FHR Descriptors - 1) Baseline
2) Variability
3) Presence of accels
4) Presence of decels
5) Changes in trends overtime
FHR Baseline - Average FHR rounded to nearest 5 during a 10 min window
-110 to 160
-excludes accels, decels, & marked variability
-must have 2 mins to identify as a baseline (doesn't need to be continuous)
Fetal Bradycardia - <110 for ≥10 min
-Causes: hypotension (ex: after epi), cord prolapse, head compression, congenital defect, rapid
descent, abruption or rupture, tachysystole, post dates, hypoglycemia, lupus (heart block)
-With ↓ O2, blood will be shunted to brain, heart, & adrenals, eventually ↓ FHR to ↓ O2
demands of heart muscle
-Verify not mom's HR, vaginal exam (r/o prolapse), resuscitate, evaluate arrhythmia, expedite
delivery
FHR Variability - Irregular in amplitude & frequency, quantified by peak to trough
-Caused by sympathetic vs parasympathetic, r/t neuro maturity
, -Less in preterm due to undeveloped CNS
-Absent: undetectable, flat
-Minimal: ≤5 bpm but detectable
-Moderate: 6-25 bpm
-Marked: >25 bpm (indeterminate baseline), significance unknown
Minimal variability - ≤5 bpm but detectable
Sleep, sedated, or sick
-Sleep cycle: 20-60 mins
-Sedated: CNS depressant (ex: mag), 1-2 hrs
-Sick (acidemia): unresolved w intervention
-Priority: maximize oxygenation (position, bolus, O2 if needed)
Moderate variability - 6 to 25 bpm
-Reliably predicts the absence of metabolic acidosis (even w decels)
FHR Accelerations - Reliably predicts absence of metabolic acidemia (spontaneous or
stimulated)
-Onset to peak in <30 sec
-For ≥32 wks: 15x15 (peak ≥15 bpm above baseline lasting ≥15 sec)
-For <32 wks: 10x10
-Prolonged accel: 2-9 mins (at 10 becomes change of baseline)
Early deceleration - Nadir aligns w contraction peak, gradual onset (≥30 secs to nadir), benign
vagal response
1) Pressure on fetal head
2) Increased intracranial pressure
3) Alteration in cerebral blood flow
4) Central vagal stimulation
5) FHR deceleration
Periodic vs Episodic - Periodic: caused by contractions
-recurrent: occurs w ≥50% of contractions in 20 min
-intermittent: w <50% of contractions in 20 mins
Episodic: spontaneous
Variable deceleration - Caused by cord compression
-Interventions: position change, amnioinfusion
-Abrupt onset: <30 seconds from onset to nadir dropping ≥15 bpm lasting 15 secs to <2min
-Transient rise in PCO2 & fall in PO2
Mechanisms of variable decelerations - Abruptness r/t pressure changes
1) Vein obstruction → reflex tachy
-↓ venous return & cardiac output → hypotens → baroreceptor reflex ↑ in FHR to maintain BP
2) Arterial obstruction → decreased FHR
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