Pain has been defined by the International Association for the Study of Pain (IASP) as "an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage". Labour pain is the pain experienced during labour and childbirth and it's characterised by nociceptive pain accompanied by sympathetic activation.

Since more than fifty years, the development of hospital obstetric assistance for labour, allowed the implementation of the pain relief culture in the demanding parturients population.

The ideal labour analgesic technique should provide consistent pain relief at any stage of labour, have a long duration of action, while being safe both for the mother and the foetus. It should also anticipate undesirable side effects, such as motor block.

The current gold standard for obstetric analgesia is the lumbar epidural technique using the administration of local anesthetics combined with opioids. However, the best administration mode is currently under debate, the main interest being the local anesthetic sparing responsible for various maternal side effects and the quality of maternal analgesia.

Despite the intense research in the field, the evaluation of the labour pain remains difficult as performed by the midwife and the anesthesiologist based on the patient's behaviour and her subjective self-assessment.

The PMD100™ (Medasense Biometrics Ltd., Ramat Yishai, Israel) is a non-invasive multiparametric nociception monitoring that has proved its interest in the intraoperative evaluation of patient's physiological response to pain under general anesthesia, using the NOL index variation. Nonetheless, it has been barely investigated in patients receiving locoregional anesthesia and never in the context of obstetrical pain.

The investigators support the idea that the NOL index monitoring could allow us to assess the degree of nociceptive stimulation related to obstetric labour and its variation under epidural analgesia, as well as to compare the efficacy of sensitive block using different epidural administration modes.

The aim of this pilot study is to evaluate the NOL Index variation during labour pain management with epidural analgesia.

The investigators will focus on the evaluation of analgesia in relation with the self-reported pain intensity, and secondly, the characteristics of the sensory block, the hemodynamic variables and side effects.

1. Design:

   The investigators will conduct a prospective, repeated measures, monocentric, observational pilot study.

   The study will be carried out in the anesthesia department of the Saint Pierre University Hospital in collaboration with the obstetrics department.

   Parturient women in labour admitted into the delivery room, during the beginning of the first stage of labour demanding for an epidural will be recruited after signed written informed consent.

   The number of patients to be included has been calculated to be 55.

2. Anesthetic management:

   An epidural will be placed, initiated and maintained by the investigators according to the department's usual practice (including monitoring, technique and pump protocol).

   The epidural will be considered successful when the sensitive block has reached a T10 level within maximum 30 minutes.

   If the patient is not relieved within 30 minutes a new bolus readministration will be administered by the Patient-Controlled Epidural Analgesia (PCEA) pump.

   In case of:

   • Dura mater breach : exclusion of the patient from the protocol
   • Venous puncture : epidural replacement at another level
   • Hypotension (defined as a 20% drop in baseline blood pressure) needing vasopressors
   • Hypotension and fetal heart rate abnormalities

3. Nociception monitoring NOL Index is based on several variables nonlinear combination of heart rate, heart rate variability, photoplethysmograph wave amplitude, skin conductance, skin conductance fluctuations, and their time derivatives and variation upon activation of the sympathetic nervous system in response to a stimuli. The normal range of the NOL index has been set between 10 and 25, a value above 25 indicates that the patient is experiencing a nociceptive stimulation.

The monitoring will be placed on the contralateral side to the non invasive blood pressure (NIBP) upon recruitment and it will be calibrated during 30 seconds to 2 minutes period of time without uterine contraction, objectified by the toco monitoring and confirmed by the parturient before epidural placement.

Consented patients will be taught how to use the 0-10 numeric rating scales (NRS) to report pain intensity (where zero indicates no pain and 10 indicates the worst possible pain).

The NOL monitor will be hidden throughout the procedure, to reduce any bias during self-reporting.

The patient will be asked to report the self-evaluated pain at each contraction using the NRS scale during the initial 15 minutes following the initial bolus.

The characteristics of the block achieved (sensory and motor), analgesic and hemodynamic variables will be collected throughout the study period (1 hour after the implementation of the epidural) at several time points as follows :

T0 - Epidural request T1 - End of loading dose (bolus) T2 - Loading dose + 15 mins T3 - Loading dose + 30 mins T4 - Loading dose + 45 mins T5 - Loading dose + 60 mins

If a supplementary bolus is needed (PCEA) all the aforementioned variables will be collected.

Inclusion Criteria:

• Patients > 18 years old, able to self-report
• American Society of Anesthesiologists (ASA) score I to II
• Gestational age > 36 weeks of amenorrhea
• Primiparous or multiparous
• In labour
• Request and indication for epidural analgesia
• Height 160-175cm
• Intensity of pain objectified by Visual Analogue Scale (VAS) > 3/10

Exclusion Criteria:

• Patient refusal
• Contraindications to epidural analgesia (allergy to local anesthetics, coagulopathy, local infections)
• BMI > 40 kg/m2
• Weight > 110kg
• History of caesarean section
• Pre-eclampsia or pregnancy-induced hypertension
• Cardiac arrhythmias (including atrial fibrillation)
• Treatment with β-blockers
• Chronic opioid use
• History of substance abuse/dependency
• Psychiatric pathology (including depression, psychosis, etc.)
• Total language barrier
• Epidurals at uncomfortable times (night)

Parturient population

Pregnant women in labour requesting an epidural analgesia