Postoperative Pain Management. Nimmaanrat S, MD, FRCAT, MMed (Pain Mgt)

Transcription

1 Postoperative Pain Management Nimmaanrat S, MD, FRCAT, MMed (Pain Mgt)

2 Topics to be Covered Definition Neurobiology Classification Multimodal analgesia Preventive analgesia Step down approach Measurement Methods of treating postoperative pain (various routes) Patient-controlled analgesia (PCA) Non-opioids Weak opioids Strong opioids Regional analgesia

3 Pain An unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage

4 Neurobiology of Pain

5 Descartes (Cartesian) s Model of Pain

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10 Classification of Pain Duration Acute Chronic Pathophysiology Nociceptive Neuropathic

11 Insult The Continuum of Pain Time to resolution Acute Chronic <1 month 3-6 months Usually obvious tissue damage Increased nervous system activity Pain resolves upon healing Serves a protective function Pain for 3-6 months or more Pain beyond expected period of healing Usually has no protective function Degrades health and function

12 Progression from Acute to Chronic Pain

13 Incidence of Chronic Pain after Surgery Amputation Thoracotomy Mastectomy Cholecystectomy Inguinal hernia Vasectomy Dental surgery % 5-67 % % 3-56 % 0-63 % 0-37 % 5-13 %

14 Risk Factors for Chronic Postsurgical Pain Preop factors Pain, moderate to severe, > 1/12 Repeat surgery Psychologic vulnerability Workers compensation Intraop factors Surgical approach with risk of nerve damage Postop factors Pain (acute, moderate to severe) Radiation to area Neurotoxic chemotherapy Depression Psychologic vulnerability Neuroticism Anxiety

15 Adverse Consequences of Uncontrolled Postoperative Pain Physiological effects Psychological effects

16 Physiological Adverse Effects Increase sympathetic activity Increase risk of MI Decrease GI motility (ileus) Increase incidence of pulmonary complications (atelectasis, hypoxia) Suppress immunity

17 Psychological Adverse Effects Receive less attention than those asso. w chronic pain But not less important Failure to control postop. Pain Anxiety Insomnia Inability to think and interact w others etc.

18 Postoperative Pain Management Multimodal analgesia Preventive analgesia Step down approach

19 Multimodal Analgesia

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21 Clinically Meaningful Adverse Events CMEs The incidence of clinically meaningful adverse events is dose-related (level II)

22 Preventive Analgesia

23 Step Down Approach

24 Measurement of Pain

25 Pain Measurement Pain is a subjective, personal experience The logical and true assessment of pt s pain must therefore be pt s own report Self report is gold standard Unidimension Multidimensions

26 Unidimensional Tools Categorical scales Numerical rating scales (NRS) Visual analog scales (VAS) Picture scales / pain drawings

27 Methods of Treating Postoperative Pain

28 Methods of Treating Postoperative Pain Traditional administration of opioids Parenteral administration of opioids Non-parenteral administration of opioids Local anesthetic techniques Non-opioid analgesics Non-pharmacological methods

29 Parenteral Administration of Opioids Bolus IV administration Continuous IV infusion Patient-controlled analgesia (PCA) Bolus IV Bolus + infusion Subcutaneous

30 Non-parenteral Administration of Opioids Sublingual Oral Transmucosal Rectal Transdermal Nasal Inhalation Intra-articular opioids

31 Non-opioid Analgesics Non-steroidal anti-inflammatory drugs (NSAIDs) Selective COX-2 inhibitors (COXIBs) Paracetamol NMDA antagonists Central α 2 -adrenergic agonists

32 Patient-controlled Analgesia (PCA)

33 Patient-controlled Analgesia (PCA)

34 Patient-controlled Analgesia (PCA)

35 Advantages of PCA

36 Non-parenteral Opioid Administration

37 Non-parenteral Administration of Opioids Sublingual Oral Transmucosal Rectal Transdermal Nasal Inhalation Intra-articular opioids

38 Sublingual Opioids Cooperation required No need for painful injections Popular for pts Convenient for nurses Buprenorphine Partial agonist / ceiling effect

39 Oral Route All opioids undergo extensive first-pass metabolism Low oral bioavailability (20-30%) Immediate postop. period : invariably reduction of gastric emptying

40 Oral Route Absorption may be delayed, with poor analgesia If given on regular basis : a danger of a large dose being propelled into upper GI tract when gastric motility returns to normal Over dosage Ventilatory depression

