Suprapubic aspiration and urinary catheterisation: SAQ

This infant has the unexplained fever at six months that mandates the low-contamination urine specimen before any antibiotic. 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, because the bag and the pad specimen have a contamination rate of up to 50 to 85 percent that produces the false positive and the unnecessary antibiotic. The bladder volume of 18 millilitres exceeds the threshold of greater than 10 millilitres for a successful suprapubic aspiration. [1]

Question 1 (10 marks)

Outline the four urine collection methods, their contamination rates, and the indication for each, and explain why the bag specimen is unacceptable for the culture. [5]

The four urine collection methods are the suprapubic aspiration, the urethral catheterisation, the clean catch, and the bag or pad specimen. The suprapubic aspiration is the gold standard with the contamination rate under 1 percent, because the needle samples the bladder urine directly and bypasses the urethral and the perineal flora. Any organism grown from a suprapubic aspirate, at any colony count, is a true pathogen because the bladder urine is normally sterile. [5]

The urethral catheterisation is the acceptable alternative with the contamination rate of approximately 1 to 10 percent, and it is the commonest method in the emergency department because it is easier to learn and more readily accepted. The catheter specimen uses the threshold of the single organism at greater than 10 000 to 50 000 colony forming units per millilitre for the true infection, and the mixed growth or the low count suggests the contamination. [5]

The clean catch is the first-line method for the toilet-trained child who can cooperate, with the contamination rate of approximately 25 to 30 percent because the stream passes the perineum. The bag or pad specimen has the contamination rate of up to 50 to 85 percent because the periurethral and the perineal flora multiply in the bag and the pad. The bag specimen is suitable only for the screen dipstick: 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 diagnosis of the urinary tract infection from a bag specimen is the source of the false positive, the unnecessary antibiotic, the antibiotic resistance, and the missed alternative diagnosis. [5]

Question 2 (10 marks)

Describe the technique of the suprapubic aspiration in this infant, the role of the point-of-care ultrasound, and the management of a failed first attempt. [8]

The infant is positioned supine in the frog-leg position with the hips slightly flexed and abducted, and an assistant stabilises the pelvis and the limbs. The non-pharmacological analgesia of the oral sucrose 1 to 2 mL of a 24 percent solution and the pacifier is given two minutes before the procedure, and the topical local anaesthetic may be applied at the site in the planned setting. The skin is cleaned with the chlorhexidine and the sterile field is prepared. [8]

The needle entry point is the midline one to two centimetres above the pubic symphysis. A 21 or 22 gauge needle attached to the syringe is advanced at 90 degrees to the skin with the gentle aspiration, directed slightly toward the bladder, and the urine appears in the syringe as the bladder lumen is entered. The depth in the infant is typically 2 to 3 centimetres. If no urine is aspirated, the needle is withdrawn slowly with the continuous aspiration, because the bladder may be entered on the way out. [8]

The point-of-care ultrasound is the standard preparation wherever available. The systematic review by Abosamak and colleagues and the randomised trial by Mahdipour and colleagues showed that the ultrasound guidance raises 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. This infant has the bladder volume of 18 millilitres, which predicts a successful tap. [8]

The management of the failed first attempt 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 reinsertion without the reassessment repeats the failed attempt, and the forceful or repeated attempts raise the risk of the bowel injury and the bladder wall trauma. The transient microscopic haematuria in 1 to 8 percent resolves in twenty-four to forty-eight hours without the intervention, and the rare bowel injury occurs when the bladder is empty and the bowel is in the needle path. [8]