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In another study, coadministration of droperidol and morphine via PCA resulted in morphine‐
sparing and reduced the frequency of postoperative nausea and vomiting (Lo et al, 2005
Level II).
Droperidol given separately was as effective as adding droperidol to PCA morphine (Gan et al,
1995 Level II). The cost‐benefit and risk‐benefit of the routine addition of droperidol to PCA
opioids must therefore be considered because all patients receive the drug when not all will
need it and some patients might receive inappropriately high doses of droperidol.
Evidence of benefit from the addition of 5HT3 antagonists to PCA is unclear. Ondansetron,
given both as a bolus at the end of surgery and mixed with morphine in the PCA solution,
reduced the incidence of nausea and the need for antiemetics, but not the patients’
perception of this or their satisfaction (Cherian & Smith, 2001 Level II). However Tramèr’s group
(Tramèr & Walder, 1999 Level I) concluded that 5HT3 receptor antagonist drugs (eg ondansetron)
showed no evidence of worthwhile antinauseant effect, although they may be effective for
vomiting with an NNT of approximately 5. A more recent study showed that ondansetron
given as an initial dose of 4 mg followed by 0.2 mg/1 mg morphine PCA morphine can reduce
nausea and vomiting – although pain scores were higher (Boonmak et al, 2007 Level II). Another
study reported a reduction in vomiting with the addition of ondansetron alone to morphine
PCA and a lower incidence of nausea with the addition of a combination of ondansetron plus
prochlorperazine (Jellish et al, 2009 Level II).

Ketamine
In general, concurrent administration of ketamine reduced PCA opioid requirements and the
incidence of nausea and vomiting (Bell et al, 2006 Level I). However, the same benefit may not
be derived from adding ketamine to the PCA opioid solution, although the evidence is
conflicting. In the meta‐analyses by Bell et al (Bell et al, 2006 Level I), six studies are listed where
ketamine was added to the PCA opioid and results were mixed; pain was reduced in four of
CHAPTER 7 these studies and morphine consumption in three. A more recent study of 352 patients also
showed a lack of benefit (Sveticic et al, 2008 Level II), but in another, the addition of ketamine
to morphine PCA reduced pain scores and the incidence of nausea and vomiting, was opioid‐
sparing, and led to shorter duration of use of PCA compared with PCA morphine alone
(Kollender et al, 2008 Level II). In patients after thoracotomy, although the addition of ketamine
to PCA morphine did not improve pain relief it was opioid‐sparing, and patients in the
ketamine group spent less time with oxygen saturation levels <90% and had better forced
expiratory volumes (Michelet et al, 2007 Level II).
Naloxone
There was no analgesic benefit of adding naloxone to the PCA morphine solution (Sartain et al,
2003 Level II; Cepeda et al, 2002 Level II; Cepeda et al, 2004 Level II); in ‘ultra low doses’ but not in
the higher dose studies, the incidence of nausea and pruritus was decreased (Cepeda et al, 2004
Level II).

Other adjuvants
Ketorolac added to morphine (Chen, Wu et al, 2005 Level II; Chen et al, 2009 Level II) or tramadol
(Lepri et al, 2006 Level II) PCA did not improve pain relief or alter the incidence of side effects,
however it was opioid‐sparing and led to earlier return of bowel function after colorectal
surgery (Chen et al, 2009 Level II).
The addition of lignocaine (lidocaine) to morphine conferred no benefit in terms of pain relief
or side effects (Cepeda et al, 1996 Level II).
The addition of clonidine to IV PCA morphine resulted in significantly better pain relief for the
first 12 hours only and less nausea and vomiting compared with morphine alone; there was no
174 Acute Pain Management: Scientific Evidence