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Pathophysiology of Pain Treatment of Acute Postoperative Pain

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1 Pathophysiology of Pain Treatment of Acute Postoperative Pain
Dr Sajith Damodaran University College of Medical Sciences & GTB Hospital, Delhi

2 Objectives: Definition of Pain
Anatomy and Physiology of pain perception Adverse effects of untreated postoperative pain Modalities of treating postoperative pain Special patient populations

3 Pain: Definition An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage. [IASP] Subjective Sensation and emotion Unpleasant Psychological, in absence of any stimulus or pathophysiological cause An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage. Note: The inability to communicate verbally does not negate the possibility that an individual is experiencing pain and is in need of appropriate pain-relieving treatment. Pain is always subjective. Each individual learns the application of the word through experiences related to injury in early life. Biologists recognize that those stimuli which cause pain are liable to damage tissue. Accordingly, pain is that experience we associate with actual or potential tissue damage. It is unquestionably a sensation in a part or parts of the body, but it is also always unpleasant and therefore also an emotional experience. Experiences which resemble pain but are not unpleasant, e.g., pricking, should not be called pain. Unpleasant abnormal experiences (dysesthesias) may also be pain but are not necessarily so because, subjectively, they may not have the usual sensory qualities of pain. An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage. Note: The inability to communicate verbally does not negate the possibility that an individual is experiencing pain and is in need of appropriate pain-relieving treatment. Pain is always subjective. Each individual learns the application of the word through experiences related to injury in early life. Biologists recognize that those stimuli which cause pain are liable to damage tissue. Accordingly, pain is that experience we associate with actual or potential tissue damage. It is unquestionably a sensation in a part or parts of the body, but it is also always unpleasant and therefore also an emotional experience. Experiences which resemble pain but are not unpleasant, e.g., pricking, should not be called pain. Unpleasant abnormal experiences (dysesthesias) may also be pain but are not necessarily so because, subjectively, they may not have the usual sensory qualities of pain. Many people report pain in the absence of tissue damage or any likely pathophysiological cause; usually this happens for psychological reasons. There is usually no way to distinguish their experience from that due to tissue damage if we take the subjective report. If they regard their experience as pain and if they report it in the same ways as pain caused by tissue damage, it should be accepted as pain. This definition avoids tying pain to the stimulus. Activity induced in the nociceptor and nociceptive pathways by a noxious stimulus is not pain, which is always a psychological state, even though we may well appreciate that pain most often has a proximate physical cause.

4 Pain: Definition Pain is what the patient says hurts [John Bonica]
Affected by the mental and emotional state, preconditioning, past experiences and memories. Always subjective. Varies from person to person Pain is the Fifth vital sign [JCAHCO]

5 Acute Pain Normal predicted physiological response to an adverse chemical, thermal or mechanical stimulus. Generally lasts less than one month Poorly managed pain leads to chronicity Pathophysiological changes in both PNS & CNS

6 Hyperalgesia and Allodynia

7 Anatomy and Physiology of Pain
Nociceptive Receptors: Naked Nerve Endings In all tissues Specific for pain Stimulus not specific Pain is not produced by overstimulation of other receptors

8 Anatomy and Physiology of Pain
Nociceptive Pathways: Afferent Three neuron First order neurons in Dorsal Root Ganglia Second order neurons in Dorsal horn Third order neurons in Thalamic nuclei Second order neurons include nociceptive specific and WDR Dual ascending system Lateral corticospinal Dorsal column medial leminiscal Descending modulation by cortex thalamus and brain stem Nocicpetive neurons respond only to pain. Invloved in sensory-discriminative aspects of pain. WDR neurons respond to both noxious and non noxious stimuli. Involved in motivational-affective component.


