Critically ill patients frequently endure significant pain, arising both from routine procedures and their underlying conditions. Procedures such as chest tube removal, tracheal suctioning, wound care, repositioning, and arterial line insertion are consistently identified as particularly painful experiences for these patients[1, 2]. If acute pain is not effectively managed in adult Intensive Care Unit (ICU) patients, it can lead to a cascade of adverse short-term and long-term consequences. These complications range from postoperative myocardial infarction and disrupted sleep patterns to the development of posttraumatic stress disorder[3-6].
Current best practices emphasize a personalized and goal-oriented approach to pain management in the ICU. A cornerstone of this approach is the systematic and regular assessment of pain, utilizing validated pain scales that are appropriate for the patient’s level of consciousness. However, pain assessment in critically ill patients presents unique challenges. Factors such as mechanical ventilation, the severity of illness itself, the administration of sedatives and analgesics, and fluctuating levels of consciousness can all impede a patient’s ability to self-report their pain. In situations where self-reporting is not feasible, clinical guidelines recommend the use of validated behavioral pain scores to effectively assess pain in this vulnerable patient population[6, 7].
Two comprehensive systematic reviews have rigorously evaluated the psychometric properties of various pain assessment tools designed for ICU patients who cannot articulate their pain experiences[8, 9]. Among these tools, the Critical Care Pain Observation Tool (CPOT) and the Behavioral Pain Scale (BPS) have emerged as leading options, receiving the highest quality scores in these assessments. Consequently, both CPOT and BPS are endorsed in recent clinical practice guidelines as reliable methods for pain assessment in nonverbal, critically ill adults[7, 10, 11].
The Critical Care Pain Observation Tool (CPOT) was specifically developed to assess pain in the unique context of critically ill patients. This observational tool evaluates patient behavior across four key domains: facial expression, body movements, muscle tension, and, depending on intubation status, either compliance with mechanical ventilation or vocalization. Each domain is scored on a scale from 0 to 2, resulting in a total possible score ranging from 0 (indicating no pain) to 8 (representing maximum pain). A CPOT score greater than 2 is generally considered to be indicative of pain during nociceptive procedures[7, 12].
One recognized limitation of the CPOT is the relative scarcity of research specifically focused on its application in critically ill patients experiencing delirium. Delirium is a frequent and serious complication in the ICU, with incidence rates following cardiac surgery varying widely from 3% to as high as 55%[13]. The overall incidence of delirium in the broader critically ill population typically ranges from 30% to 50%[14]. Obtaining self-reported pain assessments from patients with delirium is inherently complex due to communication barriers, fluctuating consciousness levels, and potentially atypical pain presentations. Therefore, validating behavioral pain assessment tools like the CPOT in delirious critically ill patients is a crucial area of investigation[8].
Kanji and colleagues directly addressed this gap in knowledge by conducting a study to evaluate the validity and reliability of the CPOT in adult critically ill patients diagnosed with delirium[15]. Their study involved 40 ICU patients who were confirmed to have delirium using the Confusion Assessment Method for the ICU (CAM-ICU). Patients who were unable to demonstrate a consistent physical response to pain were excluded. The researchers meticulously assessed several key psychometric properties of the CPOT, including discriminant validity, interrater reliability, and internal consistency. Discriminant validity refers to a scale’s ability to differentiate between distinct conditions, often assessed by comparing pain scores during painful versus non-painful procedures. Interrater reliability measures the degree of agreement between different observers assessing the same patient at different times[8, 16]. Kanji et al. used non-invasive blood pressure measurement as a non-painful procedure and repositioning, endotracheal suctioning, or dressing changes as painful procedures. They found a statistically significant mean difference in CPOT scores between baseline and painful procedures of 3.13±1.56 (P<0.001). Kanji et al. concluded that their findings suggest that the CPOT is a valid and reliable instrument for detecting pain in non-comatose, delirious adult ICU patients.
