Pain Monitoring and Management in Intensive Care Unit: A Narrative Review
- In ICU
- Fri, 17 May 2024
ICU Management & Practice, Volume 24 - Issue 3, 2024
Pain is defined as an unpleasant sensory and emotional experience. Among patients admitted to the Intensive Care Unit (ICU), severe untreated pain is associated with an increase in mortality, length of hospital stays and worsening in everyday quality of life after hospital discharge. Pain in critically ill patients is more difficult to monitor and manage due to several factors, such as the presence of patients unable to communicate and severe clinical alterations limiting the use of analgesic drugs or the application of analgesic locoregional techniques. We present an extensive narrative review on ICU pain treatment, focusing on tools used to detect this condition and multimodal strategies adopted to reach adequate analgesia.
Introduction
The Association for the Study of Pain (IASP) defines pain as "an unpleasant sensory and emotional experience associated with actual or potential tissue injury or described in terms of such damage'' (Pain 1979).
International PATHOS study (Benhamou et al. 2008), involving 746 European hospitals, highlighted the suboptimal management of postoperative analgesia, supporting the need for improving pain treatment in surgical European wards. This assessment becomes even more critical when considering intensive care unit (ICU) patients. According to recent reports, more than 5 million patients are admitted to ICU in the United States every year. Pain at rest is detected in over half of them, and this number increases to 80% when considering procedural pain (Devlin et al. 2018).
Analgesia in critically ill patients can be very difficult to manage due to several factors, including a limited or a total loss in the patient's ability to communicate, severe emotional distress and important biological alterations that can alter the pharmacokinetic and pharmacodynamic profile of the analgesic drug, restricting their use. Untreated ICU pain is associated with an increase in death, in-hospital delirium, and the development of chronic pain, with a negative impact on the quality of life after hospital discharge (Yamashita et al. 2017). We present an extensive narrative review on ICU pain treatment, focusing on tools used to detect this condition and multimodal strategies adopted to reach adequate analgesia.
Pain Monitoring
Pain is a negative experience for patients in the ICU, where they often undergo invasive and non-invasive procedures (turning, endotracheal suctioning, wound care, central venous catheter and arterial line insertion) (Puntillo et al. 2014). Furthermore, they may experience pain from surgical wounds and underlying conditions. Pain monitoring is important for reducing adverse outcomes such as ICU length of stay and duration of mechanical ventilation (Payen et al. 2007), delirium, post-traumatic stress disorder (PTSD) and increased mortality (Kastrup et al. 2009; Payen et al. 2009). However, assessing pain in critically ill patients can be challenging due to factors such as sedation, mechanical ventilation, and altered consciousness; indeed, all these factors prevent patients from verbally communicating their pain (Ahlers et al. 2008).
According to a 2021 review on pain monitoring in the ICU, pain assessment should take place on admission to the ICU, adopting, even before assessment scales, mnemonic tools useful for focusing on certain aspects of pain. The PQRSTUV mnemonic (Nordness et al. 2021) is frequently used, and it is based on these items:
- Provocative/Palliative factors: Pain cause; pain-relieving strategies;
- Quality: Pain sensation;
- Region: Pain location;
- Severity: Pain intensity;
- Time: Pain duration or temporality;
- Understand: Previous pain experience and known problems;
- Values and preferences for pain treatment.
Pain assessment in the ICU relies on subjective measures such as self-reporting in conscious patients or observational scales for unconscious patients (Devlin et al. 2018). These methods are very useful, but they are limited by several factors, such as subjectivity in evaluation and the need for patient cooperation. There is a high risk of not capturing fluctuations in pain levels over time.
Rating scales commonly used in intensive care are divisible into:
- Unidimensional scales, which measure only intensity, include the Numeric Rating Scale (NRS), Visual Analogue Scale (VAS) and Verbal Rating/Descriptive Scale (VRS/VDS) (Chanques et al. 2022).
- Behavioural scales include Behavioural Pain Scale (BPS), Critical Care Pain Observational Tool (CPOT), Non-Verbal Pain Scale (NVPS) and Pain Assessment in Advanced Dementia (PAINAD).
Numeric Rating Scale
The Numeric Rating Scale (NRS) provides a simple and standardised method for quantifying pain intensity, allowing healthcare providers to assess and monitor pain in ICU patients. This unidimensional scale is a self-reporting scale where individuals rate their pain intensity by selecting a number from 0 to 10 verbally (Puntillo et al. 1997) with:
- 0 = no pain
- 1-3 = mild pain
- 4-6 = moderate pain
- 7-10 = severe pain
The NRS has a maximum acceptable score of 3 (Hamill-Ruth et al. 1999) and can be used across different populations, including adults, children older than eight years and elders, due to its simplicity and ability to provide a quantitative measure of pain intensity (Sessler et al. 2008). The NRS is also the most used scale in cancer patients (Oldenmenger et al. 2017). In the ICU, NRS can also be administered to patients unable to communicate through visual aids (NRS-V), preferably in a large format, making it a usable scale even in lightly sedated patients (Richmond Agitation-Sedation scale (RASS) score greater than -2) (G. Chanques et al. 2022). The pros and cons of NRS are reported in Figure 1.
