An elongate
oxygen sensor (1, 201, 301, 401) for
insertion into a
urinary drainage lumen of an elongate
catheter (101). The elongate
oxygen sensor (1, 201, 301, 401) includes: a sensor tip (2, 202, 302, 402), located at a distal end of the elongate
oxygen sensor (1, 201, 301, 401), having a first width; a spacer portion (10, 210, 310, 410), for spacing the sensor tip (2, 202, 302, 402) away from a wall of the
urinary drainage lumen, the spacer portion (10, 210, 310, 410) having a second width (21, 221a, 221b, 321a, 321b, 421a, 421b), larger than the first width and located further from the distal end than the sensor tip; and a body portion (12, 212, 312, 412), located further from the distal end than the spacer portion (10, 210, 310, 410), the body portion having a third width, smaller than the second width.