Acute renal failure: oliguria: mannitol may improve urine output.

Clinical bottom line (level 4)

  1. Around half of patients with oliguric acute renal failure increased their urine output when given mannitol.
  2. Patients with oliguria who failed to respond to mannitol were more likely to die (NNF = 2 for unknown) .
  3. In patients with oliguria who responded to mannitol, the mean increase in urine output was 80 ml/hour.
Luke et al: American Journal of Medical Science 1970; 259: 168-174
Expires July 2003

The study

Inception cohort study with objective outcomes, not adjusted for confounding factors, not validated in an independent set of patients.

Setting: renal unit of university hospital, UK

37 patients (aged range 17 to 75 years; mean 54, 64% male) rising urea and oliguria (<23 ml/h) and low urinary urea (not defined) and low urine:plasma urea ratio (not defined)

Excluded if
  • oliguria responded to replacement of fluid deficit


    • Patients had urethral catheters inserted and those without elevated jugular venous pulsations received infusions of colloid or crystalloid. Patients had mannitol 20% 100 ml i.v. over 30 minutes. Repeat doses of mannitol (up to two further doses) were given if the urine output improved but did not reach 50 ml/h. If no improvement was noted, no further mannitol was given.

    100% followed for until discharge
    Outcomes studied:
  • death

    • Precipitating events were surgery (62%), trauma (11%), obstetrical (5%) and medical problems (22%). Mean duration of oliguria prior to mannitol was 35 hours, and mean urea concentration was 57 mmol/l.
    • Patients were considered to be responders to mannitol if:
      • urinary output increased to an average of 50 or more ml/h for the four hours after the last infusion of mannitol
      • blood urea subsequently fell with maintained diuresis, unless death due to the underlying condition supervened

    The evidence

    outcome time to outcome number of patients/total number %
    (95% CI)
    death until discharge 17/27 46%
    (30% to 62%)

    prognostic factor for
    death     		time to outcome unadjusted RR
    (95% CI)    		 NNF+
    (95% CI)
    no response to mannitol until discharge 3.97
    (1.37 to 11.5)     		2
    (1 to 15)

    • 54% (95% CI: 38% to 70%) of patients responded to mannitol.
    • For those with a response: urine output was 15 ml/h (S.D. 2) pre-mannitol, and 99 ml/h (S.D. 2) post-mannitol. This was a mean difference of 84 ml/h (95% CI: 83 to 85).

    Comments

    1. Patients who responded to mannitol had been oliguric for fewer hours, and had a higher urine output before starting mannitol.
    2. Whether the observed differences in prognosis are due to the response to the diuretic itself or to differences in underlying characteristics that determine responsiveness cannot be determined by a study of this design. The lack of a control group limits the inferences that can be drawn from this work.

    Citation

    1. Luke RG, Briggs JD, Allison MEM, et al: Factors determining response to mannitol in acute renal failure. American journal of Medical Science 1970; 259: 168-174
    Search Terms: acute renal failure [MeSH] and oliguri* [textword] or oliguria [MeSH]
    Contributor: Catherine Clase, Chris Ball and Clare Wotton, April 2000
    Reviewer: Catherine Clase

    Clinical Question.
    Patient acute renal failure and oliguria
    Intervention or Exposure mannitol
    Outcome death