Correction for loss of CO2 from blood during measurement of osmotic pressure

Abstract

During osmolality measurement by the vapor pressure method, exposure of the blood sample to air lowers the blood CO2 content and osmolality. A modification of the sample holder of a vapor pressure osmometer is described allowing exposure of the blood sample to a gas mixture with known concentration of CO2 and O2 while inside the closed sample chamber. This restores its CO2 content and hence osmolality. Data are presented comparing the unmodified and modified vapor pressure method with the freezing point of depression method. A table was prepared for further correction of osmolality in case the blood''s PCO2 [CO2 partial pressure] differs from that of the gas mixture.