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Renal disease and the surgical patient: Minimizing the impact

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ABSTRACT

Chronic kidney disease (CKD) is common in patients scheduled for surgery and increases the risk of postoperative acute kidney injury, major adverse cardiac events, and death. Acute kidney injury is a common complication of cardiac and noncardiac surgery and negatively affects both short- and long-term outcomes. If we can detect underlying CKD and other risk factors for acute kidney injury before surgery, we may in theory be able to give preventive therapies and improve perioperative outcomes.

KEY POINTS

  • Many patients undergoing surgery have CKD—up to 30% in some cardiac surgery populations.
  • CKD is a risk factor for perioperative complications including acute kidney injury and death.
  • Although challenging, early detection of renal injury is crucial to improving outcomes in this patient population. New biomarkers are being investigated.
  • Preoperative assessment and perioperative management of renal dysfunction may reduce the risk of adverse postoperative outcomes.


 

References

Chronic kidney disease (CKD) is estimated to affect 14% of Americans, but it is likely underdiagnosed because it is often asymptomatic.1,2 Its prevalence is even higher in patients who undergo surgery—up to 30% in cardiac surgery.3 Its impact on surgical outcomes is substantial.4 Importantly, patients with CKD are at higher risk of postoperative acute kidney injury (AKI), which is also associated with adverse outcomes. Thus, it is important to recognize, assess, and manage abnormal renal function in surgical patients.

WHAT IS THE IMPACT ON POSTOPERATIVE OUTCOMES?

Criteria for chronic kidney disease
CKD is defined in various ways, making it difficult to derive exact numbers about its impact on surgical outcomes. The definition (Table 1) and categories (Table 2) devised by the Kidney Disease Improving Global Outcomes (KDIGO) program are now the most widely accepted.5,6

Cardiac surgery outcomes

Defining the severity of chronic kidney disease
In cardiac surgery patients, CKD is strongly correlated with higher postoperative inpatient and 30-day mortality rates, both all-cause and cardiovascular.7–10 It is a strong predictor of death in the first 30 days after surgery, with a 35% to 43% higher risk of death for every 10 mL/min/1.73 m2 of preoperative decrease in estimated glomerular filtration rate (GFR).10

Moreover, in patients undergoing coronary artery bypass grafting (CABG), the worse the renal dysfunction, the higher the long-term mortality rate. Patients with moderate (stage 3) CKD had a 3.5 times higher odds of in-hospital mortality compared with patients with normal renal function, rising to 8.8 with severe (stage 4) and to 9.6 with dialysis-dependent (stage 5) CKD.11

The mechanisms linking CKD with negative cardiac outcomes are unclear, but many possibilities exist. CKD is an independent risk factor for coronary artery disease and shares underlying risk factors such as hypertension and diabetes. Cardiac surgery patients with CKD are also more likely to have diabetes, left ventricular dysfunction, and peripheral vascular disease.

Noncardiac surgery outcomes

CKD is also associated with adverse outcomes in noncardiac surgery patients, especially at higher levels of renal dysfunction.12–14 For example, in patients who underwent major noncardiac surgery, compared with patients in stage 1 (estimated GFR > 90 mL/min/1.73 m2), the odds ratios for all-cause mortality were as follows:

  • 0.8 for patients with stage 2 CKD
  • 2.2 in stage 3a
  • 2.8 in stage 3b
  • 11.3 in stage 4
  • 5.8 in stage 5.14

The association between estimated GFR and all-cause mortality was not statistically significant (P = .071), but statistically significant associations were observed between estimated GFR and major adverse cardiovascular events (P < .001) and hospital length of stay (P < .001).

The association of CKD with major adverse outcomes and death in both cardiac and noncardiac surgical patients demonstrates the importance of understanding this risk, identifying patients with CKD preoperatively, and taking steps to lower the risk.

WHAT IS THE IMPACT OF ACUTE KIDNEY INJURY?

AKI is a common and serious complication of surgery, especially cardiac surgery. It has been associated with higher rates of morbidity, mortality, and cardiovascular events, longer hospital length of stay, and higher cost.

Several groups have proposed criteria for defining AKI and its severity; the KDIGO criteria are the most widely accepted.15 These define AKI as an increase in serum creatinine concentration of 0.3 mg/dL or more within 48 hours or at least 1.5 times the baseline value within 7 days, or urine volume less than 0.5 mL/kg/hour for more than 6 hours. There are 3 stages of severity:

  • Stage 1—an increase in serum creatinine of 1.5 to 1.9 times baseline, an absolute increase of at least 0.3 mg/dL, or urine output less than 0.5 mL/kg/hour for 6 to 12 hours
  • Stage 2—an increase in serum creatinine of 2.0 to 2.9 times baseline or urine output less than 0.5 mmL/kg/hour for 12 or more hours
  • Stage 3—an increase in serum creatinine of 3 times baseline, an absolute increase of at least 4 mg/dL, initiation of renal replacement therapy, urine output less than 0.3 mL/kg/hour for 24 or more hours, or anuria for 12 or more hours.15

Multiple factors associated with surgery may contribute to AKI, including hemodynamic instability, volume shifts, blood loss, use of heart-lung bypass, new medications, activation of the inflammatory cascade, oxidative stress, and anemia.

AKI in cardiac surgery

The incidence of AKI is high in cardiac surgery. In a meta-analysis of 46 studies (N = 242,000), its incidence in cardiopulmonary bypass surgery was about 18%, with 2.1% of patients needing renal replacement therapy.16 However, the incidence varied considerably from study to study, ranging from 1% to 53%, and was influenced by the definition of AKI, the type of cardiac surgery, and the patient population.16

Cardiac surgery-associated AKI adversely affects outcomes. Several studies have shown that cardiac surgery patients who develop AKI have higher rates of death and stroke.16–21 More severe AKI confers higher mortality rates, with the highest mortality rate in patients who need renal replacement therapy, approximately 37%.17 Patients with cardiac surgery-associated AKI also have a longer hospital length of stay and significantly higher costs of care.17,18

Long-term outcomes are also negatively affected by AKI. In cardiac surgery patients with AKI who had completely recovered renal function by the time they left the hospital, the 2-year incidence rate of CKD was 6.8%, significantly higher than the 0.2% rate in patients who did not develop AKI.19 The 2-year survival rates also were significantly worse for patients who developed postoperative AKI (82.3% vs 93.7%). Similarly, in patients undergoing CABG who had normal renal function before surgery, those who developed AKI postoperatively had significantly shorter long-term survival rates.20 The effect does not require a large change in renal function. An increase in creatinine as small as 0.3 mg/dL has been associated with a higher rate of death and a long-term risk of end-stage renal disease that is 3 times higher.21

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