Following the discussion on patient-controlled-analgesia (PCA) in our June issue of the Clinical Communiqué, we present a supplementary expert commentary with pertinent clinical advice for our readers on the use of oral opioids with PCAs.
Professor Pam Macintyre BMedSc MBBS MHA FANZCA FFPMANZCA Director, Acute Pain Service Department of Anaesthesia, Pain Medicine and Hyperbaric Medicine Royal Adelaide Hospital and University of Adelaide, Adelaide
One of the key safety features of intravenous (IV) patient-controlled analgesia (PCA), is that when a patient is over-sedated from an excessive dose of opioid – sedation being the earliest clinical sign of opioid-induced ventilatory impairment (OIVI) – the patient will not usually be able to press the demand button to obtain further doses.
When a background (continuous) infusion is included as part of the PCA prescription, opioid will continue to be delivered regardless of the patent’s level of sedation. Routine use of these infusions is known to significantly increase the risk of OIVI (George et al, 2010) and for this reason, background infusions with PCA are used very infrequently.
However, it is not uncommon in many centres for an opioid-naïve patient given IV PCA to also be prescribed oral opioids concurrently – for example slow-release (SR) or immediate-release (IR) oxycodone – even when the institutional practice is to avoid PCA background infusions. Not surprisingly, this practice has also led to OIVI (or respiratory depression) and patient harm.
Administration of SR or IR oral opioids in addition to PCA, other than an opioid that the patient has been taking on a long-term basis prior to admission (where the drug(s) and dose(s) have been independently confirmed) is essentially the same as adding a background infusion.
Therefore, the same care must be taken as the same risks exist (Macintyre & Schug, 2015). If sedation occurs as a result of a combination of background SR opioids in addition to PCA bolus doses, then the sedation is likely to be more sustained than it would have been if the background opioid was delivered via PCA.
While initial use of a background infusion or addition of oral opioids to a PCA regimen (other than a patient’s usual long-term opioids) is generally not safe, relative safety may be increased if they are introduced only once a patient’s PCA opioid requirements are known. The rate of the infusion, or the dose of oral opioid, can then be prescribed according to these requirements.
One approach is to ensure that the oral opioid dose or PCA background infusion or provides no more than 50% of a patient’s total opioid requirements (Macintyre & Schug, 2015) – and usually even less (25-30%). As daily opioid requirements may decrease rapidly in the acute pain setting, the rate of a background infusion or the dose of oral opioid, should be reassessed frequently and reduced appropriately, so that these doses remain a similar proportion of the patient’s overall daily opioid requirement.
In patients who are opioid-tolerant, background infusions may sometimes be used in place of the patient’s normal (preadmission) maintenance opioids. But in this setting, the patient’s baseline opioid requirements at least are already known.
Anaesthetists and other doctors who prescribe oral opioid analgesia concurrently with PCA need to consider these issues as they would when prescribing a PCA background infusion and take appropriate steps to minimise the risk of OIVI. In some patients with low PCA opioid requirements, such concurrent prescriptions may be best avoided.
Resources
George JA, Lin EE, Hanna MN et al (2010) The effect of intravenous opioid patient-controlled analgesia with and without background infusion on respiratory depression: a meta-analysis. J Opioid Manag 6(1): 47-54.
Macintyre PE & Schug SA (2015) Acute Pain Management a Practical Guide. Boca Raton, CRC Press, Taylor and Francis Group.