Perioperative anaelgesia Flashcards
What’s anaesthesia triad?
- muscle relaxation
- anaesthesia
- hypnosis
Analgesic ladder
What drugs are used to provide intra-operative analgesia?
Stages 2 and 3 are most commonly used to provide intraoperative analgesia
- Stage 2 e.g. diclofenac or ibuprofen
- Stage 3 e.g. morphine or fentanyl
Is simple analgesia of any use in the provision of analgesia during surgery?
Simple analgesics, such as paracetamol, and NSAIDs, such as diclofenac and ibuprofen, may provide sufficient analgesia for short, day-case analgesia, sometimes in combination with local anaesthesia
What’s the most commonly used intraoperative analgesia for more painful surgery?
Opioid → Fentanyl
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
What happens to the opioid dose requirement if local or regional anaesthesia is used?
The opioid requirements will be markedly reduced
What’s the difference between ‘opiate’ and ‘opioid’?
Opiate → naturally-occurring opioid e.g. morphine
Opioid → synthetic drugs e.g. fentanyl
How are syringes containing opioid drug identified?
By blue labels
What’s more potent: morphine or fentanyl?
Fentanyl is about 100 times more potent than morphine
When an initial dose of Fentanyl is given (in terms of surgery)?
At induction because:
- it takes 5 mins to be effective
- it reduces the response to laryngoscopy
(if endotracheal intubation is planned)
How long does Fentanyl analgesic effect last?
15-30 minutes in usual doses (50-100 µg intraoperatively)
* it may be repeated (depending on the duration of surgery, analgesic plan, painful surgical stimulation)
Where is fentanyl metabolised?
in the liver
Side effects of fentanyl
- intraoperative
- post-operative
Intraoperative:
- bradycardia
- fall in BP
- respiratory depression (due to a reduction in respiratory rate)
Postoperative:
- nausea and vomiting
- urinary retention
- constipation and itching
When and how to use morphine + fentanyl in combination?
- Morphine has a slower onset time than fentanyl
- It is more common to use fentanyl initially
- then use morphine intraoperatively if further analgesia is required, particularly if severe pain is anticipated in the early postoperative phase in recovery
How long does analgesic effect of morphine last?
For the usual intraoperative dose of morphine (2-5 mg bolus) it last 30-40 min
*repeated-dose usually needed
Can we give morphine 10 minutes before surgery ending?
The longer onset time to peak effects means that the timing of intraoperative morphine requires to care
if given within 10 min of surgery ending → respiratory depression may slow recovery
*In a surgery that is anticipated to be very painful postoperatively, an intravenous bolus dose of morphine of 0.1-0.15 mg/kg can be given about 45 min before the end of surgery.
Where does the metabolism of morphine occur?
In the liver
What’s morphine-6-glucuronide?
- an active metabolite of morphine
- it is more potent than morphine
- it is only important in patients with renal failure who receive repeated doses of morphine
Side effects of morphine
- bradycardia
- fall in BP
- Respiratory depression
- Nausea and vomiting postoperatively
- Urinary retention
- Constipation
- Itching
*Morphine can also cause histamine release; in asthmatics bronchospasm may be triggered
How can Diclofenac be given intraoperatively?
IV or suppository
(consent must be gained for suppository)
Can we combine NSAIDs + Paracetamol + Fentanyl?
It is useful to combine NSAIDs with paracetamol and fentanyl in theatre, since the NSAIDs have a further opioid-sparing effect that not only allows less fentanyl to be used, but also reduces the postoperative opioid requirements by 20-30%
How can Paracetamol be given intraoperatively?
IV or suppository
Usually 1g for an adult person
How does IV Paracetamol should be given?
the vial contains 1 g of paracetamol as a solution in 100 ml; this should be given intravenously over about 20 min
When should suppository Diclofenac or Paracetamol be given?
It should be placed per rectum after induction of anaesthesia and before surgery starts to allow time for absorption
Do we prefer to give intraoperative simple analgesia by IV or suppository routes?
The rectal route is less reliable than the intravenous route for drug administration, but is sometimes preferred for very short duration surgery
Do we need to repeat paracetamol dose intraoperatively?
The duration of action of paracetamol is much longer than for the intravenous opioids; a repeat dose is rarely used unless surgery takes more than 6 h.
Contraindications to Ibuprofen use
- Previous or existing upper GI ulcers
- Avoid in asthmatics who are intolerant of aspirin
- Use with care in patients with renal impairment
Side effects of Ibuprofen
The most common side-effects are upper GI tract bleeding and inhibition of platelet aggregation.
Contraindications to Diclofenac use
- Previous or existing upper GI ulcers
- Avoid in asthmatics who are intolerant of aspirin
- Use with care in patients with renal impairment
- Porphyria
Side effects of Diclofenac
Like ibuprofen, the most common side-effects of diclofenac are upper GI tract bleeding and inhibition of platelet aggregation
How often morphine could be administrated to a patient on patient-controlled analgesia (PCA) device?
- 1-2 mg (whichever is preset by the anaesthetist) to be given on demand with a 5 min lockout period
*The lockout period may be set by the anaesthetist and is to prevent overdose, which carries the risk of respiratory depression
* Close and charted observation is required if PCA is prescribed
Can strong opioids be used in day cases?
NO
If NSAIDs are not tolerated and it is anticipated that a stronger analgesic than paracetamol is needed, then codeine phosphate may be prescribed for a limited period: usually enough for 72 h. The dose of codeine phosphate is 30-60 mg every 4 h
