Introduction to Fetal Heart Rate Analysis Study Notes

Umbilical and Fetal Circulation Characteristics

Umbilical Cord Structure
- The cord is anatomically structured as AVA: 2 Arteries and 1 Vein.
- Wharton’s Jelly: This is a gelatinous substance that surrounds and protects the blood vessels within the umbilical cord.
- Umbilical Vein: Carries OXYGENATED blood and nutrients from the placenta to the fetus.
- Umbilical Arteries: Carry DEOXYGENATED blood, carbon dioxide, and waste products away from the fetus back to the placenta.
Fetal Circulation Dynamics
- There is NO MIXING of maternal and fetal blood.
- All exchange for gases, nutrients, and waste occurs via diffusion within the intervillous space of the placenta.
- Path: Blood flows from the placenta, through the cord to the fetus, and returns to the placenta.
Fetal Circulatory Shunts
- Ductus venosus: Connects the umbilical vein directly to the inferior vena cava.
- Ductus arteriosus: Anatomic shunt connecting the main pulmonary artery to the aorta.
- Foramen ovale: An anatomic opening located between the right and left atrium of the fetal heart.

Fetal Heart Rate (FHR) Assessment Methods

Purpose: Fetal monitoring serves as a clinical picture of the oxygenation status of the fetus.
Intermittent Monitoring Tools
- Fetoscope: Traditional tool; less commonly used in modern practice.
- Doppler: Used intermittently to find Fetal Heart Tones (FHT).
- Limitation: Intermittent tools provide FHT but do not provide a comprehensive picture of the oxygenation status.
Continuous Electronic Fetal Monitoring (EFM)
- External: Uses an ultrasound transducer.
- Internal: Uses a fetal scalp electrode.
- Capability: Provides a continuous graphic record and a clear picture of fetal oxygenation status.
- Objectives:
  - Provide data on fetal oxygenation.
  - Prevent fetal injury resulting from impaired oxygenation.
  - Detect FHR changes early, before they become prolonged or profound.

External and Internal Monitoring Techniques

External Technique (Non-invasive)
- Tocodynamometer ("Toco"): Placed over the uterine fundus to monitor uterine contractions (UC).
- Ultrasound Device (US): Placed over the area of the fetal back to transmit FHR data.
- Placement Guide: Use Leopold's maneuvers to determine fetal position and optimize monitor placement.
  - Cephalic position: FHR is heard best in lower quadrants below the umbilicus.
  - Breech position: FHR is heard best in upper quadrants above the umbilicus.
Internal Technique (Invasive)
- Criteria for Use:
  - Skilled practitioner must be available for insertion.
  - Fetal presenting part must be low enough for electrode placement.
  - Cervix must be dilated at least $2\,cm$ .
  - Membranes must be ruptured.
- Fetal Scalp Electrode (FSE): A small coiled clip twisted into the infant's scalp.
  - Provides a definitive FHR reading.
  - Warning: Should NEVER be placed into a fontanel.
- Intrauterine Pressure Catheter (IUPC): Inserted into the uterus to report actual pressure (intensity) of contractions.

Interpreting the Fetal Monitor Strip Grid

Vertical Scale (Upper Grid): Measures FHR in beats per minute (bpm). Range typically shows $30$ to $240\,bpm$ .
Vertical Scale (Lower Grid): Measures uterine activity in millimeters of mercury ( $mmHg$ ). Range typically shows $0$ to $100\,mmHg$ .
Horizontal Scale (Time):
- One small rectangle = $10\,seconds$ .
- One large block (marked by dark vertical lines) = $1\,minute$ .

Fetal Heart Rate Patterns: Baseline and Variability

FHR Baseline: The average FHR over a period of time.
- Normal Baseline: $110-160\,bpm$ .
- Tachycardia: Baseline > 160\,bpm.
- Bradycardia: Baseline < 110\,bpm.
Variability: Irregular fluctuations in the FHR amplitude.
- Pathophysiology: Indicates an intact brainstem with the Sympathetic Nervous System (SNS) and Parasympathetic Nervous System (PNS) working together.
  - SNS: "Fight or Flight" — speeds up the heart rate.
  - PNS: "Rest and Digest" — slows down the heart rate.
- Variability Categories:
  - Absent: Undetectable amplitude.
  - Minimal: Amplitude range < 5\,bpm.
  - Moderate: Amplitude range $6-25\,bpm$ (This is the clinical goal/reassuring sign).
  - Marked: Amplitude range > 25\,bpm.
Sinusoidal FHR Pattern:
- Characterized by a smooth, regular, wave-like pattern.
- Clinical Significance: Indicates severe fetal anemia or fetal cardiac anomalies; the baby is compromised and requires immediate intervention.

