INTRAPARTUM ASSESSMENT Ch. 14. INTRAPARTUM ASSESSMENT 부산백병원 산부인과 R1 손영실

# Intrapartum Fetal Assessment

INDEX 1. Internal Electronic Fetal Hearth Rate Monitoring 2. External (Indirect) Electronic Fetal Heart Rate 3. Fetal Heart Rate Pattern - Baseline Fetal Heart Activity

◎ Continuous graph paper of fetal heart rate - Potentially diagnostic in assessing pathophysiological events affecting the fetus ① Electronic fetal heart rate monitoring provided accurate information ② The information was of value in diagnosing fetal distress ③ It would be possible to intervene to prevent fetal death or morbidity ④ Continuous electronic fetal heart rate monitoring was superior to intermittent methods

FETAL HEART RATE MONITORING INTERNAL ELECTRONIC FETAL HEART RATE MONITORING ◎ Measured by attaching a bipolar spiral electrode directly to the fetus - the wire electrode penetrate the fetal scalp and the second pole is the metal wing on the electrode - vaginal body fluids create a saline electrical bridges that completes the circuits and permits measurement of the voltage differences between two poles ◎ The electrical fetal cardiac signal – P wave, QRS complex, and T wave – is amplified and fed into a cardiotachometer for heart rate calculation

FETAL HEART RATE MONITORING INTERNAL ELECTRONIC FETAL HEART RATE MONITORING ◎ Electrical cardiac complexes detected by electrodes include those generated by mother - maternal ECG signal is approximately five times stronger than fetal ECG - but, its amplitude is diminished when it is recorded through fetal scalp electrode ① In a live fetus - this low maternal ECG signal is detected but masked by the fetal ECG ② If the fetus is dead - the weaker maternal signal will be amplified by the automatic gain control circuitry in the fetal monitor and displayed as “fetal” heart rate

FETAL HEART RATE MONITORING INTERNAL ELECTRONIC FETAL HEART RATE MONITORING Standard fetal monitor tracing of heart rate using fetal scalp electrode shown at top. Bottom two tracings represent cardiac electrical complexes detected from fetal scalp and maternal chest wall electrodes. Spiking of the fetal rate in the monitor tracing is due to the premature atrial contractions. (F=fetus; M=mother; PAC=fetal premature atrial contraction.)

FETAL HEART RATE MONITORING INTERNAL ELECTRONIC FETAL HEART RATE MONITORING Placental abruption: The fetal scalp electrode detected heart rate first of the dying fetus. After fetal death, the maternal ECG complex is detected and recorded.

EXTERNAL (INDIRECT) ELECTRONIC FETAL HEART RATE MONITORING ◎ External detectors to monitor fetal heart and uterine action ⇒ the necessity for membrane rupture and uterine invasion may be avoided ◎ FHR (fetal heart rate) ⇒ detected through the maternal abdominal wall using the ultrasound Doppler principle

EXTERNAL (INDIRECT) ELECTRONIC FETAL HEART RATE MONITORING ◎ Consist of the unit ① transducer - emits ultrasound ② sensor - detect a shift in frequency of the reflected sound • transducer ⇒ placed on the maternal abdomen at a site where fetal heart action is best detected • coupling gel must be applied (∵ air conducts ultrasound poorly) • the device is held in position by a belt • care should be taken that maternal aortic ulsations are not confused with fetal cardiac motion

FETAL HEART RATE PATTERNS ◎ Scaling factors (by the workshop) - 30 bpm per vertical cm (range, 30 to 240 bpm) - 3 cm/min chart recorder paper speed # Baseline fetal heart activity 1) Rate • with increasing fetal maturation → the heart rate decreases • baseline FHR decreased an average of 24 bpm (between 16 weeks and term) approximately 1 bpm/week • 16 weeks : 160 bpm 40 weeks : 150 bpm

