Renal Failure and Dialysis Patients: What the EMS Provider Should Know

Your crew is dispatched to a local dialysis center for a patient experiencing chest pain. The dispatcher advises that your patient is a 56-year-old male, who was undergoing hemodialysis when he experienced chest pain. Upon your arrival, the dialysis technician reports that the patient was asymptomatic when he started hemodialysis. Dialysis was uneventful until two liters of fluid were removed. The patient then developed substernal chest pain, mild shortness of breath and dizziness. His vital signs then showed pulse 118, respiratory rate 26 and blood pressure 80/52. The dialysis technician gave a 500cc fluid bolus and put the patient into the Trendelenburg position. The patient remained symptomatic, so dialysis was stopped and EMS was called. The technician also tells you that the patient is dialyzed three days a week; his dry weight is 88 kg, and he weighed 92 kg before dialysis today. His past medical history includes diabetes complicated by chronic renal failure and coronary artery disease. Knowing that this patient has renal failure, you are able to focus your history and physical exam accordingly.

Anatomy and Physiology

EMS providers are called on to take care of patients with renal failure for a variety of reasons. It is important to understand renal anatomy, physiology, pathophysiology and, in some cases, the dialysis procedure to assess and treat these patients.

The kidneys are located in the retroperitoneal space (behind the abdominal cavity), just inside the lower ribs. Blood enters the kidneys through the renal arteries that branch directly from the abdominal aorta. After entering the kidney, the blood is filtered as it passes through a series of structures called nephrons, which are the essential functional units of the kidney. There are over a million nephrons in the kidney, each divided into two parts: the glomerulus and the tubule. The glomerulus can be thought of as a “ball of capillaries” surrounded by a “funnel” known as Bowman’s capsule. These capillaries have special fenestrated walls that allow filtration to occur. Pressure in the capillaries forces fluid, electrolytes and other molecules through the holes of the capillary walls, creating “filtrate.” Larger constituents, such as red blood cells, white blood cells, platelets and large proteins, are not able to pass through the fenestrations. Once the filtrate is formed, it flows through the tubule, where it is modified to become urine. In the tubule, important fluid and electrolytes are returned to the bloodstream, while further “waste” products are secreted into the filtrate. The newly formed urine then flows from the tubules to the collecting ducts, on to the renal pelvis, then to the ureter. Each ureter carries urine from a kidney to the bladder, where it is stored until it is expelled from the body via the urethra during urination.

Functions of the Kidney

The kidneys maintain the volume and composition of blood and other bodily fluids. They are a major regulator of blood pressure, fluid balance, electrolyte balance and acid-base homeostasis. These vital organs also function to rid the body of waste, stimulate red blood cell production and produce urine. The kidneys filter the volume of fluid in your body four times a day. A total of 50 gallons of blood flow through the kidneys each day.

Modification of urine is carried out through the exchange of components between the filtrate and the blood that surrounds the tubule. One part of the tubule particularly relevant to EMS is the loop of Henle. It is in this part of the tubule that sodium, potassium and chloride are removed from the filtrate and reintroduced back into the blood. This is important because furosemide (Lasix) and all other “loop” diuretics work by blocking this process. We know that water follows sodium. The reduction in the return of sodium to the blood results in an increased volume of water being retained in the urine for excretion from the body. Unfortunately, more potassium also remains in the urine when this mechanism is blocked, making these patients susceptible to hypokalemia.