Instruct to summarize the article below, incorporating key points, tables, and numbers while using abbreviations for brevity (e.g., ↑, ↓, ->) retaining clinical data, examples, and classifications. Rewrite this information with headings and side headings and  as succinct bulleted points (<9 words each), Encourage the use of abbreviations,comparison tables and symbols, avoiding repetition. Emphasize prioritizing accuracy and relevance, ensuring integrity in clinical data. Deliver the output in a well-designed markdown format,should be consistent with the information provided in the article;-
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Risk factors
Evidence from epidemiological studies has established the major
risk factors for perioperative ARF (Table 2). Two risk stratification
tools for ARF after cardiac surgery have recently been tested
and validated.6, 7 Similar risk scoring systems for ARF after noncardiac surgery are under development. The incidence is increasing
because of the increasing age of the surgical population and the
performance of more complex surgery.
Prevention
The identification of high-risk patients and the implementation of
prophylactic measures are the goals of perioperative renal protection. Strategies to reduce the occurrence of renal injury in patients
without evidence of acute renal dysfunction are referred to as
primary prevention. The avoidance of additional renal injury in the
setting of established acute renal dysfunction is termed secondary
prevention. Both non-pharmacological and pharmacological interventions may be considered.
Non-pharmacological strategies
These include intravascular volume expansion, maintenance of
renal blood flow and renal perfusion pressure, avoidance of nephrotoxic agents, strict glycaemic control, and appropriate management
of post-operative complications.
Intravascular volume expansion
Perioperative hypovolaemia should be rapidly corrected by volume
expansion with i.v. fluids, whether occurring before, during, or
after surgery. The role of crystalloids compared with colloids for
intravascular volume expansion remains unclear. Although not a
primary outcome measure, a large multi-centre trial of fluid resuscitation in critically ill patients found no difference between
albumin and 0.9% sodium chloride in terms of the risk of ARF.
The renal effects of different colloids have not yet been fully
elucidated. Albumin and gelatin appear to be safe in patients with
normal renal function. The safety of hydroxyethyl starch solutions
in the setting of established renal impairment has not been clarified. Recent evidence suggests that hydroxyethyl starch is associated with a higher incidence of ARF than Ringer’s lactate in
critically ill patients with severe sepsis.
Table 2 Risk factors for perioperative acute renal failure. IABP, intra-aortic balloon
pump; CPB, cardiopulmonary bypass
Pre-operative factors Intra-operative factors Post-operative factors
Chronic disease Type of surgery Acute conditions
Advanced age Cardiac Acute cardiac
dysfunction
Female sex Aortic Haemorrhage
Chronic renal disease Peripheral vascular Hypovolaemia
Diabetes mellitus Non-renal solid organ
transplantation
Sepsis
Chronic cardiac failure Cardiac surgery Rhabdomyolysis
Aortic and peripheral
vascular disease
Prolonged CPB time Intra-abdominal
hypertension
Chronic liver disease Combined procedures Multiple organ
dysfunction syndrome
Genetic pre-disposition Emergency surgery Drug nephrotoxicity
Acute conditions
Hypovolaemia Previous cardiac surgery
Sepsis Aortic surgery
Preoperative IABP Aortic clamp placement
Multiple organ
dysfunction syndrome
Intra-operative
radiocontrast
Drug nephrotoxicity
Table 1 The RIFLE classification of acute renal dysfunction. GFR, glomerular
filtration rate; UO, urine output; ARF, acute renal failure; ESRD, end-stage renal
disease
Grade Glomerular filtration rate
criteria
Urine output criteria
R, Risk Serum creatinine increase:
1.5-fold; GFR decrease:
.25%
UO ,0.5 ml kg21 h21 for 6 h
I, Injury Serum creatinine increase:
2-fold; GFR decrease: .50%
UO ,0.5 ml kg21 h21 for 12 h
F, Failure Serum creatinine increase:
3-fold; GFR decrease:
.75%; serum creatinine
decrease: .350 mmol litre21
(4 mg dl21
) with acute
increase .44 mmol litre21
(0.5 mg dl21
)
UO ,0.3 ml kg21 h21 for 24 h
or anuria for 12 h
L, Loss Persistent ARF¼complete loss of renal function for .4 weeks
E, End-stage ESRD¼complete loss of renal function for .3 months
Perioperative renal protection
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The benefit of isotonic i.v. fluid expansion for the prevention of
radiocontrast-induced nephropathy has been clearly demonstrated.
However, the ideal composition of such fluid and the optimal rate
of infusion have not been determined and should be individualized.
Surgical patients receiving contrast will benefit from the use of the
lowest possible volume of non-ionic, iso-osmolar contrast in conjunction with isotonic i.v. fluids.
