Obstetrics
Kristin M. Ondecko Ligda
Manuel C. Vallejo
INTRODUCTION
Airway management of parturient patients presents a challenge to the health care practitioner as two lives are being cared for at one time. Maternal complications such as failure to maintain an airway can contribute to fetal morbidity or even death.
In a review of the Centers for Disease Control and Prevention Pregnancy-Related Mortality Surveillance System, 2.5% of maternal deaths were attributed to anesthesia, and the most important cause (58%) of anesthesia-related maternal mortality was failure to maintain the airway.1 Although there have been significant advancements in airway management technology such as the laryngeal mask airway and the GlideScope, and in the development of the American Society of Anesthesiologists (ASA) Difficult Airway Algorithm, the obstetric patient continues to be at risk of failed intubation when compared with the general population.
During an evaluation of anesthesia-related maternal mortality between 1979 and 1990, general anesthesia presented a greater risk of maternal mortality than regional anesthesia. Maternal death occurred most frequently during cesarean delivery (82% of deaths). Of these, 52% of deaths were the result of complications from general anesthesia, which were attributed to hypoxia, difficult or failed intubations, or pulmonary aspiration.2
PREGNANCY-RELATED ANATOMIC AND PHYSIOLOGIC CHANGES
There are several pregnancy-related changes to the parturient’s anatomy and physiology that places her at increased risk for airway management difficulties (Fig. 53-1).
Weight gain: the average parturient gains approximately 12 kg or 17% of her prepregnancy body weight as the result of an increase in the size of the uterus, placenta, and fetus; an increase in blood and interstitial fluid volumes; and an increase in fat deposition.3 Increased body mass and obesity, in particular, increase the risk of the patient having a difficult airway and also the risk of emergency cesarean delivery.4
Enlarged breast tissue: Enlarged breast tissue, especially in the supine parturient, can affect the practitioner’s ability to manipulate the laryngoscope and obtain adequate laryngeal views and alignment of the laryngeal, pharyngeal, and mouth axes during intubation.5
Airway edema: Contributors to airway edema include higher estrogen levels and increased blood volume. Comorbidities such as preeclampsia or respiratory infections may also contribute to airway edema. These all can lead to mucosal edema of the nares, tongue, oropharynx, and larynx, in addition to engorgement of the capillary beds with mucosal friability. Tongue enlargement may also hinder adequate placement of the laryngoscope blade into the mouth and larynx. Airway edema may make placement of the endotracheal tube challenging, if not impossible.6,7,8,9 Hence, because of airway edema in the parturient, the best laryngoscopic intubation attempt is often the first attempt. Repeated attempts can often lead to further mucosal bleeding and subsequent intubation failure.
Risk of aspiration: The obstetric patient, due to increased levels of progesterone, experiences decreased lower esophageal sphincter tone. The gravid uterus also contributes to increase in intragastric pressures and distorts the anatomy of the lower esophageal sphincter, diaphragm, esophagus, and stomach. These all can contribute to gastroesophageal reflux throughout pregnancy.10,11,12 Additionally, advanced labor can contribute to delayed gastric emptying times. Although pain is thought to contribute to the delay, the delay in gastric emptying is still present even with an effective epidural anesthetic.13
Risk of hypoxia: Pregnancy induces changes to respiratory mechanics and physiology. Pregnancy has not been shown to change the FEV1, FEV1/FVC, flow-volume loops or closing capacity; however, pregnancy is known to increase diaphragmatic excursion and decrease chest wall excursion. The gravid uterus displaces the diaphragm, which contributes to a decrease in residual volume. Tidal volumes increase early in pregnancy, and increase up to 45% from prepregnancy values, which leads to increased minute ventilation.14 Oxygen consumption increases in pregnancy due to the increased metabolic requirements of the fetus and mother, alongside increases in carbon dioxide production, further contributing to the increase in minute
ventilation.15Related posts:
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