Fetal monitoring Flashcards
What are the influences on the fetal heart rate?
Central nervous system - regulates autonomic NS
Autonomic nervous system
When is the ANS expected to be fully developed by?
32 weeks
What are the two parts of the ANS are?
- Parasympathetic NS
- Sympathetic NS
What does the parasympathetic NS do? What stimulate it?
Vagus nerve stimulation –> slow HR
Stimulated by pressure on fetal head
Can also stimulate passage on meconium
What does the sympathetic NS do? What is it stimulated by?
Increase HR and strength of heart contraction
Stimulated by loud noise, vibration, stimulation of scalp of pressure on maternal abdomen
What changes is the ANS sensitive to?
Oxygen exchange
CO2 production
BP changes
What are chemoreceptors? What do they respond to? What do they cause?
Receptors in the carotid arch and CNS
Respond to changes in fetal O2 CO2 and pH levels
Stimulation –> increase or decrease HR
What are baroreceptors? What do they respond to? What do they cause?
Receptors in the carotid and aortic arch
Detect pressure changes
Stimulation –> vasodilation, decrease BP, and reflexive increase HR
What are the influences on FHR?
Fetal reserves
Utero-placental unit
Factors that affect fetal perfusion
What are fetal reserves? What occurs w/o fetal reserves?
Reserve O2 available to fetus to withstand change in BF during labor
W/O –> won’t withstand changes
How does the Utero-placental unit affect FHR?
ability to transfer oxygen to fetus and remove waste products
What are factors that affect fetal perfusion? (9)
Maternal HTN or HypoTN
Abruptio placenta
Diabetes
Smoking
Substance abuse
Maternal supine position
Post-term pregnancy
Uterine tachysystole
Cord compression
How does maternal HTN/HypoTN affect FHR?
Decrease perfusion
How does abruptio placenta affect FHR?
Placenta has separated before delivery –> decrease BF to fetus
How does diabetes and smoking affect FHR?
Vasoconstriction –> decrease BF
How does maternal substance abuse affect FHR?
Causes abruption
How does maternal maternal supine position affect FHR?
Hypotension
How does maternal uterine tachyststole affect FHR?
Too frequent contractions (more than 5/min) –> decrease perfusion because not enough time to recover/absorb in between contractions
What occurs to the fetus when the uterus contracts?
Fetus holds their breath and using reserves
When uterus relaxes, reserves are restored
If healthy, fetus will have enough reserve to tolerate respective contractions
Where do problems with O2 transfer occur? What do these all cause?
Placenta (cause decrease O2 transfer during relax)
Uterus
Maternal perfusion
All cause hypoxemia in fetus
What are the results of decreased placental perfusion?
Normal oxygen (decrease PaO2/amount of O2 available)
Hypoxemia (blood shunted to vital organs)
Tissue hypoxia
Increased lactic acid
Metabolic acidosis d/t anaerobic metabolism in tissue
Injury or death
What are 3 different methods for FHR assessment?
Intermittent auscultation with doppler or fetoscope
External ultrasound transducer
Fetal spiral electrode
What are 3 methods for contraction assessment?
Palpation
External tacodynomometer “toco”
Intrauterine pressure catheter (IUPC)
What are considered normal contractions?
5 contractions or less in 10 minutes averaged over 30 minutes
What are considered tachysystole contractions?
more than 5 contractions in 10 minutes averaged over 30 minutes
When do you use intermittent auscultation and palpation? What is the nurse ratio for this?
Assessment in low risk low - every 30 minutes and every 15 minutes
Requires 1:1
When is FHR assessed while using intermittent auscultation and palpation?
Before, during and after contraction
What are the benefits to using intermittent auscultation and palpation?
Non-invasive
Doesn’t hook mom up to a bunch of machines
Increases hands on patient care
What are the disadvantages to using intermittent auscultation and palpation?
No permanent record
Maternal size and position can inhibit ability to auscultate FHR and palpation of contraction
Difficult to assess uterine pressure quantitatively
Time intensive
When palpating contractions what 3 things should be assessed?
Duration: length of one contraction from beginning to end
Frequency: onset of one contraction to the onset of the next contraction
Intensity
What are 3 different intensities used for assessing palpations?
Mild - push on nose
Moderate - push on chin
Strong - push on forehead
What focus feels like
What does the red line mean? pink lines?
Red : 1 minutes
Pink: 10 seconds
What is uterine activity measured in?
Intensity - mmhm
What does the ultrasound transducer measure? Placement? Compare to?
Measures FHR by reflecting high frequency sound waves off the movement of the fetal heart valves
Placed over the area of max intensity on moms abdomen (fetal back)
Compare rate to maternal pulse
What type of gel should be used in ultrasound transducer?
Water soluble gel
What does the tocodynomometer measure? Placement? How does it work?
Frequency and duration of uterine contraction
DO NOT measure intensity so need to palpate
Placed on fondus
As uterus contacts –> button is pressed
What does the fetal spiral electrode (FSE) measure? Placement? What are the requirements?
Measures FHR by reading fetal ECG
Fine wire placed under skin of presenting part
Require ruptured membranes and cervical dilation at least 1-2cm
What are the benefits of FSE? Disadvantages?
More accurate picot of FHR and not affected by movement
Invasive and risk of infection
What does the intrauterine pressure catheter measure (IUPC)? Placement?
Measures pressure in uterus (mmhg)
Frequency and duration
Resting tone of uterus bt/n contractions (tension in uterus bt/n contraction)
Intensity of contraction
Placed in uterus alongside fetus to the fondus
What is the IUPC used for?
Evaluate effectiveness of contractions
Amniofusion - putting fluid back into uterus
What would you do a amniofusion?
If there is too little fluid –> cord compression so you want to do IV fluid to help cushion the cord
What are Montevideo units (MVUs)? What do they assess?
The total of the intensity of each contraction in a 10 minute period
Assess if contractions are adequate: over 200 means labor will likely process. Under 200 means labor might still or not progress properly
How do you calculate MVUs?
Add up each pressure of contraction in a 10 minute period
Make sure to subtract the baseline pressure from each contraction pressure before adding
What is FHR baseline?
Mean FHR in a 10 minute period
Rounded to nearest 5 bmp
Exclude accelerations nad decelerations
Must be
FHR usually ____ with gestational age
Decreases
Bradycardia is… Causes?
Less than 110 for at least 10 minutes
Caused by vagal nerve stimulation (baby drops down into the pelvis)
Drugs
Maternal hypotension (epidural)
fetal hypoxemia
Tachycardia is… Causes?
Over 160 for at least 10 minutes
Maternal: fever, dehydration, drugs/meds, infection, anemia
Fetal: infection, activity, compensation after acute hypoxemia, chronic hypoxemia, cardiac abnormalities, tachyarrythmia, anemia
What are non-reassuring FHR patterns?
Absent or minimal activity
Late or severe variable decelerations
What is the most important predictor of adequate fetal oxygenation? What does it reflect?
Baseline variability
Interplay between fetal sympathetics and parasympathetic NS
Well functioning NS if able to make changes
What is baseline variability?
Visible irregular fluctuations in FHR above and below the baseline FHR
Two or more cycles per minute
Assessed between any FHR changes
What are categories of variability?
Absent
Minimal
Moderate
Marked