Fetal Monitoring: Assessing Uterine Activity and Fetal Heart Rate

General Announcements and Logistics

• Clinical Lab (This Week):

  • Location: Skills lab.

  • Reference: Handbook page 6 for activities.

  • Populations: Labor and delivery patients, and newborns immediately after delivery (building on previous couplet care on postpartum).

  • Resources: Various videos linked in the course document for clinical understanding of labor process, pain management, etc.

• Exam Review:

  • Exam grades have been posted.

  • Full exam review cannot happen this week as one student still needs to take the exam.

  • Next Monday (afternoon class at $12:30$ PM):

    • Exams will be available for review after the lecture.

    • Students can stay, put away belongings, and receive their exam and ZIP grade form (marked with correct answers) for review.

  • Office Hours:

    • Professor's Availability: Spartan Network (Mondays/Wednesdays $2-4$ PM, Tuesdays $11-12$ PM).

    • Alternative: Email specific dates and times if scheduled hours don't fit.

• Recording Issues: Attempting to record lectures; microphone communication issues. Will stay stationary to improve audio quality. Video will be captioned and posted to the course if audio is problematic.

Introduction to Fetal Monitoring

• Purpose: Fetal monitoring is a visual representation of what is happening in utero, picking up uterine activity and fetal heart rate.

• Goal: Historically intended to prevent all negative outcomes, but challenges exist.

• Equipment:

  • Classic fetal monitor: Blood pressure cuff, external devices (transducers) wrapped around mom with Velcro belts.

  • Skills Lab: Hands-on experience with equipment this week.

• Data Archiving: Formerly printed out on paper, now mostly archived digitally in computers/hard drives.

• Terminology: FHT (fetal heart tone) or FHR (fetal heart rate).

• Oxygenation: Fetus receives oxygen from the mother. Maternal oxygenation (influenced by position, systemic oxygen) is crucial for transfer through the placenta and umbilical cord.

  • Fetal Red Blood Cells: Primed to pick up oxygen and release carbon dioxide efficiently.

  • Problem Response: FHR tracing issues often lead to interventions to improve maternal oxygenation, hoping for better transfer to the fetus.

Uterine Activity

• Uterus: Smooth muscle; contractions start at the fundus and wave downwards.

• Causes of Contractions (Beyond Labor):

  • Dehydration: Common, especially in active environments (e.g., amusement parks). Dehydrated muscles (like runner's legs cramping) can contract.

  • Bleeding: Blood acts as an irritant against muscle, causing contractions.

  • Infection: Can also cause uterine contractions.

• Triage Aspect: Experienced nurses are essential in labor and delivery triage to identify the reason for contractions.

• External Monitoring (Tocodynamometer - Toco transducer):

  • Mechanism: Pressure button flat against mom's abdomen, picks up changes in uterine muscle tone.

  • Challenges:

    • Maternal movement can interfere.

    • Maternal size: Very thin moms can show exaggerated responses due to less subcutaneous tissue. Moms with significant subcutaneous tissue may show minimal response, making accurate tone changes difficult to pick up.

• Internal Monitoring (Requires Amniotic Sac Rupture):

  • Fetal Scalp Electrode (FSE): Directly attached to the lowest part of the baby (ideally head) with a coil. Picks up every single fetal heartbeat, similar to EKG pads.

  • Intrauterine Pressure Catheter (IUPC): Tip senses and reads intrauterine pressure in millimeters of mercury ($mmHg$), transmitting information about tension changes (tone).

Assessing Contractions

• Documentation Parameters:

  • Frequency: Start of one contraction to the start of the next one. Measured in minutes (e.g., contractions every $2$ minutes).

  • Duration: How long each contraction lasts, from the beginning of the ascent to the end of the descent. Measured in seconds.

  • Intensity/Force: How strong the contraction is.

• Paper Tracing: Bottom part records contraction activity, top part records FHR activity.

  • Time Scale: Each small box horizontally represents $10$ seconds. Darker lines typically mark minute intervals (six boxes).

• Intensity Measurement:

  • External Monitoring (Palpation): Cannot trust mountain height on external tracing due to maternal girth.

    • Nurses use palpation of the fundus at the peak of contraction.

    • Face Analogy:

      • Mild: Feels like palpating your nose (easily indentable, firm but soft).

      • Moderate: Feels like your chin (firmer).

      • Strong: Feels like your forehead (very firm, unable to indent).

    • Palpation is correlated with research to represent mild, moderate, or strong contractions.

  • Internal Monitoring (IUPC & Montevideo Units): Can trust mountain height.

    • Montevideo Units (MBUs): Only applicable with IUPC in place.

    • Calculation: For each contraction in a $10$-minute tracing, subtract the resting tone ($mmHg$) from the peak pressure ($mmHg$). Sum these differences for all contractions in that $10$-minute period.

    • Significance: $ext{200 or more MBUs}$ in $10$ minutes are expected to create enough force for labor progress.

