Sunday 14 May, 2006

IV fluid therapy in post-obstruction polyuria

Posted in Medicine, Michael Tam, Surgery, Wards at 20:21 by Michael Tam

Index: Intravenous fluid therapy :: Printer friendly

Original article by: Michael Tam

Foley catheter

Urine output in these patients can be hundreds of millilitres per hour. This can lasts for a few days. Most commonly, these patients are post-operative urology patients.

The polyuria in these patients is partly physiological due to the expansion of the extracellular fluid during obstruction. A brief diuresis may not compromise fluid status as long as it is brief. The diuresis is generally electrolyte rich.

Nevertheless, there can be a substantial and huge loss of fluid leading to shock. These patients can literally lose their intravascular volume in a matter of hours. Given this is the case, these patients must have an indwelling urinary catheter and urine output measured on an hourly basis. Daily blood tests for electrolytes, urea and creatinine as well as serum calcium, magnesium and phosphate are a must.

Fluid choice: 0.9% NaCl (“normal saline”)

Rate: IV fluid rate (mL/h) = urine output of the past hour

That is, if the urine output between 0900 and 1000 was 300 mL, then the rate of intravenous fluid between 1000 and 1100 would be 300 mL/h. Obviously, the input rate needs to adjusted on an hourly basis.

DO

  • Strict urine output measurements hourly is a must
  • Regular physical examination for under- and over-hydration – probably at least every 3-4 hours until resolution of polyuria
    • Mucous membranes – ? dry
    • JVP – ? raised
    • Thirst
    • Heart rate
    • Auscultate lung fields
  • Review if hourly urine output greater than 500 mL
  • Consider use of a central line for jugular venous pressure monitoring
  • Daily UECs and Ca, Mg, PO4 and treat electrolyte disturbances
  • Re-insertion of a peripheral intravenous cannula in the event of failure is obviously an urgent priority in these patients.

If polyuria is prolonged (especially if there was renal failure with subsequent tubular dysfunction), specialist input from a renal physician or the renal team is advised.

In the mildly dehydrated patient, you can try using a formula of 40 mL/h + hourly urine output (rate adjusted hourly). A seriously dehydrated patient or one that is shocked should be given vigorous fluid resuscitation.

Be aware that over-hydration will prolong polyuria.

Updated: Michael Tam (19 June 2006)

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3 Comments »

  1. nicholas talley said,

    I apply the advice today

  2. Hildy said,

    If you’re replacing with NS at the same rate as urine output, then A) the ECF volume never decreases and B) you’re giving these people a rather large sodium load (probably much higher than what they’re excreting).

  3. Michael Tam said,

    Firstly it is a rule of thumb; which works. ;-)

    Secondly, urine is not the only means by which the human body loses water. The replacement fluid in this schema is less than what is being lost, but SLOWLY, which is what we want in post-obstruction diuresis.

    Yes, overhydration (as per my article) will lead to prolongation of the polyuria. However, underhydration can quickly lead to shock and death. Where unclear, I would always err on the side of caution (i.e., overhydration).

    Cheers.


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