Perioperative pain relief
(acute
pain
Optimal management of acute postoperative pain requires planning,
patient and staff education, and tailoring to the type of surgery and the needs
of the individual patient. Patients vary greatly (up to eight-fold) in their
requirement for analgesia, even after identical surgical procedures.
Under-treatment results in unacceptable levels of pain with tachycardia,
hypertension, vasoconstriction and ‘splinting’ of the affected part. Painful
abdominal and thoracic wounds restrict inspiration, leading to tachypnoea, small
tidal volumes, and inhibition of the patient from effective coughing and
mobilisation. This predisposes to chest infection, delayed mobilisation, deep
venous thrombosis, muscle wasting and pressure sores.
However,
analgesic administration above the patient’s requirement increases the risks
of side effects such as nausea, vomiting, somnolence and dizziness or, if
greatly in excess, severe central effects including depressed consciousness and
respiration. This is fortunately rare, and can be avoided by sensible
initial dosing followed by titration until the patient is comfortable.
Exaggerated fears of opioid induced central depression and addiction have led
all too commonly to inhibition amongst staff from prescribing and
administering adequate doses of opioids. Intermittent intramuscular dosing
also leads to delays in administration of the ‘controlled’ opioids
compounded by the time to onset of action of action.
As
a result of these common deficiencies, a Joint Working Party of the Royal
Colleges of Anaesthetists and Surgeons was convened, which published the report Pain
after Surgery in 1990. It recommended the establishment of acute pain teams,
comprising medical and nursing specialists, to oversee the implementation of
guidelines for practice including routine recording of pain levels, and
educating both staff and patients. Combinations of analgesic methods [local
anaesthesia and nonsteroidal anti-inflammatory drugs (NSAIDs) with opioid drugs]
were advocated, as were the more sophisticated methods of pain management such
as ‘patient-controlled analgesia’.
The
Working Party report also encouraged further use of combined treatments (termed
balanced analgesia) such as with:
• local anaesthetic blocks — excellent short-term analgesia, but
requires skill and has a small failure rate. Continuous catheter techniques
prolong pain relief but are only appropriate for inpatients;
• spinal opioids — generally very useful for appropriate types
of surgery, but again requires skill, and is limited by concerns over severe
respiratory depression;
• NSAIDs — in combination reduce requirement for opioids and alone
are useful for moderate pain, but are limited by concerns over side effects,
such as renal impairment, peptic ulceration and inducing acute bronchospasm in
asthmatics. They are not adequate as sole analgesic therapy after major surgery.
The report called for further research
and, amongst other aims, hoped for the advent of a powerful analgesic on a par
with morphine, but without marked respiratory depressant activity. While the
development of tailor-made opioid agonists with differential receptor activity
has not yet solved this problem, attention turned more to finding alternative
pathways at which to attenuate the afferent pain impulses. For example,
clonidine has been administered epidurally to stimulate the spinal cord
adrenergic inhibitory mechanisms.
Severe
acute pain increases morbidity after trauma or surgery.
Appreciation
of pain pathways and the three main classes of pain — nociceptive, neuropathic/sympathetic
and that of mainly psychological origin — together with enhanced awareness of
pain, has led to new and multimodal treatment strategies.
The
methods of prevention are:
• adequate analgesia by intravenous narcotic drugs at the time of
surgery;
• regional anaesthesia alone or supplementing general anaesthesia
during surgery to prevent excitation of central pathways;
• the use of prostaglandin inhibitory drugs during surgery. Diclofenac
suppositories are effective in reducing the pain from tissue damage in bone and
muscle, and are used at the time of operation.
These
three approaches used together are good at preventing the cycle of pain and
muscle spasm from becoming established in the recovery period.
The
same methods can be used for managing the pain of acute trauma.