10 Anatomy and Physiology of Pain
Fast Pain or First Pain: Sharp or stinging well localised By stimulation of thermo-mechanical nociceptors Carried by A delta fibres Transmitted by the Lateral spinothalamic tract Monosynaptic pathway Usually disappears when stimulus ends

11 Anatomy and Physiology of Pain
Slow Pain or Second Pain Delayed, Diffuse Stimulation of polymodal nociceptors Carried by C fibres Transmitted by the dorsalcolumn medial leminiscal tract Polysynaptic pathway. Collaterals to midbrain, pontine and medullary RF, PAG, Hypothalamus Engage Descending modulatory system Involved in the reflex response to pain and emotional and motivational aspect The paleospinothalamic tract is polysynaptic. Ascends to the medial thalamic nuceli, sends collaterals to the midbrain, pontine an medullary reticaular fromation, periaqueductal gray & hypothalamus. Synapse onto neurons that project to forebrain limbic structures. Primarily involved in refelex response to pain…. Respiratory, circulatory, endocrine. Secondary afferents aslo engage descending modulatory systerm. Reticulospinal and spinomesencephalic tracts also supply afferents. All involved in producing emotoinal and behavioural response to pain.k

12 Anatomy and Physiology of Pain
Small Myelinated Aδ Fibres Carry Fast pain 2-5 μm diameter 12-30 m/s End mainly in lamina I, II & V of dorsal horn Small unmyelinated C Fibres Carry slow pain μm diameter 0.5-2 m/s End in Lamina I & II of dorsal horn

13 Anatomy and Physiology of Pain
Efferent modulation of pain: Descending inhibition Cortex, thalamus, brain stem PAG, nucleus raphe magnus, locus ceruleus Descend in dorsal column to dorsal horn


15 Anatomy and Physiology of Pain
Gate Control Theory: Explains the highly variable and non linear relationship between pain and injury Pain is ‘gated’ at the Dorsal Horn Involves WDR neuron Excited by nociceptors and also Aβ fibres Inhibitory interneurons, excited by Aβ fibres, inhibited by Aδ and C fibres MOA of TENS, Rubifascients and counterirritants

16 1.The projection neuron (P) carries both nociceptive stimulation from small fibers (S) and
non-nociceptive simulation from large fibers (L) on the way to the brain. 2.With no stimulation, the inhibitory neuron (I) keeps the gate "closed," and there is no painful sensation. 3.With painful stimulation, the small fiber (S) blocks the inhibitory neuron (I), "opening" the gate for the projection neuron (P) to send on the painful stimulus. 4.With the addition of non-painful stimulation, the large fiber (L) activates the inhibitory neuron (I), partially or completely closing the gate depending on the strength of the stimulation, and competes with the painful stimulation for access to the projection neuron (P).

17 Anatomy and Physiology of Pain
Other Types of Pain: Deep Pain Poorly localised, nauseating eg: periosteal pain, pain from ligaments Muscle Pain Due to ischemia P factor. ? Potassium Relieved by restoration of blood supply

18 Anatomy and Physiology of Pain
Visceral Pain Poorly localised and dull – sparse receptor concentration Usually felt in midline Associated with nausea and autonomic disturbances Afferents carried by ANS Spinal pathways are same as for somatic pain Referred to other areas

19 Anatomy and Physiology of Pain
Referred Pain Dermatomal Rule Pain from visceral sites referred to the somatic structure that developed from the same embryonic segment of dermatome Role of experience: Pain from abdominal structures may be referred to site of previous surgery Role of convergence Visceral and somatic sensory input converge on Dorsal Horn. More fibres in the peripheral nerve than the STT

20 Anatomy and Physiology of Pain
Neuropathic Pain: Direct nerve damage like entrapment, cutting, traction, compression etc. Presents with burning, tingling and other unpleasant sensations in addition to pain Common surgical procedures Limb amputations Breast surgery Gall bladder surgery Thoracic surgery Inguinal hernia repair Responds poorly to typical analgesics

21 Anatomy and Physiology of Pain
Pain Processing - 4 Elements Transduction Noxious mechanical, chemical and thermal stimuli are converted to action potential Transmission AP conducted through nervous system Modulation Alteration of neural transmission along the pain pathway, principally at dorsal horn Perception Final common pathway. Integration of painful input into somatosensory and limbic cortex. Usual analgesic approaches target only perception

22 Anatomy and Physiology of Pain
Modulation: Augmentation: Sensitisation due to neuronal plasticity (acute pain induced changes in the CNS) Inhibition: GABA, Glycine by intrinsic neurons NA, serotonin, Endorphins by descending efferent cortical and subcortical input

23 Pain Processing

24 Anatomy and Physiology of Pain
Chemical Mediators of Pain Processing: Tissue damage and inflammation activate nociceptors Release of numerous algogenic substances from the activated macrophages, mast cells, platelets and lymphocytes Direct pain transduction and facilitation of transduction by increasing the excitability of nociceptors

