Swallowing topically administered 4% lidocaine results in nausea and vomiting

In preparing adult volunteers for insertion of an upper airway device, we observed a high incidence of nausea and vomiting in the first 16 consecutive volunteers who were allowed to swallow topically administered 4% lidocaine (50% and 31%, respectively). We tested the hypothesis that swallowing the topically administered 4% lidocaine caused the nausea and vomiting by comparing the incidence of nausea and vomiting in these first 16 volunteers with the incidence of nausea and vomiting in the next 162 consecutive awake adult volunteers who were not allowed to swallow the 4% lidocaine. All 178 volunteers were prepared by administering 2 mg midazolam and 100 micrograms fentanyl intravenously, spraying 10 to 15 mL of 4% lidocaine into the upper airway, and bilaterally blocking the lingual branch of nerve IX and the superior laryngeal branch of nerve X. The first 16 volunteers were allowed to swallow the 4% lidocaine (swallow/no suction, group A); the next 162 volunteers were not allowed to swallow the 4% lidocaine, and all of the 4% lidocaine was suctioned out of the upper airway (no swallow/suction, group B). Groups A and B were otherwise and subsequently treated identically. The incidence of nausea and vomiting in group A was 50% (8/16) and 31% (5/16), respectively, and in group B, 4% (7/162) and 1% (2/162), respectively. The difference in the incidence of nausea and vomiting between group A and group B was highly significant by chi-square analysis (P < 0.01). We found that swallowing topically administered 4% lidocaine results in a significant increase in the incidence of nausea and vomiting. Our experimental design did not allow us to rule out either of two basic mechanisms, higher blood levels and a direct toxic effect, or to distinguish between them. The clinical implication of this study is that suctioning all topically administered 4% lidocaine will decrease the incidence of nausea and vomiting.