PB#106: Intrapartum Fetal Heart Rate Monitoring: Nomenclature, Interpretation, and General Management Principles Flashcards
Percentage of term pregnancies w/ fetal asphyxia w/o any known risk factors
63%
General principle behind FHR for monitoring fetal oxygenation
Fetal brain modulates FHR through sympathetic and parasympathetic factors
Limitations of EFM (3)
Poor interobserver and intraobserver reliability, uncertain efficacy, high false-positive rate
Calculation of ctxs when analyzing FHT
Number present in 10 min window averaged over 30 min period
Definition of normal contractility
5 or fewer ctxs in 10 mins averaged over 30 min period
Definition of tachysystole
> 5 ctxs in 10 mins averaged over 30 min period
How should tachysystole always be qualified?
In the presence/absence of decels
Does tachysystole apply to spontaneous labor or induced/augmented labor?
Both
When are decels considered recurrent?
If they occur w/ >50% of ctxs
Definition of FHR baseline
Mean FHR rounded to increments of 5 bpm over 10 min segment, excluding periodic/episodic changes, periods of marked variability, and/or segments of baseline that differ by >25 bpm
Minimum time requirement for FHT to be considered a baseline
2 mins in any 10 min segment, or else baseline for that period is indeterminate (in which case one may refer to prior 10 min window for determining baseline)
Normal baseline
110-160 bpm
Fetal tachycardia
> 160 bpm
Fetal bradycardia
<110 bpm
Definition of FHR variability
Fluctuations in baseline FHR that are irregular in amplitude and frequency, visually quantitated as amplitude of peak-to-trough in bpm
Absent variability
Undetectable amplitude range
Minimal variability
Amplitude range detectable but <5 bpm
Moderate variability
Amplitude range 6-25 bpm
Marked variability
Amplitude range >25 bpm
Definition of accels
Visually apparent abrupt increase (onset to peak <30 secs) in FHR
Criteria for accels at 32+wga; criteria for accels at <32wga
Peak >15 bpm above baseline, w/ duration of >15 secs but <2 mins from onset to return; peak >10 bpm above baseline, w/ duration of >10 secs but <2 mins from onset to return
Definition of prolonged accel
Lasting >2 mins but <10 mins in duration
What is it considered if an accel lasts >10 mins?
Baseline change
Definition of early decels
Visually apparent usually symmetrical gradual decrease and return of FHR associated w/ ctx, wherein onset to nadir is >30 secs, and nadir of decel occurs at same time as ctx peak
Timing of onset/nadir/recovery of early decel as it relates to ctx (in most cases)
Coincident w/ beginning/peak/ending of ctx, respectively
Definition of late decels
Visually apparent usually symmetrical gradual decrease and return of FHR associated w/ ctx, wherein onset to nadir is >30 secs, and nadir of decel occurring after peak of ctx
Timing of onset/nadir/recovery of late decel as it relates to ctx (in most cases)
Occur after beginning/peak/ending of ctx, respectively
Definition of variable decels
Visually apparent abrupt decrease in FHR, wherein onset to nadir is <30 secs, decrease is >15 bpm, and lasts >15 secs but <2 mins in duration
Are onset/depth/duration of variable decels consistent across ctxs?
No, they commonly vary w/ successive ctxs
How is decrease in FHR calculated when evaluating decels?
From onset to nadir
Definition of prolonged decels
Visually apparent decrease in FHR, wherein decrease is >15 bpm, and lasts >2 mins but <10 mins in duration
What is it considered if a decel lasts >10 mins?
