Pulse Oximeter as a Potential Screening Tool of Lower Extremity Arterial Disease

Transcription

1 Pulse Oximeter as a Potential Screening Tool of Lower Extremity Arterial Disease Hussien Rizk [1], Hesham Boshra [2], Essam Baligh [1], Noha Mamdouh [2] Department of Cardiovascular Medicine, Cairo [1] and Beni Suif [2] Universities, Egypt. Background Pulse oximeter is a new non invasive diagnostic technique for the investigation of peripheral vascular disease (PVD) that uses difference in limb and trunk transcutaneous oxygen saturation (SaO2) to asses the adequacy of local perfusion. Aim of the Work To detect the efficiency of pulse oximeter as screening tool of PVD. Patients & Methods The study enrolled 150 patients who were divided into three groups; group I: 50 patients above the age of 60 years who have no symptoms of PVD, normal ankle brachial index (ABI) >0.9 and normal duplex findings, group II: 50 asymptomatic patients who have ABI < 0.9, and group III: 50 patients who have symptoms of PVD. All of these patients had oxygen saturation measurements by pulse oximeter Results There were no significant differences between study groups in terms of age, gender, or prevalence of hypertension. Diabetes, dyslipidemia, and smoking were more prevalent in patients with PVD. In group I, normal SaO2 was detected in 97(97%) limbs. In group II, abnormal SaO2 was detected in 43 limbs (78.2%) with significant lesions. In group III, abnormal SaO2 was detected in 65 limbs (93%) with significant lesions and in 5 limbs (7%) with insignificant lesions. In group II, abnormal SaO2 was detected in 43 limbs (78.2%) with abnormal (<0.9) ABI. In group III, abnormal SaO2 was detected in 53 limbs (75.7%) with abnormal ABI. Taking ABI as a golden standard to diagnose significant PVD, pulse oximeter has 84.2% sensitivity and 85.4% specificity. On taking duplexderived data as the golden standard, pulse oximeter has 84.4% sensitivity and 93.5% specificity. Conclusion Taking duplex and ABI as golden standards, pulse oximeter is a relatively sensitive and specific simple tool to diagnose PVD in symptomatic and asymptomatic patients. Key wards: peripheral vascular disease, pulse oximeter, ankle brachial index. 1

2 Introduction PVD is a much more common problem than originally thought. According to published research, more than 1 in 5 people older than age 70 have PVD. Fewer than half of the patients with PVD know they have a problem; many patients with PVD do not have leg symptoms and can only be diagnosed by physical examination or by the ABI test [1]. Because surgery for PVD is offered only to patients with symptomatic disease, the rationale for the early detection of asymptomatic PVD is that risk factor modification following detection might lower subsequent morbidity and mortality from PVD and systemic atherosclerotic disease [1]. The ABI is a simple, non-invasive bedside tool for diagnosing PVD. An ABI of less than 0.9 is diagnostic of PVD, the majority of patients with claudication have ABI ranging from 0.5 to 0.9 [2]. Duplex arterial testing has been proven to be a highly sensitive, specific and accurate method of assessing the patient with PVD [3]. Regional transcutaneous oximetry is a new, noninvasive diagnostic technique for the investigation of PVD that uses difference in limb and trunk SaO2 to assess the adequacy of local perfusion [4]. A source of light originates from the probe at two wavelengths (650nm and 805nm). The light is partially absorbed by hemoglobin, by amounts which differ depending on whether it is saturated or desaturated with oxygen. Objectives of the work To detect the efficiency of pulse oximeter in detecting PVD Patients and Methods This study included 150 patients coming to the Cardiology Departments at Cairo and Beni Suif universities. Patients were divided into three groups: Group I (patients with no PVD): 50 patients (100 limbs) above the age of 60 years with no symptoms of PVD with normal ABI (>0.9) and normal duplex findings. Group II (patients with asymptomatic PVD): 50 patients (55 limbs) with no symptoms of PVD but with ABI less than 0.9. Group III (patients with symptomatic PVD): 50 patients (96 limbs) with symptoms of PVD (claudications or rest pain). Clinical data were obtained from all patients including: age, gender, major risk factors for atherosclerosis (smoking, diabetes mellitus, hypertension and dyslipidemia) and manifestations of vascular atherosclerosis (evidence of cerebrovascular disease [CVD]or coronary artery disease[cad]). Patients with amputated upper or lower limbs were excluded. Hypotensive patients or those in heart failure or respiratory failure were also excluded. We used a hand held pulse oximeter (NPB-40; Nellcor puritan Bennett Inc) to measure SaO2 of both index fingers; of both big toes with patients in supine position and at 12-inches(supported) elevation of the foot, at room air. Abnormal pulse oximetry of the toes was defined as a SaO2 value of more than 2% lower than the fingers value or a decrease of more than 2% on elevation of the leg (decrease from the value at the supine position) [5]. Brachial and ankle systolic pressures were measured by sphygmomanometer cuff and a hand held 8-MHz Doppler probe with the patient placed in a supine position. The higher systolic pressure of the anterior tibial or posterior tibial 2

