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

Area of Science:

• Geriatric Medicine
• Respiratory Physiology
• Clinical Pathology

Background:

• Accurate interpretation of blood gases is crucial in medical practice.
• Normal ranges for arterial blood gases (ABG) are not well-established in the elderly.
• Venous blood gases and the venous-arterial pCO2 gradient require investigation in older populations.

Purpose of the Study:

• To determine the normal range for arterial blood gases (ABG) in the elderly.
• To assess the bias and limits of agreement for the arterial-venous difference in CO2 in older adults.

Main Methods:

• Recruited 130 patients aged over 70 years.
• Obtained simultaneous venous and arterial blood gas measurements.
• Categorized patients into healthy, stable chronic pulmonary disease, acute respiratory illness, and non-respiratory hospitalization groups.

Main Results:

• Mean PaCO2 values were comparable across healthy, stable COPD, and non-respiratory hospitalized groups, but elevated in respiratory hospitalization (42.3 ± 11.4 mmHg).
• Mean bias between venous and arterial CO2 was +10.0 mmHg.
• 95% limits of agreement for the venous-arterial CO2 difference ranged from 2.7 mmHg to -22.8 mmHg.

Conclusions:

• Elderly patients exhibit PaCO2 ranges similar to established clinical norms.
• The venous-arterial PCO2 gradient in the elderly demonstrates high bias and wide agreement limits.
• Findings suggest caution when inferring arterial from venous CO2 in older individuals.