Maternal oxygen administration has been used in an attempt to reduce fetal distress by increasing the available oxygen from the mother. Even though healthy women in labor have high blood oxygen saturation (SpO₂), it has been suggested that increasing inspired O₂ increases blood O₂ tension and results in more O₂ delivered to the fetus (₂₈). Studies have shown that there was a more rapid increase in fetal oxygen saturation (FSpO₂) when O₂ was given, compared with the decrease in FSpO₂ when it was discontinued, suggesting that the fetus responds to the new placental O₂ gradient by accepting O₂ more rapidly than it gives it up (₂₈). Fetal hemoglobin has a higher affinity for O₂ than adult hemoglobin, and fetal hematocrit is higher than adults. These physiologic factors allow for a steeper increase in fetal oxygen concentration and FSpO₂ during maternal O₂ therapy. Further, fetuses with low FSpO₂ may benefit more from O₂ therapy than fetuses with normal FSpO₂ (₂₉).

Although results suggested that short-term (15 minutes) O₂ therapy may be beneficial for the fetus during labor, the results cannot be extrapolated to suggest that long-term O2 therapy during labor is of similar benefit (₃₀,₃₁,₃₂). On the effects of long-term O₂ therapy during labor, Thorp and colleagues in a randomized trial found that more than 10 minutes of O₂ administration during the second stage of labor resulted in lower umbilical artery cord blood gas values compared with less than 10 minutes of O₂ administration, and no O₂ administration (₃₃). In their report on the efficacy of 3 common intrauterine resuscitation techniques used during labor, Simpson and James prospectively evaluated intrauterine resuscitation techniques in healthy women during labor (₂₉). Women were randomized to either a 500mL or 1,000mL intravenous (IV) fluid bolus over 20 minutes. Women were further randomized to 1 of 6 position sequences including supine, with the head elevated 30°, and left lateral and right lateral for 15 minutes each in succession. Differences in FSpO₂ were evaluated before, during, and after each intervention. Their results showed that an IV fluid bolus of 1,000 mL had a greater effect on FSpO₂ than an IV fluid bolus of 500 mL, further, fetal oxygen saturation was higher in a lateral position than in a supine position. Oxygen administration increased FSpO₂, and the effect persisted for more than 30 minutes after the O₂ was discontinued. For fetuses with FSpO₂ less than 40% before maternal O₂ administration, the increase was greater than for those with FSpO₂ of 40% or greater. They concluded that O₂ administration at 10 L/min via non-rebreather face mask was effective in increasing FSpO₂ during labor.

It seems evident that when administering oxygen to the mother, that it is important to use the method that provides the highest fraction of inspired oxygen (FiO₂) to achieve maximum benefit. A non-rebreather facemask works best because the FiO₂ at 10 L per minute is approximately 80% to 100%, as compared to a simple face mask (FiO₂ 27%–40%) or nasal cannula (FiO₂ 31%) (₂₉). Other studies have not found any fetal benefit from maternal oxygen administration (₃₄,₃₅,₃₆). However, it may have a role during acute fetal distress, based on its effect over the short term at caesarean section (₃₇).

Maternal body position can influence fetal well-being without uterine contractions; results of non-stress tests (NSTs) are most unfavorable when mothers lie on their back (₃₈,₃₉,₄₀,₄₁). 'Aortocaval compression' describes compression of the inferior vena cava and the aorta by the gravid uterus in women at term (₄₂,₄₃,₄₄). Acute fetal distress can be caused by either hypoperfusion of the uteroplacental unit secondary to maternal hypotension, or occult aortic compression causing a reduction in iliac arterial flow. The compression of the aorta by the pregnant uterus decreases the blood pressure and, especially, pulse pressure distal to the affected level (supine hypotensive syndrome) (₄₅). Further, in the supine position, the lung function is also worsened in late pregnancy, causing a lower oxygen tension of the blood (₄₆,₄₇,₄₈). Due to the dextrorotation of the gravid uterus and its anatomical relation to the inferior vena cava some believe that a left lateral tilt is better for the fetus, however, other studies (₂₉,₄₉) have shown no significant differences in fetal status between left and right positions. Maternal cardiovascular compromise and fetal stress in maternal supine position, and their relief in the full lateral position, are well recognized (₅₀,₅₁,₅₂). Inferior vena cava compression is demonstrable up to 12.5°–15° of lateral tilt, and aortic compression up to 30°. The use of 15° of tilt at cesarean section, and 30° during labour, reduces the effects considerably. This amount of tilt, if applied correctly, reduces inferior vena cava compression (₅₃).

