Introduction

In the first half of the last century, the morbidity rate of neurosurgical operations in critical brain areas was almost 100% along with a high mortality rate. At that time, the primary concern was to preserve life. Microsurgery and modern imaging have led to a decisive reduction in mortality and morbidity. Thus, neurosurgery was no longer so much a matter of preserving life, but rather of preserving function in the sense of functionally oriented surgery. Despite these technical advances, there remained a significant risk of neurological complications, which is also true for ENT, orthopedic, vascular, or even general surgical procedures whenever nervous structures are involved. Intraoperative neuromonitoring (IONM) has proven to reduce and minimize the risk of neurological deterioration under general anesthesia and is now a standard part of numerous procedures on the nervous system, thus ushering in a new era, the era of functionally guided surgery.