1. 9/10/2015PAIN1 PAIN!! Definition, assessment, physiology and treatment Dr Simon Holbrook

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3. 9/10/2015PAIN3 Aims & Objectives Aim Aim –To improve overall understanding of pain management Learning Objectives Learning Objectives –To define pain –To describe methods of pain assessment –To illustrate pain pathways –To describe commonly used drugs & methods of administration –To define the analgesic ladder –To calculate safe doses of local anaesthetic agents –To define chronic pain –To illustrate briefly the management of chronic pain

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10. 9/10/2015PAIN10 Definition of pain “An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage” International Association for the Study of Pain

11. 9/10/2015PAIN11 Assessment An objective estimate of a subjective perception (i.e. it’s difficult!) An objective estimate of a subjective perception (i.e. it’s difficult!) Scales Scales –Pictures for children –Numerical for adults Clouded by personality and culture Clouded by personality and culture

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19. 9/10/2015PAIN19 POSTOPERATIVE PAIN Why bother? CVS CVS –Tachycardia –Hypertension –Increased myocardial O 2 demand GI GI –Nausea and vomiting –Ileus RS RS –↓ Vital Capacity –↓ FRC –Basal atelectasis –Respiratory infection Other Other –Urinary retention –DVT + PE

20. 9/10/2015PAIN20 ANALGESICS Site of Action They may act at site of injury – decrease pain associated with nerve conduction They may act at site of injury – decrease pain associated with nerve conduction They may alter nerve conduction They may alter nerve conduction They may modify nerve transmission in dorsal horn They may modify nerve transmission in dorsal horn They may affect the central component They may affect the central component

21. 9/10/2015PAIN21 ORAL ANALGESICS 1 Paracetamol Paracetamol –Inhibits prostaglandin production –Central action – COX 3 –Dose = 10-20mg/kg up to 1g –Repeat 4 times a day (max 4g/day) –Good opioid sparing effect if given regularly –Good antipyretic –Poor anti-inflammatory

22. 9/10/2015PAIN22 ORAL ANALGESICS Paracetamol Paracetamol –Side-effects extremely rare unless taken in overdose –1% is metabolised to toxic metabolite and normally inactivated by conjugation –In overdose glutathione groups depleted –Excess metabolite binds to SH groups on liver macromolecules –hepatic necrosis –R x N-acetylcysteine (-SH donor)

23. 9/10/2015PAIN23 ORAL ANALGESICS NSAIDs Cyclo-oxygenase inhibitors Cyclo-oxygenase inhibitors Blocks prostaglandin and thromboxane production Blocks prostaglandin and thromboxane production Prostaglandins potentiate action of bradykinin & other polypeptides at pain receptors Prostaglandins potentiate action of bradykinin & other polypeptides at pain receptors

24. 9/10/2015PAIN24 ORAL ANALGESICS NSAIDs COX 1 constitutive isoenzyme responsible for homeostatic mechanisms (renal and gastric mucosa) COX 1 constitutive isoenzyme responsible for homeostatic mechanisms (renal and gastric mucosa) COX 2 inducible form in response to inflammation COX 2 inducible form in response to inflammation Selective COX 2 inhibitors with fewer side effects Selective COX 2 inhibitors with fewer side effects Side effects: Bronchospasm, GI effects, renal, platelets Side effects: Bronchospasm, GI effects, renal, platelets

25. 9/10/2015PAIN25 ORAL ANALGESICS Compound analgesics Compound analgesics –Paracetamol plus weak opioid –Codeine, Dihydrocodeine –E.g. Co-codamol, Co-dydramol –Mild to moderate pain –Beware overdose Oral opioids Oral opioids –Codeine, dihydrocodeine (weak) –Morphine (strong)

26. 9/10/2015PAIN26 OPIOID RECEPTORS Mu – OP3 – analgesia, respiratory depression, euphoria, miosis, bradycardia, physical dependence Mu – OP3 – analgesia, respiratory depression, euphoria, miosis, bradycardia, physical dependence Delta – OP1 – unclear Delta – OP1 – unclear Kappa – OP2 - analgesia, respiratory depression, miosis, sedation, dysphoria Kappa – OP2 - analgesia, respiratory depression, miosis, sedation, dysphoria

27. 9/10/2015PAIN27 ORAL ANALAGESICS Tramadol Tramadol –mu receptor agonist –Increases inhibitory descending activity (5HT & noradrenaline) –PO / IM / IV 50 – 100mg/ 4-6 hourly –Not controlled drug –Lower incidence of some side effects