FETAL HEART RATE PATTERNS • during 3rd trimester, normal mean FHR is between 120 and 160 bpm baseline FHR less than 110 bpm ⇒ bradycardia baseline FHR greater than 160 bpm ⇒ tachycardia sympathetic system ⇒ accelerator influence parasympathetic system ⇒ decelerator factor mediated via vagal slowing of heart rate

FETAL HEART RATE PATTERNS A. Bradycardia • mild bradycardia : 100 ~ 119 bpm - observed in 2% of monitored pregnancies, averaged about 50 minutes in duration - attributed to head compression from occiput posterior or transverse positions, particularly during 2nd stage labor • moderate bradycardia : 80 ~ 100 bpm • severe bradycardia : less than 80 bpm

FETAL HEART RATE PATTERNS • other cause : congenital heart block and serious fetal compromise Fetal bradycardia measured with a scalp electrode in a pregnancy complicated by placental abruption and subsequent fetal death.

FETAL HEART RATE PATTERNS B. Tachycardia • mild : 161 ~ 180 bpm severe : 181 bpm or more • cause maternal fever from amnionitis (m/c) fetal compromise cardiac arrhythmias parasympathetic (atropine) or sympathomimetic (terbutaline) drugs • fetal compromise with tachycardia ⇒ concomitant heart rate deceleration (key point)

FETAL HEART RATE PATTERNS 2) Beat-to-beat variability • an important index of cardiovascular function • regulated largely by the autonomic nervous system A. Short-term variability • instantaneous change in FHR from one beat to the next • time interval between cardiac systoles

FETAL HEART RATE PATTERNS B. Long-term variability • the oscillatory changes that occur during the course of 1 minute - result in waviness of the baseline - normal frequency : 3 ~ 5 cycle/min

FETAL HEART RATE PATTERNS • physiological and pathological processes (affect or interfere with beat-to-beat variability) ① fetal breathing ② fetal body movements ③ advancing gestation - after 30 wks, fetal inactivity → diminished variability activity → variability increased

FETAL HEART RATE PATTERNS ④ maternal acidemia - cause decreased fetal beat-to-beat variability ⑤ analgesic drugs given during labor - diminished variability (narcotics, barbiturates, phenothiazines, tranquilizer) - MgSO4 : decrease variability only in the third hour of the infusion : be deemed clinically insignificant : blunted the frequency of acceleration

FETAL HEART RATE PATTERNS Grades of baseline fetal heart rate variability. (1) Undetectable, absent variability; (2) minimal≤5 bpm variability; (3) moderate (normal), 6 to 25 bpm variability; (4) marked,＞25 bpm variability; (5) sinusoidal pattern.

FETAL HEART RATE PATTERNS 3) Cardiac arrhythmia ◎ first suspected signs - baseline bradycardia - tachycardia - abrupt baseline spiking (m/c)

FETAL HEART RATE PATTERNS 4) Sinusoidal heart rates ◎ true sinusoidal pattern - observed with serious fetal anemia • from D-isoimmunization • ruptured vasa previa • fetomaternal hemorrhage • twin to twin transfusion ◎ insignificant sinusoidal pattern • administration of meperidine, morphine, alphaprodine, and butorphanol • amnionitis, fetal distress, and umbilical cord occlusion

FETAL HEART RATE PATTERNS ◎ definition ① stable baseline heart rate of 120 ~ 160 bpm with regular oscillations ② amplitude of 5 ~ 15 bpm (rarely greater) ③ frequency of 2 ~ 5 cycles/min long-term variability ④ fixed or flat short-term variability ⑤ oscillation of the sinusoidal waveform above or below a baseline ⑥ absence of accelerations

FETAL HEART RATE PATTERNS ◎ pathophysiology of sinusoidal patterns is unclear Sinusoidal fetal heart rate pattern associated with maternal intravenous meperidine administration. Sine waves are occurring at a rate of 6 cycles/min.

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