Final answer:
The second phase of acute renal failure is indicated by option B. Urine output less than 400 mL/day, which is characterized as oliguria. This condition signifies a reduced ability of the kidneys to perform essential filtration functions necessary to sustain bodily health.
Step-by-step explanation:
The second phase of acute renal failure is indicated by the sign characterized as oliguria, which is a significant decrease in urine output. The correct answer to which sign indicates the second phase of acute renal failure is B. Urine output less than 400 mL/day. Acute renal failure (ARF), also known as acute kidney injury (AKI), can be caused by various factors, with oliguria being a key indicator. This condition implies a diminished capacity of the kidneys to filter blood and produce urine, leading to potential accumulation of waste products in the body. Conditions such as fever, shock, vomiting, and diarrhoea can lead to oliguria. An even more severe lack of urine production, anuria, occurs when urine output drops below 10 mL/day. Acute renal failure can be delineated into three stages: Injury, Failure, and Loss, with specific diagnostic criteria involving creatinine levels and urine output. It's crucial to note that the kidneys must produce a minimum volume of about 500 mL/day to efficiently eliminate metabolic wastes. Outputs below this level are termed oliguria, and the complete absence of urine production is termed anuria.