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Vascular catheters designed for continuous in vivo measurement of arterial blood gases and pH without removing blood. These catheters include an optical fiber that conducts light and interacts with the indicator (either is absorbed, reflected, or causes fluorescence); the magnitude of the change in the light characteristics depends on the concentration in the blood of the substance being measured. Blood-gas/pH-monitoring catheters use a detector that combines an optical fiber with a fluorescent dye; the detector may be used either on the distal tip of the catheter as an intraarterial gas monitor or as an extraarterial system within a sensor cassette that is inserted in series with the arterial catheter tubing, usually near the patient\'s wrist. Three detectors are needed for pH, PO2, and PCO2 measurements. These catheters may be used for continuous arterial monitoring of blood gases and pH to improve management and treatment in critically ill patients.
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