- Patients are able to titrate their plasma analgesic concentration into the 'analgesic window', that is the plasma concentration between:
- The minimum effective analgesic concentration, below which there is inadequate analgesia
- The minimum toxic concentration, above which side-effects occur
- In some cases, the window is so narrow that it's impossible to provide adequate analgesia without some side-effects
Patient Controlled Analgesia
Patient Controlled Analgesia
The intermediate curriculum asks for applied pharmacological knowledge of the 'principles of patient controlled analgesia'.
Resources
- Acute Pain Management: Scientific Evidence, Section 6 (Australian and New Zealand College of Anaesthetists and Faculty of Pain Medicine, 5th Edition, 2020)
- Patient controlled opioid analgesia versus non‐patient controlled opioid analgesia for postoperative pain (Cochrane, 2015)
- Safety and efficacy of patient-controlled analgesia (BJA, 2001)
- Patient‐controlled analgesia (BJA Education, 2002)
- Standard modes of analgesic delivery are unable to account for:
- Individual differences in the response to opioid analgesics, which can be profound
- Flexible requirements on account of dynamic pain e.g. during mobilisation
- PCAs attempt to circumvent these issues by allowing the patient to receive the appropriate dose at the appropriate time
| Advantages | Disadvantages |
| Equal or ↑ efficacy of analgesia vs. other routes | Potential equipment error |
| ↑ patient satisfaction | Requires patient cooperation, understanding and ability to use device |
| More consistent plasma concentrations than other routes | Not suitable for all patient groups |
| Avoids issues of other routes e.g. poor enteral absorption, pain from IM injection | Requires extra monitoring, especially in the obstetric environment |
| Similar rate of adverse effects as other routes | Requires staff training and device management |
| Consumes less nursing time |
Routes of administration
- Intravenous
- Subcutaneous
- Epidural (PCEA)
- Via surgical wound site catheter
- Perineural
- Intranasal
- Transdermal (iontophoretic fentanyl)
Suitable drugs
- Morphine
- Oxycodone
- Fentanyl
- Remifentanil
- Ketamine
- Tramadol
- Pethidine
- There is little evidence, on a population basis, to suggest major differences in efficacy or side-effects between the opioids
- On an individual basis, however, one opioid may be better tolerated than another
Bolus dose
- Should be the smallest amount producing an appreciable analgesic effect
- Examples:
- Morphine: 1-2mg
- Oxycodone: 1mg
- Fentanyl: 20-40μg
- Remifentanil: 20-40μg
Lockout interval
- Usually set such that a second dose isn't requested before the first has reached its peak effect
- Examples include 2mins (remifentanil) or 5mins (morphine, oxycodone, fentanyl)
Background infusion
- There's little robust evidence to suggest adding a background infusion improves efficacy of analgesia, quality of sleep or reduces bolus dose demands
- Increases the risk of adverse effects, especially respiratory depression (odds ratio nearly 5), or other issues such as equipment programming errors
- May improve analgesia in those with high opioid requirements or inadequately controlled, continuous pain