Original article
Exploring the validity of the bispectral index, the Critical-Care Pain Observation Tool and vital signs for the detection of pain in sedated and mechanically ventilated critically ill adults: A pilot study

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Summary

This pilot study aimed to explore the validity of the bispectral (BIS) index, the Critical-Care Pain Observation Tool (CPOT) score, and vital signs (mean arterial pressure, heart rate) during rest and painful procedures in sedated and mechanically ventilated ICU adults. A convenience sample of nine patients with various diagnoses participated in this observational repeated measures study. Patients were observed during 2 minute periods at rest (baseline), and during procedures known to be painful: turning and endotracheal suctioning. Both the BIS index and the CPOT score were found to increase when patients were exposed to procedures compared with rest, and were found to be more sensitive to procedures compared with vital signs. Indeed, vital signs remained quite stable during procedures in this sample. Results from this study support the recommendation that behavioural indicators (i.e. in this case, the use of a behavioural pain scale called the CPOT) be used for the detection of pain in nonverbal ICU patients. However, in some situations (e.g. deep sedation, use of blocking agents), behavioural indicators may no longer be observable, and all that is left are physiologic signs. The BIS seems to be an interesting technique and further research is required in order to establish if it could be used to guide clinicians for the detection of pain in this vulnerable population.

Introduction

Pain assessment in sedated and mechanically ventilated patients in the intensive care unit (ICU) remains a clinical challenge for the multidisciplinary team (Shannon and Bucknall, 2003). Indeed, many patients are unable to self-report their pain. As more than 50% of critically ill patients experience moderate to severe pain in the ICU (Puntillo et al., 2001, Stanik-Hutt et al., 2001), it remains crucial that pain be adequately assessed and properly treated in this vulnerable population. However, pain remains undertreated in most critically ill patients (Gélinas et al., 2004, Gélinas, 2007, Stanik-Hutt et al., 2001). In the Thunder Project II, less than 20% of critically ill adults (n = 5957) received opiates before and during procedures (Puntillo et al., 2002). Still, many procedures such as turning, drain removal, wound care and endotracheal suctioning have been identified to be painful to critically ill patients, these procedures are performed on a regular basis in the patients routine care (Puntillo et al., 2001). Poor treatment of acute pain may lead to the development of serious complications (Kehlet, 2006) including neurohumoral changes, neuronal remodelling and long lasting psychological distress which may negatively impact clinical outcomes of critically ill patients (Dunwoody et al., 2008). Also, when acute pain remains unrelieved, it becomes a risk factor for chronic pain (Garcia et al., 2003, Kaarlola et al., 2003), which may seriously impact the patient's functioning, quality of life and well-being in the long-term. Such evidence reinforces the importance of providing attention to pain in this specific context of care.

Since the initial definition of pain by the International Association for the Study of Pain (IASP, 1979) which implies that only the patient's self-report indicates the presence of pain perception, the statement “the inability to communicate verbally does not negate the possibility that an individual is experiencing pain and is in need of appropriate pain-relieving treatment” was added to pain terminology (IASP, 1994). Based upon this, pain assessment must be designed to conform to the communication capabilities of the patient. Thus, other means of pain assessment must be valued and pain should be suspected in the nonverbal patient whenever there is a reason to suspect it (e.g. acute condition related to pain, procedures known to be painful, etc.) (Herr et al., 2006).

When the patient's self-report is unobtainable, the use of a valid behavioural scale for the detection of the presence of pain (e.g. behavioural pain scale [BPS: Payen et al., 2001] and critical-care pain observation tool [CPOT: Gélinas et al., 2006]) is recommended by the American Society for Pain Management Nursing (ASPMN) (Herr et al., 2006) in intubated/unconscious patients. However, in some situations, behaviours may become undetectable as a result of the use of high doses of sedative agents which induce a state of deep sedation, or the use of neuromuscular blocking agents, which inhibits motor function. For patients whose behaviours cannot be detected, no other useful indicators for the detection of pain are available. Whilst vital signs are easily accessible in the ICU, their validity for pain assessment is questionable. In fact, they are not associated with the patient's self-report of pain (Gélinas and Arbour, 2009, Gélinas and Johnston, 2007) and seem to either increase both during painful and non-painful procedures (Young et al., 2006) or remain stable during painful procedures (Siffleet et al., 2007). Moreover, vital signs are not recommended indicators of pain assessment in nonverbal patients in the ASPMN guidelines (Herr et al., 2006), and as little work has been done to examine their validity, further research is still needed. Also, the time has come to look at other physiological measures that could support the clinicians in the pain assessment process of nonverbal ICU patients.

