Advanced Fetal Monitoring Flashcards

Fetal Monitoring Key Concepts

Cat 1 category rules out fetal acidemia.
Maternal conditions like severe asthma, cardiac issues, and eclampsia significantly impact fetal oxygenation.
The intervillous space is the site for maternal-fetal exchange of O2 and nutrients.
Oxygen is transferred to the fetus via maternal arteries to the intervillous space, through villi, into the umbilical vein, then to the fetus. Deoxygenated blood is returned through umbilical arteries.
Diffusion occurs where O2 moves from high to low concentration (mother to fetus) and CO2 moves from low to high concentration (fetus to mother).
Spiral arteries in the placenta carry O2 into the intervillous space and are maximally dilated, limiting further expansion.
Factors that decrease uteroplacental blood flow include maternal conditions (e.g., pre-eclampsia, cardiac disease), hypotension, placental changes (abruptions, infections, edema, size), excessive uterine activity, and vasoconstriction.
Spiral arteries constrict during pre-eclampsia, reducing blood flow.
Supine position after 20 weeks compresses the aorta and vena cava, resulting in decreased uteroplacental blood flow.
Maternal hypotension after regional analgesia occurs due to sympathetic pathway blockage, leading to blood pooling and reduced flow back to the heart.
Uteroplacental blood flow decreases by 60% during contractions.
Pathway for maternal-fetal exchange begins at the environment, moving through lungs, heart, vasculature, uterus, placenta, and umbilical cord.
The fetus has the least O2 blood in limbs, kidneys, and descending aorta, with most O2 in the umbilical vein and ductus venosus.

Fetal Circulation and Physiological Responses

Ductus venosus connects the umbilical vein to the inferior vena cava, bypassing the liver and directing O2 blood to the fetal heart.
Three crucial shunts in fetal circulation are the ductus venosus, foramen ovale (connecting both atria), and ductus arteriosus (bypassing pulmonary circulation).
Fetal heart circulation can lead to increased heart rate due to sympathetic nervous system stimulation.
Parasympathetic nervous system regulates heart rate; acetylcholine release decreases intrinsic heart rate.
Bradycardia and reduced variability may indicate fetal distress or underlying problems such as hypoxia or acidemia.
Fetal Hct levels range from 51-56% at term.
Increased heart rate in response to sympathetic stimulation indicates the activation of the fight-or-flight response.

Variability and Deceleration Patterns

Decreased FHR variability can be a sign of conditions like fetal sleep cycles, acidemia, and certain medications (e.g., opioids).
Normal fetal movement count should be at least 10 distinct movements within two hours.
Reactive NST for gestations greater than 32 weeks shows accelerations peaking over 15 bpm for longer than 15 seconds, while less than 32 weeks shows accelerations over 10 bpm for longer than 10 seconds.
Late decelerations arise from uteroplacental insufficiency, while early decelerations indicate fetal head compression effects.
Conditions leading to prolonged decels include umbilical cord compression, maternal hypotension, and uterine rupture.
Sinusoidal patterns in FHR may suggest severe fetal conditions, such as anemia or metabolic acidemia.

Intervention and Risk Management

Contraindications for terbutaline include any type of bleeding.
For low-risk patients, heart tones should be charted every 30 minutes from the latent phase to the second stage. High-risk patients require monitoring every 15 minutes.
Exogenous oxytocin rates are set at approximately 2-4 mu for mothers and 3 mu for fetuses during the first stage of labor.
Significant acidemia can occur within 60-90 minutes when oxygen depletion is present.
Interventions during the second stage of labor aim to maintain fetal physiological reserve and oxygenation.

Miscellaneous

Increased caffeine intake can lead to irregular fetal rhythms, while hypoxemia may reduce amniotic fluid index (AFI).
Fetal heart block can occur from maternal conditions like lupus, with complete heart block requiring pacemaker implantation as treatment options.
Mixed acidemia reflects a partial oxygen deficit, leading to a combination of respiratory and metabolic responses.