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redicting neonatal acidemia by computer analysis: Costa et alhristian M. Pettker, MD; George A. Macones, MD, MSCE, Associate Editor

he article below summarizes a roundtable discussion of a study published in this issue of the Journal in light of its methodology, relevance to practice, and

mplications for future research. Article discussed:

osta A, Ayres-de-Campos D, Costa F, et al. Prediction of neonatal acidemia by computer analysis of fetal heart rate and ST event signals. Am J Obstetynecol 2009;201:464.e1-6.

he full discussion appears at www.AJOG.org, pages e1-4.

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DISCUSSION QUESTIONS

What is the specific question beingasked?

What do the inclusion and exclusioncriteria tell us about the study?

What was the primary outcome?

Why were tracings from the last hour oflabor used?

What difference does lack of traditionalfetal heart rate interpretation make?

Would you categorize this tool as adiagnostic test or a screening test?

Which statistical assessments weremost important?

What evidence supports higheraccuracy of combined computeranalysis?

rom Yale University School of Medicine,ew Haven, CT:

oderatorhristian M. Pettker, MDssistant professor

iscussantstephen F. Thung, MDssistant professor

ntonette Dulay, MDhird-year fellow

hristina Han, MDirst-year fellow

nzila Ali, MDhief resident

002-9378/free2009 Published by Mosby, Inc.

oi: 10.1016/j.ajog.2009.08.006

eSee related article, page 464

ntrapartum fetal assessment, a criticaland ubiquitous tool in obstetrical

anagement, is also a limited and vexingart of practice. In 1957, Yale Universityesearchers Hess and Hon introducedlectronic fetal heart rate monitoringEFM) as a window into fetal status dur-ng labor. Since then, EFM has becomeighly controversial, a point exemplifiedy its universal adoption despite failureo demonstrate a beneficial impact onesarean rates or long-term fetal/neona-al injury. The test has a very poor posi-ive predictive value (PPV) and a highalse-positive rate; the American Collegef Obstetricians and Gynecologists hasoncluded that only 1-2/1000 abnormalracings leads to cerebral palsy. In the 50ears since EFM became available— cer-ainly, adequate time to assess and de-elop the technology—it has shownomewhat limited effectiveness in im-roving perinatal outcomes. The arti-le discussed in this month’s meetingf the Journal Club introduced a newechnology for fetal monitoring: themniview-SisPorto 3.5 (Speculum,isbon, Portugal).

URRENT STATE

lassic EFM, appropriate for both high-nd low-risk patients, uses intervals be-ween heart beats (for external or Dopp-er monitoring) or between R waves (fornternal or electrocardiogram—ECG—

onitoring) to calculate heart rates. Thisalculated rate is then mapped to the fe-al heart rate (FHR) strip to demonstrateharacteristics that can be read by a pro-ider. As a result, the technology is de-endent on the knowledge and experi-

nce of the interpreter. D

NOVEMBER 2009 Am

Over the last 10-15 years, progress haseen made into the standardization ofHR characteristics to facilitate interpre-ation. The rationale behind such effortss that guidelines formalizing the assess-

ent of FHR patterns may improve thebility of providers to recognize and ifecessary, act on strips that have beenhown to correlate with poor outcomes.

Recent technological advances, suchs the STAN S31 ECG FHR monitorNeoventa Medical AB, Mölndal, Swe-en), show promise in the monitoring ofigher-risk patients. An FDA-approvedevice, the STAN uses internal fetalonitoring to examine specific ECG

hanges, such as T-wave amplitude andT-interval duration; much like an adultCG. The device alerts the provider tovents associated with fetal hypoxemiand/or acidemia. Study results indicatehat STAN might reduce the incidence ofetal scalp pH sampling (relative riskRR], 0.65; 95% confidence intervalCI], 0.59 – 0.72) and operative vaginalelivery (RR, 0.88; 95% CI, 0.80 – 0.97).

