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Acute Perioperative Pain Management Dr. Mahmoud Abdel-Khalek What is pain? An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage IASP Pain Definition (1994, 2008) IASP: International Association for the study of Pain Introduction: Nociception Introduction: Nociception Refers to the detection, transduction and transmission of noxious stimuli Substances generated from thermal, mechanical or chemical tissue damage, activate free nerve endings, which we refer to as nociceptors These afferent fibers have their cell body located in the dorsal root ganglion From DRG axons go into dorsal horn of the spinal cord where axons synapse with the second order neuron as well as with regulatory interneuron. In addition synapses occur with the cell bodies of the sympathetic nervous system and ventral motor nuclei, either directly or through the internuncial neurons The cell body of the second order neuron lies in the dorsal horn. Axonal projections of this neuron cross to the contralateral hemisphere of the spinal cord and ascend to the level of the thalamus In the thalamus, the second order neuron synapses with a third order afferent neuron, which sends axonal projections into the sensory cortex Postoperative Pain Postoperative pain can be divided into acute pain and chronic pain: Acute pain is experienced immediately after surgery (up to 7 days); Pain which lasts more than 3 months after the injury is considered to be chronic. Why Treat Pain? Basic human right! ↓ pain and suffering ↓ complications – next slide ↓ likelihood of chronic pain development ↑ patient satisfaction ↑ speed of recovery → ↓ length of stay → ↓ cost ↑ productivity and quality of life Adverse Effects of Poor Pain Control CVS: MI, dysrhythmias Respiratory: atelectasis, pneumonia GI: ileus, anastomotic failure Endocrine: “stress hormones” Hypercoagulable state: DVT, PE Impaired immunological state: Infection, cancer, delayed wound healing Psychological: Anxiety, Depression, Fatigue Pathophysiology Inadequately treated pain following chest& abdominal incisions → diaphragmatic muscle splinting → ↓ ability to cough& clear secretions → atelectasis, hypoxemia& pneumonia Nociceptive stimuli reaching the spinal cord → sympathetic stimulation → hypertension, tachycardia → ↑ heart work load → ↑ oxygen demand → myocardial ischemia in vulnerable patients& myocardial infarction Pathophysiology Also increased sympathetic tone → ↑ intestinal secretions& slows gut motility& ↑ smooth muscle tone → gastric stasis, nausea and vomiting, ileus and urinary retention Poorly controlled acute pain → initiation and maintenance of stress response seen with the trauma of major surgery → hypercoagulability → DVT, p. embolism, MI, ↓ immunity, hypermetabolism, Hyperglycemia, protein catabolism and delayed wound healing Pain Assessment Pain History O – Onset P – Provoking / Palliating factors Q – Quality / Quantity R – Radiation S – Severity T – Timing Pain Assessment Severity: Visual Analogue Scale Severity of postoperative pain Pain Assessment Current Pain Medications Accuracy and detail are very important: Name, dose, frequency, route i.e. Oxycontin 10mg PO TID Co-existing conditions Renal disease: avoid morphine, NSAID’s Vomiting: avoid oral forms of medication Drug allergies Document drug, adverse reaction and severity Intolerances Nausea / vomiting, hallucinations, disorientation, etc. Methods to Treat Pain Pharmacologic Medications (po, iv, im, sc, pr, transdermal) Acetaminophen NSAIDs e.g. Aspirin, diclofenac, ibuprofen.. etc. Opioids e.g. Morphine, pethidine, fentanyl, codeine.. etc. Gabapentin NMDA antagonists e.g. ketamine Alpha-2 agonists Procedures Regional Anesthesia LA infiltration at incision site Surgical Intervention Removal of cause of pain e.g. distended urinary bladder WHO Analgesic Ladder Acetaminophen (aka Paracetamol) First-line treatment if no contraindication It is relatively safe It is analgesic and antipyretic Mechanism: thought to inhibit prostaglandin synthesis in CNS → analgesia, antipyretic It does not cause gastric irritation Typical dose: 650 to 1000 mg PO Q6H Max dose: 4 g / 24 hrs from all sources Warning: ↓ dose / avoid in those with liver damage NSAIDs Also, first-line treatment Mechanism Block cyclooxygenase (COX) enzyme → ↓ prostaglandin synthesis COX-2 → Prostaglandins → pain, inflammation, fever COX-1 → Prostaglandins → gastric protection, hemostasis NSAIDs Warnings: ↓dose / avoid