Baseline change
Definition of sinusoidal pattern
Visually apparent, smooth, sine wave-like undulating pattern in FHR baseline w/ cycle frequency of 3-5 per min, which persists for >20 mins
Info that FHTs can provide on acid-base status of fetus
ONLY current acid-base status
General classification, acid-base status prediction, and recommended monitoring for Cat 1 FHTs
Normal, strongly predictive of normal fetal acid-base status at time of obs, can be monitored in routine manner (no specific action required)
Criteria for Cat 1 FHTs
Include all of the following: normal baseline, mod variability, absent late/variable decels, present/absent early decels, present/absent accels
General classification, recommended monitoring, potential considerations for Cat 2 FHTs
Indeterminate, require evaluation and continued surveillance/reevaluation, may require ancillary testing of fetal wellbeing and/or intrauterine resuscitative measures
Acid-base status prediction of Cat 2 FHTs
Not predictive of abnormal fetal acid-base status, but not enough evidence to classify as Cat 1 or Cat 3
Criteria for Cat 2 FHTs
Brady not accompanied by absent variability; tachy; min variability; absent variability w/o recurrent decels; marked variability; absence of induced accels after fetal stim; recurrent variable decels accompanied by min/mod variability; prolonged decel; recurrent late decels w/ mod variability; variable decels w/ other characteristics (ie slow return to baseline, overshoots, “shoulders”)
General classification, acid-base status prediction, and recommended monitoring for Cat 3 FHTs
Abnormal, associated w/ abnormal fetal acid-base status at time of obs, require prompt evaluation
Possible measures to provide expeditious resolution of Cat 3 FHTs (5)
Provision of maternal O2 (if indicated), position change, discontinuation of induction/augmentation measures, management of maternal hypotension, tx of tachysystole w/ FHT changes
Next step if Cat 3 FHT does not resolve w/ resuscitation measures
Delivery
Criteria for Cat 3 FHTs
Include either: absent variability + recurrent late decels/recurrent variable decels/brady, or sinusoidal pattern
How often should FHT be reviewed in a pt w/o complications in first stage of labor, in second stage of labor?
q30mins, q15mins
How often should FHT be reviewed in a pt w/ complications (ie FGR, pre-E) in first stage of labor, in second stage of labor?
q15mins, q5mins
How is efficacy of intrapartum EFM judged?
By ability to decrease complications (ie neonatal seizures, CP, intrapartum demise) while minimizing need for unnecessary OB interventions (ie OVD, C/S)
Effect of EFM on overall C/S rate (and RR); effect of EFM on C/S rate for abnormal FHT and/or acidosis (and RR), compared to intermittent auscultation
Increased overall C/S rate (RR = 1.66); increased C/S rate for abnormal FHT and/or acidosis (RR = 2.37)
Effect of EFM on OVD (and RR)
Increased risk for both vacuum and forceps OVD (RR = 1.16)
Effect of EFM on perinatal mortality (and RR w/ 95% CI)
No reduction (RR = 0.85, 95% CI = 0.59-1.23)
Effect of EFM on neonatal seizures (and RR)
Reduced risk (RR = 0.50)
Effect of EFM on CP (and RR w/ 95% CI)
No reduction (RR = 1.74, 95% CI = 0.97-3.11)
PPV of NRFHT pattern to predict CP among singleton newborns w/ birth weights >2500g
0.14% (meaning out of 1,000 fetuses w/ NRFHT pattern, 1-2 will develop CP)
False positive rate of EFM for predicting CP
> 99%
Principal explanation for why prevalence of CP has not diminished despite use of EFM
Because 70% of cases occur before labor onset
Percentage of cases of encephalopathy that can be attributed solely to intrapartum events
4%
Rec for cEFM or intermittent auscultation in pt w/o complications
Either is acceptable
Rec for cEFM or intermittent auscultation in pt w/ complications (ie FGR, pre-E, DM1)
cEFM
Guideline recs regarding frequency of intermittent auscultation during active phase of first stage of labor, during second stage of labor
q15mins, q5mins
In interpretation of FHTs, is interobserver variability high or low; is intraobserver variability high or low?
High; high
Under what circumstances is FHT interpretation more consistent?
When tracing is normal
When is a reviewer more likely to find evidence of fetal hypoxia (and criticize management) while reviewing an intrapartum FHT?
If outcome was poor (vs good)
Is reinterpretation of FHT (especially if neonatal outcome is known) reliable?
No
Rec for cEFM or intermittent auscultation for pt undergoing C/S for indications related to preterm fetus
cEFM
Percentage of pts w/ PTL that exhibit NRFHTs; most common FHT abnormalities in pts w/ PTL
60%; decels and brady, followed by tachy and min/absent variability
Are variable decels more common among preterm or term deliveries?
Preterm (55-70% vs 20-30%)
Measures if FHT abnormalities are persistent in setting of preterm fetus (3)
Resuscitative measures, ancillary tests of fetal well-being, poss delivery
Poss effects of epidural analgesia w/ local anesthetic agents (ie lidocaine, bupivacaine) on maternal/fetal physiology (4)
Sympathetic blockade, maternal hypotension, transient uteroplacental insufficiency, alterations to FHR
Effects of parenteral narcotics w/ or w/o added antiemetics on FHT (2)
Decreased variability, decreased frequency of accels
Equivalent of meperidine, morphine, fentanyl, nalbuphine
75mg meperidine = 10mg morphine = 0.1mg fentanyl = 10mg nalbuphine
Effects of IV meperidine, compared to epidural anesthesia w/ 0.25% bupivacaine, on FHT (2)
Decreased variability, and significantly less common accels w/ IV meperidine
Is rate of brady, emergent C/S for NRFHTs, and adverse neonatal outcomes higher for pts w/ combined spinal-epidural anesthesia or w/ IV meperidine?
