A new non-invasive continuous blood monitor could reduce the number of blood transfusions given during surgery, according to the results of a small clinical trial presented at a conference in the US on Monday.

A report of the trial, presented at the American Society of Anesthesiologists annual meeting in San Diego on 18 October, showed that using only conventional lab testing to measure hemoglobin levels during surgery resulted in 4.5% of patients having to have a blood transfusion during their operation, compared to only 0.6% whose red blood cell levels were also measured with a non-invasive “real time” monitor.

As well as increasing the length of stay in hospital, having a blood transfusion during surgery can increase a number of risks for patients, such as the likelihood of postoperative infection, the chance of cancer recurrence, and impaired lung function, said Jesse Ehrenfeld, director of the Center for Evidence Based Anesthesia at Vanderbilt University Medical Center, in Nashville, Tennessee, who led the trial.

So while it would be better for patients, as well as helping to conserve the national blood reserve, to avoid unnecessary blood transfusions, the challenge that surgical teams face when a patient starts to bleed during surgery is getting an accurate assessment of how much blood is lost and whether the patient has enough red blood cells or hemoglobin left to complete the procedure without a blood transfusion.

Current methods rely on observation and lab tests, which can only be done intermittently and can take 15 to 45 minutes to get back to the surgical team, so in the absence of timely results, surgeons often go for the safest option, contributing to the 1.9 million transfusions given during surgery every year in the US.

This problem has challenged companies like Masimo Corp of Irvine, Calfornia, to come up with a new technology known as continuous and noninvasive hemoglobin (Hb) monitoring which they term “SpHb monitoring” that counts surgical patients’ red blood cell levels continuously in real time, that is as it is happening and without delays and it also does it without puncturing the skin.

The SpHb monitor that Ehrenfeld and his team tested in a randomized prospective controlled trial lasting 6 months was Masimo’s Radical-7 Pulse CO-Oximeter and R1-25 Rainbow Adhesive Sensor, Revision E device.

The device measures hemoglobin levels using near-infrared light of several different wavelengths to assess the relative quantity of circulating red blood cells, said Dana Banks, a spokesperson for Masimo, according to a report in Scientific American.

For the trial, Ehrenfeld and colleagues recruited 327 elective orthopedic surgery patients scheduled for procedures such as hip replacement (31% of patients), knee replacement (29%), and spinal surgery (14%) and randomly assigned each to receive either standard care alone (157 patients) during their surgery (that is where observation and lab tests were used to monitor hemoglobin levels), or standard care plus SpHb monitoring (150 patients).

They compared the frequency of transfusions done during operations and the mean number of blood units transfused, in the two groups, and they also compared the frequency of lab Hb testing and agreement between the SpHb counts and the lab Hb counts.

They also assessed complication rates for each group 30 days after the surgery.

The results showed that:

  • There were no significant differences between the groups in terms of physical status, gender, lab count of hemoglobin before they had surgery, and duration or type of surgery.

  • More patients received blood transfusions during their operations in the standard care group compared to the SpHb group (4.5% vs 0.6%, p=0.03).

  • The mean number of units of blood used in the transfusions was significantly higher in the standard care group than the SpHb group (0.10 vs 0.01, p=0.0001).

  • There was little difference between the groups in frequency and mean number of lab Hb tests (16.3% vs 11.8%, and 0.21 vs 0.24 tests per case, p=ns, in both cases).

  • The values of Hb obtained by SpHb and lab tests showed good agreement.

  • There were no transfusions in either group in the 12 hours after surgery and there was no difference between the groups in the 30-day complication rates.

Ehrenfeld and colleagues concluded that:

“Use of SpHb monitoring resulted in fewer intraoperative blood transfusions.”

Masimo’s SpHb device is already in use at Brookdale University Hospital and Medical Center in Brooklyn, New York, where according to Dr Thomas Crimi, the Director of their Blood Conservation program, it is helping them “proactively identify and address patients requiring blood transfusions much earlier, while avoiding unnecessary transfusions and other invasive tests”.

However, more data is needed before the device is more widely adopted.

Ehrenfeld said the next stage will be to do a larger trial to see how the device affects transfusion rates in other groups of patients, including those undergoing trauma and cardiac surgery, where more blood is often needed.

“Impact of Continuous and Noninvasive Hemoglobin Monitoring on Intraoperative Blood Transfusions.”
Jesse M. Ehrenfeld, Justin P. Henneman.
Presented at American Society of Anesthesiologists, Annual Meeting, San Diego, 18 October 2010.
Abstract Number: LB05.

Sources: Scientific American, Masimo, ASA Annual Meeting 2010 Abstracts.

Written by: Catharine Paddock, PhD