if GI ulceration Bleeding disorders / Coagulopathy Renal dysfunction Asthma Allergy Opioids They are highly effective class of analgesics which operates at several levels in the nervous system Intramuscular morphine or meperidine on prn basis remains the most popular form of acute postoperative pain management at most hospitals Opioids: mechanism of action They dampen the transmission of nociceptive stimuli by binding to opioid receptors within substantia gelationsa of the dorsal horn of spinal cord They release inhibitory neurotransmitters such as noradrenaline, serotonin and GABA Decrease inflammatory response in the periphery Affect mood and anxiety Intramuscular opioid administration limitations Responsibility for management of pain is delegated to the nursing staff, who err on the side of caution in the administration of opioids. They tend to give too small a dose of drug too infrequently because of exaggerated fears of producing ventilatory depression or addiction. Because the administration of drugs is left entirely to the discretion of the nursing staff, the degree of empathy between nurse and patient affects analgesic administration. Because the measurement of pain is difficult, it is seldom possible to adjust the dose of drug to match the extent of pain. There are enormous variations in the extent of analgesic requirements depending upon the type of surgery, pharmacokinetic variability pharmacodynamic variability, etc. Opioids: Side effects Nausea / Vomiting Sedation Respiratory Depression Pruritus Constipation Urinary Retention Ileus Tolerance Opioids Morphine Most commonly prescribed opioid in hospital Metabolism: Conjugation with glucuronic acid in liver and kidney Morphine-3-glucuronide (inactive) Morphine-6-glucuronide (active) Impaired morphine glucuronide elimination in renal failure Prolonged respiratory depression with small doses Due to metabolite build-up (morphine-6-glucuronide) Opioids Hydromorphone (Dilaudid) Better tolerated by elderly, better S/E profile Preferred over morphine for renal disease patients Low cost, IV and PO forms available Oxycodone Good S/E profile, but $$ PO form only Percocet (oxycodone + acetaminophen) Opioids Codeine 1/10th Potency of morphine Metabolized into morphine by body Ineffective in 10% of Caucasian patents Challenge with combination formulations Meperidine (Demerol) Not very potent Decreases seizure threshold, dystonic reactions Neurotoxic metabolite (normeperidine) Avoid in renal disease Opioids - Formulations Short acting forms Need to be dosed frequently to maintain consistent analgesia Controlled Release forms Provides more consistent steady state level Helpful for severe pain or chronic pain situations Never crush / split / chew controlled release pills Management of Opioid Overdose Ddx: Seizure, stroke Hypoxia, Hypercarbia Hypotension Other medication effect Severe electrolyte or acid base abnormalities MI Sepsis …..etc. Management of Opioid Overdose For ↓level of consciousness, somnolent patient: Stimulate patient Vitals/Monitors/Lines Airway Breathing Circulation CODE BLUE? Management of Opioid Overdose Opioid Reversal Naloxone - opioid antagonist Reverses effects of opioid overdose (for 30-45min) MUST BE diluted before use: 0.4mg ampule Dilute: 1mL Naloxone + 9mL Saline = 0.04 mg/mL Give 0.04 to 0.08 mg (1 to 2 mL) IV q3-5 minutes If no change after 0.2mg, consider other causes Opioids: PCA Patient-controlled analgesia (PCA) permits the patient to administer the delivery of his own analgesic by activating a button, which then triggers the intravenous delivery of a predetermined dose of an opioid such as morphine. Limits are set on the number of doses per four-hour period and on the minimum time that must elapse between doses (lockout interval). The pharmacokinetic advantage of PCA is that by self administering frequent, small doses, the patient is able to come closer to achieving a steady state analgesic level in the blood, avoiding the high peaks and low troughs that can be found with intermittent (intramuscular) opioid administration. Benefits of PCA PCA has been shown to provide equivalent analgesia with less total drug dose, less sedation, fewer nocturnal disturbances and more rapid return to physical activity. In addition, patient acceptance is high since patients have a significant level of control over their pain management. PCA analgesia is not without side effects, the most common of which is nausea and vomiting, Excessive