A 2012 Cochrane meta-analysis of 6 randomized controlled trials concluded that the combination of electronic FHR and ST waveform analysis compared with electronic FHR monitoring without ST waveform analysis did not decrease the incidence of severe neonatal metabolic acidosis, Apgar scores <7 at 5 minutes, neonatal encephalopathy, or the number of cesarean deliveries.42 All of the trials were performed in Europe or Asia. Because the current evidence does not show that fetal ST waveform analysis decreases the cesarean delivery rate, it has not gained popularity in the United States. However, the National Institute of Child Health and Human Development is currently recruiting participants for a multicenter, randomized controlled trial comparing neonatal outcomes in fetuses monitored with both electronic FHR monitoring and STAN versus electronic FHR monitoring alone.d Primary outcome measures include intrapartum fetal death, neonatal death, Apgar score ≤3 at 5 minutes, neonatal seizure, umbilical cord artery pH ≤7.05 and base deficit ≥12 mmol/L, intubation at delivery, and presence of neonatal encephalopathy.
Adult pulse oximetry has been shown to increase the early detection of hypoxemia in both the operating room and the recovery room.43,44 Fetal pulse oximetry was developed as an adjunct to confirm or refute nonreassuring FHR tracings, with the goal of reducing the number of unnecessary or unindicated operative vaginal deliveries (vacuum, forceps) and cesarean deliveries.45 The pulse oximetry probe is placed on the fetal cheek, temple, back, or buttocks.41,46 The probe functions on the principle of reflectance (as opposed to the principle of transmittance in adult pulse oximeters), thus the light-emitting diode and photodetector are adjacent to each other (as opposed to opposite). Normal fetal SpO2 is 30% to 60%; fetal SpO2 <30% for ≥10 minutes in the last 60 minutes before delivery has been shown to correlate with umbilical artery pH <7.15, whereas SpO2 >30% correlates with umbilical artery pH >7.15.47,48 Currently, the ACOG Committee on Obstetric Practice does not endorse fetal pulse oximetry because its use has not decreased the overall cesarean delivery rate.49–51 Their concern is that the “introduction of this technology to clinical practice could further escalate the cost of medical care without necessarily improving clinical outcome.”51
The patient presenting with potential uteroplacental insufficiency may have had 1 or more antepartum NSTs, BPPs, and UADV evaluations. She may present in spontaneous labor, for induction of labor, or for cesarean delivery. Although the fetal risks and benefits of individual anesthesia techniques for these patients is unknown, it is recognized that the fetus will experience additional hypoxia during uterine contractions, which may lead to FHR decelerations and need for emergency cesarean delivery. In addition, decreased uteroplacental blood flow associated with maternal hypotension in the labor room or operating room may further compromise the fetus. The goals of the anesthesiologist should optimally include early anesthesia evaluation, early epidural catheter placement when appropriate, reassessment of both the mother and fetus during labor, and communication with the obstetricians and nurses regarding the delivery plan (Fig. 6).
An early anesthesia evaluation and management plan is recommended for safe delivery of the fetus with suspected uteroplacental insufficiency (Fig. 7, which shows a checklist for a patient with abnormal fetal assessments). Emphasis should be placed on the airway examination, as airway complications remain the predominant cause of anesthesia-related death in obstetric patients.52,53 Situational factors relating to emergency deliveries, including unpreparedness for a potentially difficult airway, contribute to failed tracheal intubation.53,54
Because fetuses with suspected uteroplacental insufficiency based on abnormal antepartum (NST, BPP, UADV) and/or intrapartum (electronic fetal monitoring) assessments may not tolerate additional decreases in uteroplacental blood flow associated with uterine contractions, they are at higher risk for emergency cesarean deliveries. It is important that whenever feasible, these patients have functioning epidural catheters. The case-fatality ratio of anesthesia-related deaths during cesarean delivery is shown to be decreased with the use of neuraxial anesthesia compared with general anesthesia (GA).55 Placement of a preemptive epidural catheter may improve the likelihood of avoiding GA if an emergency cesarean delivery is required.56 Some anesthesiologists recommend avoiding combined spinal-epidural analgesia in these cases. The effectiveness of a conventional epidural or intrathecal catheter can be confirmed immediately after placement, whereas the effectiveness of a catheter placed using a combined spinal-epidural technique cannot be fully confirmed until the spinal medication wears off.
