Response to James Reagor and Colleagues’ Article “Spectrum Medical Quantum or Terumo CDI 500: Which Device Measures Hemoglobin and Oxygen Saturation Most Accurately When Compared to a Benchtop Blood Analyzer?”

We would like to thank Mr. Reagor and colleagues for their follow-up study comparing the hemoglobin and oxygen saturation measured with the Terumo^® CDI^® Blood Parameter Monitoring System 500 (System 500) continuous blood gas monitor (Terumo Cardiovascular Systems Corporation, Ann Arbor, MI) and Spectrum Medical Quantum (Spectrum Medical, Fort Mill, SC). Having thoroughly reviewed the article, we would like to clarify two claims made by the authors: one regarding gas calibration for the CDI System 500 and the second regarding the rate of measurement for hematocrit and hemoglobin. Also, of concern, is a flaw in the methodology used in venous and arterial sampling to compare the two devices has been noted.

In the discussion portion of the paper, the authors make the following statement: “the quantum device does not require gas calibration before use as is recommended for the CDI 500 representing both a preparation time and cost savings (1).” This statement is misleading and may be due to misreading the CDI System 500’s Instructions for Use. Gas calibration is for the System 500’s shunt sensor only and does not apply to the hematocrit/saturation (H/S) cuvette. If a user is using only the H/S cuvette, as in this study, no gas calibration is required.

The focus of the authors’ research was a comparison of hemoglobin and oxygen saturation between the two devices. The authors used the CDI H/S cuvette on the venous line of a perfusion circuit to measure venous hemoglobin, hematocrit, and saturations to compare those same indices measured on the Quantum. The CDI System 500 incorporates optical reflectance technology in its H/S probe. This probe completes a self-test that checks for optical drift in the H/S module (2). Further validation is accomplished through the performance of an in vivo calibration completed once cardiopulmonary bypass has begun and the circuit has stabilized before sampling is obtained.

Some clinicians only use the optical reflectance technology to measure hematocrit, hemoglobin, and saturation. Thus, they do not need to complete a gas calibration because they are not using the shunt sensor.

Note: Additional parameters of pH, pO₂, pCO₂, and potassium are measured using a shunt sensor that incorporates optical fluorescence technology. Shunt sensors are recommended to be gas calibrated before each use (2). To achieve the full benefit of continuous monitoring with the CDI System 500, it is recommended to use both the shunt sensor(s) and the HSAT cuvettes to continuously monitor arterial and or venous pH, pO₂, pCO₂, potassium, hematocrit, hemoglobin, and oxygen saturation.

An additional point of clarification is the rate of measurement for the hematocrit and hemoglobin for the CDI System 500. In their paper, the authors stated “Data generated by the Quantum was collected every second. Data produced by the CDI 500 was collected every 6 seconds, the limit of the device (1).” The CDI 500 measures hemoglobin and oxyhemoglobin every 18 milliseconds and averages those results to accommodate a screen refresh rate of 6 seconds (3).

Finally, questions regarding the methodology used to compare both monitors exist. It appears, by the author’s own disclaimer, that they had concerns over the limitation of their study: “One limitation to this study was the comparison of venous hemoglobin measurements from the CDI 500 to arterial hemoglobin measurements from the Quantum (1).” Does this mean that venous samples for hematocrit, hemoglobin, and saturation from the CDI System 500 were compared to arterial samples for the Quantum? And what type of samples were measured on the ABL 90 as the reference device? It is commonly recognized that there are differences in measured hemoglobin and hematocrits between venous and arterial samples and that these differences may be amplified by adding volume to a perfusion circuit while on cardiopulmonary bypass (4).

We look forward to a response from Mr. Reagor and his colleagues to help us better understand the methodology used to compare the CDI System 500 continuous blood gas monitor to the Spectrum Medical Quantum.

Sincerely,

Suzanne C. Osborne, CCP Emeritus

Director of Clinical Services, Terumo Cardiovascular

Ann Arbor, MI

E-mail: suzanne.osborne@terumomedical.com

Steven Pregulman, MD

Chief Medical Officer, Terumo Cardiovascular

Ann Arbor, MI

E-mail: steven.pregulman@terumomedical.com