Abstract Rationale The oxygen dissociation curve (ODC) and the corresponding p50 value reflect changes in hemoglobin’s affinity for oxygen based upon factors such as pH, pCO2, and temperature. These factors are frequently altered in critically ill patients. Therefore, variations in p50 may correlate with illness severity. While prior studies in adults have shown inconsistent results regarding the implications of ODC shifts, data in pediatrics remains limited. Only one retrospective pediatric study exists to date that suggests higher p50 values are associated with greater disease severity and mortality. The aim of this study is to provide prospective data on the correlation between shifts in the ODC and severity of illness in critically ill pediatric patients. Methods This single-center, prospective observational cohort study included patients aged 0-18 years diagnosed with septic shock and/or pediatric acute respiratory distress syndrome (pARDS). p50 values were calculated from blood gases obtained upon diagnosis and for the following 7 days using the Hill equation. Primary outcomes included mortality, ventilator-free days, vasopressor-free days, and ICU-free days. The secondary outcome of organ dysfunction was assessed daily for seven days using Pediatric Logistic Organ Dysfunction-2 (PELOD-2) scores. Associations between p50 and the outcomes were evaluated using either linear or logistic regression. Repeated-measures correlations were calculated to assess the relationship between serial p50 values and daily PELOD-2 scores. Results Prospective data was collected on nineteen patients; 84% had pARDS and 26% had septic shock. The median p50 reference 24-28 mm Hg at diagnosis was 31.19 (SD 2.65 mm Hg) for patients with pARDS and 30.1 (SD 2.89 mm Hg) for patients with septic shock. Higher p50 values were significantly associated with higher PELOD-2 scores (β = 0.29, 95% CI 0.16-0.42, p 0.001); for every one unit increase in p50, the PELOD-2 score increased by 0.29. Repeated-measures analysis also demonstrated a significant positive within-subject correlation between p50 and PELOD-2 scores (r = 0.41, p 0.0001), suggesting that increases in p50 over time paralleled worsening organ dysfunction within individual subjects. The p50 value at diagnosis was not significantly associated with mortality, ventilator-free days, vasopressor-free days, or ICU-free days. Conclusions In this small cohort of 19 critically ill pediatric patients with pARDS and/or septic shock, p50 upon diagnosis was increased, and higher p50 values were associated with increased organ dysfunction. These findings suggest that P50 may reflect illness severity and warrant further investigation as a potential physiological biomarker in pediatric critical illness. This abstract is funded by: None
Vaughn et al. (Fri,) studied this question.