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 cluster of laser diodes which emit infrared light in different wavelengths which are necessary to monitor the level of blood oxygenation in the patient. The assembly also contains a light guide mounted 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 laser diodes and the patient's skin, and therefore controls the intensity of the area on the patient's skin which is illuminated by the laser diodes. The light guide also provides a planar interface between the assembly and the patient's skin which the laser diodes are illuminating. The light guide may include a light attenuator and/or diffuser, such as a filter, which allows the usage of higher energy laser diodes to produce a safer lower energy light field on the patient's skin. The assembly also includes an LED safety device which is operable to turn the laser diodes off in the event that the assembly accidentally becomes detached from the patient's skin. 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 EMI interference. 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.
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