However, while the study by Kanji et al. was rigorously designed and executed, it is premature to draw definitive conclusions about the universal applicability of the CPOT in delirious patients based solely on this study. One area of concern is the absence of detailed data regarding the severity and subtype of delirium, as well as the correlation between Richmond Agitation-Sedation Scale (RASS) scores and CPOT scores. The DSM-V classifies delirium into three subtypes: hyperactive, hypoactive, and mixed. Hyperactive delirium is characterized by heightened vigilance, restlessness, aggression, and intense emotions like anger or anxiety. Hypoactive delirium presents with reduced alertness, minimal speech, and apathy. The mixed subtype involves fluctuations between hyperactive and hypoactive states. Peterson et al. have proposed defining these subtypes based on RASS scores[17]. Hyperactive delirium may be indicated by persistently positive RASS scores (+1 to +4). In delirious patients, agitation and pain can be intertwined, potentially leading to elevated CPOT scores that reflect agitation rather than pain. Furthermore, the influence of sedation on CPOT scores requires further investigation[9]. Kanji et al. reported a median RASS score of 0, with a range from −3 to +3, indicating the inclusion of patients exhibiting anxious or apprehensive movements (RASS +1), frequent non-purposeful movements or patient-ventilator dyssynchrony (RASS +2), or aggressive behavior towards staff (RASS +3). It is plausible that all four domains of the CPOT could be influenced by higher RASS scores, potentially resulting in inappropriately elevated CPOT scores. These falsely elevated scores could then lead to the unnecessary administration of analgesics when anti-delirium medication might be more appropriate. A recent study examining the validity of both the CPOT and BPS in a small subgroup of seven agitated patients (RASS +1) found no significant increase in CPOT scores between rest and painful procedures, and no difference at all between non-painful and painful procedures. Interestingly, the baseline CPOT scores in this small agitated subgroup were also higher than in patients with lower RASS scores [18]. Although based on a limited sample size, this finding suggests that the validity of the CPOT in patients with hyperactive delirium and/or RASS scores greater than +1 warrants further scrutiny.
In contrast to previous research methodologies, Kanji et al. reported interrater reliability for each of the four CPOT domains individually, rather than for the overall CPOT score during different procedures (painful vs. non-painful or rest). A limitation of this approach is that it deviates from typical ICU practice, where the CPOT is used as a composite score across all four domains during various clinical scenarios like tracheal suctioning or rest. Therefore, the interrater reliability of the overall CPOT score in delirious patients during different procedures remains an area that requires further study.
Furthermore, in the study by Kanji et al., as well as in several prior studies, pain assessments were conducted, at least in part, by investigators or physicians. However, in routine clinical practice, pain assessment in the ICU is predominantly performed by nurses. Bedside nurses, due to their prolonged and close patient contact, are potentially better positioned to interpret subtle patient reactions. Future research on interrater reliability should therefore involve a broader range of raters, including bedside nurses, to better reflect real-world clinical application[10]. Finally, it is important to note that there are at least six different versions of the Intraclass Correlation Coefficient (ICC), and their application to the same dataset can yield varying results[16, 19]. Kanji et al. did not specify which ICC model was used in their analysis, making it unclear whether the most appropriate model was selected.
In conclusion, the study by Kanji and colleagues represents a valuable initial step in validating the CPOT for use in critically ill patients with delirium. However, future assessments of the CPOT‘s interrater reliability should more closely mirror daily ICU practice. Larger-scale studies, including sufficient numbers of patients with delirium, and specifically addressing the three delirium subtypes and patients with RASS scores > +1, are essential before we can definitively conclude that the CPOT is a fully valid and reliable pain assessment tool in mechanically ventilated, critically ill patients suffering from delirium.
Acknowledgements
None.
Footnotes
Provenance: This is an invited Commentary commissioned by the Section Editor Zhongheng Zhang (Department of Critical Care Medicine, Jinhua Municipal Central Hospital, Jinhua Hospital of Zhejiang University, Jinhua, China).
Conflicts of Interest: The authors have no conflicts of interest to declare.
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