Fetal bradycardia has been described in healthy fetuses after the administration of neuraxial local anesthetic and opioids. Increased uterine tone has been observed with administration of intrathecal fentanyl and sufentanil.57,58 Initiation of neuraxial analgesia causes a rapid decrease in circulating maternal epinephrine levels. It is hypothesized that the lower epinephrine levels lead to decreased β-agonism (uterine relaxation) and increased α-agonism (uterine contraction). Increased uterine tone may lead to decreased uteroplacental blood flow and subsequent fetal hypoxia and bradycardia.59 There is inconsistency among studies regarding the incidence of fetal bradycardia and whether the incidence is opioid dose-dependent.59–64 Wong et al. found no significant differences in the incidence of nonreassuring FHR abnormalities among parturients randomized to receive intrathecal opioids in doses ranging from 0 to 25 mcg for fentanyl63 and 2.5 to 10 mcg for sufentanil.64
Because the data are inconsistent, and some studies suggest a relationship between intrathecal opioids and fetal bradycardia, some anesthesiologists suggest that using a conventional epidural technique may be a safer alternative for fetuses with known or suspected uteroplacental insufficiency. An already compromised fetus may not tolerate the decreased oxygen delivery associated with uterine tachysystole. Unfortunately, no studies have been published comparing the incidence of fetal heart monitoring abnormalities after combined spinal-epidural versus conventional epidural for fetuses with various BPP scores, UADV abnormalities, or category II and III tracings.
In addition, anesthesiologists practicing in hospitals in which obstetricians are not continuously in-house may consider requesting that the obstetrician be present before initiation of neuraxial blockade.
Understanding intrapartum fetal heart tracings is essential for the anesthesia provider, since it is the primary monitoring tool influencing the need for urgent intrapartum operative vaginal and cesarean deliveries. Some category II tracings may deteriorate into category III tracings, thus communication with the obstetricians regarding their level of concern for possible operative delivery allows for early anesthesia evaluation and planning.
Excellent communication with the parturient, obstetrician, and labor nurse is of key importance. Emphasizing the strong preference for neuraxial anesthesia and a plan to place a preemptive epidural catheter, if cesarean delivery is likely, may improve maternal safety. The anesthesia provider can also assess the need for preemptive difficult airway preparation (such as calling for additional anesthesia provider backup, video laryngoscope, supraglottic airway device, fiberoptic laryngoscope, surgical backup, etc.).
For patients entering the operating room without functioning neuraxial catheters, understanding that an FHR tracing may deteriorate from category II to III may improve communication with obstetricians regarding the urgency of delivery, limiting repeated attempts to initiate neuraxial blockade, and the need for immediate induction of GA. The benefit to the compromised fetus of prompt delivery after induction of GA may outweigh the risks of repeated attempts at a difficult neuraxial blockade, especially for parturients without anticipated difficult airways.
Choice of anesthetic technique is a risk-benefit discussion between the obstetrician and anesthesiologist that considers the well-being of both mother and fetus. The American Society of Anesthesiologists Task Force on Obstetric Anesthesia states that “the decision to use a particular anesthetic technique for cesarean delivery should be individualized, based on several factors. These include anesthetic, obstetric, or fetal risk factors (e.g., elective vs. emergency), the preferences of the patient, and the judgment of the anesthesiologist. Neuraxial techniques are preferred to GA for most cesarean deliveries.”56 GA may be the most appropriate choice for situations demanding immediate delivery, including profound fetal bradycardia.56
A conversation between the obstetrician and anesthesiologist for every clinical scenario, particularly for category III tracings, regarding time available to initiate anesthesia, as well as maternal anesthetic risks, is necessary. Some tracings may allow for a brief time period to attempt neuraxial anesthesia, while immediate GA may be preferred for other tracings.