25 Neurochemistry of impulse processing at peripheral nerve ending

26 Anatomy and Physiology of Pain
Neurotransmitters in Spinal Cord: Excitatory Amino Acids Aspartate & Glutamate Excitatory Neuropeptides Substance P, Neurokinin A Inhibitory Amino Acids GABA, Glycine

27 Anatomy and Physiology of Pain
Pain Receptors in Spinal Cord: NMDA (N-methyly-D-Aspartae): Ca++ channel dependent AMPA (alpha-amino-3-hydroxy-5-methylisoxazole-4-propionicacid): Na+ channel dependent Kainate: Na+ channel dependent Metabotropic Opioid Receptors: Inhibitory Alpha2 Adrenergic Receptors: Inhibitory The sodium channel dependent receptors are essential for fast synaptic afferent input. NMDA is only activated following prolonge dedpl of cell mem. Involoved in secondary hyperalgesia. All the peripheral and central neurotransmitters and the receptors are potential targets for modulation of pain processing. However presently very few of these are clinically available.

28 Postoperative Pain Management:
Why manage postoperative pain? Humanitarian consideration Improved quality of care Better patient satisfaction Lesser morbidity ? Economic benefits due to enhanced patient well being and early rehabilitation

29 Consequences of poorly managed postoperative pain
Cardiovasuclar Tachycardia, Hypertension, increased cardiac work Respiratory Splinting, Decreased VC, Atelectatsis, Hypoxia, Increased risk of pulmonary infection Gastrointestinal Postoperative Ilieus Renal Increased risk of oliguria and urinary retention Coagulation Increased risk of thromboemboli Immunological Impaired immune function Muscular Musce weakness and fatigue, increased risk of DVT Psychological Anxiety, Fear, Frustration

30 Assessment of pain Background Pain Pain that is persistant
May vary over time Breakthrough Pain Pain that escalates above a persistant Background pain Transitory and Intermittant Pain that is episodic in the absence of background pain

31 Assessment of pain Simple Pain Scales:
Useful for evaluation of acute pain Visual Analouge Scale Validated for research Simple to use Sensitive to small changes Not useful in visually impaired, cognitively impaired and small children Numerical Rating Scale Less sensitive Requires patient to be able to translate pain severity to number. Not useful in visually impaired cognitively impaired and children Verbal Rating Scale Easy to Use Useful in mildly cognitively impaired Insensitive to small changes in pain intensity

32 Assessment of pain

33 Useful in children <7
Assessment of pain Useful in children <7 Useful in non-verbal

34 Assessment of pain

35 Assessment of pain Useful for evaluating chronic pain
Include pain intensity as well as mood, behaviour, thoughts and belifes, physiological effects and their interaction with each other McGill Pain Questionnaire Breif Pain Inventory The Memorial Pain Assessment Card Neuropathic Pain Scale The Leeds Assessment of Neurpathic Symptoms and Signs (LANSS) However, the best way to evaluate and assess pain is to ask about it and listen to what the patient says. Pain is a subjective feeling and hence what the patient says has to be taken to face value. Doctors and nurses frequently underassess pain which leads to undertreatment. Drug seeking behaviour is much rarer than undertreated pain.

36 Assessment of pain Best assessment: Ask & Listen
Features asked for during assessment: Onset Temporal Pattern Site and Radiation Characeter and Intensity Exacerbating and Relieving factors Associated symptoms Response to analgesics, and other interventions Interference with activities of daily living Psychological effects

37 Strategies of Acute Pain Management
Proactiveness Assess, treat, reassess Have predefined pain treatment plan in place Plan should be flexible to include breakthrough pain Multimodal Approach Treat all the possible steps in pain processing Benefits: Synergism, lower side effects, flexibillity Escalating Approach Patient control Patient controlled analgesia

38 Strategies of Acute Pain Management
Systemic Medications Opioids NSAIDs NMDA Receptor Antagonists Alpha-2 adrenergic agonists Calcium Channel Ligands Other Adjuncts: Lidocaine, Corticosteroids Neuraxial Techniques Epidural Analgesia Intrathecal Analgesia Peripheral Nerve/Plexus Blocks Patient Controlled Analgesia Non Pharmacological Methods

39 Strategies of Acute Pain Management: Pre-Emptive Analgesia
Prevention of Central Sensitisation and hyperexcitability induced amplification, at NMDA receptor. Pre-requisites: Adequate depth to block all nociceptive input during surgery Extensive enough to cover the whole surgical field Duration should include both surgical and post-surgical period Theoretically can reduce acute postoperative pain/hyperalgesia and chronic pain after surgery Definite evidence of clinical benefit lacking.

