Fetal Surveillance During Labor Flashcards
What can cause adverse fetal neonatal outcomes?
- Antepartum complications
- Suboptimal uterine perfusion
- Placental dysfunction
- Intrapartum events
What was fetal heart rate monitoring developed for?
- To detect FHR patterns that may be frequently associated with delivery of infants and poor outcomes
What are some benefits to FHR monitoring?
- Most studies reveal the incidence of neurologic damage and perinatal death with the use of electronic FHR monitoring is NOT significantly lower than that documented with older methods
What have some studies shown is highly associated with FHR monitoring?
- Increase in operative vaginal deliveries and C sections
Why do we not revert back to traditional fetal monitoring systems?
- Reassurance that >90% of a good fetal outcome is associated with normal continuous FHR data
- Great expense involved with 1:1 patient to nurse that is mandatory for intermittent auscultation
- The knowledge that non reassuring continuous FHR monitoring may provide warning of potential problems and a gauge of fetal response to actions undertaken to improve fetal conditions
What are the different types of fetal monitoring?
- External (continuous)
- Internal (will provide most accurate tracings)
What are some different external monitoring systems?
- Doppler ultrasound inducer
- Pressure sensitive tocodynamometer transducer
What does a doppler ultrasound transducer do?
- Placed on maternal abdomen overlying the fetal heart
- Records reflected sound waves from the fetal heart back to the transducer
What does a pressure sensitive tocodynamometer do?
- Detects and records contractions
- Useful for measuring the frequency of contractions but NOT the strength
What may hinder the results of external fetal monitoring?
- Maternal obesity
What are some internal fetal monitoring systems?
- Fetal scalp electrode (FSE)
- Intrauterine pressure catheter
What does a fetal scalp electrode do?
- Rate is computed from the R wave pekas of the fetal echocardiogram
- Maternal and fetal movement will not alter the quality of the signal
- Rare cases of fetal pustules have been reported
- Avoid in HIV patients
What does a intrauterine pressure catheter do?
- Soft plastic catheter placed transcervically
- Gives precise measurement of the intensity of the uterine contractions in mm Hg
What is required for internal monitoring systems?
- Membranes to be ruptured
How big is the fetal oxygen reserve?
- Only big enough to meet its metabolic needs for approximately 1-2 minutes
How does blood flow to the fetus changed during contractions?
- Blood flow from maternal circulation is momentarily interrupted during a contraction
- The normal fetus can tolerate the temporary reduction in blood flow to the placenta without suffering hypoxia because adequate oxygen exchange occurs during the intervals between contractions
What happens to the fetus under hypoxic conditions?
- Chemoreceptors and baroreceptors in the peripheral arterial circulation of the fetus influence the FHR by giving rise to contraction related or periodic FHR changes
What does severe hypoxia result in?
- Anaerobic metabolism, resulting in the accumulation of pyruvic and lactic acid causing fetal acidosis (fetal scalp blood pH <7.20)
What happens to the blood flow to the uterus as the contraction begins to subside?
- Uterine myometrial arteries reopen, allowing oxygenated blood and nutrients to flow from mother to baby
- Uterine myometrial veins reopen, allowing blood carrying fetal waste products to flow from the baby to the mother
What does the upper and lower tracings look at on a fetal monitoring strip?
- Upper: monitors FHR
- Lower: monitors uterine contractions
What is normal uterine activity?
- 5 contractions or less in 10 minutes averaged over a 30 min window
What is tachysystole?
- > 5 contractions in 10 minutes, averaged over a 30 min window
- Presence or absence of associated FHR decelerations
What is the baseline FHR?
- Is rounded to increments of 5 bpm during a 10 minute segment
- Normal is 110-160
What is bradycardia and tachycardia in FHR?
- Bradycardia: baseline <110 bpm
- Tachycardia: baseline >160 bpm
What are some causes of bradycardia in FHR?
- Fetal hypoxia - late sign of hypoxia
- Obstetric anesthesia
- Pitocin
- Maternal hypotension
- Prolapsed or prolonged compression of the umbilical cord
- Heart block
What are some causes of tachycardia in FHR?
- Fetal hypoxia - early sign of hypoxia
- Medications (excessive oxytocin augmentation)
- Arrhythmias
- Prematurity
- Maternal fever
- Fetal infection (chorioamnionitis - Most common cause)
What contributes to fetal heart changes and variability?
- Opposing sympathetic and parasympathetic inputs contribute to the R-R variability from one heart cycle to the next
What do chemoreceptors and baroreceptors do in the fetal heart rate?
- Chemoreceptors: produce tachycardia in response to hypoxia
- Baroreceptors: influence FHR via the vagus n in response to changes in fetal BP
What is baseline variability quantified as?
- Amplitude of peak-to-trough in bpm of change in baseline rate
What are the different changes in baseline variability?
