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Blood osmolar gap as a prognostic indicator in critically ill patients: preliminary results


The evaluation of the osmolar gap of incoming patients in the ICU as a prognostic indicator of outcome.

Materials and methods

The difference between measured and calculated osmotic pressure (osmolar gap) was recorded in 72 patients admitted to two medical–surgical intensive care units (ICU). The measurement took place immediately after their admission in the ICU independent of the cause of admission. The SAPS II and APACHE II scores were recorded as well as the ICU outcome. Patients were separated retrospectively into two groups on an outcome basis: A = Alive, B = Dead.


The results are presented in Table 1.

Table 1


The osmolar gap calculated during admission as well as the measured osmolarity may be good indicators of the ICU mortality. Although the calculated osmolarity does not seem to be a reliable prognostic indicator in critically ill patients, it is used in the calculation of the osmolar gap, which seems to be a better prognostic indicator of the ICU mortality in comparison with the calculated osmolarity. Patients with an osmolar gap > 24 at their admission in the ICU have 53% probability of death, while patients with an osmolar gap < 14 have 28% probability of death. An osmolar gap of 35 mosm/l at admission is related with increased probability of death by 1.33 times (odds ratio), according to our preliminary results.

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Aloizos, S., Myrianthefs, P., Zidianakis, V. et al. Blood osmolar gap as a prognostic indicator in critically ill patients: preliminary results. Crit Care 8 (Suppl 1), P334 (2004).

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