Maintenance of renal blood flow and renal
perfusion pressure
Maintenance of adequate renal blood flow and perfusion pressure
involves the defence of both cardiac output and systemic arterial
pressure. The initial approach should be intravascular volume
expansion to reverse hypovolaemia. Inotropic and vasopressor
therapy may then be initiated for the management of low cardiac
output and systemic arterial hypotension, respectively. Despite
historic concerns, norepinephrine is an excellent first-line vasopressor agent. There is no firm evidence to suggest that the drug
compromises renal, hepatic, or gastrointestinal blood flow when
used to treat arterial hypotension. Vasopressin and terlipressin
may be useful agents in the treatment of post-operative
catecholamine-resistant vasodilatory shock. The optimal therapeutic target for systemic arterial pressure for renal protection has
not been established. A minimum mean arterial pressure of 65–75
mm Hg is often targeted in clinical practice; however, a higher
target may be necessary in patients with pre-existing hypertension.
Avoidance of nephrotoxic drugs
Minimizing perioperative exposure to nephrotoxic drugs is crucial
in the prevention of ARF. The use of once-daily aminoglycoside
dosing and the use of lipid formulations of amphotericin B have
been demonstrated to lower the risk of nephrotoxicity associated
with these drugs. There are concerns regarding the risk of renal
injury associated with the antifibrinolytic agent aprotinin. Recent
controversial evidence suggests that the use of aprotinin during
coronary artery bypass graft (CABG) surgery may be associated
with an increased risk of ARF requiring dialysis.
Glycaemic control
Strict glycaemic control using intensive insulin therapy improved
survival and reduced the incidence of ARF requiring RRT in a
landmark trial in mechanically ventilated surgical ICU patients.
Perioperative hyperglycaemia during cardiac and vascular surgery
is associated with increased renal morbidity and overall mortality.
Although the current evidence suggests that strict normoglycaemia
is required for optimum benefit, this approach increases the risk of
hypoglycaemia, the clinical significance of which is unknown in
the ICU setting. It is not yet clear whether rigorous intra-operative
glycaemic control reduces morbidity and mortality in patients
undergoing cardiac and vascular surgery.
Cardiac surgery
The conduct of CPB during cardiac surgery may affect the incidence of post-operative ARF. Limiting the duration of CPB and
maintaining adequate flow and perfusion pressure are of primary
importance. Several other strategies related to the management of
the CPB circuit may reduce renal injury, including avoidance of
excessive haemodilution, avoidance of red cell transfusion, extracorporeal leucodepletion, and haemofiltration during CPB. Many
of the postulated mechanisms of ARF after cardiac surgery relate
to the use of CPB, hence off-pump surgery may theoretically offer
renal protection. However, the evidence that off-pump CABG
(OPCABG) surgery reduces renal morbidity is conflicting.8 New
developments in minimally invasive surgical techniques that avoid
ascending aortic manipulation may result in a reduction in renal
morbidity.
Vascular surgery
Endovascular aneurysm repair (EVAR) is rapidly becoming the
technique of choice for repair of abdominal aortic aneurysms, in
preference to open surgical repair. Both techniques are associated
with worsening renal dysfunction in patients with pre-existing
renal insufficiency. At present, it is not clear whether there is a significant difference between open repair and EVAR in terms of the
occurrence of acute post-operative renal dysfunction in patients
with CRF.9
Post-operative complications
A number of post-operative complications are known to be associated with renal dysfunction. Prompt diagnosis and management of
acute cardiac dysfunction, haemorrhage, sepsis, rhabdomyolysis,
and intra-abdominal hypertension are essential to prevent the development of ARF. Rhabdomyolysis should be initially treated with
aggressive intravascular volume expansion; diuretic therapy and
urinary alkalinization may be considered. Abdominal compression
syndrome caused by intra-abdominal hypertension is associated
with diminished renal perfusion and may precipitate ischaemic
ATN. Timely recognition of abdominal compression syndrome, by
intra-vesical pressure measurement, followed by decompressive
laparotomy may provide the optimal management of this condition.