Rate of brady and emergent C/S for NRFHTs is significantly higher for pts w/ combined spinal-epidural anesthesia; not significantly different neonatal outcomes between two both groups
Effects of mag sulfate on FHT (2)
Decreased short-term variability (related to early gestational age, not serum mag level), inhibition of accels w/ advancing gestational age
Poss effect of butorphanol on FHT in pts in labor (2); associated neonatal outcomes
Transient sinusoidal pattern (in 75% of pts), slightly increased FHR (compared to meperidine); not associated w/ adverse outcomes
Poss effects of cocaine exposure on FHT (2)
Decreased long-term variability, frequent ctxs (even when labor unstimulated)
Effects of morphine on fetal BPP and on FHT in antepartum pts
Decreased fetal breathing movements, decreased number of accels
Effects of BTMZ on FHT (2); duration until return of FHT to pre-tx status; effect on OB interventions/adverse outcomes
Transient decrease in variability, decrease in rate of accels (and diurnal fetal rhythms); 4-7 days; no effect
Effects of terb on FHT (2)
Increased FHR baseline, increased incidence of fetal tachy
Effects of zidovudine on FHT
No effects
What does presence of accels indicate?
Fetus is not acidemic
Predicted umbilical artery pH if mod variability is observed
Strongly associated w/ pH >7.15
Predicted umbilical artery pH if late/variable decels are observed in setting of mod variability
> 7.00 in 97% of cases
Prediction of mod variability re fetal status and acidemia
Reassuring fetal status, absence of metabolic acidemia
Techniques to elicit accel if EFM has min/absent variability w/o spontaneous accels (4); methods that are preferred (2)
Fetal scalp sampling, Allis clamp scalp stim, vibroacoustic stim, digital scalp stim; less invasive methods (vibroacoustic stim, digital scalp stim) preferred
Between scalp stim and scalp pH sampling, method that provides more info about likelihood of fetal acidemia
Similar info between two methods
What does it mean if an accel follows stim?
Acidemia unlikely and labor may proceed
Poss technique in setting of persistent Cat 3 FHT
Fetal scalp blood sampling for determination of pH or lactate (though use of technique is decreasing)
Sensitivity of scalp pH <7.21 (75%ile) to predict umbilical artery pH <7.00; PPV of scalp pH <7.21 (75%ile) to predict umbilical artery pH <7.00
36%, 9%
Sensitivity of low scalp pH to identify newborn w/ HIE; PPV of low scalp pH to identify newborn w/ HIE; NPV of scalp pH to identify newborn w/o HIE
50%; 3%; 97-99%
Effect of intrapartum scalp sampling for pH vs lactate level on rates of acidemia at birth/APGARs/NICU admissions
No difference demonstrated
Is pulse ox clinically useful in evaluating fetal status?
No
Initial evaluation/tx of Cat 2-3 FHT (5)
Discontinuation of labor stim agent; SVE to determine cord prolapse/rapid cervical dilation/descent of fetal head; changing maternal position to L/R lateral recumbent, reducing compression of IVC and improving uteroplacental blood flow; monitoring maternal BPs for evidence of hypotension (especially in pts w/ regional anesthesia); assessment for tachysystole by evaluating ctx frequency/duration
Recommended tx for Cat 2-3 FHT if maternal hypotension present and suspected 2/2 regional anesthesia (2)
Volume expansion and/or ephedrine, or phenylephrine
Has supp O2 been shown to improve FHT?
No
Options for tocolytic therapy to stop ctxs and poss avoid cord compression (3)
Terb, hexoprenaline, mag sulfate
Comparison of using tocolytic therapy over no therapy re rates of perinatal mortality, low 5-min APGAR, NICU admission
No differences
Class of med used for managing tachysystole w/ associated FHT changes; two meds in this class; percentage of cases that respond to tx
Beta-2 adrenergic meds; hexoprenaline, terb; 98%
Technique that can be used to relieve cord compression in case of recurrent variable decels
Amnioinfusion
RR in rates of decels w/ amnioinfusion; RR in rates of C/S for suspected fetal distress w/ amnioinfusion; general effect of amnioninfusion on pt/newborn hospital stay >3 days
RR = 0.54; RR = 0.35; decreased
Between bolus and continuous infusion technique for amnioinfusion, which method has better ability to relieve recurrent variable decels?
Similar ability
