Utility of Bedside Bladder Ultrasound Before Urethral Catheterization in Young Children

METHODS

A prospective, nonrandomized, nonconcurrent control study was performed in the setting of an urban pediatric emergency department from August 2003 to February 2004. Children who were between the ages of 0 and 24 months and undergoing urethral catheterization for urine culture and urine analysis were enrolled. Patients were excluded from the study when they had genitourinary abnormalities that precluded urethral catheterization. The study was divided into 2 phases. During the observation phase (August 2003 to November 2003), consecutive eligible patients were enrolled. Urethral catheterization was performed as usual, and the amount of urine obtained during the first attempt was recorded for each patient. During the intervention period (December 2003 to February 2004), patients were consecutively enrolled when at least 1 of 2 pediatric emergency medicine physicians (L.C. or A.L.H.) was available to perform a bladder ultrasound. After obtaining informed consent from the parent or guardian, a rapid bedside ultrasound of the bladder was performed by a pediatric emergency medicine physician immediately before urethral catheterization. The amount of urine present in the bladder was estimated with a standard formula.⁶ When a sufficient amount of urine, defined as >3 mL, was seen, catheterization was conducted in the usual manner by the nursing staff. Otherwise, catheterization was deferred and repeated ultrasound was performed at 30-minute intervals until sufficient urine was identified. The amount of urine obtained was recorded.

Urethral catheterizations were conducted using standard procedures. After cleansing the periurethral area with 2% iodine tincture (Aplicare; Aplicare Inc, Branford, CT), a 5F or 8F flexible catheter (Indwell feeding tube; The Kendall Company, Mansfield, MA) was introduced into the urethral opening with aseptic technique. Urine was aspirated with a 10-mL syringe. The nursing staff attempted to obtain at least 2 mL of urine during each catheterization.

All ultrasound studies were performed using a Sonosite 180 (Sonosite Inc, Bothell, WA) fitted with a microconvex transducer. A transverse view of the bladder was obtained, and the width of the bladder was measured using standard calipers. Then the transducer was rotated 90 degrees, and a sagittal view of the bladder was obtained. The height and depth of the bladder were measured (see Fig 1). The total urinary bladder volume was calculated using the formula Volume (cc) ∼ Width (cm) × Height (cm) × Depth (cm) × 0.9.⁶

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Fig 1.

Transverse and sagittal views of a moderately distended urinary bladder in a 9-month-old female infant. A, Transverse view, width. B, Sagittal view, depth. C, Sagittal view, height.

The 2 authors (L.C. and A.L.H.) who performed all the ultrasound studies completed a 1-month rotation in emergency ultrasound in the affiliated adult emergency medicine department. They also attended a 2-day emergency ultrasound workshop given by the American College of Emergency Physicians. The study was approved by the Human Investigation Committee of our University Hospital.

RESULTS

During the observation phase, 136 children who were younger than 2 years underwent urethral catheterization. In 10% (n = 14) of the children, the nursing staff failed to obtain any urine during the first attempt. In another 17% (n = 23) of the children, the staff succeeded in obtaining sufficient urine for culture only. Overall, the rate of success, defined as obtaining >2 mL of urine, sufficient for culture and other routine studies, was 72% (95% CI: 66%–78%). The success rates in boys and girls were 77% and 65%, respectively. A total of 112 subjects were enrolled during the intervention phase. The 2 groups did not differ significantly in terms of age or the proportion of boys (Table 1). Sufficient urine was identified on the first ultrasound in 76% (n = 85) of the patients. Among these, 98% (n = 83) underwent successful urethral catheterization during the first attempt. Among those in whom insufficient urine was identified initially (n = 27; 24%), subsequent ultrasound revealed sufficient amount in all patients within 90 minutes. Among these, 93% (n = 25) underwent successful urethral catheterization during the first attempt. Overall rate of success of initial urethral catheterization during the intervention phase was 96% (95% CI: 93%–99%). The success rates in boys and girls were 98% and 93%, respectively. Compared with the success rate during the observation phase, the differences were statistically significant (P < .001; Fig 2).

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Fig 2.

