Clin: Fetal Heart Monitoring - Moulton Flashcards
how often do you monitor an uncomplicated pregnancy in the first and second stages of labor?
1st: q 30 minutes
2nd: q 15 minutes
how often do you monitor a complicated pregnancy in the first and second stages of labor?
1st: q 15 minutes in active phase (following contraction)
2nd: q 5 minutes
what does a pressure sensitive tocodynanmometer transducer measure?
detects and records the frequency of contractions, NOT strength
does internal or external monitoring give the most accurate readings?
internal
internal electronic fetal monitoring:
- rate computed from the R wave peaks of fetal echocardiogram
- maternal and fetal movement will not alter quality of signal
fetal scalp electrode (FSE)
when should you avoid internal fetal monitoring?
HIV patients
internal electronic fetal monitoring
- soft plastic catheter placed transcervically
- gives precise measurement of intensity of the uterine contractions in mmHg
intrauterine pressure catheter (IUPC)
fetal oxygen reserve is only enough to meet it’s metabolic needs for how long?
1-2 minutes
- blood flow from maternal circulation, which supplies the fetus with oxygen thru placental exchange of respiratory gases, is momentarily interrupted during contractions
- normal fetus can tolerate temporary reduction in blood flow without suffering because adequate oxygen exchange occurs between contractions
what determines fetal heart rate?
atrial pacemaker
what modulates fetal heart rate?
innervation via vagus (decelerator) and sympathetic (accelerator) nerves
if fetus is not getting adequate blood supply between contractions, what happens?
will beome hypoxic
- chemoreceptors and baroreceptors in peripheral arterial circulation of the fetus influence FHR by giving rise to contraction related or periodic FHR changes
what happens if hypoxia becomes severe?
anaerobic metabolism -> accumulation of pyruvic and lactic acid -> fetal acidosis
what is the normal pH of fetal scalp blood?
7.25-7.3
what is considered fetal acidosis?
< 7.2
with each contraciton, blood flow from mom to baby ceases as what are compressed?
uterine myometrial vessels
- at this point, mom and baby are physiologically separated
what happens as the contraction begins to subside?
- uterine myometrial ARTERIES reopen, allowing oxygenated blood/nutrients to flow from mom to baby
- uterine myometrial VEINS reopen, allowing blood carrying fetal waste products to flow from baby to mother
what does the upper tracing on fetal monitoring strip measure?
FHR (BPM)
what does the lower tracing on fetal monitoring strip measure?
uterine contractions (mmHg)
what is considered normal uterine activity in active labor?
5 contractions or less in 10 minutes, averaged over a 30-minute window
what is considered tachysystole?
> 5 contractions in 10 minutes, averaged over 30 minute window (LOWER STRIP)
- may or may not be associated FHR decelerations (UPPER STRIP)
how are contractions measured?
from peak to peak
3 contractions in 8 minutes, occurring every 2-3 minutes
normal
a measure of uterine contraction intensity (LOWER STRIP) during labor
- units are calculated via INTERNAL pressure monitor
- subtract baseline resting tone from the peak pressure of uterine contraction (done over 10 minute interval)
Montevideo units (mmHg)
what is the threshold number that is considered necessary for adequate labor to bring about dilation and effacement during the active phase of labor
> 200 MVUs
what is the normal range of FHR?
110-160 bpm
what is considered tachycardia?
> 160 bpm
what is considered bradycardia?
< 110 bpm
when do you measure baseline FHR?
BETWEEN uterine contractions, NOT during
- fetal hypoxia (late sign of hypoxia)
- obstetric anesthesia
- pitocin
- maternal hypotension
- prolapsed or prolonged compression of umbilical cord
- heart block
causes of fetal bradycardia
- fetal hypoxia (early sign of hypoxia)
- medications (excessive oxytocin augmentation)
- arrhythmias
- prematurity
- maternal fever
- fetal infection (chorioamnionitis is MCC)
causes of fetal tachycardia
chemoreceptors produce tachycardia in response to what?
hypoxia
baroreceptors influence FHR via vagus n. in response to what?
changes in fetal blood pressure
how is baseline variability quantified?
amplitude of peak to trough (bpm) change in baseline rate
no detectable variability around baseline (line doesn’t really change)
absent variability
persistently minimal or absent FHR variability appears to be the most significant intrapartum sign of fetal compromise
amplitude range detectable, but < 5 bpm
minimal variability
what is the normal variability range?
moderate variability = 6-25 bpm
amplitude range > 25 bpm
marked variability
Reasons for absent variability
- inadequate oxygenation
- fetal central nervous system or cardiovascular anomaly
- pre-existing fetal brain injury
- effects of maternal medication administration (MgSO4 or narcotics)
- OR might just indicate normal fetal sleep patterns!
