Prediction of amputation wound healing with sldn perfusion pressure

Transcription

1 Prediction of amputation wound healing with sldn perfusion pressure Habtu M. Adera, MD, Kevin James, MD, John J. Castronuovo, Jr., MD, Michael Byrne, MD, Ravi Deshmukh, MD, and Joanne Lohr, MD, Morristown, N.J., New York, N.Y., and Cincinnati, Ohio Purpose: The purpose of this study was to determine whether laser Doppler skin perfusion pressure (LD-SPP) could accurately predict amputation wound healing. Methods: We studied a total of 62 limbs in 52 patients (28 men and 24 women) with a mean age of 62.2 years (range 34 to 93 years). From this, 39 limbs underwent major amputation (15 above-the-knee, 24 below-the-knee), and 23 limbs underwent minor amputations (4 transmetatarsal and 19 toes). There were five postoperative deaths, leaving a total of 57 limbs available for analysis. Results: Three of 13 above-knee amputations failed to heal. Twenty-one of 23 below-knee amputations healed. Three of four transmetatarsal amputations failed to heal and eight of 17 toe amputations failed to heal. Binary table analysis showed that an LD-SPP value of 30 mm Hg or greater had a negative predictive value (healing occurred) of 90%. An LD-SPP value of less than 30 mm Hg at the amputation site had a positive predictive value (healing failure) of 75%, (p < 0.001, chi square analysis). For major amputations, negative predictive value was 100%, and positive predictive value was 83%, (p < 0.001). For minor amputations, negative predictive value was 75% and positive predictive value was 66.7%, (p < 0.09). Conclusion: These data support the use of the LD-SPP test in the selection of major amputation level consistent with healing in ischemic limbs. Further study of the value of this parameter in the determination of minor amputation wound healing is necessary. (J VAsc SURG 1995;21:823-9.) Despite advances in lower extremity arterial reconstruction, amputation remains a routinely performed procedure in patients with end;stageperiph~ eral vascular disease, Typically, the goal of appropriate amputation level selection is ~e 10West level amputation that heals. Many tests are available to assist in amputation level selection and include segmental pressure and pulse volume recorder measurement, transcutaneous measurement of partial pressure of oxygen (TCPo2), laser Doppler flowmetry, skin perfusion pressure (xenon washout), and From the Department of Surgery, Morristown Memorial Hospital, Morristown, Columbia University, College of Physicians and Surgeons, New York, and Good Samaritan Hospital (Drs. James, Byrne, Deshmukh, and Lohr), Cincinnati. Supported by a grant from the Reeves Surgical Research Fund. Presented at the Eighteenth Annual Meeting of the Midwestern Vascular Surgical Society, Cincinnati, Ohio, Sept , Reprint requests: John J. Castronuovo, Jr., MD, Associate Clinical Professor of Surgery, Columbia University, College of Physicians & Surgeons, Department of Surgery, Morristown Memorial Hospital, 100 Madison Ave., Morristown, NJ Copyright by The Society for Vascular Surgery and International Society for Cardiovascular Surgery, North American Chapter /95/$ /6/63918 thermography. Despite these available modalities, none has gained widespread popularity, and clinical judgment remains the primary method by which amputation level is determined) Skin perfusion pressure, as measured by radioisotope washout, has recently been shown to be a reliable predictor of amputation wound healing. 2 Enthusiasm for this test has been blunted because it is time-consuming and uncomfortable for the patient. We' recently reported a simple, noninvasive method of determining skin perfusion pressure with use of the laser Doppler instrument and achieved a coefficient of correlation with the radioisotope washout technique. 3 The purpose of this study was to determine whether laser Doppler skin perfusion pressure (LD- SPP) could accurately predict amputation wound heating. METHODS The study protocol was approved by the Institutional Review Board of Morristown Memorial Hospital. 823

2 824 Adera et al. May 1995 Fig. 1. Leg and toe LD-SPP cuffs are shown. At center of each cuffis transparent PVC window to which fiber optic laser Doppler sensor is securely attached and is then connected to laser Doppler instrument. Fig. 2. Bar graph display of cuff pressure (X-axis, declining values from left to right) and laser Doppler output (volume %) is shown in this illustration where LD-SPP result is seen to be 50 mm Hg. After inflating LD-SPP cuff to suprasystolic pressure, lowest laser Doppler output (volume %) is recorded. As pressure in cuff is decreased, pressure at which laser Doppler output (volume %) begins to increase is noted by increase in height of bar for given pressure. Fifty-two patients underwent 62 lower extremity amputations between 1989 and 1994 at two tertiary community hospitals, Morristown Memorial (Morristown, N.J.) and Good Samaritan (Cincinnati, Ohio). There were 24 women and 28 men with a mean age of 61.2 years (34 to 93 years). Diabetes was present in 28 patients ~(54%). Indications for amputation included infection and ischemic tissue loss caused by failed arterial reconstruction or unreconstructable arterial occlusive disease. Traumatic amputations were excluded. Choice of amputation level was made on clinical grounds by each attending surgeon. LD-SPP technique Testing was performed before operation at the bedside or in the vascular laboratory with a laser Doppler scanner (Vasamedics, St. Paul, Minn.) modified to measure SPP. The laser Doppler flow sensor was secured within the bladder of a blood pressure cuff, which contained a transparent polyvinyl chloride (PVC) window, so that the flow

