Objective Nociceptive Assessment in Ventilated ICU Patients: A Feasibility Study Using Pupillometry and the Nociceptive Flexion Reflex

Summary

Pain assessment in anesthetized patients who cannot communicate with the outside world in any way remains challenging despite the development of innovative objective pain evaluation tools. In this project, the pupillary dilation reflex and the nociception flexion reflex are assessed in critically ill, mechanically ventilated adult patients.

Abstract

The concept of objective nociceptive assessment and optimal pain management have gained increasing attention. Despite the known negative short- and long-term consequences of unresolved pain or excessive analgosedation, adequate nociceptive monitoring remains challenging in non-communicative, critically ill adults. In the intensive care unit (ICU), routine nociceptive evaluation is carried out by the attending nurse using the Behavior Pain Scale (BPS) in mechanically ventilated patients. This assessment is limited by medication use (e.g., neuromuscular blocking agents) and the inherent subjective character of nociceptive evaluation by third parties.

Here, we describe the use of two nociceptive reflex testing devices as tools for objective pain evaluation: the pupillary dilation reflex (PDR) and nociception flexion reflex (NFR). These measurement tools are non-invasive and well tolerated, providing clinicians and researchers with objective information regarding two different nociceptive processing pathways: (1) the pain-related autonomic reactivity and (2) the ascending component of the somatosensory system. The use of PDR and NFR measurements are currently limited to specialized pain clinics and research institutions because of impressions that these are technically demanding or time-consuming procedures, or even because of a lack of knowledge regarding their existence.

By focusing on the two abovementioned nociceptive reflex assessments, this study evaluated their feasibility as a physiological pain measurement method in daily practice. Pursuing novel technologies for evaluating the analgesia level in unconscious patients may further improve individual pharmacological treatment and patient related outcome measures. Therefore, future research must include large well-designed clinical trials in a real-life environment.

Introduction

Many critically ill patients in the Intensive Care Unit (ICU) are prone to experience pain during daily care or during diagnostic or therapeutic procedures. Substandard nociceptive evaluation and consequent suboptimal pain management may increase stress and anxiety¹. Persistent pain not only increases circulating catecholamines, compromises tissue perfusion and reduces oxygen delivery² but also activates catabolic hypermetabolism, thus contributing to hyperglycemia, lipolysis and muscle loss. All of these elements impair the healing process and increase the risk of infections^3,

Protocol

This single-center cohort study was performed in accordance with the ethical standards of ICH-GCP and the Declaration of Helsinki after it was approved by the institutional review board and ethics committee of the Antwerp University Hospital, Belgium (study identifier: 16/33/334). The study was registered at Clinicaltrials.gov (NCT02916004) before its initiation.

All included patients were sedated in accordance with the standard hospital sedation protocol before study enrollment. The patients were titrated to a Richmond Agitation-Sedation Scale (RASS) set by the ICU physician. Patients were sedated to a RASS - 4 prior to study inclusion. Al....

Results

We used both reflex assessments in a total of 40 critically ill ventilated subjects (38% females) at the ICU department using the previously described protocol. Patients with various indications for analgo-sedation were included: 58% for primary respiratory insufficiency, 23% due to multiple organ failure, 10% of the patients had a septic shock, and 9% were defined as being sedated for other reasons (e.g., cardiogenic reasons). All measurements were performed by the same investig.......

Discussion

This paper describes the application of two nociceptive reflex devices for objective (patient-independent) pain assessment in adult ICU patients. Moreover, the evaluation of the PDR and the NFR characteristics are described.

Pain and delirium are common in hospitalized patients, often in combination, and may adversely affect outcome parameters. In the ICU, opioids are frequently administered, sometimes in combination with other sedative agents, to protect patients against stressful stimuli suc.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Neurolight Algiscan	ID Med, Marseille, France	Pupillometre 13235	Infra red camera for pupil dilation reflex measurement
Paintracker	Dolosys GmbH, Belin, Germany	Paintracker V1 2497	Nociception flexion reflex assessment tool
Red DotTrace Prep	3M, Ontario, Canada	CV-0001-7353-0	Skin surface preparation tape
Electrodes - BlueSensor N	Ambu, Ballerup, Denmark	BlueSensor N N-00-S/25	Low-impedance Ag-AgCl skin electrodes