California College of Midwives
|Nov 1999||Principles of Mother-Friendly Childbearing Services|
Characteristics of Clinical Competency associated with
Science-Based Maternity Care Systems
Technical Bulletin No. 2
Intermittent Auscultation augmented with
Episodic Electronic Fetal Monitoring (EEFM)
for Community-based Midwives
For a healthy mother at term with a normal pregnancy and spontaneous onset of progressive labor at term, the parameters of Intermittent Auscultation (IA) are perfectly adequate and the most appropriate form of fetal surveillance the vast majority of the time. However, there are a few rare FHR patterns that reflect a serious medical problem that are difficult or impossible to pick up solely from an auditory pattern. Examples are a sinusoidal rhythm and slight but repetitive late decelerations in a baby with a "silent" baseline variability (this combination is considered to be a pathological pattern until proven otherwise).
One reason is that it is hard to accurately count the FHR during a uterine contraction (UC), especially in advanced active labor. In the first place it is hard to hear FHT clearly during the UC and secondly the mother often cannot stand or lie still enough to permit the high-level of accuracy necessary with IA to detect slight decels. Without a printout that spans considerable time it may be difficult to determine the significance of a slightly raised or slightly lowered baseline rate which can be either a normal adaptation to mild stress or may be an indicator of increasing levels of fetal distress. This latter category is a potential concern with post-mature pregnancies.
Advantages of Having EEFM Available
Without a dependable way to identify other aspects of either reassuring or suspicious factors, the mother will have to be transported, perhaps unnecessarily, for medical care. Access to episodic EFM can increase the ability to of the midwifery model of care to meet maternal-fetal needs and permits additional latitude in midwifery management. This can be accomplished with the very portable (slightly larger than a laptop computer) and inexpensive new antepartal / intrapartal fetal heart monitors recently made available for under $3,000 called the Baby Dopplex 3000, (manufactured in the UK by Huntleigh). No doubt other companies will follow suit. Due to the great cost, such a monitor could be owned jointly by the midwives in a geographical area. Hand-held dopplers which connect to a small hand-held printer are also available for about $1500 total. Use of either system of electronic fetal monitoring permits the community-based midwife to expand the parameters of her care and interface with the obstetrical community in a way more satisfactory to physicians.
In addition some maternal-fetal circumstances benefit from antepartal evaluation of fetal wellbeing (particularly mothers who are slightly small for dates, have a high normal or mildly elevated BP and post date pregnancies). There are also intrapartum occasions in which a fetus has a slightly increased risk or situation of concern but not of the order of magnitude requiring transfer of care. In these circumstances an initial tracing should be obtained when the midwife first arrives at the parents home (or the mother is admitted to a OOH birth center) to help determine whether it is appropriate to provide intrapartum care in a domiciliary setting. If the increased concern continues through out labor, then episodic re-assessment by EEFM q 2-3 hours in first stage and the early, middle and late in 2nd stage is useful, (assuming the mother does not deliver so rapidly that the baby free-falls through the birth canal, in which case additional EFM is not feasible!).
Last but not least is the importance of advocating for hospitalized patients (for example after transfer) which is improved by the midwifes through understanding of EFM principles and a well-developed ability to recognize and interpret FHR patterns. For this reason there are reference to the effect of narcotic and anti-hypertensive medications on EFM tracing. However, it is assumed that these are labors occurring in the hospitals and is in no way a suggestion that they should be used in a domiciliary setting.
Background Information and Principles of Episodic EFM
Much of the material in this section comes from a book entitled "Fetal Monitoring In Practice" written by Dr David Gibbs & S. Arulkumaran, MD. These two obstetricians, one from London, England and the other from Singapore, are consultants for hospitals that have 26,000 birth per year and which enjoys a "shared maternity care" system -- that is, a healthcare system in which midwifery is normative. These authors are specifically supportive of midwifery care for hospitalized patients of all risk levels (in collaboration with physicians) and they adhere to the WHO guidelines for promoting safe motherhood which are:
To optimize the health of the mother,
To optimize the health of the offspring
To optimize the emotional satisfaction of the mother and her family.
These obstetricians go on to say that
"Excessive technology should not be applied to those who are manifestly at low-risk. It may confer no benefit, can generate both non-medical and medical anxiety and through subtle effects may cause significant harm. Such unthinking application is counter- productive. A relationship of trust and professionalism should bear fruit. It is acknowledged that the introduction of EFM has contributed to an increase in the number of cesarean birth. This is largely due to failure to understand the principles of the technique, but may also be attributed to a fear of litigation. Both can be effectively countered."
Referring to the nature of maternity care and status of childbearing women they say:
"... are unique in that they are not sick. On the contrary, they are experiencing one of the most important events of their lives with enormous emotional impact. The intimacy of this experience should not be compromised except in the genuine interest of safety for mother and child. This information should help us recognize the 'genuine interest. Without this we will not earn the approbation of those who have entrusted their care to us. " Dr David Gibbs & S. Arulkumaran, MD
In spite of a patent load of more than 26,000 deliveries a year these physicians had only two EFM machines available. Since it was impossible to use continuous electronic monitoring on every labor patient these doctors had to develop methods for determining who needed or would benefit from continuous electronic monitoring and who were better served by intermittent auscultation (IA). This resulted in their developing very good understanding and guidelines for IA and EEFM which are reproduced in this technical bulletin.
It is their opinion is that the expression 'fetal distress' should be reconsidered and a different vocabulary developed: An EFM trace that is not normal may result from physiological, iatragenic or pathological causes, meaning that the so-called distress of the fetus may be a healthy stress response -- i.e. not an indication of distress. So called 'fetal distress' may be provoked either by improper care or indicate a problem originating within the fetus. The clinical situation and the dynamic evolution of features of the EFM trace will clarify the situation with time. The underlying principle is to detect fetal compromise using the concept of fetal distress very critically.
