Anesthetic Management of a Pregnant Patient Undergoing Oral Surgery

Abstract

Urgent or emergent dental or oral and maxillofacial surgery procedures are acceptable at all stages of pregnancy and encouraged for maintaining the overall wellness of parturients. However, the risks and benefits of nonobstetric surgical procedures under general anesthesia should be weighed carefully because pregnant patients experience significant physiologic remodeling, and many anesthetic drugs and techniques may cause inhibition of fetal development as well as preterm labor and delivery. This case report discusses the choice of anesthetic technique based on the changes in maternal physiology, maintenance of adequate uteroplacental perfusion, avoidance of potentially dangerous drugs during fetal development, and prevention of preterm labor and delivery to ensure maternal safety and maintenance of pregnancy. The case presented highlights the importance of a multidisciplinary approach to ensure adequate anesthetic management in pregnant women.

Women can present with dental or oral surgical needs during pregnancy that require intervention. Such treatment can be considered acceptable at all stages of pregnancy when necessary and can be encouraged to help maintain the overall wellness of the parturient. However, the risks and benefits of providing dental or oral surgical interventions under general anesthesia should be weighed carefully, as pregnant patients experience significant physiologic remodeling that may complicate care.¹

Additionally, animal models have revealed that some general anesthetic agents have been associated with inappropriate neuronal apoptosis and behavioral deficits later in life. However, whether these same concerns exist with the human fetus remains unknown.²

Therefore, if pregnant patients have urgent or emergent dental needs that require treatment under general anesthesia, care should be taken during general anesthesia to promote the well-being of and minimize the risks to the mother and the developing fetus. Considering that virtually all general anesthetic agents cross the placental barrier and the noted variability in recommendations on what drugs to use or avoid, no optimal general anesthetic technique has been established for use in pregnant patients.²

Herein, we present the case of a pregnant woman who underwent oral surgery with general anesthesia and discuss specific anesthetic considerations for such patients.

CASE PRESENTATION

A 32-year-old woman (height, 160 cm; weight, 50 kg; body mass index, 19.5 kg/m²) who was 25 weeks pregnant was diagnosed with lymph node metastasis in the left neck about 1 year after partial glossectomy for squamous cell carcinoma of the tongue. Therefore, it was planned for her to undergo a neck dissection under general anesthesia at our institution.

The patient had no notable findings in her medical and surgical history other than the partial glossectomy and denied taking any medications or having any drug allergies. Although she had had a partial glossectomy, her tongue movements were satisfactory, and she was able to eat, speak, and swallow without issue. However, she was not gaining weight well despite being pregnant. Assessment of her airway did not reveal any major risk factors that suggested difficulties in managing her airway.

During the preoperative evaluation, her blood pressure and heart rate readings were 108/73 mm Hg and 91 beats/min in the sitting position, 100/71 mm Hg and 89 beats/min in the left lateral position, and 110/68 mm Hg and 87 beats/min in the right lateral position. Her preoperative blood tests showed mild anemia with a red blood cell count of 3.75 × 10⁶/µL, hemoglobin level of 11.6 g/dL, and hematocrit of 34.3%. No cardiac abnormalities were noted in her preoperative 12-lead electrocardiography. Routine chest radiography and spirometry were not performed due to her being pregnant. The fetus had no signs or symptoms of preterm labor preoperatively and had a baseline heart rate of 150 beats/min. Fetal movements were good, and the fetus’s overall condition was otherwise normal.

An oral surgeon and obstetrician were consulted to help develop the following treatment plan. First, the right neck dissection under general anesthesia was scheduled promptly because the patient was 25 weeks pregnant. The baby was scheduled for a cesarean delivery to occur after 31 weeks of gestation. Finally, chemotherapy and radiotherapy were scheduled to begin following delivery.

