A non-invasive near
infrared spectrophotometric monitoring
transducer assembly includes a housing member, which is adhered directly on a patient's
skin. The housing member contains a
prism coupled to a flexible and lightweight
single core optical
light guide, which provides a means of transferring narrow spectral bandwidth light from multiple distant
laser diodes of different wavelengths by use of a multi-
fiber optic light combining
assembly. Different wavelengths are needed to monitor the level of
blood oxygenation in the patient. The
assembly also contains a planar
light guide mounted on the
prism located in the housing member, which
light guide contacts the patient's
skin when the housing member is adhered to the patient's
skin. The light guide controls the spacing between the
prism and the patient's skin, and therefore controls the intensity of the area on the patient's skin which is illuminated by the
laser light. The housing member contains a
photodiode assembly, which detects the
infrared light at a second location on the skin to determine light absorption. The
photodiode assembly is preferably shielded from ambient
electromagnetic interference (EMI) by an optically transparent EMI attenuating window. This rigid window placed over the
photodiode also provides a planar interface between the assembly and the skin, improving
optical coupling and stability as well as reducing the
capacitive coupling between skin and the photodiode resulting in further EMI attenuation. The housing may be associated with a disposable sterile hydrogel coated
adhesive envelope, or pad, which when applied to the patient's skin will adhere the housing to the patient's skin. The
transducer assembly will thus be reusable, and skin-contacting part of the device, i.e., the envelope or pad can be discarded after a
single use. The assembly also includes a
laser safety interlock means, which is operable to turn off the
laser light output in the event that the assembly accidentally becomes detached from the patient's skin.