In all situations it is the consideration of the overall clinical picture that would provide the clues to whether fetal compromise is present or the caregivers need to rectify situations of their own making (iatragenic factors). Many suspicious EFM tracing are generated by healthy fetuses demonstrating a healthy ability to respond to stress. Cesarean surgery should not be used to treat caregiver distress resulting from a misunderstanding of EFM principles or anxiety over EFM tracing that is not reassuring. The purpose of monitoring (of all kinds) is the babys well-being and not primarily to protect professional caregivers from criticism or litigation.
EFM takes advantage of the fact that human being are better at (and happier with) pattern recognition that they are computing. EFM does the math and prints out the pattern, which is one of the reasons that it is so popular in the medical community. The next step in dealing intelligently with EFM information is to systemize the output data by charting samplings of it on a graph (flow sheet). For midwives using IA, this same concept is employed by charting audible variability as a visual pattern of a numerically-defined bandwidth. (See Intermittent Auscultation Long-term Variability form on the back of the Intrapartum flow sheet and Technical Bulletin No. 1, 1999).
How EFM Works
Electronic fetal heart rate monitors compute the heart rate based on averaged intervals between beats extrapolated to what the rate would be if the beat intervals remained constant. In other words, a read out of 60 or spikes to 180 bpm does not actually represent a heart rate of 60 or 180 bpm unless it stays up or down for one full minute or longer. Most up-to-date monitors recompute the rate every 2 seconds. Autonomic nerve impulses of the fetus immediately and constantly take effect, changing the beat intervals and immediately altering the heart rate. This is how baseline variability is generated and it indicates the integrity of the autonomic nervous system. Baseline variability is actually seen on the tracing (or heard with IA).
Mechanical or electrical interference / artifacts: Old EFM machines without auto-correction may give the appearance of false baseline variability by having a lots of up and down spikes that reflect maternal motion -- not fetal heart action. Old fetal monitors are not reliable for determining variability as they can erroneously create the appearance of variability where none exists. Another form of mechanical interference is cause by poor contact between the baby and a scalp electrode. This creates a "picket fence" pattern -- constant sharp ascending and descending vertical lines that tract the baseline. It also will sometimes half the rate or give an irregular rate. Newer monitors are more reliable with external system that the older scalp electrodes. The newest versions still give unreliable information in the internal monitoring mode if they are not making good contact between the fetus, the scalp electrode and the mother's body.
Other Electrical Interference / TENS: Extraneous electrical influence can produce artifacts in the baseline variability (BLV). If the electrical disturbance exceeds the frequency of signals obtained from the FHR using a scalp electrode it can completely confuse the FHR signal resulting in no FHR tracing. The use of transcutaneous electrical nerve stimulation -- a TENS stimulator -- of the obstetrical pulsar used for pain relief can produce this problem. With TENS external ultrasound monitoring is preferred.
False baseline because of characteristics of EFM technology which erroneously doubles the true cardiac rate: In normal circumstances the atrium and ventricle chamber of the fetal heart beat almost simultaneously followed by the next complete cardiac movement of these chambers. This describes the healthy action of the heart and is the mechanism upon which the ultrasound depends for calculating a baseline fetal heart rate. The reflected ultrasound from these two chambers or even from one of the walls (atrium, ventricle or the valves) is used by the machine to compute the FHR.
When the FHR is slow (70-80 bpm) there is a longer time interval between the atrial and ventricle contraction. The machine recognizes each of the reflected sound (one from the ventricle and the other from the atrium) as two separate beats and computes the rate which may mimic a normal FHR as it will be in the expected range for a normal baseline. For most observers the sound generated will also give an impression that the FHR is within the normal range (WNR) because the heart sounds from the machine are always the same for every baby -- they are electronic noise (a canned sound built into the circuitry and triggered by each pulse of ultrasound).
During the false counting or doubling of the FHR episode, listening with a fetal stethoscope or doptone will reveal the true situation. The suspicion that something is amiss will be aroused by the FHR tracing, which may show a stretch of baseline reading, for example of 140 bpm, but at other times will record a rate half that (70bpm). Because it is a double counting phenomenon the upper rate on the recording paper will be exactly double that of the lower rate and can be easily checked by auscultation. Such a trace can also be due to the machine recognizing an atrial rate of 140 bpm and a ventricular rate of 70 bpm at different times in a case with complete heart block. The mother in these instances may have an autoimmune disorder. These circumstances would be an indication for use of fetal electrode.
Practical skills and their application to episodic EFM
An important point of departure from the hospital model customarily used in the United States is acknowledgment of the benefit of an initial abdominal exam before any attempt to utilize EFM (or IA). (note -- a recent study in the US -- 2002 -- calls this into question, claims that an initial trace is not predective of outcome) Abdominal palpation should be undertaken to determine fundal height measurement, fetal position, estimation of fetal size, lie, presentation and station of presenting part, as well as the nature of the UCs and an estimate of amniotic fluid volume.
Lastly is the location of FHTs with fetascope or doptone. This is important for two reason. First, it is easier to pick up FHTs with a hand held doppler allowing the midwife to position the EFM transducer with speed and accuracy. Second in the event of a fetal demise, the true situation is picked up immediately without the emotional agony of mistaking the mothers heart rate through the fetus body (perhaps doubled by the EFM software), leading everyone to erroneously think that everything is fine when it fact it is not. One of the known hazards of EFM is its propensity to use the body of the deceased baby as a transmitter for the maternal pulse. Dont go there!
Hypoxia: Hypo = lesser or low amounts // oxia = oxygen
i.e. a sub-lethal level of oxygen deprivation
Anoxia: An = absence or lack of // oxia = oxygen
i.e.. a potentially lethal deprivation of O2
Acute = rapidly developing or immediate
Chronic = slowly developing or long term
Fetal Responses to labor:
Effective contractions (the powers) of the uterus are an essential prerequisite for labor and vaginal delivery. The progress of labor, evidenced by dilatation of the uterine cervix and descent of the presenting part, is the final measure of contractions. During the journey through the birth canal (the passage), the passenger is intermittently squeezed and stressed by the contractions. Maternal blood flow into the uteroplacental space ceases when the intrauterine pressure exceeds 30mmHg. A well-grown fetus with good placental reserve tolerates this as normal stress and normally displays no change in the fetal heart rate or rhythm during the dilatation phase of labor.
