Nervous System Drugs Flashcards
Drugs acting on the nervous system include?
Anticonvulsants, antiparkinsons, neuromuscular blocking - surgery, anxiolytic - anxiety/hypnotic - sleeping, anaesthetics.
Excitatory neurotransmitters? Do they speed up or slow down?
Speed up - noradrenaline - speeds up response, dopamine - associated with parkinsons, serotonin, acetylcholine, glutamate.
Inhibitory neurotransmitters? Do they speed up or slow down?
Slow down - GABA, glycine.
General anaesthetics?
Act mainly in CNS, Inhalation or IV. Analgesia, unconsciousness, amnesia, loss of reflexes - too much can cause DEATH.
How do GA’s work?
Act on CNS to promote insensitivity. Lipid-soluble so can cross blood-brain barrier and enter CSF. May act on membrane receptors to reduce excitability of neurones. May act on ion channels by changing fluidity of cell membrane - stop ions passing through. Act on membrane receptors - Propofol acts on GABA receptor to slow down responses - stops messages crossing the brain. GABA also linked to chloride(-) channels, causing membranes to hyperpolarize - less positive or more negative, decreasing action potential likelihood.
Synapses action?
AP travel down neurone. Calcium channels open due to depolarisation of membrane - more positive - voltage gated calcium channels responds to action potential. Calcium causes neurotransmitters to be exocytosed into membrane and synapse, bind to post synaptic cells. Sodium enters post synaptic cells generating further action potential.
Enzyme in synaptic cleft, bind to neurotransmitters and degrade them stopping the response. Some get taken back up pre-synaptic neurone.
Side effects of GA’s
Nausea and vomiting, Bp and CO reduced, shallow and rapid breathing, loss of temp control - hypothalamus unable to regulate temp so can cause hypothermia, kidney perfusion, cross placenta, polypharmacy GA’s - anticoagulants, extra bleeding during surgery, come off steroids before GA, careful in cardiovascular disease, respiratory disease or hypotension - exacerbation by GA’s.
Stages of GA
Induction - IV - quickly, cant control dose once given.
Maintenance - Inhalation - Easier controlled - switch concentration, need to ensure enough oxygen or result in hypoxia, stressed with facemask.
Pain relief
Excitement - agitation
Skeletal muscle relaxation and loss of reflexes
Paralysis of medulla - responsible for maintenance of BP, breathing, coughing.
Can slip between stages.
Types of GA’s
Barbiturates, Gases, Non-barbiturates, Volatile Liquids.
Nitrous Oxide
N20 Laughing Gas Maintaining anaesthesia Potent analgesic - not as anaesthetic Used in combination Low level long term exposure may damage foetus
Other inhaled anaesthetics
Isoflurane - hangover effects, desflurane - exacerbate respiratory illness, sevoflurane - halogenated - contain halogen.
Administer by vaporiser - volatile liquid.
Need at least 25% oxygen or become hypoxic.
Control concentration.
Can cause cardiovascular depression, CSF decrease in pressure, arrhythmias, hypotension.
IV anaesthetics
Propofol, thiopentone.
Propofol - Non-Barbiturate. 40 seconds to start acting, short hangover effects - cleared from system quickly.
Side effects are pain on injection, anaphylaxis and convulsions.
Thiopentone - Barbiturate - Start in 30 seconds, lasts 5-10 minutes. Enters other tissues - fatty, stays for long period of time, sedative effects can last 24 hours - driving, sleepiness, slowed reaction time.
Etomidate - Can cause muscle movements - minimised by opioid analgesic. No hangover effect, less hypotension, suppresses adrenocortical function. Not used for maintenance.
Ketamine - uncommon - used in children. Can be used in shocked patients due to raising HR and BP, Bp is lowered during shock. Agitated on awakening - bad dreams/hallucinations. Use anxiolytics. Problems with raising HR and BP - head injuring increased ICP already, would make it worse. Class C drug abuse.
Children are at risk of what after GA’s?
Broncospasm
Other drugs used in surgery
Benzodiazepines - Anxiolytics - calm patient.
Hypnotics - induce sleep.
Neuroleptics and antiemetics - Induce artificial hibernation, reduce blood flow.
Antiemetics - stop vomiting.
Opioid analgesics - reduce pain.
Antihistamines - Promethazine - counter histamine effects released in surgery - constricts airways, vasodilation.
Anticholinergic - atropine and hyoscine - control secretions in lungs, mouth - choking.
Drug of choice for anxiety?
Benzodiazepine - sedation, increased to sleeping/unconsciousness. Oral, IV, rectal. Midazolam - premed 20mins before surgery safe children, side effects nausea and vomiting.
