Variability of the Peripheral Perfusion Index (PI) During Epidural Analgesia for Labor: A Single-Centre Prospective Observational Study

Background: The Perfusion Index (PI) is the ratio of the pulsatile (AC) to the non-pulsatile (DC) component of light absorption in the photoplethysmographic waveform recorded during pulse oximetry, expressed as a percentage. Originally used as an indicator of pulse-oximeter signal quality, PI is now recognised as a non-invasive measure of peripheral perfusion. Because both signal components are influenced chiefly by vascular tone and vascular-bed filling, PI changes across clinical states. Spontaneous vaginal labor involves changes in cardiac output, peripheral resistance and blood redistribution, and therefore in PI. Neuraxial (epidural) analgesia further modifies PI: the sympathetic block it produces causes vasodilation and compensatory changes in peripheral resistance in non-blocked regions, altering peripheral perfusion. These changes can be captured systemically by the finger pulse oximeter routinely used to monitor labor analgesia. Analysing PI during epidural monitoring may therefore provide clinically useful information about correct block placement, drug distribution in the epidural space across successive stages of labor, and thus analgesic effectiveness.

Design and population: Prospective observational study. Participants are patients admitted to the labor ward of the Department of Obstetrics and Gynaecology, Gynaecologic Oncology and Gynaecologic Endocrinology, University Clinical Centre in Gdańsk, who receive epidural analgesia during vaginal delivery - either as the sole regional technique or as combined spinal-epidural (CSE) analgesia. For CSE, only intrathecal opioids may be administered (the standard approach in these patients); intrathecal local anaesthetic is an exclusion criterion. Both spontaneous-onset and induced labors are eligible.

Recorded haemodynamic parameters: PI is recorded automatically together with peripheral oxygen saturation (SpO2). Additional parameters recorded with standard monitors are arterial blood pressure, maternal heart rate (HR) and fetal heart rate (FHR). Monitoring begins before placement of the regional block.

Measurement schedule: Parameters are recorded every 5 minutes for the first 30 minutes after administration of local anaesthetic (LA) into the epidural space, and every 15 minutes thereafter. When bolus LA doses are given into the epidural space, 5-minute recording is resumed for 30 minutes from the time of administration. Data are archived as printouts from the labor-ward telemetry system.

Regional block data: The type of block and the doses/volumes and concentrations of all administered drugs are recorded with exact times. For drugs given by infusion, the flow rate per unit time and the time range for each rate are recorded.