However, a compromised fetus may show FHR changes with the stress of labor. Prolonged stress eventually advances to distress. In FHR patterns with poor variability lasting longer than 90 minutes (even though no decelerations are seen) should be investigated to identify the cause. The principle can be established that the FHR pattern identifies the onset of stress (decels that increase in frequency, length and depth) and the onset of distress (maximal elevation of baseline FHR with baseline variability of less than 5bpm). [page 182) Although the onset of stress and distress can be identified, the duration of the distress period before the fetus becomes hypoxic and develops acidosis cannot be predicted. A plain English example would be an automobile gauge on "empty" but the driver can't tell if there is a gallon left (enough to safely drive to the gas station) or the engine is going to suddenly quit running in the middle of the street. In regard to evidence of fetal distress, no one can predict how long the baby can keep going on "empty" once the unmistakable signs of distress become apparent. A good trace within a reasonable period of the onset of deterioration with an acute event such as a cord accident suggests that rapid intervention with be productive (assuming a reasonable gestational age).
If the baseline FHR has risen by 20-30 beats or more and is not rising any further while showing a reduction in variability to less than 5 beats then distress is probable. Despite the fetus having increased its cardiac output by increasing fetal heart rate, the functioning of the autonomic nervous system controlling the baseline variability is compromised by hypoxia. The time course of the process may be referred to as the 'stress to distress' period. This period varies from fetus to fetus depending on the physiological reserve.
This reserve is critically low in high risk situations of postmaturity, IUGR, intrauterine infection and those with thick meconium and scantly amniotic fluid. Once the FHR shows a distress pattern, the time it takes for metabolic acidosis to develop is unpredictable. After an undefined duration of the distress pattern (the distress period) the FHR starts to decline in a rapid stepwise pattern, culminating in terminal bradycardia and death (the distress to death period). Clinical interpretation of FHR patterns will identify the onset of stress and the stress to distress period. It will also identify the fetus in the distress period. During the final decline phase (distress to death period), when the fetal heart rate drops irretrievably within a short period, it is often too late to intervene.
Overview of principle of cardiac function for fetus:
Control of the fetal heart is complex and incompletely understood. Fortunately we dont need a highly developed knowledge of the intricacies of it to acquire useful information that can be put to practical use.
In general fetal cardiac activity is under the involuntary control of the central nervous system (cortical and subcortical influence) and the cardio-regulatory center of the brain stem. It is drastically influenced by the quantity and quality of blood volume (hemorrhage or anemia from Rh sensitivity) and mediated by circulating catecholamines. It has both chemical receptors and barometric pressure receptors. There is constant interplay with the autonomic nervous system and resulting heart rate and rhythm.
The autonomic nervous system is composed of the sympathetic and para-sympathetic systems with constant input varying from second to second. Sympathetic impulses drive the heart rate up (fight or flight response, a positive adaptive attempt to "outrun" the problem) while para-sympathetic impulses slow the heart rate and in general are associated with relaxed states (kick back after busy day with reduced heart and respiratory rates). For midwives, this para-sympathetic activity is most familiar as the "vagal" response associated with head compression. This trigger of the vagal response is akin to a mammalian diving reflex (diving whales experience a slower heart rate to conserve O2 triggered by increased pressure on cranial bones by deeper water). Vagal systems can be suppressed by drugs such as atropine & narcotics, which reduce baseline variability.
In addition, certain pathological physical insults can also trigger this para-sympathetic "slow mode" which appears to function as an oxygen-conserving attempt when activity (increased heart rate) cannot actively repulse the danger (i.e. cant be "outrun") or the biological adaptive ability of the organism has been exhausted. In that case the best adaptive response is to temporarily suspend secondary biological activity ("play dead"). As with the submerged whale, if the circumstances are not reversed in a timely fashion, cardiac activity can no longer be maintained at even this low level and death results without further warning (terminal bradycardia). As terminal bradycardia is developing the rate and rhythm may wander wildly for the last 2 or 3 minutes, creating a trace with no variability that looks like the path of a drunken sailor skiing downhill.
The usual course of events for a stressed then distressed fetus would be first to have reduced and then absent accelerations, followed by a rise in baseline (increasing tachycardia), then the loss of baseline variability (silent or flat pattern), then development of decels of greater and greater length and depth with slower and slower recovery, followed by a period of bradycardia which if uninterrupted will be terminated by death. Terminal bradycardia is only "diagnosed" after the fact. Before the crash one cannot tell the difference with certainty unless the other aspects of a "reassuring" trace are maintained -- such as variability and accelerations. This would occur in heart block which is a non-lethal condition in which the "normal" heart rate is 60 to 80 bpm.
Principle of Accelerations -- the hallmark of fetal health: The example that authors Gibbs and Arulkumaran use is to picture a healthy child playing in a field. The child has a normal pulse rate (baseline rate) and minor movements of the limbs suggestive of activity (good baseline variability) and is tossing a ball up and down (accelerations). If the child is tired or unwell it will start restricting its physical activity. First the child will stop tossing the ball (absence of acceleration is the first thing to be noticed when hypoxia develops) suggesting that the child is either tired or not well. Then the child would either sit or lie down to rest. In such a situation it is difficult to differentiate healthy or "normal" tiredness from impending sickness. A persistently raised pulse rate (baseline tachycardia) represents an attempt to compensate in response to evolving hypoxia. The fetus cannot respond to developing hypoxia (i.e. a need for more oxygen) by increasing the cardiac stroke volume (moving more blood with each beat) so instead it must increase its heart rate (moving more blood by triggering more beats per minute). Reduction in baseline variability and finally a flat baseline are progressive features of increasing hypoxia.