40 Systemic Medications: Opioids
Opioid Receptors: μ, κ and δ receptors Location of receptors: Periphery following inflammation Spinal cord dorsal horn Supraspinally in the brainstem, thalamus and cortex PAG, nucleus raphe magnus and RVM in descending pathway Periaqueductal gray, rostral ventral medulla

41 Systemic Medications: Opioids

42 Systemic Medications: Opioids
Mechanism of Action: Spinal Inhibition of Ca++ influx presynaptically Enhacing K+ efflux postsynaptically Activation of descending inhibitory GABAergic circuit Peripheral Inhibition of release of proinflammatory and pronociceptive substances

43 Systemic Medications: Opioids
Adverse Effects & Problems: Respiratory Depression Nausea and Vomiting Sedation Urinary Retention Euphoria/Dysphoria Constipation Tolerance Dependence and Addiction Tolerance: A change in dose response relationship due to exposure to drug and manifest as higher dose requirment to achieve a particular effect. Develops at varying rates to different effects: Least for analgesia. Usually tolerance to analgesia is not a clinical problem Dependence: development of withdrawal symptoms following drug withdrawal or administration of antagonist. May develop after only a few days of administration. Not a problem if drug is tapered gradually (50%/d) Addiction: Uncontrolled compulsive use despite harm to self and others. Not seen in patients with pain.

44 Systemic Medications: Opioids
Morphine: Most commonly used opioid for postoperative analgesia Routes of Administration IV, IM, SC, PO Dose Upto mg/Kg in titrated boluses IV 15mg q8-12 hrs (Sustained release) Onset of Action: IV: 5 minutes IM, SC: min Duration of Action 4-5 Hours Monitor for Respiratory Depression, Sedation, Nausea & vomiting, Urinary Retention, Biliary spasm

45 Systemic Medications: Opioids
Transdermal Fentanyl Delivery System (Ionsys) Needle free, patient activated system for in-hospital use Iontophoresis Low intensity electrical field used to transport fentanyl across skin into circulation Each double click delivers 40mcg over 10 min For us in adults > 18 years Used for 24 hours or 80 doses iontophoresis -- a process in which a low-intensity electric field, which is generally imperceptible to the patient, is used to rapidly transport fentanyl across the skin and into the circulatory system of the body.

46 Systemic Medications: Opioids
Oral Transmucosal Fentanyl (ACTIQ): To treat breakthrough cancer pain in opioid tolerant patients To be sucked by placing in between cheek and lower gums Each unit to be consumed in 15 minutes Supplied in strengths of 200, 400, 600, 800,1200 & 1600mcg

47 Systemic Medications: Opioids
Pethidine: Phenylpiperidine derivative μ and κ receptor agonist. Also has Na+ channel blocking and Atopinergic action Routes IM, IV, PO Duration of Action 2-4 hours Side effects CNS excitation- seizures, myoclonus due to nor-pethidine toxicity Interaction with MAO inhibitors, antidepressants Dose 100mg IV/IM q 4 hr 300 mg PO q 4 hr Watch for Nausea,vomiting, euphoria, ventillatory depression sedation

48 Systemic Medications: Opioids
Tramadol: Moderate affinity μ receptor agonist. Acts on spinal modulating pathways Inhibition of neuronal NA and Serotonin uptake Stimulation of presynaptic serotonin release Adverse Effects: Nausea & Vomiting Ondansetron interferes with analgesic effect Non addictive, less sedation Dose: 3 mg/kg IM/IV/PO for moderate to severe pain

49 Systemic Medications: Opioids
Pentazocin: Agonist-Weak antagonist Dose mg IV/ 50 mg PO for relief of moderate pain Side Effects: Dysphoria Sedation Tachycardia, Hypertension (catecholamine release)

50 Systemic Medications: Opioids
Butorphanol: Agonist-Antagonist Dose: 2-3 mg IM Also available as intranasal spray Side Effects: Sedation Nausea Tachycardia, hypertension Less dysphoria than other agonist antagonists Antagonise other opioids if used together

