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How do you minimize
the risk of perioperative renal injury?
There is an increased risk of renal injury during the perioperative
period, for a variety of reasons. This is particularly true of those
patients requiring intensive post-operative care (such as patients
undergoing abdominal aneurysm surgery).
-
Avoid nephrotoxins
if
pre-existing renal injuries are present.
-
Prevent pigment
nephropathy (rhabdomyolysis)
by aggressively
fluid loading patients at risk for this complication. This includes most
patients involved in trauma and those with compartment syndromes and
those undergoing limb revascularization.
-
Identify patients at
risk: up
to 50% of patients undergoing cardiac surgery, and 26% of patients
undergoing major vascular surgery (emergency AAA, 4% for elective
cases), have post operative renal insufficiency. The way to treat this
is prevent it: many of the post op cardiac injuries can be prevented by
keeping the patients blood pressure within normal limits on bypass, by
minimizing cross-clamp and bypass times and by treating myocardial
dysfunction with intra-aortic balloon counterpulsation. Post op AAA
repair patients are at obvious risk if a supra-renal cross clamp has
been applied, but short cross clamp times and patience will resolve most
injuries. Many patients undergoing liver surgery, liver transplantation
or who are jaundiced are at risk for hepatorenal syndrome, due to renal
vasoconstriction and renal vein dysfunction.
-
Maintain adequate
preoperative and intraoperative hydration.
The kidneys like fluid, and it is much better to give patients too much
fluid, than too little.
-
Maintain renal
perfusion pressure.
All anesthetic drugs have vasodilatory effects, and although they reduce
cerebral metabolic rate, they have no effect on the kidneys, which are
vulnerable to hypoperfusion. You must have a blood pressure target for
your patients (based on baseline pressure readings), and keep the mean
arterial pressure within 25% of this baseline. When the urinary catheter
is placed, check that it is not being compressed, and that there is good
flow from the start, watch the output hourly, and bolus fluids to
maintain an output >0.5ml/kg/hour.
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Pharmacologic
interventions.
No therapy to date has been shown to improve renal outcome, either
perioperatively or in critical care. Diuretics may worsen pre-renal
syndrome. Dopamine does not improve outcome, and is potentially harmful
(as a beta agonist it increases heart rate in patients [vascular
surgery] whose outcome is improved by using beta-blockers). Selective
DA-1 agonists such as fenoldopam may be useful as a renal protective
agent, but without evidence by randomized controlled trials, are
currently not indicated. Mannitol increases medullary oxygen demand and
can worsen acute renal injuries, except in renal transplantation, when
given prior to release of the cross clamp (and perhaps in rhabdomyolysis).
There is no magic
bullet to prevent peri-operative renal injury. The only proven methods are
the sensible ones – keep the body well hydrated, keep the mean arterial
pressure in the autoregulation range, and avoid nephrotoxins.
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