This study on the use of liquid nitrogen as a cryotherapeutic agent was, in a large measure, prompted by the questions of residents and interns: "With how much pressure, for how long, and what lesions should we treat?"
An attempt to develop an exact measurement time and pressure system was found to be beset with many variables. Therefore such a system would probably not replace the art involved in using cryotherapy.
A knowledge of the histopathology, vascularity, and preconceived depth of each lesion treated is necessary for the successful therapeutic use of cryoagents.
Kee CE. Liquid Nitrogen Cryotherapy. Arch Dermatol. 1967;96(2):198-203. doi:10.1001/archderm.1967.01610020090026