Editor's note: Last issue, we examined how to use a bladder scanner. Join us in this issue as we take a look at how to use a venous Doppler device.
A continuous wave venous Doppler is a portable, handheld ultrasound device that evaluates the patency of major veins in the arms, legs, and neck by detecting blood flow. This painless, noninvasive procedure is often referred to as a “bedside Doppler” by clinicians.
Continuous wave venous Doppler devices are used by nurses in a variety of healthcare settings, such as the:
* medical-surgical unit
* physician's office
* wound care clinic
* long-term care facility
* home health setting.
How does it work?
Conductive ultrasound gel is applied to the skin over the selected blood vessel. The handheld wand (transducer) is pressed into the gel against the skin, directing high-frequency sound waves over the blood vessel. These sound waves enter the tissue and bounce off the flowing blood, creating an ultrasonic echo; the transducer detects and converts these echoes into a sound wave. The repetitive sound waves are bounced off the blood cells as they course through the vessel with each heartbeat and are sent back to the transducer, filtering through two piezoelectric crystals that vibrate at 8 million cycles per second.
The speed and flow of blood coursing through the vein is interpreted by the amplified ultrasound as a “whoosh” sound. The presence or absence of this repetitive sound can help clinicians measure the patency of venous blood vessels and assist with diagnosing potentially life-threatening conditions. If the blood vessel is patent, a loud, repetitive “whoosh” will be heard. If the vein is partially occluded, a faint “whoosh” sound may be heard. If the vein is completely occluded, there will be no sounds other than the continuous baseline static noise emitted from the device.
Mind the eight P's
You should perform a quick neurovascular check before performing the venous Doppler procedure. A basic neurovascular check includes the eight P's:
* paresthesia (numbness or tingling)
* pattern of hair growth
* presence of warmth
* proportional symmetry of extremities.
When performing a neurovascular assessment, carefully observe for hair growth patterns on the patient's extremities. Minimal hair growth can potentially indicate peripheral arterial disease (PAD). You should also assess for symmetry of the extremities. If the patient's extremities aren't symmetrical, you should measure the circumference of both extremities to allow for accurate documentation of the anomaly. An asymmetrical, swollen extremity could indicate deep vein thrombosis (DVT). Immediately report all abnormal exam findings to the healthcare provider.
Catch the wave
A continuous wave venous Doppler device is commonly used to assess the:
* radial artery
* dorsalis pedis artery
* tibial artery
* femoral artery
* popliteal artery
* carotid artery.
To perform the procedure:
* Inspect the device to ensure that all the components are present and attached correctly and that no visual defects are noted.
* Explain the procedure to the patient.
* Assess the patient's temperature and BP before performing the procedure. If the temperature or BP is very low, blood vessels will be constricted and the results may be altered.
* Provide privacy.
* Help the patient into a supine position with the extremities slightly rotated in an outward position.
* Apply a liberal amount of room temperature or warmed ultrasound gel to the patient's skin surface over the selected area. It's essential that conductive ultrasound gel be used for any Doppler exam to ensure adequate ultrasound signals are transmitted and received.
* If utilizing a stethoscope Doppler device, you should ensure that the stethoscope cable is firmly plugged into the output port of the ultrasound box. Some instruments have the capacity to allow for a second stethoscope listener via a second output.
* Adjust the volume control to medium and place the transducer tip into the ultrasound gel.
* Press the ON button. It may be located on the front or side of the unit.
* Adjust the volume as needed. The volume control button may be located on either the front or the side of the device.
* Gently and firmly press the transducer tip downward into the conductive ultrasound gel, making contact with the skin at a 45-degree angle. Slowly move the transducer tip over the desired area, tilting the tip toward the desired blood vessel until a repetitive “whoosh” sound is auscultated. Be careful not to press too hard because it can occlude the blood flow.
* If you're unable to auscultate a loud “whoosh,” you should reposition the extremity and attempt the procedure again.
* When finished, clean any remaining ultrasound gel off the patient's skin.
* Document if pulses were present or absent. Notify the healthcare provider immediately if you're unable to hear a pulse. The absence of an audible pulsating “whoosh” sound is a medical emergency. If the blood vessel is completely occluded from dangerous blood clots, edema, or a disease process, no sound will be heard. If blood supply isn't quickly restored, tissue cell death will rapidly occur.
* Clean all components of the device after usage, according to your facility's policy.
* Return the device to the proper storage area.
Why can't I hear any sounds?
If no sound is being emitted from the device, you should thoroughly assess it to ensure that:
* the batteries are fully charged
* the cord is securely fastened, attaching the transducer to the monitor
* the tip of the transducer is clean and free from debris
* there are no visible defects to the monitor box, cord, or transducer.
Inability to palpate or auscultate pulses may signal that circulation to the area is impaired. If you're unable to auscultate pulses after troubleshooting for mechanical failure, perform a second neurovascular assessment and immediately notify the healthcare provider of the results.
* A continuous wave Doppler device should only be utilized on intact skin surfaces. Avoid incision lines and open wounds.
* The depth of skin tissue to which the acoustic waves penetrate is completely dependent on the frequency emitted. A handheld Doppler device that produces a 3 to 5 MHz signal can penetrate up to 3.1 inches (7.87 cm) into the tissue.
* Obese patients may require a more in-depth ultrasound procedure that can be used to penetrate through an increased depth of subcutaneous tissue.
* If the extremity on which you're performing the exam is cool to the touch, consider applying a warm blanket to the area. Vasoconstriction can occur as a result of the cool temperature, which can alter the results.
* The presence of extensive extracellular fluid may limit the transducer's ability to detect blood flow in patients with conditions such as lymphedema or extensive edema.
* The continuous wave Doppler device can only pick up a signal if the flow of blood is fast enough. The minimum speed of blood flow detectable is 1.1 inches (2.79 cm) per second.
* To detect blood flow, the device must distinguish the signal in a noisy environment. The frequency resolution is critical to detection success.
* The patient must be still during the exam otherwise the tissue motion will block the blood velocity signal that's being interpreted by the transducer.
* In an emergency situation, a continuous wave venous Doppler device can be utilized to obtain a systolic BP.
Time costs tissue
When pulses can't be palpated or auscultated, it's a medical emergency. Absence of a pulse in an extremity can point to the reduction or absence of oxygen-rich blood flow. A delay in treatment can lead to tissue hypoxia, necrotic tissue, septicemia, amputation, and death. The venous Doppler device can provide a quick, noninvasive, and painless verification of vein patency. Combined with a thorough nursing clinical assessment, the venous Doppler device can assist you in saving a patient's life or limb!
Conditions that can cause a loss of pulse
* antiphospholipid syndrome
* arterial insufficiency
* Buerger disease
* cardiac arrhythmias (especially atrial fibrillation)
* cardiovascular collapse
* cardiogenic shock
* compartment syndrome
* extravasation of a toxic medication
* factor V Leiden disorder
* myocardial infarction
* heart failure
* infected/gangrenous wounds
* intra-aortic balloon catheter migration
* patent foramen ovale
* peripheral vascular disease
* polycythemia vera
* pulmonary embolism
* recent surgery
* restraint use
* venous stasis ulcers
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