Quantitative pupillometry to assess nociception in a sedated patient with hemispheric cerebral infarction

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Editor,
Self-reporting by patients represents the gold standard for pain assessment in the ICU. However, many patients are unable to communicate because of sedation and/or brain lesions. Although recommended clinical scales exist in the practice guidelines for noncommunicative ICU patients,1 uncertainties remain over their performance in brain-injured patients.2 Recent interest surrounds the use of videopupillometry to assess nociception through the measurement of pupil reflex dilation during noxious stimulation in anaesthetised patients (see review).3 However, no data yet exists on the use of pupillometry to measure pupil reflex dilation amplitude in brain-injured patients. We report a case in which pupil reflex dilation was used in a sedated patient with hemispheric cerebral infarction and describe our findings of an asymmetric pupil reflex dilation response between the two eyes during tetanic stimulation. The Institutional Review Board of Sud-Est V (CS 10217, 38043 Grenoble, France) approved the publication of this case on 1 March 2016 (Ref CPP#16-RNI-04).
A 41-year-old man, with no medical history, presented with agitation and left hemiplegia because of the spontaneous occlusion of the right middle cerebral artery. His initial National Institute of Health Stroke Score was 14. Despite intravenous thrombolysis, his condition rapidly worsened with loss of consciousness. Under sedation and mechanical ventilation, the patient experienced a progressive rise in intracranial pressure because of marked space-occupying mass effect of the stroke. A right decompressive craniectomy was planned 24 h after the stroke. An i.v. infusion of midazolam and sufentanil was maintained postoperatively until the hemispheric cerebral oedema had resolved. Both pupils remained reactive and symmetric to light.
To assess nociception and analgesic requirements during this period of sedation, a portable infrared pupillometer (Algiscan, IDMed, Marseille, France) was used to determine pupil reflex dilation during a protocol of tetanic stimulation (100 Hz) applied to the skin area innervated by the ulnar nerve of each forearm. The intensity of the electric stimulation was automatically stepwise increased by 10 mA every second, from 10 to 60 mA, until pupil size had increased by 13% compared with baseline. The maximum intensity value allowed the determination of a pupillary pain index score ranging from 1 (pupil reflex dilation <5% for 60 mA) to 9 (pupil reflex dilation >13% for 10 mA): the higher the pupillary pain index value, the higher the sensibility to nociception.
Pupillary measurements were performed at day 2 and 8 under continuous sedation. Results obtained for pupil reflex dilation during endotracheal suctioning and pupillary pain index showed no evidence of nociception at day 2 (Table 1). The clinical behavioural pain scale score during endotracheal suctioning was low (3). At day 8 however, the patient was more reactive during endotracheal suctioning, as reflected by pupil reflex dilation measurements and higher behavioural pain scale score (5) and the pupillary pain index values obtained from left and right ulnar stimulations were asymmetric (Table 1). Midazolam and sufentanil infusions were stopped at day 10 and the tracheal tube was removed at day 15. The patient was discharged from the ICU with a persistent left hemiplegia. A cranioplasty was performed at day 90 after stroke.
Evaluating nociception in noncommunicative patients in the ICU, while challenging, has been associated with positive outcomes such as a shorter duration of mechanical ventilation and length of ICU stay.4 However, behavioural clinical indicators of pain cannot be observed with accuracy in too sedated or paralysed patients or in patients with brain lesions. In this context, the use of quantitative infrared pupillometry in the ICU has led to some promising findings. The pupil reflex dilation of sedated patients in response to noxious procedures was of greater magnitude than their haemodynamic changes.

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