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Spontaneous pain: this type of pain occurs unexpectedly.

Incident pain: this pain is related to specific events and can be classified into four categories (Davies 2006).

1 Volitional pain is precipitated by a voluntary act, for example walking.

2 Non-volitional pain is precipitated by an involuntary act, for example coughing.

3 Procedural is a type of pain related to a therapeutic intervention, for example wound dressing.

4 End-of-dose failure is related to analgesic dosing (declining analgesic levels).

The ideal treatment for breakthrough pain is an analgesic with good efficacy, a rapid onset and short duration of action, and which causes minimal adverse effects. In order to try and deliver more effective treatment, various routes of administration have been explored including the transmucosal routes (Zeppetella 2009). These are discussed below.

Methods of drug delivery

Oral analgesia

Oral opioids are used less frequently in the immediate postoperative period because many patients may be nil by mouth or on restricted oral intake for a period of time. Often this route is used if patients require strong analgesics following discontinuation of epidural or intravenous analgesia. Morphine is an ideal oral preparation because it is available as a tablet (Sevredol) or an elixir (Oramorph). Oxycodone can be given as second-line opioid treatment if patients are allergic/sensitive to or fail to respond to morphine.

Intravenous analgesia

Continuous intravenous infusions of opioids such as morphine, diamorphine and fentanyl are effective for controlling pain in the immediate postoperative period. Their use is often restricted to critical care units where patients can be closely monitored because of the potential risk of respiratory depression (Macintyre and Schug 2007). Compared with PCA, continuous infusions of opioids for acute pain management in a general ward setting resulted in a fivefold increase in the incidence of respiratory depression (Schug and Torrie 1993).

Patient-controlled analgesia is an alternative and safer technique for giving intravenous opioids (usually morphine, diamorphine, fentanyl or oxycodone) in the ward environment (Sidebotham et al. 1997). With PCA, patients self-administer intermittent doses of opioids, by using an infusion pump and timing device. When in pain, the patient presses a button connected to the pump and a set dose of opioid is delivered (usually intravenously but it may also be given subcutaneously) to the patient (Macintyre and Schug 2007).

There are a number of advantages of using PCA.

PCA is more likely to maintain reasonably constant blood concentrations of the opioid within the analgesic corridor. This is the blood level where analgesia is achieved without significant side-effects. The flexibility of PCA helps to overcome the wide interpatient variation in opioid requirements (Macintyre and Schug 2007).

PCA allows patients to titrate analgesia against daily variations in the pain stimulus (Tye and Gell-Walker 2000). By using a PCA pump, patients can administer analgesia as soon as pain occurs and titrate the dose of analgesia according to increases and decreases in the pain stimulus. This is particularly helpful for controlling more intense pain during movement.

PCA prevents delays in patients receiving analgesics (Chumbley et al. 2002).

Whilst PCA may be very effective for controlling pain for a number of patients undergoing surgery (Macintyre and Schug 2007), it is not suitable for the groups listed in Box 9.14.

Box 9.14 Patients for whom PCA is inappropriate

Those who are unable to activate the PCA device due to problems with dexterity or visual impairment.

Those who are unable to understand the concept of PCA, particularly the very young or patients who are confused.

Those who do not wish to take responsibility for their pain control.

(Tye and Gell-Walker 2000)

Epidural analgesia

Epidural analgesia refers to the provision of pain relief by continuous administration of analgesic pharmacological agents (usually low concentrations