Tachypnea in response to hypoxemia decreases with age in older patients

To investigate if tachypneic response to hypoxia is decreased in older patients.

We included all patients ≥65 years of age attending 52 Spanish emergency departments (EDs) for whom peripheral arterial oxygen saturation (SatO₂) measured by pulsioxymetry and respiratory rate (RR) were registered at ED arrival. We assessed the relationship between SatO2 and RR in different models, and with the best-fitting model, we independently analyzed this relationship in four subgroups according to patient age (65-69, 70-79, 80-89, and ≥90 years). Five sensitivity analyses using different subsets of patients were carried out to check for the consistency of the results.

We included 7126 patients, with medians for SatO₂ and RR of 97% (interquartile range [IQR]: 94-98) and 15 bpm (IQR: 15-16), respectively. We found significant associations (P < 0.001) between SatO₂ and RR in every model tested (P < 0.001 for all), with the quadratic model obtaining the best fit (R²: 0.098) over those obtained with linear (R²: 0.096) and logarithmic (R²: 0.092) models. The same was observed in sensitivity analyses, with R² for quadratic models ranging from 0.069 in patients with low comorbidity and 0.102 in patients breathing room air. The mean RR for 100% SatO₂ was 15 bpm and increased as SatO₂ decreased, although with a progressive slowing of the slope, with a mean RR of 27 at 50% SatO₂. We detected a decreased RR response to increasing hypoxemia according to age and, while the RR curve was higher and with a progressively steepening slope in the 972 patients aged 65-69 (mean RR of 42 bpm with 50% SatO₂), a progressive slowing of slope was observed in the 2693 patients aged 70-79 (mean RR of 28 with 50% SatO2), the 2582 aged 80-89 (mean RR of 25) and the 879 aged ≥90 (mean RR of 23). Sensitivity analyses provided very similar results.

Tachypneic response to hypoxemia in older patients decreases as age advances, regardless of the reason leading to hypoxemia. Geriatr Gerontol Int 2024; 24: 1120-1129.