澳纽专科考题2--ANZCA exam question & answer

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2000A:2




Justify the measures you would use to minimise the risk of acute tubular
necrosis if the surgeon is to clamp the supra-renal aorta in Abdominal aortic aneurysm surgery.

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Renal dysfunction is a result of hypoperfusion and renal ischaemia during the period of cross-clamping. The most dangerous complication of alteration of renal blood flow is ATN and subsequent ARF.

ARF after aortic aneurysm repair is associated with a mortality of >40%. Decreased renal function is observed in many patients after aortic cross-clamping (even when the clamp is place distal to the renal arteries).

There are a number of physiological and pharmacological method that can be used to minimize the risk of ATN.

Prior to Aortic Clamping.
-Potential damage to the kidneys can be limited by avoiding a prerenal injury before clamp placement. Volume resuscitation (crystalloid/colloid), with maintenance of cardiac output and adequate circulating blood volume are the best way to accomplish this goal.

-Various pharmacological manipulations are begun in anticipation of the aortic cross-clamp:


->Dopamine (1-3micrograms/Kg/min) increases renal blood flow and improves urine output. Decreased incidence in preventing post-op ATN/ARF not proven however.


->Mannitol (0.25g/Kg) attenuates the reduction of renal cortical blood flow before, during and after renal ischaemia and causes concurrent increase in GFR. May also act as a scavenger of free radicals, decrease rennin secretion and increase renal prostaglandin secretion.


->Frusemide (up to 1mg/Kg) may also improve urine output. Care to avoid hypovolaemia and hypokalaemia.

(Strong clinical evidence is currently lacking, although experimental evidence tends to support these pharmacological practices.)

During Cross-Clamping.
-Maintenance of adequate circulating blood volume remains the mainstay. Compensating for volume loss with crystalloid, colloid or blood products as appropriate.

-Use of cold renal perfusate induces renal hypothermia and allows the kidneys to tolerate longer periods of hypoperfusion.

-The most direct approach is to provide perfusion to the renal arteries while the cross-clamp is on. Selective renal perfusion (ie.small catheters used to cannulate the renal arteries with blood flow being diverted from the upper aorta) and distal aortic perfusion (ie. CPB or Left atrial-left femoral artery bypass) are techniques employed for renal protection from ischaemia.

Post Cross-Clamping.
-Anticipate declamping shock, which be another late yet significant insult to renal
perfusion. Hypervolaemia and systolic hypertension are short term goals that must be achieved just prior to removal of the cross-clamp.

-Volume resuscitation if hypotensive with crystalloid or colloid.

-Pharmacologically, temporary ionotropic support to maintain blood pressure and cardiac output.


REF. Yao & Artusio 5th edn; pp. 297, 302-303, 308, 330.

Miller 5th edn; p. 1865.