Postoperative renal dysfunction after noncardiac surgery

  • Vaara ST, Bellomo R.
  • Curr Opin Crit Care. 2017;23(5):440–6.

Acute kidney injury (AKI) affects one-fifth of major surgery patients increasing the risk of long-term mortality and renal dysfunction. Therefore, it is important to broaden our understanding of the epidemiology and prevention of postoperative AKI. This review paper by Vaara and Bellomo discusses recent study data, aiming to fill the knowledge gaps surrounding postoperative AKI.

What is postoperative AKI?

Variations in diagnostic criteria have long complicated the diagnosis of AKI and the assessment of its incidence (Kellum et al., 2002). The current consensus was reached in 2012, when Kidney Disease: Improving Patient Outcomes (KDIGO) published their recommendations including a definition of postoperative AKI:

  • increase in creatinine
    • an abrupt increase from premorbid baseline of at least 150% within a week
    • or a 27 μmol/L increase within the last 48 hours
  • changes in urine output
    • less than 0.5 mL/kg/h for at least 6 hours
  • commencing renal replacement therapy (KDIGO, 2012).

However, challenges do exist in implementing these diagnostic criteria in the perioperative setting. These include when a true creatinine baseline isn’t obtained (Englberger et al., 2011), when fluid loading decreases the serum creatinine concealing the loss of glomerular filtration rate, and when fluids along with diuretics cause inaccurate readings of urine outputs (Goren & Matot, 2015).

Incidence and AKI risk factors

Every surgery runs its own risks, even more so with major surgery - found to be the second most common predisposing factor for AKI (Uchino et al., 2005). The different types of surgery have varying levels of AKI incidence, table 1 demonstrates how wide these variations can be.

Table 1: Postoperative AKI incidence rates for different surgery types.

Table 1: Postoperative AKI incidence rates for different surgery types.

It is important to remember that the risks of AKI begin before surgery is even considered. Cardiovascular diseases, diabetes, chronic kidney disease (CKD), obesity, sepsis and/or the need for critical care are some of the most important risk factors indicated for perioperative AKI (KDIGO, 2012; Goren & Matot, 2015).

Postoperative AKI outcomes

The seriousness of postoperative AKI should not be overlooked. When comparing patient outcomes, there was a risk ratio of over 12 for mortality reported in patients who developed postoperative AKI following major abdominal surgery compared to those who didn’t develop AKI (O’Connor et al., 2016). In fact, in all types of major surgery, AKI was associated with increased postoperative all-cause mortality, increased risk of CKD development, and a two-fold risk for long-term cardiovascular mortality compared to patients without postoperative AKI (Hobson et al., 2015; Ozrazgat-Baslanti et al., 2016).

Prevention of postoperative AKI

Preventing postoperative AKI should be at the forefront of the medical teams’ mind before, during and after surgery, taking steps to avoid any increased risk. These steps include:

  • correcting or optimising an individual’s clinical state, such as correcting anaemia (Goren & Matot, 2015)
  • selecting surgical approaches that are typically less injurious to the kidneys
  • maintaining adequate organ perfusion (using fluids, blood products, vasopressors, and inotropes)
  • avoiding nephrotoxic drugs
  • avoiding intraoperative hypervolemia
  • avoiding intraoperative hypotension
    • maintaining a mean arterial pressure (MAP) over 60–65 mmHg, or higher if a patient has chronically high blood pressure, has been shown to be desirable in data from critically ill patients.

Prevention: surgery-standard or goal-directed therapy?

There have been many comparisons between standard therapy and the strategy of goal-directed therapy to investigate the prevention of postoperative AKI (figure 1).

A flow chart comparing standard therapy to goal-directed therapy for the prevention of postoperative A K I

Figure 1: Comparison of standard therapy to goal-directed therapy for the prevention of postoperative AKI (Adapted from Vaara & Bellomo, 2017).

Prevention: fluid management

Intraoperative hypotension and hypervolemia should be carefully considered and avoided during surgery to prevent the risk of postoperative AKI, one method of avoiding these clinical complications is through fluid management. There has been a change in fluid use over recent years, and the information surrounding the safety of their use has been a major concern to healthcare professionals (Taylor et al., 2017), resulting in increased use of balanced solutions due to concerns around the use of 0.9% sodium chloride (Verma et al., 2016). There is a growing body of evidence to suggest there are risks associated with fluid use – especially the use of starch-based colloids which are unlikely to be beneficial to patients undergoing surgery and are particularly harmful for patients who are at high risk of postoperative AKI (Hartog et al., 2014). Data also suggest that the use of restrictive perioperative fluid may help avoid oedema, while high cumulative fluid balances have been shown to be harmful to the kidneys of critically ill patients (Zhang et al., 2015; Perner et al., 2017). 

The use of restrictive versus liberal fluid use is an ongoing debate with contradicting evidence. One large database analysis found that both methods of fluid therapy were associated with an increased risk of AKI (Shin et al., 2018), whereas a retrospective registry study of colorectal surgery patients found smaller total perioperative volumes of fluid to be more beneficial, aiding quicker recovery and long-term outcomes (Asklid et al., 2017). It is hoped that the restrictive versus liberal fluid therapy in major abdominal surgery (RELIEF) trial will help to answer questions around fluid use and AKI.

The data from RELIEF will be featured here next month.

Prevention: avoiding nephrotoxic drugs

The final step Vaara and Bellomo recommend to prevent postoperative occurrence is the avoidance of drugs which are harmful to the kidneys. Drugs typically administered to surgical patients that may cause further damage to the kidneys include non-steroidal anti-inflammatory drugs (NSAIDS), vancomycin, aminoglycosides, diuretics, and contrast media (KDIGO, 2012). Diuretic use in pre or perioperative scenarios has been shown to be associated with an increased risk of AKI in noncardiac patients after adjustment for presence of CKD (Tagawa et al., 2015). Finally, a Cochrane systematic review did not find evidence supporting the use of any pharmacological interventions to either prevent or treat AKI (Zacharias et al., 2015).

The future of postoperative AKI

Vaara and Bellomo conclude that the most logical steps in avoiding incidence of AKI perioperatively are prompt treatment of intraoperative hypotension and hypoperfusion, and avoidance of nephrotoxins. Future research is still needed, with studies using the consensus definition of AKI and inclusion of urine output. One hope for the future of diagnosing AKI is through the identification of novel predictive biomarkers. These biomarkers are key to future research and will aid a quicker and more precise diagnosis. The RELIEF data is also hoped to bring some clarity to the ongoing fluid debate.

Explore the Fluid Management Knowledge Centre to discover more about the role of fluid therapy in cardiac surgery, critically ill patients, liver cirrhosis, and more.

Catch-up on the debate surrounding hydroxyethyl starch use as we take you on an interactive journey through its changing fortunes. Do you think current restrictions will be enough to change clinical practice?


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