Anaesthetics - Analgesia Flashcards
What is pain?
An unpleasant sensory/emotional experience associated w/ actual/potential tissue damage OR described in terms of such damage
How is pain transmitted?
A-delta fibres = sharp, immediate pain
C-fibres = slower onset, prolonged pain
Sensory impulses enter cord via dorsal root, ascend in dorsal post column/spinothalamic tract
What are the adverse effects of pain?
Multiple psychological effects
Catecholamine release
-vasoconstriction –> inc cardiac work/delayed healing
What is the WHO pain ladder?
Non opioid +/- adjuvant
Weak opioid +/- non-opioid +/- adjuvant
Strong opioid +/- non opioid +/- adjuvant
What is the MoA of Paracetamol?
Unknown
- acts similar to NSAIDs
- inhibits CNS prostaglandin synthesis
When is Paracetamol indicated?
Mild-mod pain
Pyrexia
What are the benefits of Paracetamol?
Good analgesic/antipyretic properties
Weak anti-inflame activity
Oral doses achieve PPC w/i 1hr
Side effects uncommon
What is the dose of Paracetamol?
1g PO/IV QDS
- max of 4g/day
- dose reduced in pts <50kg
- max of 3g/day if risk factors for hepatotoxicity
What is the MoA of NSAIDs?
Inhibition of COX enzymes (produce PGs/TXA2)
- COX-1 = expressed in most tissues, platelet aggregation, renal blood flow autoregulation, GI production
- COX-2 = induced in active inflame cells, sensitises nociceptors/afferent pain fibres
What are the benefits of NSAIDs?
Anti-inflammatory/analgesic effects
Weak antipyretic effect
When are NSAIDs indicated?
Inflammatory pain
What are the side effects of NSAIDs?
Inhibition of COX-2
- dyspepsia & gastric ulceration
- bronchospasm
- renal insufficiency
- cardiotoxicity
- dec platelet count
- skin reactions
What are the absolute contraindications to NSAIDs?
Severe heart failure
History of GI bleeds/ulceration
What are the cautions to NSAIDs?
Asthma
Elderly
Coagulopathies
Renal/hepatic/cardiac impairment
What are the doses of NSAIDs?
Ibuprofen 400mg QDS
- co-prescribe PPI w/ NSAIDs
- can be oral/topical
What are coxibs?
COX-2 selective inhibitors
- licensed for use in RA/OA
- 1st line for thrombocytopenia/high risk of GI comp
- still co-prescribe PPIs
What is the MoA of opioids?
Act on u-opioid receptors in CNS/throughout body, decreasing neuro-excitability
-not effective in neuropathic pain
What are the side effects of opioids?
Resp depression N/V (40%) Constipation Sedation/depression of cough reflex Gall bladder concentration
What are the absolute contraindications to opioids?
Acute resp depression
Acute alcoholism
Risk of paralytic ileus
Raised ICP
How should morphine be prescribed in the acute setting?
Healthy adults = 5mg IV, titrate up
Elderly = 2mg IV, titrate up
What drugs should be co-prescribed w/ morphine?
Metoclopramide 10mg IV TDS
Senna
Lactulose
How are opioid doses converted?
Convert all opiate doses into oral morphine equivalence
Total 24hr dose
Divide into 2h modified release doses of Zomorph
Prescribe 1/6th total daily dose prn Oramorph
How should opioid overdose be managed?
400 mcg Naloxone IV
-if no response after 1min give 800mcg
-if no response after 2min give 800mcg
2mg/4mg doses given in severely poisoned pts
What are the indications for PCA?
Post-op
Palliation in oncology
What is PCA?
Syringe driver allowing boluses of painkiller to be delivered on patient demand
- locks out for a set time
- can be set to provide continuous background dose
What are the options for non-drug analgesia?
Splinting Cold therapy TENS Acupuncture CBT
