Anaesthetics Flashcards
who are the members of the theatre team?
- surgeon
- theatre sister: coordinate the theatre team in association with the anaesthetist
- anaesthetist
- ODP/anaesthetic nurse: assists anaesthetist
- theatre nurses
What is the surgical safety checklist?
The World Health Organization (WHO) has developed a new Surgical Safety Checklist that has been shown to reduce avoidable complications
- Before induction of anaesthesia (sign in): check pt identity, correct surgical site, anaesthesia machine and medication, allergies, airway/aspiration risks and risk of haemorrhage
- Before skin incision (time out): members of team introduction, confirm pt name, procedure and site of incision, Abx ppx within past hour if needed, anticipated critical events and need for imagine during surgery
- before pt leaves operating room (sign out): nurse confirms correct procedure and labelling, rest of team confirm if any concerns for recovery
What is the triad required for balanced anaesthesia?
Unconsciousness
Muscle relaxation
The inhibition of pain
(triad of general anaesthesia:
- hypnotics
- analgesics
- neuromuscular blockers)
What are the different types of drugs used in anaesthesia?
- volatile agents
- IV anaesthetics
- benzodiazepines
- muscle relaxants (neuromuscular blockers)
- simple analgesics
- opiates
- regional anaesthesia
General Anaesthetics - 2 major groups
- IV agents: propofol, barbiturates (e.g thiopentone), katamine, etomidate (not commonly used anymore)
potent in producing unconsciousness - commonly used in induction (see next card)
effect mediated by GABAa receptor - Inhalation agents (nitrous oxide, xenon, cyclopropane, halothane, “flurane”s)
weaker unconscious effect but produce analgesia, sedation - used in maintenance phase of anaesthesia
NMDA receptor inhibitors (glutamate antagonist)
Name commonly used IV induction agents
- Propofol: widely used especially for maintaining sedation on ITU, total IV anaesthesia and for daycase surgery. Also has antiemetic properties. Can lead to respiratory depression and hypotension. Reduces CO so careful in pts with poor cardiac function *
- Thiopentone: extremely rapid onset of action making it the agent of choice for rapid induction
- Ketamine (IV or IM): produces little myocardial depression so suitable in those who are haemodynamically unstable. Potent bronchodialator (severe asthma?).
May induce state of dissociative anaesthesia resulting in nightmares, hallucinations, delirium
- long term use can lead to propofol infusion syndrome –> met acidosis, rhabdomyolysis and renal failure
Neuromuscular blockers / paralytics drugs
Neuromuscular blocking drugs are mainly in surgery as an adjunct to anaesthetic agents. They cause muscle paralysis which is necessary prerequisite for mechanical ventilation. Binds to nicotinic acetylcholine receptors and antagonise them, blocking transmission at the nuromuscular junction and causing muscle relaxation.
DEPOLARISING: Binds to nicotinic acetylcholine receptors resulting in persistent depolarization
NON-DEPOLARISING: Competitive antagonist of nicotinic acetylcholine receptors
Examples: Succinylcholine (also known as suxamethonium), Tubcurarine, atracurium, vecuronium, pancuronium
Adverse effects: Malignant hyperthermia, Hyperkalaemia (normally transient), Hypotension
What are volatile agents?
- produce unconsciousness when an adequate depth of anaesthesia has been achieved. Also contribute towards analgesia, however not anymore after the postoperative period. Their spinal reflexes suppression inhibit movement to pain and relaxes muscles.
- the potency of an inhalation agent in quantified by its minimum alveolar concentration (MAC) - concentration of vapour in the lungs needed to prevent 50% of patients moving when subjected to a surgical incision
e.g. desflurane, halothane, nitrous oxide
Local Anaesthetics
- Lidocaine: Local anaesthetic and a less commonly used antiarrhythmic (affects Na channels in the axon)
Features of toxicity: Initial CNS over activity then depression as lidocaine initially blocks inhibitory pathways then blocks both inhibitory and activating pathways. Cardiac arrhythmias. - Bupivacaine: It has a much longer duration of action and this may be used for topical wound infiltration at the conclusion of surgical procedures with long duration analgesic effect.
Other: prilocaine, procaine, mepivacaine etc.
Regional Anaesthesia
Prevents transmission of nociceptive (painful) stimuli to the CNS. For example, an effective epidural blocks the perception of pain during a laparotomy.
Analgesia in anaesthetics - analgesic ladder
Stage 1 - simple analgesics
Stage 2 - simple analgesics + mild opioids +/- NSAIDs
Stage 3 - simple analgesics +/- NSAIDs + strong opioids
Stages 2 and 3 are most commonly used to provide intraoperative analgesia. Simple analgesics, such as paracetamol, and NSAIDs, may provide sufficient analgesia for short, day-case analgesia, sometimes in combination with local anaesthesia.
For more painful surgery an opioid is used. Fentanyl is the most commonly used intraoperative opioid. It is useful to combine simple analgesics and NSAIDs with fentanyl to reduce the total dose of opioid required, and provide a degree of postoperative analgesia, as well as to limit unwanted effects of opioids (multimodal anaesthesia).
Morphine vs Fentanyl
Fentanyl is about 100 times more potent than morphine
Bradycardia is common after fentanyl and blood pressure may also fall. Like all opioids, fentanyl may cause respiratory depression due to a reduction in respiratory rate. Other side-effects include:
- Nausea and vomiting postoperatively
- Urinary retention
- Constipation and itching
Morphine has a slower onset time (but longer duration of action) than fentanyl. It is more common to use fentanyl initially, then use morphine intraoperatively if further analgesia is required
Morphine may cause blood pressure and heart rate to fall. Morphine may cause the same S/E as fentanyl.
Morphine can also cause histamine release; in asthmatics bronchospasm may be triggered.
Other analgesic measures
- wound infiltration with local anaesthetic agents blocks pain transmission
- regional anaesthesia - post-operative analgesia provided by a continued use of a regional technique. For abdominal, thoracic or lower limb surgery an epidural catheter is commonly inserted for this. If not sufficient, it can be augmented by administering a bolus dose top up via the epidural infusion device
- oral postoperative analgesia: usually paracetamol, NSAIDs or morphine
Post-operative Nausea and Vomiting
Anaesthetic agents such as opioids, volatile agents and N2O can all cause PONV: this requires treatment with antiemetics. Commonly used antiemetics fall into four classes:
5HT3 antagonists - ondansetron (usually 1st line)
H1 antagonists - cyclizine
Dopamine (D2) antagonists - prochlorperazine (IM), metroclopramide
Dexamethasone (used for ppx)
(the easiest way to prevent it is to be NBM when anesthesia is provided.)
Feeding options in surgical patients
- Oral intake
- Nasogastric feeding - safe to use in patients with impaired swallow. Complications relate to aspiration of feed or misplaced tube
- Naso jejunal feeding - safe to use following oesophagogastric surgery
- Feeding jejunostomy - Surgically sited feeding tube
Low risk of aspiration and thus safe for long term feeding following upper GI surgery - Percutaneous endoscopic gastrostomy (PEG). Indications: dysphagia, stroke, anatomical problems, sedation, cancer cx, advanced demantia etc.
- Total parenteral nutrition (TPN) - definitive option in patients in whom enteral feeding is contra indicated
