Clinical Practice Guideline
for
RENAL COLIC
Developed for the
Aerospace Medical Association
by their constituent
organization
American Society of Aerospace Medicine Specialists
Overview: The
peak incidence of upper urinary tract stones in aviation is in individuals
between 20 and 30 years of age.
Dehydration is one of the contributing factors. There is usually a gradual onset of flank,
abdominal or back pain over an hour or more before onset of acute colic. Flyers who have previously had renal colic
will often find this sufficient warning to abort a flight. The risk of recurrence ranges from 20-50%
over 10 years; a lifetime recurrence rate of 70% has been reported. In patients who have required lithotomy, the
reported recurrence is 80%. In most
cases stones less than 8-10mm in diameter will pass spontaneously within a few
days to two weeks.
Aeromedical
Concerns: The pain of renal colic can be severe and is potentially
incapacitating in flight. Conservative
management aimed at encouraging natural passage of the stone, surgery or
extra-corporeal shock wave lithotripsy will necessitate grounding until
recovery. Prolonged flights at altitude
may predispose to dehydration and renal stone formation. Anecdotal accounts of incapacitation are
similar to those associated with cramps in swimmers after eating.
Medical
Work-up: A full investigation is necessary to try to determine if
there is an underlying cause of stone formation. Approximately 75% of all stones are calcium
oxalate; of these approximately 5% are due to Primary Hyperparathyroidism,
50-75% are due to Idiopathic Hypercalciuria, 30% to low urinary citrate level,
20-30% to hyperoxaluria and 30% to hyperuricosuria.
The test for primary hyperparathyroidism
is a serum calcium level above 10.1mg% (2.52mmol/liter). The differential diagnosis of hypercalcemia
in persons who form stones includes (1) sarcoidosis (2) familial hypocalciuric
hypercalcemia (3) malignant neoplasms (4) use of a thiazide diuretic (5)
overuse of Vitamin D supplements (6) treatment with Lithium, and other uncommon
causes.
The test for
Idiopathic hypercalciuria is the 24-hour urinary calcium excretion with an
upper limit of normal for women of 250mg (6.2mmol) /day and for men 300 mg
(7.5mmol) /day. Alternatively, 140mg
(3.5mmol) /gram of creatinine or 4mg (0.1mmol) /kg body weight in patients of
either sex are considered positive. If the 24-hour urinary calcium levels are
elevated and the serum calcium level is normal, suspect idiopathic
hypercalciuria.
For urine citrate, the normal averages 59.5mg% in women 43.2mg% in men. Low levels are indicated by 31.9mg% for men and 42.3mg% for women. Hyperoxaluria is (normal levels for both males and females is about 45mg/day) is due to dietary excess of certain foods (spinach, rhubarb, Swiss chard, cocoa, beets, peppers, wheat germ, pecans, peanuts, okra, chocolate and lime peel) and rarely metabolic errors. Above 60mg/day should be considered abnormal.
Hyperuricosuria
(levels greater than 800mg (4.8mmol) /day in men and 750mg (4.5mmol) in women)
may predispose to calcium oxalate stone formation via heterogeneous nucleation
or reduction of naturally occurring urinary inhibitors.
The next largest
category of all stones is the struvite (magnesium ammonium phosphate) stone
(10-20%). The usual causative bacteria include Proteus, Klebsiella, Pseudomonas and Enterococci but never E.
coli.
Patients who pass
stones are most likely to have idiopathic hypercalciuria, normal renal function
and to produce both struvite and calcium oxalate stones. Those who produce only struvite stones
present with large stones that cause bleeding, obstruction or infection without
stone passage; they rarely have idiopathic hypercalciuria and often have reduced
renal function. Struvite stones require removal.
Another 5% of all
stones are pure uric acid. These usually
occur in the presence of low urinary pH (5.1-5.9) and urinary uric acid levels
of 1200mg (7.1mmol) or greater excreted daily.
Treatment is by raising the urinary pH to 6.0-6.5 and treating with
allopurinol.
Around 5% of all
stones are calcium phosphate; these are caused by renal tubular acidosis, which
can be determined by measuring the blood pH and serum bicarbonate level. If
metabolic acidosis is present, along with 24 hour urinary pH values above 6.5
and hypercalciuria, treatment is with potassium alkali and monitoring of
urinary pH, citrate and calcium.
Less than 1% of all
stones are cystine; associated with a hereditary defect of amino acid
transport. Cystine is soluble in urine
to the level of 24-48mg% but the rate of excretion in these patients ranges
from 480 to 3600mg/day. Urinary cystine
is measured and the amount of urinary volume necessary estimated. If it is within 4 liters daily, high fluid
intake and increase of urinary pH above 7 is used to increase solubility. If volume plus pH adjustment is insufficient,
treatment with penicillamine or tiopronin is initiated.
Aeromedical
Disposition (military & civilian): A stone should be recovered if possible and sent for
analysis. Information should confirm
that metabolic and renal functions are normal and should be performed
locally. This should include KUB, IVP,
urinalysis, 24-hour urine sample after normal diet along with 12-hour fasting
blood specimen. The urine and blood
samples should be checked for calcium, magnesium, phosphorus, uric acid and
creatinine. In addition, the blood should be checked for sodium, potassium,
chloride and bicarbonate and the urine should be checked for oxalate, citrate,
pH, sodium nitroprusside for cystine and volume.
Waiver
Experience (military): A history of stone is compatible with waiver as long as
there is not an underlying cause predisposing the individual for further stone
formation or a therapy necessary that is incompatible with waiver.
Unrestricted waiver
is also allowed for retained stones provided they are in the renal parenchyma
or in a calyceal diverticulum where there is relative certainty that they will
not escape the renal calyx, that metabolic and renal function are normal and
they are asymptomatic.
All cases of retained
renal calculi will be fully evaluated by an urologist prior to forwarding case
for waiver.
Waiver Experience (civilian): These recommendations also apply to civilian airmen. If there are recurring renal stones then
medical certification is usually not granted.
If there happens to be retained stones, then the airman is given a
time-limited certificate and yearly statements from an urologist or
nephrologist is required. In the case of
retained stones, the FAA would like to know the location, size, and if
possible, a statement from the treating urologist of the likelihood of passage. If the stone is large enough, it is
preferable to have shock wave lithotripsy performed prior to requesting medical
certification. As of
References:
AFPAM
48-132, Attachment 4,
Coe, Fredric, et al. The
pathogenesis and treatment of kidney stones. New Engl J Med,
DA HSX-AER (40-501), APL 27-89, Kidney Stones,
Rayman, RB, Clinical Aviation Medicine, 3rd edition,
Castle Connolly Graduate Medical Publishing, LLC, 2000, pp. 271-74.
July 9, 2002