Photoplethysmographic evaluation of sympathectomy during epidural analgesia for vaginal delivery: ropivacaine versus levobupivacaine

INTERVENTION: Before administration of epidural analgesia, all of the patients will be given a prehydration consisting of 1000 ml Ringer's lactate solution intravenously. Before administration of epidural analgesia, a non‐invasive finger photoplethysmography probe will be placed around the first toe of the left leg, as well as the 3 ECG electrodes which will be placed on the chest and a cuff of the mercury sphygmomanometer which will be placed around the left upper arm. Every measurement of the finger photoplethysmography signal (measured simultaneously with the ECG) will be recorded between the contractions during labour, in a sequence of 30 seconds and will be automatically storaged in the BIOPAC SS4LA software. The mentioned finger photoplethysmography software enables re‐run of every single measurement to extract certain parameters (area under the curve, amplitude and the pulse transit time) from the finger photoplethysmography curve. Epidural space will be identified in the L3‐4 interspace by the loss of resistance technique, using 17 G Tuohy needle, in the lying or left lateral position of the patient. After identification of epidural space, epidural cathether will be inserted 4‐5 cm into the epidural space. After the aspiration test and administration of a test dose (3 ml of 2% lidocaine), the patients will be given a bolus dose of epidural analgesia, in the lying position with slightly (up to 30 degrees) elevated head of the bed. The patients will be randomised by the type of the local anesthetic solution given into the epidural space: group 1 will be given 10 ml of 0.125% ropivacaine + 100 mcg of fentanyl and group 2 will be given 10 ml of 0.125% levobupivacaine + 100 mcg of fentanyl. Dose, volume and concentrations of two local anesthetics are the same in both groups, as well as the dose of the opioid added in the mixture. The bolus dose of epidural will be applied in the following manner: first 5 ml of the local anesthetic/opiod solution will be given as a bolus, and the rest of the solution (5 ml) will be given after 3‐4 minutes, also as a bolus. The described procedure is a standarised protocol for painless vaginal delivery used at our institution. The study will be conducted in the labour ward, with a controlled ambient temperature of 24 degrees celsius. CONDITION: lumbar epidural analgesia sympathectomy mediated vasodilation vaginal delivery PRIMARY OUTCOME: Difference in the area under the curve of the finger photoplethysmography between the two groups. Area under the curve represents the whole surface area under the finger photoplethysmography curve and is derived from every single finger photoplethysmography measurement. The unit of measurement for the area under the curve of the finger photoplethysmography is mcvs (microvoltseconds). ; INCLUSION CRITERIA: The study will include all of the patients in whom lumbar epidural analgesia, as a standard method for painless vaginal delivery, is indicated. SECONDARY OUTCOME: Any abnormality of the fetal heart rate (decelerations) will be recorded in both of the groups by the cardiotocography which is continuously recorded during vaginal delivery in all of the patients. Any episode of the maternal hypotension will be recorded in both of the groups by the manual non‐invasive mercury sphygmomanometer. Maternal hypotension is defined as a drop of systolic blood pressure below the 90 mmHg. Difference between the amplitude of the finger photoplethysmography between the two groups. The amplitude of the finger photoplethysmography represents the maximum height of the finger photoplethysmography curve and is derived form every single finger photoplethysmography measurement. The unit of measurement for the amplitude of the finger photoplethysmography is mcv (microvolts). Difference in systolic and diastolic blood pressure between the two groups. The systolic and diastolic blood pressure will be measured by the non‐invasive mercury sphygmomanometer cuff which will be placed on the left forearm. Difference in the pulse transit time between the two groups. The pulse transit time is defined as the the time (in seconds) between the middle of the R wave of the electrocardiogram and the amplitude (maximum height) of the following finger photoplethysmography curve (i.e. the time needed for the pulse to travel from the heart to the peripheral blood vessels). Difference in visual analogue scale of pain (VAS score) between the two groups.