Pain perception in patients with chronic disorders of consciousness: What can limbic system tell us?

OBJECTIVE

Although it is believed that patients with Unresponsive Wakefulness Syndrome (UWS) do not feel pain, recent neuroimaging and neurophysiologic studies have demonstrated some residual traces of nociceptive processing.

METHODS

To confirm this growing evidence, we evaluated 21 patients suffering from chronic disorders of consciousness (DOC) (both UWS, n=11, and Minimally Conscious State - MCS -, n=10), using an Event-Related Potential (ERP) Low-Resolution Brain Electromagnetic Tomography (LORETA) approach, based on nociceptive repeated laser stimulation (RLS). We delivered laser stimuli to the dorsum of both hands and analysed the γ-band LORETA activations and the ERP γ-power magnitude induced by laser stimulation, as well as the heart rate variability (HRV).

RESULTS

We found partially preserved cortical activations and ERP γ-power magnitude in all MCS and two UWS individuals. These effects were paralleled by a purposeful behaviour, and a reduced HRV concerning nociceptive stimulation, whereas the two UWS individuals showed no more than reflex behaviours, besides a strong limbic activation.

CONCLUSIONS

Some UWS patients may somehow perceive the affective components of nociceptive stimulation.

SIGNIFICANCE

The diagnosis of functional locked-in syndrome should be taken into account when dealing with DOC differential diagnosis.

Detecting pain in traumatic brain-injured patients with different levels of consciousness during common procedures in the ICU: typical or atypical behaviors?

PURPOSE

Pain behaviors such as grimacing and muscle rigidity are recommended for pain assessment in nonverbal populations. However, these behaviors may not be appropriate for critically ill patients with a traumatic brain injury (TBI) depending on their level of consciousness (LOC). This study aimed to validate the use of behaviors for assessing pain of critically ill TBI adults with different LOC.

METHODS

Using a repeated measure within subject design, participants (N=45) were observed for 1 minute before (baseline), during, and 15 minutes after 2 procedures: (1) noninvasive blood pressure: NIBP (non-nociceptive); and (2) turning (nociceptive). A behavioral checklist combining 50 items from existing pain assessment tools and video recording were used to describe participants' behaviors. Intrarater and interrater agreements of observed behaviors were also examined.

RESULTS

Overall, pain behaviors were observed more frequently during turning (median=4; T=-5.336; P≤0.001) than at baseline (median=1), or during noninvasive blood pressure (median=0). TBI patients' pain behaviors were mostly "atypical" and included uncommon responses such as flushing, sudden eye opening, eye weeping, and flexion of limbs. These behaviors were observed in ≥25.0% of TBI participants during turning independent of their LOC, and in 22.2% to 66.7% of conscious participants who reported the presence of pain. Agreements were >92% among and between the 2 raters.

CONCLUSIONS

This study support previous findings that critically ill TBI patients could exhibit atypical behaviors when exposed to nociceptive procedures. As such, use of current recommended pain behaviors as part of standardized scales may not be optimal for assessing the analgesic needs of this vulnerable group.