FHR Components

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Author:
newmeximama
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263546
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FHR Components
Updated:
2014-02-23 21:06:29
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fetal OB
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Advanced fetal monitoring notes: chapter 4
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  1. Needed to determine baseline
    2 minutes of identifiable baseline segments in 10 minute period
  2. Typical baseline range
    110-160
  3. High baseline is normal in less than ____wks.
    32
  4. Lower baseline normal in greater than 32 weeks because of
    increase in vagal tone. Parasympathetic nervous system starts exerting control at 28 weeks. HR drops to midnormal by 32 weeks.
  5. Def of baseline shift
    Change in baseline greater than 10 minutes
  6. Bradycardia in this situation may be ok
    • Moderate variability
    • 2nd stage of labor
    • HR 90-110
  7. Congenital heart block in infant is related to this in mother
    Congenital heart block (CHB) associated with maternal anti-SSA/SSB antibodies. CHB detected in utero is strongly associated with maternal antibodies to SSA (Ro) and SSB (La). The mothers of affected infants frequently had autoimmune disease (systemic lupus erythematosus, Sjögren's syndrome) or were entirely asymptomatic. It is very difficult to identify pregnant asymptomatic mothers carrying anti-SSA/SSB antibodies.
  8. FHR tracing when infant has CHB
    • BL less than 70 without variability
    • Use ultrasound or echocardiogram to diagnose
    • Can NOT use fetal heart rate to monitor oxygenation of fetus
    • Scalp pH is better measurement tool
  9. Hypoxic causes of fetal bradycardia
    • Maternal hypotension
    • Tachysystole or uterine rupture
    • cord prolapse, compression
    • placental abruption
  10. Non-hypoxic causes of fetal bradycardia
    • Vagal stimulation during 2nd stage of labor
    • Maternal hypothermia
    • Drugs such as beta blockers
    • Bradydysrhythmias
    • Prolonged hypoglycemia
    • Nonhypoxic causes are usually associated with moderate variability and outcomes that are not as ominous.
  11. Definition of tachycardia
    Baseline is higher than 160 for more than 10 minutes
  12. Causes of fetal tachycardia
    • Gever
    • Chorioamnionitis
    • Dehydration
    • Fetal sepsis
    • Fetal anemia
    • Chronic hypoxemia
    • Parasympatholytic drugs (atropine)
    • Fetal heart failure (fetal hydrops) 
    • Fetal tachyarrhythmias (SVT)
  13. Fetal SVT typically has HR higher than
    220
  14. Fetal SVT can cause
    high-output cardiac failure
  15. Def of variability
    Fluctuations in baseline fetal HR that are irregular in amplitute and frequency. Variability is visually quantitated over a 10-minute period as the amplitude of the peak-to-trough in beats per minute, excluding accelerations and decelerations. Generally there are 3–5 cycles of variability per minute, though anything over 2 cycles per minute is considered variability.
  16. Variability Guidelines
    Fluctuations around the usual fetal heart rate

    Assess at the same time as baseline—not during accelerations or decelerations

    • Most important FHR component—indicates intact mature central nervous system (CNS)
    • Absent (no fluctuations), minimal (amplitude peak to trough ≤5 bpm), moderate (>6 and ≤25 bpm), or marked (>25 bpm)*
  17. Def of absent variability
    amplitude peak to trough undetectable
  18. Minimal variability
    amplitude >undetectable to ≤5 bpm
  19. Def of moderate variability
    amplitude ≥6 and ≤25 bpm
  20. Def of marked variability
    amplitude >25 bpm
  21. Absent or minimal variability can be indicative of fetal hypoxia if associated with
    recurrent late or variable decelerations or a bradycardia.
  22. Lack of variability: Hypoxic causes
    • Placental abruption 
    • Excessive uterine activity
    • Maternal hypotension
  23. Lack of variability: Non-hypoxic causes
    • Prematurity (<32 weeks)  
    • Fetal sleep  
    • Fetal tachycardia
    • Dysrhythmias
    • Fetal CNS abnormality
    • Medications (CNS depressants such as meperidine hydrochloride or morphine)
  24. Definition of acceleration
    Accelerations, like decelerations, usually represent episodic or periodic changes from the baseline. In contrast, tachycardia, bradycardia, and variability represent changes to or fluctuations in the baseline.
  25. Accel guidelines
    Term: abrupt (onset to peak <30 sec), ≥15 bpm above baseline, duration ≥15 sec and <2 min

