- 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
Bibliography
Crews J C. Multimodal pain management strategies for office-based and ambulatory procedures. JAMA
2002; 288: 629-632.
Rigg J R A, Jamrozik K, Myles P S et al. Epidural anaesthesia and analgesia and outcome of major
surgery: a randomised trial. Lancet 2002; 359: 1276-1282.
Schecter W P, Bongard F S, Gainor B J, Weltz D L, Horn J K. Pain control in
outpatient surgery. J Am Coll Surg 2002; 195: 95-104.
Taylor M S. Managing postoperative pain. Hosp Med 2001; 62: 560-563.
White P F. The role of non-opioid analgesic techniques in the management of pain after ambulatory
surgery. Anesth Analg 2002; 94: 577-585. |