Session 12 - Lecture 1 - Anaesthetics Flashcards
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2 - Learning Objectives
Lecture Outline-Learning Objectives.
- To provide a very general overview (taster) of anaesthesia from a pharmacological perspective.
- To provide a comparison of general, regional and local anaesthesia.
- To provide an overview of the concepts and terminology used to describe anaesthetic potency.
- To integrate molecular, cellular and systems level target sites to the discussion.
- I am NOT going to give you dosing information.
“1. taster for theatres
- concepts and terminology used for the state of anaesthesia, anaesthetic potency and things about drug interactions
- Try and integrate molecular mechanistics stuff from Year 1 membranes and receptors, the important stuff and give it an anaesthetic taste.
- but NOT dosage info – well beyond the scope of this lecture, you’ll learn that in wards and anaesthetic room with BNF in your pocket.”
3 - Types of Anaesthesia
Anaesthetic Techniques.
These Can Be Combined.
Anaesthesia
- General
- – Inhalational or ‘volatile’
- – Intravenous
- Local
- – Regional
Conscious sedation: use of small amounts of anaesthetic or benzodiazepines to produce a ‘sleepy-like’ state. (Maintain verbal contact but feel comfortable)
“General (probably most familiar with) = state of unconsciousness, immobility, effective sympathetic insensitivity.
- typically using a gas (volatile), halothane, isoflurane etc.,
- intravenous injection – e.g. propofol (MJ juice, white milky substance)
Locally (one region) – benzocaine lozenge for a sore throat or dental extraction, but we can take that further and anaesthetise, effectively, a part of the body. So if we put a anaesthetic in a nerve tract or root then we can anaesthetise the whole region.
These modes of anaesthesia are describable as separate entities but can be mixed and matched/combined. So typically you’d put a pt asleep IV infusion bolus dose to get them to sleep, might switch to volatile. During the procedure you might stick in a local, might give them a regional for pain process. So important to remember they are separate entities but they are almost always mixed and matched.
Just as a reminder, Particularly densistry i.e. conscious sedation – step-down from anaesthesia - pt is effectively awakw and can communicate but in a sleepy, dream-like state – induce with a reasonable dose of BZD – typically dental work at dental clinic, conscious sedation is probs what you’re going to have”
4 - Give an outline for how you would anaesthetise a patient undergoing surgery.
Anaesthesia From a Practical Viewpoint.
- Premedication (Hypnotic-benzodiazepine).
- Induction (usually intravenous but may be inhalational).
- Intraoperative analgesia (usually an opioid).
- Muscle paralysis-facilitate intubation/ventilation/stillness.
- Maintenance (intravenous and/or inhalational).
- Reversal of muscle paralysis and recovery which includes postoperative analgesia (opioid/NSAID/paracetamol).
- Provision for PONV.
- POINT: during anaesthesia many (interacting) pharmacological agents “on board” requiring excellent pharmacological knowledge and skill to manage.
“1. Go see the pt on the ward, explain what they’re going to do, they’re pretty nervous, can see they’re in an excited state, very anxious: so firstly give them a BDZ – a hypnotic, diazepine, to make them nice and calm and compliant – some pts might need more.
- Pt then goes through to anaesthetic room, then something like propofol, ketamine or a barbiturate, count back from 10, down to 6, they’ll be asleep.
- Surgery will be painful, so at Dose of induction but perhaps before that give them a dose of opioid, opioid gives them cover for whatever the surgeon is going to do.
- So pts now induced, RR become depressed, so the pt is now starting to go, the opiates are a resp depressant, so next thing you need to do is take over their respiration by getting a tube in there. So in order to get a tube in there, you need to do some form of muscle relaxation, muscle paralysis – nurofonium, succonofonium (if they have a funny tummy) you will paralyse the pt, they will then become v still, allows you to a tube past the cord. Then stick the tube in, Once the tube’s in, got a pt who you need to worry a lil bit less about them. Paralysed, intubated, ventilated and anesthesised.
- But does of IV anaesthetic is going to start wearing off, so you need to maintain at a state appropriate for the surgery/surgeon then switch over to maintenance – this can either be switching induction agents, IV pump anaesthetic agent – more typically what will happen is you switch a pt to a volatile mass, switch on whatever conc of anaesthetic is you decide on (can calculate and decide).
- Surgeon then does his worst and at the end the pt is now able to come off anaesthetic – so need to do a lot of things – reverse paralysis to start breathing - reversal agent – astgmaine, pyrolate so no bradycardia, the opiates are starting to wear off: awake pt with pain is no fun so give another opioid, NSAID rectally
- but they’ve had an opiate/anaesthetic, they’re going to feel sick so give them something for post-operative nausea and vomiting.
Point we’re trying to make is anaesthesia is the supreme example of polypharmacy – only other instance is probably psychiatry – where you’re giving so many agents working on diff classes of receptors, targets, pathways to the same pt at the same time. So we’re gonna spend the next 40 mins or so trying to tease apart some of those agents and understand how some of them work.”
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