Final answer:
Alcohol-based solutions are contraindicated for surgical prep when electrocautery is used due to flammability. Current flows from the sharp edge of the scalpel in electrocautery, and high-frequency AC is used to reduce electric shock risks.
Step-by-step explanation:
The solution that is contraindicated as a surgical prep if electrocautery is being used during the procedure is one that contains alcohol. This is because alcohol-based preparations are flammable and can pose a fire risk when used in conjunction with electrocautery, which involves the use of electric currents. Most of the current from an electrocautery device flows from the sharp edge of the scalpel due to the higher electric field intensity at points with smaller radii, which is characteristic of sharp edges. Typically, high-frequency AC is employed in electrocautery to minimize the risk of electrical shock and to ensure that the current tends to flow over the surface of the body rather than through it (skin effect).