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29. 9/10/2015PAIN29 INTRAVENOUS ANALGESICS OPIOIDS IV opioids for severe pain e.g. morphine, diamorphine, oxycodone IV opioids for severe pain e.g. morphine, diamorphine, oxycodone Strong OP3 receptor agonists Strong OP3 receptor agonists Can be given po / im / transcutaneous /spinal / epidural Can be given po / im / transcutaneous /spinal / epidural PCAS PCAS Effective for C-fibre pain Effective for C-fibre pain Ineffective for Aδ-fibre pain Ineffective for Aδ-fibre pain

30. 9/10/2015PAIN30 INTRAVENOUS ANALGESIA OPIOIDS Opioid side-effects Opioid side-effects –Respiratory depression: Tidal Volume ↑, Respiratory Rate ↓: Overall MV ↓ –Hypotension: Sympathetic tone ↓, vagal tone ↑, histamine release * –Euphoria, decreased conscious level –Constipation –Tolerance and dependence

31. 9/10/2015PAIN31 LOCAL ANAESTHETICS (LA) Prevent pain by causing a reversible block of conduction along nerve fibres. Prevent pain by causing a reversible block of conduction along nerve fibres. Inhibition of Sodium channel in axon preventing K/Na exchange Inhibition of Sodium channel in axon preventing K/Na exchange Membrane stabilisation affect Membrane stabilisation affect

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35. 9/10/2015PAIN35 LA - History Cocaine isolated from Erythroxylon coca Cocaine isolated from Erythroxylon coca Eye surgery - Koller 1884 Eye surgery - Koller 1884 Nerve blocks – Hall & Halsted Nerve blocks – Hall & Halsted Epidural / spinal? - Corning 1885 Epidural / spinal? - Corning 1885 Spinal - Bier 1899 Spinal - Bier 1899 Caudal Epidural 1901 Caudal Epidural 1901 Procaine – Einhorn -1904 Procaine – Einhorn -1904 Lumbar epidural – Pages 1921 Lumbar epidural – Pages 1921

36. 9/10/2015PAIN36 Structure Two groups - Esters and Amides Two groups - Esters and Amides Difference is in the link Difference is in the link Esters include cocaine, amethocaine Esters include cocaine, amethocaine Amides include lidocaine, bupivacaine, prilocaine, mepivacaine, etidocaine Amides include lidocaine, bupivacaine, prilocaine, mepivacaine, etidocaine

37. 9/10/2015PAIN37 Mechanism of Action LA in 2 forms - hydrochloride salt (acid) and free base LA in 2 forms - hydrochloride salt (acid) and free base Only free base can penetrate lipid to get to Na channel Only free base can penetrate lipid to get to Na channel Free base concentration depends on dissociation which depends on pH tissue Free base concentration depends on dissociation which depends on pH tissue

38. 9/10/2015PAIN38 Types of Nerves Blocked Sensory – anaesthesia – primarily pain fibres Sensory – anaesthesia – primarily pain fibres Autonomic - mainly loss of sympathetic tone Autonomic - mainly loss of sympathetic tone Motor - paralysis/ weakness Motor - paralysis/ weakness i.e. all nerves!!! i.e. all nerves!!!

39. 9/10/2015PAIN39 Side Effects Sympathetic blockade after epidural and spinal anaesthetic causing hypotension = common Sympathetic blockade after epidural and spinal anaesthetic causing hypotension = common Dural puncture headache 1/200 Dural puncture headache 1/200 Rarely epidural haematoma, abscess, nerve / spinal cord damahe Rarely epidural haematoma, abscess, nerve / spinal cord damahe Allergy very rare - dentists Allergy very rare - dentists SYSTEMIC TOXICITY SYSTEMIC TOXICITY

40. 9/10/2015PAIN40 Systemic Toxicity LA leaks into circulation and acts on brain and heart LA leaks into circulation and acts on brain and heart Changes seen due to membrane stabilising effect Changes seen due to membrane stabilising effect Effects depend on dose of LA, injection site and speed, vasoconstrictor, metabolism Effects depend on dose of LA, injection site and speed, vasoconstrictor, metabolism Worst if large dose of poorly metabolised LA injected into very vascular area Worst if large dose of poorly metabolised LA injected into very vascular area

41. 9/10/2015PAIN41 Signs and Symptoms Tingling - mouth and nose Tingling - mouth and nose Tinnitus Tinnitus Light-headedness, anxiety, drowsiness Light-headedness, anxiety, drowsiness Convulsions and loss of consciousness Convulsions and loss of consciousness Respiratory depression Respiratory depression Cardiovascular collapse Cardiovascular collapse

42. 9/10/2015PAIN42 Treatment of Toxicity Stop injection of drug Stop injection of drug Give oxygen Give oxygen ABC ABC

