Near-infrared spectroscopy in the evaluation of lower limb ischemia in hemodialysis patients

Near-infrared spectroscopy (NIRS) is used to assess dialysis patients at risk for limb ischemia. Diabetes mellitus and hypertension are the leading causes (± 70%) of end-stage renal disease; hence, hemodialysis patients are at a high risk for having peripheral vascular disease (PVD). Many dialysis patients complain of leg pain and cramping associated with the dialysis procedure. A cause for this may be exacerbation of limb ischemia during ultrafiltration; NIRS noninvasively measures oxygenated and deoxygenated hemoglobin at wavelengths of 840 nm and 750 nm and can assess tissue oxygenation. It can be used to determine the change in the percentage of oxygen saturation in patients with vascular efficiency. We have used NIRS to determine the incidence of PVD in our hemodialysis patients, and furthermore, we have determined the effect of hemodialysis treatment on lower extremity oxygenation. We studied 15 stable patients on hemodialysis who had normal ankle-brachial index (ABI) measurements at rest (1.08 ± 004). Before dialysis, the baseline percentage of oxygen saturation in the calf was 65.2 ± 1.7%, which fell to 57.3 ± 1.9% upon exercise (p < 0.005). The same patients studied the same day after dialysis, however, had a significantly lower baseline calf oxygen saturation of 59.7 ± 1.7%, which fell further to 53.0 ± 2.1% upon exercise (p < 0.005). We therefore conclude that NIRS may be a more sensitive means of diagnosing PVD in hemodialysis patients who may have normal ABI measurements because of vascular calcification. We also conclude that hemodialysis patients who have abnormal calf oxygen saturation levels after exercise have further worsening of their oxygen saturation after hemodialysis. This later finding may explain, in part, the high incidence of hemodialysis-induced lower extremity cramps in this patient population.