sedation and pruritus Standardized orders provide “as needed” orders for medications to counteract both nausea and pruritus. Benefits of PCA Although it does not obviate the need for close monitoring, PCA frees nursing personnel from administering analgesic medication. Since patients titrate their own therapy with PCA, they must be capable of understanding the principle, willing to participate and physically able to activate the trigger. Consequently, use is prohibited at the extremes of age as well as in very ill or debilitated patients Typically, the PCA modality is used for 24-72 hours. The patient must be capable of oral (fluid) intake prior to converting from PCA to oral analgesics Opioids – PCA Management of Opioid Side Effects Nausea / Vomiting Ondansetron (Zofran) Dimenhydrinate (Gravol) Metoclopramide (Maxeran) Changing medication(s) / ↓ dose Pruritus Diphenhydramine (Benadryl) Changing medication(s) / ↓ dose Gabapentin Anti-epileptic drug, also useful in: Neuropathic pain, Postherpetic neuralgia, CRPS Blocks voltage-gated Ca channels in CNS Additive effect with NSAIDs Reduces opioid consumption by 16-67% Reduces opioid related side effects Drowsiness if dose increased too fast Regional Anesthesia Involves blockade of nerve impulses using local anesthetics (LA) LA bind sodium channels preventing propagation of action potentials along nerves Wide variety of LA with different characteristics: i.e. Lidocaine – fast onset, short duration of action i.e. Bupivacaine (Marcaine) – slow onset, longer duration Central neuraxial analgesia Central neuraxial analgesia involves the delivery of local anesthetics and/or opioids to either the intrathecal (spinal) space or the epidural space. Opioids added to the (spinal) local anesthetic solution provide long-lasting analgesia after a single injection, lasting well into the post-operative period The duration of effect is directly proportional to the water-solubility of the compound, with hydrophilic compounds such as morphine providing the longest relief Epidural catheters are safe and easy to insert Epidural Analgesia Epidural analgesia can be used to provide pain relief for days through the infusion of a solution containing local anesthetic, opioid or both. The infusion is usually delivered continuously Continuous epidural infusions provide a steady level of analgesia while reducing the side-effects associated with bolus administration Overall, epidural analgesia can provide highly effective management of post-operative pain Benefits of Epidural Analgesia Superior analgesia to IV, PCA in open abdominal procedures & specifically in colorectal surgery Reduce incidence of paralytic ileus Blunt surgical stress response Improves dynamic pain relief Reduces systemic opiate requirements Regional Anesthesia Peripheral Nerve Blocks Upper Limb: Brachial plexus Lower Limb: Femoral, sciatic, popliteal, ankle Abdomen: TAP blocks Thoracic: Paravertebral, intercostal blocks Use of Ultrasound Imaging has revolutionized peripheral nerve blockade Safety? Accuracy / Improved Success Efficiency Contraindications to Neuraxial Blockade Absolute: Pt refusal or allergy to LA Uncorrected hypovolemia Infection at insertion site Raised ICP Coagulopathy Relative: Uncooperative patient Fixed cardiac output states Systemic infection/sepsis Unstable neurological disease Significant spine abnormalities or surgery Peripheral Nerve Blocks Almost any peripheral nerve that can be reached with a needle can be blocked with local anesthetics The brachial plexus, intercostal and femoral nerves are examples of nerves which are commonly blocked to provide post-operative analgesia A block may be used as the sole method of post-operative analgesia or it may be useful as an adjunct to decrease the required dose of systemic opioids The major drawback of this method of post-operative analgesia is that the duration of effect of a single block is limited, usually to less than 18 hours A typical example of the use of a peripheral nerve block for postoperative pain would be the use of a femoral/sciatic nerve block for a patient undergoing total knee arthroplasty. The block would be augmented with oral opioids and other adjuncts Summary Accurate pain assessment Use Multimodal pain management Superior analgesia, ↓ side effects means: Improved patient satisfaction Better rehabilitation Earlier functional return Earlier discharge from hospital ↓ likelihood of chronic pain Reduced health care costs Thank you