Effect of body position on arterial oxygen tension in the elderly

Background. It is well known that body position can have an effect on gas exchange though the magnitude of this effect has not been studied thoroughly in the elderly. Objectives: This study analyzes the effect body position change has on arterial oxygen tension (PaO2) and arterial carbon dioxide tension (PaCO2) in healthy elderly. Methods: We tested 46 'lung-healthy' elderly, including 30 women and 16 men, 67-88 years of age. Blood was drawn from the radial artery first in the sitting position and subsequently in the supine position. Spirometry was performed. Results: Mean (SD) sitting PaO2 was 10.53 kPa (1.22), whereas mean supine PaO2 was 9.85 kPa (1.33). The difference between sitting and supine PaO2 was 0.68 kPa (0.86) and was statistically significant. Sitting PaCO2 was 5.06 kPa (0.47) and supine PaCO2 was 5.05 kPa (0.54). The difference between sitting and supine PaO2 correlated positively with FEV1/FVC %, negatively with the corresponding difference between sitting and supine PaCO2, and negatively with BMI. Conclusions: We conclude that the significant difference in PaO2 in sitting and supine positions clearly shows that the position needs to be considered both when attempting to establish reference values and when evaluating gas exchange in elderly persons. The positional changes in oxygenation are related to the corresponding change in PaCO2, and to FEV1/FVC% and BMI. Copyright (C) 2002 S. Karger AG, Basel.