Real-Time Hemoglobin Monitoring During Surgery Cuts Blood Transfusions

Jim Kling

October 25, 2010

October 25, 2010 (San Diego, California) — Continuous noninvasive hemoglobin (Hb) monitoring results in fewer blood transfusions during orthopaedic surgical procedures, according to research presented here at the American Society of Anesthesiologists (ASA) 2010 Annual Meeting.

Blood transfusions are costly and carry significant risk for patients, including infection, cancer recurrence, and impaired pulmonary function. They can also increase the length of hospital stay and mortality.

Laboratory Hb values are generally used to determine the need for blood transfusions, but testing is done intermittently and the results are not available immediately. Using the Pulse CO-Oximeter and multiwavelength adhesive sensor, it is now possible to perform continuous noninvasive Hb (SpHb) monitoring, noted lead investigator Jesse Ehrenfeld, MD, MPH, director of the Center of Evidenced-Based Anesthesia at Vanderbilt University in Nashville, Tennessee.

"There is a lot of technology that is brought to market, and unfortunately very few clinical trials that help us to understand how we can use it most effectively. There are no randomized controlled trials of the Pulse CO-Oximeter and multiwavelength adhesive sensor. [We wanted to] sort through these technologies and determine the most effective ones for patients," Dr. Ehrenfeld, who presented the research, told Medscape Medical News. The research was performed while he was at Massachusetts General Hospital in Boston.

The researchers conducted a prospective randomized controlled trial to determine the effect of SpHb monitoring on transfusions in patients undergoing elective orthopaedic surgery. Over a 6-month period, 327 patients were randomized to receive standard care (n = 157) or standard care plus SpHb monitoring (n = 170). The researchers compared the frequency of intraoperative transfusions and the mean number of blood units transfused. They also analyzed the frequency of laboratory Hb testing and compared SpHb and laboratory Hb values. Finally, they compared complication rates for both groups at 30 days postsurgery.

Surgeries included hip replacement (31%), knee replacement (29%), and spinal surgery (14%). The standard care and SpHb groups were similar in ASA physical status (2.2 vs 2.2), age (60.8 vs 61.9 years), the number of males (54% vs 48%), preoperative lab Hb (13.6 vs 13.5 g/dL), surgical duration (127 vs 114 minutes), and surgical type. The standard care group had a higher rate of intraoperative transfusions than the SpHb group (4.5% vs 0.6%; P =.03), and a greater mean number of units of blood transfused (0.10 vs 0.01; P = .0001). No transfusions were done in the 12 hours immediately after surgery in either group.

The standard care and SpHb groups had a similar (nonsignificant) frequency of intraoperative Hb testing (16.3% vs 11.8%) and mean number of Hb tests performed (0.21 vs 0.24 tests per case). Intraoperative SpHb and laboratory Hb values were similar (mean difference, 1.1 ± 0.68 g/dL), and both groups had similar 30-day complication rates.

"This was a pilot study, but I think it raises the question of what is the right patient population to use this in. It's not necessarily appropriate in all patients [because of the cost of the technology]. . . . In ambulatory surgery where the risk is very low, it may not be as useful as in other procedures, where the risk of a blood transfusion is higher," said Dr. Ehrenfeld.

His team is compiling other data to determine patient characteristics that are most likely to predict the need for blood transfusion, and so might warrant continuous monitoring, such as comorbidities, age, and preoperative Hb status.

He also plans to conduct a multicenter prospective trial to identify who would best be served by the technology.

"A lot of times we give blood because we see bleeding and we worry. We feel like the time course doesn't allow us to wait [for blood tests to come back]. This real-time monitor lets you do that. I think this has the potential to pay for itself many times over in blood not transfused," Avery Tung, MD, professor of anesthesiology at the University of Chicago in Illinois, who moderated the session, told Medscape Medical News.

The study did not receive commercial support. Masimo (the manufacturer of the Pulse CO-Oximeter and multiwavelength adhesive sensor) provided the instruments and disposable sensors. Dr. Ehrenfeld and Dr. Tung have disclosed no relevant financial relationships.

American Society of Anesthesiologists (ASA) 2010 Annual Meeting: Abstract LB05. Presented October 18, 2010.