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

This method may help answer key questions in the pain assessment research fields such as objective pain monitoring protocols focusing on individual nociceptive reflexes in adult ICU patients who cannot self-report their pain scores due to an altered level of consciousness, the use of sedative agents, or mechanical ventilation. The main advantage of this technique is that it may offer a monitoring tool for individual and analgesic titration. Begin by positioning the patient in the bed to maintain angles of 120 degrees of flexion of the hip and 130 to 160 degrees at the knee.

Place the palm or side of the wrist upwards. Next, shave hair at the application sites. Remove any body lotion by cleaning the skin with soap and water, and rub the skin gently with a dry washcloth or gauze.

Ensure the application site is clean and dry. Use skin preparation paper to abrade the application site to ensure best contact with the electrode. For the pupil dilation reflex or PDR assessment, place two silver-silver chloride electrodes with highly conductive wet gel at the wrist on the skin area enervated by the median nerve, keeping the palm or side of the wrist facing upwards.

Then, for the nociceptive flexion reflex, or NFR assessment, place two stimulation electrodes at the ankle distal to the lateral malleolus, stimulating the sural nerve area. Next, place two registration electrodes for EM tube recording at the biceps femoris muscle four finger breadths above the popliteal fossa, posterior to the iliotibial band on the ipsilateral leg. Finally, place one reference electrode on the quadriceps tendon.

Begin by attaching the lead wire to the stimulation electrodes at the wrist. Verify that the black labeled part is attached to the most distal electrode, and perform an impedance control indicated by the colored symbols. Then, select the measurement protocol, pupillary pain index or PPI, through menu selection on the touch screen display.

Next, open the eyelid and place the camera in an optimal position. Let the rubber eyecup rest on the orbit enclosing the whole eye. Center the pupil in the middle of the screen and verify the position by pursuing a pupil completely colored green.

Ensure the contralateral eye is closed in order to decrease the consensual light response. Wait for at least five seconds to start the measurement, ensuring a stabilization period necessary for pupil accommodation. Following the stabilization period, start the test by pushing the trigger button and hold the button for a few seconds until the pupil assessment is complete.

Ensure that the entire measurement cycle is executed by two audible signals heard at the start and finish. Finally, review the results automatically displayed after 15 seconds on the screen. Begin by attaching the lead wires for stimulation, recording, and reference.

Verify whether the black labeled parts are attached to the most distal electrodes. Note the white is for reference value recording at the knee. Turn the device on when connected to a power supply.

Then, start the measurement. Identify the currents applied to the patient and number of stimulations. Observe the raw EMG displayed 200 milliseconds before to 300 milliseconds after stimulation.

Feel the EMG electrode on the thigh. Finally, note the reflex range and the reflex threshold value shown in milliamps. From a group of 40 critically ill, ventilated patients in the ICU department, a range of people characteristics indicate different PPI scores based on the level of electrode stimulation.

Further, the NFR was identified in 72%of the patients. While NFR threshold tracking was not possible in 13%of the patients despite optimal measurement conditions, suggesting a deep analgosedation level, excessive nociceptive stimulation above 100 milliamps was not used. Once mastered, this technique can be done in several minutes for PDR evaluation, and less than 30 minutes for NFR assessment in critically ill adult ICU patients.

While attempting these procedure, it’s important to remember to optimally do the skin preparation and apply the electrodes properly. Following these procedure, other physiologic pain measurements and behavior pain scales should be further explored, validated, and combined for an analgesic health titration in individual ICU patients. After its development, this technique paved way for other researchers in the field of pain assessment techniques to further explore nociceptive reflexes in adult ICU patients.

After watching this video, you should have a good understanding how to perform PDR and NFR assessment in critically ill patients. Don’t forget that working with nociceptive stimulation in critically ill can be potential hazardous, and safety precautions should be followed all the time.