Watch ORA System Architect Peter Crnokrak present the Fetal Halo system during his Visualized Conference Keynote.
The architectural requirements for creating HALOs that represent intrapartum fetal heart rate patterns revolve around using the existing ORA system in a manner that is intuitive with the data being expressed. The use of symbolic or abstract representation can be useful with regard to signalling value to the doctor, but cannot be too obtuse, in turn requiring a steep learning curve to understand and read the Halo. The more direct in terms of the representation of the data coming off of the medical device sensors, the easier the system will be to learn. The proposed mapping of the various measures of heart rate pattern are done so in a manner where the intuitive representation is as close as possible to a 1:1 relation between foetus state and visualisation.
The other primary requirement is to devise a system that allows for the continuous accumulation of data to be displayed as both real-time present–state visualisations and as an overall aggregate–state visualisation. Both types are critical for the system as the practitioner will want to know what is the state of the foetus’ vitals in the here-and-now, but also want an overall analysis of their state.
The best way to accommodate this requirement is to have two view modes :
present–state which shows the immediate, moment to moment state that the foetus is in, and
aggregate–state that shows the state of the foetus for the entire duration of birthing. The two different modes answer two distinct questions : what is happening now, and what is the fetus’ health phenotype?
In the above two scenarios, a single Halo system can be designed that uses a universally common visual language to express the data coming off of medical device sensors.
The signaling and behavioral aspects of the fetal Halo system is designed around the following specific requirements :
visualize the present state of fetal heart rate patterns
visualize the run-up to a predicted state change (evolution risk state)
visualize the deviation from normality (quantitative and/or qualitative degree of differentiation from normal state)
visualize the historic record of important events (eg. # of decelerations, stage during decelerations, periodicity)
visualize a cumulative summary state (net gain or loss)
algorithmic acidosis state
HALO MODES AND DATA ASSIGNMENT
The system is comprised of two modes :
present–state which shows the immediate state currently occupied by the fetus, and
aggregate–state that shows the cumulative state of the foetus for the entire duration of birthing.
To represent the different data shown in the different modes, the lines that comprise the halo represent different values : for the aggregate–state each line is summary of one sample of sensor data, and for the present-state each line represents a quantitative value directly representative of sensor data. The behaviour of the lines in the aggregate–state mode will require a carefully considered analytic approach to determine what data is most salient to represent.
Present–State:
In the present–state mode, the Halo architecture allows for six different data streams to be incorporated into one structure. The advantage to such as system is that combinations of different data types can be combined to form distinct “data–pictures”. This is particularly advantageous in the case of visualising intrapartum fetal heart patterns as certain metric states when present on their own (eg. severe recurrent late decelerations) are not a cause for concern, but when found in concert with others events (eg. minimal HR variability) are serious cause for concern. The assignment of the six Halo axes to individual HR metrics is outlined below.
The present–state Halo will also feature a playback function which allows the Halo states recorded during the duration of birthing to be viewed as an animation. This is particularly advantageous to be able to see meta patterns over time.
Aggregate–State:
In the aggregate–state mode, the Halo is stratified by time (akin to a tree-ring system where each ring represents a measure of time) where lines form every second (or at whatever sample rate is deemed most useful) starting on the outside edge and moving toward the centre. For every line created on the outside, one will decay inside. As data is visually represented as individual lines, the amount of data that can be represented is relatively limited and will have to be prioritized. There are three line behaviors that will stream data : 1. complexity, 2. color, and 3. speed (see Part 2 for data assignment).
The aggregate–state mode will be primarily used to detect time-based patterns (with playback animation) in HR that signal deviation from normality such as the timing of decelerations with uterine activity and dangerous states such as sinusoidal heart rate patterns.
RESEARCH INTO INTRAPARTUM FETAL HEART MONITORING
Criticisms of the routine use of electronic fetal monitoring (** to be addressed in the Halo architecture where applicable)
poor understanding of the pathophysiological background of the measurements collected
indirect fetal monitoring treated by some as a direct monitor of fetal condition
numerous technical problems that affect its usefulness
variability in measurement and recording techniques
qualitative nature of information obtained, requiring complex pattern recognition**
an absence of agreed systems of classification**
confusion about the many influences on the fetal heart rhythm and rate
significant intra-and inter-observer variation in interpretation of data**
low validity of findings and high false-positive finding rate
a screening investigation to detect the presence of fetal distress being misused as a diagnostic tool
inevitably leads to an increase in instrumental or surgical deliveries, due to the high false-positive rate**
no satisfactory criteria on how, when and whom to monitor
contributes significantly to medicolegal vulnerability of doctors who manage childbirth
NATIONAL INSTITUTE OF CHILD HEALTH & HUMAN DEVELOPMENT CATEGORIES OF INTRAPARTUM FETAL HR PATTERNS :
Category I : Normal
The fetal heart rate tracing shows ALL of the following :
Baseline FHR 110-160 BPM, moderate FHR variability, accelerations may be present or absent, no late or variable decelerations, may have early decelerations.
Strongly predictive of normal acid-base status at the time of observation. Routine care.
Category II : Indeterminate
The fetal heart rate tracing shows ANY of the following :
Tachycardia, bradycardia without absent variability, minimal variability, absent variability without recurrent decelerations, marked variability, absence of accelerations after stimulation, recurrent variable decelerations with minimal or moderate variability, prolonged deceleration > 2minute but less than 10 minutes, recurrent late decelerations with moderate variability, variable decelerations with other characteristics such as slow return to baseline, and “overshoot”.
