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Intrauterine fetal monitoring is used by the obstetrician to determine fetal status before and during labor. It is the anesthesiologist’s responsibility to understand and be aware of fetal status in order to optimize communication with their obstetric colleagues and respond to emergencies in a timely manner. Fetal heart rate (FHR) monitoring may be noninvasive with a Doppler transducer on the maternal abdomen or invasive with a fetal scalp electrode (FSE).
In order for an FSE to be placed, the following criteria must be met: the fetus is at an appropriate station to be low enough in the pelvis to reach the head, rupture of membranes has occurred, and the cervix dilated to at least 1 cm. Any decelerations in the fetal heart rate are always interpreted relative to uterine contractions. Contractions may be measured with a tocodynometer on the maternal abdomen (noninvasive) or an intrauterine pressure catheter (invasive).
The purpose of antepartum fetal monitoring is to identify fetuses at risk for intrauterine asphyxia, which can lead to severe lifelong neurologic impairment or even death. It has an excellent predictive value for the identification of well-oxygenated fetuses. It is not a sensitive test for the identification of fetuses who are suffering the effects of hypoxia. Although the incidence of late decelerations and decreased variability is increased in patients who subsequently develop cerebral palsy, the vast majority of fetuses who exhibit these abnormalities in the FHR tracing are completely normal.
The false positive rate for FHR abnormalities is approximately 99%. In extreme situations such as umbilical cord prolapse, FHR monitoring is extremely useful in identifying life-threatening abnormalities. Despite the limitations of this monitoring modality, it is the currently the most widely accepted measurement of fetal well-being and its use to guide obstetrical decision making in the developed world is nearly universal.
The decision to perform fetal monitoring is made based on maternal and prenatal indications. Healthy women without labor analgesia giving birth to low risk babies may choose to deliver in a birth center where little fetal monitoring may be performed. Often in these cases fetal monitoring is performed intermittently at pre-determined intervals.
The American Congress of Obstetricians and Gynecologists (ACOG) recommends that the obstetrical practitioner review the FHR tracing every 30 minutes in the first stage of labor and every 15 minutes in the second stage of labor in healthy parturients without complications. Continuous fetal monitoring is performed whenever a patient has labor analgesia or maternal conditions such as preeclampsia, previous cesarean delivery, diabetes, prolonged rupture of membranes, or other coexisting disease.
Fetal indications for continuous fetal monitoring include intrauterine growth restriction, induced labor or congenital anomalies. For more complicated patients, ACOG recommends that the FHR tracing be reviewed every 15 minutes during the first stage and every 5 minutes in the second stage of labor.
The risk of delay to obtain additional information depends on the urgency of the situation. If an operative intervention is planned, it is always appropriate to attempt a brief airway assessment and query the patient about allergies, previous anesthetic problems, and medical history.
Emergent: The purpose of FHR monitoring is to identify fetuses most at risk for intrauterine asphyxia who would benefit from immediate delivery. Category III FHR tracings often require immediate delivery and include situations such as prolonged bradycardia (possibly due to umbilical cord prolapse), or repetitive late decelerations without variability.
Urgent: Many situations in obstetrics require urgent delivery and are guided by the FHR tracing. Usually the patient has a Category II or occasionally Category III FHR tracing. Examples may include recurrent variable deceleration or late decelerations with minimal variability.
Elective: Patients who exhibit Category I and often Category II FHR tracings will have either elective cesarean deliveries for other obstetrical indications (e.g., repeat cesarean, breech position, maternal diabetes) or will progress to have normal spontaneous vaginal deliveries.
The FHR tracing is displayed on either paper or a computer screen with beats per minute (bpm) on the vertical display (typically 30 bpm per centimeter) and time (usually minutes) on the horizontal axis. Each vertical solid line is 1 minute.
Uterine contractile activity is measured below the FHR display with the same time scale as the FHR tracing in the horizontal axis and the vertical axis measuring pressure in millimeters of mercury or centimeters of water. The pressure scale is only valid if an intrauterine pressure catheter is in use.
Normal baseline FHR is 110-160. Variability of the FHR tracing is the fluctuation in the FHR and is controlled by the autonomic nervous system. Variability may be mild, moderate, or marked. Moderate variability is normal and is defined as 6-25 bpm from peak to trough. Loss of variability in the presence of late or variable decelerations is an ominous sign of fetal compromise and acidosis.
Accelerations are increases in the FHR above baseline in response to uterine contractions. Accelerations are associated with a well-oxygenated fetus.
Early decelerations are decreases in the FHR which occur with a contraction. The shape is in the form of a "U" with the nadir of the deceleration being at the peak of the contraction. Early decelerations represent a fetal vagal response to head compression and are a normal pattern.
