Dr. Robert Kurrle, M.D., Senior AME
Kidney stones affect over 500,000 Americans each year. It is estimated that 10% of people in the US will have at least one kidney stone during their lifetime. The pain from kidney stones can be excruciating and incapacitating. The presence of a kidney stone is generally disqualifying for the FAA medical. Once the pilot is stone free, flying may resume after clearance from the AME or FAA.
The urinary system has four components: a pair of kidneys, a pair of ureters, a bladder, and a urethra. The kidneys are about four inches long, two inches wide, and one inch thick. They filter the blood, removing the end products of the body metabolism and excesses of water, and regulate the concentrations of sodium, potassium and other ions. The ureter is about 16 inches long and conveys the urine from each kidney to the bladder. The bladder is a sac that stores the urine that is then excreted through the urethra.
A kidney stone is a solid lump (from as small as a grain of sand to as large as a golf ball) made up of crystals that separate from urine and build up in the inner surface of the kidney. About 75% of stones are composed of calcium oxalate, while some stones contain uric acid or cysteine. Stones may be present in any part of the urinary system, but usually are most symptomatic when they migrate down and become lodged in the ureter. This can manifest as severe, acute pain in one flank or lower back as the stone blocks the ureter and urine output. Diagnosis includes microscopic blood in the urine and an x-ray using dye, called an IVP, or sometimes a CT scan.
Treatment of kidney stones consists of removing the stone. This can sometimes be accomplished by hydration, i.e. trying to wash the stone through the system and then catching it with a urine screen. Other common treatments include: Extracorporal Shock Wave Lithotripsy (ESWL), Ureteroscopic Stone Removal (Basket Extraction) and Percutaneous Nephrolithostomy. The treatment is dependant upon the size and location of the stone. The recovered stone is sent to the lab for analysis. Usually an X-Ray is performed after treatment to verify that the stone is gone. Prevention of stones is best accomplished by maintaining hydration. In some cases certain medications may be prescribed to change abnormal concentrations of substances in the urine that show up in the stone analysis. Some people will benefit from changing their diet to reduce the intake of foods high in purine, oxalate, or calcium.
The FAA is concerned about incapacitation from kidney stones. The FAA allows certification following diagnosis and successful treatment of kidney stones, but certain documentation is required. You will need to bring two reports after an initial kidney stone: (1) A summary letter from the treating urologist that includes a summary of your history of stones, date of diagnosis, method of treatment, current status, and prognosis for recurrence. (2) The test report that documents absence of stones after the treatment, usually an IVP or ultrasound. If there are no complications or retained stones, the AME may issue the medical. If a pilot has a retained stone, the application must be deferred to Oklahoma. Documentation then must show that the stone appears stable and is unlikely to pass spontaneously. The FAA is concerned that a retained stone may pass during flight and could be immediately incapacitating or interfere with the safe operation of the aircraft. A history of recurring stones must also be deferred.
Hydration is the easiest way to reduce the chance of kidney stones. A pressurized aircraft has a very dry environment, but even our small airplanes present a dehydration risk on long, hot trips. We are continuously losing fluids. In normal conditions, an adult needs about five pints of water to replace what is lost through sweating, breathing, and excretion. Combine the fluid loss with the hot Florida temperatures during long flights or exercise, and dehydration can easily become a problem. An interesting web site that calculates fluid loss for different activities for your body weight is www.gatorade.com/products_perform/thirst_quench/calculator.html. Drink adequate amounts of fluids before and during activities, especially in hot weather, to stay hydrated and reduce the chance of kidney stones. Take a bottle of water with you when you fly.