Philip A. Warrick

Classification of Normal and Hypoxic Fetuses From Systems Modeling of Intrapartum Cardiotocography

Recording of maternal uterine pressure (UP) and fetal heart rate (FHR) during labor and delivery is a procedure referred to as cardiotocography. We modeled this signal pair as an input-output system using a system identification approach to estimate their dynamic relation in terms of an impulse response function. We also modeled FHR baseline with a linear fit and FHR variability unrelated to UP using the power spectral density, computed from an auto-regressive model. Using a perinatal database of normal and pathological cases, we trained suport-vector-machine classifiers with feature sets from these models. We used the classification in a detection process. We obtained the best results with a detector that combined the decisions of classifiers using both feature sets. It detected half of the pathological cases, with very few false positives (7.5%), 1 h and 40 min before delivery. This would leave sufficient time for an appropriate clinical response. These results clearly demonstrate the utility of our method for the early detection of cases needing clinical intervention.

Graded classification of fetal heart rate tracings: association with neonatal metabolic acidosis and neurologic morbidity.

OBJECTIVE The objective of the study was to measure the performance of a 5-tier, color-coded graded classification of electronic fetal monitoring (EFM). STUDY DESIGN We used specialized software to analyze and categorize 7416 hours of EFM from term pregnancies. We measured how often and for how long each of the color-coded levels appeared in 3 groups of babies: (A) 60 babies with neonatal encephalopathy (NE) and umbilical artery base deficit (BD) levels were greater than 12 mmol/L; (I) 280 babies without NE but with BD greater than 12 mmol/L; and (N) 2132 babies with normal gases. RESULTS The frequency and duration of EFM abnormalities considered more severe in the classification method were highest in group A and lowest in group N. Detecting an equivalent percentage of cases with adverse outcomes required only minutes spent with marked EFM abnormalities compared with much longer periods with lesser abnormalities. CONCLUSION Both degree and duration of tracing abnormality are related to outcome. We present empirical data quantifying that relationship in a systematic fashion.

Third- and fourth-degree perineal lacerations: defining high-risk clinical clusters

OBJECTIVE Statistical methods that measure the independent contribution of individual factors for third-/fourth-degree perineal laceration (TFPL) fall short when the clinician is faced with a combination of factors. Our objective was to demonstrate how a statistical technique, classification and regression trees (CART), can identify high-risk clinical clusters. STUDY DESIGN We performed multivariable logistic regression, and CART analysis on data from 25,150 term vaginal births. RESULTS Multivariable analyses found strong associations with the use of episiotomy, forceps, vacuum, nulliparity, and birthweight. CART ranked episiotomy, operative delivery, and birthweight as the more discriminating factors and defined distinct risk groups with TFPL rates that ranged from 0-100%. For example, without episiotomy, the rate of TFPL was 2.2%. In the presence of an episiotomy, forceps, and birthweight of >3634 g, the rate of TFPL was 68.9%. CONCLUSION CART showed that certain combinations held low risk, where as other combinations carried extreme risk, which clarified how choices on delivery options can markedly affect the rate of TFPL for specific mothers.

A VRML-based anatomical visualization tool for medical education

The advent of the Virtual Reality Modeling Language (VRML) as a portable file format for describing three-dimensional (3-D) scenes has enabled researchers, educators, and students to share anatomical models on the World Wide Web (WWW). The implication for medical teaching is that students can interactively examine anatomical structures and their 3-D spatial relationships by using current personal computer (PC) technology. This paper describes the creation of 3-D anatomical models that are accessible on the WWW, using high-resolution middle-ear data as an example. The 3-D models are created by interactive segmentation of the source images (histological and MRI sections) and 3-D surface reconstruction. The resulting models are translated into VRML format. Section images can be superimposed on the model, allowing students to view a section in its 3-D context. To enhance the viewing of these scenes, a VRML browser was modified to support transparent rendering of surfaces. Finally, a WWW interface was designed to allow users to choose the model structures, section images, and associated viewing parameters to build their own 3-D scenes.

The limits of electronic fetal heart rate monitoring in the prevention of neonatal metabolic acidemia