Late decelerations are decreases in the FHR that occur after a contraction. The shape is in the form of a "U" with the nadir occurring AFTER the contraction has occurred. Late decelerations represent uteroplacental insufficiency and are often concerning for fetal hypoxia.
Variable decelerations are decreases in FHR with an abrupt onset that are variable in all respects, including timing and shape. Variable decelerations may represent an autonomic response to umbilical cord compression but prolonged severe variable decelerations may result in the inability of the fetus to maintain cardiac output.
Often the anesthesiologist will be consulted when the FHR is concerning for asphyxia and cesarean delivery is being considered. In order to improve communication regarding the types of FHR tracing abnormalities and the relationship to urgency of delivery, FHR tracings were recently divided into a three-tier system by the National Institute of Child Health and Human Development. This nomenclature replaces previous nomenclature of "reassuring" and "nonreassuring" and the term "fetal distress."
Category I FHR tracings: Are normal and associated with a well-oxygenated fetus. Characteristics of a category I FHR tracing include:
Baseline FHR 110-160
Moderate baseline FHR variability
Late or variable decelerations are absent
Early decelerations are present or absent
Accelerations are present or absent
Category II FHR tracings: Are indeterminate and require clinical judgment. A patient with a category II FHR may require a non-urgent cesarean delivery.
Category III FHR tracings: Are abnormal and usually require delivery within 30 minutes. Therefore, a patient with a category III tracing may require emergent cesarean delivery.
Absent baseline FHR variability AND any of the following: Recurrent late decelerations, recurrent variable decelerations, or bradycardia.
Medically unstable conditions warranting further evaluation include: Any concerns with emergently inducing general anesthesia such as a concerning maternal airway examination or co-existing maternal disease should be evaluated prior to an emergency whenever possible.
Delaying surgery may be indicated if: the patient may have an unstable disease that would respond with unfavorable hemodynamics in case of rapid sequence induction for cesarean delivery (e.g., severe aortic stenosis). Suspicion of extremely difficult maternal airway management may warrant delaying surgery to obtain proper airway management devices or personnel. Communication with the obstetrical staff should be undertaken in order to avoid a situation where the patient requires urgent or emergent delivery due to abnormalities on the FHR tracing. In high-risk patients, a thorough anesthetic evaluation and proper precautions should be taken when the patient arrives on the labor deck. Close monitoring of the FHR tracing by all staff members is warranted.
The standard preoperative history for any parturient includes allergies, previous anesthetic history, previous obstetrical history (to include mode of delivery, any anesthetic intervention, and any potential complications), and past medical history. Physical exam should include special attention to current vital signs, airway examination, back examination, and neurological exam if necessary.
Ongoing communication with the obstetrical and nursing staff is essential with any parturient but especially those who are at high risk for cesarean delivery or postpartum complications. Periodic review of the FHR tracing aids in multidisciplinary team management and decisions regarding timing of other procedures on L&D.
Maternal medication administration may have a significant effect on the fetal heart rate tracing. For example:
Benzodiazepines, opioids: May cause significant decreases in the fetal heart rate variability. If maternal hypoventilation or oxygen desaturation is present, late decelerations may be observed. Systemic opioids have been also associated with a fetal sinusoidal pattern.
Magnesium sulfate: May be administered as seizure prophylaxis in cases of severe preeclampsia and/or for neuroprotection of the preterm neonate. Its administration typically results in decreased variability.
Ephedrine: May cause increased variability and fetal tachycardia which may also be due to fetal metabolic acidosis.
Epinephrine, or beta-adrenergic agonists (e.g., terbutaline): May result in fetal tachycardia.
Atropine: May result in fetal tachycardia and/or decreased variability.
Oxytocin: Excessive administration may result in uterine hypertonicity, which may lead to uteroplacental insufficiency and fetal bradycardia.
In general, maternal medications taken during pregnancy should be continued in the peripartum period and should not affect fetal monitoring.
Documented: Avoid all trigger agents such as succinylcholine and inhalational agents:
Proposed general anesthetic plan: Rapid sequence induction using 1 mg/kg rocuronium rather than succinylcholine followed by a total intravenous anesthetic.
Ensure MH cart available: [MH protocol]
Family history or risk factors for MH: Treat as MH susceptible.
Hemoglobin levels: Assessment ofhemoglobin may be important when late decelerations are observed asmaternal anemia and hypovolemia may lead to inadequate fetal oxygenation and/or uteroplacental perfusion.
Electrolytes:Assessment of maternal electrolytes is usually unnecessary in theabsence of indications such as severe preeclampsia or underlying renaldisease.
