- Intravenous urography (IVU):
The patient should come for this investigation after a thorough
bowel evacuation (laxative is to be given the night before and enema on
the morning of the day of examination) and with the fluid intake restricted
(to allow concentration of the dye and consequently proper visualization
of the urinary tract). An iodinated contrast media is injected intravenously
and x-ray films are taken immediately, 1 minute and 15 minutes after
injection. Sometimes late films are taken (e.g. when artery stenosis is
suspected).
Nephrogram is the film obtained immediately after injection of
contrast medium. It shows the dye concentrated in the nephrons and the
kidney appears opacified but no dye yet in the renal pelvis. This film
shows the site, the size, the contour of the two kidneys. It also shows
whether the kidneys are functioning equally or not. In cases of renal artery
stenosis, the nephrogram of the affected kidney appears delayed than the
other healthy kidney. After nephrogram, dye will appear in the renal
pelvis, ureter then the bladder (Fig. 2.7). So, IVU shows the anatomy of
the kidney and urinary system (any mass, stones, back pressure changes)
and also demonstrates the kidney function.
As the contrast media used is ionic and with high viscosity and the
technique is done with dehydration, this can result in kidney damage
(contrast media nephropathy) with rise in serum creatinine-even acute
renal failure may occur. There is a group of patients who are more
vulnerable to contrast media nephropathy. These are diabetics, elderly,
hyperuricaemics, patients with multiple myeloma, presence of renal
dysfunction, patients receiving other nephrotoxic drugs (e.g. gentamycin),
and those with congestive heart failure.