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Toronto Notes 2019 Pain Management
Pharmacological Management of Acute Pain
• askthepatienttoratethepainoutof10,orusevisualanalogscale,todetermineseverity • pharmacologicaltreatmentguidedbyWHOanalgesialadder
• patientcontrolledanalgesia(PCA)
■ involves the use of computerized pumps that can deliver a constant infusion and bolus breakthrough doses of parenterally-administered opioid analgesics
■ limited by lockout intervals
■ most commonly used agents: morphine and hydromorphone
■ see Table 17, A26 for suggested infusion rate, PCA dose and lockout intervals
Anesthesia A25
Table 15. Commonly Used Analgesics
• Asthma
• Coagulopathy
• GI ulcers
• Renal insufficiency
• Pregnancy, 3rd trimester
Opioid Conversion Parenteral (IV)
Cautionary Use of NSAIDs in Patients with
Acetaminophen
Tylenol®
First-line for mild acute pain
Unclear, hypothesized cyclooxygenase-2 (COX-2) inhibition Unclear, hypothesized modulation of endogenous cannabinoid system
Limited by analgesic ceiling beyond which there is no additional analgesia Opioid-sparing
Max dose of 4 g/24 h
Considered relatively safe
Liver toxicity in elevated doses
Relative Dose to 10 mg Morphine IV
200 mg PO
NSAIDs
Aspirin®, ibuprofen, naproxen, ketorolac (IV)
Mild-moderate pain
Non-selective COX-1 and 2 inhibition reducing proinflammatory prostaglandin synthesis
Limited by analgesic ceiling beyond which there is no additional analgesia Opioid-sparing
Significant inter-individual variation in efficacy
Gastric ulceration/bleeding Decreased renal perfusion Photosensitivity Premature closure of
the ductus arteriosus in pregnancy
Opioids
Oral: codeine, oxycodone, morphine, hydromorphone Parenteral: morphine, hydromorphone, fentanyl
Oral: moderate acute pain
Parenteral: moderate-severe acute pain
Dampens nociceptive transmission between 1st and 2nd order neurons in the dorsal horn
Activates ascending modulatory pathways resulting in release of inhibitory neurotransmitters
Inhibits peripheral inflammatory response and hyperalgesia
Affects mood and anxiety – alleviates the affective component of perceived pain
No analgesic ceiling (except for codeine)
Can be administered intrathecally (spinal block) or by continuous infusion
Respiratory depression
Constipation and abdominal pain Sedation
N/V
Pruritus
Confusion (particularly in the elderly) Dependence
Equivalent Oral Dose 30 mg
4 mg
200 mg 20 mg N/A
Examples Indications
Mechanism of Action
Dosing/ Administration
Side Effects/ Toxicity
Table 16. Opioids
Agent
Codeine
Meperidine (Demerol®)
Morphine
Oxycodone Controlled Release (Oxyneo®)
Oxycodone Regular Tablet (Oxy IR®)
Hydromorphone (Dilaudid®)
Fentanyl
Morphine Hydromorphone Codeine Oxycodone Fentanyl IV
10 mg 2 mg 120 mg N/A 100 μg
75 mg IV
10 mg IV 20 mg PO
15 mg PO
15 mg PO
2 mg IV 10 mg PO
100 μg IV
(no IV)
Moderate Dose
15-30 mg PO
2-3 mg/kg IV
0.2-0.3 mg/ kg IV 0.4-0.6 mg/ kg PO
10-20 mg PO (no IV)
5-15 mg PO
40-60 μg/kg IV 2-4 mg PO
2-3 μg/kg IV
Onset
Late (30- 60 min)
Moderate (10 min)
Moderate (5-10 min)
Late (30- 45 min)
Moderate (15 min)
Moderate (15 min)
Rapid (<5 min)
Duration
Moderate (4-6 h)
Moderate (2-4 h)
Moderate (4-5 h)
Long (8-12 h)
Moderate (3-6 h)
Moderate (4-5 h)
Short (0.5- 1 h)
Special Considerations
Primarily post-operative use, not for IV use. Not ideal as analgesic effect depends on highly variable CYP2D6 metabolism
Anticholinergic, hallucinations, less pupillary constriction than morphine, metabolite build up may cause seizures
Decreased use for pain management due to potential toxicity compared to other opioids. Typically reserved to treat post-operative shivering. Absolute contraindication in patients taking MAO-inhibitors
Histamine release leading to decrease in BP
Do not split, crush, or chew tablet (but can be difficult to swallow)
Percocet® = oxycodone 5 mg + acetaminophen 325 mg
Less pruritus, N&V, and sedation compared to morphine
Transient muscle rigidity in very high doses
Common Side Effects of Opioids
• N/V
• Constipation
• Sedation
• Pruritus
• Abdominal pain
• Urinary retention
• Respiratory depression
When prescribing opioids, consider: • Breakthrough dose
• Anti-emetics
• Laxative
PCA Parameters
• Loading dose
• Bolus dose
• Lockout interval
• Continuous infusion (optional) • Maximum 4 h dose (limit)
Advantages of PCA
• Improved patient satisfaction
• Fewer side effects
• Accommodates patient variability • Accommodates changes in opioid
requirements
Patient Controlled Opioid Analgesia vs. Conventional Opioid Analgesia for Post- Operative Pain
Cochrane DB Syst Rev 2006;4:CD003348
Purpose: To evaluate the efficacy of patient controlled analgesia (PCA) as compared to conventional ‘as-needed’ analgesia administration providing pain relief in post- operative patients.
Methods: Meta-analyses of randomized controlled trials comparing PCA vs. conventional administration of opioid analgesia. Assessment employed a visual analog scale (VAS) for pain intensity along with overall analgesic consumption, patient satisfaction, length of stay, and adverse side effects.
Results: 55 studies with a total of 2,023 patients receiving PCA and 1,838 patients with standard as-needed opioid administration. PCA provided significantly better pain control through 72 h post-operatively, but patients consumed significantly more opioids (>7 mg morphine/24 h, p<0.05) Significantly more patients reported pruritus in the PCA group compared to control with a number needed to harm of 13. No significant difference in overall length of stay in hospital, sedation level, N/V, or urinary retention. Conclusions: PCA is more effective than standard as-needed administration for reducing post-operative pain. However, patients using PCA consume more opioids overall and have more pruritus.