Background. Urethral catheterization is the method of choice for obtaining samples for urine culture and urine analysis in infants. Before the procedure, there is little certainty of the presence or amount of urine in the bladder. Consequently, this relatively invasive and uncomfortable procedure often needs to be repeated. The newly available technology of portable ultrasound may be useful in reducing the number of unsuccessful procedures.
Objective. To investigate the utility of bedside ultrasound of the bladder performed by pediatric emergency medicine physicians before catheterization in reducing the number of unsuccessful attempts.
Methods. A prospective, 2-phase 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 were enrolled. During the observation phase, the amount of urine obtained during the first catheterization was recorded for each patient. During the intervention period, a rapid bedside ultrasound of the bladder was performed by a pediatric emergency medicine physician immediately before urethral catheterization. When a sufficient amount of urine was seen, catheterization was conducted as usual. 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.
Results. During the observation phase, 136 infants underwent urethral catheterization. Overall, the rate of success during the first attempt, defined as obtaining >2 mL of urine, sufficient for culture and other routine studies, was 72% (95% confidence interval: 66%–78%). A total of 112 subjects were enrolled during the intervention phase. 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% confidence interval: 93%–99%). Compared with the success rate during the observation phase, the differences were statistically significant. The results were consistent after being adjusted for gender.
Conclusion. 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.
Urethral catheterization is often undertaken as a part of diagnostic evaluation of young children in the pediatric emergency department. It is the method of choice used to obtain urine from non–toilet-trained children who are suspected of having urinary tract infections (UTIs).1 Treatment decisions frequently need to be made before the availability of culture results. Consequently, other diagnostic tests, such as urine dipstick analysis, microscopy, and Gram-stain, are usually performed. A moderate amount of urine is needed for these additional tests. Furthermore, recent evidence suggests that discarding the first few drops of urine during catheterization will improve the specificity of the urine culture.2 Although urethral catheterization is often performed successfully without complications, it is invasive and uncomfortable. Before the procedure, there is usually no certainty of the presence of urine in the bladder. A significant number of the catheterizations result in inadequate amounts of urine. The treating physician is often left with the choice of either making management decisions without the necessary information or subjecting the infant to repeated attempts at an invasive procedure. Our study aims to investigate the utility of bedside ultrasound of the bladder in decreasing the number of such failures.
The new generation of ultrasound machines offers great portability and flexibility. As a result, these are well suited to the emergency department settings. Since the late 1990s, there has been a dramatic increase in the use of bedside ultrasonography in emergency medicine, especially as performed by emergency medicine physicians.3 An expanding array of applications has been well established in the adult literature, such as the use of focused abdominal sonography for trauma scan and transvaginal scan for ectopic pregnancies and ovarian pathologies.4 There is a paucity of evidence, however, on the utility of this newly available technology as applied to patients in pediatric emergency departments.5
In many ways, the pediatric patient is the ideal candidate for ultrasound studies. The body habitus of most pediatric patients offers great acoustic windows for ultrasound transmission. The technique is noninvasive and pain-free. It requires less cooperation by the patient than other imaging modalities. Ultrasound offers dynamic images that are important in many disease processes. Another important advantage of ultrasonography that is especially relevant in pediatrics is that it does not use ionizing radiation. It is an ideal modality for serial examinations in evolving disease processes. This is especially relevant in pediatric patients, in whom cumulative radiation side effects are of special concern. Furthermore, repeated examinations can be performed without significant incremental costs.
Previous research has demonstrated the accuracy of ultrasound measurement of urinary bladder volumes in children.6 In addition, previous research has shown increased yield in suprapubic aspiration of urine with ultrasound guidance.7 We undertook this project to investigate whether bedside 2-dimensional ultrasound of the bladder performed by pediatric emergency medicine physicians before urethral catheterizations could decrease the number of unsuccessful procedures.
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
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.
Previous historical data at our institution showed that urethral catheterization was successful at obtaining >3 mL of urine 50% to 75% of the time. With ultrasound guidance, we expected a success rate close to 95%. To detect a statistically significant difference in success rates (power of 0.8 and α of .05), we would need ∼70 to 120 patients in each group. Data are presented as proportions with 95% confidence intervals (CIs). Success rates of initial urethral catheterization with and without ultrasound were compared using χ2 analysis. Statistical analyses were performed using SPSS Version 11.5 for Windows (SPSS Inc, Chicago, IL).
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).
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).
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.
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.
- Accepted July 1, 2004.
- Reprint requests to (L.C.) Department of Pediatric Emergency Medicine, Yale University School of Medicine, 20 York St, WP143, New Haven, CT 06511. E-mail:
No conflict of interest declared.
- ↵Moore CL, Gregg S, Lambert MJ. Performance, training, quality assurance and reimbursement of emergency physician performed ultrasonography at academic medical centers. J Ultrasound Med.2004;23 :459– 466
- ↵Gorelick MH, Shaw KN. Screening tests for urinary tract infection in children: a meta-analysis. Pediatrics.1999;104(5) . