurontin)
What are the delivery routes for local anaesthetics?
Epidural (+/- Opiates) Intrathecal (+/- Opiates) Wound Catheters Nerve Plexus Catheters Local Infiltration of wounds
What scoring systems can be used to rate pain?
Verbal Rating Score Numerical Rating Score Visual Analogue Scale Smiling faces Abbey Pain Scale (for confused patients)
What non-pharmaceutical treatments can be used for pain?
RICE
Surgery
Acupuncture, massage, physio
Psychological meassures - explanation, reassurance, counselling
What is the pain ladder?
Step 1:
>Non-opoids (Aspirin, NSAIDS, paracetamol)
Step 2
>Mild opoids (codeine) w/ or w/o non-opoids
Step 3
>Strong opoinds (morphine) w/ or w/o non-opoids
Where do you start/stop someone on the pain ladder?
Mild Pain: Start at Bottom of Pain Ladder
Moderate Pain: Bottom of Pain Ladder plus Middle Rung
Severe: Bottom of Pain Ladder plus Top of Ladder. Miss out the middle
To stop, move down one rung at a time
What is the RAT approach?
Recognise
>Do they have pain (ask/look)
Assess
Treat
How do you assess in RAT?
What is pain score (rest/movement)
How does pain affect patient (can they move, cough work?)
Type
>Look for neuropathic features
>Burning/shooting pain, phantom limb, parasthesia
Other factors
>Physical/psychological (other illness, anger, anxiety etc)
How do you treat neuropathic pain?
Traditional drugs may not be useful Use other drugs early >Amitriptylline >Gabapentin >Duloxetine Don’t forget non-drug treatments