Coagulationpanel: A coagulation panel should be considered in patients who havesevere variable decelerations or late decelerations as thesetracings may be consistent with placental abruption, which can lead to a consumptive coagulopathy.
Imaging:Rarely, the FHR tracing cannot be transduced with the abdominal monitordue to conditions such as extreme maternal obesity or multiplegestations. If the membranes are intact, ultrasound may be used tovisualize the fetal heart rate.
Nonstress Test (NST): The NST is typically performed antepartum in situationswhere documentation of fetal well-being is necessary such as cases ofdecreased fetal movement, post-dates gestation, suspected placentalinsufficiency, or other high-risk situation. The test involves measuring FHR tracing and uterine contractile activity for 30-40 minutes. Anormal NST has a normal baseline FHR, moderate variability, accelerations present and the absence of decelerations. An NST isconsidered "reactive" if there are 2 or more accelerations in the FHR in20 minutes.
Biophysical Profile (BPP): While not used in labor, the BPP may be used antepartumin the third trimester to assess fetal well-being in cases of high-riskpregnancies. Five variables are recorded and scored: gross bodymovements, fetal tone, amniotic fluid volume, fetal breathing movements, and the NST. Of the five variables, low amniotic fluid volume(oligohydramnios) is associated with adverse outcomes more frequentlythan low scores in the other measurements.
Contraction Stress Test (CST): The CST measures the response of the fetus tocontractions. Oxytocin or nipple stimulation is used to inducecontractions while the FHR is measured. If no late or significantvariable decelerations are observed, the test is negative. Like FHRmeasurement in general, the test has an excellent negative predictivevalue, meaning that the absence of FHR abnormalities is reassuring ofgood fetal status. The presence of late or significant variabledecelerations is a positive test and may indicate cord compressionand/or placental insufficiency, usually requiring caesarean delivery due to fetal intolerance of labor.
Please refer to the chapter on Regional Anesthesia for Obstetrics
Fetal status will determine when emergent or urgent delivery is needed. If the decision is made to move to the OR, urgency will dictate whether there is time for an existing epidural to be extended, a spinal to be placed, or whether general anesthesia is necessary. Pediatricians should be present for delivery if the fetal status has been nonreassuring.
If decelerations are present, all efforts should be taken to optimize the maternal condition, including left or right uterine displacement, knee-chest position, ensuring adequate blood pressure for uterine perfusion, and correcting maternal acidosis, electrolyte abnormalities, and hypoxia.
(A NIH Consensus Conference concluded that electronic fetal monitoring (EFM) has led to a significant increase in cesarean and forceps deliveries, higher insurance costs and physicians dropping obstetrics from their practices, but has not reduced cerebral palsy or fetal death. A new method of categorizing fetal heart rate patterns is proposed.)
ACOG Practice Bulletin No. 116: Management of Intrapartum Fetal Heart Rate Tracings. Obstet Gynecol 2010;116:1232–40.
(The purpose of this document is to provide practitioners with a framework for evaluation and management of intrapartum EFM patterns based on the three tiered categorization.)
MoaveniDM BirnbachDJ RanasingheJS YasinSY. Fetal assessment for anesthesiologists: are you evaluating the other patient? Anesth Analg 2013;116:1278–92.
(This review aims to improve anesthesia providers’ understanding of antepartum and intrapartum fetal assessment modalities with the goal of improved communication with obstetricians and improved planning of cesarean deliveries for high risk obstetric situations.)
JacksonM HolmgrenCM EsplinMS HenryE VarnerMW. Frequency of fetal heart rate categories and short-term neonatal outcome. Obstet Gynecol 2011;118:803–8.
(This study reviewed 48,444 patients’ fetal heart rate data and neonatal outcomes to determine the time spent in each category and short-term neonatal outcomes. They found Category I was present 78% of the time, Category II 22% of the time, and Category III 0.004% of the time. If more than 75% of the last two hours of labor were Category II, 5-minute Apgar scores < 7 doubled and NICU admissions increased from 0.2% to 0.7%.)
OyeleseY VintzileosAM. Uses and limitations of the fetal biophysical profile. Clin Perinatol 2011;38:47–64.
(The biophysical profile allows a more thorough evaluation of fetal well-being and has the potential to significantly reduce the false-positive rate of the non-stress test (NST) and contraction stress test (CST).)
LivingstonEG. Intrapartum Fetal Assessment and Therapy. In: ChestnutDH WongCA TsenLC Ngan KeeWD BeilinY MhyreJM, eds. Chestnut’s Obstetric Anesthesia, 5th ed. Philadelphia, PA; Elsevier Mosby, 2014.
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This article originally appeared on Clinical Pain Advisor