A child who was in good health a few minutes ago cannot suddenly become sick without an obvious reason. The absence of accelerations and reduced baseline variability may merely suggest that the fetus is in the quiet phase. This interpretation is further strengthened when there is no increase in the baseline FHR. Quiet sleep is associated with absence of accelerations (i.e. no movement) and episodes of decreased variability which generally last for up to 40 minutes. Appropriate interpretation of an EFM trace is absolutely dependent on recognition of this physiological phenomenon.
Development of Biophysical Characteristics
Fetal responses to hypoxia do not occur at random but are initiated and regulated by complex, integrated reflexes of the fetal central nervous system. Stimuli that regulate the biophysical characteristics of fetal movement, breathing and tone arise from different sites in the brain. There is some evidence that the first physical activity to develop is fetal tone at 8 weeks gestation. It is also the last to cease functioning when subjected to increasing hypoxia. Fetal movements develop at 9 weeks and fetal breathing at 20 weeks. FHR activity matures last, by about 28 weeks, and is the first to be affected by hypoxia. In hypoxia FHR characteristics may be abnormal first, followed second by breathing efforts, then body and limb movements and finally by tone.
In antepartum assessment of biophysicial profile, fetal movements, tone, breathing and amniotic fluid volume are assessed by scan. The AFI (amniotic fluid index) is the more sensitive in predicting fetal morbidity than the largest single vertical pocket of amniotic fluid. An AFI of less than 5 is associated with a poor fetal outcome and delivery should be considered. If only one vertical pocket is measured, a value of less than 3 cms in the largest pool is an indication for delivery.
NST is considered in combination with the biophysical profile and for each quality or indicator of well-being a score of 2 or 0 is given, there being no intermediate score (unlike apgar which has a 2, 1 or 0). When the NST is not reactive it may be useful to assess the fetal biophysical profile. A score of 8 or 10 indicates a fetus in good condition. If the score is 6 then the baby should be re-evaluated in 4-6 hours later and a decision made based on the newest score. When the biophysical profile is equal or less than 2 on one occasion or equal or less than 4 on two occasions (6 - 8 hrs apart), delivery is indicated if the fetus is adequately mature and has a good chance of survival.
With gradually increasing hypoxia, fetal heart rate changes take place first, followed by alteration in breathing movements, body movements and finally tone. However, sudden demise can occur when there is reduced amniotic fluid. When there is fetal body movement for over 3 seconds it is associated with FHR accelerations. The clinical outcome is similar when the NST is reactive with or without Fetal Acoustical Stimulation Test (FAST) to produce accelerations. It is therefore possible to simplify fetal assessment at the outpatient clinic or domiciliary setting.
A hand-held Doptone with a digital display will give a digital reading of FHR (or mobile EFM such as the Baby Doppler 3000 by Huntleigh would produce a tracing). Application of FAST at this time will result in maternal and observer perception of fetal movement and FHR acceleration. If the fetus continues to move, there will be further accelerations. In BPP scoring, these two features (FHR accelerations and fetal movement) will indicate a score of 4. Since the tone is the last feature to disappear it is fair to give two points for tone when the fetal movement are plentiful with FHR accelerations.
Non-stress testing is usually used for diagnostic purposes and has not been proven to be of value as a screening test. The ability of the test to identify the problem being investigated should be known. A normal NST indicates fetal health/well-being. However, with chronic placental dysfunction, fetal adaptation occurs and a normal (i.e., reactive) NST does not indicate the degree by which placental function may be reduced. Thus the predictive value of a normal NST is governed by the clinical situation.
Antepartal Assessment Criteria:
at least two accelerations (greater than 15 beats for greater than 15 second) in 10 minutes (reactive trace), baseline heart rate 110-150 bpm, baseline variability 5-25bpm, absence of decels
Sporadic mild decels (amplitude less than 40 bpm, duration less than 30 seconds) are acceptable following an acceleration
When there is moderate tachycardia (150 - 170bpm) or moderate bradycardia (100 - 110bpm), a reactive trace without decels is reassuring of good health
Repeat according to clinical situation and the degree of fetal risk
Absence of accelerations for greater than 40 minutes (non-reactive trace)
Baseline heart rate of 150-170bpm or 110-100bpm
Baseline variability greater than 25 bpm in the absence of accelerations
Sporadic decels of any type unless severe as described below
Continue for 90 minutes until trace becomes reactive or repeat NST within 24 hrs or vibro-acoustic stimulation (VAS), AFI / biophysical profile
Pathological / abnormal
Base line heart rate below 100 or greater than 170 bpm
Silent pattern of less than 5 bpm for greater than 40 minutes
Sinusoidal pattern (oscillation frequency of less than 2-5 cycles per minute, amplitude of 2-10 bpm for greater than 40 minutes with no accelerations and no area of normal baseline variability)
Repeated late, prolonged (greater than 1 minute) and severe variable decels (greater than 40 bpm)
Further evaluation (VAS, AFI, BPP, Doppler ultrasound blood velocity waveform) Deliver if clinically appropriate.
Problems Associated with
interpretation of the EFM Traces
In the past much time and effort has been spent on categorizing decels into early, late and variable. However such efforts are better directed instead to interpreting the EFM record as a whole in relation to the clinical situation. A given trace may be considered normal in the late first stage/early 2nd stage when the same tracing would not be accepted as normal in the early first stage of labor. At times it is difficult to classify the decels as they may have mixed features of both variable and late decels. It is far more important to categorize any trace as (1) normal, (2) suspicious/ questionable or (3) abnormal rather than focus solely on defining the decels. All features of a given trace must be considered before it is categorized as normal, questionable or abnormal. The subsequent management depends on this.
Accelerations and normal baseline variability (BLV) are the hallmark of fetal health.
A hypoxic fetus can have a normal baseline rate, other features being abnormal.
In the absence of accelerations, repeated shallow decels (below 15 bpm) are ominous when BLV is less than 5 bpm.
Classification of fetal heart rate patterns by the Federation of International Gynecologists and Obstetricians subcommittee is divided into (a) normal, (b) suspicious (or questionable) and (c) pathological.
