"ISA"-Information System Anesthesia-will support the anesthesiologist by presenting information concerning the anesthesia approach. In addition to computing patient data (monitoring), there are three special fields where computers are used in anesthesia: (1) simulation systems for anesthesia training (preventing critical incidents); (2) critiquing systems to comment on the planned anesthesia decisions; and (3) reference systems for rapid information gathering. Simulation and critiquing systems are mainly useful for personal training. Reference systems present information concerning the anesthesia problems to aid in decision-making. ISA is a reference system designed to support the decision process for neurosurgical operations; a new method of presenting information by personal computer in the surgical working area. For each neurosurgical operation there is a graduation of condensed and detailed information with the option of also obtaining general anesthesia knowledge.