Medic Basics

First five minutes

Low Urine Output Algorithm

Catheter first, then pressure, volume, the kidney and who to call

Reviewed by Alex G, BSN, RN, CEN, CCRN, CMC, NREMT-P · From the Reference tab of the app

Each step lists what to do, then the choices that lead on. In the app the algorithm is tapped through one decision at a time.

1 Check the patient first

  • Vitals now: BP and MAP, HR, temperature, SpO₂, mental status; low urine can be the first sign of shock
  • Work out the goal: 0.5 mL/kg/h or more (35 mL/h at 70 kg); add up the last 6 hourly volumes
  • Shock, new confusion, breathlessness, K 6 or more or peaked T waves: call the provider now (rapid response outside the ICU)

Next: is it real? → step 2

2 Is the output really low?

  • Foley: look for kinks, dependent loops, a clamp or closed port, a full bag; keep the bag below the bladder
  • Bladder scan: urine pooling in the bladder despite a Foley means it is blocked or misplaced
  • No Foley: a full bladder on the scan (often 400 mL or more) is retention
  • Check the charting: missed hourly totals, urine sitting in the tubing, other outputs (nephrostomy, urostomy)

Blocked catheter or full bladder → step 3Real: catheter patent, bladder empty → step 4

3 Drainage problem: fix it

  • Straighten kinks and loops; empty the bag; keep it below the bladder and off the floor
  • Flush or replace a blocked catheter per policy; clots or hematuria: three-way catheter and irrigation per order
  • Retention without a Foley: catheterize per order and record the volume drained
  • After a large retention: watch for brisk diuresis (over 200 mL/h) and replace losses per order

Still low once draining freely → step 4

4 Is the MAP high enough for the kidneys?

  • Most kidneys need MAP 65 or more; a usually hypertensive patient may need more: compare with the usual BP
  • Low flow can starve the kidneys at a normal MAP: cool skin, slow capillary refill, low cardiac output
  • Kidney perfusion is roughly MAP minus CVP or bladder pressure: congestion and a tense abdomen hurt too

MAP under 65 or well below the usual → step 5MAP at target → step 6

5 Low MAP: restore it first

  • Treat it as new hypotension: confirm the reading, check perfusion, find the cause (New Hypotension algorithm)
  • Fluid only if fluid responsive and not overloaded; otherwise a vasopressor to the MAP target per order
  • Usually hypertensive: ask whether a higher MAP target suits this patient
  • Recheck urine output 1–2 hours after the MAP is restored

Next: volume status → step 6

6 What is the volume status?

  • Dry: losses (drains, NG, diarrhea, bleeding), negative balance, flat neck veins, tachycardia, dry mucosa
  • Wet: edema, crackles, high CVP, rising O₂ need, weight up, large positive balance
  • Unsure: passive leg raise; stroke volume or cardiac output up 10% or more predicts a fluid response

Dry or fluid responsive, and not overloaded → step 7Overloaded, or not fluid responsive → step 8

7 Fluid challenge

  • Balanced crystalloid 250–500 mL over 10–15 min per order; reassess after each bolus
  • Stop for crackles, rising O₂ need or JVD, and tell the provider
  • Replace ongoing losses; hold diuretics while dry
  • Urine picks up within 1–2 hours: likely prerenal; keep replacing losses and report the response

Next: how long has it been low? → step 9

8 Overloaded or not responsive: no more fluid

  • More fluid will not restore urine and can harm: a high CVP itself lowers kidney perfusion
  • Overload: loop diuretic per order (furosemide 40–80 mg IV, more if on a home dose) to treat the overload, not the number
  • Cold and congested (failing heart): the kidneys need cardiac output; inotrope or cardiology per the provider
  • Overload with high potassium or acidosis may need dialysis: ask about nephrology

Next: how long has it been low? → step 9

9 How low, for how long? (KDIGO)

  • AKI stage 1: under 0.5 mL/kg/h for 6–12 h, or creatinine up 0.3 mg/dL in 48 h or 1.5 times baseline
  • Stage 2: under 0.5 mL/kg/h for 12 h or more, or creatinine 2–2.9 times baseline
  • Stage 3: under 0.3 mL/kg/h for 24 h, anuria for 12 h, creatinine 3 times baseline or 4 mg/dL or more, or dialysis started
  • Sudden anuria: recheck the catheter, then think obstruction or a blocked renal artery (ultrasound)

Next: find the cause → step 10

10 Find the cause

  • Prerenal: low volume, low MAP or low cardiac output; concentrated urine, urine sodium under 20
  • Intrinsic: sepsis, prolonged hypotension, contrast, nephrotoxic drugs, rhabdomyolysis (dark urine, high CK)
  • Postrenal: catheter, prostate, clots, stones; renal ultrasound for hydronephrosis
  • Tense abdomen, large positive balance, abdominal surgery or rising airway pressures: measure bladder pressure

Possible abdominal compartment syndrome → step 11Next: stop nephrotoxins, send labs → step 12

11 Bladder pressure (intra-abdominal pressure)

  • Supine; zero the transducer at the mid-axillary line at the iliac crest; instill no more than 25 mL saline (closed kit per policy)
  • Read in mmHg at end-expiration, with the abdominal muscles relaxed
  • 12 mmHg or more is intra-abdominal hypertension; over 20 with new organ failure is abdominal compartment syndrome
  • Compartment syndrome: call the surgeon now; NG and rectal decompression, deeper analgesia and sedation, no positive balance

Next: stop nephrotoxins, send labs → step 12

12 Stop nephrotoxins and send labs

  • Hold or question: NSAIDs, aminoglycosides, amphotericin, IV contrast, ACE inhibitors and ARBs; vancomycin by levels
  • Ask pharmacy to renally dose every drug; hold metformin; no renal-dose dopamine
  • Pause potassium supplements and potassium in IV fluids until potassium and urine output are reviewed
  • Send BMP (creatinine, potassium, bicarbonate), magnesium, phosphate, CBC, urinalysis with microscopy
  • Also urine sodium and creatinine (FENa), CK, lactate and a blood gas; renal ultrasound if obstruction is possible

Next: when to call → step 13

13 When to call, and what to report

  • Call now: MAP under 65, anuria, K 6 or more or ECG changes, pH under 7.15, overload with hypoxemia, new confusion
  • Report within the hour: under 0.5 mL/kg/h for 2 hours in a row (or per unit parameters), or creatinine up 0.3 mg/dL
  • S and B: hourly volumes for 6 h in mL and mL/kg/h, how you confirmed them, baseline creatinine, fluid balance, contrast and nephrotoxins
  • A and R: MAP, volume status and fluid response, bladder pressure, K and creatinine; ask for orders, and nephrology if dialysis may be needed

End of this path.

Drugs in this algorithm

Related one-pagers

Practice free in your browser2,450+ exam-style questions with rationales. No account, no ads. Also free on the App Store and Google Play.

For education and exam preparation only. Follow your institution’s protocols. Study aid with typical adult values; follow your local protocols and medical direction, and current AHA guidelines.