Masimo , the inventor of Pulse CO-Oximetry™ and Measure-Through Motion and Low Perfusion pulse oximetry, announced that a new clinical study published in the March 2010 issue of Anesthesia & Analgesia, shows Masimo PVI successfully predicts the hemodynamic effects of Positive End-Expiratory Pressure (PEEP) in mechanically ventilated patients after cardiac surgery. According to study researchers, the ability of PVI to predict the effects of PEEP may allow physicians to "optimize the respiratory uptake in oxygen and its delivery to the tissues."
It is critically important for clinicians to accurately determine whether the addition of PEEP, a ventilator setting that can alter cardiac output (the amount of blood the heart pumps), will have positive or negative hemodynamic effects. PEEP can be beneficial if it improves PaO2 (arterial oxygenation and oxygen delivery during anesthesia) by opening collapsed alveoli to increase gas exchange, but harmful if it decreases blood flow to the tissues (most often measured as cardiac output). Masimo PVI has been shown on multiple clinical studies to continuously and noninvasively predict fluid responsiveness in mechanically-ventilated patients under general anesthesia. However, researchers in this study approached the relationship between PVI and fluid responsiveness in the reverse manner from which it is usually evaluated. Instead of looking at whether PVI predicts a positive response by the patient, they evaluated whether PVI predicated a negative response (decreased preload) with the addition of PEEP.
Researchers from the Louis Pradel Hospital, Department of Anesthesiology and Intensive Care, in Lyon, France, and the University of California, Irvine, School of Medicine in Irvine, California, studied 21 mechanically-ventilated and sedated patients in the postoperative period after coronary artery bypass graft (CABG) surgery. Patients were monitored via invasive pulmonary artery catheter for end-expiratory central venous pressure (CVP), end-expiratory pulmonary capillary wedge pressure (PCWP), cardiac index (cardiac output indexed to body surface area) (CI), pulse pressure variation, and stroke volume (SV), and PVI via a Masimo Rainbow SET Pulse CO-Oximeter sensor attached to the finger. Hemodynamic data was recorded at three successive tidal volumes (VT of 6, 8, and 10 mL/kg) during zero end-expiratory pressure (ZEEP) and after the addition of 10 cm H2O PEEP for each VT and hemodynamically instable (HI) patients were defined as those with >15% decrease in CI after the addition of PEEP.
Results showed that at a VT of 8 mL/kg, PVI was significantly higher in the HI group than in the non-HI group (13% + 5% vs 9% + 4%, P<0.03) and a PVI of 12% at ZEEP predicted a significant decrease in CI after the addition of PEEP in 6 patients with a sensitivity of 83% and a specificity of 80%. Pulse pressure variation was also significantly higher in the HI group than in the non-HI group; however CI, CVP, and PCWP were not different. At VT of 10 mL/kg, PVI was still significantly higher in the HI group than in the non-HI group (16% + 7% vs 10% + 4%, P<0.01) and a PVI of 13% at ZEEP predicted a significant decrease in CI after the addition of PEEP in 9 patients with a sensitivity of 78% and a specificity of 83%. Researchers concluded that Masimo PVI may be "useful in automatically and noninvasively detecting the hemodynamic effects of PEEP when VT is > 8 mL/kg in ventilated and sedated patients with acceptable sensitivity and specificity."
The current study reinforces the value of PVI compared to invasive measures and highlights PVI's value for reliably detecting the hemodynamic effects of PEEP and predicting hemodynamic instability. PVI is available as part of Masimo Rainbow SET Pulse CO-Oximetry—a breakthrough noninvasive blood constituent monitoring platform capable of measuring multiple blood constituents that previously required invasive procedures, including: total hemoglobin (SpHb®), oxygen content (SpOC™), carboxyhemoglobin (SpCO®), methemoglobin (SpMet®), and PVI®, in addition to oxyhemoglobin (SpO2), pulse rate (PR), and perfusion index (PI).