Monitoring Within-Person Dynamics in Adolescents Hospitalized for Acute Suicidal Distress: Protocol for an Intensive Longitudinal Study

Background Adolescence represents a developmental period marked by heightened vulnerability to suicidal thoughts and behaviors (STBs), which remain a leading cause of death among youth, particularly psychiatric inpatients and after discharge. Contemporary ideation-to-action models conceptualize suicidal crises as dynamic processes driven by proximal psychological factors rather than static risk markers. While recent work has begun to examine these processes as they unfold in daily life, their integration into the clinical course of suicidal distress remains limited. From this perspective, relating short-term microlevel processes of STBs to their broader temporal changes across the transition of adolescents from acute inpatient hospitalization to early ambulatory aftercare constitutes an important area for further investigation. Objective This protocol describes a multimodal, intensive longitudinal study examining the temporal unfolding of suicidal distress across complementary timescales. The integrative framework aims to identify prototypical trajectories of STBs from inpatient admission through the early postdischarge period. It further seeks to characterize heterogeneity in within-person processes central to ideation-to-action theories and STB-related affect regulation. Finally, the study aims to interrelate these microlevel dynamics of suicidal distress with its longitudinal trajectories at the macrolevel. Within this framework, the study examines how modifiable bioregulatory factors, including sleep and physical activity, as well as clinical process factors such as therapeutic alliance, are dynamically implicated across timescales. Methods The study plans to recruit 100 adolescents hospitalized at a single site in French-speaking Switzerland. Within 72 hours of admission, participants start a first assessment period of up to 14 days, comprising 4 daily Ecological Momentary Assessment (EMA) surveys and continuous actigraphy recordings. A second assessment period follows participants for the 10 days after discharge and includes 2 daily EMA surveys. In addition, 4 in-person assessment sessions contextualize the intensive longitudinal time series with baseline clinical characteristics, diagnostic status, therapeutic processes, and episodic stressors. Planned analyses will use multilevel and latent class modeling approaches to identify longitudinal patterns of STBs, characterize between-person differences in within-person dynamics, and examine how these patterns relate to contextual factors. Results Recruitment began on October 31, 2025, and is expected to continue until June 2028. The protocol was developed through the active integration of former patients’ perspectives and clinicians’ lived experience. Feedback from the first 5 participants supported the current implementation of the protocol. Conclusions By focusing on the link between intraindividual short-term processes and clinical trajectories of STBs, this study will advance our understanding of how STBs and related psychological and behavioral processes interact over time during a critical period of distress. These insights aim to inform targeted, person-centered approaches to acute psychiatric care, offering better support for vulnerable adolescents transitioning from inpatient to outpatient care. International Registered Report Identifier (IRRID) DERR1-10.2196/93016