Ben Resner
MAS 863
September 14, 1999
Assignment: Design a new body organ (internal or external) for yourself. Include a parts list, a block diagram of the functional elements, and a rendering of it with you. For extra credit, make it.
Companion Dialysis
The dumbest kidney is smarter than the smartest doctor
- Medical Student Wisdom
Companion Dialysis is a means to provide essential renal (kidney) function to patients who would otherwise require bulky external dialysis. Companion Dialysis offers people with kidney failure new degrees of freedom.
BACKGROUND:
The kidney is an essential organ that filters the blood of impurities, maintains fluid and electrolyte balance, and secretes erythropoietin (EPO), a hormone necessary for red blood cell formation. Currently there are more than 260,000 Americans with no kidney function, who require an artificial kidney machine (dialysis) to stay alive.
Dialysis is the process of providing kidney function through artificial means. There are two types of dialysis, hemodialysis and peritoneal dialysis. Hemodialysis requires the patient to be attached to a refrigerator sized machine for four hours three to four times per week. Similar to a live kidney, the hemodialysis machine filters blood through a semi-permeable membrane to remove excess urea and restore electrolyte balance. These machines are expensive, and require supervision by trained nurses. Home hemodialysis is only an option for the extremely wealthy. There is no significant prospect of a portable hemodialysis machine.
Peritoneal dialysis replicates kidney function in the peritoneum, or abdomen. A tube is surgically placed in the patient's abdomen allowing the peritoneum to be filled with saline solution. By osmosing across the peritoneum, renal function is performed. The advantage of peritoneal dialysis is that it can be performed at home. The recipient must do three to four flushes per day, plus a nine hour cycle each night. While peritoneal dialysis can be performed without any electricity, it requires about four gallons of purified saline per day, making backpacking or remote travel unfeasible.
Both hemodialysis and peritoneal dialysis are "dumb" in that they provide no realtime feedback of essential blood chemistry. Blood is taken before and after treatment, and the results are used to adjust future sessions. While turnaround time for blood tests can be as fast as 30 minutes, logistics and patient backlog often conspire to keep this data from reaching a patient for several days. During this time, the patient is left miserable because of improper body chemistry. Furthermore, changes in activity, diet, or sleep patterns will change patient needs from session to session.
Both forms of dialysis also require weekly EPO injections and associated monitoring. As mentioned above, EPO is necessary for red blood cell formation.
While kidney transplantation has become increasingly successful over the years, the waiting list for donor kidneys is about three years, and the recipient needs to take anti-rejection drugs for the remainder of her life. Waiting time can be reduced to zero if a willing donor is produced -- donors can live with one kidney without any adverse health effects.
In recent years the possibility of growing a genetically identical kidney from patient DNA has shown promise. But due to the complexity of kidney function, this is still decades away. There is still no signifigant progress towards manufacture of implantible artificial kidneys, or kidneys from other species such as pigs or chimpanzees.
COMPANION DIALYSIS:
Companion Dialysis is a portable external artificial kidney that does not require power, fluids, or bulk. It allows the recipient freedom to travel where dialysis is unavailable or could not be performed safely. The only restriction is the patient spend nine hours per day in close proximity tethered to a donor with healthy kidney function.
A healthy person uses far less than half their kidney function, as evidenced by the ease with which the body compensates a missing kidney. Therefore, the kidneys should be more than capable of doubling their load. Companion Dialysis allows a healthy person to provide kidney function to someone without functional kidneys.
With Companion Dialysis, blood from the patient and donor comes into contact through a semi-permeable membrane. The membrane allows urea, electrolytes, and water to pass through. Over time, the donor and patient will come into equilibrium, and the donor kidneys will be working to bring this equilibrium to a healthy balance for both participants.
For example, the optimal potassium (K) level is 3.5 and 5 mEq/L. If the donor has a K of 3.5, and the patient has a K of 7, simply mixing the blood across a semi-permeable membrane will neutralize K to 5.25. But as the donor kidneys reduce this to 5 for the donor, the patient will eventually come down to this level as well.
Because external dialysis is being performed by an actual living kidney, the results are going to be better than dialysis with a machine A machine has no intrinsic sense of the correct chemical balance, but relies on time-delayed blood tests for feedback. A live kidney gets it right because of millions of years of evolution.
It is important to not mix blood directly primarily because of incompatible blood types. Separating donor and patient blood with the membrane blocks proteins from mixing, and avoids donor-patient rejection. Therefore the donor and patient do not need compatible blood types. Separating blood also minimizes the risk of infection. (Though viral particles could potentially pass through the membrane -- depending on the permeability of the membrane.)
Similar to Hemodialysis and Peritoneal dialysis, the patient will still require EPO injections and periodic monitoring of EPO levels. Because these are protein sized molecules, they will not pass across the membrane and must be manually injected into the patient.
Companion dialysis is similar to the function of the placenta for a developing embryo. During gestation, a mother provides kidney function to her baby through the placenta, even if the baby and mother have different blood types.
Companion dialysis rests on the following assumptions:
MECHANICS:
Chemical exchange takes lace in coiled dialysis tubing. This tubing has a sterile impenetrable casing, with an internal semi-permeable membrane running the diameter. Blood is moved through this dialysis tubing with normal cardiac pressure. There are no pumps or other active devices. The fact that no more thant 20% of a person’s blood can be outside the body will limit dialysis tube distance, as well as the distance between donor and patient. The dialysis tubing is coiled inside a portable canister for safety and ease of transport.
The reliance of cardiac activity for flow pressure necessitates a direct connection to an artery. Unlike veins, arteries are not easily accessible, and both the patient and donor will require simple surgeries to install ports for easy access. Both donors will also require ports attached to veins.
MODIFICATIONS:
EVALUATION:
Reasons to choose companion dialysis
OPEN DESIGN QUESTIONS:
SOCIAL ANALYSIS:
There are instances of donating bodily products without harm to the donor, most notably blood. But this is the first instance of donating a bodily service. Medicine is traditionally seen as a contract between patient and doctor. Companion Dialysis is revolutionary in that the essential healing function is performed by another individual.
PARTS:
