There has been increasing pressure to liberalize oral intake during the active stage of labor. This has potentially disastrous consequences for patients with comorbid disease or those needing an emergent general anesthetic. Nothing by mouth (NPO) policies were first introduced on labor and delivery wards in the late 1940s and early 1950s. The hope was that by making patients NPO, the devastating consequences of pulmonary aspiration of gastric contents could be avoided if general anesthesia becomes necessary. Curtis Mendelson, MD (who was actually an obstetrician, not an anesthesiologist), first illustrated the dire consequences of aspiration in 1946. In his study of more than 44,000 pregnancies, 66 women experienced pulmonary aspiration of gastric contents. Of these 66, only 2 died, and the suggested cause of death was asphyxiation by solid food. Those who developed aspiration pneumonitis survived. This may be a good point to emphasize—volume, pH, and particulate matter are the main determinates of pulmonary injury and outcome following aspiration.

Factors that increase the risk of aspiration for the laboring woman can be broken down into two broad categories. First are the physiological changes due to pregnancy. These changes start in the second trimester. Increasing intragastric pressure is due to the expanding uterus. At the same time, the lower esophageal sphincter is pushed up and to the left, a similar situation to a hiatal hernia. Sphincter tone is decreased due to circulating hormones, mainly progesterone. This leads to an incredibly high incidence of gastric reflux in pregnant women, even if asymptomatic. Gastric pH becomes more acidic as the placenta begins to produce gastrin. The active phase of labor slows gastric emptying. It should be noted, however, that pregnancy, by itself, appears to have no effect on gastric emptying.

Second are the difficulties that laboring women present in airway management. It is well known that the morbidity and mortality associated with anesthesia in pregnant women are primarily related to difficulties in controlling the airway and intubation. The airway is more edematous with increased vascularity and friability. Young women tend to have intact dentition. Increase in breast size during pregnancy and the gravid abdomen make positioning of the laryngoscope difficult at best.

So, we have a situation in which there is an increased gastric volume, decreased pH, and delayed gastric emptying during the active phase of labor. The good news is that there have been advances in anesthetic techniques since 1946. The advent of rapid sequence intubation with cricoid pressure in the 1970s and the more heavy reliance on regional techniques may have played a role in the decline seen in maternal deaths since Mendelson’s study. In addition, treatment with H₂ blockers and nonparticulate antacids may have helped. There has been increased training of anesthesiologists since that time as well. If we couple these with NPO guidelines, it would seem that we are following the Hippocratic Oath to do no harm. Or are we?