Study of light transmission through gauze pad effected by blood or liquids to detect needle dislodgement.

Objective: Serious accidents during hemodialysis such as a large amount of blood loss are often caused by venous needle dislodgement. To develop a bleeding sensor based on a photo sensor for monitoring the needle sites, we studied effects of liquids and porcine blood on light transmission through a thin gauze pad with a basic photo sensor.

Methods: The photo sensor consisted of an ordinary electrical circuit, a light emitting diode (LED, lambda max = 645 nm), a photo diode (PD), and a thin gauze pad placed between the LED and PD that were tightly attached to the edges of a plastic clip. The light transmitted through the gauze pad, soaked with liquids or porcine blood dropped on it, was measured with a digital voltmeter. The liquids were reverse osmosis water, physiological saline, glucose in water at 5, 10, 20, 40 and 50%, porcine plasma, and porcine blood (Hct 40, 30 and 20%).

Results: The liquids on a tight-weave gauze pad, significantly increased the voltage (light transmission) from 0.412 +/- 0.003 V (SD) to 0.794 +/- 0.025 V (minimum, by reverse osmosis water) and to 0.945 +/- 0.011 V (maximum, by 50% glucose). The porcine blood significantly decreased the voltage from 0.412 to 0.195 +/- 0.030 V in Hct 40%, to 0.334 +/- 0.035 in Hct 30%, to 0.397 +/- 0.007 V in Hct 20%. The higher the concentration of glucose, the more the light transmission increased. The higher concentration of Hct, the more the light transmission decreased. Similar results were also shown for the loose-weave pad.

Conclusions: Using two types of gauze pads, we confirmed that liquids significantly increased light transmission through gauze pad, but porcine blood decreased light transmission. This opposite response can be used to distinguish liquids from blood on a gauze pad.