Cardiac Surgery-Associated Acute Kidney Injury (CSA-AKI)Cardiac surgery-associated acute
kidney injury (CSA-AKI) is a common and serious complication, with an incidence of up to
40% in cardiac surgery patients. Approximately 3% of these patients will require at least
temporary hemodialysis sessions. Patients with AKI have increased perioperative
mortality, prolonged ICU stay, increased hospitalization costs, and 25% of them will
progress to chronic renal failure within 3 years. It is defined by KDIGO as an increase
in serum creatinine > 0.3 mg/dl within 48 hours, or an increase in creatinine >1.5 times
the baseline which is known or presumed to have occurred within the previous 7 days, or
urine output < 0.5ml/kg/h for 6 hours.A range of factors with increased risk of
developing CSA-AKI has been identified: patient-related, anesthesia-related,
surgery-related, and cardiopulmonary bypass-related. The pathophysiology is
multifactorial and not fully understood. Renal hypoperfusion, reperfusion injury,
inflammation, oxidative stress, neurohormonal activation, nephrotoxins, and genetic
polymorphisms are involved in the pathophysiology of CSA-AKI. In the vast majority of
patients, AKI is a consequence of a decrease in glomerular filtration rate (GFR) due to
hemodynamic disturbances.Renal blood flow is determined by the pressure gradient between
inflow pressure (mean arterial pressure) and outflow pressure (central venous pressure or
intra-abdominal pressure) 1 and by vascular resistance to flow (radius of afferent and
efferent renal arteriole). Therefore, the injury may be due to reduced perfusion due to
hypovolemia or reduced cardiac output and/or venous congestion. The management of these
patients focuses on reversing renal hypoperfusion by improving cardiac output
(administration of fluids and/or inotropes), hypotension (vasoconstrictors), congestion
(diuretics, hemodialysis), and exposure to nephrotoxic agents. The traditional strategy
of fluid administration to restore diuresis and renal function is often ineffective
because it does not lead to improved renal perfusion. Moreover, the assessment of
response to fluid administration is problematic with the use of central venous pressure
and ultrasound assessment of the inferior vena cava, which are commonly used in clinical
practice. Aggressive hydration can lead to volume overload, which is associated with
peripheral organ dysfunction and increased mortality. Given that AKI due to systemic
venous congestion is more common than hypovolemic AKI, the management of these patients
should be individualized, taking into account the hemodynamic profile and the possibility
of causing damage to peripheral organs. Transthoracic echocardiography is a non-invasive,
cost-effective, bedside method for qualitative and quantitative assessment of myocardial
function and hemodynamic profile. It can guide the administration of fluids and
vasoactive drugs, detect complications, and contribute to etiological diagnosis in
patients with renal injury. Its use can improve the outcome of patients with AKI
hospitalized in the ICU. Ultrasound can also assess extravascular fluid in the lung even
in subclinical congestion with high specificity, and it is useful for monitoring
respiratory distress in patients with acute kidney injury. A new multiparametric
ultrasound method for assessing splanchnic congestion is the Venous Excess Ultrasound
Score (VExUS), the use of which is becoming established in specialized centers. It
involves the combined assessment of the size and variation of the inferior vena cava, as
well as Doppler assessment of blood flow in the liver (portal, hepatic veins) and kidney
(renal vein and artery). VExUS findings can quantify splanchnic congestion even in cases
where the results of traditional assessment methods are conflicting or even normal. Also,
they are independently associated with acute kidney injury, both in hospitalized patients
with heart failure and after cardiac surgery.The integration of multiparametric
ultrasound assessment in clinical practice can identify reversible causes early, identify
patients who will develop severe renal dysfunction, and recognize complications early.
Therefore, it can guide clinical management from empirical approaches and supportive
measures to an individualized approach to CSA-AKI in the perioperative period.