43. 9/10/2015PAIN43 Safe Doses All have published safe doses based on mg per kg All have published safe doses based on mg per kg A 1% solution has 10 mg per ml A 1% solution has 10 mg per ml Bupivacaine max. dose 2mg/kg Bupivacaine max. dose 2mg/kg Lignocaine max. doses Lignocaine max. doses –3mg/kg –7mg/kg with adrenaline

44. 9/10/2015PAIN44 Toxic Dose Calculation Look at the back page now and work in groups through the questions

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46. 9/10/2015PAIN46 Routes of Administration Topical - EMLA, Ametop Topical - EMLA, Ametop Mucosal - ENT procedures Mucosal - ENT procedures Tissue infiltration - around incision Tissue infiltration - around incision Peripheral nerve block – e.g. femoral Peripheral nerve block – e.g. femoral Plexus block – e.g. brachial Plexus block – e.g. brachial Epidural Epidural Spinal Spinal

47. 9/10/2015PAIN47 Epidural Analgesia 1 Local anaesthetic & opioid mixture Local anaesthetic & opioid mixture Concentration of LA sufficient to block C- and Aδ-fibres but not the larger fine touch, proprioception and motor fibres Concentration of LA sufficient to block C- and Aδ-fibres but not the larger fine touch, proprioception and motor fibres Only way to prevent fast pain on moving and coughing Only way to prevent fast pain on moving and coughing

48. 9/10/2015PAIN48 Epidural Analgesia 2 Side-effects Side-effects –Hypotension related to sympathetic blockade. –Epidural abscess, haematoma, spinal cord/nerve damage is rare Added opioids allows high concentration at spinal mu receptors keeping systemic levels low, limiting side-effects. Added opioids allows high concentration at spinal mu receptors keeping systemic levels low, limiting side-effects. Also adding opioids decreases required concentration of local anaesthetic – aids patient mobility Also adding opioids decreases required concentration of local anaesthetic – aids patient mobility

49. 9/10/2015PAIN49 Epidural Analgesia 3 Do not remove – leave it to the pain team Do not remove – leave it to the pain team Hypotension and pain free => reduce rate Hypotension and pain free => reduce rate Hypotension and in pain => fluid bolus & discuss with anaesthetist / pain team Hypotension and in pain => fluid bolus & discuss with anaesthetist / pain team Only stop it if severe hypotension present Only stop it if severe hypotension present –Call pain team or on-call anaesthetist immediately –Ephedrine 3mg bolus iv (only if you have to, comes as 30mg in 1ml vials) Never inject down it Never inject down it –Make sure you know which is the iv line

50. 9/10/2015PAIN50 OTHERS Good communication because of unrealistic expectations Good communication because of unrealistic expectations Alternatives Alternatives –Local anaesthetic infiltration/nerve blocks –Heat pads/ massage –TENS / acupuncture –+/- visitors

51. 9/10/2015PAIN51 CHRONIC PAIN Definition “Persistent and intractable pain lasting more than 6 months”

52. 9/10/2015PAIN52 CHRONIC PAIN Often neuropathic in origin Often neuropathic in origin 2 characteristic types of pain 2 characteristic types of pain –Sharp, shooting –burning Examples Examples –Nerve root compression, pancreatitis, ischaemic pain Pain experienced beyond area of original injury (neural plasticity) Pain experienced beyond area of original injury (neural plasticity) Allodynia – light touch feels unpleasant Allodynia – light touch feels unpleasant

53. 9/10/2015PAIN53 CHRONIC PAIN Multidisciplinary Multidisciplinary –Anaesthetist (coordinates) –Pain nurses, psychologist, physiotherapist, pharmacist Patient must understand there is no cure Patient must understand there is no cure Treatment is aimed at symptom control & minimizing lifestyle restrictions Treatment is aimed at symptom control & minimizing lifestyle restrictions

54. 9/10/2015PAIN54 Drugs Used in Chronic Pain Conventional analgesics Conventional analgesics Antidepressants e.g. amitriptyline Antidepressants e.g. amitriptyline Antiepileptics Antiepileptics –Phenytoin, carbamazepine, sodium valproate –Gabapentin Clonidine – alpha 2 agonist Clonidine – alpha 2 agonist Ketamine Ketamine Corticosteroids Corticosteroids Capsaicin Capsaicin –C fibres –Depletes substance P

55. 9/10/2015PAIN55 APPLY THIS KNOWLEDGE TO THE PAPERMAN!!

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57. 9/10/2015PAIN57 Local anaesthetics NSAID’s TENS Heat Massage Nerve blocks Sympathetic block Epidural Spinal Opioids

58. 9/10/2015PAIN58 Questions