Pharmacological strategies
The postulated pathophysiology of ATN suggests that perioperative
interventions that optimize renal oxygen delivery may prevent
ARF. However, pharmacological strategies (Table 3) that increase
renal blood flow or decrease renal oxygen consumption have not
proved successful. Despite extensive investigation, few drug interventions have been demonstrated to provide clinical benefit and
some have been clearly shown to be ineffective. A recent systematic review examined 37 randomized, controlled trials comprising
1227 patients and concluded that there is no evidence that
Perioperative renal protection
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pharmacological interventions are effective in protecting renal
function during surgery.10
Dopamine agonists
Dopamine acts on a number of different types of receptors. Renal
blood flow is increased by dopaminergic receptor-mediated renal
vasodilatation, beta-adrenoreceptor stimulation increases cardiac
output, and alpha-adrenoreceptor increases renal perfusion
pressure. A large multi-centre trial has demonstrated that low-dose
dopamine does not prevent ARF, avert the need for RRT, or
reduce the mortality in critically ill patients with early acute renal
dysfunction in ICU. In the perioperative setting, dopamine
increases post-operative urine output but does not improve
outcome. A number of systematic reviews have concluded that
there is no role for low-dose dopamine for clinically significant
renal protection.11
Dopexamine is a synthetic dopamine analogue with betaadrenergic and dopaminergic effects. Perioperative use of dopexamine does not provide renal protection for cardiac or vascular
surgical patients.12
Fenoldopam increases renal blood flow by its selective action
on dopamine-1 receptors. At present, there is conflicting evidence
regarding its usefulness as a potential renal protective agent.
Recent trials suggest that the drug does not prevent radiocontrast-induced nephropathy in patients with pre-existing renal
impairment, does not improve outcome in critically ill ICU
patients with early acute renal dysfunction, and does not protect
perioperative renal function in high-risk cardiac surgical patients.
However, a meta-analysis of 16 randomized, controlled trials comprising 1290 patients suggested a beneficial impact of fenoldopam
in critically ill patients.13
Other renal vasodilator agents
Theophylline, an adenosine antagonist, reverses adenosinemediated renal arterial vasoconstriction, but it does not appear to
prevent perioperative ARF during CABG. Similarly, calciumchannel antagonists and angiotensin-converting enzyme inhibitors
have not been shown to produce renal protection. A recent single
centre trial demonstrated that sodium nitroprusside administration
during the rewarming phase of CPB in patients undergoing CABG
decreases the incidence of post-operative ARF.
Diuretics
In the setting of acute renal dysfunction, diuretics increase urine
output by decreasing tubular re-absorption through several mechanisms. Increasing tubular flow maintains patency and prevents
obstruction and back-leak. Loop diuretics inhibit tubular
re-absorption in the loop of Henle´ whereas mannitol acts primarily
as an osmotic diuretic. The available evidence for the use of diuretics in surgical and critically ill patients is scarce. The perioperative use of neither loop diuretics nor mannitol demonstrates
significant renal protection in patients undergoing cardiac surgery.
However, a recent meta-analysis of five randomized, controlled
trials enrolling 555 patients demonstrated that loop diuretics did
not increase mortality in patients with ARF.14 A randomized trial
of loop diuretic treatment for ARF in critical illness has been
proposed.
Natriuretic peptides
Natriuretic peptides induce a natriuretic and diuretic effect by
increasing glomerular perfusion pressure and filtration. These peptides have shown conflicting results in the prevention of ARF.
Large multi-centre trials have demonstrated that atrial natriuretic
peptide (ANP) does not prevent death or dialysis in critically ill
patients with ARF. However, in a small single centre trial, recombinant human ANP has been shown to reduce the need for dialysis
in post-operative cardiac surgical patients with early acute renal
dysfunction.
N-acetylcysteine
Substantial evidence supports the prophylactic use of the antioxidant N-acetylcysteine (NAC), along with intravascular volume
expansion, for the prevention of radio-contrast nephropathy.
Disappointingly, recent trials in the perioperative and ICU settings
have shown a lack of renal protective benefit of NAC. These trials
have been performed in high-risk patients undergoing cardiac
surgery,15 open abdominal aortic aneurysm repair,16 and abdominal aortic EVAR.
Future strategies
Several experimental strategies are currently undergoing investigation including volatile anaesthetic agents, insulin-like growth
factor-1, erythropoietin, and mesenchymal stem cells.
Practical strategies
Practical strategies for perioperative renal protection are set out in
Table 4.
Table 3 Postulated pharmacological perioperative renal protection strategies
Drug
Vasodilators Dopamine agonists
Adenosine antagonists
Calcium-channel antagonists
Angiotensin-converting enzyme inhibitors
Sodium nitroprusside
Diuretics Loop diuretics
Osmotic diuretics
Natriuretic peptides Atrial natriuretic peptide
Urodilatin
B-type natriuretic peptide
Antioxidants N-acetylcysteine
Corticosteroids
Other agents Volatile anaesthetic agents
Insulin-like growth factor-1
Erythropoietin
Mesenchymal stem cells
Perioperative renal protection
Continuing Education in Anaesthesia, Critical Care & Pain j Volume 8 Number 5 2008