Critical illness and intensive careAcute renal failure
Section snippets
Definition
Numerous definitions of ARF have been published. A consensus definition for ARF has recently been developed and validated in hospitalized and critically ill patients.1, 2, 3 This definition divides renal dysfunction into the categories of risk, injury and failure (RIFLE) based on bedside measurements of kidney function (e.g. changes to serum creatinine and urine output; Figure 1). The RIFLE classification is likely to be the dominant approach to defining ARF for the next 5 to 10 years. With
Risk factors
The risk factors for ARF are listed in Table 1.
Assessment of renal function
Renal function is complex (acid–base balance, water balance, regulation of calcium and phosphate, erythropoiesis, disposal of some cytokines, lactate removal).
Glomerular filtration rate (GFR): monitoring of renal function in the clinic is reduced to the indirect assessment of GFR by the measurement of serum creatinine and urea. These waste products are insensitive markers of GFR and are heavily modified by numerous factors (e.g. age, sex, muscle mass, nutritional status, corticosteroid use,
Clinical classification
Dividing causes according to the probable source of renal injury is the most useful approach to the diagnosis of ARF.
Major surgery
ARF is a common complication after major surgery.8 The incidence depends on comorbidity, preoperative kidney function, and the type and urgency of surgery. Intraoperative events can hinder kidney function (Table 4); any of these factors, alone or in combination, may contribute to critical reductions in renal blood flow and ischaemia, impaired delivery of oxygen (see Ward, CROSS REFERENCES), and toxin- or inflammatory-mediated injury. Postoperative ARF is believed to be, in part, mediated by
Resuscitation
Intravascular volume must be maintained or rapidly restored; this may require admission to an ICU and invasive haemodynamic monitoring (central venous catheter, arterial cannula, pulmonary artery catheter or pulse contour cardiac output catheters). Oxygenation must be maintained. An adequate haemoglobin concentration (at least >70 g/l) must be maintained or restored. Some patients remain hypotensive once intravascular volume has been restored (mean arterial pressure <70 mmHg). Hypotension
Diagnostic investigations
An aetiological diagnosis of ARF must be determined, and may be obvious on clinical grounds. In many patients, all possibilities should be considered and common treatable causes excluded using simple investigations.
Urinalysis is a simple and non-invasive test that can yield important diagnostic information. One important investigation is microscopic examination of the urinary sediment.
Anaemia: evidence of marked anaemia in the absence of blood loss may suggest acute haemolysis, thrombotic
Basic concepts
The principles of management of established ARF is shown in Table 7.
Nutritional support (see Kaushal, CROSS REFERENCES) must be started early and must contain adequate calories (30–35 Kcal/kg/day as a mixture of carbohydrates and lipids) and protein (at least 1–2 g/kg/day). There is no evidence that specific renal nutritional solutions are useful.
Hyperkalaemia (>6 mmol/l) must be promptly treated with insulin and dextrose, bicarbonate if acidosis is present, nebulized salbutamol, or all of the
Prognosis
Renal recovery after ARF is an important measure of morbidity. Persistent chronic renal impairment or need for RRT can negatively influence quality of life, and contribute to considerable healthcare expenditures. Recovery to independence from RRT occurs in ≈68–85% of critically ill patients by the time of hospital discharge, and usually peaks by 90 days.5, 8 Older patients and those with pre-existing comorbidities such as chronic kidney disease or cardiovascular disease are less likely to
Summary
The branch of nephrology concerned with ARF (‘critical care nephrology’) has undergone many advances in recent years, but mortality remains high because sicker, older patients undergo more complex, prolonged and higher-risk surgery. Consensus definitions have been developed that guide research and potentially provide better outcomes.
The general principles of management consist of identification, treatment and/or removal of the precipitant(s) while maintaining physiological homeostasis to allow
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