Anaesthetics Flashcards
What is the effect of general anaesthetics?
Produces insensibility in the whole body, usually causing unconsciousness - centrally acting drugs (hypnotics/analgesics)
What is the effect of regional anaesthetics?
Produces insensibility in an area or region of the body - local anaesthetics applied to nerves supplying the area
What is the effect of local anaesthetic?
Produces insensibility in only the relevant part of the body - applied directly to the tissues
Which three components make up the triad of anaesthesia?
Analgesia, hypnosis and relaxation (skeletal muscle)
Which components of the triad do opiates do?
Analgesia and hypnosis
Which components of the triad do general anaesthetics do?
Hypnosis and relaxation (+ some anaesthesia)
Which components of the triad do muscle relaxants do?
Muscle relaxants
Which components of the triad do local anaesthetics do?
Analgesia and relaxation
How does balanced anaesthesia work?
- Different drugs do different jobs
- Titrate dose separately and therefore more accurately to requirements
- Avoid overdose
- Enormous flexibility
What are the potential problems of balanced anaesthesia?
- Polypharmacy: increases chance of drug reactions/allergies
- Muscle relaxation: needs artificial ventilation and airway control
- Separation of relaxation and hypnosis: awareness
How do general anaesthetic agents work?
- Interfere with neuronal ion channels
- Hyperpolarise neurons making them less likely to fire
- Inhalation agents dissolve in membranes
- IV agents: allosteric binding to GABA receptors (opens chloride channels)
What effect does general anaethesia have on the body?
- Cerebral function is lost from top to bottom (LOC first hearing later)
- Reflexes relatively spared
How are those under general anaesthetic managed?
- ABC (long drawn out resus)
- Airway management
What are the problems with general anaesthetics?
- Impair resp function and control of breathing
- Impacts CVS function
What are the features of IV anaesthesia?
- Rapid onset of LOC
- Rapid recovery (due to disappearance of drug from circulation)
In what order do tissues uptake anaesthesia?
- Blood + vessels rich organs
- Viscera
- Muscle
- Fat
What do inhalational anaesthetics consist of?
Halogenated hydrocarbons
How are inhaled anaesthetics uptaken and excreted?
Via the lungs
What is MAC?
Minimum alveolar conc.
- Measure of potency
- Low number = high potency
What are the main features of inhalational anaesthetics?
- Slow induction
- flexible maintenance
- Awaken by stopping inhalation of the gas
What is the most common sequence of general anaesthesia?
Induction (Inhalational or IV) and maintenance (inhalational or IV) +/- additional regional analgesia/anaesthesia
What effect does GA have on the CVS centrally?
It depresses the CV centre:
- reduces sympathetic output
- negative inotrophic/ chronotrophic effect on the heart
- reduces vasoconstrictor tone
What effect does GA have on the CVS directly?
- Negatively inotropic
- Vasodilation: decreased peripheral resistance
- Venodilation: decreased venous return and decreased cardiac output
What effect does GA have on the respiratory system?
- All anaesthetics are respiratory depressants
- Reduce hypoxic and hypercarbic drive
- Decrease tidal volume and increase rate
- Paralyse cilia
- Decrease FRC: lower lung volumes and cause VQ mismatch
What are the indications for the use of muscle relaxants?
- Ventilation and intubation
- When immobility is essential (microscopic and neuro surgery)
- Body cavity surgery (access)
What are the problems with using muscle relaxants?
- Awareness
- Incomplete reversal (airway obstruction and ventilatory insufficiency post op)
- Apnoea: dependence on airway and ventilatory support
Why give intraoperative analgesia?
- Prevention of arousal
- Opiates contribute to hypnotic effect of GA
- Suppression of reflex responses to painful stimuli e.g. tachycardia, hypertension
Why give regional anaesthesia intraoperatively?
Intense/complete analgesia with no hypnotic effect
What are the main features of local and regional analgesia?
- Retain awareness/consciousness
- Lack of global effects of GA
- Derangement of CVS physiology (proportional to size of anaesthetised area)
- Relative sparing of resp. function
What is the limiting factor in the use of local anaesthetics?
Toxicity
- IV injection
- Absorbtion> rate of metabolism = high plasma levels
What does the toxicity of local anaesthetics depend on?
Dose used
Rate of absorption
Patient Weight
Drug (bupivacaine > lignocaine >prilocaine
Name the signs and symptoms of LA toxicity
Circumoral and lingual numbness and tingling Light headedness Tinnitus, visual disturbances Muscular twitching Drowsiness CVS depression Coma Cardio-respiratory arrest
How do LAs block pain fibres but not motor fibres?
