Dialysis fluid mixing and electro-hydraulic ESWL

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.

 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.

 [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.