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1.5.5 Adverse psychological effects
Psychological changes associated with acute pain have received less attention than those
associated with chronic pain, however they are no less important. Sustained acute nociceptive
input, as occurs after surgery, trauma or burns, can also have a major influence on
psychological function, which may in turn alter pain perception. Failure to relieve acute pain
may result in increasing anxiety, inability to sleep, demoralisation, a feeling of helplessness,
loss of control, inability to think and interact with others — in the most extreme situations,
where patients can no longer communicate, effectively they have lost their autonomy (Cousins
et al, 2004). In some forms of acute pain (eg low back pain), psychological and environmental
responses in the acute phase may be major determinants of progression to a persistent phase
(Young Casey et al, 2008).
In acute pain, attention has been focussed on postoperative cognitive dysfunction (POCD).
Although the aetiology of POCD is unknown, factors probably include dysregulation of cerebral
neurotransmitters, patient factors (age, comorbidities, preoperative cognitive function and CHAPTER 1
general health) (Newman et al, 2007; Monk et al, 2008), surgical procedures (eg coronary artery
bypass) and perioperative drug therapy (Flacker & Lipsitz, 1999). Elderly patients have an
increased incidence of POCD and are more likely to have prolonged symptoms (see
Section 11.2.3). Neurotransmitters involved may include acetylcholine and serotonin and
inflammatory mediators (eg cytokines) may also contribute, especially in the elderly (Caza et al,
2008). POCD after cardiac surgery may also be due in part to cerebral microembolism, global
cerebral hypoperfusion, cerebral temperature perturbations, cerebral oedema, and possible
blood‐brain barrier dysfunction (Flacker & Lipsitz, 1999; Gao et al, 2005).
Key messages
1. Recognition of the importance of postoperative rehabilitation including pharmacological,
physical, psychological and nutritional components has led to enhanced recovery (N)
(Level II).
The following tick box represents conclusions based on clinical experience and expert
opinion.
Acute pain and injury of various types are inevitably interrelated and if severe and
prolonged, the injury response becomes counterproductive and can have adverse effects
on outcome (U).
1.6 PHARMACOGENOMICS AND ACUTE PAIN
An increasing number of genetic variants modulating nociception, susceptibility to pain
conditions, as well as response to pharmacotherapy have been discovered.
Pharmacogenomics deals with the influence of genetic variation on drug response in patients.
By correlating gene expression or single‐nucleotide polymorphisms with a drug's efficacy or
toxicity, the aim is to develop rational means to optimise drug therapy with respect to the
patient’s genotype and ensure maximum efficacy with minimal adverse effects. For example,
genetic factors regulating opioid pharmacokinetics (metabolising enzymes, transporters) and
pharmacodynamics (receptors and signal transduction elements) contribute to the large inter‐
patient variability in postoperative opioid requirements (Anderson & Palmer, 2006). Information
from genotyping may help in selecting the analgesic drug and the dosing regimen for an
individual patient (Lotsch & Geisslinger, 2006). Although there is currently limited information,
often from small numbers of subjects, for translation into clinical practice (Stamer & Stuber,
Acute pain management: scientific evidence 21
