Oxyhemoglobin desaturation as a function of age and hypercapnia from ventilatory pump failure (VPF)

Abstract

Background:Supplemental O2 is often administered without knowledge of CO2 levels for patients with ventilatory pump failure (VPF). This can render oximetry ineffective as a gauge of alveolar ventilation, airway secretions, and lung disease. We have noted that diurnal hypoventilation with hypercapnia tends to be symptomatic when O2 saturation levels decrease below 95% and patients extend sleep noninvasive ventilatory support (NVS) into daytime hours. We also noted that with advancing age, less hypercapnia results in desaturation. This study was designed to explore oxyhemoglobin desaturations (O2 desats) as a function of age and hypercapnia for patients with VPF.Methods:A retrospective analysis of 8933 consecutive patient visits for whom end-tidal CO2 and O2 sats were measured. O2 sats < 95% at CO2 levels of 45, 50, and 60 cmH2O were correlated with 10 years age intervals to age 80.Results:Of 8933 visits, 8642 had complete data. Outcomes for CO2 levels > 50 cmH2O were the most significant including for visit-ages < 30 and ≥ 30 years. There was a statistically significant 4% decrease in the odds of O2 desat for every one-year increase in age to age 30 (OR = 0.96, 95% CI = [0.93, 0.99], p = 0.02) and for visit-ages ≥ 30 a significant 30% increase in the odds of O2 desat for every 10-year increase in age (OR 1.3, 95% CI = [1.1, 1.6], p = 0.006). Relationship for ages ≥ 30 years were also significant for CO2 levels over 45 mmHg also. 40% of the time when CO2 was greater than 45 mmHg O2 sat was low.Discussion:This study demonstrated a significantly lower risk of O2 desat occurring at EtCO2 levels ≥ 50 mmHg for patients from 10 to 20 years of age than those younger than 10 and a significantly greater risk of O2 desat for 10 years intervals after age 20. Thus, with age, less hypercapnia results in desats and dyspnea with patients tending to extend NVS into daytime hours. This may be due to increases in physiological shunting, decreased pulmonary elasticity, and worsening ventilation/perfusion ratios with age.