Animal studies have shown that boluses of intravenous crystalloids increased maternal arterial blood pressure and placental site blood flow, and decreased vascular resistance, however, there was no rise in fetal pO2 (₅₄). In hypovolemic or hypotensive women, blood volume shifts away from the uterus affecting oxygen delivery to the fetus. A bolus of 500ml of lactated Ringer's solution over 20 minutes significantly increases fetal oxygen saturation. The positive effects on fetal oxygen status continues for more than 30 minutes after the fluid bolus (₂₉). An added benefit of boluses of intravenous crystalloids is its tocolytic effect on the uterus, however, the uterine activity returns to baseline after 20 minutes (₅₅). It has been postulated that the tocolytic effects are related to naturetic peptide release from distension of the atrium (₃₇). Beneficial effects of intravenous fluids might be due to an increase in cardiac output (₅₆), a reduction in uterine contractions (₅₅), or a decrease in blood viscosity (₅₄). However, caution should be exercised when increasing IV fluids or giving repeated IV fluid boluses in certain clinical situations such as preeclampsia, preterm labor treated with magnesium sulfate, the use of corticosteroids, and beta-sympathomimetic drugs, all of which confer an increased risk for pulmonary edema. Oxytocin has an antidiuretic effect; thus prolonged use of large dosage oxytocin can also lead to fluid overload if too much IV fluid is administered, particularly if the fluid is not isotonic.

Uterine contractions cause a cessation of maternal intervillous placental blood flow resulting in relative fetal hypoxia with recovery taking 60-90 seconds (₅₇). If this intermittent interruption of blood flow becomes too frequent the fetus is at risk for hypoxemia and acidosis. It stands to reason that reducing both the frequency and intensity of uterine contractions will improve placental perfusion. This can be affected by either reducing or discontinuing oxytocin infusion, or administering tocolytics. Oxytocin can cause hyperstimulation resulting in fetal distress (₅₈); a simple means of reversing its effects is to stop the infusion. However, the effects of the discontinued oxytocin may still be evident. After 15 minutes of cessation, there is a 22% reduction in activity, by 30 minutes, a 39% reduction, and by 45 minutes a 48% reduction (₅₉). To achieve a more rapid reduction in oxytocin action, tocolytics may be used (₆₀,₆₁). The commonly used ?-agonist tocolytic is terbutaline 250?g given either subcutaneously or intravenously (₆₁). Glyceryl trinitrate (GTN), with a half-life of 3 minutes is likely to have a faster onset of action and elimination than other tocolytic agents (₆₂). Its use as a sublingual spray has also been described for acute uterine relaxation (₆₃).

Briozzo et al (₆₄), conducted a prospective randomized study to determine whether FIR using tocolysis and delayed delivery was better for the fetus than emergency delivery when fetal hypoxia was suspected because of a non-reassuring FHR pattern using conventional heart rate monitoring. They concluded that tocolysis and delayed delivery rendered better immediate neonatal results than emergency delivery when fetal distress was suspected because of a non-reassuring fetal heart pattern. In addition, it may decrease the need for emergency delivery without increasing maternal and fetal adverse side-effects.

Hyperstimulation may also follow the use of prostaglandins and their analogues when used for pre-induction cervical ripening or induction of labor. When this occurs, the remaining medication should be manually removed, the vagina irrigated, and if needs be tocolytics given (₃₇).

Amnioinfusion prevents or relieves umbilical cord compression usually caused by oligohydramnios. Amnioinfusion has been shown to reduce the incidence of variable fetal heart decelerations, but not late decelerations or reduced variability (₆₅,₆₆,₆₇). In a randomized prospective study by Mino et al (₆₆), 200 term pregnancies with low amniotic fluid due to vaginal loss were randomly chosen to receive intrapartum amnioinfusion or standard obstetric care without amnioinfusion. Fetal heart rate pattern, method of delivery and neonatal acid–base status were compared. They found that amnioinfusion improved fetal heart rate pattern, lowered the incidence of operative delivery, and improved neonatal acid–base status. In another prospective randomized study, Miyazaki and Nevarez (₆₇), investigated the effect of intrauterine saline amnioinfusion for the relief of repetitive variable decelerations in the first stage of labor. Their study showed that saline amnioinfusion was a simple, safe, and effective therapy for the relief of repetitive variable decelerations in the first stage of labor and could lower the incidence of cesarean sections for fetal distress in nulliparous patients.

