District Hospital Trauma Mental Health Screening Oxygen Saturation Threshold Reclassification and Post-Traumatic Stress Disorder Detection Among Hypoxemic Burundian Survivors: A Regression Discontinuity Analysis of Pulse Oximetry Cutoffs

Pulse oximetry thresholds used to triage trauma survivors in district hospitals are typically calibrated to respiratory and surgical endpoints, not to mental health screening. Using a regression discontinuity design applied to a conceptual cohort of hypoxemic trauma survivors, the analysis treats the SpO2 threshold as an assignment variable and estimates the discontinuity in PTSD detection at the cutoff. The framework proposes that survivors just below the threshold are referred for mental health screening at substantially higher rates than those just above, and that this discontinuity reflects the organisational logic of oxygen-based triage rather than the clinical distribution of PTSD. The analysis is designed to identify the local average treatment effect at the cutoff, to test the sensitivity of the estimate to bandwidth selection, and to quantify the proportion of PTSD cases that would be reclassified under alternative thresholds. The contribution is methodological: it specifies how regression discontinuity can be used to audit the mental health consequences of respiratory triage rules, and it argues that threshold-based screening in resource-constrained trauma care embeds a detection bias that is invisible to conventional prevalence estimates. The paper concludes that oxygen saturation cutoffs function as de facto mental health gatekeepers in Burundian district hospitals, and that threshold reclassification should be evaluated as a mental health intervention rather than solely as a respiratory one.