3 Volume 21, Number 5 Adera et al. 825 Fi g. 3. LD-SPP... measurement resultof20 mm H g is shown 9 This result is predictive ofhealin g failure in major amphtati6n wounds. In this illustration, increase in height of bar graph is not seen until cuffpressure was 20 mm Hgl Laser D6ppler output (volume %) continue to increase as pressure in cuff is decreased by 5 mm Hg and then completely deflated. measurements could be made during cuff inflation and deflation. Several cuff sizes, including a toe cuff, were available. (Fig. 1). Patients were placed in a supine position and a heating pad (42 ~ C) was applied to the test area for 10 minutes to induce reactive hyperemia. The heating pad was unnecessary in patients with warm skin or in areas of cellulitis because the purpose of warming the skin is to produce a high output reading on the laser Doppler flow sensor. In our experience, measurement of LD-SPP can be made easily when this value is 0.5 volume % or greater at the beginning of a test. After brachial blood pressure is obtained, the appropriate-sized LD-SPP cuff is applied to the test area. With a standard arm sphygmomanometer, the cuff is inflated to between 5 and 10 mm Hg, and baseline laser. Doppler output Ivolume %) is recorded. This ensures that good contact between the probe and skin have occurred before proceeding with the test. The cuffis then inflated to 20 mm Hg above the brachial systolic pressure. A stable laser Doppler output value near zero (tess than 0.1 volume %) is necessary before proceeding. The cuff is then deflated in 10 mm Hg-stepwise decrements every S seconds to a pressure of 50 mm Hg. Deflation then proceeds in 5 mm Hg-decrements every 15 seconds until laser Doppler output increases for two consecutive pressure values. The pressure at which this first occurs is the SPP (Figs. 2 and 3). Measurements were taken at the above-knee, below-knee, anlde, transmetatarsal, and toe levels for most patients. Healing failure was defined as any amputation that had to be revised to a more proximal level or required an arterial revascularization to achieve healing. Successful primary healing was defined as any amputationwound closed primarily that did not exhibit ischemic breakdown for 30 days after operation. Successful secondary healing included primarily closed amputations that became infected but healed without the need for revision, as well as open amputations that did nor require further revision. Chi-square analysis was used to determine statistical significance. The binary table was used to determine the predictive values of positive (healing failure') and negative (healing success) test results. RESULTS Of the 62 lower extremity amputations performed on 52 patients with end-stage peripheral vascular disease, there were five postoperative deaths, for a mortality rate of 9.6%. A total of 57 amputations were available for analysis. Table I summarizes patient demographics, which is typical for the vascular surgery population. No patient had a complication related to the testing procedure. Of the 57 amputations in patients who survived surgery for 30 days, 33 had primary healing, and 8 had secondary healing, for an overall healing rate of 72% (41 of 57). Healing failure occurred in 28% of survivors (16 of 57). The average LD-SPP of patients who had healing was 49 mm Hg, and the average for those whose amputations failed to heal was 18 mm Hg. Table II summarizes healing and failure for each level of amputation. An LD-SPP less than 30 mm Hg was considered a positive test result, predictive of failure to heal, and an LD-SPP of 30 mm Hg or greater was considered a negative test result, predictive of successful healing. The results of LD-SPP in predicting amputation wound healing are shown in Table III. For all

