Download CKD case 2 - Ipswich-Year2-Med-PBL-Gp-2

EXTRA CASE 2
PRESENTATION
Ellen, 85 years, regular patient
 PC: nocturia disturbing her sleep
 HPC: happening for several weeks

WHAT BASIC MECHANISMS OR
PROCESSES CAN CAUSE
NOCTURIA? RATHER THAN
TRYING TO GENERATE A LARGE,
RANDOM LIST OF HYPOTHESES,
TRY TO THINK OF THE MOST
BASIC MECHANISMS FIRST, AND
THEN BUILD FROM THERE.
WHAT BASIC MECHANISMS OR PROCESSES
CAN CAUSE NOCTURIA?

Polyuria

Incomplete bladder
voiding
DM
 Subvesical obstruction
 Psychogenic polydipsia
 Calculi
 Diuretics
 b-blockers
 Detrusor instability
 Caffeine
 Neurogenic bladder
disorders
 RHF
 Overactive bladder
 Dec bladder capacity
 Bladder inflammation
 External/internal
 Distal ureteral stone
pressure
(bladder/prostate
cancer; cyst)

PMH

HT for decades  taking ACEI and thiazide

BP always well-controlled
Weight 42kg; height 152cm; looks frail
 Lives alone, but manages well

IT IS IMPORTANT TO REMEMBER
THAT PROBLEMS OUTSIDE OF THE
URINARY SYSTEM CAN CAUSE
URINARY SYMPTOMS, AND YOU
SHOULD HAVE COVERED MANY OF
THESE IN CONSIDERING YOUR
ANSWER TO Q1. REALISTICALLY –
WHAT ARE THE LIKELY PROBLEMS
(OCCURRING OUTSIDE OF THE
URINARY SYSTEM ITSELF) IN A
WOMAN OF THIS AGE AND GENERAL
CIRCUMSTANCES, THAT MIGHT BE
IMPLICATED IN HER PROBLEM OF
NOCTURIA? REMEMBER THAT
COMMON THINGS OCCUR COMMONLY!
WHAT PROBLEMS OUTSIDE OF THE URINARY
SYSTEM COULD CAUSE THESE SX IN ELLEN?
T2DM
 Metabolic syndrome
 RHF
 Cervical/uterine cancer

INVESTIGATIONS

Serum creatinine: 150umol/L
WHY IS CREATININE AN APPROPRIATE
SUBSTANCE TO USE WHEN ESTIMATING
GFR?
Produced at an ~constant rate
 Freely filtered at glomerulus
 Neither absorbed nor secreted along tubules

Plasma levels increase as filtration decreases
(but large reserve)
 Creatinine clearance will decrease as filtration
decreases


Inulin clearance is gold standard, but this is
invasive (requires injection) whereas creatinine is
produced naturally
WHAT ARE THE PITFALLS IN USING SERUM
CREATININE TO ESTIMATE KIDNEY FUNCTION?
Large reserve  renal function needs to drop by
~50% to affect serum creatinine
 Does not differentiate between dec GFR,
damaged tubules, blockage of outflow, etc

WHAT ABOUT ARRANGING CREATININE CLEARANCE
MEASUREMENT? WHY WOULD YOU NOT DO THIS?
 She
is frail, lives alone. Collection of 24 hour
urine MUST include all urine passed within 24
hour period, therefore it can be difficult to collect
all. eGFR can provide a good estimate.
INSTRUCTIONS FROM UPTODATE ON 24 HR URINE COLLECTION

You should collect every drop of urine during each 24-hour period. It does not matter how much or little
urine is passed each time, as long as every drop is collected.

Begin the urine collection in the morning after you wake up, after you have emptied your bladder for the
first time.

Urinate (empty the bladder) for the first time and flush it down the toilet. Note the exact time (eg, 6:15 AM).
You will begin the urine collection at this time.

Collect every drop of urine during the day and night in an empty collection bottle. Store the bottle at room
temperature or in the refrigerator.

If you need to have a bowel movement, any urine passed with the bowel movement should be collected. Try
not to include feces with the urine collection. If feces does get mixed in, do not try to remove the feces from
the urine collection bottle.

Finish by collecting the first urine passed the next morning, adding it to the collection bottle. This should be
within ten minutes before or after the time of the first morning void on the first day (which was flushed). In
this example, you would try to void between 6:05 and 6:25 on the second day.

If you need to urinate one hour before the final collection time, drink a full glass of water so that you can
void again at the appropriate time. If you have to urinate 20 minutes before, try to hold the urine until the
proper time.

Please note the exact time of the final collection, even if it is not the same time as when collection began on
day one.
ESTIMATE ELLEN’S GFR
http://www.kidney.org.au/HealthProfession
als/eGFRClinicalTools/tabid/632/Default.asp
x
 Ellen: wt 42 kg, age 85
 Serum creatinine: 150μmol/L
 MDRD calculator formula:


Answer: 29mL/min/1.73m3
WHAT STAGE OF CHRONIC KIDNEY
DISEASE DOES THIS REPRESENT
CALCULATE THE EGFR, USING THE MDRD
GFR CALCULATOR AND THE COCKCROFT AND
GAULT EQUATION CALCULATOR


http://www.sydpath.stvincents.com.au/other/Calc
sCrClCGumol.htm
Constant is 1.23 for men and 1.04 for women
SERUM CREATININE LEVELS IN ML/MIN???
I’M GOING TO ASSUME A MISTAKE AND TRY
FOR THESE AS ΜMOL/L

Male aged 46, wt. 70 kg, Serum creatinine 110 mL/min

– MDRD: 63 , C-G: 74

Male aged 46, wt. 110 kg, Serum creatinine 110 mL/min

–MDRD: 63 , C-G: 116

Female aged 46, wt. 70 kg, Serum creatinine 90 mL/min

- MDRD: 58 , C-G: 76

Female aged 46 wt. 110 k, Serum creatinine 90 mL/min

- MDRD: 58, C-G: 120

Female aged 85, wt. 45 kg, Serum creatinine 90 mL/min

- MDRD: 52 , C-G: 29

Female aged 85, wt. 65kg, Serum creatinine 90 mL/min

– MDRD: 52 , C-G: 41

Female aged 25, wt. 45 kg, Serum creatinine 90 mL/min

- MDRD: 66 , C-G: 60

Female aged 25, wt. 65kg, Serum creatinine 90 mL/min

- MDRD: 66 , C-G: 87


All units of eGFR
in mL/min/1.73m3
These examples
show how MDRD
equation for eGFR
do not take into
account the
patient’s weight,
and how this can
have a dramatic
effect on the
eGFR.