For the right neck dissection surgery, the patient was not administered any premedication. Standard anesthesia monitoring was started after the patient arrived at the operating room and consisted of a noninvasive blood pressure cuff on the left upper arm, an electrocardiogram (lead II), a peripheral thermometer, pulse oximetry, and capnography. Her heart rate (89 beats/min), blood pressure (108/70 mm Hg), temperature (35.8°C), and saturation of percutaneous oxygen (98%) were recorded before anesthesia induction. A 20-gauge intravenous (IV) cannula was inserted into the dorsum of her left hand to infuse a Ringer acetate solution, and the patient was placed in the reverse Trendelenburg position before anesthesia induction.

After 5 minutes of preoxygenation with 100% oxygen via face mask, general anesthesia was induced using propofol (70 mg) and a continuous IV infusion of remifentanil (0.5 μg/kg/min), which was infused over 2 minutes. After confirming loss of consciousness, IV rocuronium (30 mg) was administered, and oral intubation was performed using a McGrath video laryngoscope. After confirming successful intubation of the patient, general anesthesia was maintained with sevoflurane (1.5%), oxygen (1 L/min), and air (2 L/min) along with an infusion of remifentanil (0.25 μg/kg/min).

Depth of anesthesia was assessed during the case using an entropy monitor (GE HealthCare Entropy, GE Healthcare), which is an electroencephalography-based monitor used for determining hypnotic and analgesic levels. This specific monitor showed both the state entropy (SE) and response entropy (RE) values. The recommended range for adequate depth of general anesthesia regarding each parameter (SE and RE) was 40 to 60, and per the patient’s anesthetic record, both SE and RE values varied from 40 to 60 units during the anesthetic.

Assessment of the patient’s blood pressure after induction revealed hypotension (blood pressure, 78/50 mm Hg; heart rate, 100 beats/min). Subsequently, IV phenylephrine (0.1 mg) was administered, and a modest fluid challenge of Ringer acetate solution (100 mL) was rapidly infused.

During anesthesia, her preoperative systolic blood pressure was maintained at approximately (100 mm Hg), and her end-tidal carbon dioxide tension (EtCO₂) was between 30 mm Hg and 35 mm Hg. To avoid aortocaval compression, the patient was positioned at 15° left lateral tilt. Before the operation, 10 mL of 1% lidocaine with 1:200,000 epinephrine was used for infiltration anesthesia (total dose, 100 mg of lidocaine and 0.05 mg of epinephrine). Local anesthetic was administered slowly 2 times (ie, 5 mL + 5 mL), to minimize any major hemodynamic changes before the surgery.

Her hemodynamic parameters and other vital signs were stable throughout the procedure. The surgery was completed in 5 hours and 5 minutes.

To prevent postoperative vomiting and subsequent aspiration, gastric suctioning was performed before extubation. After adequate spontaneous ventilation and full recovery from neuromuscular blockade were confirmed, the patient was extubated and admitted into the ward, where she was awake and had stable vital signs. Fetal monitoring by an obstetrician did not show any abnormal signs or symptoms postoperatively. Acetaminophen (1000 mg) was administered twice a day to reduce postoperative pain. The patient was discharged from the hospital without any complications on postoperative day 9. A month after surgery, the baby was delivered safely by cesarean section, and then her chemotherapy and radiotherapy were started as planned.

DISCUSSION

During pregnancy, 1% to 2% of women undergo nonobstetric surgeries, including appendectomy, surgery for cancer, and orthopedic procedures.³ However, nonobstetric surgeries under general anesthesia during pregnancy are associated with spontaneous abortion and low birth weight.³ Although a recent study reported that the risks associated with general anesthesia for nonobstetric surgeries are relatively low and surgical procedures during pregnancy are generally safe,⁴ anesthesiologists should take care to perform as safe an anesthetic as possible to maximize the well-being of the mother and fetus.