The bispectral (BIS) monitor is a non-invasive technology measuring different indices including the BIS index value, electromyographic activity (EMG) of the corrugator supercilii muscle, a signal quality index (SQI) and for some models, it may include extended electroencephalographic (EEG) data and density spectral array (DSA). The BIS index is the key component of this system. It represents a single number from 0 (complete EEG suppression) to 100 (fully awake) which is a complex mathematical transformation of EEG data including power, frequency and other parameters (Rampil, 1998, Rosow and Manberg, 2001). The main use of the BIS index has been to quantify changes in the electrophysiological state of the brain during sedation and anaesthesia (for a review, see Rosow and Manberg, 2001). Whilst this technology is still new in the study of pain, one recent study by Li et al. (2009) examined the reactivity of the BIS index during a noxious stimulation (endotracheal suctioning or turning) in postoperative cardiac surgery ICU patients (n = 48). Significant increases in the BIS index (+10%) were observed from baseline (rest) compared with noxious stimulation, peaked within the first minute and remained elevated five minutes post-procedure (p < 0.001). Of note, 10 patients were able to self-report and indicated that the procedure was painful (yes by head nodding). Interestingly, no significant changes of the BIS index were observed during a non-noxious stimulation (i.e. gentle touch). Such results tend to support the validity of the BIS index in this sample and specific context. Thus, the BIS index could be a potential indicator in the detection of the presence of pain. However, little research in this field has yet been done in order to determine that it may be considered a useful indicator of pain.

The aim of this pilot study was to further explore the validity of the BIS index in sedated and mechanically ventilated ICU adults for the purpose of pain assessment. To fulfil this goal, other measures such as a valid behavioural pain scale, the Critical-Care Pain Observation Tool (CPOT) (Gélinas et al., 2006) and vital signs as monitored in the ICU were also documented. More specifically, changes in the BIS index and EMG, the CPOT score, and vital signs (mean arterial pressure [MAP] and heart rate [HR]) between baseline (rest) and procedures known to be painful (turning, and endotracheal suctioning) were described.

Section snippets

Design, sample and ethics

An observational repeated measures within-subject design was chosen for this study. The project was conducted in the surgical and medical ICUs of a tertiary healthcare center of 642 beds in a suburban region of the province of Quebec in Canada. The Research Ethics Committee of the setting approved the pilot study and consent was waived as it was an observational study.

Eligible patients were sedated and mechanically ventilated, aged 18 years or older, had a score between 2 (very sedated) and 3

Study sample

Nine participants were included in this pilot study (seven men and two women) (see Table 1 for participant's characteristics). Median age was 66 years (range from 27 to 79 years), and diagnoses were variable. Five participants were admitted in the ICU postoperatively, two had a medical diagnosis, and two had a trauma diagnosis. Sedative and analgesic agents were administered according to physician's orders and were not standardised for the purpose of this study.

Changes in the BIS index, EMG, CPOT score, and vital signs

Both BIS parameters (BIS index

Discussion

The BIS index, EMG and the CPOT score were found to be higher during procedures known to be painful. The BIS index and the CPOT seemed to be more sensitive indicators to the procedures than vital signs which remained quite stable. Compared with its baseline value, the BIS index increased of more than 20% during turning, and endotracheal suctioning. In a previous study, the BIS index significantly increased during a noxious stimulation in sedated and mechanically ventilated postoperative cardiac

Conclusions

Although results from this study are preliminary and cannot be generalised to unconscious ICU patients, the BIS may be an interesting technique to further study in the pain assessment process because of its non-invasive nature and its suitability for use at the bedside. Consistent with previous studies, the BIS index was sensitive to painful procedures in this small sample of unconscious ICU patients. Whilst further research is warranted to establish the validity of the BIS in larger

Acknowledgements

Special thanks to Dr. Marcel Martin, Dr. Dominique Bérard, Dr. Jean-Pierre Tétrault, Nicole St-Onge, Flore Béland, Isabelle Martineau, Louis-Marie Decoste and the nursing staff of the Medical-Surgical ICU of the CHUS. Also, thank you to the research assistants, Étienne St-Louis and Katya Daigle.

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