SEATTLE – Septic patients are more likely to respond to fluid therapy if their velocity time integral – a Doppler ultrasound measurement of blood flow across the left ventricular outflow tract – increases by 15% or more with a passive single-leg raise, according to a preliminary, observational study of 32 patients at New York Methodist Hospital in Brooklyn.
A passive leg raise to 45 degrees simulates a 250- to 500-cc fluid bolus. "We have found that people who don’t respond with a VTI greater than 15% have higher repeat lactate levels. Instead of giving them 2 L [of fluid] and then reassessing, maybe they’re patients you want to start on pressors right away," Dr. Andrew Balk said at the annual meeting of the American College of Emergency Physicians.
Dr. Andrew Balk
Echocardiogram machines can automatically calculate VTI. The measurement, which Dr. Balk and his associates obtained from the apical five-chamber view, is a surrogate for, and can be used to calculate, cardiac output. Poor response to fluid challenge indicates that fluids are less likely to increase cardiac output and more likely to cause fluid overload, said Dr. Balk, associate director of the clinical ultrasound division at the hospital.
The patients’ mean age was 68 years, and those with valvular pathology and atrial fibrillation were excluded from the study.
The group’s mean baseline VTI was 22 cm (range, 15-29 cm), which leg raises raised to a mean of 26 cm (18-34 cm), an increase of about 18% (4%-36%). A subsequent 2-L normal saline challenge increased VTI to a mean of 33 cm.
The mean baseline lactate level was 3.2 mmol/L (1.2-5.2 mmol/L), and 2 mmol/L (1-3 mmol/L) after the 2-L challenge. The percent change in VTI correlated significantly with the percent change in serum lactate levels. "Below-average responsiveness to the initial small fluid bolus was associated with a higher repeat lactate value, ... which suggests an inverse relationship between a patient’s fluid responsiveness as observed by the change in VTI and the severity of sepsis," the researchers concluded.
The VTI/leg-raise approach looks promising as a possible quick bedside marker that identifies patients who need aggressive treatment, without the need for central line measurements, Dr. Balk said. "The quickest initial fluid bolus you can get is a passive leg raise. You can watch for changes" in real time, and don’t have to move the probe from the point of maximum impact.
Dr. Balk reported having no disclosures.
Dr. Steven Q. Simpson
Dr. Steven Q. Simpson commented: The search for noninvasive measures of or predictors for volume responsiveness in septic patients continues. VTI is the integral of velocity and time, i.e., the distance a small blood bolus travels. When multiplied by cross-sectional area of the aortic outflow tract, this would result in stroke volume. Since one would not expect the cross-sectional area to change significantly after a fluid bolus, alterations in VTI should reflect alterations in stroke volume. While promising, this technique is not as easy as the authors make it sound
and is operator dependent, even though the machine does the calculating. The incident angle of the probe must remain constant during the leg raise (at least 90 seconds). The user must know whether valve pathology or LV impairment are present and, if so, the degree. Massively volume depleted patients may fail to respond adequately to a passive leg raise.
One would be remiss to rely on this small study, which does not report sensitivity or specificity, to establish a reliable percent increase for predicting lactate response or to guide fluid therapy. However, this research is certainly aimed in the right direction.
Dr. Steven Q. Simpson is professor of medicine and director of fellowship training in the pulmonary disease and critical care medicine division at the University of Kansas Medical Center, Kansas City.