Morphine (PCA — Post-Operative Pain)

How it works

Morphine is a strong agonist at mu-opioid receptors in the central nervous system, reducing nociceptive transmission and altering the affective response to pain.

Prescribing in practice

• Opioid-induced respiratory depression is the principal hazard — programme an appropriate bolus, lockout interval and any background infusion carefully, ensure only the patient activates the handset (never staff or family), and have naloxone and monitoring immediately available.
• Set the PCA programme on a dedicated infusion pump with the giving set protected by an anti-reflux/anti-siphon valve, and avoid concurrent systemic opioids or sedatives unless explicitly co-prescribed and monitored.
• Morphine and its active metabolite accumulate in renal impairment, so reduce reliance on PCA morphine or consider an alternative opioid in significant renal dysfunction or the frail elderly.

Monitoring

Monitor sedation score, respiratory rate, oxygen saturation, pain score and cumulative dose regularly, with closer observation after any programme change.

Counselling the patient

• Press the handset when you feel pain — you cannot easily overdose because of the built-in lockout.
• Only you should press the button, never a visitor or nurse on your behalf.
• Tell staff promptly if you feel very drowsy, sick or your pain is not controlled.

Evidence & guidelines

PCA morphine is well established for post-operative analgesia and is supported by long-standing anaesthetic and acute pain service practice.