Content Reviewers:Antonella Melani, MD, Lisa Miklush, PhD, RNC, CNS, Ashley Mauldin MSN, APRN, FNP-BC, Gabrielle Proper, RN, BScN, MN
Contributors:Patricia Nguyen, MScBMC, Cassidy Dermott, Sam Gillespie, BSc, Anca-Elena Stefan, MD, Mary Roberts MSN, RN
Alright, let’s quickly review the anatomy and physiology of the urinary tract. The kidneys are bean-shaped organs located behind the peritoneum on either side of the vertebral column, just below the rib cage. Now, the kidneys are composed of the renal parenchyma and a collecting system. The renal parenchyma is the solid, functional part of the kidneys, where blood is filtered and urine is produced. This urine is then drained into the renal pelvis, which then narrows to form the ureter, and transports urine to the bladder. Ultimately, urine exits the bladder through another structure called the urethra.
Now, pyelonephritis is most often caused by bacterial infection; and the most common bacteria are Escherichia coli. Other potential bacteria include Proteus species, Enterobacter species, Enterococcus species, and Klebsiella species, as well as Pseudomonas aeruginosa. Less frequently, pyelonephritis is caused by Staphylococcus species, Salmonella species, and fungi like Candida species.
One of the main risk factors for pyelonephritis is urinary stasis or retention. This occurs when the bladder is not able to completely empty, and can be associated with prolonged bed rest or paralysis, or with obstruction of the urinary tract. Obstruction can be caused by structural abnormalities like strictures; kidney stones or tumors; and scarring from pelvic radiation or surgery, recurrent infections, or traumatic injuries.
Another important risk factor for pyelonephritis is urinary reflux, which refers to the backflow of urine from the bladder to the ureters or kidneys. This can be caused by structural abnormalities, like narrowing in the bladder neck or urethra, or an abnormal ureter valve that stays open even when the bladder is full, allowing backflow of urine. Other causes of urinary reflux include bladder stones, bladder tumors, and benign prostate enlargement.
In addition, both stasis and reflux can also occur due to reduced bladder tone from diabetic neuropathy, spinal cord injuries, and neurodegenerative diseases like multiple sclerosis. Finally, additional risk factors for pyelonephritis can include having a lower urinary tract infection, as well as being assigned female at birth, hospitalization, having indwelling urinary catheters, and being immunocompromised.
Most often, the pathology of pyelonephritis develops as an ascending urinary tract infection, meaning bacteria start by colonizing the urethra and bladder, and then make their way up the ureters and kidneys. Less frequently, the kidneys can get infected via spread through the bloodstream, usually as a consequence of bacteremia.
Once bacteria reach the kidneys, they usually start by adhering to the renal epithelium of the tubules; this ultimately triggers an inflammatory response, and attracts white blood cells that fight off the infection.
Now, pyelonephritis can either be acute or chronic. With acute pyelonephritis, there’s a sudden infection of the kidney that results in inflammation, local edema, and even necrosis. On the other hand, chronic pyelonephritis usually results from recurrent episodes of acute pyelonephritis, which can eventually lead to fibrosis and scarring of the kidney.
Moving on to the clinical manifestations, clients with acute pyelonephritis usually experience fever, chills, and malaise, along with flank pain or abdominal discomfort, as well as nausea and vomiting.
Now, chronic pyelonephritis has a similar presentation, and additionally, clients can often present with hypertension.