Decompressive craniectomy (DC) primarily aims at decreasing intracranial pressure (ICP) by allowing for the brain tissue to expand. However, it is uncertain to what extent DC impacts the transmission of vasogenic slow waves and thus the validity and utility of the pressure reactivity index (PRx). The purpose of this systematically performed scoping review is to assess the current knowledge of the impact of DC on ICP waveforms and measures of vascular reactivity. This scoping review considered studies including patients over 18 years old suffering from acute brain injuries (ABIs), who underwent secondary DC and had a perioperative (pre/post-DC) recording of ICP or waveform analysis. A search was conducted in EMBASE, PubMed, Web of Science, Scopus, and Medline from November 2023 till January 2024, yielding 787 studies. Duplicated studies were automatically removed, and two researchers independently screened the remaining studies. After examining 586 titles and abstracts, 38 full-text studies were assessed for eligibility, and 4 studies were included in the final review. The review suggests that cerebrovascular reactivity and slow waves are altered after DC, with positive PRx values and reduced slow power. One study suggested that the nature of slow waves and interactions is on the whole largely preserved. However, the findings should be interpreted with caution due to methodological limitations and the low number of studies.