Measuring analgesia in ICU: no pain, no gain?

Pain was defined in 1968 by Margo McCaffrey as "whatever the experiencing person says it is, existing whenever he says it does”.¹ Memories of painful experiences are commonly described in intensive care unit (ICU) survivors.2, 3 Accordingly, the evaluation and management of pain in ICU patients is important. This is particularly relevant in those who are mechanically ventilated, sedated and cannot readily communicate, so that appropriate therapy can be initiated and titrated to effect.

There are several scoring systems available for pain assessment in the ICU. Self-reporting pain assessments in adults who are able to communicate include a visual analogue scale, a numerical rating scale (traditionally 0-100 or 0-10), faces pain scale, and various verbal rating scales/ pain intensity descriptive scales.4, 5 In mechanically ventilated patients, assessments can be made with a behavioural pain scale6, 7 and the Critical Care Pain Observation Tool⁸ for those who are otherwise unable to assess.

Use of pain assessment tools has been associated with reductions in duration of mechanical ventilation, fewer nosocomial infections and reduced ICU length of stay.9, 10 In addition, unchecked use of high dose opioid infusions is associated with short term risks, including constipation, respiratory depression, tolerance, and dose-related delirium,¹¹ as well as significant long term risk of opioid dependence.12, 13, 14 The Clinical practice guidelines for the prevention and management of pain, agitation/ sedation, delirium, immobility, and sleep disruption in adult patients in the ICU (PADIS guidelines)¹⁵ recommend that "Management of pain for adult ICU patients should be guided by routine pain assessment", although "routine” is not defined. It is currently unclear how frequently pain assessment should be performed.

Despite the importance of this issue, there are few Australian and New Zealand studies examining contemporary practice relating to pain assessment and use of analgesia. In this issue of Critical Care and Resuscitation, Moran and colleagues¹⁶ report results from a point prevalence study of the use of pain assessment tools and analgesic management in 499 patients aged > 16 years admitted to 45 ICUs in Australia and New Zealand on one of two days in August and November 2016. This study provides useful insight into Australia and New Zealand practice and reveals several important findings. Firstly, pain assessments were common, occurring at least once in 77% of ventilated and 83% of non-ventilated patients. In mechanically ventilated patients who were potentially receiving sedative medications, the most common tool used was a numerical rating scale followed by the Critical Care Pain Observation Tool and a behavioural pain scale, aligned with current recommendations.¹⁵

However, only 54% of mechanically ventilated patients and 56% of non-ventilated patients had pain scores assessed at least every 4 hours. Furthermore, a large proportion of ventilated patients (39%) had their pain assessment documented only once a day or not at all, accepting that some patients may have had undocumented or informal pain assessments. This relative low level of regular assessment is even more significant, considering that most ventilated patients received an intravenous opioid. This may be problematic, because in the absence of regular structured pain assessment, it is unclear how the doses of opioid were titrated and what, if any, criteria were used to adjust dosing. It is possible there was reliance on sedation scores for opioid titration in the mechanically ventilated patients. However, if sedation was the endpoint, there is a risk the opioid dose delivered was more than that required for analgesia, with increased the risk of dose-related side effects.¹⁷ Moreover, fentanyl was the opioid most commonly used, and its contextsensitive half-time is related to both dose and duration of therapy, with a larger cumulative dose leading to prolonged elimination half-life.¹⁸

Finally, despite the PADIS guidelines recommending adjuncts as opioid-sparing agents,¹⁵ less than half of the cohort received paracetamol and only a relatively small percentage (17%) received gabapentinoids, ketamine or regional analgesia.

Analgesia and sedative use in ICU patients are almost ubiquitous. While ICU clinicians may aspire to using evidence-based guidelines, this study highlights many potential deficiencies in care, especially for mechanically ventilated patients. The findings of Moran and colleagues¹⁶ suggest that ventilated ICU patients may be at risk of a "set and forget" approach to opioid infusion therapy. However, it is important to point out this study was conducted almost 6 years ago, and it is possible that secular trends may mean that management is different today. In addition, the relatively low use of adjuncts for pain management suggests that, despite being recommended in guidelines, clinicians either do not believe that they make a difference or have little consideration for the pain ventilated patients may be experiencing.

Further research needs to focus on the method and frequency of pain assessment, choice of opioid therapy, and the optimal use of non-opioid adjunct analgesics. This is particularly important in mechanically ventilated patients where assessment and risks may be more challenging. Such practice should aim to provide these most vulnerable patients with timely comprehensive assessment of their analgesic needs, with the overall intention of decreasing harm through the avoidance of unnecessarily excessive or insufficient opioid administration, using a truly patient-centred approach.

Competing interests

All authors declare that they do not have any potential conflict of interest in relation to this manuscript.