Plasma Volume Predicts Hospital Stays, Death Across PH Types

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by Lindsey Shapiro PhD |

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Plasma volume status (PVS) — an indirect, non-invasive measure of heart congestion — is a predictor of short-term hospital stays and mortality outcomes in people with multiple types of pulmonary hypertension (PH), a study reported.

According to the researchers, plasma volume could be used to monitor patients who might be at risk for these outcomes.

“Our study suggests that PVS, a simple method of evaluating vascular congestion, might help clinicians identify … PH patients at increased shortterm risk of death and hospitalization,” the researchers wrote, adding that “routine non-invasive monitoring of volume status with PVS may be beneficial.”

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The study, “Utility of Plasma Volume Status in Ambulatory Patients with Pulmonary Hypertension,” was published in Pulmonary Circulation

Types of PH are classified into five groups created by the World Health Organization (WHO) based on the cause of the disease.

While some risk factors for serious adverse outcomes — including hospitalization and/or death — in PH have been identified, studies usually focus on PH patients in WHO group 1, which includes people with pulmonary arterial hypertension (PAH).

Other types of PH, classified in WHO groups 2–5, are often excluded from risk-factor studies. This makes it harder for clinicians to know which of these patients are high-risk, the research team noted.

“There is a dearth of easily used and readily available tools for clinicians to identify PH patients, from all WHO groups, at high risk of adverse events,” the researchers wrote.

Broadly, PH is characterized by high blood pressure, or hypertension, in the arteries that carry blood from the heart to the lungs. One consequence of PH is congestion — an overfilling of blood vessels that often accompanies heart failure.

Plasma volume estimates, a measure of blood volume, can be used as an indirect assessment of congestion levels — and has been previously used as a predictor of mortality and hospitalization in heart failure patients, who share some common features with types of PH.

Now, researchers at Virginia Commonwealth University, in Richmond, tested whether plasma volume might also predict short-term outcomes in patients with PH across all WHO groups.

To do this, the team performed a retrospective analysis of plasma volume in 129 patients treated in 2018 at the university’s PH clinic, and correlated those measurements with death or hospitalization events within 90 days (about three months) of the measurement.

Among the patients analyzed, the majority were female, with a mean age of 61.

Home oxygen use was observed more frequently in the group of patients with hospitalization or mortality, which were the study’s primary outcomes. Specifically, 68% of the individuals in that group used home oxygen, compared with 43% of the patients with neither of those outcomes.

Overall, 28 patients (22%) were hospitalized or died during the 90-day period. Four patients (3%) did not survive.

To determine PVS, the researchers calculated how each patient’s actual plasma volume — measured using the individual’s weight and red blood cell count — differed from an expected plasma volume for a person of that weight.

Patients were split into three groups, or tertiles, based on their PVS levels. Those in tertile one had the lowest PVS — more than a 14% reduction from expected — while patients in tertile two had intermediate PVS, between a 4.1% and 14% reduction. People with the highest PVS were in tertile three, encompassing patients with any PVS higher than tertile two. Of note, a higher PVS indicates more congestion.

Fewer patients in tertile one (9%) were hospitalized or died compared with those in either tertile two or three. In tertile two, 33% were hospitalized or died, with 23% of those in tertile three having those outcomes.

Furthermore, the average time to the first hospitalization or death was shorter in tertiles two and three compared with tertile one.

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Taken together, the results suggest that patients with higher plasma volume are more likely to be hospitalized or die in the short term, the researchers concluded.

“Patients with lower PVS had decreased risk of hospitalization and death within 90 days of clinic visit, compared to those with higher PVS,” they wrote.

To understand if this risk stratification applied to all PH patients, the researchers compared the data between patients in WHO group 1 to those in other groups. They observed no differences in hospitalization or death between the groups, indicating that plasma volume remains a predictor of outcomes across all of the PH types.

The team suggested there may be a threshold level for PVS, above which patients become at high risk for hospitalization and/or mortality. This is consistent with findings previously observed in heart failure patients, although the actual threshold level might be different between PH and heart failure.

According to the researchers, one advantage of using PVS as a monitoring tool is that it is simple to calculate and can be easily measured in an outpatient setting. It also can be used as a short-term assessment measure, whereas other strategies for monitoring congestion show prognostic value over longer periods of several years, they added.

“Further study into the predictive value of PVS, and its utility as a target for treatment, is warranted,” the team concluded.