Differential blockade: LAs penetrate into the different nerve types differently.
Motor fibres are relatively hard to block whilst pain fibres are much easier to block
How does a neuraxial block effect the CVS?
The sympathectomy causes veno and vasodilatation. Regional block effects are limited to the area covered by the block (opposite to GA)
List the examples of regional and local anaesthesia in increasing order of physiological impact
Local anaesthesia Field blocks Plexus blocks Limbs block Central neural (neuraxial) block (epidural and spinal)
How does a neuraxial block effect the respiratory system?
Inspiratory function relatively spared Expiratory function relatively impaired Decrease FRC (airway closure similar to GA) Increased V/Q mismatch
Name the steps in preparation of anaesthesia
- Planning
- Right patient, right operation
- Right side
- Pre-medication
- Right equipment, right personnel
- Drugs drawn up
- IV access
- Monitoring
Why should there be quiet when someone is being inducted?
Hearing is the last thing to go - want to make it easier to let them go over
What is the most common drug used for IV induction?
Propofol
What drugs might you add when inducting a frailer patient?
Drugs to maintain blood pressure etc.
What are the features of IV induction?
- Rapid: one arm-brain circulation
- No obvious planes
- Easy to overdose
- Generally rapid loss of airway reflexes
- Apnoea is very common
Which gas is commonly used in gas induction?
Sevoflurane (can also use Halothane)
What are the features of gas induction?
Slow
- More obvious planes of anaesthesia
- Commonly used in children
Name the planes of anaesthesia
- Analgesia
- Excitation (note heightened reflexes)
- Anaesthesia: light to deep
- Overdose
How can conscious level be monitored whilst under anaesthesia?
- Loss of verbal contact
- Movement
- Respiratory pattern
- Processed EEG
- Stages or planes of anaesthesia
What happens to the tongue in an unconscious patient?
It ends up resting on the posterior pharyngeal wall - can occlude airway
What is the “Triple Airway Manoeuvre”?
Head tilt/chin lift/jaw thrust
What apparatus can be used to maintain an airway?
- Face mask
- Oropharyngeal (Guedel) airway
- Nasopharyngeal airway
- Laryngeal mask airway
When can an oropharyngeal airway not be used and why?
When a patient is not fully unconscious - can cause vomiting or laryngospasm
When can i-gels be used?
Resuscitation (don’t protect from aspiration)
List some of the causes of airway obstruction
- Ineffective triple airway manoeuvre
- Airway device malposition/kinking
- Laryngospasm (forced reflex adduction of the vocal cords)
Why is aspiration a possible complication of anaesthesia and surgery?
- Anaesthesia causes loss of protective airway reflexes (gag, swallow, cough etc.)
- Foreign material in the lower airway (gastric contents, blood and surgical debris)
What is the difference between maintaining and protecting an airway?
- Maintained just means open and unobstructed
- Protected means the airway is protected from contaminants (only a cuffed tube in the trachea does this)
Explain the method of endotracheal intubation
- Placement of a cuffed tube in the trachea
- Laryngeal reflexes must be abolished
- Possible in awake patient using local anaesthesia and fibre-optic scope
What are the indications for intubation?
- Protect airway from gastric contents (e.g. full stomach in unfasted emergency patients)
- Need for muscle relaxation
- Shared airway with risk of blood contamination e.g. ENT surgey
- Need for tight control of blood gases (esp. CO2 in neurosurgery
- Restricted access to airway e.g. maxfax surgery
What are the risks to an unconscious patient?
- AIRWAY
- Temp.
- Loss of other protective reflexes e.g. corneal, joint position
- DVT and PE risk
- Consent and ID
- Pressure areas
How are patients under anaesthesia monitored?
- Minimum: SpO2, ECG, NIBP, FiO2 and ETCO2
- Resp. parameters
- Agent monitoring
- Temp., urine output and NMJ
- Invasive venous/arterial monitoring
- Processed EEG
- Ventilator disconnect
What are the risk factors for awareness?
- Paralysed and ventilated
- Previous episode
- Chronic CNS depressant use
- Cardiac surgery
- Major trauma (need careful balancing of anaesthetic as too much may push them over the edge)
- GA C/Section
What are the steps of emergence/awakening?
- Muscle relaxation reversed
- Anaesthetics agent off
- Resumption of spontaneous respiration
- Return of airway reflexes/control
- Extubation
What are the two types of respiratory failure?
Type 1: oxygenation failure
Type 2: oxygenation + ventilation failure
Which type of respiratory failure is best suited to non invasive ventilation?
Type 2
Name the types of shock
Septic/distributive Hypovolaemic Anaphylactic Neurogenic Cardiogenic
Which types of drugs can be used to treat cardiovascular failure and how do they work?
