Analgesia - pediagenosis
Article Update

Sunday, June 2, 2019


Patients often arrive at the Emergency Department in pain, and painkillers are often used before a definitive diagnosis is made. This is humane, and enables a thorough examination to be per- formed: there is no reason to withhold analgesia.

Patients are asked to rate the pain out of 10, with 0 being no pain, and 10 being the worst pain they can imagine. This procedure is repeated to gauge the effectiveness of the treatment and ensure the pain is controlled.
In general, a patient’s reported pain is taken at face value: ‘pain is what the patient feels’ and is treated as such. Patients seeking opiates may fake pain, but this is rare.
Non-pharmacological analgesia
Splinting of fractures immobilises the bones, reducing pain. A patient’s anxiety and pain makes them tense, which may make pain worse: a calm, supportive atmosphere and excellent nursing care help to keep the patient relaxed.

Analgesia, Non-pharmacological analgesia, Nitrous oxide, Paracetamol (acetaminophen) and compound analgesics, Moderate opiates, Major opiates: morphine, fentanyl, pethidine (meperidine), Non-steroidal anti-inflammatory drugs, Local anaesthesia and nerve blocks, Intravenous regional anaesthesia (Bier’s block),

Nitrous oxide
Nitrous oxide (N2O) combined with oxygen in a 1:1 mix in cylinders (Entonox®) is often used, particularly out of hospital. It is a short-term analgesic, effective only while the patient is breathing the gas, as it is rapidly cleared from the body. This ‘laughing gas’ is generally very safe, but should not be used in patients with a possible pneumothorax.

Paracetamol (acetaminophen) and compound analgesics
Paracetamol (acetaminophen) is effective and safe and can be given orally, rectally or intravenously. Compound analgesics consist of paracetamol combined with another analgesic, usually low-dose codeine. They come in different strengths, the weaker of which are sold without prescription. They are useful analgesics for patients to be able to take home on discharge, but prescribing the constituent drugs separately may allow more flexibility.

Moderate opiates
   Codeine is a common component of compound analgesics, and is effective but tends to cause constipation. Oxycodone and dihydrocodeine are more powerful variants of codeine, but offer little extra benefit, and have high abuse potential.
   Tramadol may be more effective than codeine. It has less abuse potential than other drugs of comparable potency but should be used with caution in the elderly.

Major opiates: morphine, fentanyl, pethidine (meperidine)
Opiates induce a feeling of well-being: patients, while still aware of the pain, are not distressed by it. Young patients with major fractures may require large doses of morphine, as will opiate addicts who need analgesia. Intravenous opiates are used because intramuscular absorption is unreliable and the intravenous route enables analgesia to be titrated to response.
   Intravenous morphine is the gold standard of Emergency Department analgesia. It is safe, predictable and effective. Morphine is not as lipid soluble as other opiates, so does not give a significant ‘high’. Morphine often causes mild histamine release that should not be confused with an allergic reaction. The duration of action of morphine is approximately 3 hours.
   Fentanyl is a short-acting synthetic opiate that is particularly useful when performing short procedures, as it is cleared from the body within 30 minutes.
   Pethidine (meperidine) is quite lipid soluble and therefore sought after by opiate addicts as it crosses the blood–brain barrier, giving a ‘high’. It offers no benefits over morphine and should not be used unless a patient has a definite allergy to morphine and there are no other alternatives.

Non-steroidal anti-inflammatory drugs Injectable non-steroidal anti-inflammatory drugs (NSAIDs), e.g. ketorolac, are very effective in an Emergency Department setting. They are particularly useful in patients with broken bones, colicky pain (e.g. ureteric colic) and abdominal pain, but should be avoided in elderly patients or those with active bleeding. An equally effective alternative is a suppository (e.g. indometacin, diclofenac), which lasts for 16 hours.
Oral NSAIDs are useful as they can also be given to patients on discharge. Ibuprofen is the least powerful, but has a relatively benign side-effect profile.
Diclofenac and indometacin are more powerful NSAIDs but at a cost of increased risk of side-effects.

Local anaesthesia and nerve blocks
   Lidocaine 1% is the local anaesthetic (LA) most often used for wound management and is effective for 20–30 minutes without adrenaline, or for 40–60 minutes with adrenaline.
   Adrenaline mixed with lidocaine increases length of action and causes vasoconstriction giving a ‘dry’ wound that is much easier to assess, clean and close. Fear about using local anaesthetics with adrenaline in digits was related to high concentrations (1 : 10 000); less than 1 : 100 000 adrenaline is safe.
   Bupivicaine 0.25% is a long-acting local anaesthetic, lasting for 6–8 hours. Bupivicaine is highly protein bound: adrenaline does not increase duration of action.
A safe maximum dose of lidocaine for wound infiltration is 3 mg/ kg, but with adrenaline is 6 mg/kg. For bupivicaine the maximum dose is 2 mg/kg. Local anaesthetic toxicity first causes perioral parasthesia, and then fits and arrhythmias, and is treated by lipid infusion.
Nerve blocks can offer very effective analgesia, e.g. digital and femoral nerve blocks. Bupivicaine and lidocaine can be mixed to provide a combination of rapid onset and long duration of action. Local anaesthetic can also be injected into joints, e.g. for shoulder dislocation.
A haematoma block can give good anaesthesia in minor fractures e.g. Colle’s fractures (Chapter 15). The skin is carefully cleaned with alcohol and chlorhexidine and then up to 10 mL of local anaesthetic is injected into the fracture haematoma. After about 10 minutes reduction can be performed.

Intravenous regional anaesthesia (Bier’s block)
Two intravenous cannulae are sited, one in the affected limb. A double cuff is placed on the affected limb (usually the arm), which is then lifted to exsanguinate it. The cuff is then inflated well above the systolic BP and local anaesthetic, e.g. prilocaine, injected. Bupivicaine should never be used for intravenous regional anaesthesia.
After waiting 5 minutes for the local anaesthetic to have maximal effect, the operation, e.g. fracture reduction, is performed. The cuff must not be deflated until at least 20 minutes have elapsed from injection of the local anaesthetic to avoid a bolus of undiluted local anaesthetic perfusing the heart, potentially causing asystole.

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