Thank you to Kenny for his sense of humor AND for presenting an elderly patient with h/o BPH, recent acute prostatitis, now presenting with altered mental status and acute renal failure w/ hyponatremia 2/2 multiple mechanisms including obstruction with concurrent use of NSAIDs and an ACEi. We discussed the management of post-obstructive diuresis, hyponatremia, and volume overload.
- The old rule of thumb that you get an elevation in creatinine of 1 for each day of renal injury turns out NOT to be totally accurate. [20mg/kg/day with volume distribution of 0.6 allows for increases in Cr by as much as 3mg/dL per day!!]
- Approach to AKI anatomically: Pre, Intrinsic and Post-renal (more below)
- Postobstructive diuresis is primarily a problem with CHRONIC, not ACUTE, urinary retention with management details outlined below.
More Review on AKI
– Definition: < 48 hours (abrupt) time course with 1 or more of the following:
- Increase in serum Cr > 0.3 mg/dL
- Greater than 50% increase in serum creatinine from baseline
- Reduction in urine output of < 0.5 mL/kg/hr for > 6 hours
– Oliguria is defined as UOP < 400 mL/day, while anuria is < 100 mL/day
Approach to AKI based on anatomy
- Pre-renal – 70% of community acquired and 40% of hospital acquired AKI
- Hypovolemia: vomiting, diarrhea, diuretics, hemorrhage, burns
- Decreased effective circulation volume: Cardiorenal, hepatorenal
- Change in renal vascular tone: ACEi, NSAIDs
- Intrinsic Renal – urinalysis is the key here!
- Glomerular – RBCs; Anti0GBM, Pauci-immune, Immune complex
- ATN – muddy brown casts; prolonged pre-renal -> ischemic, toxic, septic shock (most common)
- AIN – WBCs; drug-induced, Infectious (fevers, rash and eosinophilia ~ 15% of pt)
- Vascular – micro: HUS/TTP or macro: renal artery stenosis, thrombosis
- Post-renal – important to exclude early
- Obstruction from BPH, acute prostatitis, constipation, pelvic masses, neuogenic bladder
- A postobstructive diuresis is primarily a problem with CHRONIC, not ACUTE, urinary retention and usually represents an appropriate attempt to excrete excess fluid retained during the period of obstruction
- Management of post-renal obstruction:
- Relieve the obstruction
- Anticipate a post-obstructive diuresis if chronic (more below)
- Frequent monitoring of I/Os and electrolytes (q6-q8)
- If going to give fluid, caution with chloride-containing fluids: Loss of hypotonic urine, may need replacement fluid, usually in a 2:1 ratio (replace approximately half the volume the patient is putting out).
- Fluid replacement is usually with one-half isotonic solution
- Remember that “The kidney is a better judge of the volume status than the doctor!” per Dr. Chi Hsu – In most patients, things will correct themselves.
Altered Mental Status (AMS)
Remember the MISTO mnemonic for AMS:
- Metabolic (electrolytes, esp Na and Ca; endo, esp thyroid and glucose; liver; kidney)
- Structural (stroke, mass, bleed)
- As Jen O mentioned in report “AMS” can be a very nonspecific description – it’s helpful to break this down into more specific characteristics, such as decreased level of consciousness, agitation, confusion, disorientation, etc. This helps one to narrow your differential – also remember MISTO!!