Labour Pain: 1. Painful uterine contraction of labour causes respiratory stimulation, increasing tidal volume, minute volume with a much greater increase in alveolar ventilation. As a result of hyperventilation there occurs maternal respiratory alkalosis, which causes O2 dissociation curve shift to left with increased maternal oxygen affinity and decreased release at the tissue level. 2. Hypocarbia due to hyperventilation also leads to hypoventilation between contractions which may decrease maternal pao2. 3.
Oxygen consumption is increased during painful (powerful) contractions of the uterus during labour. 4. In addition to the above factors, hypocarbic uteroplacental vasoconstriction is potential causes of fetal hypoxia. (Mechanism; Double Bohr Effect; maternal hyperventilation, maternal alkalosis, gives less oxygen to foetus causing foetal acidosis ) 5. Labour pain causes increased…