51 Systemic Medications: Opioids
Buprenorphine: Semisynthetic, Agonist-Antagonist Routes of administration: IV, IM, Neuraxial, SC, SL, Trasdermal Useful in morphine intolerant patient Ceiling effect for respiratory depression, but not for analgesia. Antiflammatory action Useful in intra-articular injections Prolongs duration of analgesia in peripheral nerve blocks with LA

52 Systemic Medications: Opioids
Opioid equianalgesic dose Drug IV/IM/SC Oral Morphine 10mg 30 Hydromorphone 1.5-2 mg 6-8 Hydrocodone NA 30-45 Oxymorphone I mg 10 Oxycodone 10-15 mg 20 Levorphanol 2 mg 4 Fentanyl 100 mcg Pethidine 100mg 300 Codeine 100 mg 200

53 Systemic Medications: Opioids
Methadone: Synthetic broad spectrum opioid Mu receptor agonist NMDA antagonist Inhibitor of monoamine transmitters Useful in treatment of neuropathic pain Orally well absorbed No dose adjustment in renal disease Drug most commonly used for opioid rotation

54 Systemic Medications: NSAIDs
Mechanism of Action Inhibition of Cyclo-oxygenase enzymes (type 1 & 2) Reduce concentrations of PGE2 PGE2 Centally Increase Substance P and Glutamate Increase sensitivity of second order neurons Decrease NTs from descending pathway Sensitise peripheral nociceptors to histamine and bradykinin

55 Systemic Medications: NSAIDs
Benefits: Opioid Sparing Reduced incidence of opioid side effects Anti-inflammatory effects Adverse Effects: Platelet Dysfunction Gastrointestinal Ulceration Nephrotoxicity Impaired bone healing Hypersensitivity

56 Systemic Medications: NSAIDs
Drug Route & Dose (mg) Precautions Acetaminophen Hr PO Hepatotoxicity Aspirin q4-6 Hr PO Reye’s syndrome Variable half life Ibuprofen 400 mg q 4-6 Hr, PO Naproxen 250mg 6-8 Hr, PO Indomethacin 25 mg Hr, PO Ketorolac 30 mg initialy, followed by mg q 6-8 Hr, IV Correct hypovolumia Elderly Diclofenac 50 mg 8 Hr, PO Piroxicam 20-40 mg q 24 Hr, PO

57 Systemic Medications:α2 Adrenergic Agonists
Primarily preoperative and intraoperative use Clonidine: α2 agonist, α2: α1 biding 220:1 PO, IV, TD, Neuraxial routs Reduced postoperative opioid requirement SE: Sedation, Bradycardia, hypotension Dexmedetomedine: Superselective α2 agonist: α2:α1 binding 1620:1 Supraspinal, Spinal & Peripheral action No respiratory depression

58 Systemic Medications: NMDA Antagonists
Ketamine: NMDA receptor antagonism theoretically reduces central sensitisation, hyperalgesia and opioid tolreance Currently role in postoperative pain relief is uncertain Insignificant difference in pain Clinically insignificant opioid sparing Psychomimetic side effects – hallucination, nighmares

59 Neuraxial Analgesia: Epidural Analgesia
Superior to systemic opioids Efficacy determined by Catheter-incision site congruency Choice of analgesic drugs LA+Opioid Rates of infusion Duration of epidural analgesia At least 2-4 days Type of pain assessment Dynamic Vs Rest

60 Neuraxial Analgesia: Epidural Analgesia
Dermatomal Guide to placement Of epidural cathetres

61 Neuraxial Analgesia: Epidural Analgesia
Recommended catheter insertion sites Location of incision Examples of surgical procedure Congruent epidural placement Thoracic Lung reduction, Radical mastectomy Toracotomy, thymectomy T4-T8 Upper Abdominal Cholycystectomy, esophagectomy, gastrectomy, hepatic resection, whipple’s T6-8 Middle Abdominal Cystoprostatectomy, nephrectomy T7-T10 Lower Abdominal AAA repair, Colectomy, TAH, Radical prostatectomy T8-T11 Lower Extremity Femoral-Popliteal bypass, THR, TKR L1-L4

