385 - Toe-Brachial Index and PVD, Best Diets 2021, Home Oxygen Therapy
Take 3 – Practical Practice Pointers©
From the Literature
1) The “Toe-Brachial Index” – What Does it Diagnose or Predict?
The toe-brachial index (TBI, or toe-brachial pressure index) is a variant of the ankle-brachial index – it compares the systolic pressure in the arms with that found in the great (or second) toe. An ultrasound probe is used to detect the pressure signal at both sites, and yes, there is a very small toe blood pressure cuff involved.
A ratio of toe to brachial systolic pressure of less than 0.6 or 0.7 (recommendations vary) is abnormal and can suggest the presence of peripheral artery disease (PAD). The purported advantage of the TBI is that the smaller arteries of the toe are not as calcified as the larger arteries of the leg, so using the TBI may reduce the false negative rates associated with the ankle-brachial index (ABI).
Diagnosing PAD in a population without symptoms is of uncertain value, as many of the therapies for PAD are directed toward symptom relief if there is no evidence of tissue compromise (slow-healing wounds, etc.). Predicting CAD is another potential benefit of diagnosing PAD, however, the USPSTF found insufficient evidence to make a recommendation for ABI testing for either PAD diagnosis or CAD risk prediction in an otherwise healthy population. TBI testing was not included in this review.
Three recent studies have looked at ABI and TBI use in different populations and for different outcomes. A brief synopsis:
- A systematic review looked at the accuracy of TBI and ABI in diagnosing clinically important PAD in a general population (although 60-82% had diabetes).
- 35 studies (over 1300 patients) on ABI, 9 studies (250 patients) on TBI
- TBI (threshold varied from 0.6-0.75) - Sensitivity - 81%, Specificity - 77%
- ABI (threshold usually 0.9) - Sensitivity - 61%, Specificity - 92%
- Another systematic review examined ABI and TBI performance (and some other non-invasive tests) in a population limited to those with diabetes.
- 9 studies (over 1300 limbs evaluated (not patients) on ABI, 3 studies (221 limbs) on TBI.
- TBI (threshold varied from 0.64-0.75) - Sensitivity of 83%, Specificity of 66%
- ABI (threshold 0.9) - Sensitivity of 64%, Specificity of 89%
- An observational study (~740 patients) in Sweden measured the TBI in those with diabetes and found an increased risk of Major Adverse Cardiac Events in the patients in the lowest tertile of TBI (0.2 to 0.8) compared to those in the highest tertile (0.9-1.3) after an average of 9 years.
John’s Comments (With Guest Commentary):
See how to measure the TBI. Insurance companies have begun performing these tests on patients and calling us with the results, so it’s important for us to know how to interpret them. Until we get well-vetted guidelines, it seems reasonable to ensure that we are optimizing already-recommended cardiovascular preventive measures (smoking cessation, statin use, blood pressure and blood sugar control) in asymptomatic patients who have positive tests. For those with T2D, especially with neuropathy, careful attention to foot protection guidelines would be advisable. For symptomatic patients and patients with foot ulceration, further workup and treatment for PAD for positive patients seems warranted.
I reached out to Joshua Adams, MD, a vascular surgeon and Director of the Carilion Clinic Aortic Center for some comments. He writes, “When patients present with lower extremity pain consistent with claudication, noninvasive vascular labs studies are helpful in diagnosing PAD as the underlying cause. ABI'S tend to be the most commonly reported study but may be falsely elevated in patients with DM and ESRD and may be less sensitive than the TBI. In fact, the studies may be viewed as complimentary to achieve the highest sensitivity and specificity. Thankfully, when one orders ABI's at the Carilion Clinic Vascular Labs, TBI's are provided, as well.”
- Herraiz-Adillo Á et al. The accuracy of toe brachial index and ankle brachial index in the diagnosis of lower limb peripheral arterial disease: A systematic review and meta-analysis. Atherosclerosis. 2020;315:81-92. Link
- Normahani P et al. A systematic review and meta-analysis of the diagnostic accuracy of point-of-care tests used to establish the presence of peripheral arterial disease in people with diabetes. Journal of Vascular Surgery. Published online December 3, 2020. Link
- Chisalita SI et al. Toe brachial index predicts major acute cardiovascular events in patients with type 2 diabetes independently of arterial stiffness. Diabetes Research and Clinical Practice. 2020;161:108040. Link
From the US News and World Report
2) “Best Diet” Rankings for 2021
U.S. News recently released its annual assessment of the best diets, offering extensive data and information on 39 popular diet plans. The rankings were established by a panel of experts, including nutritionists, dieticians and physicians rated each diet in seven categories: how easy it is to follow, its ability to produce short-term and long-term weight loss, its nutritional completeness, its safety and its potential for preventing and managing diabetes and heart disease.
For the 4th consecutive year, the Mediterranean Diet ranks as the No. 1 Best Diet Overall. The Mediterranean Diet also rated best in multiple other categories; best plant-based diet, easiest diet to follow, best diet for healthy eating (tie), best diet for diabetes (tie), and ranked 2nd for best diet for heart health. The DASH Diet and the Flexitarian Diet (a plant-based plan, with meat in moderation) were tied for 2nd best overall diet. The WW (Weight Watchers) diet was 4th.
