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Patient-controlled analgesia (PCA)

Created: 17/7/2017
Updated: 14/7/2021


PCA is the delivery of analgesia via an infusion pump that is programmed to deliver a pre-determined bolus when triggered by the patient. The pump has a lockout period, during which time no further boluses can be administered.

It is most commonly utilised with intravenous opioids: morphine, fentanyl, oxycodone

It can also be delivered by different routes: epidural (patient-controlled epidural analgesia [PCEA]), nerve catheter, iontophoresis

PCA programmes include:

1. Bolus dose

This is the dose administered as a single bolus when the demand button is pressed. This should be large enough to provide an appreciable difference in pain but not so large as to result in a drug overdose.

Drug dose suggested:
  • Morphine 1 mg [1, 2] 
  • Fentanyl 20 µg [3]

2. Lockout period

This is the period during which further demands of drug will not be administered. The duration of the lockout period is determined by the size of the bolus dose and the drug pharmacokinetics, particularly the time taken for the specific drug to reach peak plasma concentration. For example, the morphine peak plasma concentration is achieved around 4 minutes after intravenous administration, so the lockout period should be longer than this.

3. Background infusion

A background drug is infused, regardless of the patient pressing the demand button, with the aim compensating for patients with pre-existing opiate use or inadequate pain control with demand boluses.



The management of acute moderate to severe pain (e.g. postoperative pain, burns, sickle cell crisis)
If oral medication is not tolerated.



Patients who are physically incapable of using the device (e.g. rheumatoid arthritis, hand trauma)
Patients who have difficulty in understanding the use of a PCA device (e.g. critically ill, young children, confused, learning difficulties)



  • Allows the analgesic regime to be tailored to individual patient needs
  • Empowers patients by giving them a degree of control over their pain management
  • Immediate analgesic delivery
  • Predictable drug delivery
  • Improved patient satisfaction



  • Risk of drug toxicity
  • Respiratory depression can still occur with opiate PCA
  • The addition of the background infusion increases the risks associated with opiate toxicity
  • Risk of inappropriate analgesic delivery by relatives/staff
  • Patients can wake up in pain, and it can then take time to re-achieve satisfactory analgesia

A systematic review [4] comparing conventional opioid administration and PCA found that:

  • PCA provided better pain control
  • PCA resulted in greater patient satisfaction
  • PCA was associated with higher opioid consumption
  • PCA was associated with more pruritis
  • The incidence of side -effects other than pruritis was similar between the different methods of opiate delivery
  • There was no difference in length of hospital stay


Choice of opiate


  • Most commonly used drug 
  • Caution in patients with:
    • Decreased respiratory reserve: risk of respiratory failure
    • Hepatic or renal impairment: increased circulating levels of morphine-6-glucuronide
    • Head injury/raised intracranial pressure: miosis secondary to morphine use may mask the development of intracranial pathology
    • Biliary tract pathology: morphine may cause an increase in smooth muscle tone within the biliary tract, resulting in biliary colic.


  • Indicated in morphine intolerance
  • Useful in patients with renal impairment as it does not rely on renal excretion.


  • Indicated in morphine intolerance
  • Useful in patients with mild hepatic or renal impairment.


Monitoring and ongoing care

PCA should be administered via a dedicated line with an anti-syphon and anti-reflux valve Patients must be cared for by a trained nurse/operating department practitioner

Monitoring should include:

  • Blood pressure 
  • Respiratory rate 
  • Pain score 
  • Sedation score 
  • Nausea and vomiting.

Observations should be recorded every 30 minutes for the first 2 hours, then every hour for the next 4 hours, then two-hourly for the duration of the PCA.

Emergency treatment (including naloxone, intravenous fluids) for complications should be available:

  • If respiratory rate is <8, stop PCA, inform duty doctor/anaesthetist. Give naloxone up to 400 µg (in 40 µg increments) 
  • If unrousable/reduced consciousness, stop infusion, inform duty doctor/anaesthetist, administer O2 
  • If moderate, administer paracetamol/non-steroidal anti-inflammatory drug and reassess.

No additional opioids should be given, unless specifically supervised by trained staff and with additional monitoring instituted. Where appropriate, the acute pain team/doctor should ideally assess the PCA daily. 



1. Owen H, Plummer JL, Armstrong I, Mather LE, Cousins MJ. Variables of patient-controlled analgesia. Bolus size. Anaesthesia 1989; 44: 7–10.
2. Gould TH, Crosby DL, Harmer M et al. Policy for controlling pain after surgery: effect of sequential changes in management. BMJ 1992; 305: 1187–93.
3. Camu F, van Aken H, Bovill JG. Postoperative analgesic effects of three demand-dose sizes of fentanyl administered by patient-controlled analgesia. Anesth Analg 1998; 87: 890–5.
4. Hudcova J, McNicol E, Quah C, Lau J, Carr DB. Patient controlled opioid analgesia versus conventional opioid analgesia for postoperative pain. Cochrane Database Syst Rev 2006; 4: CD003348.

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