Surgery – Blood drawn and replaced or treated and returned to body – Constituent removed from blood and remainder returned to body
Reexamination Certificate
2000-11-06
2003-10-21
Sykes, Angela D. (Department: 3762)
Surgery
Blood drawn and replaced or treated and returned to body
Constituent removed from blood and remainder returned to body
C604S006090, C604S004010, C604S006060, C604S005010, C210S646000, C210S647000, C210S650000, C210S321710, C210S321720, C210S929000
Reexamination Certificate
active
06635026
ABSTRACT:
DESCRIPTION OF THE INVENTION
1. Field of the Invention
The present invention relates to a haemofiltration machine for independently controlling the concentration of at least two ionic substances in a patient's internal medium.
2. Background of the Invention
The present invention relates to a haemofiltration machine for independently controlling the concentration of at least two ionic substances in a patient's internal medium.
The kidneys fulfil many functions, among which are the removal of water, the excretion of catabolites (or metabolic waste, such as urea and creatinine), the regulation of the concentration of ionic substances in the blood (sodium, potassium, magnesium, calcium, bicarbonates, phosphates and chlorides) and the regulation of the acid-base equilibrium of the internal medium, which is obtained in particular by removing weak acids (phosphates, monosodium acids) and by the production of ammonium salts.
In individuals who have lost the use of their kidneys, since these excretory and regulatory mechanisms no longer work, the internal medium becomes loaded with water and metabolic waste and has an excess of certain ionic substances (in particular sodium), as well as, in general, exhibiting acidosis, with the pH of the blood plasma shifting towards 7 (the blood pH normally varies within a narrow range of between 7.35 and 7.45).
To overcome the dysfunction of the kidneys, use is conventionally made either of dialysis or of haemofiltration, which are blood treatments administered by means of an exchanger with a semi-permeable membrane (haemodialysis machine/haemofilter) which is linked to the patient via an extracorporeal blood circulation circuit.
Dialysis consists in circulating, on either side of the exchanger membrane, the patient's blood and a dialysis liquid comprising the main ionic substances of the blood, in concentrations close to those of the blood of a healthy individual. Moreover, a given volume of plasmatic water corresponding to the weight that the patient should lose during each dialysis session is made to flow by ultrafiltration through the membrane into the dialysis liquid compartment. The ultrafiltration results from a difference in pressure maintained between the two compartments of the exchanger delimited by the membrane.
The blood treatment which is carried out in the exchanger results from the diffusional transfer, across the membrane, of molecules of the same substance (ionic substances, metabolic waste) which are at different concentrations on either side of the membrane, the molecules migrating from the liquid in which they are at higher concentration to the liquid in which they are at lower concentration.
In a conventional dialysis machine, the dialysis liquid is prepared by means of a measured mixture of water and of two concentrated solutions, a first concentrated solution containing sodium chloride and sodium bicarbonate and the second concentrated solution containing calcium, potassium and magnesium chlorides as well as acetic acid. The role of the acetic acid is to limit the formation of calcium and magnesium carbonate precipitates which form unwanted deposits in the hydraulic circuit of the dialysis machine. Other dialysis devices have been proposed, in particular in documents EP 0 898 975 and EP 0 898 976, in which the dialysis liquid used contains no calcium or magnesium (as the respective bicarbonates) and in which a sodium bicarbonate solution (or a calcium or magnesium chloride solution, respectively) is infused into the patient. Irrespective of the type of dialysis administered, at the usual flow rate of dialysis liquid, i.e., 500 ml/min, 120 liters of dialysis liquid are prepared and used in the course of a four-hour dialysis session.
Haemofiltration consists in extracting from the blood circulating in the exchanger, by ultrafiltration, a large volume (up to thirty liters in the course of a four-hour session) of plasmatic water which is partially replaced by means of a simultaneous infusion of a sterile replacement liquid.
The blood treatment which is carried out in the exchanger results here from the convective transfer of molecules (ionic substances, metabolic waste) which are entrained by the plasmatic water which filters through the membrane under the effect of the pressure difference created between the two compartments of the exchanger.
The electrolyte composition of the replacement liquid used in haemofiltration is identical to that of a dialysis liquid. This liquid can be manufactured and packaged by a pharmaceutical laboratory in the form of two containers for two sterile liquids to be mixed together just before use, one of the containers containing all the bicarbonate and the other container containing all the calcium and magnesium. This replacement liquid can also be prepared at the time of use by filtration of a dialysis liquid, as is described in particular in document EP 0 622 087, the subject of which is a haemodiafiltration machine (combination of the two treatments defined above): in this machine, some of the dialysis liquid produced by a dialysis liquid generator is injected, after filtration, into the blood return tube of the extracorporeal circuit, while the rest of the dialysis liquid is circulated in the exchanger.
Despite its efficacy and its acknowledged superiority over dialysis in therapeutic terms (see, in particular,
Long
-
term morbidity: Hemofiltration vs. Hemodialysis
, by E. Quellhorst, U. Hildebrand, A. Solf, in Contrib. Nephrol. Basle, Karger, 1995, vol 113, pp. 110-119), the haemofiltration suffers from two limitations: a first limitation is associated with the cost of the treatment when the replacement liquid used is purchased ready-to-use. Since these sterile solutions packaged in split containers are expensive, the tendency is to limit the treatment administered to an exchange of liquids not exceeding thirty liters (i.e., a quarter as much as the volume of treatment liquid used during a dialysis session). The second limitation is that, even with a machine such as the one described in document EP 0 622 087 mentioned above, which provides replacement liquid at reduced cost, the exchange flow rate is limited since the ultrafiltration flow rate cannot be set at much more than a third of the flow rate of the blood in the extracorporeal circuit.
BRIEF SUMMARY OF THE INVENTION
In the light of the foregoing considerations, one aim of the invention is to produce a system for treating renal insufficiency which makes it possible to carry out a haemofiltration session in the course of which very large volumes of liquid can be exchanged, without this haemofiltration session being any longer or any more expensive than a conventional dialysis session, and also without it displaying the known drawbacks relating to the preparation of an unstable treatment liquid.
In accordance with the invention, this aim is achieved by means of a haemofiltration machine designed to cooperate with a haemofilter having a first compartment and a second compartment separated by a semi-permeable membrane, the first compartment having an inlet which can be connected to a blood withdrawing tube and an outlet which can be connected to a blood return tube, and the second compartment having an outlet which can be connected to a spent liquid evacuation tube. This haemofiltration machine comprises means for preparing a first injectable solution from at least one concentrated solution; means for injecting, at an injection flow rate Q
pre
, the first solution into the blood withdrawing tube; means for infusing into the blood return tube a second solution containing at least one ionic substance A having a given concentration [A]
post
which is different from the concentration [A]
pre
of this substance A in the first solution; means for determining an infusion flow rate Q
post
of the second solution in order for the concentration of the substance A in the patient's internal medium to tend towards a desired concentration [A]
des
, as a function of the concentration [A]
post
of
Bianco Patricia
Finnegan Henderson Farabow Garrett & Dunner LLP
Hospal Industrie
Sykes Angela D.
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