How do sensors help clinicians accurately find veins?

For routine procedures like blood analysis or for blood donations, a phlebotomist (the person who extracts the patient’s blood) applies a tourniquet to the upper arm to slow blood flow and then visually/physically locates a vein to insert the needle. While expertise varies, the best practitioners can be very precise and execute this procedure with minimal pain for the patient. When the clinician is less or even much less experienced, mistakes can occur and be quite painful for the patient.

For more critical situations/procedures, such as intravenous (IV) insertions and more, near-infrared (NIR), ultrasound sensing techniques, or transillumination technology are frequently used. Design differences provide medical professionals with options for selecting one technology over the other.

NIR vein finder technology

A portable NIR vein viewer consists of one laser diode emitting infrared light and a second laser diode emitting only visible wavelengths. Blood vessels absorb a portion of the infrared light, reflect a contrasted infrared image, and transmit a corresponding signal through a pair of silicon PIN photodiodes.

With circuitry to amplify, sum, and filter the output signals, as well as the use of an image processing algorithm, the second laser diode projects the contrasted image onto the patient’s skin surface. The projected image provides vein location, depth, diameter, and the degree of certainty of vein locations. One company’s portable vein finder’s capabilities are shown in Table 1. It uses six different color lights to be able to detect the target vein through a wide range of patient skin colors.

Ultrasound vein finder technology

Ultrasound imaging or sonography that takes advantage of the Doppler effect uses a piezoelectric transducer element that converts electric signals into acoustic waves. High-frequency sound waves travel from the probe through a gel placed on the skin into the body. The probe also collects the sounds that bounce back for a system processor (an MPU or MPU+DSP) to create an image. Since ultrasound captures images in real-time, it can show the structure and movement of the body’s internal organs as well as blood flowing through blood vessels. As shown in Figure 1, other circuitry in a typical system includes a multi-channel analog front-end, FPGA transmit and receive beamformers, a DAC pulser, a transmit/receive (T/R) switch, and a multiplex/demultiplex (MUX/DEMUX) interface to the piezoelectric transducer.

Transillumination vein finder technology

For a transillumination vein finder, high-intensity LED lights illuminate tissue from below, as shown in Figure 2. Since blood absorbs the light, veins appear as dark lines within the illuminated area. One transillumination product designed primarily for vein access includes a series of 24 dual-colored light emitting-diodes (LEDs).

Another transillumination design includes at least two sets of LEDs of two or more different colors arranged in a light head placed that is against a patient’s skin. As shown in Figure 3, electronic circuitry coupled to the light head selectively operates the LEDs in two or more user-selected modes, providing the ability to adjust the relative intensities of the different colors to best suit the skin color and vein depth of the patient.

Choosing the right technology

Among the criteria for selecting the right vein finder, penetration depth, the ability to obtain vein access in patients with underlying problems such as developmental venous anomaly (DVA), and the ability to allow the clinician to customize the image to their environment appear to be critical. Transillumination, while less accurate than ultrasound or NIR, since it uses simple LEDs for illumination instead of lasers or a piezoelectric transducer, is easy to use and less costly as well.

References

Phlebotomist Technologists & Technicians
Patent No.: US 8,463,364
Near-infrared (NIR) vein finders
Lite 2.0 + Stand
Ultrasound transducer
VeinViewer illumination technology
Venous Ultrasound
US20120101343A1 – Medical imaging device – Google Patents

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