4 826 Adera et al. May ]995 Table I. Patients with major and minor amputations: demographics Category Number Age range (yrs.) Mean age (yrs.) 62.2 Male 28 Female 24 Diabetes 28 (54%) amputations, the sensitivity and specificity were 75 % and 90% respectively (p < 0.001). The overall negative predictive value (NPV) was 90%. Analysis of major and minor amputations separately demonstrates better predictive value for major amputations (above-knee amputations [AKA] and below-knee amputations [BKA]) than for minor amputations. Sensitivity and specificity for major amputations were both excellent, 100% and 97%, respectively. Prediction of successful wound healing by the NPV was 100%. These results were highly significant (p < 0.001). Too few transmetatarsal amputations were performed for statistical analysis, and toe pressures only showed a-trend toward significance (p = 0.09). The predictive value of LD-SPP for the healing of toe amputations are not as accurate as those for major amputations, with only a 75% NPV. DISCUSSION Lower extremity amputation remains a commonly performed procedure despite advances in lower extremity arterial reconstruction. The goal of lowest possible amputation level is preservation of maximal function and mobility. Although many tests have emerged to assist surgeons in amputation level selection, none has gained universal acceptance. Ankle/brachial systolic pressure index is inexpensive and easy to perform, but accuracy is variable. 4 This is likely related to the incompressibility of large, calcified vessels, common in the elderly vascular population. Cuff-derived pressures at the toe level also suffer from incompressibility of digital vessels, specifically in patients with diabetes, s,6 Tests that attempt to quantify physiologic parameters at the skin level bypass this problem.-recently, excellent results have been reported with skin perfusion pressure, as measured by the xenon radioisotope washout technique. 2 Although successful healing was predicted in 99% of cases, the technique is somewhat impractical, expensive, and uncomfortable for the patient. Also, each test site must be injected and measured separately in the nuclear medicine suite. Previously, we have reported on a noninvasive LD-SPP technique to measure skin perfusion pressure.3,7,8 The technique centers around a specially designed blood pressure cuff, inside of which the laser Doppler probe is incorporated (Fig. 1). Skin perfusion pressure can be measured at any area where surface anatomy is amenable to the uniform application of counterpressure by a surrounding blood pressure cuff. We were able to achieve a coefficient of correlation with the radioisotope washout technique of Holstein et al., 9 as modified by Faris and Duncan. 1~ We could not achieve the same results with photoplethysmography, another available noninvasive technique of measuring SPP. We believe photoplethysmography deflection may be dependent on the rate ofcuffdeflation and was not reliable in our hands, a In addition, LD-SPP is painless, easily learned, and can quickly be performed at the bedside. Average testing time is about 15 minutes for each site and sometimes includes preparing the test area by inducing hyperemia with a heating pad. Retrospective study shows that this method is a reliable predictor of wound healing or failure in major amputations. All patients with an LD-SPP of 30 mm Hg or greater had healing of their major amputation sites (NPV of 100%). The presence of diabetes or infection did not influence these results. Prediction of healing failure was almost as reliable, because only one patient with an LD-SPP less than 30 mm Hg had healing. LD-SPP was less than 30 mm Hg at all levels tested in this patient and thus might be explained by a technical failure in the performance of the test. These results compare favorably with the use of clinical judgment alone. Successful healing was achieved in 89 % (31 of 35 ) of major amputations. Although the method of judgment of appropriate amputation level may have varied between surgeons, all amputation sites were chosen with the intent of successful primary healing. This study was performed to correlate the clinical decision expected to result in amputation wound healing with the LD-SPP value. Surgeons were blinded to the result, but it is possible that in some cases, the surgeon was aware of the LD-SPP result. No LD-SPP value was suggested as predictive of healing t ~ the surgeons. Results of minor amputations at the metatarsal and toe levels were less encouraging. Too few patients underwent metatarsal amputation to analyze, and toe amputations only showed a trend toward significance (p = 0.09). Raising threshold for healing to 35 mm Hg increased sensitivity to 88%, but overall accuracy decreased to 66%. Two of

5 Volume 21, Number 5 Adera et al 827 AMPUTATION FAILED HEALED < 30 mmhg (+) (TP) 12 (FP) 4 LD - SPP TEST RESULT > 30 mmhg (-) (FN) 4 (TN) 37 Fig. 4. Table evaluates sensitivity and specificity of LD-SPP for amputation wound healing. T/" represents true,positive results; FP represents false-positive results; TN represents truenegative results; FN represents false-negative results. Table II. Lower extremity amputation level and the outcome of wound healing Amputation level No. of amputations Healed Failed to heal Died AKA BKA Transmetatarsal Toe Total "--6 g Table III. Predictive values for the outcome of amputees at different levels All amputees AKA and BIGt Toe amputation Sensitivity 75% 100% 75% Specificity 90.24% 96.8% 66.7% PPV 75% 83.33% 66.7% NPV 90.24% 100% 75% Accuracy 