WW (Weight Watchers) and the Flexitarian Diet were tied for the top-rated Best Weight-Loss Diet and WW was the Best Commercial Diet. Mayo Clinic Diet was the 2nd Best Commercial Diet, followed by Jenny Craig and Noom (tie).
It is important to note that there isn't "a" Mediterranean diet. The cultural lifestyle of people in countries bordering the Mediterranean Sea shares common principles, including an active lifestyle, weight control, and a diet high in produce, nuts and healthy oils and low in red meat, sugar, and saturated fat. A Mediterranean diet pyramid has been developed to help guide those desiring to follow this nutritional approach (see References).
The DASH Diet (Dietary Approaches to Stop Hypertension) is promoted by the NHLBI to stop or prevent HTN. It emphasizes vegetables, fruits, whole grains, lean protein and low-fat dairy. DASH also discourages foods that are high in saturated fat, such as fatty meats, full-fat dairy foods and tropical oils, as well as sugar-sweetened beverages and sweets and sodium. The NHLBI publishes free guides on the plan (See references).
Mark’s Comments (With Guest Commentary):
I reached out to colleague, “Lifestyle Medicine guru,” and regular Take 3 contributor Beth Polk, MD, for her insights. In addition to regularly speaking nationally on this topic, Beth serves as one of 4 national faculty on an AAFP Advisory Committee for Lifestyle Medicine. Beth replied, “What stands out for me is that there is a growing consensus that a diet that consists of predominantly plants is the healthiest overall and addresses most of the chronic diseases we see every day. Increasing fruits, vegetables, beans, nuts and seeds, decreasing meat intake and eliminating processed foods is the common thread in the top diets mentioned. The best advice we are able to give our patients is still ‘eat food, mostly plants, and not too much.’”
This is the approach I follow personally. I’ve named it the “Pollanian diet” after the author Michael Pollan, who described this approach in his books In Defense of Food.
It is notable that diet plans that ranked the lowest included Atkins, Keto, Whole 30, and Dukan diets. Most of these include a limitation of carbs and an emphasis on protein and the long-term maintenance of ketosis. While these diets have become quite popular (and have been shown to be potentially effective with short-term weight loss), their long-term health impact continues to be concerning.
U.S. News Best Diets Rankings for 2021. January 4, 2021. Link
From the Guidelines and the American Thoracic Society
3) Home Oxygen Therapy for Adults with Chronic Lung Disease
Five million adults live with chronic lung disease in the US, with more than one million prescribed Long-Term Oxygen Therapy (LTOT), defined as oxygen prescribed for at least 15 h/d. The rationale for the provision of LTOT in adults is based on the survival benefit reported by two randomized clinical trials published over three decades ago in patients with COPD and severe, chronic hypoxemia. Since then, an additional clinical trial (LOTT – Long-Term Oxygen Therapy Trial) has examined the role of home oxygen therapy in patients with COPD and moderate resting hypoxemia or exertional hypoxemia. Recent data highlight significant differences in home oxygen needs for patients with different lung diseases and lifestyles. This recently published guideline provides the basis for evidence-based use of home oxygen therapy in adults with COPD or interstitial lung disease (ILD).
In adults with COPD who have severe chronic resting room air hypoxemia, prescribe long-term oxygen therapy (LTOT) for at least 15 h/d (strong recommendation, moderate-quality evidence).
Severe hypoxemia is defined as meeting either of the following criteria: 1) PaO2 < 55 mm Hg or oxygen saturation as measured by pulse oximetry (SpO2 ) < 88%; 2) PaO2 = 56–59 mm Hg or SpO2 = 89% plus one of the following: edema, hematocrit > 55%, or P pulmonale on an ECG.
In adults with COPD who have moderate chronic resting room air hypoxemia, prescribe LTOT (conditional/low).
*Moderate hypoxemia is defined as an SpO2 of 89–93%.
In adults with COPD who have severe exertional room air hypoxemia, we suggest prescribing ambulatory oxygen (conditional/moderate).
For adults with ILD who have severe chronic resting room air hypoxemia, prescribe LTOT for at least 15 h/d (strong/very low).
For adults with ILD who have severe exertional room air hypoxemia, prescribe ambulatory oxygen (conditional/low).
For patients prescribed home oxygen therapy, the patient and their caregivers should receive instruction and training on the use and maintenance of all oxygen equipment and education on oxygen safety, including smoking cessation, fire prevention, and tripping hazards (best practice statement).
I appreciated this reminder of the science behind home oxygen therapy as well as the research “gaps.” I often find myself signing the requisite approval/renewal forms for this therapy and not checking with my patients with chronic lung disease as to the quality of life impact for them. I checked with two this week. “A lifesaver” and a smile was the response from each.
Jacobs S, et al. Home Oxygen Therapy for Adults with Chronic Lung Disease. An Official American Thoracic Society Clinical Practice Guideline. Am J Respir Crit Care Med. 2020 Nov 15;202(10):e121-e141. Article
Mark and John
Carilion Clinic Department of Family and Community Medicine
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