--- title: "Dialysis fluid mixing and electro-hydraulic ESWL" subject: "Biomedical Instrumentation" chapter: 6 key: "semester_7/biomedical_instrumentation:dialysis-fluid-eswl" source: https://www.bctengineer.com/q/semester_7/biomedical_instrumentation/dialysis-fluid-eswl site: BCT Engineering --- # Dialysis fluid mixing and electro-hydraulic ESWL Biomedical Instrumentation · Chapter 6: Therapeutic Instruments - Asked in: 2075 Chaitra, 8 marks - Video: [Hemodialysis System 1 - Life Support Instruments - Biomedical Instrumentation](https://www.youtube.com/watch?v=rMtiJQDocs4) — Ekeeda - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/biomedical_instrumentation/dialysis-fluid-eswl - Whole chapter: https://www.bctengineer.com/md/semester_7/biomedical_instrumentation/chapter-6 ## Question How dialysate fluid is used with RO water in mixing chamber to artificial kidney during dialysis? Draw a lay-out diagram of Electro-Hydraulic based ESWL with its required major components. ## Short answer Dialysate: RO water and concentrate mixed (34:1), warmed, degassed, then passed counter-current through dialyzer for diffusion/ultrafiltration. ESWL: A high-voltage capacitor discharges across a spark-gap at the first focus of an ellipsoidal reflector, generating focused shockwaves that shatter kidney stones at the second focus, guided by X-ray/ultrasound. ## Answer #### Dialysate preparation with RO water In haemodialysis the artificial kidney (dialyser) removes waste (urea, creatinine) and excess water from the blood across a semi-permeable membrane into the **dialysate**. ```text Tap water -> [Pre-treatment: filter, softener, carbon] -> [Reverse osmosis (RO) unit] -> RO water Dialysate concentrate --[Proportioning pump]--+ RO water --------------[Proportioning pump]--+-> [MIXING CHAMBER] | [Heater 37 C]<-[Deaerator]<-[Conductivity/pH monitor] | [Flow meter] -> DIALYSER <-> blood (counter-current) | [Blood-leak detector] -> drain ``` **Working:** 1. RO water, free of ions, bacteria and chemicals, enters the mixing chamber. 2. The concentrate (sodium, potassium, calcium and magnesium chlorides, bicarbonate, glucose) is added by a proportioning pump, normally 1 part concentrate to 34 parts water. 3. The mixture is warmed to about 37 °C and degassed (deaerator) so that bubbles do not form in the dialyser. 4. Conductivity and pH sensors check that the mixture is correct; if not, the fluid is sent to the drain (bypass). 5. The dialysate flows (about 500 mL/min) through the dialyser in the direction opposite to the blood, so waste diffuses from the blood into the dialysate, and the pressure difference removes extra water (ultrafiltration). A blood-leak detector checks the used fluid for blood. #### Electro-hydraulic ESWL (extracorporeal shock wave lithotripsy) ESWL breaks kidney stones without surgery using focused shock waves. ```text [HV supply 10-20 kV]--[Capacitor]--[Switch/trigger] | [Spark-gap electrode F1] water-filled ellipsoidal reflector / shock waves \ / \ v focus F2 v Patient (in water bath/cushion) -> kidney STONE at F2 [X-ray (fluoroscopy)/ultrasound localisation] -> [Control unit] ``` **Components:** HV generator and capacitor, spark gap (underwater electrode) at the first focus F1 of a half-ellipsoid reflector, water medium, coupling cushion, an imaging system (X-ray or ultrasound) to position the stone at the second focus F2, and the control unit with ECG triggering. **Working:** the capacitor discharges across the electrodes, which vaporises water and creates a shock wave. The reflector focuses the shock waves on the stone at F2. Repeated shocks (1000 to 3000) crush the stone into small fragments, which pass out in the urine. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How is dialysate prepared in the mixing chamber? A. Tap water is mixed directly with blood B. RO water and concentrate are added by proportioning pumps, about 1 part concentrate to 34 parts water C. Concentrate alone is used undiluted D. RO water is mixed with air Answer: B. Proportioning pumps mix ion-free RO water with the concentrate at about 1:34. (Key point: Dialysate mixing) 2. What happens if the conductivity or pH monitor finds an incorrect mixture? A. The fluid still goes to the dialyser B. The fluid is sent to the drain (bypass) C. The blood pump speeds up D. The heater turns off and dialysis continues Answer: B. Incorrect dialysate is bypassed to drain to protect the patient. (Key point: Conductivity monitor) 3. Why does dialysate flow opposite to the blood in the dialyser? A. It prevents ultrafiltration B. Counter-current flow maintains a diffusion gradient so waste diffuses from blood to dialysate C. It heats the blood D. It stops the blood-leak detector working Answer: B. Counter-current flow keeps the concentration gradient high along the membrane. (Key point: Dialyser flow) 4. How does electro-hydraulic ESWL break a stone? A. A spark gap at F1 of an ellipsoidal reflector vaporises water, and the shock wave is focused on the stone at F2 B. A laser heats the stone at F2 C. Ultrasound resonates the stone at F1 D. The stone is placed at F1 Answer: A. Capacitor discharge across the underwater electrode at F1 creates a shock wave focused by the reflector at F2. 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