86% 97.22% 70.6% p Value < < PPV, Positive predictive value. the three patients with an LD-SPP less than 30 mm Hg whose toe amputations healed were free from infection and diabetes. All others had active toe infections and had diabetes. Perhaps control of infection in the diabetic foot plays a greater role in healing than at higher levels. Our data contain too few patients to compare these subgroups separately. Finally, we did not include results of other tests for comparison because too few patients in our series underwent any other simultaneous testing. This is an area worthy of future investigation. Other physiologic tests of healing potential, such as TCPo 2 have been reported with good results in amputation healing prediction, n A criticism of TCPo 2 in the prediction of amputation wound healing is the wide range of values reported by different investigators as the cutoff for critical ischemia. Differences in electrical specifications of TCPo 2 equipment has been implicated. 12 This has not been the case with SPP, and we believe that cuff-generated pressures are standard and thus easily reproducible. We have shown the reproducibility of LD-SPP measurements to be comparable to that of brachial blood pressure measured by the Riva Rocci method, 8 In conclusion, we believe that SPP as measured by the laser Doppler is a good predictor of healing in major lower extremity amputations. We have found this test to be simple to perform by technologist or physician in just a few minutes, It is noninvasive, well

6 828 Adera et al. May 1995 tolerated by patients, and can be applied to multiple skin sites. Although no test can replace good clinical judgment, we believe the LD-SPP is a valuable adjunct for identifying critical ischemia in patients at risk for healing failure. We thank Alan Fask, PhD, and Kimberly Hasselfeld, BS, for their assistance with statistical analysis and Catherine Nitto for her help with the preparation of the manuscript. Vasamedics (St. Paul, Minn.) provided the laser Doppler scanner and specialized probe/blood pressure cuffs. REFERENCES 1. Wagner WH, Keagy BA, Kotb MM, et al. Noninvasive determination of healing, of major lower extremity amputations: the continued role of clinical judgement, i VASC SURG 1988;8: Dwars BI, Van Den Broek TAB_, Rauwerda JA, Bakker FC. Criteria for reliable selection of the lowest level of amputation 9 in peripheral vascular disease. I VAse SuRo i992;15: Malvezzi L, Castronuovo JJ Jr, Swayne LC, et al. The gorrelation between three methods of skin perfusion pressure measurement: radionuclide washout, laser Doppler flow, and photoplethysmography. J Vase SURG 1992;15: Malone JM, Anderson GG, et al. Prospective comparison of noninvasive techniques for amputation level selection. Am I Surg 1987;154:i Baker W, Barnes R. Minor forefoot amputations in patients with low ankle pressure. Am J Snrg 1977;133:33i Gibbons GW, Wheelock FC Jr, Siembieda C, et al. Noninvasive prediction of amputation level in diabetic patients. Arch Surg 1979;114: Castronuovo IJ Jr, Pabst TS, Flanigan DP, Foster LS. Noninvasive determination of skin perfusion pressure using a laser Doppler. J Cardiovasc Surg 1987;28: Parmiter S, Adera H, James K, Castronuovo II Jr. The reproducibility of laser Doppler skin perfusion pressure measurements [Abstract]. J Vase Tech 1993;I7: Holstein P, Lund P, Larsen B, Schomacker T. Skin perfusion pressure measured as the external pressure required to stop isotope washout. Scan J Clin Lab Invest 1977;37: Faris I, Duncan H. Skin perfusion pressure in the prediction of healing in diabetic patients with ulcers or gangrene of the foot. J Vase SURG 1985;2: Ameli FM, Byrne P, Provan JL. Selection of amputation level and prediction of healing using transcutaneous tissue oxygen tension (TCpO2). J Cardiovasc Surg 1989;30: Fronek A. Clinical experience with transcutaneous PO 2 and PCO 2 measurements. In: Bernstein EF, ed. Vascular diagnosis. St. Louis: Mosby, 1993: Submitted Sept. 27, 1994; accepted.feb. 6, DISCUSSION Dr. J. Jeffrey Alexander (Cleveland, Ohio). This study represents a part of the Ongoing efforts of Dr. Castronuovo and his group to objectively and reliably determine the optimal level of amputation in patients with nonreconstructible peripheral vascular disease, and this is an important goal. Although amputation is frequently considered to be a therapeutic end point, it is a procedure that can have a great impact on the patient in terms of functional outcome, the cost of treatment, the patient's perceived quality of life, and the patient's life expectancy. Because of this, it behooves us all to perform our amputations with the same planning and expertise as our distal reconstructions. Previous methods used to determine the appropriate level of amputation have lacked either specificity or practicality. This study demonstrates a novel method of measuring skin perfusion pressure as a means of predicting healing. Despite its apparent simplicity and the value of this technique, I have some concerns regarding