Postoperative Kidney & Electrolyte disorders in Elders

Question 1

The risk of postoperative kidney failure is increased in the presence of ___ ___ ___ _____.

Answer 1

preoperative impaired kidney function

Question 2

Name 3 common etiologies for postoperative kidney failure in elders.

Answer 2

1. decreased renal blood flow intra-operatively
2. Acute tubular necrosis (may be from nephrotoxic drugs)
3. obstructive nephropathy (esp. older men w/ prostatic hypertrophy)

Question 3

Name 3 common signs of intraoperative kidney damage.

Answer 3

1. isosthenuria
2. oliguria
3. increase in serum creatinine

Question 4

When acute kidney damage is due to decreased renal blood flow, what is seen in the urine sodium concentration and the urine creatinine-to-plasma-creatinine ratio?

Answer 4

1. Urinary sodium will likely be < 40 mEq/L

2. The urine Cr: plasma Cr ratio will be > 10:1

Question 5

When acute tubular necrosis is the cause of perioperative kidney damage, what is seen in the urine sodium concentration and the urine creatinine-to-plasma-creatinine ratio? What else might be seen in the urine sediment?

Answer 5

1. Urine sodium will be >40 mEq/L.
2. Urine Cr : plasma Cr ratio will be < 10:1
3. There will probably be epithelial cell casts or granular casts in the urine sediment.

Question 6

When acute tubular necrosis is suspected, what should be done to attempt to preserve kidney function?

Answer 6

1. Withhold all potentially nephrotoxic drugs.

2. Meticulously maintain a euvolemic state in the patien (ie., don’t “flood ‘em.” and don’t let ‘em get “dry.”)

Question 7

Describe a typical physical exam finding in bladder outlet obstruction, such as can occur in older men with prostatic hypertrophy.

Answer 7

The bladder is often readily palpable above the pelvic rim.

Question 8

How does one treat postoperative bladder outflow obstruction in older men with prostatic hypertrophy?

Answer 8

1. Urinary bladder catheters.

2. Alpha-blocking medications, such as tamsulosin (Flomax).

Question 9

How do alpha-blocking medications such as tamsulosin work to help with bladder outflow obstruction?

Answer 9

Tamsulosin (and similar alpha-blocking drugs) relax the smooth muscle of the bladder neck, which allows more complete emptying of the bladder with each micturation.

Question 10

When a drug like tamsulosin has been used for postoperative bladder outflow obstruction, what is a reasonable time frame in which an attempt to withdraw the medication & a voiding trial be done?

Answer 10

Attempt a voiding trial at 2 to 4 weeks postoperatively to see if the alpha-blocking drug is still needed for bladder outflow obstruction.

Question 11

What long-term beneficial effect (for the kidneys) might the insertion of a bladder catheter for post-operative urinary outflow obstruction have?

1. Reducing the risk of developing _______, which in turn….
2. Reduces the risk of long term _____ __________.

Answer 11

1. reduces the risk of developing hydronephrosis, which in turn…..
2. reduces the risk of long-term kidney damage.

Question 12

A decrease in GFR, as will occur with intra-operative reduction in renal blood flow, results in (—–More/less—-) Sodium excreted into the urine.

Answer 12

Less Na+ will be excreted into the urine when renal artery blood flow (hence GFR) decreases.