A Medical Device Daily

Pulse oximetry specialist Masimo (Irvine, California), reported that a new independent clinical study presented at the American Society of Anesthesiologists (ASA; Park Ridge, Illinois) meeting in San Francisco demonstrated the ability of the Pleth Variability Index (PVI) to accurately and noninvasively detect changes in ventricular preload.

The newest addition to the Masimo Rainbow SET (Signal Extraction Technology) platform, PVI is a continuous and noninvasive quantified measurement of changes in the perfusion index, capturing volume changes that may compromise cardiac function and affect systemic circulation.

The study, titled “New Algorithm for Automatic Estimation of the Respiratory Variations in the Pulse Oximeter Waveform,” was conducted at the Louis Pradel Hospital (Lyon, France) by a research team headed by Maxime Cannesson, MD.

The research team indicated that while respiratory variations in the pulse oximeter plethysmography waveform amplitude are sensitive to changes in pre-load and can predict fluid responsiveness in mechanically ventilated patients, they previously were not easily measured noninvasively from a bedside monitor. However, they said the PVI algorithm, available in the Masimo Rainbow SET platform, may provide a new method for noninvasively predicting fluid responsiveness.

In the study, Cannesson and the research team tested the ability of PVI to detect changes in ventricular preload in 20 vascular surgery patients under mechanical ventilation. Mean arterial pressure (MAP) and central venous pressure (CVP) via arterial catheter and central venous catheter were recorded along with PVI at baseline and while patients were in head-down and head-up positions.

The researchers said this study is the “first to demonstrate the ability of PVI, an index automatically derived from the pulse oximeter waveform analysis, to detect changes in ventricular preload. This new index has potential clinical applications for noninvasive hypovolemia detection and fluid responsiveness monitoring.”

“Fluid management optimization in mechanically ventilated patients undergoing anesthesia is of major importance, since it may have clinical and economical impact,” Cannesson said. “Indicators of response to volume expansion relying on cardio-pulmonary interactions are the best predictors of fluid responsiveness. Ideally, continuous noninvasive monitoring of these parameters would provide valuable information to clinicians in caring for mechanically ventilated patients. Masimo’s new derived index, PVI, appears to offer such a continuous, noninvasive monitor.”

Masimo said PVI displays a numeric representation of the changes in perfusion index as a percentage on the Rainbow SET oximeter, thus allowing clinicians to track and trend these changes over time.

Commenting on the study, Kevin Tremper, MD, chairman of anesthesia at the University of Michigan (Ann Arbor), said, “One of the biggest challenges we have in the operating room is determining whether, from a fluid volume perspective, a patient is full or empty. If PVI can help us non-invasively determine this in real time, [it] will be a huge benefit to clinicians and positively impact patient care and safety.”

Built on what Masimo termed the “gold standard” of Masimo SET Read-Through Motion and Low Perfusion technology, Masimo Rainbow SET is the first upgradeable technology platform capable of continuously and non-invasively measuring carboxyhemoglobin and methemoglobin, in addition to oxyhemoglobin, perfusion index, Pleth Variability Index and pulse rate.

In other news from the Moscone Convention Center exhibit floor, SonoSite (Bothell, Washington), introduced the S-Nerve procedural tool, which it calls “the first ultrasound device designed to support the specific needs of anesthesiologists who perform regional anesthesia.”

The company, which is a global leader in hand-carried ultrasound, said it expects to begin customer shipments of the product in the fourth quarter.

SonoSite said the S-Nerve visualization tool “is built to help regional anesthesiologists perform nerve block procedures in crowded, busy operating environments or anywhere in the hospital.”

The company cited the new product’s “breakthrough image quality, speed and simplicity,” saying it was “designed with input from leading practitioners who expressed a substantive need for a small, high-performance tool, designed to function exclusively as a guidance tool for regional nerve blocks and central line placement.”

SonoSite said that, like the S-Fast ultrasound tool it introduced recently for emergency medicine, the S-Nerve device is a new concept in ultrasound.

“The S-Nerve combines excellent image quality with an optimized and targeted user interface for the anesthesiologist,” said Christopher Wiley, MD, associate professor of anesthesiology at Dartmouth-Hitchcock Medical Center (Lebanon, New Hampshire). “Anesthesiologists are not ultrasonographers. We care about ultrasound as a means to help us perform regional nerve blocks more accurately, quickly and safely.”

He added: “The S-Nerve is a major step toward getting the machine out of the way of the image by eliminating lots of knobs and buttons. Its design will make it easier for the novice user to become more expert.”

Saying that image-guided regional anesthesia “is in the early stages of a gathering tidal wave of adoption across the globe,” Wiley predicted that S-Nerve “will likely accelerate that trend.”

SonoSite said adoption of point-of-care visualization “has grown steadily in the practice of regional anesthesiology. A growing body of clinical evidence demonstrates that ultrasound guidance can significantly reduce the time for accurately performing peripheral nerve blocks and placement of catheters.”

It added: “Clinicians who have integrated hand-carried ultrasound into their medical practice credit the technology with faster, more accurate needle and catheter placement, confirmation of anesthesia spread, clear visualization of hard to reach or compromised structures, and heightened patient satisfaction.”

SonoSite previewed the S-Nerve tool as a work-in-progress at the September congress of the European Society for Regional Anesthesiology in Valencia, Spain.

To create the new visualization tool, the company said it designed a user interface, software and controls that address the procedural needs of the anesthesiologist combined with the same processing power, image quality and data management features of the recently introduced M-Turbo system, which SonoSite said is 16 times more powerful than its industry-standard MicroMaxx system.