Effect of Pain Relief on Arterial Blood Gas Values During Labor

Alterations in Cardiopulmonary Physiology During Pregnancy

“…In active labor the hyperventilation of pregnancy increases, and tachypnea caused by pain and/or anxiety may result in marked hypocapnia and respiratory alkalosis. [35][36][37] Superimposed metabolic alkalosis can be produced by volume depletion and vomiting. Alkalosis can adversely affect fetal oxygenation by reducing uterine blood flow.…”

“…38 Considerable variability occurs in the breathing rate and pattern in labor, and in some patients severe pain and anxiety may lead to rapid shallow breathing with alveolar hypoventilation, atelectasis, and mild hypoxemia.. 36 Adequate pain relief with narcotics or epidural analgesia results in significant blunting of the hyperventilation and can correct the gas exchange abnormalities associated with active labor. 36,37 Epidural anesthesia using local anesthetic agents may affect abdominal muscle function and impair peak expiratory pressure and the ability to cough. 39 Pregnancy-associated changes in lung function reverse significantly in the first 72 hours postpartum, returning to baseline within a few weeks.…”