Editing Pain and analgaesia


== Pain ==
'an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.'

* Physiological pain:
** Nociceptive
** Inflammatory
* Pathological/maladaptive pain:
** Neuropathic

=== Pathophysiology ===

* Transduction - noxious agent stimulates free nerve endings (nociceptors)
* Transmission - signal travels via nerve pathways - A and C fibres, in the spinothalamic and thalamocortical tracts
* Modulation - repression or enhancement of signal occurs in the dorsal horn of the spinal cord
* Perception - pain signal reaches cerebral cortex



Strategies to reduce pain

* Education
** Reduce anxiety by discussing likely post-operative pain levels and course beforehand
** Set realistic expectations
** Encourage early rehabilitation
* Prevention
** Various strategies to minimise tissue disruption
** Pre-emptive analgaesia
** Post-operative regional blocks/LA
* Multimodal analgaesia
** LA
** Regional anaesthesia - epidural, regional block, spinal

== Approach to seeing a post-op patient in pain ==

* Review physiological status and operative details
* Review medication chart
* Discuss with ward nurses
* Review and discuss with the patient
** Exclude a new problem, including ischaemia, bleeding, anastomotic leak and compartment syndrome
** Airway - ensure no sedation or high-risk features
** Breathing - RR and sats
** Circulation
** Disability - check LoC
** Use SOCRATES or similar to characterise pain
* Consider possibilities:
** Inadequate medication or dosage?
** Incorrect technique used?
** Unrecognised complication?
** Other supplemental techniques are not used appropriately?

=== Management options: ===

* Analgaesic medications
** Oral
** SC/IM
** IV
*** PCA
*** Bolus
* Regional anaesthetic techniques
** Spinal/epidural
** Peripheral nerve block
** LA

=== Paracetamol ===

* Analgaesic and anti-pyretic
* Exact mechanism of action not fully understood
* Metabolised by the liver
* May need to adjust dose in hepatic impairment or underweight patients
* No significant benefit to IV over PO
* 1g q6h is the usual dose
* In patients <50kg, give 15mg/kg/day

=== NSAIDs ===

* Inhibit prostaglandin synthesis by inhibiting the enzyme cyclo-oxygenase
* Contraindications
** Allergy including asthma
** Previous CABG and cardiovascular disease in general
** Pregnancy especially third trimester
** GI bleeding/gastritis
** Previous bariatric surgery
** CKD/AKI
** Diseases that impair platelet activity
** Orthopaedic injuries

=== Opioids ===

* Derived from opium alkaloids
* Act on mu-opioid receptors
* Adverse effects:
** Nausea/vomiting
** Constipation
** Pruritis
** Bladder retention
** Drowsiness and respiratory depression

=== Co-analgaesics ===

* Anticonvulsants - gabapentin
* Antidepressants - amitriptyline
* Ketamine 

[[Category:Anaesthetics]]