The definition of cardiorenal syndrome is “any acute or chronic problem in the heart or kidneys that could result in an acute or chronic problem of the other.” The term describes multiple underlying subtypes, which subdivide according to the underlying triggering pathology and chronicity.
There are five subtypes of cardiorenal syndrome:
The 2007 report on the 118465 patients admitted with acutely decompensated heart failure in the ADHERE database showed that 9.0% of patients had normal renal function on admission whereas 27.4% had mild renal dysfunction (defined as GFR 60 to 89 mL-min-1.73 m), 43.5% had moderate renal dysfunction (GFR 30 to 59 mL-min-1.73 m), 13.1% had severe renal dysfunction (GFR 15 to 29 mL-min-1.73 m), and 7.0% had a GFR less than 15 mL-min-1.73 or were on chronic dialysis. Other large databases have shown that the prevalence of cardiac or renal dysfunction increases the incidence of the other.
Type 1 cardiorenal syndrome occurs when there is acute decompensation of cardiac function leading to a decrease in glomerular filtration. Researchers have previously proposed a decline in cardiac output with decreased renal perfusion as the leading underlying cause for worsening kidney function in cardiorenal syndrome types 1 and 2. However, recent studies have postulated that increased central venous pressures are a more critical factor. When patients develop fluid overload due to worsening cardiac function, venous pressures increase and are transmitted back to the efferent arterioles; this results in a net decrease in the glomerular filtration pressure and renal injury. Other factors involved in the pathogenesis of types 1 and 2 cardiorenal syndromes include elevated intraabdominal pressures, activation of the renin-angiotensin-aldosterone system (RAAS), activation of the sympathetic nervous syndrome and increased inflammatory damage to the kidney related to heart failure. Targeting this cycle is the mainstay of therapy for type 1 cardiorenal syndrome. Types 3 and 4 cardiorenal syndromes more likely result from volume overload from renal dysfunction, abnormal cardiac function in the setting of metabolic disturbances (such as acidemia), and neurohormonal changes that accompany renal disease. Patients can develop type 5 cardiorenal syndrome in the setting of sepsis, systemic lupus erythematosus (SLE), diabetes mellitus, decompensated cirrhosis, or amyloidosis; all of these disorders can lead to disease in both the heart and kidney.
The patient’s history and physical exam can help clinicians to differentiate between acute and chronic decompensation as well as primarily cardiac or renal causes. Examples of helpful historical information would include if the patient presents with an acute myocardial ischemic event that can be triggering for severe cardiac dysfunction, which subsequently results in renal injury or recent-onset diarrhea and vomiting, causing acute renal injury, which might lead to a sharp decline in heart function. Other historical clues, such as medication use and prior laboratory values (such as creatinine), may be helpful. Although the clinical examination may not help differentiate the different types of cardiorenal syndrome, many patients will have evidence of volume overload with signs, including:
Other possible signs indicating a primary renal cause of cardiorenal syndrome may include:
Initial history and physical examination tailor the provider's approach towards the appropriate investigation for determining the underlying etiology. The initial laboratory workup should include a complete blood count (CBC), complete metabolic panel (CMP), urine studies (urinalysis with microscopy, urine protein to creatinine ratio, urine sodium), brain natriuretic peptide (BNP), and troponin. The estimated glomerular filtration rate (eGFR) is calculable from the creatinine level to help determine the degree of renal impairment. In patients with possible cardiorenal syndrome type 5, further investigations including blood & urine cultures, lupus serologies (antinuclear antibody [ANA], anti-double-stranded DNA, serum complement levels [C3, C4]), and a procalcitonin may be useful. An electrocardiogram and cardiac monitoring should be included in the initial evaluation to evaluate for any underlying arrhythmias that may be contributing to or resulting from the cardiorenal syndrome. A transthoracic echocardiogram is invaluable in evaluating for wall motion abnormalities, obtaining measurements such as the left ventricular ejection fraction (LVEF), and determining whether or not there is a pericardial effusion. A renal ultrasound can help evaluate kidney size and function. Smaller kidney disease and increased renal echogenicity are consistent with chronic kidney disease.