    Preterm (<32 weeks): abrupt (onset to peak <30 sec), ≥10 bpm above baseline, duration ≥10 sec and <2 min

    Prolonged: ≥2 min and <10 min
  26. Even in preterm fetuses, accelerations must be this to be considered indicative of normal oxygenation:
     ≥15 bpm and duration ≥15 seconds 
  27. Causes of accelerations
    Fetal movement

    Uterine contractions

    Partial umbilical cord compression

    Vibroacoustic stimulation

    Scalp stimulation (vaginal exam, application of fetal spiral electrode, scalp blood sampling)
  28. Decel Guidelines
    • Four types categorized by shape, timing relative to contractions, and gradual vs. abrupt onset: early, late, variable, and prolonged
    • Late decelerations point to uteroplacental insufficiency
    • Variable decelerations point to cord compression
  29. Definition of recurrent decelerations
    if they occur with ≥50% of uterine contractions in a 20-minute interval.
  30. Definitin of intermittent
    Decelerations are considered to be intermittent if they occur with <50% of uterine contractions in a 20-minute interval.
  31. Definition of Early Decel
    An early deceleration is defined as a visually apparent, usually symmetrical gradual (onset to nadir ≥30 sec.) decrease and return to the baseline fetal heart rate associated with uterine contractions (NICHD, 2008). The nadir of the deceleration coincides with the peak of the contraction. Early decelerations are unrelated to hypoxia or acidosis. Look for them in the active phase of labor (5–6 cm dilation).
  32. Definition of Late Decelerations
    Late decelerations look similar to early decelerations in shape and uniformity, but the timing is completely different. A late deceleration is defined as a visually apparent, usually symmetrical gradual decrease and return to the baseline fetal heart rate associated with uterine contractions (NICHD, 2008). The onset, nadir, and recovery of the deceleration follow the beginning, peak, and end of the contraction, sometimes by as much as 30 seconds. Late decelerations are a response to inadequate oxygen exchange in the intervillous space (uteroplacental insufficiency).
  33. Conditions associated with Late Decelerations
    • intrauterine growth restriction (IUGR)chronic hypertension
    • severe pregnancy-induced hypertension
    • diabetes
    • tachysystole or other excessive uterine activity.

    You need to be aware of the possibility of excessive oxytocin stimulation when you see this pattern.
  34. Four causes of variable decelerations
    Oligohydramnios:

    Onset usually in the early active phase of labor or after membrane rupture

    Descent:

    Onset usually at 8–10 cm dilation

    Often associated with nuchal cords

    Aggravated by pushing efforts

    Cord prolapse:

    Sometime after rupture of membranes

    Associated with unengaged station or abnormal presentation

    Unusual causes:

    True knots, short cords, limb entanglement, occult prolapse, etc.

    Onset and progression variably related to labor
  35. Definition of variable decel
    A visually apparent abrupt (onset to nadir in <30 sec.) decrease and return to baseline in the fetal heart rate. The decrease in fetal heart rate is ≥15 bpm, and the deceleration lasts ≥15 sec. but <2 min (NICHD, 2008). Variable decelerations are so named because their timing with respect to contractions varies. They are also variable in shape.
  36. What variable decels most often represent
    In most cases, they do not represent significant hypoxia or acidosis; instead, they indicate some degree of cord compression with mild respiratory acidosis as the result.
  37. Var decels less likely to need intervention
    Although variable decelerations cannot by definition be part of a Category I pattern, they are less likely to require intervention if the following criteria are met: 1) the fetal heart rate baseline is not increasing, 2) variability in the fetal heart rate is not decreasing, 3) accelerations are present or can be stimulated.
  38. When variable decels may mean hypoxia and acidosis---need for quick recovery
    • Recurrent variable decelerations
    • along with minimal or absent variability and/or rising baseline
  39. Causes of prolonged decel
    • 1) progressive cord compression
    • 2) tetanic uterine contractions
    • 3) maternal hypotension
  40. Definition of prolonged deceleration
    A visually apparent decrease in fetal heart rate below the baseline lasting ≥2 min. and <10 min (NICHD, 2008). A prolonged deceleration lasting ≥10 min. is a baseline change.
  41. When prolonged decelerations last longer than 3–4 minutes and do not respond to resuscitative measures, you should consider more ominous causes such as
    • 1) uterine rupture
    • 2) placental abruption
    • 3) cord prolapse
    • Typically, prolonged decelerations will follow a series of deep variable decelerations.
  42. Baseline guidelines
    Typical baseline range: 110–160 beats per minute

