Assessment of Nociception in Obstetric Patients During Epidural Analgesia

Introduction:

Epidural analgesia is the most effective method of labor pain relief to this day. The lumbar epidural analgesia aims to induce a sensory block from T10 to L1, while at the same time facilitating the motor action of the lower limbs (L2-L5), thereby enabling the continued cooperation of the mother in the birth process.

Pain assessment is crucial for pain management and to date relies almost solely on subjective monitoring using self-assessment scales of the subject, which can be affected by personality, behavior, and psychological characteristics. Objective tools to measure pain have been developed. They rely on the changes in the balance between sympathetic and parasympathetic activity and include the heart rate variability, blood pressure, skin electrical conductivity and the vasomotor reflex and the electroencephalogram pupil. Nociception represents the integrated response to painful stimuli including the neural, hormonal and behavioral activity. Combination of multiple nociception-related parameters yielded stronger associations with the noxious stimuli compared with each parameter alone.

The PMD-200 monitor with NOL technology (Medasense Biometrics Ltd. Ramat Gan, Israel) is a novel, propriety, monitoring device based on a combination of nociception related physiological variables including heart rate, heart rate variability, photo-plethysmographic waveforms, skin conductance, and their time derivative. Based on a random forest model, the device generates the Nociception level (NOL) index, displayed as a scale from 0-100 with 0 representing no nociception and 100 representing extreme nociception. A NOL level of less than 25 arbitrary units is associated with adequate analgesia in patients under general anesthesia.

So far, the objective assessment of pain has been restricted mainly to patients who were under general anesthesia. Data in conscious patients is scant . The study design is to evaluate how nociception changes in the awake patients, and especially, how its changes following blockade of the painful stimuli. Study population parturients who will be scheduled to receive epidural analgesia for labor. This allow us to study the nociceptive level index during uterine contractions before and after the onset of epidural analgesia.