Although no therapies have been demonstrated to improve outcomes in patients with cardiorenal syndrome, treatment generally is directed at the underlying etiology and to improve the complications of the syndrome as most patients with cardiorenal syndrome have volume overload, the primary treatment targets typically fluid removal either with diuretics or ultrafiltration. Loop diuretics, including furosemide, torsemide, and bumetanide, are the most potent diuretic class. They can be used alone or in conjunction with other types of diuretics. There are two strategies in terms of diuresis: either a continuous infusion dose or using intravenous boluses. Creatinine clearance can be used to help determine the dosage. For example, treatment can start with a loading dose of 40 mg intravenous furosemide loading dose followed by 10 mg/hr if the creatinine clearance is between 25 and 75 mL/min. In contrast, one can start with 80 mg to 160 mg intravenous furosemide as a maximum dose that can be repeated several times a day to achieve a desirable response for the same creatinine clearance. Definitive clinical evidence is still lacking to support either strategy over the other. However, using the continuous infusion strategy would give clinicians more opportunities to evaluate the response to therapy. Also, adding a thiazide diuretic can help overcome diuretic resistance in some cardiorenal patients. Metolazone is typically used and is considered one of the most common combinations with loop diuretics. On the other hand, ultrafiltration can be useful in resistive cases. Still, recent studies showed that diuretic therapy was better than ultrafiltration for symptom control and creatinine level decline in the initial approach towards obtaining euvolemia. Inotropes can be used for refractory cases and can help to improve cardiac function and decrease venous congestion. Unfortunately, no conclusive data has supported their use in cardiorenal syndrome. On the other hand, the treatment of cardiorenal syndrome type 3 and 4 would target treating underlying kidney disease and avoiding nephrotoxic medications and contrast. Finally, treatment of the underlying systemic conditions would be the treatment of type 5 cardiorenal syndrome.
It is difficult to determine the etiology of the cardiorenal syndrome on initial presentation in many patients as they might present without all the classic features, making the diagnosis challenging. History of a recent increase in diuretic doses, diarrhea, vomiting, skin or throat infection, heat stroke, fever, recent extensive workout, or non-steroid anti-inflammatory drug (NSAID) use can help towards a hypovolemic etiology.
The overall prognosis is poor. There are multiple mortality and readmission predictor calculators available to predict the individual patient’s prognosis further. They use multiple variables to predict in-hospital mortality and readmission rate, including the blood urea nitrogen (BUN), systolic blood pressure, serum creatinine, brain natriuretic peptide, and response to diuretics.
Medications (diuretics) and diet compliance, tracking body weight with regular interval follow up in heart failure clinic to optimize outpatient diuretic doses are crucial preventive factors for recurrence.
Enhancing healthcare outcomes for patients with cardiorenal syndrome requires close follow-up after hospital discharge and tracking the patient’s weight, symptoms, and laboratory data. This requires an interprofessional team of clinical providers, nurses, and pharmacists to achieve the best outcomes possible. The pharmacist is needed to ensure patient education on timely medication administration as well as avoiding medications that can adversely affect the disease. A key role of the pharmacists lies in communicating with the providers to ensure the patient is not started on any medications that will result in poor outcomes. The specialized nurse is needed for frequent follow up with the patient to ensure his or her weight is adequately maintained and that the patient is adhering to the various diet and activity restrictions along with the medications prescribed. The primary clinical provider, along with the cardiac and nephrology specialist need to work in conjunction to ensure optimal management of the disease and to achieve the best outcomes possible. Cardiorenal syndrome requires an interprofessional team approach, including physicians, specialists, specialty-trained nurses, and pharmacists, all collaborating across disciplines to achieve optimal patient results. [Level 5]
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