Initial catheterization results (%) in observation and intervention subjects. Error bars represent 95% CI.

During the study period, 3 children underwent ultrasound and were initially found to have an insufficient amount of urine. Urethral catheterizations were conducted nonetheless on the basis of the attending physicians' judgment that delay in catheterization could delay antibiotic administration. In 2 children, no urine was obtained. In the third child, a minimal amount of urine (<1 mL) was obtained and sent for culture. Inclusion of these children in the intention-to-treat analysis would have resulted in a success rate of 94% (95% CI: 88%–97%) in the study group. This rate was also significantly different from that of the observation group (P < .001).

DISCUSSION

UTI is one of the most common causes of bacterial infections in children. The signs and symptoms of UTI in young children are often subtle and nonspecific. Pediatric emergency medicine physicians often rely on the results of ancillary tests as adjuncts to clinical suspicions to arrive at treatment decisions.^8,9 Consequently, it is important to secure properly obtained samples, both for culture and for ancillary tests, to arrive at an accurate and prompt diagnosis. The quality as well as the quantity of urine specimen is important. The typical infant who is suspected of having a UTI is febrile and dehydrated. A child might have recently voided before the catheterization. Before initiating the invasive and often painful procedure, there is no certainty of presence of urine in the bladder. During the observation phase of the present study, we found a significant rate of failure at initial attempts of urethral catheterization (28%). One option that is commonly practiced to obtain additional specimen is using a urine bag. Previous research has shown that urine cultures obtained with bag specimen have high false-positive and false-negative rates.¹ Relying on bag specimen results caused delayed diagnoses in some patients and unnecessary treatments in others.¹ Another option is to secure the catheter in place and wait to collect the specimen. Accuracy of the results obtained with this practice has not been ascertained. In addition, such a catheter presents at least a theoretical risk of providing a route for ascending infection in these children. Therefore, the best option would be to ascertain the presence of a moderate amount of urine in the bladder before urethral catheterization. Bedside ultrasound provides a noninvasive method of measuring the amount of urine present in the bladder.

The success rate of initial attempts at urethral catheterization in young children was increased with the use of a rapid bedside ultrasound performed by pediatric emergency medicine physicians. The procedure was well tolerated and well received by the parents as well as the nursing staff. Total time spent during each scan was estimated to be <1 minute. The percentage of children who did not have enough volume at the first ultrasound in the intervention group was similar to the percentage of children who failed first catheterization in the control group. When there was a sufficient amount of urine visualized on the ultrasound, most of these children underwent successful urethral catheterization on the first attempt. With the use of this simple technique, repeated catheterizations were avoided. Finally, because sufficient urine can be obtained for appropriate studies in most of the patients, application of this technique may potentially increase the rapidity as well as the reliability of diagnosis of UTI in young children in the pediatric emergency department.

Three patients were excluded from the study because of protocol deviation. These children underwent initial ultrasound that revealed an insufficient amount of urine. In all 3 children, initial urethral catheterization failed to yield sufficient urine for routine studies. Indeed, in 2 of the 3 children, no urine was obtained at all during the initial attempt. Their course reinforces our conclusion that ultrasound is helpful in prospectively identifying children in whom urethral catheterization was unlikely to be successful.

There are several limitations to our study. Blinding was not attempted, and the sample was not randomized. Although we were unable to demonstrate significant baseline differences between the 2 groups, there may be differences and biases that were not measured or accounted for. Another limitation is that only 2 physicians performed the ultrasound studies. Part of the rationale for this was to ensure consistency in our study. It remains to be seen whether this technique can be taught and generalized easily to a large number of pediatric emergency medicine physicians. We are currently developing a curriculum to train physicians and nurses in the use of emergency ultrasound for this and other pediatric indications.

CONCLUSIONS

A rapid bedside ultrasound of the bladder performed by pediatric emergency physicians led to an increased success rate of urethral catheterization in children who were younger than 2 years. We were able to avoid repeated invasive testing with a simple noninvasive procedure. This study offers a model for additional research on the use of the new and exciting technique of emergency physician–performed ultrasound for the benefit of pediatric patients.