Intrapartum Assessment Criteria
1. Baseline rate between 110 and 150 bpm
2. Amplitude of FHR variability between 5 and 25 bpm (the FIGO guidelines do not refer to accelerations but they should be present for a designation of normal)
Suspicious / Questionable Pattern
1. Baseline rate between 150 and 170 or between 110 and 100 bpm
2. Amplitude of variability between 5 & 10 bpm for more than 40 minutes
3. Increased variability above 25 bpm
4. Variable decels
1. Baseline FHR below 100 bpm or above 170 bpm
2. Persistence of FHR variability of less than 5 bpm for more than 40 minutes
3. Severe variable decels or severe repetitive early decels
4. Prolonged decels
5. Late decels: an ominous trace is a steady baseline without variability and small decels
6. Sinusoidal pattern -- cyclic changes in FHR baseline with frequency of less than 6 cycles per minute, amplitude at least 10 bpm for 20 minutes or longer (note -- apparently a fetus that is sucking its thumb can trigger a pattern that looks very similar only the frequency is faster -- more than 6 dips per minute -- and normal variability would still be present. Also when the baby stops after 5-10 minutes the pattern returns to normal)
Terminology and Overview of Principles
Normal Fetal Heart Range: At term the FHR is between 110 and 150 bpm. Previously rates between 110 and 120 have been classified as mild bradycardia. However, this is a frequent finding among healthy fetuses and no longer considered pathological, provided the baseline is steady with normal variability. The same cannot be said of FHRs between 150 and 160 which are considered by many to be the first indicators of distress. They typically occur in late first stage and second stage of a prolonged labor with a mother who is tired, dehydrated and maybe ketodic. They call for corrective measures lest the situation deteriorate into progressive hypoxia. Asphyxia is more likely to develop with a baseline of 155 than one of 115 bpm. (Before 34 wks gestation the baseline is normally higher and up to 160 is acceptable).
High and Low Fetal Heart Rates
A bradycardia is a baseline heart rate of less than 110 bpm. A rate of 100-110 bpm is called "moderate". Provided there are accelerations, good baseline variability and no decelerations this is considered normal and associated with a healthy fetus. Hypoxia should be suspected if the FHR is below 100 bpm.
A tachycardia is baseline heart rate greater than 150 bpm. Between 150 and 170 bpm it is considered to be "moderate". Provided other features are reassuring it is associated with a healthy fetus. Tachycardia with baseline rates greater than 150 bpm should prompt a search for other suspicious features such as absence of accelerations, poor BLV and decelerations. Tachycardia is not uncommon in preterm fetuses due to earlier maturation of the sympathic nervous system.
Accelerations / not rate, not pattern /
A classification of one
An acceleration is defined as a transient increase in heart rate of 15 bpm or more and lasting 15 seconds or more. Accelerations are included in the counting of the baseline rate but not counted as an aspect of the bandwidth when the determining the spread of long-term variability. They are indications of normal fetal activity (usually movement) and thus do not occur in a predictable pattern.
The recording of at least two accelerations in a 20-minute period is considered a reactive trace. Accelerations are considered a good sign of fetal health: the fetus is responding to stimuli and displaying biological integrity of its mechanisms controlling the fetal heart. Accelerations may merge or be continuous falsely suggesting tachycardia (i.e. pseudo-distress pattern - see page # ---). A comprehensive analysis of the clinical situation will clarify this.
In general a mother who is healthy by history and examination and carrying an age-appropriate fetus at term who displays a "reassuring" fetal heart rate pattern assures a healthy fetus for the next 4 hours unless a placental or cord accident intervenes. Death of a normally formed fetus within 4 hours of a normal cardiogram is a rare event but can occur with a serious placental abruption, cord accident/prolapse, uterine rupture or amniotic fluid embolism/anaphylactoid shock, for which there may be no warning signs.
Fetal heart rate baseline variability (BLV) is the degree to which the baseline varies within a particular band width, excluding acceleration and decelerations. It is determined over a time period of 5 or 10 minutes and expressed in beats per minute (bpm). It should be assessed during a reactive period in a one minute segment showing the greatest band width. The baseline rate (normal range 110-150 bpm) is identified by drawing a line through the midpoint of the wiggleness which represents the most common rate (excluding accelerations and decelerations). The baseline variability (normal 10-25 bpm) is determined by drawing horizontals lines at the level of the highest point of the peak and lowest point of the troughs of the wiggliness of the trace in a 3 centimeter segment (for paper speed of 3cm per minute).
The variability may gradually change over time; however, for one particular period it normally remains fairly constant. Band widths are classified as 1) silent pattern (0-5 bpm), reduced (6 -10), normal (11-25) and saltatory (more than 25). The baseline variability indicates the integrity of the autonomic nervous system. Baseline variability is a good predictor of fetal wellbeing and when it is observed during the last 20 minutes before delivery, babies were in good condition regardless of the other features of the trace / FHR pattern. Research exists to indicate that the likelihood of fetal acidosis when normal BLV exists is zero.
The dynamic state of the fetal cardiovascular system and the concept of fetal behavioral states must be appreciated. Fetuses are recognized as having quiet periods associated with rapid eye movements and active periods without such movements. Active movements are associated with good variability and accelerations. Quiet sleep is associated with episodes of decreased variability with generally lasts for up to 40 minutes. Baseline variability is best interpreted during the active phase, recognized by the presence of accelerations defined as rises of 15 beats or more lasting for 15 seconds or more. The presence of two accelerations in a 20 minute (or less) period of time is termed a reactive trace and is suggestive of a fetus in good health. However, in order to be described as non-reactive it should run for a period of at least 40 minutes during which two accelerations are not identified in any 20 minute period.
High and low variability cycles: When a trace is seen with reduced baseline variability (band width < 10 bpm), the previous segments of the trace (or charted or graphic cord of such information) must be reviewed. If the preceding trace was reactive with good baseline variability (BLV), then the segment being reviewed is probably indicative of the "quite phase of the babys FHR cycle and there is no cause for alarm. The start of another active cycle can be patiently awaited, especially if there have been no decels or increase in the baseline rate (BLR) which might indicate the possibility of hypoxia. If there was no previous trace to consider (example -- at the beginning of labor or initial trace taken on arrival of midwife or admission to hospital) the clinical picture must be reviewed to identify whether the fetus is at risk (e.g. small fundal height, post-term, thick meconium, no or scanty amniotic fluid at the time of SROM, reduced fetal movement or other obstetrical or perinatal risk including medications). The trace should be continued in anticipation that reactivity with good BLV may appear.
