By Dr. W. Hussein
Acute renal failure is a common event during a hospitalization, particularly in patients requiring intensive care monitoring. Depending on the setting and the severity, this is detected as a rise in serum creatinine, electrolyte or acid-base disturbances, or volume overload. Nephrology input is required to identify the etiology and recommend the course of action to prevent further complications.
The workup of a nephrology consultation is an interesting task that involves a systematic assessment. The objectives of the assessment are:
The course of renal function decline:
The nephrologist would review previous notes and available laboratory results to identify the course of renal function decline. Patients with chronic kidney disease are more prone to acute renal failure because their reserve is lower than patients who start with normal renal function. We would also compare the trend of decline to events identified in the patient’s history, to help identify the etiology.
Identification of risks for renal impairment:
It is common that multiple risk factors are identified for renal impairment in a patient. Diabetes and hypertension are the most common causes of chronic kidney diseases. The nephrologist would enquire about their duration and control, and whether any other complications have already manifested. A background of vascular or cardiac disease (e.g. previous stroke or carotid endarterectomy, aortic aneurysm, peripheral vascular disease, coronary heart disease, or congestive heart failure) identifies patients at risk of reduced renal perfusion. The nephrologist also would consider whether any underlying disease is known to have renal involvement; e.g. connective tissue diseases.
The nephrologist focuses his history taking to symptoms that can indicate renal risks or complications of renal disease. These include features in the history prior to the current presentation, features during the admission, social history, family history, and medications.
Examination is focused on assessment of vascular function, cardiac function, features of connective tissue disease or any underlying diseases that can affect the kidneys, as well as complications of renal disease (discussed below).
The nephrologist then reviews the medical notes and investigations to identify procedures, medications, and events that might have contributed or precipitated renal dysfunction during or prior to the admission. Commonly insults follow hypotension from any cause (e.g. hypovolemia, cardiac or septic shock), nephrotoxic agents like NSAIDs, aminoglycosides and iodine contrast.
Old urinary test results are reviewed for hematuria and proteinuria, which may indicate underlying chronic kidney disease. Fresh urinary samples are checked for red cells by dipstick testing and microscopy. Proteinuria is assessed by dipstick testing and by urinary protein : creatinine ratio. Hematuria, particularly dysmorphic red cells and red cell casts, and proteinuria, may indicate glomerular disease.
This test provides information about possible acute etiologies, particularly in the settings of obstructive nephropathy and, rarely, acute renal ischemia. Small kidneys may indicate chronic renal disease with atrophy. Large kidneys may indicate diabetic renal disease or an infiltrative process. Renal ultrasound also can also identify other pathologies like polycystic kidney disease. Depending on the clinical situation, the nephrologist may indicate the urgency of acquiring a renal ultrasound.
Identifying and treating complications
Excess volume, acid-base or electrolyte disturbances are the usual immediate complications that need to be addressed in a patient with acute renal failure. Depending on the severity and duration of the renal insult, the nephrologist will decide whether these complications can be treated “medically” or that renal replacement therapy needs to be instituted. High doses of loop diuretics, with or without simultaneous administration of a thiazide diuretic can induce diuresis in oliguric patients. Sodium bicarbonate can be used for severe metabolic acidosis. Hyperkalemia, the commonest electrolyte disturbance in renal failure, may respond to treatment with insulin, dextrose, diuresis and correction of acidosis. Uremia, usually manifesting with changes in mental function, is sometimes hard to identify in a very sick patient with multiple acute conditions that can all contribute to cognitive changes. When suspected, particularly if no other causes are identified for the cognitive dysfunction, renal replacement therapy is usually indicated.
Institution of renal replacement therapy
The nephrologist makes an assessment to whether renal replacement therapy is required. If the complications are manageable without dialysis, and the severity and duration of renal failure are not significant, renal replacement therapy may be preserved. However, if the complications are severe and recovery is not eminent (based on the nature, severity and duration of the insult), the nephrologist may discuss initiation of dialysis.
In some cases, the overall condition of the patient may suggest that dialysis therapy is futile. This depends on the patient’s comorbidities, baseline condition and prognosis of other acute conditions. In this situation, the nephrologist may discuss palliative options.
When dialysis is a suitable option, and is required based on the assessment, a choice is made for the modality. Continuous renal replacement therapy (CRRT or CRT) is usually chosen for hemodynamically unstable patients, as it provides more instantaneous volume management. It is also a good option when large amounts of fluids need to be removed, as removal is carried out throughout the day. Conventional hemodialysis (standard hemodialysis) is usually carried out over two to four hours, on daily or every other day bases. This form is more suitable for patients who have good blood pressure. Because standard hemodialysis is more efficient, it is also the modality of choice for short-term treatment of severe metabolic or volume disturbances.
Aspects in the general care affected by renal dysfunction
Volume management: to suggest appropriate fluid administration, including infusions and feeds that are suitable to the patient’s volume assessment and fluid losses. For example, patients with excessive losses from ventilation, skin burns, open wounds etc, will require appropriate replacement to avoid dehydration that may worsen the renal function or delay recovery. On the other hand, patients who are receiving large volumes of fluids with no significant losses may develop complications related to hypervolemia. These patients may need to have their infusions concentrated, with or without diuretic therapy.
Avoiding nephrotoxic agents like NSAIDs and, when possible, avoiding aminoglycosides and iodinated contrast agents. There are situations where the use of such agents is extremely necessary and life saving, that they have to be used despite the potential renal damage. Angiotensin converting enzyme inhibitors and angiotensin-II receptor blockers interfere with renal autoregulation and have to be avoided in acute renal failure.
Doses of other medications may need to be adjusted to the current renal function (or dialysis). Some medications (e.g. Vancomycin) need to have their levels closely monitored in patients with renal impairment.
This summarizes the nephrology consultation for acute renal failure. The nephrologist adapts his assessment and workup to the clinical presentation and the patient’s condition. A good nephrologist is an essential part of the medical team managing an acutely ill patient.