Gereç ve Yöntem: Çalışma kritik ekstremite iskemisi olan 261 tane AE-PAH hastasının verileri retrospektif olarak incelenerek yapılmıştır. Hastaların TKV değerleri alınan kan örneklerindeki total protein ve hematokrit değerlerinden elde edilen bir formülasyon ile bulunmuştur. Analiz için SPSS 23.0 programı kullanılmıştır.

Bulgular: 51 (19.6%) hastada amputasyon gelişmiştir. Amputasyon gelişen hastaların hemoglobin, hematokrit, beyaz kan hücresi sayısı, nötrofil, platelet, yüksek kesme oranında (YKO) TKV (16.58±2.13 vs. 15.74±1.47, p<0.001) ve düşük kesme oranında (DKO) TKV (100.15±14.97 vs. 92.84±13.39, p=0.002) değeri daha yüksek bulunmuştur. Çoklu regresyon analizi sonucunda YKOTKV (OR: 1.096 95%CI (1.067-1.182), p=0.002) ve DKOTKV (OR: 6.481 95%CI (4.102-9.486), p<0.001) amputasyon gelişimini gösteren bağımsız risk faktörleri olarak bulunmuştur. Yapılan alıcı işlem karakteristikleri eğrisi analizi sonucunda YKOTKV için amputasyonu gösteren kesme değeri 16.34 (%69 sensitivite, %68.6 spesifite ve eğri altında kalan alan (EAA): 0.728(0.532-0.823), p=0.005), DKOTKV için amputasyonu gösteren kesme değeri 97.48 (%71.5 sensitivite, %70.2 spesifite ve EAA: 0.736(0.551-0.842), p=0.003) olarak bulunmuştur.

Sonuç: Kesme oranlarına göre her iki TKV değeri de kritik ekstremite iskemisi olan ve revaskülarize edilemeyen hastalarda amputasyon gelişimini öngördüren değerler olarak bulunmuşlardır.

Although revascularization is the primary treatment option in treating CLTI, some patients are unsuitable for revascularization due to anatomical and physiological reasons⁹. In addition to medical treatment, treatment options such as lumbar sympathectomy, spinal cord stimulation, hemodilution and intermittent pneumatic compression have been recommended for these patients^9-11. Indeed, Kim et al. showed that hemodilution therapy reduces major amputation in CLTI patients without a revascularization option¹⁰. The physiological rationale of hemodilution therapy is that despite the decrease in hemoglobin level, the reduction in blood viscosity increases tissue perfusion¹². Although the hemoglobin level, which is essential for oxygen delivery to the tissue, decreases in this treatment option, the improvement in blood viscosity increases tissue oxygenation, suggesting that blood viscosity is an important clinical determinant in CLTI patients. Besides, the effectiveness of whole blood viscosity (WBV) as an important predictor in different cardiovascular diseases has been shown in the literature^13,14. Based on this, we planned to investigate whether whole blood viscosity predicts amputation in CLTI patients unsuitable for revascularization.

For this retrospective study, 684 patients who underwent invasive lower extremity peripheral angiography diagnosed with LEPAD CLTI between September 2016 and November 2021 were screened. A total of 261 patients who met the criteria of being technically unsuitable for revascularization or having previously experienced an unsuccessful revascularization procedure and having pain at rest (Rutherford grade 2-3) were included in the study. Patients with a body mass index (BMI) below 18 kg/m2, acute arterial disease, major tissue loss, liver failure, kidney disease, acute or chronic infection, chronic inflammatory disease, hematological disease, heart failure, oncological disease, use the anticoagulant treatment for any reason and patients whose follow-up data cannot be accessed from hospital records were excluded from the study. In the formula used by De Simone et al. to calculate WBV, since it is recommended to use patients with plasma total protein values of 5.4–9.5 g/100 mL and values of 32-53% for HCT, patients with values outside these ranges were also excluded from the study^15,16. The patients included in the study were divided into two groups as amputated and not amputated within one year.

The patients’ blood results before the procedure were obtained from the hospital automation system, and the biochemistry and whole blood count values required for analysis were recorded. The complete blood test was evaluated using an automatic hematology analyzer (Symex XN-550 analyzer, Symex, Kobe, Japan) and biochemical tests using standard biochemical methods with Beckman Coulter LH 780 device (Beckman Coulter Inc., Brea, New York, USA). WBV values were calculated using Simone’s formula, using hematocrit (HTC) and total protein (TP) concentration for both high shear rate (HSR=208 s-1) and low shear rate (LSR=0.5 s-1). For HSR, WBV (208 s-1) = (0.12 × HTC) + 0.17 (TP-2.07), for LSR, WBV (0.5 s-1) = (1.89×HTC) + 3.76 (TP-78.42) formulas were used. HTC is in %, TP is in g/l and WBV is whole blood viscosity in centipoise (cP)^15,16.