41 Transmucosal Route Premedication in children Onset of pain relief : 9/60

42 Rectal Route Bioavailability varies according to site of suppository Venous blood from lower part of rectum drains directly into systemic circulation But upper part drains into portal circulation

43 Inhaled / Intranasal Route Intranasal spray devices for fentanyl Metered inhalers with improved pulmonary drug delivery systems and lockout times Future : may allow noninvasive PCA administration

44 Pharmacological Approach

45 Classification of Pain Medications Non-opioid analgesics Opioid analgesics Adjuvants

46 Paracetamol

47 Paracetamol (Acetaminophen) Effective analgesic with antipyretic activity Does not inhibit COX in peripheral tissues -> lack of anti-inflammatory activity Mechanism of analgesic action remains unclear

48 Paracetamol Generally well tolerated Most serious adverse effect of acute overdosage is a dose-dependent (150 mg/kg), potentially fetal, hepatic necrosis Insufficient glutathione (liver disease, alcohol consumption> 3 units/day, malnutrition etc.)

49 NSAIDs

50 Mechanisms of Action

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52 Selective COX-2 Inhibitors (COXIBs)

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54 COXIBS COX-2 is constitutively expressed in kidney Maintenance of renal blood flow Mediation of renin release Regulation of Na + excretion COXIBs & NSAIDs have similar renal adverse effects ed risk in pre-existing renal impairment, hypovolumia, hypotension, use of nephrotoxic agents & ACEIs

55 COXIBs The pharmacological class of COXIBs appears to be associated with an increased risk of CV adverse events The CV risks may increase with dose & duration of exposure The shortest duration possible & the lowest effective daily dose should be used

56 COXIBs Must not be used in pts with established Ischemic heart disease Cerebrovascular disease Peripheral arterial disease To exercise caution in pts with risk factors of heart disease Hypertension Hyperlipidemia DM Smoking

57 Opioids

58 Classification of Opioids Weak opioids (mild - moderate pain) Strong opioids (moderate - severe pain)

59 Weak Opioids Codeine Tramadol

60 Codeine Classic weak opioid Potency 1/10 of MO (CYP2D6, MO) mg q 4/24 Dose limiting side effects (constipation, N/V, confusion) Fixed combination

61 Paracetamol vs Paracetamol plus Codeine

62 Tramadol Dual-acting analgesic Tramadol & M1 (CYP2D6) have affinity at μ-opioid receptors Also inhibits reuptake of serotonin & noradrenaline Potency 1/20 1/5 of MO

63 Tramadol Max 400 mg/day Max 200 mg/day in pts with hepatic / renal impairment Tramadol Retard (12/24) Less sedation & constipation Unfortunately, N/V frequently reported

64 Strong Opioids Morphine Pethidine Fentanyl

65 Strong Opioids Mainstay for the Rx of moderate to severe pain Interpatient requirements vary greatly Doses need to be titrated to suit each pt In adults, age rather than weight is the predictor of requirement

66 Strong Opioids All full agonists given in equianalgesic doses produce the same analgesic effects & side effects One opioid is not superior over others but some are better in some pts (level II) The incidence of clinically meaningful adverse effects is dose related (level II) Pethidine should be discouraged

67 Opioids Assessment of sedation level is a more reliable way of detecting early opioidinduced respiratory depression

68 Morphine M3G & M6G are main metabolites, excreted via kidney M6G Opioid agonist May potent than morphine M3G No analgesic activity May antagonise analgesic effect May cause hyperalgesia, allodynia & muoclonus

69 Pethidine Widely used even though it has multiple disadvantages Despite common belief that it is the most effective opioid in treatment of renal colic, it is no better than morphine Pethidine & morphine have similar effects on sphincter of Oddi & biliary tract No evidence that pethidine is better in the treatment of biliary colic

70 Norpethidine Metabolized in liver to several inactive compounds and norpethidine Accumulation leads to neuroexcitatory Nervousness Tremors Twitches Multifocal myoclonus Seizures

71 Pethidine / Norpethidine Impaired renal function half-life of norpethidine Patients in renal failure are at ed risk of norpethidine toxicity Naloxone not reverses & may norpethidine toxicity Overall, the use of pethidine should be discouraged in favor of other opioids

72 Fentanyl High lipid solubility Potency 100X of morphine Lack of active metabolite Fast onset Short duration of action

73 Guideline for Postoperative Pain Management (Example)

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75 Regional Analgesia

76 Epidural Analgesia

77 Peripheral Nerve Block

78 Ultrasound-guided Peripheral Nerve Block supraclavicular brachial plexus block

79 Peripheral Nerve Block Single shot Continuous infusion

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