BACKGROUND: Despite 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. OBJECTIVE: The purpose of this study was to validate a recently published algorithm for the management of category II fetal heart rate tracings, to examine reasons for the birth of infants with significant metabolic acidemia despite the use of electronic fetal heart rate monitoring, and to examine critically the limits of electronic fetal heart rate monitoring in the prevention of neonatal metabolic acidemia. STUDY DESIGN: The potential performance of electronic fetal heart rate monitoring under ideal circumstances was evaluated in an outcomes‐blinded examination fetal heart rate tracing of infants with metabolic acidemia at birth (base deficit, >12) and matched control infants (base deficit, <8) under the following conditions: (1) expert primary interpretation, (2) use of a published algorithm that was developed and endorsed by a large group of national experts, (3) assumption of a 30‐minute period of evaluation for noncritical category II fetal heart rate tracings, followed by delivery within 30 minutes, (4) evaluation without the need to provide patient care simultaneously, and (5) comparison of results under these circumstances with those achieved in actual clinical practice. RESULTS: During the study period, 120 infants were identified with an arterial cord blood base deficit of >12 mM/L. Matched control infants were not demographically different from subjects. In actual practice, operative intervention on the basis of an abnormal fetal heart rate tracings occurred in 36 of 120 fetuses (30.0%) with metabolic acidemia. Based on expert, algorithm‐assisted reviews, 55 of 120 patients with acidemia (45.8%) were judged to need operative intervention for abnormal fetal heart rate tracings. This difference was significant (P=.016). In infants who were born with a base deficit of >12 mM/L in which blinded, algorithm‐assisted expert review indicated the need for operative delivery, the decision for delivery would have been made an average of 131 minutes before the actual delivery. The rate of expert intervention for fetal heart rate concerns in the nonacidemic control group (22/120; 18.3%) was similar to the actual intervention rate (23/120; 19.2%; P=1.0) Expert review did not mandate earlier delivery in 65 of 120 patients with metabolic acidemia. The primary features of these 65 cases included the occurrence of sentinel events with prolonged deceleration just before delivery, the rapid deterioration of nonemergent category II fetal heart rate tracings before realistic time frames for recognition and intervention, and the failure of recognized fetal heart rate patterns such as variability to identify metabolic acidemia. CONCLUSIONS: Expert, algorithm‐assisted fetal heart rate interpretation has the potential to improve standard clinical performance by facilitating significantly earlier recognition of some tracings that are associated with metabolic acidemia without increasing the rate of operative intervention. However, this improvement is modest. Of infants who are born with metabolic acidemia, only approximately one‐half potentially could be identified and have delivery expedited even under ideal circumstances, which are probably not realistic in current US practice. This represents the limits of electronic fetal heart rate monitoring performance. Additional technologies will be necessary if the goal of the prevention of neonatal metabolic acidemia is to be realized.

Neural network based detection of fetal heart rate patterns

Automated detection of fetal heart rate (FHR) patterns can potentially improve intra-partum care by providing consistent and reliable measures that assist health-care professionals in their assessment of the state of the fetus. We use the combined tools of signal processing and neural networks to detect the FHR patterns of baseline, acceleration and deceleration. Comparison to previous results reported in the literature are provided.

Variable decelerations: do size and shape matter?

Objective: To determine the ability of variable decelerations and 8 subtypes, defined by size and shape, to discriminate tracings between babies with normal umbilical artery gases (N) and those with metabolic acidemia (MA). Methods: Tracings from the last 4 hours from N—3320 babies with base deficit levels under 8 mmol/L, and from MA—316 babies with base deficits over 12 mmol/L were analyzed using computerized pattern recognition. We created receiver operating characteristic curves and area under the curves (AUCs) for each deceleration subtype. Results: Only 3 subtypes showed significant discrimination: those with a prolonged duration (AUC 0.6109 P < 0.0001), loss of internal variability (AUC 0.5694 P < 0.0001) or with “sixties” criteria (AUC 0.5997 P < 0.0001). A variable deceleration met the sixties criteria if two or more of the following were present: depth was 60 bpm or more, lowest value was 60 or less, duration was 60 seconds or longer. All other subtypes were no better than chance. Conclusions: Finer gradation within the middle category of electronic fetal monitoring classification is needed because most tracings, including those from babies with MA, will be located in the Category II. This analysis identifies which variable decelerations have a significant association with MA and which do not.

Identification of the Dynamic Relationship Between Intrapartum Uterine Pressure and Fetal Heart Rate for Normal and Hypoxic Fetuses

Labor and delivery are routinely monitored electronically with sensors that measure and record maternal uterine pressure (UP) and fetal heart rate (FHR), a procedure referred to as cardiotocography (CTG). Delay or failure to recognize abnormal patterns in these recordings can result in a failure to prevent fetal injury. We address the challenging problem of interpreting intrapartum CTG in a novel way by modeling the dynamic relationship between UP (as an input) and FHR (as an output). We use a nonparametric approach to estimate the dynamics in terms of an impulse response function (IRF). We apply singular value decomposition to suppress noise, IRF delay, and memory estimation to identify the temporal extent of the response and surrogate testing to assess model significance. We construct models for a database of CTG recordings labeled by outcome, and compare the models during the last 3 h of labor as well as across outcome classes. The results demonstrate that the UP-FHR dynamics can be successfully modeled as an input-output system. Models for pathological cases had stronger, more delayed, and more predictable responses than those for normal cases. In addition, the models evolved in time, reflecting a clinically plausible evolution of the fetal state due to the stress of labor.

New perspectives in electronic fetal surveillance

Abstract Despite its recognized limitations, fetal heart rate monitoring is a mainstay of intrapartum care. Although the basic technology in standard electronic fetal monitors has changed little in recent decades, clinical behavior in response to heart rate monitoring has changed considerably. In addition to clearly defined nomenclature and clinical guidelines, there is an increased awareness that environmental and human factors can impair clinical judgment, resulting in delayed intervention and, consequently, birth-related injury. This review examines three essential steps that affect clinical outcome: (1) signal acquisition, (2) associations with physiological outcome, and (3) clinical intervention. Only the third step is directly responsible for changing clinical outcome. However, timely initiation of interventions is dependent upon the second step, which is dependent upon the first step. Thus, deficiencies at each step tend to accumulate and contribute to the worsening of overall clinical outcome. This review article summarizes advances occurring at each step. The synergy and convergence of innovations in engineering, mathematics, and behavioral science shows considerable promise in intrapartum fetal surveillance.

Linear models of intrapartum uterine pressure-fetal heart rate interaction for the normal and hypoxic fetus

We construct input-output models by linear system-identification methods for uterine pressure - fetal heart rate data collected during labour and delivery. Using standard hypothesis tests, the impulse response model coefficients show statistically significant differences between normal and pathological cases