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A 25-year-old primigravida at 39-week gestational age presents to the case room with ruptured membranes and frequent uterine contractions. She does not want to have epidural analgesia because of a story she heard about an epidural complication suffered by one of her distant relatives. After 14 hours of labor, augmented with oxytocin, and now 2 hours of pushing, she is urgently taken to the operating room for emergency cesarean section, for prolonged late decelerations. She weighs 253 lb (115 kg) and is 5 ft 3 in (160 cm) tall, giving her a BMI of approximately 45. Airway examination reveals a Mallampati Class III and a thyromental distance of 5 cm. She has a full neck extension with normal dentition and a normal mouth opening. She has large gravid breasts. Her blood pressure is 128/68 mm Hg, heart rate 100 beats per minute (bpm), respiration rate 20 breaths per minute, and SaO2 of 99% on a 100% O2 rebreathing face mask. On arrival in the operating room, the fetal heart rate is 80 bpm.
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51.2.1 What Are the Anesthetic Options for Cesarean Section in This Patient?
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An emergency cesarean section is mandated to deliver the fetus with persistent bradycardia (late deceleration), while minimizing potential/preventable risk to the mother. Anesthesia risk factors for airway management in this patient include her BMI (45 kg·m−2) and enlarged breasts. Although regional anesthetic techniques have become the standard of anesthetic care for operative delivery in obstetrics,1 this patient has refused the regional approach.
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The concerns for emergency cesarean section under general anesthesia include securing the airway, reducing the sympathetic response to laryngoscopy and intubation, adequate fluid resuscitation, and the potential of blood loss due to volatile-agent-induced uterine atony. With respect to the first of these concerns, all labor and delivery facilities must have a difficult airway cart and contingency plans for failed laryngoscopic intubation.1
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51.3.1 What Are the Airway Considerations in Pregnant Women?
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Pregnancy is associated with fluid retention and weight gain.2 Mallampati Class III and IV seem to be more prevalent in parturients at the beginning of labor (28%) than in the general adult population (7%-17%), suggesting that tongue volume increase maybe one of the physiologic changes of a normal pregnancy.3 Structurally, the pharyngeal airway is surrounded by soft tissues, such as the tongue and soft palate, which are enclosed by bony structures, such as the mandible and spine. Size of the airway space is determined by the balance between the bony enclosure space and soft tissue volume, when pharyngeal muscles are inactivated by general anesthetics and muscle relaxants. Pharyngeal edema, presumably due to fluid retention during pregnancy, and pharyngeal swelling acutely developed during labor, increases the soft tissue volume surrounding the airway, narrowing the pharyngeal airway in parturients.2 Many have hypothesized on predictors of this event including weight gain during the pregnancy, fluid ...