Acute Pain - Conclusions
In treating acute pain, as in other areas of medicine, tradition and ill-informed prejudice sometimes hold sway over evidence and common-sense. We concentrated on gathering evidence for the treatments which are simple. This Chapter draws together that evidence in a wider frame, including interventions for which there are no systematic reviews. Wherever possible we base our recommendations on randomised trials.
Effective pain management is fundamental to quality care, and while we believe that good pain control speeds recovery, there is still no compelling evidence that this is so. Advantage can be shown with proxy measures like mobility or coughing, but evidence that good pain management led to faster recovery would increase the pressure to improve current practice, which is often less than ideal.
Non-opioids:- paracetamol, combinations and non-steroidal anti-inflammatory drugs
Effective relief can be achieved with oral non-opioids and non-steroidal anti-inflammatory drugs. These drugs are appropriate for many post-surgical and post-traumatic pains, especially when patients go home on the day of the operation. Figure 1 shows the evolving league table for analgesic efficacy compiled from randomised trials after all kinds of surgery. Analgesic efficacy is expressed as the number-needed-to-treat, the number of patients who need to receive the active drug for one to achieve at least 50% relief of pain compared with placebo over a six hour treatment period. The most effective drugs have a low number-needed-to-treat of about 2, meaning that for every two patients who receive the drug one patient will get at least 50% relief because of the treatment (the other patient may obtain relief but it does not reach the 50% level).
For paracetamol 1 g the number-needed-to-treat is nearly 5. Combination of paracetamol 650 mg with dextropropoxyphene 65 mg improves the number-needed-to-treat slightly. Ibuprofen is better at 3 and diclofenac at about 2.5.
These number-needed-to-treat comparisons are against placebo; the best number-needed-to-treat of 2 means that while 50 of 100 patients will get at least 50% relief because of the treatment, another 20% will have a placebo response which gives them at least 50% relief, so that with diclofenac 70 of 100 will have effective pain relief.
This alternative way of looking at the effect of the various analgesics is shown in Figure 2. The range is from about 25% of patients getting at least 50% pain relief with codeine 60 mg (largely because of the effect of placebo), to over 70% at the high end of the 95% confidence interval with oral NSAID. For comparison, with 10 mg intramuscular morphine about 53% of patients get more than 50% pain relief. Because the effect of placebo is added in, the comparisons between analgesics are not as stark as with NNT.
Figure 2: Oral analgesic league table - percentage with at least 50% pain relief
The clear message is that of the oral analgesics non-steroidal anti-inflammatory drugs perform best, and that paracetamol alone or in combinations is also effective. Initial prescription of oral non-steroidal anti-inflammatory drugs can be supplemented with paracetamol. As pain wanes then the prescription should be paracetamol based, supplemented if necessary by non-steroidal anti-inflammatory drugs.
There is an old adage that if patients can swallow it is best to take drugs by mouth. There is no evidence that non-steroidal anti-inflammatory drugs given rectally or by injection perform better (or faster) than the same drug at the same dose given by mouth (Chapter 11). These other routes become appropriate when patients cannot swallow. Topical non-steroidal anti-inflammatory drugs are effective in acute musculoskeletal injuries - ibuprofen has a number-needed-to-treat of 3 for at least 50% relief at one week compared with placebo.
Adverse effect data on non-steroidal anti-inflammatory drugs from long term dosing, where gastric bleeding is the main worry, rates ibuprofen the safest . In acute pain the main concerns are renal and coagulation problems. Acute renal failure can be precipitated in patients with pre-existing heart or kidney disease, those on loop diuretics or those who have lost more than 10% of blood volume. Non-steroidal anti-inflammatory drugs cause significant lengthening (~30%) of bleeding time, usually still within the normal range. This can last for days with aspirin, hours with non-aspirin non-steroidal anti-inflammatory drugs. Whether or not non-steroidal anti-inflammatory drugs cause significant increase in blood loss remains contentious.
As yet we do not have any systematic review evidence for a number of niche analgesic interventions. These include inhaled nitrous oxide, which can provide fast-onset fast-offset analgesia for obstetrics and wound dressings, corticosteroids to reduce pain and swelling after head and neck surgery, and when swelling causes pain in cancer, ketamine in emergency analgesia and anaesthesia and clonidine.
For severe acute pain opioids are the first line treatment, and to date we have only one systematic review, that for injected morphine. Intermittent opioid injection can provide effective relief of acute pain . Unfortunately, adequate doses are withheld because of traditions, misconceptions, ignorance and fear. Doctors and nurses fear addiction and respiratory depression. Addiction is not a problem with opioid use in acute pain. Over eleven thousand patients were followed up a year after opioids were given for acute pain, and just four were considered addicts .
Irrespective of the route, opioids used for people who are not in pain, or in doses larger than necessary to control the pain, can slow or indeed stop breathing. The key principle is to titrate the dose against the desired effect - pain relief - and minimise unwanted effects (Figure 3).
Figure 3. Titrate opioids to effect
If the patient is still complaining of pain and you are sure that the drug has all been delivered and absorbed, then it is safe to give another, usually smaller, dose (5 minutes after intravenous, 1 hour after intramuscular or subcutaneous, 90 minutes after oral). If the second dose is also ineffective, then repeat the process or change the route of administration to achieve faster control. Delayed release formulations, oral or transdermal, should not be used in acute pain, because delayed onset and offset are dangerous in this context.
