Mechanisms for Brain-Damaging Acute Birth Asphyxia Associated with Normal or Near-Normal Umbilical Acid-Base balance

Abstract

It is a common misconception to believe that brain-damaging birth asphyxia is consistently associated with an umbilical cord arterial pH of less than 7.00 at the time of birth. Approximately 40% of infants with brain damage attributable to birth asphyxia have an umbilical artery (UA) pH of 7.00 or greater. This paper describes the various explanations for observing brain-damaging acute birth asphyxia associated with normal or near-normal UA pH values. What is known: Approximately 40% of infants with brain damage attributable to birth asphyxia have a UA pH of 7.00 or greater. What this study adds: Various explanations are presented to explain the occurrence of brain-damaging asphyxia with normal or near-normal acid-base values. This phenomenon has not been previously described. Key messages: -Approximately 40% of infants with brain-damaging birth asphyxia have an umbilical artery cord pH of 7.00 or greater, with most having of these having a pH greater than 7.20. -Technical explanations for this phenomenon include sampling only the umbilical vein and sampling blood with air bubbles. -The two most common pathophysiologic mechanisms to explain the lack of acidemia are complete occlusion of the umbilical cord and circulatory collapse. -Other brain-damaging processes without fetal acidemia include birth trauma, synergism, intra-uterine resuscitation, and post-asphyxial hypoxia.