Your anaesthetic colleague asks for advice. He is going to anaesthetise a 70 year old diabetic hypertensive patient with chronic renal failure (creatinine 258 micromol/l) for an elective infrarenal endoluminal aortic graft. He wishes to know how he can help prevent a deterioration in the patient’s renal function perioperatively. What evidence based advice would you give him?
This patient is at high risk (baseline renal impairment, diabetes, manipulation of aorta, and requirement for intravenous contrast).
Potential causes of deterioration with Endoluminal grafts are multiple. Specific factors include: they require radiographic evaluation (ie. contrast administration), involve arterial catheter insertion and aortic manipulation (ie. particulate [including cholesterol] emboli), the patients develop a post-operative inflammatory response, and they may be associated with problems with deployment (eg. occlusion of accessory renal artery, or complications that may be associated with haemodynamic compromise, &/or reoperation).
No specific studies have looked at endovascular grafts. Prevention of intravenous dye related renal dysfunction has been studied (mainly in coronary angiography). Factors shown to be potentially of benefit include volume expansion (in particular with 154 m/eq/L sodium bicarbonate [Merten 2004 JAMA]), the use of N-acetylcysteine orally (or IV) [Alonso 2004Am J Kidney Dis], the use of lower doses of low osmolal and iso-osmolal non-ionic dyes, and the avoidance of closely spaced studies. Other standard preventative measures include avoidance of volume depletion and nephrotoxins. The role of mannitol, dopamine, loop diuretics and haemofiltration is uncertain.
The patient in question is at risk of renal failure post procedure; however, endoluminal repair is associated with a greatly decreased risk of renal failure (OR ~ 0.42) and progression to dialysis (OR ~ 0.3).
The reasons for renal failure in such a patient include the following:
- Occlusion of renal artery by graft
- Damage to renal artery by procedure
- Atheromatous embolism into the renal circulation
- Renal ischaemia due to poor perioperative perfusion
- ATN due to rhabdomyolysis
- Nephrotoxicity due to contrast.
Of these factors, the first three are within the control of the surgeon to a great extent, and the "anaesthetic colleague" has little control over them. However, the "coallgue" can protect the patient from pre-renal causes of renal failure by ensuring good cardiac output and adequate blood pressure is maintained thoughout the procedure, and by paying careful attention to the periprocedure urine output.
Rhabdomyolysis is also an unpredictable complication, and all one can sensibly do is be careful in selecting which femoral artery one decides to access, and monitoring limb perfusion intraoperatively.
The last point - contrast-induced nephrotoxicity - is where the answering candidate will really earn their marks. This part of the question closely resembles Question 12 from the first paper of 2009, "Critically evaluate strategies that have been used in the prevention of acute kidney injury (AKI) associated with the administration of iodinated radio contrast medium." A large and reasonably comprehensive table ("Protective Strategies against Contrast-Induced Nephropathy") is also presented in Required Reading section. In brief, the accepted strategies are as follows:
- Early identification of patients with risk factors
- Use of nonionic contrast media
- Use of a smaller volume of contrast media
- Pre and post-hydration
- Sodium bicarbonate
- Statins (possibly)
- Prophylactic CVVHDF
Wald, Ron, et al. "Acute renal failure after endovascular vs open repair of abdominal aortic aneurysm." Journal of vascular surgery 43.3 (2006): 460-466.
Mehran, R., and E. Nikolsky. "Contrast-induced nephropathy: definition, epidemiology, and patients at risk." Kidney International 69 (2006): S11-S15.
Kelly, Aine M., et al. "Meta-analysis: effectiveness of drugs for preventing contrast-induced nephropathy." Annals of internal medicine 148.4 (2008): 284-294.