ajog.org
Letters to the Editors
Maternal oxygen use during labor TO THE EDITORS: We read with interest the Clinical Opinion of Hamel et al1 in which the authors suggest that supplemental maternal oxygen should only be used for conditions of maternal and not fetal hypoxemia. Although the article raises important points, we believe there are indications of maternal oxygen for treatment of fetal hypoxemia. The authors note 2 randomized studies, containing relatively low numbers of laboring patients, which failed to demonstrate a fetal benefit. Notably, both studies reported no difference in umbilical cord pH among the groups. Importantly, pH is influenced by both metabolic and respiratory (ie, pCO2) acidosis, the latter of which is independent of O2 levels and may change acutely and significantly within minutes with cord occlusion. The authors’ further suggest that maternal oxygen supplementation in the presence of severe fetal acidosis may have potential detrimental effects (eg, free radical formation) and highlight the consequences of hyperoxia. However, one cannot produce fetal hyperoxia via maternal oxygen supplementation.2 Maternal O2 supplementation markedly increases maternal arterial pO2, but the minimal increase in arterial O2 content in normoxemic women results in a minimal impact on normoxemic fetal arterial O2 content. In contrast, under conditions of relative fetal hypoxemia, the fetus operates at the steep portion of the O2 saturation curve and achieves greater benefit of maternal hyperoxia.2 Late decelerations are believed to be secondary to either chemoreflex (vagal) responses to mild hypoxemia or direct myocardial suppressive effects of more severe hypoxemia. Variable decelerations result from umbilical cord compression-induced hypoxemia and result in progressively increasing level of acidosis dependent upon the severity and duration of the decelerations.3 As persistent hypoxemia results in acidosis, preventing mild or more severe hypoxemia from producing acidosis is the physiologic basis for oxygen supplementation. Although maternal hyperoxia is likely overutilized in labor management, we suggest that maternal oxygen supplementation should be continued in cases in which early fetal hypoxemia is suspected on the basis of fetal monitor tracings. Michael G. Ross, MD, MPH Department of Obstetrics and Gynecology David Geffen School of Medicine at University of California Los Angeles Los Angeles, CA Department of Obstetrics and Gynecology Harbor-University of California Los Angeles Medical Center 1000 W. Carson St., Box 467 Torrance, CA 90502 [email protected] Kevin E. Amaya, DO Department of Obstetrics and Gynecology Harbor-University of California Los Angeles Medical Center Torrance, CA The authors report no conflict of interest.
410 American Journal of Obstetrics & Gynecology MARCH 2015
REFERENCES 1. Hamel MS, Anderson BL, Rouse DJ. Oxygen for intrauterine resuscitation: of unproved benefit and potentially harmful. Am J Obstet Gynecol 2014;211:124-7. 2. Meschia G. Transfer of oxygen across the placenta. In: Gluck L, ed. Intrauterine asphyxia and the developing fetal brain. Chicago, IL: Year Book Medical Publishers; 1977. 3. Ross MG, Jessie M, Amaya K, et al. Correlation of arterial fetal base deficit and lactate changes with severity of variable heart rate decelerations in the near-term ovine fetus. Am J Obstet Gynecol 2013;208: 285-6. ª 2015 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.ajog. 2014.11.004
REPLY We appreciate the interest in our Clinical Opinion.1 After thorough consideration of the data cited in both letters (some, if not most of which was specifically addressed in our Clinical Opinion) our stance remains unchanged. The routine exposure of 1.5-2 million parturients and their fetuses annually (in the United States alone) to an unproved intervention is not supported by the current literature. Although maternal oxygen administration may make physiologic sense, it is not enough: physiologic plausibility has led to the use of many obstetric interventions that have subsequently been proven not helpful and, in some cases, clearly harmful. Pregnant women and their offspring deserve care and interventions that, whenever possible, are based on better data than are currently available to justify intrapartum oxygen use for fetal benefit. Rather than sanguinely assuming that the benefits of oxygen are selfevident, properly designed clinical trials should be conducted to assess the potential benefits and risks of intrapartum oxygen. Maureen S. Hamel, MD Warren Alpert Medical School of Brown University Department of Obstetrics and Gynecology Women and Infants Hospital 101 Dudley St. Providence, RI 02905 [email protected] Brenna L. Hughes, MD, MSc Dwight J. Rouse, MD, MSPH Warren Alpert Medical School of Brown University Department of Obstetrics and Gynecology Women and Infants Hospital, Providence, RI The authors report no conflict of interest.