Vasopressors: alpha 1 agonists
Inotropes: improve contractility
Why is adrenaline not first line in the treatment of CV failure?
It causes vasoconstriction, contractility and HR - don’t know which of these is actually the problem so tend to avoid
Give two examples of vasopressors
Metaraminol
Noradrenaline
Give two examples of inotropes
Adrenaline and dobutamine
What is the difference between colloid and crystalloid fluids?
- Colloids: fluid with large molecules (e.g. albumin or starches)
- Crystalloids: fluid that contains small molecules (e.g. sodium or plasmolyte)
Why are most colloids no longer on the market?
Because they can cause anaphylactic shock and precipitate renal failure
What is the maximum volume of fluids that can be given?
30ml/kg
Name the causes of neurological failure
- Metabolic e.g. DKA, hypoglycaemia
- Trauma e.g head injuries
- Infection e.g. meningitis, encephalitis and sepsis
- Stroke
At what GCS score are patients most likely to need to be ventilated?
<8
What are some neuroprotective measures?
- Avoid hyperthermia
- Keep CO2 low
- Avoid low O2
- Keep glucose in normal range
- Keep blood pressure stable
How does the body react to the trauma of surgery?
- Stress response
- Fluid shifts
- Blood loss
- Cardiovascular, resp, renal and metabolic stress
Which consideration are taken into account during the pre-op assessment?
- Known co-morbidities
- Unknown pathologies
- Nature of surgery
- Anaesthetic techniques
- Post-op care
What are the roles of the anaesthetist pre-op?
Assess Identify high risk Optimise Minimise risk Inform and support patients decisions Consent
Why do anaesthetist do pre-op assessment?
It reduces:
- Anxiety
- Delays
- Cancellations
- Complications
- Length of stay
- Mortality
What things would you ask in a pre-op history?
- Known co-morbidities: severity and control
- Unknown co-morbidities: systemic enquiry and clinical exam.
- Ability to withstand stress: exercise tolerance, reason for limitation and cardio-respiratory disease
- Drugs and allergies
- Previous surgery and anaesthesia
- Potential anaesthetic problems: airway, spine, reflux, obesity and rarities/FH (malignant hyperpyrexia and cholinesterase deficiency)
What are the pre-op investigations looking for?
- Detect unknown conditions
- Diagnoses suspected conditions
- Severity of known disease
- Establishing a baseline
- Detecting complications
- Assessing risk
- Guiding management
- Documenting improvement
Which investigations might you do if someone has cardiovascular problems?
ECG, exercise tolerance, ECHO, myocardial perfusion scan, stress ECHO, cardiac catheterisation, and CT coronary angiogram (don’t necessarily need all of these)
Which investigations might you do in a patient with resp. problems?
Sats, ABG, CXR, peak flow, FVC/FEV, gas transfer and CT chest (don’t necessarily need all of these)
List the ASA grading scale points
ASA1 : Otherwise healthy patient ASA2: Mild to moderate systemic disturbance ASA3: Severe systemic disturbance ASA4: Life threatening disease ASA5: Moribund patient ASA6: Organ retrieval
Name 3 examples of medications that are continued right up to surgery
Inhalers, anti-anginals and anti-epileptics
Name two examples of medications which must be stopped before surgery?
Anti-diabetic medication (oral anti-hyperglycaemics and insulin)
Anticoagulants
What is the definition of pain?
“an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage
What are the benefits of treating pain?
Physical: improved sleep, better appetite and fewer medical complications
Psychological: reduced suffering, less depression and less anxiety
For the family: improved functioning and able to keep working
-Society: lower health costs and able to contribute to society
What are the features of nociceptive pain?
- Obvious tissue injury or illness
- AKA physiological of inflamm pain
- Protective function
- Sharp +/- dull and well localised
What are the features of neuropathic pain?
- Nervous system damage or abnormality
- Tissue injury may not be obvious
- No protective function
- Burning, shooting pain +/- numbness and pins and needles
- Not well localised
What happens in the periphery in nociceptive pain?
- Tissue injury
- Release of chemicals = prostaglandins and substance P
- Stimulation of pain receptors
- Signals travel in Adelta or C nerves to the spinal cord
What happens in the spinal cord in nociceptive pain?
- Dorsal horn is the first relay station
- Adelta or C nerve synapses with second nerve
- This nerve travels up the spinothalamic tract on the opposite side of the spinal cord
What happens in the brain during nociceptive pain?
Thalamus is the secondary relay station which connects to other parts of the brain:
- Cortex: pain perception
- Limbic system: emotional side to pain
- Brainstem: CVS response to pain
How is pain modulated?