3 measurements for each foot is divided by the highest brachial systolic pressure to obtain the ABI. Abnormal values were defined as those less than 0.9. Ankle brachial indices were classified into: normal (> 0.9), mild (>0.8 to <0.9), moderate (0.5 to 0.8), or severe (<0.5). All patients underwent vascular ultrasound(duplex)wave form analysis of their lower extremity arteries (femoral, popliteal, tibial, posterior tibial and dorsalis pedis arteries) using Philips HDI 5000 machine. Lesions sites were divided into: iliac, femro-popliteal, infrapopliteal or multisite lesions. According to Doppler-derived data, lesions were classified into: (1) insignificant lesions: normal, mild (diffuse atherosclerosis) or moderate (<50% stenosis) lesions (2) significant lesions: severe lesions (>50% stenosis) or total occlusion. Table (1) velocity criteria for assessment of lower limb stenosis Percentage stenosis Peaksystolic velocity Velocity ratio (m s -1 ) Normal : : : :1 occlusion - - Statistical analysis Data were analyzed by SPSS statistical soft ware (version 12). Continuous variables were presented as mean + standard deviation while categorical data as number (percent). Comparisons between groups were done using chi-square test for quantitative variables and analysis of variants (ANOVA) for continuous variables. Validity of pulse oximeter was done by measuring sensitivity and specificity and Kappa agreement. P-value < 0.05 was considered as statistically significant. Results 1. Clinical characteristics (table 2) There were no significant differences between study groups in base line characteristic (age, gender, or prevalence of hypertension. Diabetes, dyslipidemia, and smoking were more prevalent in symptomatic patients ). Table (2) Study groups: epidemiologic and clinical features. Variables Group I Group II Group III P value Male gender 28(56%) 31(62%) 36(72%) NS Age ± ± ± 10.6 NS Diabetes mellitus 16 (32%) 28(56%) 33(66%) <0.001 Hypertension 26(52%) 27(54%) 28(56%) NS 3

4 Dyslipidemia 19(38%) 34(68%) 33(66%) <0.001 Smoking 22(44%) 31(62%) 33(66%) CAD 28(56%) 41(82%) 37(74%) <0.001 CVD 0% 6(12%) 8(16%) < Lesion characteristics (table 3) Table (3) Lesion characteristics in groups II and III Group II Group III Site Iliac artery 2(3.6%) 12(16.4%) Femro-popliteal 14(25.5%) 30(41.1%) Infra-popliteal 39(70.9%) 24(32.9%) Multi-levels 0(0) 7(9.6%) ABI Mild 8(14.5%) 4(6.8%) Moderate 47(85.5%) 40(67.8%) Severe 0(0) 15(25.4%) 3. Pulse oximeter, ABI and Duplex data (table 4) Table (4) Pulse oximeter, ABI and duplex data Variables Group I Group II Group III Sao2 Normal 97(97%) 12(21.8%) 26(27.1%) Abnormal 3(3%) 43(78.2%) 70(72.9%) ABI Normal 100(100%) 0(0%) 37(38.5%) Abnormal (100%) 59(61.5%) Duplex Insignificant 100(100%) 0(0%) 23(24%) Significant (100%) 73(76%) 4. Pulse oximeter versus duplex (table 5) In group I, abnormal SaO2 was detected in 3 limbs (3%). In group II, abnormal SaO2 was detected in 43 limbs (78.2%) with significant lesions. In group III, abnormal SaO2 was detected in 65 limbs (93%) with significant lesions and in 5 limbs (7%) with insignificant lesions. 4

