Acute and Chronic Pain

Thomas Horton, Soibhan Kelley

  • There are physiological AND emotional components to pain. Biopsychosocial factors must be addressed. Ex: anxiety/depression, physical debility, and poor social support. Many pts will never be completely free of pain, so it is important to set realistic expectations.
  • Central sensitization is a phenomenon where the nervous system persists in a state of high reactivity which lowers the threshold for pain stimuli. Two characteristics of centralized pain are allodynia (pain from non-painful stimuli) and hyperalgesia (painful stimuli perceived as more painful).

Pharmacologic Therapy

Opioid Therapy

Opioids: Frequently used in hospital for acute pain. Limit use as much as possible in chronic pain as it contributes to long-term central sensitization. May benefit some pt populations but should always be used as a component of a comprehensive, multimodal, pt-specific treatment plan.

  • Refer to section under “Opioids: General Principles and Conversions” for OME equivalents
    • If >80 OME per day, ensure pt is prescribed naloxone
    • If >120 OME per day, refer to pain clinic
  • Common choices for acute pain in hospital (always start at low end for opioid naïve):
    • Oxycodone (PO) 5-10mg q4 to 6 hours prn
    • Hydromorphone (IV) 0.25 to 1mg q2 to 3 hours prn
  • For pts on opioids at home, should always continue in hospital to avoid withdrawal unless clinically contraindicated. Can always titrate dose as needed.
  • Tramadol - Has opioid and NSAID properties. Of note, tramadol also inhibits serotonin and norepinephrine reuptake. Metabolized by CYP3A4 and CYP2D6 so there is variability between pts. Typical dose: 25 to 50mg q4 to 6 hours PRN
  • Buprenorphine – sublingual (Subutex, suboxone), buccal (Belbuca), transdermal (Butrans). Increased affinity to mu opioid receptor. Slower disassociation leads to prolonged analgesia. Preferably acts on spinal receptors (vs CNS). Can precipitate withdrawal. Increase 1st pass metabolism → low bioavailability. Ok to use in mild-mod hepatic dysfunction but avoid in severe impairment. See Opioid section for dosing.

Adjuvant Therapy

  • Acetaminophen: 650mg q6hr or 1g q8h. <3g/day. (<2g in liver pts)
    • Avoid if you are worried about masking fevers
  • NSAIDs: a great option for acute pain, especially musculoskeletal, headache, and nephrolithiasis in eligible pts (IV/PO ketorolac, ibuprofen, naproxen, etc.)
    • Avoid in acute or chronic kidney disease and ↑ risk of bleeding. Caution in CAD/PVD
  • Topical analgesics: best for localized pain but utilized frequently as part of a multimodal regimen
    • Lidocaine ointment/patches, menthol salicylate gel, Diclofenac gel, Capsaicin gel, Morphine gel (typically limited to oncology pts with tumor breakdown through skin)
    • Neuropathic pain (sciatica, peripheral neuropathy): Neuropathic agents are best for neuropathic pain but can be tried for chronic pain or as part of acute pain regimen. SNRIs and TCAs can provide additional benefit if a pt has comorbid depression, anxiety, or insomnia (TCA). Most agents take 6-8 weeks for peak effect.
    • Gabapentin (Initial: 100 to 300 mg 1 to 3 times daily). Can be used for acute pain
    • Pregabalin (Initial: 25 to 150 mg/day in 2 to 3 divided doses). Has better bioavailability. May work in pts who did not tolerate or did not have success with gabapentin
    • Duloxetine (Initial: 30 mg daily for 1 to 2 weeks, then increase to 60 mg daily as tolerated)
    • Amitriptyline (Initial: 10 to 25 mg once daily at bedtime)
  • MSK Pain (pulled muscle, muscle spasm):
    • Muscle relaxants: Should be used temporarily and intermittently but some benefit from longer term use. Great for paraplegia, spinal injury, and spasticity o Methocarbamol (Initial: 1.5 g 3 to 4 times daily for 2 to 3 days then decrease dose to ≤4.5 g/day in 3 to 4 divided doses). Preferred initial agent as has least SE.
    • Tizanidine (Initial: 2 to 4 mg every 6 to 12 hours as needed and/or at bedtime) – important to watch out for withdrawal in pts that take frequently at home. o Cyclobenzaprine (Initial: 5 to 10 mg once daily before bedtime)
    • Metaxalone (Oral: 800 mg 3 to 4 times daily)
    • NSAID, Tylenol, and topical analgesics are also effective
  • Visceral pain (pain from organ distension such as splenomegaly):
    • Steroids, opioids, NSAIDs
  • Other:
    • NMDA antagonists: usually prescribed by our pain management colleagues but worthwhile to think about as a potential option if a pt’s pain continues to be difficult to control
      • Ketamine (IV infusion): SE includes AMS/delirium, hallucinations, and dissociation.
      • Memantine (PO)

Alpha 2 agonists (central pain): not commonly utilized in everyday practice, but helpful in certain pts with chronic pain (off-label), guanfacine vs. clonidine

Acute Pain for Special Populations

Renal dysfunction

  • Check that meds are renally dosed and start with non-sedating options. Avoid NSAIDs, morphine, and codeine.
    • Acetaminophen and topicals
    • Opioids: oxycodone 2.5 to 5 mg, IV hydromorphone 0.25-0.5mg, fentanyl IV 25 to 50mcg
    • Gabapentin: Start with spot 100mg. Be extremely careful with quick up titration in CKD due to sedation risk.
    • Methocarbamol: no specific renal dosing, try 500-750mg initially

Cirrhosis

Always avoid NSAIDs, morphine, codeine, hydromorphone (may be OK in mild to moderate cirrhosis). 

  • Acetaminophen (2g max/d) and topicals are safe
  • Gabapentin: start with spot 100mg
  • Methocarbamol: no specific hepatic dosing, try 500 mg initially
  • Opioids
    • At risk for increased accumulation of toxic metabolites or increased bioavailability due to decreased first pass metabolism, liver synthetic dysfunction, and protein binding (hypoalbuminemia) i.e. opioids are stronger and last longer than expected
    • May precipitate hepatic encephalopathy
    • Degree of hepatic dysfunction determines risk of toxicity
      • Compensated cirrhosis without synthetic dysfunction is no different than general population
    • Avoid opioids if decompensated especially with hepatic encephalopathy
    • Generally, decrease typical starting doses by 50% and increase dosing intervals (start low and go slow)

History of substance use disorder

  • Overnight, always review handoff as day team likely has specific plan in place.
  • With substance use history, typically rely on multimodal agents as above. Pts who are in recovery may prefer to avoid opioids themselves.
  • However, pts with OUD can and do have acute, severe pain due to injury, infections, procedures, etc. NEVER withhold opiates if clinically appropriate, regardless of substance use history.

Consider addiction psychiatry consult, palliative care consult, and/or chronic pain service consult

  • Uncontrolled pain despite significant opioids: consider consulting the Pain Service for ketamine infusion (or lidocaine infusion if neuropathic pain component)
    • The consult is "inpatient consult to anesthesia or pain service." Most often, you will select "Chronic Pain Service" for ketamine drips.
      • "Acute Pain" may be appropriate for a peripheral nerve block (PNB). Less frequently used service, but would consider PNB In patients with well-localized, severe pain If: opioid Intolerant, are at risk of respiratory depression related to systemic opioids (OSA, lung disease, age), or pain is poorly managed despite systemic medication.
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