Suprapubic aspiration and urinary catheterisation: Case

This infant has the unexplained fever at five months that mandates the low-contamination urine specimen before any antibiotic, and the management illustrates the correct application of the point-of-care ultrasound guidance and the suprapubic aspiration. The American Academy of Pediatrics clinical practice guideline requires the urine by the catheterisation or the suprapubic aspiration in the febrile infant two to twenty-four months with the suspected urinary tract infection, and the registrar correctly chose the aspiration over the bag specimen. [1]

Clinical findings

The key findings are the unexplained fever in the well-appearing infant, the decision to obtain the urine by the low-contamination method, the correct use of the point-of-care ultrasound to confirm the bladder volume, and the deferral of the antibiotic until the culture result. The initial bladder volume of 4 millilitres is below the threshold of greater than 10 millilitres for a successful tap, and the registrar correctly avoided the blind attempt on the under-filled bladder. The repeat volume of 16 millilitres after the feed and the wait exceeded the threshold and predicted the successful aspiration. [8]

The dipstick result of the leukocyte esterase positive and the nitrite negative is the common pattern in the young infant. The leukocyte esterase is the more sensitive marker, and the nitrite is unreliable in the young infant who voids frequently and does not allow the bladder dwell time for the nitrate conversion. The dipstick raises the probability of the infection but is not sufficient to start the antibiotic without the supporting culture from the low-contamination sample. [5]

Investigations and diagnosis

The diagnostic test is the culture of the suprapubic aspirate. The defining rule is that any organism grown from a suprapubic aspirate, at any colony count, is a true pathogen, because the bladder urine is normally sterile and the needle bypasses the urethral flora. The culture result in twenty-four to forty-eight hours confirms or excludes the infection and guides the targeted antibiotic. The negative nitrite does not lower the probability in the young infant, and the decision to await the culture rather than start the empirical antibiotic is appropriate in the well-appearing infant with the careful observation. [1]

The point-of-care ultrasound guidance is the single most effective preparation for the suprapubic aspiration. The systematic review by Abosamak and colleagues showed that the ultrasound guidance raised the success rate from approximately 50 to 70 percent in the blind technique to over 90 percent, by confirming the bladder volume greater than 10 millilitres before the attempt. The use of the ultrasound in this case prevented the failed tap that would have followed the attempt on the initial volume of 4 millilitres. [8]

Management and outcome

The procedural management was correct. The infant was positioned supine in the frog-leg position with the assistant stabilising the pelvis. The non-pharmacological analgesia of the oral sucrose and the pacifier was given. The needle entry point was the midline 1 centimetre above the pubic symphysis. The 21 or 22 gauge needle attached to the syringe was advanced at 90 degrees with the gentle aspiration, and the 2 millilitres of the clear urine was aspirated and sent for the microscopy and the culture. [8]

The family was counselled on the procedure, the common and the important risks, and the plan for the result. The registrar explained that the bag specimen sticks to the skin and is too dirty to tell the answer reliably, that the suprapubic aspiration takes the urine directly from the bladder through a fine needle, that the sucrose and the pacifier help with the comfort, that a small amount of blood in the urine for a day is common and harmless, and that the result will be ready in one to two days. The transient microscopic haematuria in 1 to 8 percent resolves in twenty-four to forty-eight hours without the intervention. [5]

The outcome depends on the culture. If the culture grows a single organism, the targeted antibiotic is started and the infant is followed up for the clinical response, the imaging for the recurrent or the atypical infection, and the renal function. If the culture is negative, the infant is reassessed for the alternative source of the fever, and the antibiotic is withheld. The careful observation and the deferral of the empirical antibiotic in the well-appearing infant is the balanced approach that respects the contamination risk and the antibiotic stewardship, and the family is given the safety-net advice to return if the fever persists, the infant becomes more irritable or lethargic, or the feeding decreases. [1]