Periodic Patterns / Decelerations
Decelerations are classified as early, late or variable. A deceleration is a transient episode of slowing the fetal heart rate below the baseline of more than 15 bpm and lasting 15 seconds or more. Deceleration may be greater than this but not significant when other feature of the heart rate are within the normal range or "reassuring" (baseline heart rate, variability, etc). A decel immediately following an acceleration and returning to baseling within 30 seconds is considered normal. When there is abnormal or absent variability (less than 5 bpm) in a non-reactive trace, decels may be very significant even when less than 15 bpm in amplitude.
FHR decelerations describe a transient event. Early decels in the late first stage and early second stage of labor generally indicate head compression and rarely compromise of the fetus. Late decels indicate transient hypoxia with impaired uteroplacental perfusion which may well proceed to established acidosis. Variable decels are often due to cord compression but are also seen in fetus in breech presentation and OP positions when the postulated mechanism or trigger is assumed to be pressure on the supraorbital region of the head.
Developing hypoxia and acidosis are suggested by the absence of acceleration, a rise in the baseline rate and a reduction in baseline variability. Accelerations continue to be a hallmark of fetal health.
Classification of the Patho-Physiological
Mechanism of Decelerations
Early decels are synchronous with UCs, are usually associated with fetal head compression and therefore appear in the late first stage and second stage of labor with decent of the fetal head. They are usually but not invariably benign. Early decels are seen on EFM tracing as symmetrical and bell-shaped inversion of the UC. They are most commonly due to compression of the fetal head. A rise in intracranial pressure is associated with stimulation of the vagal nerve and bradycardia. Head compression decels are most frequently seen in the late stages of labor when descent of the head is occurring. On some occasion the onset of second stage can be deduced from the presence of early decels. Head compression decels can also be seen at the time of vag exams and artificial rupture of membranes. Before assuming that head compression is the explanation for early decels the clinical situation should be reviewed to see if that is a likely explanation.
Late decelerations are late in timing with respect to the uterine contractions. A decel immediately following an acceleration and recovering within 30 seconds or less is considered normal. On the monitor tracing late decels begin at the height of the UC and get more pronounced as the UC fades. Sometimes they continue on well past the end of the UC and for some time during the uterine resting phase. Rapid recovery indicates a baby with good reserves, slow recovery bodes badly as it indicated lack of biological resources or exhaustion. In a normally oxygenated fetus, there is increased variability during a decel on account of the autonomic response. When hypoxia develops there is a tendency to reduced variability.
The pathological mechanism usually indicates impaired placental perfusion (including small areas of placental separation or previa) and is associated with a transient hypoxia. In normal uteroplacental function there is a reservoir of oxygenated blood in the retro-placental space which continues to provide for the exchange gases during the UC. The size of this space varies and is smaller in a fetus suffering from intrauterine growth restriction. A fetus experiencing impaired uteroplacental function uses up the reservoir of oxygen in the retroplacental space as the contraction begins. Due to the restricted supply of blood a hypoxic decel begins, it continues through the remainder of the UC and does not recover fully until some time after the contraction is over and full oxygenation has been restored. The speed of recovery on the ascending limb may reflect the sufficiency of blood flow and the resilience of the fetus.
Decelerations Common in Second Stage: Early decels that gradually becoming deeper and develope variable features are characteristic of the second stage of labor. Reassurance is provided by a good recovery from each decel and a return to normal rate and variability (however short) before the next contraction. Under these circumstances assisted delivery is not necessary except for other reasons relating to maternal conditions. Signs of hypoxia are gradual tachycardia, reduced baseline variability in between and during decels, additional late decels and failure of FHR to return to the baseline rate after decels.
Variable decels hold the key to understanding fetal heart rate patterns and are the most common of all. They are called variable because they vary in shape, size and sometimes in timing with respect to each other and the uterine contractions. They vary because they are a manifestation of compression of the umbilical cord and it is compressed in a slightly different way each time. On some occasion it may not be compressed at all and thus no decel occurs with that particular contraction. Variable decels are more often seen when the amniotic fluid volume is reduced. In the US they are referred to as cord compression decels.
The mechanism occurs because the umbilical vein (the single larger vessel) has thinner wall and lower intra-luminal pressure than the umbilical arteries (the two smaller vessels). When compression occurs blood flow through the vein is interrupted before that flowing through the arteries. The fetus therefore looses some of its circulating blood volume. When a healthy individual or fetus loses some of its circulating blood volume the natural response effected by the autonomic nervous system is a rise in pulse rate to compensate (note the fetus cannot increase cardiac stroke volume so it must raise its heart rate).
After that the umbilical arteries are also occluded, the circulation is relatively restored (i.e. a balance between the venous and atrial system is restored) followed by an increase in systemic pressure, the barometric pressure receptors are stimulated and there is a precipitous fall in the fetal heart rate. The decel is at its nadir with both vessels occluded. During release of the cord compression arterial flow is restored first, with a consequent autonomically mediated sharp rise in heart rate due to systemic hypotension of being pumped out, culminating in a small acceleration after the decel. These accelerations are called "shouldering" and are a manifestation of a fetus coping well with cord compression.
The way the cord is being compressed will vary depending on exactly how it is positioned with respect to the structure compressing it. On the same basis, variable decels may change if the posture of the mother is changed. Normal well-grown fetuses can tolerate cord compression for a considerable length of time before they become hypoxic. Small growth restricted fetuses do not have the same resilience. To assess this process it is necessary to analyze the features of the decel and also the character of the trace as it evolves.