Not predictive of abnormal fetal acid-base status, but requires continued surveillance and reevaluation.
Category III : Abnormal
The fetal heart rate tracing shows EITHER of the following :
Sinusoidal pattern OR absent variability with recurrent late decelerations, recurrent variable decelerations, or bradycardia. Predictive of abnormal fetal-acid base status at the time of observation. Depending on the clinical situation, efforts to expeditiously resolve the underlying cause of the abnormal fetal heart rate pattern should be made.
CTG FACTOR CLASSIFICATION :
Baseline FHR:
Normal/reassuring : 100-160 bpm but FHR between 100-109 bpm is only reassuring if all other features are also reassuring
Non-reassuring : 161-180 bpm
Abnormal : <100 bpm or >180 bpm, although a stable baseline of 90-99 bpm with normal variability may be normal
Baseline variability:
Reassuring : >5 bpm
Non-reassuring : reduced by <5 bpm for 30-90 minutes
Abnormal : reduced by <5 bpm for >90 minutes
Decelerations:
Reassuring : no or early decelerations
Non-reassuring : either variable decelerations of ≤60 bpm and taking ≤60 seconds to recover, present for >90 minutes and
occurring with >50% of contractions or variable decelerations of ≥60 bpm or taking ≥60 seconds to recover, present for up to 30 minutes and occurring with >50% of contractions or late decelerations present for up to 30 minutes and occurring with >50% of contractions
Abnormal : either non-reassuring variable decelerations still observed 30 minutes after starting conservative measures with >50% of contractions or late decelerations not improving with conservative measures, present for over 30 minutes and occurring with >50% of contractions or a bradycardia or single prolonged deceleration for more than 3 minutes
Accelerations:
• Reassuring : accelerations present. However, the absence of accelerations with otherwise normal trace does not indicate acidosis
A normal CTG has all four features that are reassuring. A CTG is non-reassuring if it has one feature which is non-reassuring, but the others are reassuring. An abnormal CTG has two or more features which are non-reassuring, or any abnormal features.
MNEMONIC CLASSIFICATION OF FHR TRACINGS
DR C BRAVADO : mnemonic for interpretation of continuous electronic fetal monitoring
DR : Determine Risk
high, medium, or low risk (i.e., risk in terms of the clinical situation)
C : Contractions
rate, rhythm, frequency, duration, intensity, and resting tone
BRA : Baseline rate
bradycardia (< 110 bpm), normal (110 to 160 bpm), or tachycardia (> 160 bpm); rising baseline
V : Variability
reflects central nervous system activity: absent, minimal, moderate, or marked
A : Accelerations
spontaneous; stimulated; none
rises from the baseline of ≥ 15 bpm, lasting ≥ 15 seconds preterm: ≥ 10 bpm, lasting ≥ 10 seconds
D : Decelerations
absent, early, variable, late, or prolonged
O : Overall assessment and written plan
FIVE TIER FHR INTERPRETATION SYSTEM
Note: categories with file names correspond to specific Halo states modeled below:
METRIC DEFINITIONS AND THRESHOLDS
Acceleration is a visually abrupt increase in the fetal heart rate (FHR) above the baseline with onset to peak of the acceleration less than 30 seconds. For fetuses > 32 weeks gestational age the peak heart rate must be> 15 beats per minute (BPM) above the baseline and must last for> 15 seconds but less than 2 minutes from the initial change in heart rate to the time of return of the fetal heart rate to the baseline. For fetuses < 32 weeks of gestation the accelerations must have a peak heart rate > 10 beat and a duration of > 10 seconds but less than 2 minutes. An acceleration > 2 minutes but less than 10 minutes in duration is called a prolonged acceleration. An acceleration lasting > 10 minutes is a baseline change.
Accelerations may be further categorized as episodic or periodic. Episodic accelerations occur independent of uterine contractions. Periodic accelerations are associated with uterine contractions. Accelerations may be present or absent in an otherwise normal category I fetal heart rate tracing.
Deceleration is a decrease in the fetal heart rate below the fetal baseline heart rate. An early deceleration is defined as a waveform with a gradual decrease and return to baseline with time from onset of the deceleration to the lowest point of the deceleration (nadir) >30 seconds. The nadir of the early deceleration occurs with the peak of a contraction. A late deceleration also has a waveform with a gradual decrease and return to baseline with time from onset of the deceleration to nadir >30 seconds. However, the late deceleration is “shifted to the right” of the contraction.
If oxygen continues to be limited (hypoxia) to the fetal tissues acidosis can develop as result of increased anaerobic metabolism. Significant levels of acid in the blood (acidemia) can suppress the fetal nervous system leading to decreased variability and direct myocardial depression made evident by shallow late decelerations.
METRICS INCORPORATED IN THE FETAL HALO
baseline FHR
baseline FHR variability
presence of accelerations
intensity of accelerations (degree of change in FHR)
presence of decelerations
intensity of decelerations (degree of change in FHR)
trends of periodic or episodic decelerations
degree of acidosis
changes or trends of summary composite of FHR patterns over time (acidosis patterns)
frequency and intensity of uterine contractions
INTRAPARTUM FETAL HEART RATE HALO ARCHITECTURE
