Serum osmolality gap in postoperative patients in intensive care

The serum osmolality gap (OG), the difference between measured and predicted serum osmolality, was determined in 161 postoperative patients. A significantly increased OG was found in patients with failure of one or more organs, but rarely seen in those without organ failure. OG in non-survivors was significantly increased and sustained at a high level. Thus, the change in OG correlated with the severity of the patients' condition and their outcome. There was also a significant correlation between OG and hepatic cell function tests (arterial ketone body ratio and hepaplastin test). Analysis of non-aminoacid OG revealed that about 75% of the increased OG could be attributed to increased aminoacid concentrations, but that the remainder should be attributed to other undetermined solutes. Serial determination of OG provides information on metabolic abnormalities and prognosis of patients with progressively developing organ failure.