Prevention of haemodialysis-induced hypotension by biofeedback control of ultrafiltration and infusion

Background. Haemodialysis-induced hypotension is still a severe complicatio n in spite of all the progress in haemodialysis treatment. Because of its m ultifactorial causes, haemodialysis-induced hypotension cannot be reliably prevented by conventional ultrafiltration and sodium profiling in open-loop systems, as they are unable to adapt themselves to actual decreases in blo od pressure. Methods. A blood-pressure-guided closed-loop system, for prevention of haem odialysis-induced hypotension by biofeedback-driven computer control of bot h ultrafiltration and saline infusion was clinically tested in 237 treatmen ts of seven patients prone to hypotension. As medical knowledge on multifac torial causes of hypotension is characterized by a lack in deterministic kn owledge; fuzzy logic and linguistic variables were used to involve clinical experience on hypotension phenomena in terms of fuzzy knowledge. Biofeedba ck control is based on frequent measurements of blood pressure at 5 min int ervals. Blood pressure behaviour is described by linguistic variables and f uzzy sets. Adaptive rule bases were used for the simultaneous fuzzy control of both the ultrafiltration and infusion of hypertonic saline (20% NaCl). Proper adaptation of control features to patient's conditions was provided by the critical borderline pressure, which was set by the physician individ ually at the beginning of each treatment. During the initial and medium pha ses of the sessions, ultrafiltration rates up to 150% of the average rates were applied as long as decreases in blood pressure could be compensated by saline infusion. The surplus of ultrafiltrate volume was used for blood pr essure stabilization in the final phase in most instances by low ultrafiltr ation rates. Results. The advantages of biofeedback-controlled haemodialysis were demons trated by both decreasing the frequency of hypotonic episodes and by increa sing or maintaining constant levels of systolic blood pressure during the f inal phase in 88% of treatments. As saline infusion was applied mainly in t he initial and medium phases, blood sodium levels were not significantly hi gher at the end of the sessions, and interdialytic weight gain was not elev ated. Conclusion. The application of fuzzy logic in the blood-pressure-guided bio feedback control of ultrafiltration and sodium infusion during haemodialysi s is able to minimize haemodialysis-induced hypotension.