Reasons for marked variability
- early stages of fetal hypoxemia
- OR may be a normal finding. Therefore,
why baseline variability is a key assessment
Reasons for moderate variability
- intact neurological modulation of fetal heart rate
- normal cardiac responsiveness, and fetal reserve
- reliably predicts the absence of fetal metabolic acidemia and usually indicates that the fetus is well-oxygenated at that point in time
why are NST’s only performed after 28 weeks?
fetal ANS does not finish developing until 30 weeks, so measuring FHR before then will not give an accurate reading
indicator of possible fetal stress
- is ominous if associated with persistent late delerations
- is associated with hypoxia and acidemia (lack of oxygen build up of acid in the fetus depresses FHR and CNS)
decreased variability
- prematurity
- sleep cycle
- maternal fever
- fetal tachycardia (chorioamnionitis)
- fetal congenital anomalies
- maternal hyperthyroidism
- maternal drugs (caffeine nicotine, cocaine, narcotics)
cases of decreased baseline variability
what are the 4 types of FHR decelerations?
- early
- variable
- late
- prolonged
- an abrupt increase in FHR is a normal, reassuring response
- if >32 weeks: HR > 15bpm above baseline for 15 seconds or more
- if <32 weeks: HR > 10bpm above baseline for 10 seconds or more
accelerations
what is considered a prolonged acceleration?
last more than 2 minutes
what is considered a change in baseline?
if acceleration last more than 10 minutes
what are the main causes of accelerations?
- spontaneous fetal movement
- scalp stimulation or vibro-acoustic stimulation
- vaginal exam
what are the 3 types of decelerations?
- early
- variable
- late
secondary to fetal head compression
- fetal ANS response (vagus) to increased intracranial pressure caused by transient compression of fetal head -> decreases HR
- NOT associated with fetal distress
- nadir of decel (lowest point/trough of FHR) occurs at the same time as the peak of contraction -> MIRROR IMAGE
early deceleration
secondary to umbilical cord compression
- abrupt decrease in FHR d/t fetal hypovolemia -> activates baroreceptors and chemoreceptors (stimulates vagus)
- can occur before, during, or after the contraction starts
- decrease in FHR > 15 bpm, lasting >15 seconds and more than 2mins in duration
- onset, depth and duration can vary
variable deceleration
- V is variable! looks like a wide V
what happens if the umbilical cord is only slightly compressed?
it will obstruct the umbilical VEIN (low pressure system), which returns re-oxygenated blood to fetal heart
- normal fetal response is slight increase in FHR to compensate for lack of blood return and the slowly diminishing oxygen supplies
- increase in FHR is followed by major drop in FHR -> called a “shoulder”
secondary to uterine placental insufficiency (UPI)
- OMINOUS
- repetitive decels usually indicate fetal metabolic acidosis and low arterial pH
- nadir of the decel occurs AFTER the peak of contraction
late decelerations
what are two potential causes of late decelerations?
- excessive uterine activity
- maternal supine hypotension
decrease in FHR from baseline that is > 15 bpm last more than 2 mins, but less than 10
- disruption of oxygen transfer from environment to the fetus at one or more points along oxygen pathway
- commonly seen during maternal pushing
prolonged deceleration
smooth, sine wave-like undulating pattern in FHR baseline with a cycle frequency of 3-5 per minute
- seen with fetal anemia
sinusoidal pattern
- very bad sign :((
instillation of normal saline, can alleviate cord compression (can help resolve some variables)
- initially 250-1000cc infused 15cc/min
- followed by continuous infusion 100-200cc/hour
- infused thru transcervical IUPC
amnioinfusion
- minimal or absent variability
- recurrent late decelerations
- prolonged decelerations
- tachycardia
- bradycardia
- variable, late or prolonged decelerations occurring with maternal pushing
category II (indeterminate) - not predictive of abnormal acid-base status, but insufficient data to classify as category I or III
category II, INTERMITTENT variable decelerations (<50% of contractions)
common finding usually associated with normal outcomes
- no intervention required
category II, RECURRENT variable decelerations (>50% of contractions)
umbilical cord compression with impending acidemia
- moderate variability and/or accelerations suggest fetus is not acidemic
GOAL: to alleviate cord compression (promote fetal oxygenation) -> repositioning, amnioinfusion (in 1st stage), modification of pushing efforts (push w/every other contraction)
what is the goal/management of tachysystole?
reduce uterine activity
- lateral positioning
- IV bolus
- decrease oxytocin rate
- removal of cervadil insert
- if no response, give uterine tocolytic (tertbutaline)
absent baseline variability (increased risk fetal acidemia)
- recurrent late decels
- recurrent variable decels
- bradycardia
sinusoidal pattern (increased risk hypoxemia and acidemia)
category III -> prepare for delivery
- reposition mom
- IV bolus
- oxygen supplementation
- scalp stimulation test
- if no improvement, delivery is advisable
used to differentiate fetal sleep from acidosis, when the fetal tracing shows reduced variability but no decelerations
fetal scalp stimulation
what is the expected pH value when an acceleration of 15bpm lasts 15 seconds?
fetal pH almost always 7.22 or greater (good sign, baby just sleeping)
