Near-Infrared Spectroscopy (NIRS) to measure nociception following noxious stimulation in critically ill infants

Background An admission to the intensive care unit causes major physical and psychological stress for children. Pain contributes significantly to this distressing experience. To optimize pain relief, a sound pain assessment tool is essential. Although this need is recognized, only a few pain assessment instruments have been thoroughly tested with this population using a rigorous scientific approach, and none have been shown to be superior to the other. Recent studies using near-infrared spectroscopy (NIRS) in term and premature infants indicate that nociceptive stimuli cause haemodynamic changes in specific cortical regions. This suggests a new avenue for assessing and quantifying pain processing in critically ill infants that could be more sensitive and specific to the nociceptive response.;Aims In this series of studies we examined regional cerebral and systemic haemodynamic changes, as well as behavioural reactions in critically ill infants with congenital heart defect (CHD) during chest drain removal following open heart surgery. Specifically, we examined changes within subjects, as well as individual factors (age, sex, medication) affecting the change and associations between cerebral haemodynamic changes, systemic physiological changes, and Face Legs Activity Cry Consolability (FLACC) pain scores.;Subjects Critically ill infants less than 12 months of age admitted to a cardiac intensive care unit after cardiac surgery for CHB comprised the sample.;Outcome measures Changes in cerebrovascular haemoglobin concentrations (NIRS), as well as heart rate (ECG), systemic arterial oxygen saturation (pulse oximetry), and mean arterial blood pressure (arterial line) were recorded during three distinct epochs (Baseline, Tactile stimulation, and Chest-drain removal). Behavioural manifestations were also captured through video and were subsequently rated for pain with the FLACC scale.;Design Descriptive correlational design.;Results We studied 32 infants with CHD and obtained FLACC pain scores in 20 of these infants. Cerebral deoxygenated haemoglobin concentrations significantly increased across the epochs (p<.01). Physiological systemic responses were not found to be associated with the cerebral haemodynamic parameters. Mean FLACC pain scores significantly increased across the epochs (p < .001) with a mean score of 7/10 during the noxious procedure, despite administration of an analgesic agent (morphine). Sex of patients was found to be a determining factor in the cerebral haemodynamic responses and pain FLACC scores. Pharmacological treatments, age and weight of patients were significantly associated with cerebral and systemic haemodynamic responses, as well as the FLACC pain scores. The administration of a sedating agent (midazolam) had a significant dampening effect on the pain behaviours as assessed by the FLACC scale.;Conclusions Using a multidimensional pain measurement approach, we demonstrated that significant cerebral, physiological and behavioural activity was present in response to a noxious procedure in critically ill infants despite the administration of analgesic treatment. Although pain behaviours were significantly dampened by the sedating agent, the cerebral response was still evident. Thus, assessment of cerebral haemodynamics in the context of pain seems to be an important addition when a sedating agent is administered. Our data suggest that NIRS is a potentially useful technique for assessing pain evoked cerebral activation in critically ill infants.