Nitrous Oxide for External Cephalic Version

Inclusion Criteria: * Female 18 years or greater * Scheduled to undergo external cephalic version due to singleton breech presentation * Not scheduled to have spinal or epidural anesthesia during the version procedure * American Society of Anesthesiology (ASA) Physical Status 1, 2 or 3. * Able to provide informed consent and adhere to study protocol Exclusion Criteria: * Current or historical evidence of any clinically significant disease or condition, especially cardiovascular or neurological conditions that, in the opinion of the Investigator, may increase the risk of exposure to nitrous oxide or complicate the subject's post-procedural course. * Significant medical conditions or laboratory results that, in the opinion of the Investigator, indicate an increased vulnerability to study drugs and procedures.