62 Neuraxial Analgesia: Epidural Analgesia
Opioids: Site of action: Lipophilic: systemic Hydrophilic: spinal Cathetre-Site congruency not essential No motor blockade No hypotension Analgesia superior to systemic opioids Local Anaesthetics Act on spinal nerve roots, dorsal root ganglion or spinal cord itself. High incidence of motor block Hypotension Sign \\\ificant failure rate due to regression and inadequate analgesia

63 Neuraxial Analgesia: Epidural Analgesia
Differences between lipophilic and hydrophilic opioids Property Lipophilic Opioids Hydrophilic Opioids Common Drugs Fentayl, Sufentanyl Morphine, Hydromorphone Onset of analgesia Rapid (5-10 min) Delayed (30-60min) Duration of analgesia Shorter (2-4 Hrs) Longer (6-24 hrs) CSF Spread Minimal Extensive Site of action Spinal ± Systemic Spinal Side Effects Lower nausea and vomiting, pruritus Early respiratory depression Nausea & vomiting, pruritus Early (<6 Hr) and Delayed (> 6 Hr) respiratory depression

64 Neuraxial Analgesia: Epidural Analgesia
Local Anaesthetic-Opioid Combinations Additive Effect Superior analgesia, including dynamic pain relief Limits regression of sensory blockade Decreased LA dose requirement Analgesia superior to IV PCA with opioids

65 Neuraxial Analgesia: Epidural Analgesia
Adjuvants: Clonidine: 5-20 μg/Hr Dose dependent hypotension, bradycardia Epinephrine conc. Of 2.5 μg/ml Ketamine Theoretically useful in attenuating central sensitisation

66 Neuraxial Analgesia: Epidural Analgesia
Doses of Epidural Opioids Drug Epidural Single Dose Epidural continuous Fentanyl μg μg/Hr Sufentanyl 10-50 μg 10-20 μg/Hr Alfentanyl 0.5-1 mg 0.2 mg/Hr Morphine 1-5 mg 0.1-1 mg/Hr Diamorphine 4-6 mg - Pethidine 20-60 mg 10-60 mg/Hr Extended release Morphine 5-15 mg Not recommended Depodur: Extended release morphine. Morphine encapsulated with liposomal delivery system. Upto 48 hrs. only for lumbar. (Controlled release Upto 48 hrs)

67 Epidural Analgesia: Adverse Effects
Hypotension 0.7 – 3 % with epidural LAs Motor Block 2 – 3 % with epidural LAs More with cathetre-incision incongruence Resolves within 2 hours of stopping infusion If persistant, think of Spinal hematoma/abscess, cathetre migration Nausea & vomiting 20 – 50 % with single dose neuraxial opioid 45 – 80 % with continuous opioid infusion Dose depdndent. Due to cephalad migration Less with fentanyl than morphine Treated with Naloxone, Ondansetrone, Droperidol, Metoclopramide, Dexamethasone

68 Epidural Analgesia: Adverse Effects
Pruritus 60% with Opioids; % with LAs Due to cephalad migration and activation of trigeminal nucleus. ?? Itch centre Treated with Naloxone, Droperidol Respiratory Depression Incidence 0.1 – 0.9 % with opioids Equivalent to systemic administration of opioid Early < 6 hr, Delayed > 6 hr Delayed depression with Morphine. Due to cephalad spread Risk Factors: Increasing dose, increasing age, concomitant sedatives, prolonged and extensive surgery, thoracic surgery Treatment: Naloxone 0.5 – 5 μg/kg/hr Urinary Retention Higher than with systemic opioids 10 – 30% with epidural Las Higher with higher infusion rates of LA

69 Epidural Analgesia Benefits: (LA based epidurals)
Better attenuation of stress response to surgery Earlier return of GI function without contributing to bowel dehiscence Decreased postoperative pulmonary complications Decreased incidence of postop MI with thoracic epidural Better postop analgesia Risks: Higher incidence of spinal hematoma with LMWHs Infections: Meningitis, Spinal Abscess (1/10000 with catheter < 4 days) Superficial cellulitis: 4-14 % Catheter migration: Intrathecal, Intravascular, subcutaneous

70 Neuraxial Analgesia: Intrathecal Analgesia
Intrathecal Opioids: Dosing Opioid Dose Fentanyl 5-25 μg Sufentanyl 2-10 μg Morphine mg Diamorphine 1-2 mg Pethidine 10-30 mg

