The Nociception Level (NOL) Index for Pain Assessment in the Adult Intensive Care Unit

Background: Assessing pain in adult intensive care units (ICU) is challenging because self-report is often non-feasible due to patients' critical care conditions, mechanical ventilation and/or sedation. The Critical-Care Pain Observation Tool (CPOT) is the reference standard alternative measure of pain, but patients must be capable of expressing behaviors. Therefore, these cannot be used in patients who are heavily sedated or unresponsive (e.g., in coma), and other pain assessment methods must be explored. Vital signs alone (e.g., heart rate, blood pressure) are not valid for ICU pain assessment with inter-individual variability being a major limiting factor. The newly developed Nociception Level (NOL) index (Medasense Biometrics Ltd., Ramat Gan, Israel) is a numeric value from 0 to 100 obtained from simultaneous different parameters including heart rate, heart rate variability, photoplethysmography pulse wave amplitude, skin conductance level, number of skin conductance fluctuations, skin temperature, and their time derivatives. A NOL value>25 would indicate nociception and related pain in the field of anesthesia. The NOL could adequately classify nociceptive versus non-nociceptive stimuli with an area under the curve (AUC) >0.90 in anesthetized patients. The use of the NOL in the ICU is new. The investigators completed pilot work showing feasibility and promising validity results of the NOL for the detection of self-reported pain intensity and CPOT scores as reference criteria during chest tube removal and endotracheal suctioning in medical and surgical ICU patients.

The goal of this study is to validate the NOL index for the assessment of nociception and related pain in the ICU. Specific objectives are to examine the NOL's ability to:

1. detect pain in patients able to self-report and in non-communicative patients able to exhibit behavioral responses (i.e., criterion validation);
2. correlate with the patients' self-reports of procedural pain distress during nociceptive procedures (i.e., convergent validation); and
3. discriminate between non-nociceptive and nociceptive procedures as well as before and after the administration of a breakthrough dose of an opioid (i.e., discriminative validation).

As a complementary objective, feasibility and clinical utility of the NOL's use will be described from the ICU nurses' perspective.

Methods: A prospective cohort observational design will be used in two medical-surgical ICUs in Montreal where the research team has developed the expertise in the NOL's use. Using consecutive sampling, the sample will include three patient groups representative of the ICU population who: a) can communicate (able to self-report) and exhibit behaviors, b) cannot communicate but can exhibit behaviors, and c) cannot communicate nor exhibit behaviors. Participants will be observed before, during and 15 minutes after non-nociceptive (i.e., soft touch, cuff inflation) and nociceptive procedures (e.g., chest tube or drain removal, endotracheal suctioning, arterial or intravenous catheter insertion, wound care, bed turning) part of standard care. The NOL will be continuously monitored during all these time points, patients able to self-report will rate their 0-10 pain intensity and procedural pain distress, and patients unable to self-report in whom behaviors are observable will be assessed with the CPOT. Analgesic and sedative agent use will also be documented. Mixed linear models for repeated measures will be used to compare time points, procedures, and their interactions. Receiver Operating Characteristic curve analysis of the NOL will be performed using self-reported pain intensity and CPOT scores as reference criteria. A convenience sample of ICU nurses will also be recruited to offer them the opportunity to learn more about the NOL device, to be exposed to its application at the bedside, and to evaluate its feasibility and potential clinical utility for ICU pain assessment.

The expected outcomes include the validation of a multi-parameter technology in a new context of care which could be used as an alternative measure to detect nociception and related pain and to improve pain management and evaluation of analgesia effectiveness in vulnerable ICU patients.