Periodic and Episodic FHR Changes

Definitions:
- Periodic: Changes associated with a uterine contraction.
- Episodic: Changes NOT associated with a uterine contraction.
Accelerations (Accels):
- Defined as an increase in FHR of at least $15\,bpm$ above baseline lasting for at least $15\,seconds$ ( $15 \times 15$ rule).
- Duration must be < 2\,minutes.
- Significance: Usually reassuring; indicates adequate oxygenation.
Decelerations (Decels):
- Early Decelerations:
  - Cause: Fetal head compression.
  - Description: Mirror image of the contraction. The decel starts when the contraction starts; returns to baseline when the contraction ends.
  - Nadir: The lowest point of the deceleration aligns with the peak of the contraction.
- Late Decelerations:
  - Cause: Placental insufficiency (decreased blood flow or oxygen from the placenta).
  - Description: The onset of the deceleration occurs AFTER the peak of the contraction.
- Variable Decelerations:
  - Cause: Umbilical cord compression.
  - Description: Abrupt onset (< 30\,seconds). The drop is at least $15\,bpm$ below baseline for at least $15\,seconds$ but < 2\,minutes.
  - Shape: Often shaped like "Vs" or "Ws."
  - Mechanics: Compression of the vein happens first (initial FHR increase), followed by compression of the arteries (FHR drop), then a rebound as arteries open back up.
- Prolonged Deceleration:
  - A deviation below baseline of at least $15\,bpm$ lasting for at least $2\,minutes$ but less than $10\,minutes$ .

VEAL CHOP Mnemonic

Variable — Cord Compression
Early — Head Compression
Accelerations — Okay (Oxygenated)
Late — Placental Insufficiency

Uterine Contraction Interpretation

Frequency: Measured from the beginning of one contraction to the beginning of the next (reported in minutes, e.g., $2-3\,minutes$ apart).
Duration: Measured from the beginning of a contraction to the end of the same contraction (reported in seconds, e.g., $70-90\,seconds$ ).
Intensity:
- Palpation: Qualitative assessment (mild, moderate, strong).
- IUPC: Quantitative assessment of actual pressure in $mmHg$ .
Resting Tone: The period between contractions when the uterus relaxes; should feel soft upon palpation.
Tachysystole: Defined as > 5 contractions in a $10\,minute$ period, averaged over $30\,minutes$ .
- Interventions for Tachysystole:
  1. Decrease or D/C Oxytocin (Pitocin).
  2. Administer fluid bolus.
  3. Turn patient on their side.
  4. Notify provider if unresolved.
  5. Consider tocolytics if FHR is unreassuring.

Nonstress Test (NST)

Objective: Conducted to ensure fetal well-being.
Duration: At least $20\,minutes$ .
Reactive Criteria by Gestational Age:
- $28/0$ to $31/6$ weeks: $2$ accelerations of at least $10\,bpm$ lasting for at least $10\,seconds$ .
- $32$ weeks and above: $2$ accelerations of at least $15\,bpm$ lasting for at least $15\,seconds$ .
Note: Cannot be performed before $28$ weeks because the PNS is not yet fully developed.

Intrauterine Resuscitation

Goals: Maximize oxygenation and uterine blood flow.
Specific Interventions:
- Position Change: Preferably to the left side; avoid the supine position entirely.
- IV Bolus: At least $500\,mL$ (caution with pre-eclamptic patients).
- Induction Agent Cessation: Turn off Pitocin, hold Cytotec, or pull Cervidil.
- Modified Pushing: Stop pushing in lithotomy; reduce pushing frequency.
- Oxygen: $10\,L/min$ via non-rebreather mask.
Priority Order of Action:
1. Step 1: Turn patient on their side (FIRST ACTION).
2. Step 2: Administer IV fluid bolus.
3. Step 3: Turn off Pitocin/Induction agents.
4. Step 4: Administer Oxygen.

Umbilical Cord Blood Gas Analysis

Normal pH: $\geq 7.2$ .
Purpose: Low cord pH (fetal acidosis) identifies intrapartum hypoxia and is linked to neonatal morbidity/mortality and cerebral palsy.
Arterial Gas: Shows how the fetus tolerated labor (final endpoint of oxygenation). Low pH/High $CO_2$ indicates distress before delivery.
Venous Gas: From placenta TO fetus. Easier to obtain. Used as a comparison to ensure the arterial sample is accurate.

Clinical Categorization of EFM Tracings

Category I (Normal/Reassuring):
- Baseline $110-160\,bpm$ .
- Moderate variability.
- Accelerations may/may not be present.
- Early decelerations may be present.
- No late or variable decelerations.
Category II (Indeterminate).
Category III (Abnormal/Nonreassuring):
- Recurrent late or variable decelerations.
- Minimal or absent variability.
- Prolonged deceleration (> 2\,minutes).
- Bradycardia (< 110\,bpm).

Questions & Discussion

Q: A laboring patient suddenly develops recurrent late decelerations on the fetal monitor after receiving oxytocin. Which nursing intervention is the priority to improve fetal oxygenation?
- A: Reposition the patient to a lateral position. (Priority action is always position change first).
Q: A nurse is reviewing a fetal heart rate tracing for a laboring patient. The baseline fetal heart rate is $140\,bpm$ with absent variability noted for $20\,minutes$ . Which interpretation by the nurse is most appropriate?
- A: Absent variability may indicate fetal hypoxia or acidosis. (Moderate variability is necessary to predict the absence of acidemia).
Q: A laboring patient’s fetal monitor tracing shows a baseline fetal heart rate of $135\,bpm$ with moderate variability and occasional accelerations. Which action should the nurse take?
- A: Continue routine monitoring and supportive care. (These findings are indicative of a Category I, reassuring strip).