Avoiding maternal hypotension before cesarean delivery of fetuses with uteroplacental insufficiency may be particularly important in maintaining neonatal acid-base status.65 Mueller et al.66 reported that among 5800 elective cesarean deliveries in healthy parturients with uncomplicated singleton term pregnancies, neonatal acidemia was significantly increased in the neuraxial (spinal and epidural) anesthesia group compared with the GA group due to hypotension. Although term healthy infants seem to tolerate mild maternal hypotension,67 it is possible that an already compromised fetus may develop postnatal complications subsequent to placental hypoperfusion.68 The degree and duration of fetal metabolic acidosis correlates linearly with umbilical cord base deficit values, and values >12 mmol/L are associated with moderate to severe newborn encephalopathy.68
Low-dose combined spinal-epidural anesthesia and aggressive use of fluids and vasopressors to maintain maternal arterial blood pressure at baseline may be useful methods to avoid further fetal hypoxia. Recent clinical studies69–73 have demonstrated that ephedrine is associated with a greater propensity toward fetal acidosis compared with phenylephrine, however minimal data are available comparing vasopressor use in potentially compromised fetuses. In 1 retrospective study, Cooper et al.74 found no significant difference in umbilical artery base excess between ephedrine and phenylephrine use during cesarean delivery with spinal anesthesia for patients with high-risk conditions including nonreassuring FHR, hypertensive disorders of pregnancy, IUGR, and cord prolapse. Factors such as low ephedrine doses and short time interval between administration of anesthesia and delivery may have contributed to the results.74 Continuous FHR monitoring during neuraxial blockade may detect a deteriorating tracing and need for maternal position change or an anesthesia plan change (neuraxial to general). Presence of the obstetrician in the operating room, ready for these changes, will also expedite delivery.
Reevaluation of the pregnant patient during labor is essential. The FHR tracing may deteriorate, a previously functioning epidural catheter may become ineffective and require evaluation or replacement, and Mallampati scores can increase throughout labor.75,76 Labor is an ever-changing dynamic state that may require analgesia and anesthesia management plans to change as well.
Teamwork is an essential component of effective communication and prevention of medical errors. This is especially relevant to the labor and delivery unit, as many health care providers (obstetricians, labor nurses, midwives, anesthesiologists, nurse anesthetists, pediatricians, operating room technicians) participate in the care of the parturient, fetus, and neonate. Lack of communication is the leading cause of medical errors in obstetric care.4 A component of effective teamwork is planning and decision making among team members,77 thus anesthesiologists’ understanding of the fetal assessments that influence obstetric management may enhance interdisciplinary teamwork.
Use of protocols, team training, and electronic fetal heart monitoring certification for staff involved in FHR interpretation have decreased the incidence of adverse sentinel events and compensation payments,78 as well as improved the staff members’ perception of teamwork, safety, and job satisfaction.7,79 Electronic FHR monitoring certification for anesthesiologists has not been described in the literature, but we believe this education would enhance communication with the obstetric staff.
A 32-year-old G4P2 at 35 weeks’ gestation presents for induction of labor for a BPP of 4 of 10 and decreased umbilical artery Doppler flow. The obstetrician shares this information with the anesthesiologist, who evaluates the patient and learns that she is obese and has a difficult airway. The anesthesiologist counsels her regarding the benefits of a neuraxial block, including avoiding potential complications of GA if she needs an emergency cesarean delivery. On examination of her back, a potentially difficult neuraxial catheter placement is anticipated due to her obesity. A decision is made to place a preemptive neuraxial catheter using ultrasound.80 Backup airway equipment is checked and placed in or near the operating room, and the backup anesthesiologist is made aware. At a cervical examination of 4 cm dilation/80% effacement/−2 cm station, the labor nurse notices recurrent late decelerations, calls the obstetrician and anesthesia providers, and an emergency cesarean delivery is planned. An adequate anesthetic level is acquired using the in situ neuraxial catheter and the surgery proceeds successfully without complications.
Anesthesiologists are integral to the safe care of laboring women and those in need of operative deliveries. Effective teamwork requires that labor nurses, obstetricians, midwives, anesthesiologists, and nurse anesthetists speak the same language and understand each other’s concerns. An important first step is anesthesiologists learning about obstetric concerns and obstetricians learning about the anesthetic concern of airway management. It is our hope that this review will motivate anesthesiologists to promote mutual understanding and ultimately improve patient safety.
a Salman M, Kumar R, James E. Intrapartum fetal assessment: do obstetric anaesthetists know enough? SOAP Meeting 2011. Poster Session #2, Abstract #180. Las Vegas, Nevada.
b If the amniotic fluid MVP is ≥2 cm, but the amniotic fluid index is <5 cm (oligohydramnios), there may be concern for fetal hypoxia and further evaluation may be indicated.
c FDA Approval of STAN®S31 Fetal Heart Monitor. Available at: http://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/DeviceApprovalsandClearances/Recently-ApprovedDevices/ucm078446.htm. Accessed August 26, 2012.
d Fetal ST Segment and T Wave Analysis in Labor (STAN). Available at: http://clinicaltrials.gov/ct2/show/study/NCT01131260. Accessed August 26, 2012.
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