Anaesthesia and Asthma Flashcards
Which volatile gas is a good anaesthetic for kids?
Xe
-most of the volatile gases are fluoronated hydrocarbons
Which anaesthetics are given intravenously?
- propofol
- barbiturates
- etomidate
- ketamine
What are Guedel’s signs?
Stage 1: analgesia and consciousness
Stage 2: unconscious, breathing erratic but delirium could occur, leading to an excitement phase
Stage 3: surgical anaesthesia, with 4 levels describing increasing depth until breathin weak
stage 4: if no intubation and ventilation then respiratory paralysis and death
What is anaesthesia a combo of?
- analgesia
- hypnosis
- depression
- muscle relaxation
What factors increase or decrease MAC (minimum alveolar concentration)
Increase -age: high in infants -hyperthermia -pregnancy -alcoholism -central stimulants Decrease -age: low in elderly -hypothermia -other anaesthetics and sedatives -opioids (MAC sparing)
What are the effects of nitrous oxide on MAC?
- has analgesic and MAC sparing effect
- helps to decrease the amount of anaesthesia put in
- added to other volatile agents to reduce dosing
What is the main intravenous anaesthetic?
- propofol ad barbiturate (rapid)
- ketamine (slower) (mainly in kids)
- TIVA: Total IntraVenous Anaesthesia
- all potentiate GABAa except Ketamine
Give examples of local anaesthetics and their characteristics?
-examples: lidocaine, bupivacaine, ropivcaine, procaine
Characteristics
-lipid solubility: potency (higher greater potency)
-dissociation constant (pKa) time of onset, lower pKa fast onset
-chemical link: metabolism
-protein binding: duration (higher for longer duration)
Inhaled corticosteroids (ICS) (beclometasone, budesonide, fluticasone)
- regular preventer when reliever alone not sufficient
- passes through plasma membrane, activate cytoplasmic receptors, activated receptor then passes into nucleus to modify transcription
- anti inflammatory, bronchodilator and reduction in mucus
- reduces symptoms, exacerbations and prevent death
- can cause a local immunosuppressive action: candidiasis, hoarse voice
- pneumonia risk possible in COPD
- if taken correctly very few significant ADRs
- poor oral bioavailability but high affinity for glucocorticoid receptor
- lipophilic side chain added so slow dissolution in aqueous bronchial fluid
- if steroids is absorbed orally then its transported from stomach to liver by hepatic portal system, then goes through almost complete first pass metabolism
- high doses of ICS can produce systemic side effects
How do steroids work?
Gene activation
- increases B2 receptors
- anti-inflammatory mediators
Gene repression
-inflammatory mediators: interleukins, chemokines, cytokines
B2 agonists
- SABA: symptom relief through reversal of bronchoconstriction, only to be used prn (as required)
- LABA: add on therapy to ICS and prn SABA
- major action on airway smooth muscle and also increases mucus clearance by action of cilia
- prevention of bronchoconstriction prior to exercise (SABA/LABA)
- can be used in athletes and asthmatic patients
- when used regularly can it reduce asthma control-tolerance? A: quick fix, especially in young adults
What are the adverse effects and interactions of B2 agonist?
- adrenergic: fight or flight effects, tachycardia, palpitations, anxiety and tremor
- Supraventricular tachycardia.
- increase in glycogenolysis in liver and increase in renin in kidney
- muscle cramps (LABA)
- LABA should only be prescribed alongside ICS
- increased risk of death when prescribed alone
- B blockers may reduce effects of B2 agonists
Montelukast
- leukotriene receptor antagonist (LTRA) p.o.
- alternative to LABA in NICE guideline
- LTC4 released by mast cells/eosinophils —> increase in bronchoconstriction, mucus, oedema through CysLT1 —> GPCR
- LTRA block CysLT1 (so signalling cascade is blocked which inhibits mucus and oedema)
- useful in about 15% asthmatics most end up taking LABA
- ADRs: headache, GI disturbance, dry mouth, hyperactivity
- no major drug interactions reported
Tiotropium
- long acting muscarinic antagonist (LAMA)
- severe asthma and COPD
- relative selectivity for M3 (SAMA much less selective)
- anticholinergic effects through inhibition of muscarinic receptors
- ADRs: typical anticholinergic effects, dry mouth, urinary retention, dry eyes
Theophylline
- theophylline a methylxanthine p.o.
- adenosine receptor antagonist
- aminophylline soluble form: I in some acute asthma patients)
- narrow therapeutic index because oral drug
- potentially life-threatening complications including arrhythmia
- interaction with CYP450 inhibitors: increase concentrations of theophylline