5 Table 5: SaO2 according to lesion severity as determined by Duplex Insignificant lesions Significant lesions Normal SaO2 Abnormal SaO2 Normal SaO2 Abnormal SaO2 Group I 97(100%) 3(100%) Group II (100%) 43(100%) Group III 18(69.2%) 5(7.1%) 8(30.8%) 65(92.9%) 5. Pulse Oximeter versus ABI (table 6) In group II, abnormal SaO2 was detected in 43 limbs (78.2%) with abnormal (<0.9) ABI. In group III, abnormal SaO2 was detected in 53 limbs (75.7%) with abnormal AB with significant statistical value (P<0.001).I. Table 6: SaO2 according ABI Normal ABI Abnormal ABI Normal SaO2 Abnormal SaO2 Normal SaO2 Abnormal SaO2 Group I 97(100%) 3(100%) Group II (100%) 43(100%) Group III 20(76.9%) 17(24.3%) 6(23.1%) 53(75.7%) 6. Pulse oximeter sensitivity and specificity: Taking ABI as a golden standard to diagnose significant PVD, pulse oximeter has 84.2% sensitivity and 85.4% specificity. On taking duplex-derived data as the golden standard, pulse oximeter was associated with 84.4% sensitivity and 93.5% specificity. Discussion Pulse oximeter is a valuable simple tool for the diagnosis of PVD since it can be performed in out patient clinics in short time. Furthermore, it avoids the problem of media sclerosis [1]. Actually, approximately 5% of persons with PVD have a normal ABI, often because calcified lower-extremity arteries, resulting in artificially increased ABI [6]. Accordingly, pulse oximeter has been studied in diabetic patients who are known to have significant media sclerosis [7,8,9]. Unfortunately, little data exist regarding the role of oximeter in nondiabetic patients. Of note, 61% of our patients with PVD in our study were diabetic. The importance of detection of PVD extends beyond its medical or surgical management. Actually, the mere presence of PVD is known to be associated with increased cardiovascular morbidity and mortality [10]. Accordingly, it is important to find a simple tool that can detect PVD accurately and 5

6 that may aid in better risk stratification and prevention of cardiovascular mortality. In our study we found that abnormal SaO2 measurements present in (72.9%) of limbs in the symptomatic group and (78.2%) limbs in the asymptomatic group. Joyce et al found that resting SaO2 levels were reduced in 57 diabetic patients with a spectrum of PVD including claudications and critical ischemia (31% of them had PVD detected by duplex). In this study, pulse oximetry had a sensitivity of 77% and a specificity of 97% [11]. This compares favorably with the results of our study. In our study 3% of limbs in the normal group had abnormal SaO2 for unknown reason. It is known that reduction in peripheral pulsatile blood flow produced by peripheral vasoconstriction (hypovolemia, severe hypotension, cold, cardiac failure, cardiac arrhythmias) may result in an inadequate signal for analysis [12]. Of note, none of these conditions were present in those 3 patients. In our study, among patients with significant PVD (as detected by duplex), SaO2 measurements were normal in 31% of symptomatic patients. This can be explained partially by the development of collateral vessels that can maintain sufficient distal perfusion [13] Limitations -The number of patients enrolled in this single center study is limited Conclusion Taking duplex and Pulse oximeter as golden standards, pulse oximeter is a relatively sensitive and specific simple tool to diagnose PVD in symptomatic and asymptomatic patients. Pulse oximeter has high sensitivity (84.4%) and high specificity (93.5%). REFERENCES 1. Vogt MT, Cauley JA, Newman AB, et al. Decreased ankle/arm blood pressure index and mortality in elderly women, JAMA 1993; 270: Zheng z,sharrett A, C hambless LE, et al. Assotiations of ankle-brachial index with clinical coronary heart disease, stroke, preclinical carotid and peripheral atherosclerosis: the Atherosclerosis Risk in Communities(ARIC) study.atherosclerosis1997;131: Katsamouris AN, Giannoukas AD, Tsetis D, et al. Can ultrasound replace arteriography in the management of chronic arterial occlusive disease of the lower limb? Eur J Vasc Endovasc Surg.2001; 21: Hauser CJ, Klein SR, Mehringer CM, Appel P,Shoemaker WC. Assessment of perfusion in the diabetic foot by regional transcutaneous oximetry. Diabetes.1984; 33: Pearamswaran, Kathy Brand, James Dolan; Pulse Oximetry as a Potential Screening Tool for Lower Extremity Arterial Disease in Asymptomatic Patients with Diabetes Mellitus. ARCH INTERN MED. 2005; Feb. 28 vol 165 6

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