New Study Compares Two Methods of Guiding Goal-Directed Fluid Therapy, Noninvasive Masimo PVi® and Invasive Esophageal Doppler

Masimo (NASDAQ: MASI) announced today the findings of a study recently published in BMC Anesthesiology in which researchers at University Hospital Linköping, Sweden, compared the performance of goal-directed fluid therapy (GDFT) using invasive esophageal Doppler to GDFT using Masimo PVi® (pleth variability index, measured noninvasively and continuously using SET® pulse oximetry sensors) in patients undergoing major abdominal surgery.[1]

Noting the value of GDFT in aiming to determine “the optimal amount of fluid for an individual patient,” Dr. Hans Bahlmann and colleagues sought to compare the effects of two methods of GDFT, stroke volume optimization guided by invasive esophageal Doppler (control group) and fluid optimization guided by noninvasive PVi (intervention group), on patients who were scheduled for open abdominal surgery lasting two or more hours. The effects compared were incidence of complications and length of hospital stay.

The researchers collected data from 146 patients who had surgery between November 2011 and January 2015, who were randomly divided into the two groups. In the intervention group, PVi was noninvasively and continuously measured with a Masimo Radical-7® Pulse CO-Oximeter® with software version 7.8.0.1 and SET® sensors. After an initial fluid bolus (given to all patients irrespective of PVi value), a fluid bolus was given if PVi was ≥ 10%, repeated at 5 minute intervals until PVi fell below 10% or did not decrease at all. In the control group, esophageal Doppler measurements were performed using a Deltex Medical CardioQ apparatus. After an initial fluid bolus, Doppler measurement was performed after 5 minutes and fluid boluses were repeated until stroke volume did not increase by 10%, in accordance with published protocols.

Observers blinded to each patient’s group assessed complications for 30 postoperative days using a pre-specified list of complications, as well as length of hospital stay. The researchers found that noninvasive PVi and invasive Doppler performed with no statistical difference, with similar incidences of complications and lengths of stay between the two groups. In the intervention/PVi group, there were 64 complications (corresponding to 51% of patients), with a median length of stay of 8.0 days (interquartile range [IQR] 8.0 days). In the control/Doppler group, there were 70 complications (corresponding to 49% of patients), with a median length of stay of 8.0 days (IQR 9.5).

The researchers concluded, “No difference in clinical outcome, as defined by number of postoperative complications, and length of hospital stay, was found when goal-directed fluid therapy was applied using PVi as an alternative to esophageal Doppler. PVi appears to be an acceptable alternative to esophageal Doppler for goal-directed fluid therapy during major open abdominal surgery.”

In discussing other PVi-related clinical studies, the researchers also noted that “Based on these reports and our findings, a clinician wishing to pursue GDFT can choose PVi over esophageal Doppler in the large majority of patients undergoing major open abdominal surgery. PVi, in contrast to esophageal Doppler, is not sensitive to interference from diathermy and does not require frequent access to the patient’s head for probe repositioning. Also, PVi can be measured without single-use equipment, avoiding the cost for single-use esophageal probes (USD 130 in our setting). However, as illustrated by the request for Doppler data in two PVi patients, the clinician might still want to have access to a reliable method for measuring intraoperative cardiac output to increase the amount of hemodynamic information during unusually complex situations or in cases of known vascular and/or myocardial dysfunction.”

As a study limitation, the researchers noted the absence of a control group with neither PVi nor Doppler guiding fluid therapy, and therefore “it is not possible to tell whether PVi and Doppler both result in similar improvements in outcome, or whether neither method improves outcome when compared to treatment without GDFT.” They also noted that because of determining sample size using a 10% difference in the number of complications at 30 days, “the study was not powered to detect smaller albeit still significant differences in postoperative outcome.”

PVi has not been cleared by the FDA to assess fluid responsiveness.

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