Hypovolemia (also hypovolaemia or oligemia) is a state of decreased blood volume; more specifically, decrease in volume of blood plasma.

It is thus the intravascular component of volume contraction (or loss of blood volume due to things such as bleeding or dehydration), but, as it also is the most essential one, hypovolemia and volume contraction are sometimes used synonymously.

Hypovolemia is characterized by sodium (salt) depletion and thus differs from dehydration, which is defined as excessive loss of body water.

In a retrospective study, from all 142 adult patients admitted to a surgical intensive care unit (ICU) with aneurysmal subarachnoid hemorrhage between March 2004 and November 2010.

The mean patient age was 54 ± 14 years, 62.7 % were female, and the median Hunt and Hess Stroke Scale was 3. The proportions of patients with poor outcome (Glasgow Outcome Scale Score ≤3) were 58.4, 54.2, and 52.1 % at 3, 6, and 12 months, respectively, after the SAH. The ICU and hospital mortality rates were both 12.7 %, and the median lengths of stay in the ICU and the hospital were 16 (IQ 7-25) and 26 (IQ 18-34) days, respectively. In multivariable analysis, older age and greater cumulative fluid balance within the first 7 days in the ICU were independently associated with a greater risk of poor outcome.

In this cohort of patients, older age and greater cumulative fluid balance were independently associated with a greater risk of poor outcome up to 1 year after the initial insult. The data suggest that mild hypovolemia may be beneficial in the management of these patients ¹⁾.