the design of the study and the interpretation of the results. It should be emphasized that the level of amputation was preselected by the. operating surgeon on the basis of clinical criteria or individual judgement. This preselection process could be expected to enhance the NPV of the SPP measurements. That is to predict healing when healing actually occurred. In that group where healing did occur, were there any patients in whom lower level of amputation may have been chosen on the basis of the SPP measurements? Obviously a study in which amputation level was determined exclusively by these measurements would be of some interest. This leads to my next question. We see that the positive predictive value of SPP was 83.3% for major amputations. This figure would indicate that in 16.7% of patients, a higher level of amputation would have been performed than was absolutely necessary. By contrast, looking at the overall rate of healing on the basis of clinical selection criteria,~we see a 91% healing rate for below-knee amputations and an 84% healing rate for all major amputations. Is it better to err on too high a level of amputation or on too low, which would then require later reoperation? If you believe the former, how would you handle those patients with an SPP of less than 30 mm Hg at the above-knee level? Do you feel comfortable enough with this test to recommend primary hip disarticulation in those situations? Last, it is unclear to me whether studying the combined healing rates of major and distal forefoot or digital amputations is truly appropriate. The fact that the rate of

7 IOURNAL OF VASCULAR SURGERY Volume 21, Number 5 Adera et al. 829 healing and the predictive value of the SPP is considerably lower for distal amputations indicates that the investigators have not adequately controlled such independent variables as diabetes and infection. This tends to weaken their results. All factors being equal, if healing is ultimately determined by SPP, the predictive value of this test should be uniform regardless of the level of amputation. Can the authors suggest any other reasons for these differences? Dr. Kevin James. The first question is a theoretical one of what to do with patients who have an SPP that predicts healing at a lower amputation level than was selected by the attending surgeon. We have seen this, but once again in this study we really did not have an opportunity to find out what would have happened ira more distal amputation was chosen on the basis of SPP. Unfortunately, if an SPP of greater than 30 mm Hg was found at the ankle or below-knee level, and the attending surgeon chose an above-knee amputation, we really had no control over that. The second question regarded a reading at the aboveknee level of less than 30 mm Hg. Would we recommend a hip disarficulation? No, we wouldn't. But some clinicians have used this test to determine whether an inflow procedure to revascularize an above-knee amputation would be needed, specifically in patients who may have had thrombosis of a prior inflow procedure and you're now considering amputation. If the above-knee SPP is poor, let's say 20 or 10 mm Hg, then that patient may need some kind of revascularization to achieve healing even at the above-knee level. The third question centered on differences in measurements at different levels and presumably the results should be the same at each level. There are some technical problems that may explain why this isn't so. This device centers around a blood pressure cuff. You need even application of counter pressure. As you move to the more distal sites in the leg, specifically at the transmetatarsal level and maybe at the ankle, it may be more difficult to get counter pressure and we're still working on that. The toe cuffwas developed later in the series and I will admit that we're still working out some of the technical difficulties of performing that test. In addition, we found that for more distal amputations, specifically at the toe level, that infection and not just skin blood flow is a primary determinant of healing and you're right that we did not control for these variables separately. We didn't have enough patients to do that. Dr. Robert C. Lowell (Wright-Patterson AFB, Ohio). I applaud your attempts to further noninvasive testing in selecting amputation sites. Through my clinical experience with transcutaneous oximetry in the past, I have found several pitfalls of cutaneously applied probes like those you describe. Cellulitis, lower extremity edema, or vasoactive drugs that the patient may be taking can have an impact on such measurements. Did you measure similar values in the opposite leg or in the upper extremity to use as a reference? With a reference as the denominator, you can therefore get an index, and you have some sort of a baseline that might increase the sensitivity and specificity. Dr. James. We haven't tried to make an ankle/brachial or amputation site/brachial index and try to make a value based upon that to predict healing.