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Postoperative pain assessment

What are the challenges of measuring response to analgesia postoperatively? In this article, Dr Fausto Morell-Ducos explains.
Doctor touching hands of patient after surgery at bed in hospital

In this step, Dr Fausto Morell-Ducos, Consultant in Anaesthesia and Pain Management at UCLH, discusses the multidimensional assessment of pain following surgery.

As you discovered in Week 1, the main goals of pain management after surgery are:

1) Improvement in pain experience (pain relief).
2) Facilitation of restoration of function after surgery.
3) Attenuation of the surgical stress response.
These goals should be matched to the type of surgery and to the stage of recovery. But how do you gauge whether these outcomes have been met?

Can you tell me how much it hurts?

Pain assessment is an essential part of postoperative care as it allows us to ascertain the adequacy of analgesia already given, guides further medication changes, and alerts us to the need for further interventions or investigations.
As discussed in Step 1.7 and in Step 1.16, over-reliance on unidimensional pain scores, target pain scores and patient satisfaction has been linked to an increase in opioid use and opioid-related harm without leading to a better pain experience or outcomes (ie the increased opioid use does not lead to lower pain scores) [1].
It is not entirely clear why this is, but it may be related to driving unrealistic patient expectations, an increased focus on pain leading to increased pain perception, and an increased reliance on pharmacological pain management strategies for psychological symptoms related to pain.
This is not to say that pain reduction and patient satisfaction are not important goals. They obviously are. But achieving these goals is more complex than aiming for a simple number.

What is the best way to measure pain?

There is no currently clinically available way of objectively measuring pain experience. Pain measures are either self-reported or observed. Both are prone to subjective bias. The frequently-used numerical rating scales or analogue scales use self-reported pain intensity alone. They should be appropriate to the patient’s cognitive ability, language and age. They are validated for use in the postoperative setting, but they must be used with caution. One person’s ‘8 out of 10’ might be another person’s ‘20 out of 10’. We also know that factors such as anxiety and perceived lack of autonomy can influence reported pain intensity.
Multidimensional pain scales and questionnaires use other self-reported parameters, such as pain quality, or effect on mood and anxiety. These allow for a more nuanced appraisal of a patient’s pain experience, as well as helping to detect specific issues such as the presence of neuropathic pain. They are, however, also affected by subjective bias, and more difficult and time-consuming to administer.
Observed parameters (functional ability, markers of autonomic arousal such as heart rate and blood pressure, behaviour), although often considered more ‘objective’, do not measure pain directly.
At times such observational pain assessment tools may be the only scales available for specific patients, for example in the presence of severe cognitive deficits or for sedated patients in the intensive care unit. They must also be used with caution, as pain-related behaviours can vary significantly with similar levels of nociceptive input, and they are can also fall prey to subjective bias. There is substantial evidence which shows that patient ethnicity, for example, influences prescribers’ perception of risk of opioid misuse and the amounts of analgesics offered in spite of similar levels of self-reported pain [2].

Functional pain scales

Over the last decade recommendations that administration of immediate-release opioid analgesia should be guided by functional outcomes in conjunction with validated self-reported pain scales have been issued, and several functional outcome tools have been developed.
Assessment of pain with activity is important as pain which is tolerable at rest can be severe during movement, and interfere with function (eg deep breathing after laparotomy, or swallowing after tonsillectomy) and recovery. It is important to note that these functional goals are procedure and time-specific.
One functional pain scale which is gaining increasing acceptance is the Functional Activity Scale, mentioned by Dr Jane Quinlan in Step 1.19:

Functional Activity Scale

FAS-A No limitation: the patient is able to undertake the activity without limitation due to pain
FAS-B Mild limitation: the patient is able to undertake the activity, but experiences moderate to severe pain
FAS-C Significant limitation: the patient is unable to complete the activity due to pain or pain treatment-related adverse effects

Post-operative pain assessment

In many ways, the pain trajectory is more important than the absolute pain intensity. Repeated elevated pain scores which do not respond to analgesia, or increases in pain intensity from those previously reported, should prompt a pain assessment (see table below) and not be treated solely with the administration of further opioids.

Suggested elements of postoperative pain assessment

Adapted from Chou et al. (J Pain 2016)

1. Onset and pattern When did the pain start? How often does it occur? Has its intensity changed?
2. Location Where is the pain? Is it local to the incisional site, referred, or elsewhere
3. Quality of pain What does the pain feel like?
4. Intensity How severe is the pain?
5. Aggravating and relieving factors Aggravating and relieving factors
6. Previous treatment What types of treatment have been effective or ineffective in the past to relieve the pain?
7. Effect How does the pain affect physical function, emotional distress, and sleep?
8. Barriers to pain assessment What factors might affect accuracy or reliability of pain assessments128 (eg, cultural or language barriers, cognitive barriers, misconceptions about interventions)?

Surgical complications, neuropathic pain, and psychological distress can all present with abnormally elevated pain scores, yet their management is rarely if ever appropriately addressed by administering increasing doses of opioids alone, as discussed in Step 2.10.


1. Quinlan J, Lobo DN, Levy N. Postoperative pain management: time to get back on track. Anaesthesia 2020;75:e10-3.

2. Hyland SJ, Brockhaus KK, Vincent WR, et al. Perioperative pain management and opioid stewardship: A practical guide. Healthc 2021;9:1-56.

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Opioids and Surgery

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