71 Neuraxial Analgesia: Intrathecal Analgesia
Intrathecal Adjuvants: Dosing Drug Dosing Comments Clonidine 15-45 μg Improves quality of blockade Epinephrine mg Prolongs motor block & urinary retention Neostigmine 6.5 – 50 μg Motor blockade Nausea & vomiting

72 Peripheral Regional Analgesia
Pain control superior to systemic opioids Fewer side effects compared to systemic opioids Fewer neurologic and infectious complications compared to neuraxial block Prolonged duration Single injection and continuous catheter techniques

73 Peripheral Regional Analgesia
Indications of peripheral Nerve Blocks Peripheral Nerve Blockade Indications Interscalene Rotator cuff repair, Shoulder arthroplasty, ORIF Supraclavicular Anaesthesia to entire upper limb with single injection Risk of pneumothorax Infraclavicular Surgery on distal upper arm, forearm, wrist and hand Axillary Surgery distal to elbow Separate block for musculocutaneous and intercostobrachial nerves required Midhumeral Surgery of forearm, wrist and hand Provides better block of radial nerve than axillary

74 Peripheral Regional Analgesia
Indications of peripheral nerve blocks Peripheral Nerve Block Indication Lumbar plexus Surgery of knee Femoral Nerve TKA, ACL repair, femoral neck fracture, saphenous vein stripping, muscle biopsy of anterior, medial or lateral thigh Sciatic Nerve AK amputation (combined with lumbar plexus block Ankle replacement, arthrodesis Calcaneal osteotomy Achilles tendon repair Popliteal Fossa BK amputation (combined with saphenous nerve block) Ankle surgery: Triple arthrodesis, Achilles tendon repair Foot surgery: Bunion surgery, Transmetatarsal amputation

75 Peripheral Regional Analgesia
Paravertebral Block: Suited for thoracic, breast surgery, VATS, cholecystectomy, nephrectomy etc Used to treat rib fracture pain Potential space, contains anterior and posterior ramus of the spinal nerve root with white and grey rami communicantes Single injection or continuous catheter technique Comparable to thoracic epidural blockade No hypotension, PONV, urinary retention

76 Peripheral Regional Analgesia
Paravertebral Block

77 Peripheral Regional Analgesia
Other Techniques: Rectus Sheath Block Transversus abdominis plane block Placement of continuous wound catheter Continuous intra-articular infusion of LA Periarticular soft tissue injection of LA Intrapleural or Intraperitoneal Analgesia

78 Peripheral Regional Analgesia
Complications: Intravascular injection Unintentional neuraxial spread Scalene block Lumbar plexus block Paravertebral block Nerve Damage Incidence 1:10000 – 1:30000 Significant nerve damage 1: Direct injury, hematoma, infection, ischemia >90% recover within 1 week 92 -97% within 4-6 weeks, 99% within 1 year

79 Patient Controlled Analgesia
Definition: Any technique of pain management that allows the patients to manage their own analgesia on demand Compensates for interpatient and intrapatient variability in analgesic needs, variability of serum drug levels, administrative delays

80 Patient Controlled Analgesia
Benefits: Better patient satisfaction Better analgesia Equivalent side effects Less demand on nursing time Variables programmed with PCA: Bolus Dose Incremental (demand) dose Lockout interval Background infusion rate

81 Patient Controlled Analgesia
Usual IV Opioid PCA Regime Opioid Demand Dose Lockout (min) Basal Infusion Morphine 1-2 mg 6-10 0-2 mg/hr Hydromorphone mg 0-0.4mg/hr Fentanyl 20-50 μg 0-60 μg/hr Sufentanyl 4-6μg 5-10 0-8 μg/hr Tramadol 10-20 mg 0-20 mg/hr Pethidine 5-25 mg Pentazocin 5-30mg 5-15 Buprenorphin mg 8-20

82 Patient Controlled Analgesia
PCEA Regimes Analgesic Solution Continuous rate (ml/hr) Demand dose (ml) Lockout interval (min) General Regimes 0.05% Bupivacine+ 4μg/ml Fentanyl Bup + 5 μg/ml Fentanyl 0.1% Bup + 5μg/ml Fentanyl 0.2% Rop + 5μg/ml Fentanyl 4 4-6 6 5 2 3-4 10 10-15 20 Thoracic Surgery 0.0625% % Bup + 5μg/ml Fen 2-3 Abdominal surgery 0.125% Bup + 5μg/ml Sufentanyl % Rop + 2μg/ml Fentanyl 3-5 2-5 12 10-20 Lower Extremity Surgery 0.0625%-0.125% Bup + 5μg/ml Fent