The timing of nonobstetric surgeries is related to fetal outcomes. Miscarriage rates increase for surgery in the first trimester, and exposure to teratogens can cause major structural organ abnormalities because organogenesis primarily occurs between the third and eighth weeks. In the third trimester, potential difficulties in maternal airway management must be considered, as pregnant women have a significantly higher rate of failed or difficult intubations vs nonpregnant woman. Furthermore, the more advanced the pregnancy is, the higher the risk of uterine irritability and preterm labor. Therefore, the second trimester is generally preferred for surgical procedures that cannot be delayed until after delivery, as this period minimizes the risks for preterm labor and delivery, fetal growth retardation, and structural abnormalities caused by drug exposure.⁵ In the present case, the patient was 25 weeks pregnant when she was diagnosed with lymph node metastasis. Therefore, her urgent surgery was scheduled in a week so as to occur within the second trimester.

General anesthetic techniques for pregnant patients undergoing nonobstetric procedures should be selected based on maternal physiological changes. When the patient is placed in the supine position, the gravid uterus compresses the lungs, reducing the functional residual capacity by 20%, which along with the increased oxygen consumption rate contributes to a rapid decrease in maternal oxygen saturation during brief apnea.⁶ In addition, soft tissue changes during pregnancy can lead to difficulties during intubation. Although a higher incidence of intubation failure during anesthesia induction in pregnant patients has been debated, not all pregnant patients are difficult to intubate.^7–11 However, intubation failure is the most common cause of anesthesia-related maternal mortality.¹² To avoid these issues in the present case, the patient was placed in the reverse Trendelenburg position prior to anesthesia induction, and she was preoxygenated using 100% oxygen via face mask for 5 minutes. In addition, the McGrath video laryngoscope was used to facilitate visualization of the vocal cords and increase the potential for successful intubation.

When the patient is placed in the supine position after 20 weeks of gestation, the gravid uterus compresses the inferior vena cava,¹³ which can result in severe hypotension and impaired uteroplacental perfusion. The patient in the present case was positioned at 15° left lateral tilt to mitigate this risk during the surgery even though her preoperative blood pressure did not change when she was placed in the right lateral position.

Hypoventilation and hypercapnia can also result in impaired uteroplacental perfusion. Minute ventilation is increased (ie, hyperventilation) in pregnant women because the pregnancy-induced reduction in functional residual capacity combined with a rise in oxygen consumption lowers the mother’s oxygen reserve. This increases arterial CO₂ (PaCO₂) levels in the mother, which can also impair CO₂ discharge from the fetus. Thus, the use of nonpregnant ventilatory patterns in pregnant patients may result in respiratory acidosis in the fetus and the mother.^14,15 Therefore, positive-pressure ventilation was used with care, and the EtCO₂ level was maintained between 30 mm Hg and 35 mm Hg, which corresponds with normal PaCO₂ values for the second trimester.

Intraoperative electronic fetal monitoring was not performed in this case because the American College of Obstetricians and Gynecologists (ACOG) Committee on Obstetric Practice acknowledged that its use did not generate data to support specific recommendations regarding nonobstetric surgery and anesthesia in pregnancy. Furthermore, the ACOG states that the decision to use fetal monitoring should be individualized. However, those guidelines also recommend monitoring electronic fetal heart rate and contractions before and after the procedure to assess fetal well-being and ensure the absence of contractions.¹⁶ Thus, we complied with the ACOG guidelines by assessing the fetus preoperatively and postoperatively.

