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Vascular Assessment of the Neuropathic Foot

Strauss, Michael MD, FACS, AAOS; Barry, Diane D. DPM, FACFAS

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JPO Journal of Prosthetics and Orthotics: April 2005 - Volume 17 - Issue 2 - p S35-S37
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In Brief

Vascularity is essential for survival, function, and healing of the neuropathic foot. Sometimes the clinician is confronted with the paradox of too much vascularity, as in the Charcot arthropathy. More frequently the perfusion problem is too little vascularity, causing ischemia of the foot. Consequences of ischemia include: 1) increased vulnerability to injury and subsequent wound formation; 2) muscle deterioration with atrophy, imbalances, and contractures; 3) nerve damage leading to motor, sensory, and autonomic dysfunction; 4) failure of wounds to heal; 5) inability to control infections; and 6) pain. Consequently, vascular assessment during examination of the neuropathic foot is certainly a crucial component.

In the past, the ankle-brachial index (ABI) was used as the standard for vascular assessment of the neuropathic foot.1 Unfortunately, information from the ABI is not uniformly valid for assessing vascularity, especially in the diabetic limb. Spurious readings caused by the inability of calcified blood vessels to compress, may generate a pulse wave, but not accurately reflect perfusion. There is no substitute for the clinical evaluation. However, there are other ways to assess circulation and tissue oxygenation that are more accurate and give better predictive values for outcomes.

In addition, it must be appreciated in the steady-state situation that blood flow requirements to noncritical tissues at rest, as is expected to be found in the neuropathic foot, are small. If the resting metabolic requirement for a noncritical tissue is arbitrarily assigned a value of one, then for healing and infection control, the requirement may need to increase 20-fold or more.2 If the body cannot meet these demands, a nonhealing wound situation will arise. This concept generates three branches to an algorithm for the vascular assessment and subsequent management of wounds or infections in the neuropathic foot (Figure 1).

Figure 1.
Figure 1.:
Perfusion evaluation and permutations.

THE ROLE OF VASCULAR EVALUATION

The vascular evaluation must be considered in the context of a comprehensive wound evaluation. The four other components of this evaluation are:

  1. Appearance of the wound base;
  2. Size of the wound (including recesses and tunneling);
  3. Depth of the wound; and
  4. Infection load in or around the wound.

Each finding can be graded on a 0-to-2 noncontinuous scale, with 2 being best and 0 being worst (Table 1). This simple assessment integrates well with the three permutations of the algorithm for the vascular assessment and the logical interventions that are used for each. Detection of palpable pulses is the optimal situation and correlates well with normal healing without special interventions. Biphasic or triphasic Doppler pulses also predict healing. However, in these situations a multidisciplinary approach to wound healing often is required. If no pulses are obtainable or the Doppler reveals a monophasic pattern, the foot is profoundly ischemic. Without angioplasty or revascularization, a lower limb amputation is almost inevitable. When pulses are not palpable because of edema, cicatrix, previous sloughs, or debridements, or if Dopplers are not available, one must rely on secondary and tertiary methods of evaluating perfusion and oxygenation. Secondary evaluations include assessing capillary refill and skin temperature (Table 2).

Table 1
Table 1:
Clinical evaluation of perfusion
Table 2
Table 2:
Secondary evaluations of perfusion

When transcutaneous oxygen measurements (PtcO2) are available, they can be used as a tertiary assessment of wound oxygenation directly and perfusion indirectly. Normal wound healing is predicted if PtcO2 measurements in room air are >40 mm Hg.3,4 Thirty- to 40-mm Hg recordings represent the transition at which wounds may or may not heal. If less than 30 mm Hg, healing is unlikely. Hyperbaric oxygen (HBO) can be used, if available, as a diagnostic and therapeutic intervention for the transitional group. Strauss et al.5 showed that if PtcO2 levels increase to greater than 200 mm Hg pressure during HBO exposure regardless of the room air reading, wound healing is predictable in 88% of the cases when HBO is used as an adjunct to wound management. When the oxygen readings are less than 50 mm Hg during HBO exposure, vascular surgery consultations are indicated, with consideration for angiography, angioplasty, or revascularization. Unfortunately, in 10 to 20% of the cases, lower limbs of patients with wounds in neuropathic feet have already been revascularized or revascularization is not feasible. Thus, lower limb amputation may be the only alternative. Primary wound healing was observed in 50% of the cases with adjunctive HBO therapy when the P O2 readings were in the 50–200 mmHg range.5 However, 90% of the wounds that failed to heal primarily after surgery and HBO treatments went on to secondary healing.6 These wounds passed through four clearly definable, uniformly observed stages: 1) a period of deterioration with slough or dehiscence of the wound; 2) a period of no change, the so-called latency period; 3) the stage of angiogenesis with the generation of a tissue base covered with healthy granulation tissue; and 4) epithelialization of the wound by in-growth from the margins.

SUMMARY

Of the five parameters of wound evaluation, perfusion assessment is one of the most important components for wound healing. Certainly no wound heals without an adequate blood supply. If perfusion is nil, the other components of the wound evaluation are likely to be equally poor. With the use of these described algorithm and evaluation techniques, a logical and rational approach to wound perfusion is provided. Although there are no randomized control trials, this approach has ecological validity by virtue of 1) the sensitivity of Doppler measurements and the objectivity of transcutaneous oxygen measurements; 2) the approach herein described for vascular assessment is logical and one that is a standard of practice for evaluation of tissue perfusion and oxygenation; and 3) the high positive predictive value (0.88) for wound healing in which HBO is used as adjunct in the hypoxic wound in which transcutaneous oxygen measurements exceed 200 mm Hg during a trial HBO exposure.

RECOMMENDATIONS FOR FUTURE STUDIES

  1. Correlation studies of primary, secondary, and tertiary vascular evaluations with wound healing.
  2. Cohort studies of outcomes in which HBO is and is not used for each of the three limbs of the evaluation algorithm.
  3. Randomized control trials of outcomes in which transcutaneous oxygen is in the 30- to 40-mm Hg range with and without HBO therapy.
  4. Outcome studies of patients who have angioplasty or revascularization for each of the permutations of the vascular evaluation.
  5. Comparisons of ABIs and transcutaneous oxygen as predictors of outcomes for the three permutations of the vascular assessment.

REFERENCES

1.Wagner FW Jr. A classification and treatment program for diabetic, neuropathic and dysvascular foot problems. Am Acad Ortho Surg Inst Course Lect 1979;28:143–165.
2.Strauss MB. Diabetic foot and leg wounds: principles, management, and prevention. Primary Care Rep 2001;7:187–198.
3.Wyss CA, Matsen FA III, Simmons CW, Burgess EM. Transcutaneous oxygen tension measurements on limbs of diabetic and non-diabetic patients with peripheral vascular disease. Surgery 1984;93:339–345.
4.Hunt TK, Zederfeldt B, Goldstick TK. Oxygen and healing. Am J Surg 1969;118:521–525.
5.Strauss MB, Bryant BJ, Hart GB. Transcutaneous oxygen measurements under hyperbaric conditions as a predictor for healing problem wounds. Foot Ankle Int 2003;23(10):933–937.
6.Strauss MB, Hart GB. Delayed healing of failed flaps in problem wounds after hyperbaric oxygen and surgery. Undersea Hyperbaric Med 2001;25(Suppl):14–16.
© 2005 American Academy of Orthotists & Prosthetists