Association between estimated plasma volume status and all-cause mortality in critically ill patients with non-traumatic subarachnoid hemorrhage: analysis of the MIMIC-IV database

Why balancing blood volume matters after brain bleeding

When a blood vessel on the surface of the brain suddenly bursts, it can cause a type of stroke called subarachnoid hemorrhage. Even when patients reach an intensive care unit in time, doctors still struggle to predict who will recover and how best to guide treatment. One key challenge is getting the amount of fluid and blood in the circulation “just right” — too little or too much can both be dangerous. This study asks whether a simple calculation, based on routine blood tests, can flag which critically ill patients are at higher risk of dying and point toward safer fluid management.

A quick measure taken from routine blood tests

The researchers focused on a measure called estimated plasma volume status, or ePVS. Plasma is the liquid part of blood, and ePVS is a way to infer how concentrated or diluted that blood is by combining two common lab values: hemoglobin and hematocrit. Instead of relying on invasive catheters or imperfect pressure readings, ePVS offers a rough snapshot of blood volume using information already collected in most intensive care units. Although earlier work linked higher ePVS to worse outcomes in heart disease and brain hemorrhage inside the brain tissue, its role after bleeding around the brain — non‑traumatic subarachnoid hemorrhage — had not been examined.

Mining a large intensive care database

To investigate, the team turned to the MIMIC‑IV database, a rich trove of anonymized records from patients admitted to intensive care at a major U.S. hospital between 2008 and 2019. They identified 750 adults with non‑traumatic subarachnoid hemorrhage who stayed in the ICU for at least 24 hours and had complete blood count data. For each patient, they calculated ePVS from blood tests taken within the first day of ICU admission and tracked whether the patient died within one month, three months, or one year. They also pulled information on age, illness severity scores, vital signs, other diseases such as heart or kidney problems, infections, and treatments like mechanical ventilation or blood‑pressure‑lowering drugs, then used statistical models to account for these factors.

A danger at both low and high blood volume

When the researchers plotted mortality risk against ePVS, a striking U‑shaped curve appeared. Patients in the middle range of ePVS had the lowest death rates, while those with either very low or very high values were more likely to die, even after adjusting for many other risk factors. A more detailed analysis suggested a turning point at an ePVS value of about 3.94. Below this point, slightly higher ePVS — implying somewhat more circulating fluid — was linked to lower one‑month mortality. Above it, further increases in ePVS were associated with sharply rising risk. In practical terms, both under‑filling and over‑filling the circulation in these fragile patients seemed harmful, and the safest zone lay in between.

How misbalanced fluids might harm the brain and body

The pattern fits with what is known about the tight fluid balance required after subarachnoid hemorrhage. If effective blood volume is too low, blood pressure and brain perfusion can fall, possibly worsening vessel spasm, delayed brain ischemia, and kidney injury. On the other hand, excess fluid can strain the heart and lungs, leading to heart failure or pulmonary edema, complications already observed in past trials of aggressive fluid therapy. Because ePVS is derived from hemoglobin and hematocrit, which are themselves altered by bleeding, transfusions, and early treatment decisions, it may reflect both disease severity and how clinicians have managed fluids. This means ePVS is a powerful warning sign but does not, by itself, prove cause and effect.

What this means for patients and future care

The study suggests that a simple formula based on routine blood tests can help flag critically ill subarachnoid hemorrhage patients whose blood volume may be too low or too high, both of which are linked to an increased risk of death. For patients and families, the message is that careful, individualized fluid management after this type of brain bleed is crucial, and more is not always better. For clinicians, ePVS could become a quick, low‑cost tool to guide closer monitoring and more balanced fluid strategies. The authors caution that their findings come from a single hospital and from retrospective data, so large prospective studies are needed before firm treatment targets can be set, but the work opens a promising path toward safer care in a highly vulnerable population.

Citation: Mei, Q., Zhang, J. & Shen, H. Association between estimated plasma volume status and all-cause mortality in critically ill patients with non-traumatic subarachnoid hemorrhage: analysis of the MIMIC-IV database. Sci Rep 16, 11725 (2026). https://doi.org/10.1038/s41598-026-47116-2

Keywords: subarachnoid hemorrhage, blood volume, critical care, fluid management, mortality risk