There is no compelling evidence that one opioid is better than another, but there is good evidence that pethidine has a specific disadvantage  and no specific advantage. Given in multiple doses the metabolite norpethidine can accumulate and act as a central nervous system irritant, ultimately causing convulsions, especially in renal dysfunction. Pethidine should not be used when multiple injections are needed. The old idea that pethidine is better than other opioids at dealing with colicky pain is no longer tenable .
Morphine (and relatives diamorphine and codeine), has an active rather than a toxic metabolite, morphine-6-glucuronide. In renal dysfunction this metabolite can accumulate and result in greater effect from a given dose, because it is more active than morphine. If you are, as you should be, titrating dose against effect, this will not matter. Less morphine will be needed. Accumulation can be a problem with unconscious intensive care patients on fixed dose schedules when renal function is compromised.
Opioid adverse effects include nausea and vomiting, constipation, sedation, pruritus, urinary retention and respiratory depression. There is no good evidence that the incidence is different with different opioids at the same level of analgesia. There is good evidence that the risk of adverse events is increased when high-tech approaches are used for drug administration .
There are strong arguments, based on minimising risk, for using one opioid only, so that everyone is familiar with dosage, effects and problems. Our first choice opioid is morphine. Whichever drug you choose, simple changes to the way opioids are used, good staff education and implemention of an algorithm for intermittent opioid dosing, can have a powerful impact on pain relief and patient satisfaction .
Nurse administered intermittent opioid injection requires good staffing levels to minimise delay between need and injection. Staffing shortage, ward distractions and controlled drug regulations all increase the delay. Patient controlled analgesia overcomes these logistical problems. The patient presses a button and receives a pre-set dose of opioid, from a syringe driver connected to an intravenous or subcutaneous cannula. This delivers opioid to the same opioid receptors as an intermittent injection, but allows the patient to circumvent delays. Not surprisingly there is little difference in outcome between efficient intermittent injection and patient-controlled analgesia . Good risk management with patient-controlled analgesia should emphasise the same drug, protocols and equipment throughout the hospital.
Novel routes of opioid administration, intended to improve analgesia and reduce adverse effects, include intra-articular (Chapter 17), nasal, active transdermal and inhalational. These may prove to have advantage over conventional routes, different kinetic profiles or greater convenience, but their place in mainstream care is unproved.
The perceived advantage of regional analgesia with local anaesthetic is that it can deliver complete pain relief by interrupting pain transmission from a localised area, so avoiding generalised drug adverse effects. This advantage is more obvious when it is possible to give further doses via a catheter, extending the duration of analgesia. Details are given in Table 1.
There is a necessary distinction between blocks done to permit surgery, and blocks done together with a general anaesthetic to provide postoperative pain relief. There is clear evidence that blocks can indeed provide good relief in the initial postoperative period , and no evidence to suggest that patients with blocks then experience 'rebound', and need more postoperative pain relief. The risk of neurological damage is the major drawback , and ideally blocks should not be done on anaesthetised patients.
Epidural infusion via a catheter can offer continuous relief after trauma or surgery, for lower limb, spine, abdominal or chest. The current optimal infusate is an opioid/local anaesthetic mixture. Opioids and local anaesthetics have a synergistic effect, so that lower doses of each are required for equivalent analgesia with fewer adverse effects . Epidurals are widely used for pain relief in labour.
The risks are those of an epidural, (dural puncture, infection, haematoma, nerve damage), those of the local anaesthetic (hypotension, motor block, toxicity) and those of the opioid, (nausea, sedation, urinary retention, respiratory depression, pruritus) (Table 2).
|Wrong doses do get given , so increased surveillance is
mandatory. The risk of persistent neurological sequelae after an epidural is
about 1 in 5000 . Debate continues about whether patients with epidural
infusions can be nursed on general wards. These techniques are only appropriate
for major trauma or surgery when the potential benefits outweigh the risks.
While experts can obtain good results with specialised procedures, such as paravertebral or interpleural injections, the evidence that in less skilled hands these are better than standard methods, (should-do rather than can-do evidence), is often lacking.
TENS and acupuncture
TENS is not effective for postoperative pain, and is of limited value for labour pain. Systematic reviews of acupuncture are confined to chronic pain.
There is evidence that psychological approaches are beneficial . Cognitive behavioural methods can reduce pain and distress in burned patients. Preparation before surgery can reduce postoperative analgesic consumption.
Clinical Settings and
There is controversy about the optimal timing of initial analgesia. The idea is that analgesia is more effective when given before pain begins than when given after. Most randomised trials comparing the same intervention given before or after pain starts have not shown clinical advantage of so-called pre-emptive analgesia . Whether poorly-controlled acute pain generates chronic pain is also controversial.
Problem pains and patients
Standard interventions and protocols will cope with most acute pain problems, but some patients, particularly in hospital, will require special management. Expertise can be developed in specific units, but if not available seek the advice of your acute pain service. In particular do not let pain in children go untreated.
The key to successful pain management is education, not new drugs or high-tech delivery systems. Existing tools can do the job if doctors and nurses are educated, both to dispel the myths and misconceptions and to take responsibility for providing good pain control. It is much easier to dispel myths when you have the evidence. For many years patients were not given adequate analgesia for abdominal pain in case it masked the signs necessary for diagnosis. This was wrong .
Pain relief should not be seen as someone else's responsibility, nor just dismissed, because "in the end the pain and the patient go away". Freedom from pain is important to patients. In 1846 the first anaesthetic provided pain-free surgery. One hundred and fifty years later patients should not have to endure unrelieved pain anywhere in hospital.