Word picture of normal shouldering:
Picture first a typical baseline with the usual variability of FHT between uterine contractions. As the UC starts, the increasing intrauterine pressure first triggers a slight acceleration which is followed by an observable decel. As the UC begins to let up the rate (and therefore the EFM tracing) begins to rise to baseline and then goes past baseline about an equal number of beats as it did during the acceleration at the beginning of the UC. Then the rate returns to normal baseline rate with normal variability. The trace looks like two equal but upside down letter "V"s at the beginning and end of the UC with a very deep "V" in the middle that is two or three times more pronounced than the acceleration on each side.
If the situation for the fetus begins to devolve the heart rate pattern will first demonstrate an exaggeration of shouldering or overshoot on the recovery acceleration (unequal "V"s with the second one twice as big as the first). Next indicator of increasing distress is a loss of shouldering, followed by a smoothing of the baseline variability within the decel which is associated with loss of variability at the baseline. Next a late recovery is seen (the ascending arm marking the recovery phase is a longer slower slop than the one going down). This is followed by a bi-phasic decel which makes the decel during the UC look like the letter "W". If the duration of the decel is more than 60 seconds and the depth is greater than 60 beats, progressive hypoxia becomes more likely.
Baseline variability and decels - exception to the rule: A decel is usually defined as a drop in heart rate by more than 15 beats from the baseline for longer than 15 seconds. However this rule does not apply when the baseline variability is less than 5 beats. Then any decel, even those less than 15 beats from baseline could be ominous. Continued electronic monitoring is essential with physician consult or transfer of care if the situation is not soon corrected or the birth imminent.
The most critical feature, however, for any questionable or even ominous pattern is the evolution of the trace over time and in relation to other clinical factors. A change in the baseline rate and change in the baseline variability are the key signs of developing hypoxia and acidosis. The time required for a fetus with a previously normal or "reassuring" FHR pattern to be come acidotic related to different types of non-reassuring patterns has been studied. In many cases it will take over 100 minutes, giving caregiver enough time to identify the problem and take effective action (including hospital transfer).
Sinusoidal FHR Pattern
Sinusoidal FHR Pattern is a description given to a trace with a waveform appearance. It is the one FHR pattern which cannot be distinguished by Intermittent Auscultation. The trace looks like a seismograph during a sustained but moderate earthquake -- a regular up and down pattern going 3-5 bpm above and then below the imaginary "middle" of a baseline at a rate of 2-5 times per minute. Because of its association with severe anemia or hypoxic fetuses it is looked upon with anxiety. It is important to realize that severely anemic fetuses do not always show sinusoidal patterns and that sinusoidal patterns can be exhibited by healthy fetuses at certain times (fetal sucking).
A typical pathological sinusoidal FHR pattern would show a stable baseline rate of 110-150bpm with regular oscillation having an amplitude of 5-15bpm (rarely greater), a frequency of 2-5 cycles (i.e.. times per minute) and a fixed or flat baseline variability. Usually the oscillation of the waveform above and below the baseline are equal. However, the most important feature is that there are no areas of normal FHR variability and there are no accelerations.
Reactivity and/or normal baseline variability in the FHR tracing prior to or just after the episode of a period of sinusoidal FHR pattern is suggestive of an uncompromised fetus. Rhythmic fetal mouth movements (sucking) as observed by ultrasound in a healthy fetus have been associated with a "physiological" sinusoidal pattern. When encountering a pattern suspected to be sinusoidal, vibro-acoustical stimulation should produce accelerations of the FHR rate if indeed it is the result of fetal sucking.
A fetus who is severely anemic or hypoxic will not show acceleration either spontaneously or in response to a stimulus (a child who is severely anemic or hypoxic not be able to throw a ball up and down and play). There is also what is called a pseudo-sinusoidal pattern which is not pathological. Interpretation of the difference between the pathological and non-pathological is difficult unless one deals with such situations frequently or is otherwise very experienced. In general the pseudo-sinusoidal pattern has a sharp saw-tooth of baseline variability which is very frequent (more than 5 ups and downs per minute) where as sinister sinusoidal patterns have smooth slow curves.
The causes of pathological sinusoidal typically are Rhesus disease, anemia due to other causes like infection, hemoglobinopathies (Barts thalassaemia), and fetal-maternal transfusion or bleeding from the fetus (vasa previa). Investigation of the cause would include testing for Rh antibiotics, the Kleihauer-Betke test to detect fetal cell in the maternal blood, detection of thalassaemia carrier state in the mother. If sinusoidal patterns are detected in a domiciliary setting perinatal consultation or rapid hospital transfer would be indicated.
Other Patterns and Variation -- normal and pathological
Moderate Baseline Tachycardia or Bradycardia with Reassuring Features: A range of 150 to 170 bpm is termed moderate baseline tachycardia and a range of 100-110 is moderate baseline bradycardia. Provided there is good BLV, accelerations and the absence of decels, these feature do not generally represent hypoxia.
Pseudo-distress pattern* describes a circumstances caused by a very active fetus with so many confluent accelerations that it is misinterpreted as tachycardia with decelerations. The clinical picture should provide clues to correct identification. It is easy to identify these patterns as non- pathological if the fetus is well grown, has a normal amniotic fluid level and is moving actively during the recording of the heart rate. This can be demonstrated by the frequent use of the event marker by the mother or evidence of fetal movement on the toco channel. Such traces should have good baseline variability both at the true rate and at the higher (i.e. acceleration) rate. Remember, a hypoxic fetus with a tachycardia with or without decel does not move actively. If the baby is moving a lot, it isnt tachy.
*The reverse of a pseudo-distress pattern can also occur -- a baby who is tachy (baseline > 170) with deep long decels (down to the 140s) can be mistaken for a normal baseline (140s) with accelerations (up to 170s). Beware! Be sure to listen for a full minute or more so that you are not falsely reassured. Normal fetal behavior argues against "constant" acceleration (greater than half the time or for 30 out of every 60 seconds). Normal acceleration is a relatively brief rise in FHR which was preceded and followed by a normal baseline. True accelerations which continued for long periods also would indicate a lot of fetal activity which the mother and usually the midwife can detect. Inversely, a "tachy" fetus will not be moving so be suspicious of really long periods of increased FHR with short periods of reduced rate that continues over the course of several minutes in the absence of fetal movement. Assume them to be pathological until proven otherwise.
