Cheryl Taylor, the attending physician at the emergency room, looked up from a chart she was studying. She had called me in to evaluate one of my patients, Casey Morita, a 2-month-old who had arrived looking very dehydrated.
"Hi, Mark, thanks for coming in," she said. "As I told you on the phone, I've given her a total of 40 cc's per kilogram of IV fluid. She's looking a little perkier, but her chemistries are really out of whack."
When I last saw Casey, just one week ago, she was perfectly healthy. So I was puzzled and worried as I went in to examine her.
Casey was sleeping in her mother's arms in the curtained-off cubicle. A brief glance and a touch told me that Cheryl had done a good job of rehydrating her: Casey's color was good, and her skin did not have the dry, wrinkly feel of severe dehydration. Casey's mother said her daughter had been well until two days ago, when she began having frequent, watery bowel movements. Last night Casey couldn't keep down any of her formula or the commercial electrolyte solution her mother had offered her. She had no fever, no congestion or cough, no rash, and no one else at home had been sick. It sounded like a simple gastrointestinal infection. But why would she get so sick so fast?
A careful examination turned up nothing unusual. To figure out what was going on with her, I'd have to look at the levels of ions and molecules in her blood.
I first looked at the electrolytes: sodium, potassium, chloride, and bicarbonate. These four ions keep all the myriad cellular processes working properly, and bicarbonate in particular maintains the acid-base balance of the blood. The levels of these four ions in the blood are usually kept in close balance by the kidneys and endocrine system. Values outside the normal range could indicate excessive fluid loss, or a serious breakdown in the control system. The lab results said something was seriously wrong. Her sodium was 126 milliequivalents per liter (normal range 136-145), potassium 6.9 (3.5-5.5), chloride 87 (94-110), and bicarbonate 12 (19-28). The low bicarbonate told me her blood was much too acidic. If her potassium went much higher, it could cause her heart to beat irregularly or even stop altogether.
Diarrhea and dehydration can wreak havoc with these ions, but two other blood test results were even more worrisome: the BUN (blood urea nitrogen) and creatinine. Urea and creatinine are cellular waste products that are normally removed by the kidneys. Casey's BUN was 52 milligrams per deciliter; the normal range is 5-15. Her creatinine was 3.7; normal is 0.1-0.6. These values, plus the abnormal electrolytes, suggested the kidneys were not doing their job. The wastes were building up.
I asked the nurse to check her blood pressure. It was 135/82—seriously elevated for a 2-month-old. That, too, meant her kidneys were not working. The kidneys secrete renin, a hormone that helps maintain normal blood pressure. When lack of local blood flow interrupts kidney function, the kidneys release lots of renin in a misguided effort to boost blood pressure and get more blood flowing.
I called the children's hospital and asked them to send an ambulance and a team from the intensive care unit for Casey. This little girl, who had been perfectly healthy just a few days before, was in danger of dying from kidney failure—and I didn't know why.
One diagnosis did come to mind, but it was for a condition I had only read about and never seen. I checked the results of some of her other tests, and they tended to confirm my suspicion. First, Casey was anemic; the level of hemoglobin in her blood was low. So was the number of red blood cells. It's normal for a 2-month-old to have a mild degree of anemia, because she is still building her blood supply. But Casey's red blood cell count was even lower than expected. And the number of platelets, the tiny cellular fragments that clump up to form blood clots, was also low. That's not normal at any age.
Anemia, low platelets, and kidney failure, together with a history of diarrhea, suggested that Casey might have hemolytic uremic syndrome. This condition is usually caused by an infection, and the cascade of effects can be catastrophic. When a certain strain of a common bacterium infects the digestive tract, it produces a toxin—verotoxin—that passes from the intestine into the bloodstream. The toxin damages the endothelial cells, which make up the inner lining of blood vessels. The cells become swollen, narrowing the diameter of the vessels. Then, as platelets glom onto the damaged endothelial cells, the platelet count goes down, and the vessels narrow even more. In addition, the red blood cells themselves are damaged as they try to squeeze through narrowed capillaries; the result is a hemolytic (literally, "broken blood") anemia.
A dense network of capillaries supplies blood to the kidneys, so they are particularly vulnerable to the toxin's effects. The swelling of the capillaries and the accumulation of damaged red blood cells and platelets can become so severe that blood simply cannot flow through the kidneys. The production of urine slows to a trickle or stops completely. Waste products, including urea, build up in the bloodstream, causing a condition known as uremia—urea in the blood. It's the combination of hemolytic anemia (indicating red blood cell breakdown) and uremia (indicating kidney failure) that gives the condition its name.
First identified in the 1980s, the syndrome made headlines in 1992, when 453 people in Washington State fell ill. Forty-five of them developed hemolytic uremic syndrome, and three died. Many of those who got sick had visited a fast-food chain and eaten hamburgers. The illness was probably spread through undercooked beef contaminated with Escherichia coli O157:H7, a bacterium that produces verotoxin. After several more outbreaks, we learned that thorough cooking of meats and careful attention to safe food-handling practices can reduce or eliminate the danger from these bacteria. We also learned that other bacteria can cause the syndrome. Casey did have E. coli O157:H7 in her stool, and this almost certainly caused her diarrhea and subsequent illness. But we don't know how she got it, because her only food was infant formula, which did not contain the bacterium. Ongoing investigation by the state health department may give us an answer.
By the time Casey reached the intensive care unit, she was in complete renal failure. Her doctors had to take over the job of the kidneys, using peritoneal dialysis. A tube inserted into her abdomen pumped fluid in and out several times a day, allowing the waste materials to be excreted across the large peritoneal membrane in the abdomen instead of through the kidneys. The capillary swelling gradually improved. Within a few days, Casey's body began to produce urine, and soon she no longer required dialysis.
Several weeks have passed, and Casey's kidneys have still not fully recovered. She is on a special formula and needs medication to control her blood pressure and chemical imbalances. While she seems to be growing well, we don't know whether her kidneys will return to normal or how long that might take. Some people with this syndrome have regained normal kidney function only to have their kidneys deteriorate years later. Casey survived. Now we hope she can avoid lasting scars.