Anesthesia for Cesarean Section - Its Effects on Neonates

What Is Anesthesia for Cesarean Section?

Delivery of babies through cesarean section (CS) is becoming more common. Obstetric anesthesia has emerged over time to include all aspects of maternal care, from cesarean section anesthesia and labor analgesia to maternal resuscitation and patient safety. Anesthesiologists are concerned with neonatal and maternal outcomes and preventing and managing comorbidities during childbirth.

Virginia Apgar, a surgeon turned obstetric anesthesiologist, is best known for developing the neonatal assessment scoring system that bears her name. Her insights demonstrate how obstetric anesthetists pursued scientific answers to questions about the effects of anesthesia on the mother, fetus, and neonate. However, the "birth" of obstetric anesthesia started in 1847, when obstetrician James Young Simpson introduced ether labor analgesia.

In the early 20th century, "twilight sleep," a mixture of Morphine and Scopolamine, became prevalent but was eventually discontinued because of its depressant effects on the newborn. In the mid-twentieth century, general anesthesia for cesarean delivery caused airway difficulties such as failed tracheal intubations, maternal aspiration, and Mendelsohn syndrome (aspiration pneumonitis). Anesthesiologists started concentrating on limiting anesthesia-related adverse newborn and maternal outcomes, such as airway morbidity and mortality. By the 1980s, neuraxial labor anesthesia was gaining more popularity, even though it was feared to be a risk factor for cesarean delivery.

What Are the Anesthesia Techniques and Their Effects on the Newborn?

General Anesthesia (GA): Although all drugs administered to the mother pass through the placenta and enter the umbilical vein, administration of the medications during the induction and maintenance phases of general anesthesia are monitored.

Factors Affecting Neonatal Outcomes:

• The time between anesthetic induction and umbilical cord clamping is a critical determinant of the neonatal outcome because it signifies fetal exposure to the maternally injected medication.

• The interval between the incision of the uterus and baby delivery is a second factor.

• A longer interval from incision to delivery is linked to a higher risk of fetal acidosis, which is thought to be caused by vasoconstriction of the uteroplacental layer. Therefore, if feasible, the time from induction to clamp should be less than ten minutes, and the time from uterine incision to delivery should be less than three minutes.

Determinants of Placental Transfer of Drugs to the Fetus:

• The properties of the drug are both physical-chemical of the drug.

• The maternal, placental, and fetal circulations characteristics of the drug.

• The anatomy and physiology of the placenta are the three determinants of drug transfer through the placenta to the fetus. They are,

  1. Induction agents.

  2. Neuromuscular blocking drugs.

  3. Inhalation agents.

Induction Agents:

• The fetal and neonatal pharmacological effects of anesthetic agents given to the mother throughout a Cesarean section performed under GA are dependent on the amount of drug reaching the fetus is difficult to estimate.

• Sodium thiopental, Methohexital, Ketamine, Propofol, and Midazolam are some of the agents used for induction to start GA. As it restores sympathetic outflow, Ketamine is typically reserved for patients involving maternal hemodynamic instability.

• If the induction time is longer, a lighter plane of maternal anesthesia (as evaluated by an electroencephalogram) and lower Apgar scores have all been linked to Midazolam and Propofol.

• The pharmacokinetic properties of Sodium thiopental and Methohexital are similar to those of Thiamylal, another lipid-soluble barbiturate that reaches its peak in umbilical arterial plasma after three to five minutes and quickly drops until 11 minutes.

• Induction of umbilical cord clamp of about ten minutes corresponds with decreasing fetal levels of these agents and, results in slight neonatal depression.

Neuromuscular Blocking Drugs:

• A quaternary ammonium ion, which tends to slow but does not eliminate drug transfer across the placenta, is shared by neuromuscular blocking drugs. Succinylcholine broken down quickly by plasma cholinesterase that effectively none reaches the fetus.

• According to the drug, the percentage of nondepolarizing neuromuscular blocking drugs crossing the placenta ranges from seven to twenty-two percent.