Reduced baseline Variability / Commonest Reasons
1. The sleep or quiet phase of the FHR cycle (lasting up to 40 minutes, longer if the mother is medicated
5. Drugs (sedative, antihypertensives and anesthetics)
6. Local anesthetic reaction
7. Congenital malformation (especially of central nervous system more than cardiovascular system)
8. Cardiac arrthymias
9. Fetal anemia (RH disease of feto-maternal hemorrhage)
10. Fetal infection
Baseline FHR: importance of recognition
of normal range for each individual fetus
When a fetus is in good health the FHR tends to vary by 10-15 bpm in an undulating way, slowing slightly in the sleep phase and after maternal sedation. It rises slightly during the active phase when the fetus moves and exhibits a number of acceleration. Gradually increasing hypoxia causes the FHR to rise gradually, eventually becoming tachy. However the initial issue is the quantity of the rise itself. If the normal rate of a particular fetus has been 110 bpm for several hours and then begins to creep up to 140 bpm, then a rate of 140 bpm represents tachycardia rather than normality. FHTs within the normal range for baseline may be abnormal or ominous on account of other features. A normal baseline rate can be associated with hypoxia and an ominous tracing.
Brow presentation results in the mentovertical diameter, which is usually about 13 cms, presenting at the pelvic brim. This leads to head compression due to a mechanical misfit. Early and variable decels are associated with this fetal position and may well show up early in labor as the baby is trying to traverse the pelvic brim.
Prolonged bradycardia that may
necessitate Immediate delivery:
Prolonged fetal bradycardia is defined as FHR below 100 for 3 minutes or below 80 for 2 minutes. Failure of the FHR to return to baseline and especially to recover to at least 100 bpm is a serious sign. Unfortunately, it is not all that infrequent in healthy fetuses that are momentarily stressed by a rapid drop into the pelvis so one must constantly access the greater picture in discerning when to hit the panic button.
In pathological circumstances it usually reflects an acute event and may be a warning signal of acute hypoxia due to cord compression or prolapse, abruptio placentae, scar dehiscence, uterine hyperstimulation or another unknown cause. It can and does occur in healthy fetuses (possibly due to cord compression). Reversible causes for such an episode are epidural top-off, vaginal examination, placing fetal scalp electrode and uterine hyperstimulation.
Simple measures such as adjusting maternal position, attending to maternal hydration (bolus of IV fluids), giving oxygen and stopping oxytocin infusion (in hospital care) may correct the condition. Most cases of prolonged bradycardia will show signs of recovery towards the baseline rate within 6 minutes. If the clinical picture does not suggest abruption, scar dehiscence or cord prolapse and if the fetus is appropriately grown at term with clear amniotic fluid and a reactive FHR pattern prior to the episode of bradycardia, return back to baseline within 9 minutes is to be expected. The recovery towards the normal baseline within 6 minutes with good baseline variability at the time of the bradycardia and during recovery are reassuring signs and one can wait with confidence for the FHR to revert to a normal rate and pattern. If the FHR does not show signs of recovery by 9 minutes the incidence of acidosis is increased and action should be taken to expedite delivery as soon as possible.
During a bradycardia the fetus reduces its cardiac output. Carbon dioxide and other metabolites cannot be cleared by the respiratory function of the placenta. The initial pH at the end of a bradycardia is low with a high Pco2 showing a respiratory acidosis. Once the FHR returns to normal the carbon dioxide and metabolites are cleared with blood gases returning to normal in 30-40 minutes. If the episode of bradycardia continues then the fetus switches to anaerobic metabolism resulting a metabolic acidosis with is harmful to the fetus, hence excessively prolonged bradycardia results in a poor outcome. Fetuses who are post-term, growth-restricted, have no amniotic fluid at rupture of membranes or thick meconium-stained fluid are at greater risk of developing hypoxia within a short time. In these situation it may be better to take action early on if the FHR display a persistent bradycardia. A delay of 20 or more minutes may result in an asphyxiated baby.
Responsive Action: Start the mother on O2 at 8-10 L by tight-fitting face mask and continue to monitor the FHR while a second person does a vaginal exam to check for prolapsed cord. If prolapsed cord is discovered you may consider placing a Foley catheter in the mothers bladder and instilling 500ml of sterile fluid while others contact EMTs and notify the hospital of emergency transport. This method is standard of care in some European countries as filling the mothers bladder lifts the baby up and out of the pelvis and thus off the cord permitting the FHR to normalize while awaiting CS delivery. If heart tones are above 100 she can be transported without needing to be in a knee-chest position. The bladder and the uterus share a membranous connection and ride up together as frequently noted PP when the mother has a full bladder.
If a Foley is not placed, put the mother in a knee-chest position and manually (vaginally with gloved hand) lift the baby off the cord while awaiting arrival of EMTs. You will have to transport with the mother in this position and your hand in her vaginal lifting the baby up so have family member supply a sheet to cover her while she is being taken to the ambulance.
Having eliminated prolapsed cord as a source of the bradycardia the midwife should initiate intra-uterine resuscitation by changing maternal position (may try knee chest while listening to FH) and instructing the mother to cease any voluntary pushing efforts unless delivery is otherwise imminent. If there are no signs of recovery or return towards to baseline or re-establishment of variability after 6 minutes of unremitting bradycardia the receiving hospital should be notified and transport (by POV or EMTs) should be immediately undertaken (dont let parents take time to pack clothes for hospital). In some institutions (primarily tertiary care hospitals with 24 hr coverage) the rule is to begin emergency response (notify people, O2, position change, start IV or stop Pitocin) at 3 minutes, begin preparing the mother for surgical intervention at 6 minutes, prepare to do forceps or CS at 9 minutes and perform forceps delivery or CS at 12 minutes. However a 30 minute from decision to incision is more commonly the standard (although not the ideal).