Statistical Analysis: Categorical data are presented as numbers and percentages. All the variables were examined with the Kolmogorov–Smirnov test for normality and the Levene test for homogeneity of variances before significance tests were used and normally distributed homogeneous data were used with the t-test in independent groups. The Mann–Whitney U test was used to evaluate the difference in the parameters that did not show normal distribution. For non-parametric data analysis, the chi-square test was used. Multivariate and univariate logistic regression was done to analyze the defined risk factors for amputation development and determine independent risk factors. Receiver operating characteristic (ROC) analysis was drove to estimate the optimal cut-off value of WBV at HSR, WBV at LSR, and HCT in indicating amputation. Sensitivity, specificity, and area under the curve (AUC) values were calculated. The significance level was accepted p<0.05 2- sided for all statistical analyses. All data was analyzed using IBM SPSS Statistics (IBM Corp., Armonk, NY, USA) for Windows.

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Table 1: Basal demographic and laboratory characteristics of the patients according to amputation status

Multivariate and univariate logistic regression analyzes were performed to investigate the predictive factors for amputation. Hemoglobin, hematocrit, WBC, neutrophil, platelet, total protein, WBV at HSR, and WBV at LSR were found to be good predictor factors for amputation (p=0.004, p=0.003, p=0.020, p=0.047, p=0.033, p=0.024), p=0.001, p<0.001, respectively). When all the factors that were affected the amputation by multivariate regression analysis were examined, WBV at HSR (OR (95%CI) 1.096(1.067-1.182), p=0.002) and WBV at LSR (OR (%95CI) 6.481(4.102-9.486), p<0.001) were determined as independent risk factors for amputation (Table 2).

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Table 2: Regression analysis results in predictive factors for amputation

ROC curve analysis for WBV at HSR and WBV at LSR showed that the ideal cut-off values of WBV at HSR and WBV at LSR as a predictor of amputation was 16.34 (69.0 % sensitivity and 68.8% specificity) for WBV at HSR and 97.48 (71.5% sensitivity and 70.2% specificity) for WBV at LSR. The AUC for WBV at HSR was found to be 0.728 (95% CI 0.532-0.823; p=0.005), and the AUC for WBV at LSR was found to be 0.736 (95% CI 0.551-0.842; p=0.003) (Figure 1) (Table 3).

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Figure 1: Receiver operating characteristic curve analysis table for amputation

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Table 3: Receiver operating characteristic curve analysis results for amputation

Although the primary treatment recommended for CLTI patients is revascularization, different treatment protocols have been proposed for patients who cannot be revascularized due to various reasons. One of them is the hemodilution method. It is thought that the main effect of the hemodilution therapy is the positive effect on the plasma viscosity and the increased flow in the micro-vessels^12,17,18. As a matter of fact, it has been shown in the literature that WBV is improved with hemodilution therapy. Kim et al.¹⁰ showed that despite the decrease in hemoglobin levels with hemodilution therapy in patients with CLTI, the tissue oxygen delivery index increased due to improved WBV, which was reflected in positive clinical results. Considering all of the above, it is seen that WBV is the treatment target that has an essential place in physiopathogenesis in patients with LEPAD. Especially in patients with multiple, long collateralized vascular obstructions, such as CLTI patients, WBV is an important factor determining endothelial shear stress, thus increasing its clinical importance in this patient group¹⁹.

In addition to the above, the atherosclerosis process is significantly influenced by hemorheological factors has been shown in the literature that increased blood viscosity plays a vital role in the atherosclerotic process by causing intravascular stasis and endothelial dysfunction²⁰. A high degree of blood viscosity causes turbulent blood flow that exacerbates endothelial disruption and impairs endothelial integrity and function ^21-23. Apart from the atherosclerotic process, endothelial shear stress also affects atherosclerotic plaque rupture and thrombosis formation ^24,25. As the main determinant of endothelial shear stress, WBV has an important role in this physiopathological pathway. As a matter of fact, Erdogan et al. showed that WBV was significantly higher in patients presenting with acute arterial occlusion compared to the control group ²⁶.

Viscometers such as falling-ball, capillary, and rotational viscometers are used for viscosity measurements²⁷. However, access to these methods is limited in daily clinical practice. The formula we used in our study, defined by Simone, provides important data on WBV through total protein level and complete blood count, which we commonly use in routine practice. With the formula described by Simone, estimated WBV values can be obtained at different shear rates¹⁵. Compared to the viscometer-measured analysis, the estimated WBV values calculated with the formula described by Simone demonstrated a smaller degree of error¹⁵.

Limitations of this study, first, the study is a single-center and retrospective study which may cause selection bias. Secondly, platelet and erythrocyte aggregability and rigidity, which may influence blood viscosity, were not assessed. And lastly, blood viscosity was not directly measured in the study. Even though other studies have proven the validity of the extrapolation method, we employed in this study, investigating the correlation between estimated WBV and blood viscosity measured directly with a viscometer could increase the effectiveness of our study.

In our study, we showed that WBV calculated using simple laboratory tests predicts amputation in LEPAD patients who do not have the option of revascularization. Considering that the population in our study has no option for revascularization, the value of WBV as a predictor of amputation in these patients is vital for identifying high-risk patients and managing their treatment.

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