• Moreover, in the case of high-dose nondepolarizing neuromuscular blockade (for example, EXIT procedures), it may be essential to maintain neonatal ventilation or administer reversal agents.

Inhalation Agents:

• Desflurane and Sevoflurane, the inhalation agents, would be expected to surpass the placenta and equilibrate in fetal tissues faster than their more soluble counterparts (for example, Isoflurane), Desflurane and Sevoflurane, the inhalation agents, would be expected to surpass the placenta and equilibrate in fetal tissues faster than their more soluble counterparts (for example, Isoflurane), ultimately resulting in neonatal depression.

• Moreover, once the newborn develops ventilation, the lungs are expected to excrete ("blow off") these relatively insoluble drugs more rapidly. Desflurane has a strong, pungent smell and is more irritating to the airway, which can cause laryngospasm. Keep this in mind when suctioning a neonate whose mother has received Desflurane.

• When compared to Isoflurane 0.5 percent, Sevoflurane one percent produced comparable maternal and neonatal outcomes. Apgar scores and cord blood gasses were equivalent. Desflurane in a subanesthetic dose (three percent), mixed with Nitrous oxide to oxygen, was deemed safe and effective for use during surgery.

Regional Anesthesia (RA):

• Under normal maternal and fetal conditions, skilled GA and RA are nearly equal in terms of neonatal well-being. Despite this, considering the risks to the mother and the link between reducing Apgar scores and GA, RA for elective, and sometimes emergency, Cesarean section is desirable.

• When there is a high risk for Cesarean section, an altered fetus may benefit from predictive maternal epidural catheter placement in labor or primary epidural or spinal anesthesia for elective Cesarean section.

• RA reduces neonatal drug exposure (mainly when the spinal technique is used), enables the mother and her partner to take part in their baby's birth, and improves maternal postoperative pain relief.

• Despite the benefits of spinal anesthesia, such as its ease, rapid progression, lower risk of systemic toxicity, the density of anesthetic block, and postoperative pain relief provided by neuraxial Morphine, the possibility for hypotension with this method presents a significant risk to mother and fetus.

• The occurrence of low blood pressure (hypotension) is comparable between epidural and spinal anesthesia, but the spinal anesthesia method takes place earlier and more rapidly. Hypotension is caused by temporary sympathectomy, an unavoidable but unwanted side effect of mid thoracic blockade.

• Reduced preload and afterload resulted in nausea, lightheadedness, dysphoria, and decreased uteroplacental perfusion. Conversely, maternal symptoms are avoided when maternal mean arterial pressure is controlled and uteroplacental perfusion improves.

• Routine measures for maintaining uteroplacental perfusion include left lateral tilt position, lower leg compression stockings, and loading of intravenous fluids. vasopressor therapy uses hypotension.

• Prophylactic use of Ephedrine in one study and therapeutic use in another may have significantly contributed to fetal acidemia.

Fetal Effects of Maternal Oxygen Administration:

• Whether the process is elective, urgent, or emergent, offering supplemental oxygen to the patient is prevalent medically. This practice has been supported by the assumption that increasing the mother's oxygen reserve generally benefits the fetus.

• Since the introduction of pulse oximetry, patients who may benefit from oxygen therapy have been more easily identified, and clinicians have been more selective in using oxygen therapeutically.

• For example, pulse oximetry results obtained during a spinal anesthesia elective Cesarean section revealed that maternal saturation was well preserved on room air and administration of 35 percent oxygen through a facemask failed to alter umbilical vein pH (potential of hydrogen) or partial pressure of oxygen significantly.

Conclusion:

The health of the newborn is a significant indicator for determining pregnant women's obstetric and anesthetic care. The administration of analgesia or anesthesia to the mother may affect the newborn. The ideal agents and techniques would be productive and valuable for the mother, and would not endanger the newborn. The anesthesiologist's challenge is to achieve the needs of the mother and the fetus or newborn while remaining adaptable enough to modify or alter the strategy as conditions permit.