Urinary bladder catheterization is the only reliable method of monitoring urinary output. Insertion of a urinary catheter is indicated in patients with con-gestive heart failure, renal failure, advanced hepatic disease, or shock. Catheterization is routine in some surgical procedures such as cardiac surgery, aortic or renal vascular surgery, craniotomy, major abdomi-nal surgery, or procedures in which large fluid shifts are expected. Lengthy surgeries and intraop-erative diuretic administration are other possible indications. Occasionally, postoperative bladder catheterization is indicated in patients having diffi-culty voiding in the recovery room after general or regional anesthesia.
Bladder catheterization should be done with utmost care in patients at high risk for infection.
Bladder catheterization is usually performed by surgical or nursing personnel. To avoid unneces-sary trauma, a urologist should catheterize patients suspected of having abnormal urethral anatomy. A soft rubber Foley catheter is inserted into the blad-der transurethrally and connected to a disposable calibrated collection chamber. To avoid urine reflux and minimize the risk of infection, the cham-ber should remain at a level below the bladder. Complications of catheterization include urethral trauma and urinary tract infections. Rapid decom-pression of a distended bladder can cause hypoten-sion. Suprapubic catheterization of the bladder with tubing inserted through a large-bore needle is an uncommon alternative.
An additional advantage of placing a Foley catheter is the ability to include a thermistor in the catheter tip so that bladder temperature can be monitored. As long as urinary output is high, bladder tempera-ture accurately reflects core temperature. An added value with more widespread use of urometers is the ability to electronically monitor and record urinary output and temperature.
Urinary output is a reflection of kidney perfu-sion and function and an indicator of renal, car-diovascular, and fluid volume status. Inadequate urinary output (oliguria) is often arbitrarily defined as urinary output of less than 0.5 mL/kg/hr, but actually is a function of the patient’s concentrating ability and osmotic load. Urine electrolyte composi-tion, osmolality, and specific gravity aid in the dif-ferential diagnosis of oliguria.