This interesting article highlights the fact we MAY be obsessing with cranking up the MAP in order to get patients to produce more urine. see here

Here, researchers use the R.I.A.D (renal interlobular artery doppler), to guide fluid therapy. What is interesting for me is that they state that often, fluid boluses associated with increased MAP and other surrogate measures of circulatory adequacy, actually decreased renal perfusion in many cases. This suggests that the renal vasculature is similar to cerebral vasculature in it’s auto regulatory ability / behaviour.

This all depends on basal renal haemodynamic state of course and many things may affect this; changes in intra-renal compliance, renal interstitial pressure, heart rate, and intra-abdominal pressure etc.

also observe that an improvement in renal perfusion can be obtained and translated into an increase in urine output even when there are no relevant (<10 %) changes in MAP. Although renal responders had higher baseline MAP, changes in MAP and PP were not associated with renal response to fluids according to their stats and various other studies.

Key messages:

  • Fluid challenge results in reduced intrarenal vasoconstriction in hemodynamically impaired ICU patients.
  • In hemodynamically impaired patients, changes in MAP after a fluid challenge cannot predict an increase in urine output.
  • However, changes in renal interlobar artery resistivity index in these patients can predict an increase in urine output.
  • Nevertheless, interlobar resistivity index cannot be recommended for routine use, because of the relatively limited magnitude of the changes and need for experienced ultrasonographers.

For me, an interesting study, but I won’t RAID as a routine, but this is useful food for thought when we drive up the MAP with fluid and see nothing!