Blood Gas Analysis: Establishing the Normal Range for Elderly Patients. A Single Center Cohort Study

Interpretation of blood gases is essential for the correct practice of medicine. Normal ranges for arterial blood gases (ABG) have not been extensively studied in the older population. Also, venous blood gases and venous-arterial pCO2 gradient have not been studied in this population, even though they signify the majority of hospitalized patients.

To determine the normal range for ABG and the bias limits of agreement for arterial-venous difference in the elderly population.

We recruited 130 elderly patients (> 70 years) and obtained blood gas measurements from venous and arterial blood. Patients were divided into four categories: healthy patients, patients with stable chronic pulmonary disease, hospitalized patients with acute respiratory illness, and hospitalized patients without respiratory disease. Samples were analyzed in a point of care analyzer.

Mean PaCO2 was 36.9 ± 4.2 mmHg for the healthy control group, 37.0 ± 4.8 mmHg in the stable chronic respiratory group, 37.0 ± 5.0 mmHg in the non-respiratory hospitalization group, and 42.3 ± 11.4 mmHg for the respiratory hospitalization group, Kruskall-Wallis, P <0.0025. Mean bias between venous and arterial CO2 was +10.0 mmHg with 95% limits of agreement between 2.7 mmHg and -22.8 mmHg.

In elderly patients, the range of PaCO2 measurements was similar to the accepted normal range in clinical practice. Venous-arterial PCO2 gradient had high bias and wide limits of agreement, similar to previously published studies.