INTRODUCTION

3M Healthcare uses a technology called optical fluorescence microsensing to produce a line of products that monitor patients' blood gas levels in the extracorporeal circuit during bypass surgery. The extracorporeal circuit, as Figure 1 depicts, transfers blood from the patient to pumps where it is oxygenated and replaces the function of the heart and lungs during the surgical procedure; it then returns the oxygenated blood back to the patient. One of the functions of our monitoring system is to give the operating room team a continuous readout of the patient's oxygen concentration (measured in units of partial pressure, mmHg), both before and after use of the oxygenating equipment. The before or "venous" measurement is used by the team to assess the patient's physiological and metabolic state, while the after or "arterial" measurement is used as feedback so that the oxygenation equipment can be adjusted by the "perfusionist" manning the extracorporeal station.

Figure 1: CDI Monitoring System Installed in the Extracorporeal Circuit During Bypass Surgery

The blood gas monitoring systems operate as follows (see Figure 2):

1. Oxygen from the patient's blood diffuses through a sterile membrane and into a small disk of polymeric material containing a fluorescing dye (this disk is called the SENSOR).

2. Light of a specific wavelength is generated and delivered by a fiber-optics cable to irradiate the sensor.

3. Once excited, the sensor chemistry fluoresces depending on the concentration of oxygen dissolved in the sensor.

4. Another fiber-optics bundle transfers a portion of the resulting fluorescence to...