A flexible medical intubation instrument provided for placement into an animal or human patient comprises a catheter with at least a pair of longitudinally extending lumens or channels including a sensor and/or actuator channel and a working channel. In the sensor/actuator channel is provided a fixed or slideably removable sensor cable having a sensor for sensing a characteristic or condition including any of the following: a visual sensor for optical viewing, a chemical sensor, a pH sensor, a pressure sensor, an infection sensor, an audio sensor, or a temperature sensor. The sensors are coupled by the sensor/actuator cable through light transmission, electric current, or radio transmission to a viewing instrument or other output device such as a meter or video screen for displaying the condition that is sensed within the body of the patient while the flexibility of the composite structure comprising the catheter and cable enable the entire instrument to flex laterally as it moves through curved passages or around obstructions during insertion or removal. While making observations through the sensor channel, the working channel simultaneously functions as a drain or an irrigation duct, a feeding tube, or to provide a passage for the insertion of one or a succession of surgical devices such that the catheter serves as a protective artificial tract or liner as surgical devices are inserted and removed through it in succession so as to minimize tissue trauma, infection, and pain experienced by the patient. The instrument can be used in urology, as well as a visually directed nasogastric tube, as a visually directed external gastrostomy tube, or as a visually directed internal gastric tube or percutaneous endoscopic gastrostomy tube and in other applications.