CREENING OR DIAGNOSIS?ne issue Journal Club members dis-

ussed was whether EFM is considered acreening test or a diagnostic test. Theuestion is important when weighing thetatistical measures of test performance:ensitivity, specificity, PPV, negativeredictive value (NPV), and positive andegative likelihood ratios. No test per-

orms perfectly, and typically, improve-ents in sensitivity or NPV lead to a re-

uction in specificity or PPV. Diagnosticests usually demand strong specificitynd a robust PPV, while screening testshould emphasize sensitivity and NPV.

etermining what kind of test is needed

erican Journal of Obstetrics & Gynecology 543

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5

an help us concentrate on the most rel-vant statistics.

EFM and its associated technologieseem to combine components of screen-ng and diagnostic tests, depending onhe evaluator’s perspective. In someases, abnormal FHR patterns can besed to screen for cases in which use of

etal scalp pH sampling or lactate testing,oth diagnostic for acidemia, would beppropriate. In other cases, however,FM is used as a type of diagnostic test

hat results in action; specifically, deliv-ry. Because of its different functions,FM appears to demand high sensitivitynd specificity, along with a reliable NPVnd PPV. These requirements likelyomplicate efforts to define the value ofFM.This quandary can probably be simpli-

ed. As noted, traditional EFM is limitedy a high false-positive rate, and thus,

ow specificity. All too often, an ominousracing leads to operative delivery of aealthy, vigorous infant who is unaf-

ected by hypoxemia or acidemia. As wevaluate new tests for our fetal assess-ent armamentarium, we should em-

hasize those that reduce the false-posi-ive rate. We still need to maintain highensitivity but in order to indicate a test islinically valuable, improvements inpecificity and PPV are required.

OMETHING NEW

n addition to incorporating STAN ECG

eadings and alerts, the Omniview-Sis- l

44 American Journal of Obstetrics & Gynecology

orto 3.5 (Speculum, Lisbon, Portugal)arns of FHR changes associated with

etal hypoxemia or acidemia; examplesre reduced variability or tachycardia.ne aim is to reduce human error in in-

erpretation of tracings and possible de-ays in taking appropriate action. An-ther goal is to supplement theechnology already in use—traditionalFM and STAN ECG—to improve thepecificity of the tests.

Costa and colleagues used a retrospec-ive analysis to compare the Omniview-isPorto 3.5 to a system that, like STAN,nly analyzes ST changes. The popula-ion included patients who were atigher risk for adverse outcomes. Thistudy showed dramatic improvementsn sensitivity with the Omniview-Sis-orto 3.5; more infants with acidemiaould be identified in the study group ex-mined with the new technology. How-ver, specificity was shown to be highith both systems, and there was little

hange in the rather modest PPV withhe new test. Regardless, the positiveikelihood ratio for predicting acidemiaas high (17.6; 95% CI, 9.0 –34.5); a pos-

tive likelihood ratio of this magnitudeould give a provider comfort in makingdecision for operative delivery, partic-larly in a patient with a high pretestrobability of an adverse event.Importantly, the test was not evalu-

ted against traditional visual FHR inter-retation, which is generally the stan-ard of care at most centers. This fact

imits our ability to judge the perfor- p

NOVEMBER 2009

ance of the Omniview-SisPorto 3.5ystem in different settings.

UTURE DIRECTIONS

he study by Costa et al is only 1 steporward in introducing a new technologyor EFM. Although important as an ex-loratory study, it is limited by its size,etrospective nature, and inclusion andxclusion criteria. Small exploratorytudies of promising new technologieseed to be followed by larger clinical tri-ls. Fetal pulse oximetry is a good exam-le of an intrapartum test that was ap-ropriately analyzed with large, rigorousrials that demonstrated little additionalenefit overall.Because both the STAN ECG and Om-

iview-SisPorto 3.5 are reserved forigh-risk patients and require internal

etal monitoring, neither will replacetandard external EFM. As a result, wetill need to seek ways to perfect EFM usen the low-risk patient. Improvements inFM interpretation may be seen with the

ntroduction of the new category systemutlined in the 2008 National Institute ofhild Health and Human Developmentorkshop report, but the clinical appli-

ation of these recommendations hasust begun, and no studies exist atresent to demonstrate their validity ortility. Evaluation and refinement of

hese recommendations may be our bestffort at remedying the problematicpplication of EFM in our daily

ractice. f