The procedure of amnioinfusion uses the following equipment: a double lumen intrauterine pressure catheter, normal saline solution at room temperature, a fetal monitor and intravenous tubing. Continuous close monitoring using a fetal scalp electrode is recommended. After obtaining informed consent, a vaginal examination is performed to evaluate for cord prolapse, establish dilatation and confirm presentation. The fetal scalp electrode is placed, followed by an intrauterine pressure catheter to document resting tone (< 15 mm Hg). Normal saline is linked to the intravenous tubing, and primed as it would be for intravenous use, and is then inserted into the infusion port on the three-way stop cock of the intrauterine pressure catheter. Recommendations for infusion protocols may vary by institution. A common protocol (₆₈), starts with an initial bolus of 250 mL infused over 20 to 30 minutes. The rate is then adjusted according to the severity of decelerations, but usually at a rate of 10 to 20 mL per minute up to 600 mL, or to resolution of the variable decelerations. An additional 250 mL beyond the volume at which decelerations resolve is administered, then the infusion is terminated, unless the decelerations resume. The infusion is a failure if 800 to 1,000 mL of saline does not result in termination of decelerations. The fetal heart rate and resting tone are assessed continuously during the intervention. If the uterine tone is persistently elevated, the infusion is discontinued, and the uterine pressure allowed to equilibrate. The resting uterine tone is reassessed, and the infusion discontinued if the new resting tone is 15 mm Hg above the baseline resting tone or 30 mm Hg maximum (₆₈).An alternative protocol (₆₉), is a bolus infusion of 250 to 1,000 mL of fluid at a rate of 10 to 15 mL/minute, followed by a continuous infusion of 100 to 200 mL/hour via pump infusion or gravity. Strong and associates (₇₀), recommended saline infusion at 10 to 20 mL per minute through a blood warmer to prevent cold-induced fetal vasospasms; they continued the infusion until an amniotic fluid index of 8 cm was obtained. Owen and co-workers (₇₁), recommended the infusion of 600 mL of normal saline at 10 mL per minute, followed by a continuous infusion at 3 mL per minute.

Prolapse of the umbilical cord is a rare obstetric emergency that in the viable fetus warrants an expeditious delivery. Traditionally, this has been managed by minimizing pressure on the cord while preparing for delivery. The steps involve manual elevation of the presenting part, a knee-chest or Trendelenberg position, instillation of fluid in the bladder and funic reduction (₇₂). Unless the cervix is fully dilated and a spontaneous or instrumental delivery can be achieved, most obstetricians would opt for delivery by cesarean section (₃₇).

While most fetuses tolerate transient hypoxic states, others with less reserve do poorly. Recurrent variable or prolonged decelerations during the second stage are associated with respiratory academia at birth (₇₃,₇₄). The use of sustained Valsalva bearing down efforts results in adverse fetal acidemia or deoxygenation. Specifically, sustained bearing down efforts result in lower maternal blood pressure and placental blood flow, lower fetal pH and PO₂, higher PCO₂, more frequent occurrence of nonreassuring fetal heart rate patterns, delayed recovery of FHR decelerations and subsequent newborn acidemia, and lower Apgar scores (₇₅,₇₆,₇₇). Clinical trials indicate that the use of “non-coached” pushing prevents fetal hypoxic effects and without the risk of adverse maternal, fetal, or neonatal outcomes (₇₈,₇₉). If the fetal heart pattern is nonreassuring during second stage pushing efforts, the best approach is to stop pushing temporarily and allow the fetus to recover (₄₉). One of the ways to reduce the stresses to the fetus during the second stage of labor is to shorten the active, sustained, coached closed-glottis pushing (₇₉,₈₀). Time spent in the phase of active bearing down is the more critical time interval than the total duration of the second stage with regards to the decline in fetal pH and the development of hypoxia and acidosis (₈₁). In women with epidural anesthesia, if there are no maternal or fetal conditions that require rapid birth, it is best to wait until the mother feels the urge to bear down rather than encourage her to push prematurely. In the PEOPLE (Pushing Early or Pushing Late with Epidural) (₈₂) multicenter, randomized, controlled trial undertaken to determine whether a policy of delayed pushing for nulliparous women with continuous-infusion epidural analgesia reduced the risk of difficult delivery. A policy of delayed pushing resulted in a reduction in the risk of difficult delivery and an increase in the likelihood of abnormal umbilical cord pH. They concluded that delayed pushing was an effective strategy to reduce difficult deliveries in nulliparous women.

