- Pain is define as 'an unpleasant sensory and emotional experience
associated with actual or potential tissue damage.'
- It is a complex process influenced by both physiological and
psychological factors
- Management of post postoperative pain has generally been shown to be
inadequate
Effects of postoperative pain
- Postoperative pain can affects all organ systems and includes:
- Respiratory - reduced cough, atelectasis, sputum retention and
hypoxaemia
- Cardiovascular - increased myocardial oxygen consumption and
ischaemia
- Gastrointestinal - decreased gastric emptying, reduced gut motility
and constipation
- Genitourinary - urinary retention
- Neuroendocrine - hyperglycaemia, protein catabolism and sodium
retention
- Musculoskeletal - reduced mobility, pressure sores and increased
risk of DVT
- Psychological - anxiety and fatigue
Assessment of pain
- Pain is a subjective experience
- Observer assessment of patient behaviour is unreliable
- Pain should be assessed and recorded by:
- Visual analogue scales
- Verbal numerical reporting scale
- Categorical rating scale
Non-pharmacological methods of pain relief
- Preoperative explanation and education
- Relaxation therapy
- Hypnosis
- Cold or heat
- Splinting of wounds etc
- Transcutaneous electrical nerve stimulation (TENS)
Pharmacological methods of pain relief
Simple analgesia
- Paracetamol is a weak anti-inflammatory agent
- Modulates prostaglandin production in the central nervous system
- Can be administered orally or rectally
- Best taken on a regular rather than 'as required' basis.
- Overdose results in hepatic necrosis
- Often combined with weak opiates (e.g. dihydrocodeine = Co-dydramol)
Non-steroidal anti-inflammatory agents
- Inhibit the enzyme cyclo-oxygenase
- Reduces prostaglandin, prostacyclin and thromboxane production
- Also have weak central analgesic effect
- Often used for their 'opiate sparing' effects
- Side effects include:
- Gastric irritation and peptic ulceration
- Precipitation of bronchospasm in asthmatics
- Impairment of renal function
- Platelet dysfunction and bleeding
Opiates
- Most commonly used drugs are diamorphine, morphine and pethidine
- Diamorphine is a prodrug rapidly hydrolysed to morphine and
6-monoacetyl-morphine
- More lipid soluble than morphine with greater central effects
- Pethidine has only about 10% the analgesic potency of morphine
- All act on mu receptors in brain and spinal cord
- Mu 1 receptors are responsible for analgesia
- Mu 2 receptors are responsible for respiratory depression
- Side effects of opiates include:
- Sedation
- Nausea and vomiting
- Vasodilatation and myocardial depression
- Pruritus
- Delayed gastric emptying
- Constipation
- Urinary retention
Routes of opiate administration
- Oral - available for codeine, dihydrocodeine and oramorph
- Subcutaneous - useful for chronic pain relief
- Intramuscular - produces peaks and troughs in pain relief
- Intravenous - reliable but can produce sedation and respiratory
depression
- Patient-controlled analgesia (PCA) - patient determines own
analgesic requirement
- 'Lock-out' period prevents accidental overdose
- Safe as sedation occurs before respiratory depression
- Epidural or spinal
- Lipid soluble opiates (e.g. fentanyl) are normally used
- Produces good analgesia with reduced risk of side effects
Local anaesthetic agents and techniques
- Can be used by:
- Wound infiltration
- Nerve or nerve plexus blockade
- Epidural infiltration
- Intrathecal (spinal) administration
- Lignocaine has rapid onset but short duration of action
- Bupivicaine has more prolonged onset but shorter duration of action
- Adrenaline and delay absorption and prolong duration of action
- Should not be used at sites of end-arteries (e.g. ear, fingers,
penis)
- Act by reducing transmission along nerve fibres
- Work by blocking sodium channels in the nerve fibres
- Block pain-fibres first but can also result in
- Neuromuscular blockade
- Hypotension due to sympathetic blockade
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