General Tips
Pain is the most common presentation in the ED (75-80%)
Pain is a symptom, NOT a diagnosis
Pain is unique to the individual and is influenced by a multitude of factors to include culture, sex, age, severity of injury, co-morbidities, etc.
Titrate treatment to patient's functionality and pain perception
Vital signs cannot be used to accurately assess pain in the ED
Achieving analgesia with minimal side effects is important and a nuanced skill
Goal of treatment is not complete eradication of pain, but to reduce to acceptable levels for safe discharge or bridge to admission
Reassess pain frequently to determine analgesia efficacy
avoid relying on personal impressions on suspected pain ratings
Acetaminophen (Tylenol)
MOA: COX-3 inhibitor
Duration: 4-6hrs
Dosing
PO: 325mg, 500mg, 650mg, 975mg, 1,000mg every 6hrs
IV: 1000mg every 6hrs
PR: 650mg every 6hrs
Antipyretic and analgesic but NO peripheral anti-inflammatory properties
2017 study found acetaminophen & Ibuprofen is as efficacious as opioid containing combinations for musculoskeletal pain
In mild-moderate pain, acetaminophen is the first line analgesic
safe in pregnancy and lactation (Category B 1st - 3rd trimester)
Maximal daily dose 4,000mg/d or 3,000mg/d in patients with liver disease or the elderly
NSAIDs
MOA: nonselective COX-1, 2 inhibitors reducing prostaglandins
Common medication dosing
Ibuprofen
PO: 200mg, 400mg, 600mg every 6hrs
Ketorolac
IV: 15mg, 30mg every 6hrs
Naproxen
PO: 500mg every 12hrs OR 250mg every 6-8hrs
Evidence to suggest Ibuprofen maximal pain efficacy dose is 400mg. Higher doses do not improve pain efficacy, but increases risks for adverse effects
Opioids
MOA: agonistic effects on Mu opioid receptors in central and peripheral nervous system
Morphine:
IV: 0.1mg/kg every 4-6hrs
PO: 10mg every 4-6hrs
Adverse effects: Hypotension, respiratory depression, sedation, histaminergic reaction, constipation
Metabolites excreted by the kidney, so will cause accumulation in renal failure patients
Fentanyl:
IV: 1mcg/kg every 1-2hrs.
Hemodynamically stable
Adverse effects: Sedation, Constipation, rigid chest syndrome
metabolized in liver, can cause accumulation in hepatic disease
Hydromorphone
IV: 0.015mg/kg every 4-6hrs
Adverse effects: Hypotension, respiratory depression, sedation, euphoria, constipation, histaminergic reaction
Oxycodone/Hydrocodone:
PO: 5-10mg every 4-6hrs
Adverse effects: Hypotension, respiratory depression, sedation, histaminergic reaction, constipation
IV | PO | IV/PO ratio | Equivalence dose ratio Morphine:X | |
Morphine | 10mg | 30mg | 1:3 | n/a |
Hydromorphone | 1.5mg | 7.5mg | 1:5 | IV 7:1; PO 4:1 |
Fentanyl | 0.1mg (100mcg) | n/a | n/a | IV 300:1 |
Oxycodone | n/a | 20mg | n/a | PO 3:1 |
Hydrocodone | n/a | 30mg | n/a | PO 1:1 |
Sodium Channel Blockers
MOA: Inhibits sodium channels and inhibits glutamate release
Lidocaine
Injection 1%, 2%
topical 4%, 5%
maximal safe dose 4-5mg/kg (5-7mg/kg with epinephrine)
Bupivacaine
injection 0.25%, 0.5%, 0.75%
Maximal safe dose 2-3mg/kg
Ropivacaine
Injection 0.2%, 0.5%, 1%
Maximal safe dose 2-3mg/kg
Adverse effects
Allergic Reaction: typically in amide compounds (does not cross react to ester compounds)
Local Anesthetic Systemic Toxicity (LAST)
Cardiovascular effects: bradycardia, hypotension, AV block, decreased cardiac output, leading to cardiac and pulmonary arrest
Neurologic effects: numbness, lightheadedness, visual and auditory disturbances, convulsions, coma
Dopamine Receptor Antagonists
MOA: antagonism to D2, D3 receptors
