To the Editors:
In retrospectively validating their algorithm for “category II” electronic fetal heart rate (FHR) monitoring (EFM) tracings, Clark et al
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compare patients with and without metabolic acidosis (MA) in cord blood from 2 hospitals using different cord acquisition strategies (universal, 111 vs selective, 9).In 120 patients with MA, the algorithm mandated intervention in only 55/120 (45.8%), but only 35/55 (60.0%) received cesareans. Adherence to the algorithm would have raised the cesarean rate, but without clear benefit. In 120 controls (non-MA category II?), clinical and algorithm-driven intervention rates were comparable (18-19%). The authors did not analyze these differences or the impact of hospital, initial tracing, labor abnormalities, timing and urgency of delivery, and long-term outcomes on the risk of MA; nevertheless, they consider their results to represent the limit of what can be done with EFM.
The authors’ explanations for the 54.2% (65/120) of patients with MA in whom the algorithm failed to recommend intervention challenge fundamental precepts of fetal monitoring. In 21/65 (32.3%, 17.5% of total MA), acidosis was not suspected. This undermines the notions that EFM has low false-normal rates and that category II tracings exclude MA. Some of these tracings may have been maternal, not fetal. Neonates with unanticipated MA had more benign patterns and likely required no special attention. FHR patterns may be better predictors of outcome than MA. In 22/65 (33.8%, 18.3%), intervention was considered “timely” (<60 minutes), but MA not prevented–a significant limitation of the algorithm given forewarning from prolonged, abnormal FHR patterns.
In 12/65 (18.5%, 10.0%), tracings were “inadequate” or stopped prematurely. Indeterminable tracings increase the risk of adverse outcome and deserve attention.
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In 10/65 (15.4%, 8.3%), presumably unpreventable MA was preceded by a sentinel event with rapid deterioration of the FHR. Factors causing the sentinel events (eg, tachysystole, hypotension) were not assessed. Avoiding both unnecessary and emergency interventions seem important goals of any algorithm.
The ultimate objective of intrapartum surveillance is the prevention of injury for which even severe MA is a poor predictor–certainly not a surrogate. Most newborns with acidemia are healthy, but nonacidemic neonates may have undergone harm during labor through decreased cerebral blood flow (ischemia) and infection/inflammation.
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EFM classifications, algorithms, and endpoints require validation. The authors have not “validated” their protocol nor, do we believe, have they defined the limits of EFM surveillance. Their report uncovers deficiencies of a classification of FHR patterns predicated solely on detecting MA. If we are to improve outcomes and cesarean delivery rates we must extend the perspective of surveillance beyond the search for MA.
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References
- The limits of electronic fetal heart rate monitoring in the prevention of neonatal metabolic acidemia.Am J Obstet Gynecol. 2017; 216: 163.e1-163.e6
- Relation of fetal heart rate signals with unassignable baseline to poor neonatal state at birth.Med Biol Eng Comput. 2012; 50: 717-725
- Intrapartum fetal heart rate patterns in infants (> or =34 weeks) with poor neurological outcome.Early Hum Dev. 2009; 85: 235-238
- Neonatal encephalopathy and the association to asphyxia in labor.Am J Obstet Gynecol. 2014; 211: 667.e1-667.e8
- Time to optimize and enforce training in interpretation of intrapartum cardiotocograph.BJOG. 2016; 123: 866-869
Article Info
Publication History
Published online: January 28, 2017
Footnotes
The authors report no conflict of interest.
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© 2017 Elsevier Inc. All rights reserved.
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- The limits of electronic fetal heart rate monitoring in the prevention of neonatal metabolic acidemiaAmerican Journal of Obstetrics & GynecologyVol. 216Issue 2
- PreviewDespite intensive efforts directed at initial training in fetal heart rate interpretation, continuing medical education, board certification/recertification, team training, and the development of specific protocols for the management of abnormal fetal heart rate patterns, the goals of consistently preventing hypoxia-induced fetal metabolic acidemia and neurologic injury remain elusive.
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