Visual Analogue Scale
Visual Analogue Scale (VAS) is a subjective pain assessment tool that measures both pain intensity and the extent of pain relief (Karcioglu et al. 2018). The VAS is represented as a continuous horizontal (HVAS) or vertical (VVAS) line of 100 millimetres in length with a cursor anchored by verbal descriptors at each end. This pain rating scale has a maximum acceptable score of 30 mm (Ahlers et al. 2008). Patients are asked to mark a point on the line that corresponds to their current level of pain intensity, with one end representing "no pain" and the other end representing "worst pain imaginable" (Jensen et al. 1986). The distance from the "no pain" end to the patient's mark is then measured to quantify pain intensity. The pros and cons of VAS are reported in Figure 2.
Verbal Rating/Descriptor Scale
Verbal Rating/Descriptor Scale (VRS/VDS) is a validated pain assessment tool that relies on verbal communication to quantify the intensity of perceived pain (Williamson et al. 2005). This evaluation typically consists of a series of descriptive terms that represent different levels of pain severity. Commonly utilised descriptors include "no pain," "mild pain," "moderate pain," and "severe pain" (Karcioglu et al. 2018). The VRS was the most successful pain scale used in patients with cognitive impairment (Shimoji 2020). The pros and cons of VRS are reported in Figure 3.
Several studies have concluded that the most accurate assessment of a patient’s pain is a patient’s self-report; the recommended and most widely used scales are NRS and VAS, but these scales can struggle with the reduced consciousness and cognitive impairments often found in ICU patients. However, according to current guidelines, the easiest pain rating scale to use in the ICU, with the highest success rate, and with the best sensitivity and negative predictive value is the NRS (Devlin et al. 2018).
Behavioural Scales
The most cited and utilised scales in intensive care therapies are the Critical-Care Pain Observation Tool (CPOT) and the Behavioural Pain Scale (BPS).
CPOT (Gélinas et al. 2004) is an observational scale that analyses four items:
- facial expression
- body movements
- upper limb muscle tension
- ventilator compliance
Each item is given two points ranging from 2 (no pain) to 8 points (maximum pain). The process of evaluating pain in patients involves several steps:
- establishing a baseline CPOT value while the patient is at rest
- closely monitoring patients’ responses during nociceptive procedures
- assessing pain levels before and after administering analgesic agents
- assigning the highest observed CPOT score during evaluation
- scoring each behaviour component of the CPOT, with special attention to muscle tension
This comprehensive approach can ensure a thorough assessment of pain in ICU clinical settings.
BPS (Li et al. 2008) is an observational scale that considers three items:
- facial expression
- upper limb movement
- ventilator compliance
Each item is assigned a score from 1 (no response) to 4 (full response).
When compared with the CPOT scale, the BPS scale showed greater variability in pain score measurement during non-painful procedures like mouthwash and oral care (Gomarverdi et al. 2019). The main limitation of BPS is its consideration of upper limb movement as an integral part of the nociceptive reflex, when in many manoeuvres, this action can be linked only to a non-nociceptive reflex stimulus (Rijkenberg et al. 2017).
Pain Assessment in Advanced Dementia
Another pain assessment scale is Pain Assessment in Advanced Dementia (PAINAD), a behaviour-observation tool developed for patients with advanced dementia who lack verbal communication abilities to express pain (Warden et al. 2003). The PAINAD assesses pain through five specific indicators: breathing, vocalisation, facial expression, body language, and consolability. Scores range from 0 to 10, with higher scores indicating more severe pain; in recent years, this tool has also been utilised for sedated or non-verbally expressive patients in ICU.
Nonverbal Adult Pain Assessment Scale
Incorporating patient parameter assessment alongside the previously described items used in CPOT and BPS, we can introduce the Nonverbal Adult Pain Assessment Scale (NVPS) (Azevedo-Santos et al. 2018). The updated version considers five responses:
- facial expression
- activity (movement) guarding
- baseline Respiratory Rate (RR)/SpO2, ventilator compliance
- physiological parameters (vital signs including blood pressure (BP), heart rate (HR), resting rate (RR).
Each parameter is rated on a scale from 0 to 2, with a total score ranging from 0 (showing no pain) to 10 (indicating maximum pain), with a cut-off of >4 indicating significant pain. The possible misinterpretation of vital signs nonspecific to pain is the main limitation of this scale.
