System for disabling oximeter in presence of ambient light

A method for measuring a selected parameter of blood as it flows through an extracorporeal blood circuit, the method utilizing a medical device operative to provide light to blood passing through the blood circuit at one or more wavelengths depending upon the parameter being measured and to generate an electrical signal based upon the amount of light reflected or transmitted back to the device, the magnitude of the signal being used in the measurement of the selected parameter, the method comprising the steps of:

• a. connecting a known reflective standard to the device;
• b. providing light from the device to the reflective standard at a first wavelength used in measurement of the parameter;
• c. measuring the amount of light reflected at the first wavelength by generating an electrical signal indicative of the amount of light reflected;
• d. determining a normalization factor based upon the magnitude of the electrical signal generated from the reflected light at the first wavelength in relationship to the magnitude of an expected electrical signal which is a known constant for the reflective standard at the first wavelength;
• e. storing the normalization factor in a manner allowing it to be recalled during use of the device for measurement of the selected blood parameter;
• f. repeating steps b through e for each wavelength used in measurement of the parameter such that a different normalization factor is calculated and stored for each wave length;
• g. connecting the device to the extracorporeal blood circuit for measurement of the selected parameter;
• h. providing light from the device to the blood in the circuit at each wavelength used in the measurement of the parameter;
• i. measuring the amount of light reflected at each wavelength used in the measurement of the parameter by generating electrical signals indicative of the amount of light reflected at each wavelength, the magnitude of the electrical signals being indicative of the amount of the selected parameter of blood being measured;
• and
• i. adjusting the measurements generated in step i. for each wave length by the appropriate normalization factor for each wave length to provide a corrected measurement of the selected parameter of blood.