What You Should Know About Using NIV Studies

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When NIV Studies Are Warranted

Atherosclerosis is the major cause of poor arterial flow in the foot. It decreases flow by narrowing or occluding the arterial lumen. In patients with diabetes, you’ll see occlusion in the distal bifurcation points. However, in non-diabetic patients, you’ll most often see the occlusion at proximal points.1 It is important that we are able to recognize the presence and severity of disease. Symptoms of claudication and ischemic rest pain are important warning signs that suggest the need to order NIV studies.

In addition to ordering NIVs for those with atherosclerosis, you should also order NIV studies for patients who have:
• diabetes;
• claudication;
• signs of critical ischemia, skin changes or gangrene;
• absent or diminished pedal pulses; or
• femoral bruits.

Then there’s the question of which NIV study is best for the given clinical situation. Here are some key points to keep in mind.
• The ABI/TBI/PPG have been shown to be closely associated with arterial physiology for vascular evaluation of the distal foot.
• Segmental pressure measurements and exercise testing can give you reliable information on iliac and femoral popliteal occlusive disease.
• Employing TCOM helps to determine the severity of lower extremity arterial occlusive disease and ascertain the greatest likelihood of healing ulcers or success in digital amputations.
• Dopplers are an excellent adjunctive modality in finding the exact location of stenosis/occlusion and when ABI and segmental pressures are inconclusive.

It’s also essential to pay close attention to the testing environment. Be aware of things like ambient temperature, the patient’s state of relaxation and limb positioning.

Understanding the limitations of these NIV studies is necessary for applying the results to clinical situations.

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NIV is a valuable tool in screening for peripheral arterial disease. The cost of NIV studies is substantially less in comparison to arteriography.
18
Author(s): 
By Dana Giacalone, DPM, and Khurram Khan, DPM

When Should You Emphasize TCOM?
TCOM is indicated in wound evaluation, hyperbaric oxygen therapy, plastic surgery and vascular surgery. You can also use TCOM to determine the level of amputation and adjunctively to help diagnose PVD.6
Accuracy in testing depends on the local factors (skin thickness, capillary formation and density, presence of inflammation or edema) and systemic factors (lung function, FI02, blood Hg level, cardiac output).4,6 Keep in mind you can’t use TCOMs on the plantar aspect of the foot, on curved surfaces like toes or malleoli or when the patient has cellulitis.4
You would obtain readings by placing electrodes in designated areas. The central reference position is 5 cm below the middle left clavicle. The peripheral positions are 10cm AK, 5 cm BK, medial foot and the lateral foot. You would apply a buffer solution to electrodes and the attached probes begin heating underlying skin. After equilibration, you should obtain readings at three- to five-minute intervals and you can add to your baseline testing by including an oxygen challenge with inhalation of 100 percent oxygen.
In order to detect positive increases in value, you would need to compare baseline readings to oxygen challenge. A positive response is an increase of at least twice the baseline reading. Successful wound healing has been shown to occur with >40mmHg. Failure to heal is indicated by <20mmHg with necrosis at 10mmH or less.6,7,8 Grolman, et. al., found that patients with a TCOM increase of 10 mmHg or greater had a 70 percent chance to heal ischemic wounds with adjunct therapy.9 They also report that TCOM was an excellent predictor of the severity of tissue hypoxia associated with peripheral arterial occlusive disease.

Final Notes
NIV is a valuable tool in screening for peripheral arterial disease. The cost of NIV studies is substantially less in comparison to arteriography. Sykes states that overall NIV testing is less than $500 versus angiograms which cost over $2,000.1
It is important to emphasize the role of recognizing peripheral arterial disease and instituting appropriate treatment regimens. A recent study, the Peripheral Arterial Disease (PAD) Detection, Awareness and Treatment in Primary Care, confirmed the relative lack of awareness of PAD by patients and their physicians. Eighty-three percent of patients with prior PAD were aware of their condition, although only 49 percent of physicians were aware of their patients’ diagnosis. Classic claudication was uncommon in 5 to 15 percent of patients.8 The study also confirmed the lack of treatment for patients with PAD in comparison with those having other cardiovascular diseases.8

Dr. Giacalone is a first-year resident and Dr. Khan is a second-year resident at the University of Texas Health Science Center.
Dr. Steinberg is an Assistant Professor in the Department of Orthopaedics/Podiatry Service at the University of Texas Health Science Center.




References:

References

1. Sykes M and Godsey J. “Vascular Evaluation of the Problem Diabetic Foot.” Clinics in Podiatric Medicine and Surgery. 15(1): 49-74, January 1998.

2. Pellerito J. “Current Approach to Peripheral Arterial Sonography.” Radiologic Clinics of North America. 39(3): 553-67, May 2001.

3. Dawson, et. al. “Treating Intermittent Claudication Secondary to Peripheral Arterial Disease.” Pharmacy and Therapeutics. 24(12): 616-623, December 1999.

4. Hoffman AF. “Evaluation of Arterial Blood Flow in the Lower Extremity.” Clinics in Podiatric Medicine and Surgery. 9(1): 19-56, January 1992.

5. Bowker J and Pfeifer M. Levin and O’Neal’s The Diabetic Foot. Edition 6, Mosby, St. Louis, Missouri, 2001

6. Rich K. “Transcutaneous Oxygen Measurements: Implications for nursing.” Journal of Vascular Nursing. 19(2): 55-59, June 2001.

7. Axelrod, et. al. “Cost of Routine Screening for Carotid and Lower Extremity Occlusive Disease in Patients with Abdominal Aortic Aneurysms.” Journal of Vascular Surgery. 35(4): 754-758, April 2002.

8. Dieter, et. al. “The Significance of Lower Extremity Peripheral Arterial Disease.” Clinical Cardiology. 25: 3-10, January 2002.

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