Evaluation of Regional Distribution of Ventilation During Labor With or Without Epidural Analgesia

With an efficient epidural analgesia the physiological effects of pain are disabled during labor. Pain may cause an increase of minute volume, oxygen consumption and a decrease of paCO2 (Arterial CO2 pressure). The study will evaluate the lung function before and after labor with and without epidural analgesia. With more efficient breathing, the occurence of atelectasis should be reduced; this effect will be investigated in these settings for the first time with the electrical impedance tomography, which is a completely non-invasive measure.