What is the purpose of a nephrostomy tube?

A nephrostomy tube is utilized primarily to drain urine directly from the kidney when normal urine flow from the kidney to the bladder is obstructed. This obstruction can arise from various conditions, such as kidney stones, tumors, or trauma. By placing the nephrostomy tube, medical professionals can alleviate pressure and prevent damage to the kidney which may occur due to the accumulation of urine, a condition known as hydronephrosis. The nephrostomy tube is inserted through the skin into the renal pelvis, allowing for direct drainage of urine into an external collection bag, providing a critical pathway for renal function in patients unable to urinate normally.

Other options do not accurately reflect the function of a nephrostomy tube. For example, while renal blood filtration occurs naturally within the kidneys, the tube itself does not aid in this process. The tube is not designed to connect the kidney and bladder, nor is it intended for the direct delivery of medication to the kidneys. Thus, option B clearly identifies the primary and correct use of a nephrostomy tube in clinical practice.