Anesthetic drugs can affect cell signaling, mitosis, and DNA synthesis. Thus, any anesthetic drugs administered during pregnancy could negatively affect fetal development.^17–19 However, the ACOG Committee on Obstetric Practice states that none of the currently used anesthetic drugs have caused teratogenic effects on humans when used in standard concentrations at any gestational age.¹⁶ Moreover, we assumed that the anesthetic drugs used perioperatively were unlikely to induce teratogenic effects due to the patient being in the second trimester (ie, 25 weeks pregnant). However, it remains a possibility that these drugs could induce some fetal dysfunction. In fact, the US Food and Drug Administration (USFDA) warned of impaired brain development following exposure to certain anesthetic agents used for general anesthesia, namely the inhalational anesthetics isoflurane, sevoflurane, and desflurane and the IV agents propofol and midazolam.²⁰ Although the pregnancy risk categories recommended by the USFDA were commonly referenced when selecting anesthetic drugs for pregnant patients, the USFDA discontinued these categories in 2014 and replaced them with narratives organized by sections and subsections intended to better describe associated risks.

Therefore, drugs were chosen in this case based on the Australian risk categorization of drug use in pregnancy.²¹ In the Australian categorization, remifentanil and propofol are classified as category C, drugs that may cause harmful effects on the human fetus or neonate without causing malformations. However, they have been widely used during pregnancy with an acceptable safety record.²² Therefore, these drugs were used in the present case. In addition, the electroencephalography-based entropy monitor was used to assess the hypnotic and analgesic effects of anesthetics for optimal drug administration.

Ephedrine and phenylephrine for treating maternal hypotension have been discussed in previous reports. Advantages of ephedrine include a long history of use and a low propensity for uteroplacental vasoconstriction. However, ephedrine may cause maternal tachycardia and depress fetal pH and base excess. Although phenylephrine can treat hypotension without causing fetal acidosis, it may decrease the maternal heart rate.^2,23 These concerns may not be valid for a single IV dose of ephedrine or phenylephrine used to treat maternal hypotension during nonobstetric surgery because these risks are primarily discussed in spinal anesthesia for cesarean delivery cases, and the half-lives of these drugs are short. In this case, IV phenylephrine was administered for hypotension after induction of general anesthesia because the mother’s heart rate was relatively high, thus phenylephrine was indicated as opposed to ephedrine.

Although previous studies^24,25 reported an increased incidence of preterm labor and delivery after nonobstetric surgery, to the best of our knowledge, a specific anesthetic drug and/or technique has not yet been reported to influence preterm labor and delivery. The efficacy of tocolytics for preventing preterm labor and delivery during and after nonobstetric surgery is debatable; however, some studies have reported that volatile anesthetic agents may help relax the uterus.^22,26 Therefore, sevoflurane was selected as the anesthetic agent in this case. Postoperative pain can cause stress in pregnant patients and consequently increase the risk of premature labor. However, nonsteroidal anti-inflammatory drugs may cause premature closure of the ductus arteriosus,²⁷ and opioid drugs can lead to opioid-induced hypoventilation. Therefore, acetaminophen was used as an analgesic after surgery. The acetaminophen worked well for this patient, and she did not require any other analgesics postoperatively.

Pregnant women are at a higher risk of regurgitation and aspiration because progesterone lowers the tone of the esophageal sphincter and the gravid uterus compresses the stomach.²⁸ Therefore, the administration of H₂-receptor antagonists and rapid-sequence induction with cricoid pressure is recommended.⁵ However, no evidence shows that this approach decreases the risks of regurgitation and aspiration.^29,30 In addition, a previous study reported that anesthesia-related maternal deaths caused by airway obstruction or hypoventilation occurred during emergence and extubation and not during anesthesia induction.³¹ Therefore, in the present case, gastric suctioning was performed before extubation to empty the stomach.

CONCLUSION

In this study, we reported on the anesthetic management of a pregnant patient undergoing urgent oral surgery. General anesthesia was utilized for this patient, emphasizing the selection of an anesthetic technique that considered changes in maternal physiology, maintenance of adequate uteroplacental perfusion, avoidance of potentially dangerous drugs during fetal development, and avoidance of preterm labor and delivery. These strategies helped ensure maternal safety and maintenance of the pregnancy. A multidisciplinary approach is highly recommended to ensure adequate anesthetic management of pregnant patients undergoing general anesthesia for urgent oral surgery procedures.