To evaluate the use of heart rate variability as a potential predictor of clinical outcomes, a prospective exploratory study was conducted with 120 patients in the first 24 h of the intensive care unit (ICU). Autocorrelation analysis was performed on the RR interval series (RR) from electrocardiograms. SD1, SD2, S, and SD21 indices were determined using the Lagged Poincaré Plot (LPP). The results showed that the LPP, performed within 6 h of ICU admission, significantly discriminated Survivors from Non-Survivors using SD1. Although the autocorrelation decreased with increasing lag k, the differences between groups did not reach statistical significance. The most important limitation of this study is the small number of cases. Despite these limitations, the findings support the idea that the LPP SD1 index could be used alongside traditional monitoring systems to analyze patient outcomes and make more accurate predictions of adverse outcomes in ICUs.