sometimes used to treat acute headaches, gastroparesis, cyclic vomiting syndrome, cannabinoid-induced hyperemesis
Metoclopramide
IV/PO: 5mg, 10mg, 20mg q4-12hrs
Max dose 40mg/d
Prochlorperazine
IV/IM/PO: 10mg q6hrs
Max dose 40mg/d
Chlorpromazine
IV/PO: 10mg q6hrs
Max dose: 25mg/d
Haloperidol
IV/IM/PO: 5-10mg q4hrs
Droperidol
IV/IM 1.25-10mg q1-2hrs
Adverse effects: Cardiac arrhythmia (QT prolongation), Extrapyramidal Syndromes, Constipation, Hypotension, Dry mouth
Dexmedetomidine
MOA: alpha 2 adrenergic receptor agonist dampening CNS sympathetic pathways
Dose
Bolus: 0.5-1 mcg/kg
Infusion: 0.4-1.4 mcg/kg/hr
Adverse effects: Hypotension, Bradycardia
Ketamine
MOA: NMDA receptor antagonist
Pain/subdissociative dose
Bolus: 0.1-0.5mg/kg
Infusion: 0.1-0.2mg/kg/hr
Adverse effects: agitation, emergence reaction
Anticonvulsants
MOA: sodium channel inhibitors
Gabapentin
PO: 100mg TID, titrated up to 1,200mg TID
Max dose: 3,600mg/d
Pregabalin
PO: 50-75mg, titrated up to 300mg
Max dose: 600mg/d
Adverse effects: fatigue, dizziness, ataxia, thrombocytopenia, angioedema, rhabdomyolysis
Clinical Pearls: Back Pain
Back pain leads to more disability than any other condition (depression, stress, exacerbation of underlying conditions)
Pain recurs in approximately 70% of patients treated in the ED
1st line treatments: NSAIDs, trigger point injections, topical lidocaine, muscle-relaxants
2nd line agents: Opioids
Resume activity as soon as possible
Recent systematic review and meta-analysis found NSAIDs resulted in a small but clinically significant improvement in back pain with an NNT = 6 (95% CI 4-10) to achieve clinically important pain reduction over placebo. NSAIDs were also shown to increase the risk of GI adverse events by 2.5x (95% CI 1.2-5.2)
Meta-analysis assessing acetaminophen for low back pain resulted in no difference in pain reduction between paracetamol (4g/d) and placebo at 1w, 2w, 4w, 12w for back pain reduction. Additionally, paracetamol did not affect quality of life, function, global impression of recovery, and sleep quality for all included periods.
2017 ACP/APS joint recommendations indicate that acetaminophen, either as mono-therapy or combined with NSAIDs, is not effective for lower back pain.
Opioid combination analgesics (acetaminophen-oxycodone) were no more effective than NSAIDs alone for acute musculoskeletal pain relief, with the opioid combinations being associated with increased adverse effects
Research shows that those patients who received greater than a one-week prescription for opioids were twice as likely to have continued work-related disability at one-year follow-up.
Several SMRs have been shown to be superior to placebo in short-term pain reduction associated with acute, non-radicular back pain.
Due to lack of efficacy over NSAIDs alone as well as high risk of adverse effects, SMRs should be limited to patients who cannot tolerate NSAIDs or have not reported sufficient relief with NSAIDs.
If provider Discretion indicates that the benefit outweighs the risks, a short 2 to 3 day prescription with a full patient discussion regarding patient anticipated side effects should be considered
Benzodiazepines (diazepam) as an NSAID adjunct offers no improvement in functional outcomes or pain at one week and three months follow-up compared to NSAIDs alone
Use of benzodiazepines for acute back pain must further be weighed against the adverse effects.
Christopher Loh, MD
References
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