- Absent - amplitude range undetected
- Minimal - amplitude range detectable but ≤5 bpm
- Moderate (normal) - amplitude range 6-25 bpm
- Marked - amplitude range > 25 bpm
What could decreased variability mean?
- Possible fetal stress
- Is ominous if associated with persistent late decelerations
- Is associated with hypoxia and acidemia
What are some causes of decreased variability?
- Prematurity
- Sleep cycle
- Maternal fever
- Fetal tachycardia
- Fetal congenital anomalies
- Maternal hyperthyroidism
- Maternal drugs or substance use
What are the categories of FHR changes due to uterine contractions?
- No change
- Acceleration
- Deceleration
What is seen during acceleration during FHR changes?
- An abrupt increase in the FHR and is normal reassuring response
- ≥32 weeks, acceleration - HR of ≥ 15 bpm above baseline for 15 sec or more
- <32 weeks, acceleration - HR ≥ 10 bpm above baseline for 10 sec or more
What is prolonged acceleration in FHR?
- Lasts for greater than 2 minutes
What is it called when the FHR is accelerated for more than 10 minutes?
- Change in baseline
What are some causes of FHR acceleration?
- Spontaneous fetal movement
- Scalp stimulation or vibroacoustic stimulation
- Vaginal examination
How can decelerations of the FHR be classified?
- Early
- Variable
- Late
What is early deceleration?
- Secondary to head compression
- Fetal autonomic response to increased ICP caused by transient compression of fetal head
- Not associated with fetal distress
- Nadir of the deceleration occurs at the same time as the peak of the contraction and thus is a mirror image
What is variable deceleration?
- Secondary to umbilical cord compression
- Abrupt decrease in FHR; can occur before, during, or after the contraction starts
- Decrease in FHR is ≥ 15 bpm lasting ≥15 sec and for longer than 2 min in duration
- The onset and duration can vary with successive uterine contractions
What happens if there is only sight compression of the umbilical cord?
- Obstruct the umbilical vein which returns reoxygenated blood to fetal heart
- Normal initial response is a slight increase in FHR to compensate for lack of blood return and the slowly diminishing oxygen supplies
- The slight increase in FHR is followed by a major drop in FHR called a “shoulder”
What is late deceleration?
- Caused by uterine placental insufficiency
- Most ominous deceleration
- Repetitive decelerations usually indicate fetal metabolic acidosis and low arterial pH
- Nadir of the deceleration occurs after the peak of the contraction
What are some potential causes of late decelerations?
- Excessive uterine activity
- Maternal supine hypotension
What is prolonged deceleration?
- Decrease in FHR from baseline that is ≥15 bpm lasting ≥2 min but < 10 min
- Disruption of oxygen transfer from the environment to the fetus at one or more point along the oxygen pathway
- Commonly seen during maternal pushing
What is sinusoidal pattern seen on a FHR strip?
- Smooth, sine wave-like undulating pattern in FHR baseline with a cyclic frequency of 3-5 per minute
- Seen with fetal anemia
What is category I for classifying FHR?
- Baseline 110-160bpm
- Moderate variability
- No late or variable decelerations
- Accelerations and early decelerations may or may not be present
What is the goal and management for category I?
- Intermittent or CEFM
What are some FHR tracings in category II for classifying FHR?
- Intermittent variable decelerations (<50% of contractions)
- Recurrent variable decelerations (>50% of contractions)
What is the goal and management of intermittent variable decelerations in category II?
- No intervention required
What is the goal and management of recurrent variable decelerations?
- To alleviate cord compression
- Repositioning
- Amnioinfusion
- Modification of pushing efforts
What is an amnioinfusion?
- Instillation of normal saline can alleviate cor compression
- Infused through a transcervical IUPC
What are some causes for tachysystole in FHR tracing in category II?
- Spontaneous labor
- Induction or augmentation
What is the goal of tachysystole?
- Reduce uterine activity
What is the FHR tracing in category III?
- Absent baseline variability
- Recurrent late decels
- Recurrent variable decels
- Bradycardia
- Sinusoidal pattern
What are some causes of category III in FHR tracing?
- Increased risk of fetal acidemia
- Increased risk of hypoxemia and acidemia
What is the goal for category III?
- Prepare for delivery
What is fetal scalp stimulation? What is it used for?
- When the scalp is stimulated
- If an acceleration of 15 bpm lasting 15 seconds occurs the fetal pH is almost always 7.22 or greater
- Used to differentiate between fetal sleep and acidosis
What are potential logistical considerations for operative delivery with category III tracing?
- Obtain informed consent
- Assemble surgical team
- Assess patient transit team and location for operative delivery
- Ensure IV access
- Review labs and assess need for availability of blood products
- Assemble neonatal resuscitation personnal