Descending pathway from brain to dorsal horn - usually decreases pain signal
What is the Gate theory?
Distractive stimulus: rubbing, massaging, application of heat etc. create a distraction signal which can reduce the perception of pain
Name some examples of neuropathic pain
Nerve trauma, diabetic pain, fibromyalgia and chronic tension headache
Describe the pathophysiology of neuropathic pain
- Increased receptor numbers
- Abnormal sensitisation of nerves (peripheral and central)
- Chemical changes in the dorsal horn
- Loss of normal inhibitory modulation
Give two examples of simple analgesics
Paracetamol
NSAIDs
Give examples of mild and strong opioids
Mild: codeine, dihydrocodeine
Strong: morphine, oxycodone and fentanyl
Name other analgesics used for pain (other than paracetamol, NSAIDs and opioids)
Tramadol Nefopam Antidepressants Anticonvulsants Ketamine Local anaesthetics Topical agents
Which pain treatments work on the periphery?
Non-drug treatments: rest, ice, compression and elevation
NSAIDs
Local anaethetics
Which pain treatments work on the spinal cord?
Non drug treatments: acupuncture, massage and TENS
Local anaesthetics
Opioids
Ketamine
Which pain treatments work on the brain?
Psychological Paracetamol Opioids Amitriptyline Clonidine
What are the advantages and disadvantages of paracetamol?
Advantages: cheap, safe, multiple modes of administration, good for mild pain and in combination for mod-severe pain
Disadvantages: liver damage in overdose
What are the advantages and disadvantages of NSAIDs?
Advantages: cheap, safe (generally) and good for nociceptive pain
Disadvantages: GI and renal side effects and bronchospasm in some asthmatics
What are the advantages and disadvantages of codeine?
Advantages: cheap, safe and good for mild-moderate acute nociceptive pain
Disadvantages: constipation and not good for chronic pain
What are the advantages and disadvantages of tramadol?
Advantages: less resp. depression, can be used with opioids and simple analgesics and is not a controlled drug
Disadvantages: nausea and vomiting
What are the advantages and disadvantages of morphine?
-Advantages: cheap, generally safe, can be given orally and IV/IM/SC and effective if given regularly (for most acute pain and also chronic cancer pain)
Disadvantages: constipation, resp. depression in high dose, addiction and controlled drug
What are the advantages and disadvantages of amitriptyline?
Advantages: cheap, safe in low dose, good for neuropathic pain and also treats depression/poor sleep
Disadvantages: anti-cholinergic side effects (e.g. glaucoma and urinary retention)
Which type of pain are anticonvulsant drugs good for?
Neuropathic pain
Which type of pain does the WHO pain ladder work for?
Nociceptive pain
What are the steps in the RAT approach to pain?
Recognise
Assess
Treat
List the different pain assessment tools?
Verbal rating score Numerical rating score Visual analogue scale Smiling faces Abbey pain scale (confused patients) Functional pain
Which non drug treatments are available for the treatment for pain?
- Rest, ice, compression and elevation
- Nursing care
- Surgery, acupuncture, massage and TENS
- Psychological
How is the total body water distributed in the body?
- TBW: 42:
- ICF: 28L
- ECF: 14L (11L ISF + 3L plasma)
Which fluids in the body make up the ECF?
- ISF
- Intravascular fluid
- Water in connective tissue
- Transcellular fluid
What is osmolality?
Number of osmoles of solute/kg
What is osmolarity?
Number of osmoles of solute/litre
What is the normal plasma osmolarity
298 (280-300mOs/L)
What is tonicity?
- Effective osmolality
- Not all particles will effect osmolality
- Na and accompanying ionsin ECF and K and macromolecules in ICF are the main particles which effect osmolality
What are the symptoms of tonicity changes?
- Swelling: raised ICP, compromised CBF and herniation
- Shrinkage: ICH venous sinuous thrombosis
Name the common crystalloid solutions
- 5% dextrose
- 0.9% saline
- Hartmann’s solution
- Plasma-lyte
- 5th normal saline in 4% dextrose
- 0.18% saline/4% dextrose
Name the common coloids
- Gelatins
- Starches
- Dextrans
- Albumin
- Blood products
What are the pros and cons of crystalloids?
- Pros: cheap and non allergenic
- Cons: ECF expansion, oedema and increased vascular pressure
What are the potentional problems with colloids?
- Anaphylaxis
- Coagulopathy
- Renal failure
- Rheology
What are the daily fluid and electrolyte requirements?
- 25-30ml/kg/day of water
- 1mmol/kg/day potassium, sodium, chloride
- 50-100g/day of glucose