83 Patient Controlled Analgesia
Risk Factors: Pulmonary disease OSA Renal or Hepatic dysfunction CHF Closed head injury Altered mental status Lactating mothers

84 Non Pharmacological Methods:
Benefits: Reduce opioid requirement/side effects Attenuate activation of sympathoadrenal system May provide postoperative analgesia Devoid of any side effects Methods TENS Acupuncture/Acupressure Psyhological Approaches Mechanism Spinal cord modulation Endogenous enkephalins Useful adjuvants to pharmacological therapy

85 Special Populations: Pediatric Patients
Barriers to effective pain control in children: Myths about pain and children: Children and infants do not feel pain Pain is not remembered Unable to tell where it hurts Don’t tell the truth about pain Difficulty in assessment Developmental, emotional and cognitive differences Difficulty in conceptualising and quantifying pain Fear of side effects: Respiratory depression, addiction transmitted by c fibres in neonates. the descending modulatory pathway is less developed and so they might feel more pain. There is less precision of impulse transmission at spinal cord.

86 Special Populations: Pediatric Patients Pain Assessment
Behavioural Observational Tools: For neonates and children < 3 yrs CRIES scale Crying O2 requirement for SP)2 > 95% Increased vital signs Expressions Sleeplessness Each parameter score 0-2 Useful for neonatal postoperative pain Neonatal-Infant Pain Scale (NIPS) Facial Expression Cry Breathing Pattern Arms Legs State of Arousal Observed for 1 minute before, during & after a procedure and numeric score applied to each NIPS > 3 implies pain Useful for children < 1 year

87 Special Populations: Pediatric Patients Pain Assessment
Behavioural Observational Tools: For neonates and children < 3 yrs FLACC Scale Face Legs Activity Crying Consolability Each component scored 0-2 Validated for 2 mo – 7 yrs Children’s Hospital of Eastern Ontario Scale (CHEOPS) Cry Facial Expression Verbalisation Touching of affected part Torso movement Position of legs Validated for children 1-7 yrs Score ≥ 4 implies pain Self report :Children > 3 yrs Wong-Baker Faces Scale VAS

88 Special Populations: Pediatric Patients Treatment:
Pharmacological interventions similar to adults PCA/NCA Non Pharmacological Interventions Sensory Rocking,cuddling, touching, massaging, dim lighting, pacifiers, heat/cold application Behavioural Distraction toys, music, videos Security object: blanket, stuffed animals Play therapy Imagery Cognitive Prayers, humor, relacation techniques

89 Special Populations: Elderly Patients
Special Considerations: Clinically significant reduction in intensity of pain perception Communication, Affective, Cognitive, Social and Ideological barriers Difficulty in assessing pain Comorbid conditions Increased adverse effects due to untreated pain and interventions Decreased analgesic requirement Increased sensitivity and decreased clearance Untreated pain is an important contributor to postopearive delerium

90 Summary Pain is both a sensation and an emotion with wide interpersonal variations and the fifth vital sign. Untreated acute pain leads to many detrimental physiological effects and to chronicity. Treatment should include assessment, intervention and reassessment. A multimodal approach targeting the various elements of pain processing should be tried in all patients. LA based epidural analgesia has many advantages over systemic opioid analgesia. Inspite of the various interventions available, postoperative pain is undertreated in a majority of patients, more so in pediatric and geriatric populations.

91 Referrences Barash, Stoelting et al, Clinical Anaesthesia, 6th ed
Miller’s anaesthesia, 6th ed Anaesthesia and Intensive Care Medicine. Volume 6:1 Jan 2005 Recent Advances in Anaesthesia, No. 22. Chapter 74. management of Acute Postoperative Pain Practice Guidelines for Acute Pain management in perioperative setting. Report by ASA task force on acute pain management. Anesthesiology 2004; 100:1573–81 Pharmacology and Physiology in Anaesthetic practice, Stoelting and Miller, 4th Edition Ganong’s Review of Medical Physiology, 22nd edition


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