Page 239 Acute Pain Management

A prospective study of 5969 patients given intrathecal morphine (200 to 800 mcg) for pain
relief following a range of surgical procedures reported a high degree of patient satisfaction
and effective analgesia in the first 24 hours. The incidence of pruritus was 37%, nausea and
vomiting 25% and respiratory depression 3% (PaCO 2 > 50 mmHg and/or respiratory rate <8)
(Gwirtz et al, 1999 Level IV).
In patients having abdominal, cardiothoracic or spinal surgery, intrathecal morphine (100 to
500 mcg) reduced pain scores by 1 to 2 cm (using a 10 cm visual analogue scale) for at least
24 hours following the procedure, with morphine‐sparing being more pronounced after
abdominal than cardiothoracic surgery (Meylan et al, 2009 Level I). Intrathecal morphine 50 to
200 mcg ± clonidine after prostatic surgery (Brown et al, 2004 Level II), 300 mcg after colorectal
surgery (Beaussier et al, 2006 Level II), and 500 mcg plus fentanyl 150 mcg after liver resection
(Roy et al, 2006 Level II) also resulted in better analgesia and lower opioid requirements than
morphine PCA during the first 24 hours postoperatively. After CABG surgery, intrathecal
morphine reduced systemic morphine use and global pain scores, but increased pruritus;
there were no significant effects on mortality, myocardial infarction, dysrhythmias, nausea
and vomiting, or time to tracheal extubation (Liu et al, 2004 Level I).
Compared with a continuous epidural infusion of ropivacaine after liver resection, patients
given intrathecal morphine 200 mcg had higher IV PCA opioid requirements in the
postoperative period and more nausea and pruritus; there was no difference in pain relief
(De Pietri et al, 2006 Level II).
For comparisons of different opioids and doses used for intrathecal analgesia see
Section 5.2.1.

Side effects
Typical side effects of intrathecal opioids include nausea and vomiting, pruritus and delayed
respiratory depression. The definition of ‘respiratory depression’ in different investigations
often lacks uniformity with a quarter of the studies cited in a review using respiratory rate
as the primary marker (Ko et al, 2003). Patients may be hypoxic or hypercapnic with a normal
respiratory rate (Bailey et al, 1993 Level IV), while others may be able to maintain normocarbia CHAPTER 7
with a lower respiratory rate (Boezaart et al, 1999 Level II). In a volunteer study, clinical signs
or symptoms including respiratory rate, sedation and pupil size, did not reliably indicate
hypoventilation or hypoxaemia, unlike peripheral pulse oximetry (Bailey et al, 1993 Level IV);
although desaturation itself is a late indicator when supplemental oxygen is being
administered (Shapiro et al, 2005 Level IV). See Section 4.1 for the use of sedation as a better
clinical early indicator of respiratory depression.
Respiratory depression occurs in up to 1.2% to 7.6% of patients (Meylan et al, 2009 Level I) given
intrathecal morphine. When measured in opioid‐naive volunteers, respiratory depression
peaked at 3.5 to 7.5 hours following intrathecal morphine at 200 to 600 mcg doses (Bailey et al,
1993 Level IV). Volunteers given 600 mcg had significant depression of the ventilatory response
to carbon dioxide up to 19.5 hours later.
When combined with local anaesthetic for analgesia following Caesarean section, the rate
of respiratory depression with intrathecal opioids (all opioids and all doses) was low and not
significantly different from controls, with a NNH of 476 for respiratory depression (Dahl et al,
1999 Level I). In patients following major surgery, the incidence of respiratory depression was
increased with intrathecal morphine over control treatment (IV PCA morphine) (OR 7.86; 95%
CI 1.54 to 40.3) (Meylan et al, 2009 Level I). Clinically detected respiratory depression in the
24 hours following 0.15 mg intrathecal morphine for Caesarean section was noted in 0.26%
of a large sample (Kato et al, 2008 Level IV).

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