Page 67 Acute Pain Management

1.5.3 Pain and analgesia: effects on injury-induced organ
dysfunction
Pain from injury sites can activate sympathetic efferent nerves and increase heart rate,
inotropy, and blood pressure. As sympathetic activation increases myocardial oxygen demand
and reduces myocardial oxygen supply, the risk of cardiac ischaemia, particularly in patients
with pre‐existing cardiac disease, is increased. Enhanced sympathetic activity can also reduce
gastrointestinal (GI) motility and contribute to ileus. Severe pain after upper abdominal and
thoracic surgery contributes to an inability to cough and a reduction in functional residual
capacity, resulting in atelectasis and ventilation‐perfusion abnormalities, hypoxaemia and an
increased incidence of pulmonary complications. The injury response also contributes to a
suppression of cellular and humoral immune function and a hypercoagulable state following
surgery, both of which can contribute to postoperative complications. Patients at greatest risk
of adverse outcomes from unrelieved acute pain include very young or elderly patients, those
with concurrent medical illnesses and those undergoing major surgery (Liu & Wu, 2008). CHAPTER 1
All relevant studies address the combination of injury and pain. The majority involve use of
epidural neural blockade, which in addition to effects on pain per se can influence the injury
response (eg via reduced sympathetic activity). As a result, the site of epidural placement and
extent of block can influence results. The impact of analgesic technique on outcome is more
fully discussed in Section 7. Epidural analgesia has been reported to improve pain and
decrease arrhythmias following cardiac surgery (Liu et al, 2004 Level I), but early reports of
reduced postoperative myocardial infarction (Beattie et al, 2001 Level I) and impact on mortality
have not been replicated (Rigg et al, 2002 Level II; Liu et al, 2004 Level I). Regional versus systemic
analgesia decreased postoperative pulmonary complications (Rodgers et al, 2000 Level I;
Ballantyne et al, 1998 Level I; Jorgensen et al, 2000 Level I) but the impact was greater following
abdominal (Nishimori et al, 2006 Level I) than hip or knee surgery (Choi et al, 2003 Level I).
Intraoperative epidural analgesia/anaesthesia (versus general anaesthesia) decreased the
odds ratio for deep vein thrombosis (DVT) and postoperative confusion, but did not reduce
mortality following hip fracture (Parker et al, 2004 Level I). Epidural local anaesthetic, when
compared to epidural or systemic opioid, enhanced return of GI function (Jorgensen et al, 2000
Level I). Compared with systemic opioid administration, intraoperative thoracic epidural
anaesthesia also led to lower plasma concentrations of adrenaline (epinephrine) and cortisol,
and prevented perioperative impairment of proinflammatory lymphocyte function (Ahlers et al,
2008 Level II). The advantages of epidural analgesia were greatest when used as part of a
multimodal, accelerated rehabilitation care pathway, since other factors may influence
GI recovery (Joshi, 2005).
There is also some evidence that regional anaesthetic and analgesic techniques might have a
beneficial effect on rates of cancer recurrence after tumour resection. Paravertebral
anaesthesia/analgesia reduced the risk of recurrence or metastases following mastectomy
from 23% to 6% compared with general anaesthesia and systemic morphine analgesia
(Exadaktylos et al, 2006 Level IV). Similarly, after prostatectomy under general anaesthesia,
epidural analgesia compared with systemic morphine reduced the risk of recurrence by 57%
(Biki et al, 2008 Level IV).

Acute pain management: scientific evidence 19