    <32 weeks: baseline is high normal

    >32 weeks: gradual decrease in baseline due to increase in vagal tone

    Changes in bpm ≥10 minutes: may indicate a baseline shift
  43. Variability Guidelines
    Fluctuations around the usual fetal heart rate

    Assess at the same time as baseline—not during accelerations or decelerations

    • Most important FHR component—indicates intact mature central nervous system (CNS)
    • Absent (no fluctuations), minimal (amplitude peak to trough ≤5 bpm), moderate (>6 and ≤25 bpm), or marked (>25 bpm)
  44. Considerations with sinusoidal patterns
    The pattern is usually related to severe fetal anemia, such as Rh sensitization or fetal–maternal hemorrhage.

    A "true" sinusoidal pattern is a Category III pattern associated with increased perinatal morbidity and mortality.

    It is usually consistent and not associated with a precipitating event.

    Even though the pattern is rare, you must be able to immediately recognize it because of the poor prognosis and the need for expeditious intervention.

    Decelerations associated with a sinusoidal pattern are an even more ominous sign.
  45. Frequency of cycle with sinusoidal pattern
    2-5 per minute
  46. Characteristics of pseudo-sinusoidal patterns
    • 1) More sawtooth pattern
    • 2) More than 5 cycles per minute
    • 3) May have accels (absent in true sinusoidal)
    • 4) Normal pattern after pseudo sinusoidal (after drug wears off)
  47. More common fetal arrythmias
    • Complete heart block
    • Supraventricular tachycardia
    • Premature ventricular contraction
  48. Fetal arrhythmias are usually benign unless
    other signs of hypoxia or fetal heart failure are present.
  49. This makes you think of fetal PVC's
    vertical excursions on strip (sharp, straight deflections up and down)
  50. More than_______ of Category II patterns have normal outcomes
    50%
  51. Category 1 characteristics
    Category I patterns are normal patterns, those with a normal baseline and moderate variability without late, variable, or prolonged decelerations. Accelerations may be present or absent.

    Category I patterns are almost invariably associated with normally oxygenated fetuses without evidence of hypoxia or acidosis.

    There is a direct association between a Category I pattern and a normal fetal outcome.
  52. Category II Characteristics
    Category II patterns are indeterminate patterns, having some characteristics suggestive of fetal acidemia but other characteristics that may indicate normal oxygenation.

    Category II patterns cannot reliably predict oxygenation of the fetus, but do not correlate directly with poor fetal outcomes.

    Category II FHR tracings require evaluation and continued surveillance and reevaluation, taking into account the entire associated clinical circumstances and the general trend of the pattern. (NICHD, 2008).
  53. Category II patterns
    Category III patterns are abnormal patterns, predictive of abnormal fetal acid-base at the time of observation. Category III patterns have absent variability with any of the following: recurrent late decelerations, recurrent variable decelerations, or bradycardia.

    Sinusoidal patterns are also considered Category III patterns.

    These patterns require prompt intervention, as they have a much higher correlation with fetal injury than Category II patterns. Interventions may include but are not limited to:

    • provision of maternal oxygen;
    • change in maternal position;
    • discontinuation of labor stimulation; and
    • treatment of maternal hypotension.
    • If these interventions do not resolve a Category III pattern, expedited delivery may be necessary.
  54. _______ is an indicator of CNS responsiveness or integrity.
    Variability

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