Anesthesiologists like to be aware of the intraoperative pulse pressure variation or PPV for a patient, but there is a cost involved in this knowledge which comes in the form of how invasive the arterial line or A-line is. It is beneficial to note, then, that there are current technological innovations which are drastically changing this landscape, and from this technological improvement comes a device which is significantly less invasive for patients who are morbidly obese.
When you derive the PPV from an A-line tracing in the course of an operation, you can assess the fluid responsiveness of a patient while being able to assist in the management of intraoperative fluids, but there are a finite number of patients for which A-line operations are indicated. For example, in patients who are morbidly obese, this procedure can be too invasive and therefore should be avoided. According to Dr. Roman Schumann, MD, an associate professor for anesthesiology working at Tufts Medical Center located in Boston, utilizing a simple device which can simplify this process can be beneficial. The ccNexfin by Edwards Lifesciences has a simple cuff which goes on the finger of the patient and is capable of monitoring the patient’s cardiac output, blood pressure, their pulse pressure variability and some other types of hemodynamic parameters as well.
Investigators created a study to allow them to compare these two modalities and their resulting measurements. The study included 68 women and men who were undergoing bariatric surgery. They had a mean age of 46±13 years and a mean body mass index (BMI) of 48±7. Each of these participants in the study received the ccNexfin on their left hand and a radial A-line in their left arm. The PPV values from each of the monitors were then recorded in simultaneous increments during six different time periods while they were receiving mechanical ventilation and general anesthesia.
As was reported in 2013 at the American Society of Anesthesiologists’ annual meeting, Dr. Schumann made a report that there were 337 PPV data pairs which had been made available to investigate. Using Bland-Altman analysis which was applied to patient averages for the measurements taken at all six of these time points, there was a bias of 0.48%±2.75% with agreement limits of 5.84% and 4.89%. What the data is indicating according to these numbers and a Pearson correlation coefficient of 0.82 with a 95% confidence level is that although the numbers are not exactly matching, in this population the ccNexfin has still proven to be a fairly useful modality method.
Dr. Schumann described that these slight inconsistencies in the PPV values for the two different approaches likely reflects the algorithms and the specific technologies which are used by each of the monitors. Because the ccNexfin is a non-invasive device that can produce very similar results, it is a viable alternative to the A-line procedure, which can be too invasive for some patients and therefore not indicated for use with them. Ashish C. Sinha, MD, Ph.D. at Drexel University College of Medicine in Philadelphia, the vice chair of research for the Department of Anesthesiology, has indicated that the technology is exciting since placing a blood pressure cuff has difficulty obtaining accurate blood pressure readings in patients who are morbidly obese, and this ccNexfin cuff will help to alleviate that problem.