Suprapubic aspiration and urinary catheterisation: Viva

Branch 1: The urine collection methods and their contamination rates

The candidate should state that the non-toilet-trained child needs a low-contamination specimen for the culture, and that the two indicated methods are the suprapubic aspiration and the urethral catheterisation. A strong candidate gives the contamination rates: the suprapubic aspiration under 1 percent, the urethral catheterisation approximately 1 to 10 percent, the clean catch approximately 25 to 30 percent, and the bag or pad up to 50 to 85 percent. The candidate should explain that any organism grown from a suprapubic aspirate is a true pathogen because the bladder urine is sterile, and that the catheter specimen uses the threshold of the single organism at greater than 10 000 to 50 000 colony forming units per millilitre. [5]

If the examiner presses on the bag specimen, the candidate should state that the bag and the pad are for the screen dipstick only and must never be used to diagnose a urinary tract infection. A negative screen lowers the probability enough to defer the invasive collection, but a positive screen must be confirmed by the catheterisation or the aspiration before the antibiotic. The American Academy of Pediatrics guideline requires the catheterisation or the aspiration before any antimicrobial in the febrile infant two to twenty-four months with the suspected infection. [1]

Branch 2: The suprapubic aspiration landmark and technique

If asked about the technique, the candidate should describe the positioning of the infant supine in the frog-leg position with the assistant stabilising the pelvis, the non-pharmacological analgesia of the oral sucrose and the pacifier, and the skin preparation. The landmark is the midline one to two centimetres above the pubic symphysis, where the full bladder rises as a dome above the pubic bone and lifts the bowel out of the needle path. The 21 or 22 gauge needle attached to the syringe is advanced at 90 degrees with the gentle aspiration, and the procedure is limited to two attempts. [5]

A strong candidate explains the anatomical rationale. The full bladder rises out of the pelvis as an intraperitoneal-to-extraperitoneal dome, and the bowel is lifted away, which is why the midline suprapubic needle reaches the bladder without encountering the bowel. The empty bladder collapses below the pubic symphysis into the true pelvis, and the bowel falls into the space, so the aspiration on the empty bladder risks the failed tap and the bowel injury. This is the reason the bladder fullness is the single most important determinant of the safety and the success. [5]

Branch 3: The point-of-care ultrasound and the failed attempt

If the examiner moves to the ultrasound, the candidate should state that the point-of-care bladder ultrasound is the standard preparation wherever available. The systematic review by Abosamak and colleagues pooled the randomised and the observational studies and found that the ultrasound guidance raised the success rate from approximately 50 to 70 percent in the blind technique to over 90 percent, by confirming a full bladder volume greater than 10 millilitres before the attempt. The earlier study by Buntsma and colleagues showed the benefit with the BladderScan device, and the randomised trial by Mahdipour and colleagues confirmed the advantage in the infants. [8]

A strong candidate discusses the management of the failed first attempt. The failed tap is the most common complication of the blind aspiration, reported in approximately 25 to 50 percent of the blind attempts, and the most common cause is the empty or the under-filled bladder. The correct response is the withdrawal of the needle, the reassessment of the bladder fullness by the ultrasound or by waiting and feeding, and the limitation to two attempts before switching to the catheterisation. The transient microscopic haematuria resolves within twenty-four to forty-eight hours, and the rare bowel injury is the indication for the surgical review. The family is counselled on the procedure, the common and the important risks, and the plan for the result in one to two days. [8]