PAIN MANAGEMENT


ACUTE PAIN MANAGEMENT


Acute pain = pain that occurs as direct result of tissue damage, <3 mos in duration


•  Can occur as a result of trauma, surgical insult, labor, infection, or inflammation


•  Acute postoperative pain → inflammation is a major cause



Treatment


•  Includes opioid & nonopioid meds


•  Opioids commonly used—can be given parenterally, helpful immediately postop


Opioid Rotation


•  Definition: Using different opioids interchangeably & via different routes


•  Presence of major organ dz (liver/kidney dysfx) can markedly ↓ dose required for adequate clinical response


•  Lack of complete cross tolerance between different opioids


→ Essential to use lower than equianalgesic doses


•  Oral & parenteral doses often dissimilar (due to pharmacokinetic differences)


•  Opioid-associated itching: Dilute naloxone & benadryl → can both be used


• Naloxone 400 mcg in 1 L of LR or NS given at 75 mL/hr


• Avoid benadryl in advanced age










MULTIMODAL APPROACH TO PAIN CONTROL (ALSO SEE CHAPTER 27)


Analgesic Delivery Systems


•  PO


• Not optimal for immediate postop pain (delayed time to peak effect)


• Opioids commonly combined with COX inhibitors


•  SC/IM


• Less desirable routes (pain on injection & erratic absorption)


• Cyclical period of sedation → analgesia → inadequate analgesia common


•  Intravenous administration


• Requires close respiratory monitoring


• Common in PACU, ICU, & specialized units


•  Patient-controlled analgesia (PCA)


• Allows pt to self-administer opioids with button push


• Physician specifies dose, minimum time period between doses (lockout), basal infusion rate, max delivered dose



Neuraxial Analgesia


•  Intrathecal or epidural routes; effective for postop pain after abd, pelvic, thoracic, & orthopedic surgeries of lower extremity


•  Opioid infusions often combined with local anesthetics (bupivacaine, lidocaine, ropivacaine)


•  Clonidine & buprenorphine also used epidurally


Epidural Opioids


•  Site of action = pre- & postsynaptic receptors in dorsal horn substantia gelatinosa


•  Opioid drugs enter CSF at rate dependent on physicochemical properties


• Molecular weight, pKa, oil:water solubility


•  Direct transport via spinal cord blood supply can occur


•  Diffusion through dural cuff regions to spinal cord can occur


•  Lipid-soluble opioids (sufentanil, fentanyl) enter spinal cord faster


• Also eliminated faster by vascular uptake, leading to a short duration of action


•  Morphine = water-soluble opioid (slower action onset, longer duration of action)




Epidural Clonidine


•  Dose = 3–5 mcg/kg; can be added to epidural mix (local or opioid)


•  Prolongs duration of epidural local anesthetic by ≈50%


•  ↓ epidural opioid requirements ≈30%


•  Side effects: Severe bradycardia (if used >1 mcg/kg/hr)


Epidural Placement Levels



Signs of an Inadequate Epidural


•  Pain at rest & with movement (pain score >5)


•  Tachycardia


•  ↑ respiratory rate


•  For thoracic & abd cases


→ Inability to breathe deeply, cough, use incentive spirometer


Testing of Epidurals


•  2% lidocaine with 1:200,000 epinephrine or 0.25% bupivacaine with 1: 200,000 epinephrine


• Give 3 mL of either via epidural → check BP, motor block & pain relief


•  May repeat 3 mL after 3–5 min


•  Consider replacing epidural if no pain relief after 8 mL of test dose over 10 min


“Splitting” Epidural with IV PCA


•  Technique:  Add IV PCA in addition to epidural infusion (must simultaneously remove opioids from epidural infusion)


•  May be necessary for


• Pt with opioid dependence


• Incomplete incisional coverage from epidural


• Upper & lower body surgeries (trauma victims)


• Large surgical incision


• Lower level epidural catheter placement



Intrathecal Opioids


•  Act on substantia gelatinosa of the spinal cord


•  Potent analgesia due to central localization of receptors


•  Side effects are mediated by mu receptors (in brain & brainstem)



Mixed Agonists/Antagonists


•  Block effects of high doses of morphine-like drugs


• By competing with morphine-like drugs to bind to mu opioid receptor


•  Produce partial agonist effects at κ (kappa) and/or δ (delta) opioid receptors



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Aug 28, 2016 | Posted by in ANESTHESIA | Comments Off on PAIN MANAGEMENT

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