REFERENCE 1. Hamel MS, Anderson BL, Rouse DJ. Oxygen for intrauterine resuscitation: of unproven benefit and potentially harmful. Am J Obstet Gynecol 2014;211:124-7. ª 2015 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.ajog. 2014.11.005
Letters to the Editors
Maternal oxygen use during labor TO THE EDITORS: We read with interest the Clinical Opinion of Hamel et al1 in which the authors suggest that supplemental maternal oxygen should only be used for conditions of maternal and not fetal hypoxemia. Although the article raises important points, we believe there are indications of maternal oxygen for treatment of fetal hypoxemia. The authors note 2 randomized studies, containing relatively low numbers of laboring patients, which failed to demonstrate a fetal benefit. Notably, both studies reported no difference in umbilical cord pH among the groups. Importantly, pH is influenced by both metabolic and respiratory (ie, pCO2) acidosis, the latter of which is independent of O2 levels and may change acutely and significantly within minutes with cord occlusion. The authors’ further suggest that maternal oxygen supplementation in the presence of severe fetal acidosis may have potential detrimental effects (eg, free radical formation) and highlight the consequences of hyperoxia. However, one cannot produce fetal hyperoxia via maternal oxygen supplementation.2 Maternal O2 supplementation markedly increases maternal arterial pO2, but the minimal increase in arterial O2 content in normoxemic women results in a minimal impact on normoxemic fetal arterial O2 content. In contrast, under conditions of relative fetal hypoxemia, the fetus operates at the steep portion of the O2 saturation curve and achieves greater benefit of maternal hyperoxia.2 Late decelerations are believed to be secondary to either chemoreflex (vagal) responses to mild hypoxemia or direct myocardial suppressive effects of more severe hypoxemia. Variable decelerations result from umbilical cord compression-induced hypoxemia and result in progressively increasing level of acidosis dependent upon the severity and duration of the decelerations.3 As persistent hypoxemia results in acidosis, preventing mild or more severe hypoxemia from producing acidosis is the physiologic basis for oxygen supplementation. Although maternal hyperoxia is likely overutilized in labor management, we suggest that maternal oxygen supplementation should be continued in cases in which early fetal hypoxemia is suspected on the basis of fetal monitor tracings. Michael G. Ross, MD, MPH Department of Obstetrics and Gynecology David Geffen School of Medicine at University of California Los Angeles Los Angeles, CA Department of Obstetrics and Gynecology Harbor-University of California Los Angeles Medical Center 1000 W. Carson St., Box 467 Torrance, CA 90502 [email protected] Kevin E. Amaya, DO Department of Obstetrics and Gynecology Harbor-University of California Los Angeles Medical Center Torrance, CA The authors report no conflict of interest.
410 American Journal of Obstetrics & Gynecology MARCH 2015
REFERENCES 1. Hamel MS, Anderson BL, Rouse DJ. Oxygen for intrauterine resuscitation: of unproved benefit and potentially harmful. Am J Obstet Gynecol 2014;211:124-7. 2. Meschia G. Transfer of oxygen across the placenta. In: Gluck L, ed. Intrauterine asphyxia and the developing fetal brain. Chicago, IL: Year Book Medical Publishers; 1977. 3. Ross MG, Jessie M, Amaya K, et al. Correlation of arterial fetal base deficit and lactate changes with severity of variable heart rate decelerations in the near-term ovine fetus. Am J Obstet Gynecol 2013;208: 285-6. ª 2015 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.ajog. 2014.11.004
REPLY We appreciate the interest in our Clinical Opinion.1 After thorough consideration of the data cited in both letters (some, if not most of which was specifically addressed in our Clinical Opinion) our stance remains unchanged. The routine exposure of 1.5-2 million parturients and their fetuses annually (in the United States alone) to an unproved intervention is not supported by the current literature. Although maternal oxygen administration may make physiologic sense, it is not enough: physiologic plausibility has led to the use of many obstetric interventions that have subsequently been proven not helpful and, in some cases, clearly harmful. Pregnant women and their offspring deserve care and interventions that, whenever possible, are based on better data than are currently available to justify intrapartum oxygen use for fetal benefit. Rather than sanguinely assuming that the benefits of oxygen are selfevident, properly designed clinical trials should be conducted to assess the potential benefits and risks of intrapartum oxygen. Maureen S. Hamel, MD Warren Alpert Medical School of Brown University Department of Obstetrics and Gynecology Women and Infants Hospital 101 Dudley St. Providence, RI 02905 [email protected] Brenna L. Hughes, MD, MSc Dwight J. Rouse, MD, MSPH Warren Alpert Medical School of Brown University Department of Obstetrics and Gynecology Women and Infants Hospital, Providence, RI The authors report no conflict of interest.
REFERENCE 1. Hamel MS, Anderson BL, Rouse DJ. Oxygen for intrauterine resuscitation: of unproven benefit and potentially harmful. Am J Obstet Gynecol 2014;211:124-7. ª 2015 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.ajog. 2014.11.005