There is a paucity of studies on the quickest and safest anesthesia for an emergency cesarean section for fetal distress. The National Sentinel Audit of Cesarean sections defined 30 minutes as a standard for decision-to-delivery interval for an emergency delivery (₅₂,₈₃). In a systematic review on the effects of epidural analgesia on labor, maternal, and neonatal outcomes, Leighton et al., reported that analgesic method did not affect fetal oxygenation, neonatal pH, or 5-minute Apgar scores; however neonates whose mothers received parenteral opioids required naloxone and had low 1-minute Apgar scores more often than did neonates whose mothers received epidurals (₈₄). In their meta-analysis to review the effects of epidural versus parenteral opioid analgesia, Halpern et al, reported that patient satisfaction and neonatal outcome were better after epidural than parenteral opioid analgesia (₈₅).

The need for general anesthesia for cesarean section for “fetal distress” is controversial, with evidence supporting the use of regional anesthesia in these cases (₈₆). If a functioning labor epidural is in-situ, it can be used in all but the most extreme cases by administration of a rapid onset local anesthetic such as 3% 2-chloroprocaine or 2% lidocaine with epinephrine. The risks and benefits of general anesthesia to the neonate have been well documented in several studies(₈₆) A comparison of general and epidural anesthesia found that the general anesthesia group had lower pH values (₈₇). Ong and colleagues (₈₈) found that general anesthesia was associated with a higher incidence of low Apgar scores as compared to regional anesthesia. Gale and colleagues (₈₉) reported that the number of neonates needing “respiratory assistance” at birth was twice as high in the group whose mothers received general as compared to epidural anesthesia, and Marx and colleagues (₉₀) reported that despite the presence of fetal distress, 1 min Apgar scores were significantly better in the group receiving spinal as compared to general anesthesia. In a small prospective, randomized study by Dyer et al (₉₁), on neonatal outcomes after spinal versus general anesthesia for cesarean delivery in preeclamptic patients with a nonreassuring fetal heart trace, spinal anesthesia for cesarean delivery was associated with a greater mean neonatal umbilical arterial base deficit and a lower median umbilical arterial pH than general anesthesia.

A meta-analysis of anesthesia for cesarean section and neonatal acid-base status included elective and emergency cesarean sections (₉₂). The conclusion was that spinal anesthesia could not be considered safer than epidural or general anesthesia for the fetus. Although differences were moderate, the reduced pH could further impact upon the outcome for an already compromised fetus. They caution that there were many good reasons to use spinal anesthesia for cesarean section, but fetal ? neonatal welfare was not amongst them. In a review of anesthesia and analgesia on the risk of fetal distress during labor and cesarean section, Bonnet et al., concluded that all obstetric anesthesia and analgesia techniques are associated with a theoretical risk of fetal distress, but given the fact that regional anesthesia techniques are also associated with well-demonstrated benefits for the mother and the newborn, the latter remains the preferred choice in obstetric practice (₉₃).

While the quality and choice of anesthesia for cesarean section has significantly improved over the last two decades, general anesthesia usage has decreased to the point where, in some centers, it is an occasionally used technique for severe fetal distress. The increase in anesthetic choices has led to inconsistencies in practice between individual anesthetists, and between regions and nations (₉₄). Spinal anesthesia is now the commonest technique used in the UK for elective cesarean section (₉₅), and its rapid onset has also established it as an alternative to general anesthesia in emergency cases (₉₄).

The choice of anesthesia used in a situation is influenced by a variety of factors such as the urgency of the procedure, maternal status, and physician and patient preference. If the cesarean section must be performed urgently because of a nonreassuring FHR pattern, an anesthetic technique that can be performed relatively quickly is preferred since anesthesia must be achieved expeditiously. Most practitioners agree that inducing general anesthesia is the most reliable means of quickly achieving operative anesthesia for cesarean. However, highly skilled individuals may be able to rapidly induce spinal anesthesia. In fact spinal anesthesia is increasingly being used as a substitute for general anesthesia in all but the most emergent situations (₉₆). In summary, not every abnormal fetal heart rate pattern should be diagnosed as “fetal distress” and many of these cases can be safely performed under neuraxial block. The American College of Obstetricians and Gynecologists has supported the use of regional anesthesia in these cases (₁).