    • Example: Peak $70 mmHg$, Rest $20 mmHg$ $= 50$ units per contraction. If three such contractions in $10$ minutes $= 150$ MBUs (not yet at $200$).

• Tachysystole (Formerly Hyperstimulation): Undesirable contraction pattern.

  • Definition: Too many or too forceful/overwhelming contractions.

  • Criteria:

    1. $ext{6 or more contractions in 10 minutes}$ (less than every $2$ minutes).

    2. Tetanic contraction: A single contraction lasting $ext{2 minutes or more}$.

    3. Contractions occurring so frequently there's little rest in between.

  • Risks: Compromises fetal oxygenation (umbilical cord compression reduces blood flow), exhausts uterine muscle (risk of postpartum hemorrhage).

Fetal Heart Rate (FHR) Monitoring

• Systematic Approach: Baseline, Variability, Changes.

• Baseline FHR: The average heart rate over a $10$-minute period, excluding accelerations, decelerations, or marked variability.

  • Normal Range: $110$ to $160$ beats per minute (BPM).

  • Measurement: Boxes going upward are $10$ BPM increments. Record FHR in increments of zero or five (e.g., $135$ BPM, not $137$).

  • Tachycardia (FHR > 160 BPM for $ ext{ extgreater}10$ min):

    • Causes: Prematurity (sympathetic nervous system matures first), maternal fever/infection, maternal smoking/drug use.

    • Concern: Indicates a potentially unfavorable or unsafe environment for fetal oxygenation.

  • Bradycardia (FHR < 110 BPM for $ ext{ extgreater}10$ min):

    • Causes: Certain drugs, fetal distress.

    • Unique Case: Fetal heart block (electrical conduction issue), where the fetus may tolerate the lower baseline.

• Variability: The beat-to-beat fluctuation in the FHR. Primary indicator of fetal oxygenation. The 'squiggliness' of the line.

  • Absent Variability: Straight line, virtually no fluctuation (<5 BPM variation). Not good; sounds monotone.

  • Minimal Variability: Slight fluctuation, about half a box (<5 BPM variation, e.g., $120, 123, 121, 124$).

    • Causes: Fetal sleep cycle, maternal narcotic administration.

    • Hope: Fetus eventually comes out of minimal variability.

  • Moderate Variability: Gold standard for fetal well-being and oxygenation. Shows $6-25$ BPM variation (e.g., $120, 130, 125$). This is what we want to see.

  • Marked Variability: Excessive fluctuation (>25 BPM variation). Not a great indication, too much fluctuation.

• Changes (Accelerations and Decelerations): Yes/No presence.

  • Accelerations: FHR increases from baseline. Second good indicator of fetal well-being and tolerating labor. Brain sending a message to the heart.

    • Criteria ($ ext{ extgreater}32$ weeks gestation): Increase of at least $15$ BPM above baseline, lasting at least $15$ seconds ($15 imes 15$ rule).

    • Criteria ($ ext{ extless}32$ weeks gestation): Increase of at least $10$ BPM above baseline, lasting at least $10$ seconds ($10 imes 10$ rule).

    • Documentation: Absent or Present.

  • Decelerations: FHR decreases from baseline. Three big culprits:

    1. Head Compression: Stimulates vagal nerve, dropping FHR.

    2. Umbilical Cord Compression: Reduces blood flow.

    3. Uteroplacental Insufficiency: Placenta not effectively transferring oxygen.

• Types of Decelerations:

  • Early Decelerations:

    • Cause: Head compression.

    • Pattern: Mirror the contraction. The lowest point (nadir) of the deceleration occurs at the peak of the contraction. The FHR drop begins and ends with the contraction.

    • Significance: Can indicate progress in labor, potentially close to delivery.

  • Late Decelerations:

    • Cause: Uteroplacental insufficiency (placenta not doing enough to transport oxygen).

    • Pattern: Delayed in onset and recovery relative to the contraction. The FHR drop begins after the contraction has peaked, and the nadir occurs after the contraction's peak.

    • Mechanism: Fetus experiences oxygen deprivation most severely at the peak of the contraction when umbilical flow is reduced and body reserves are low; recovers after contraction subsides.

  • Variable Decelerations:

    • Cause: Umbilical cord compression.

    • Pattern: Abrupt (sharp) drop in FHR. Can be U-shaped, V-shaped, or W-shaped. Can occur at any point relative to a contraction.

    • Mechanism: Intermittent compression and release of the umbilical cord affecting blood flow.

  • Prolonged Decelerations:

    • Cause: Can start as another type but lasts for an extended period.

    • Significance: Requires immediate intervention to restore fetal oxygenation status.

• VEAL CHOP Mnemonic (for understanding FHR patterns):

  • Variable Deceleration Cord Compression

  • Early Deceleration Head Compression

  • Acceleration OK (or Oxygenated Well)

  • Late Deceleration Placental Insufficiency

Next Steps

• Review material before Wednesday's lecture.

• Wednesday's lecture will start with dissecting a tracing. The week's clinical group work will also involve looking at tracings.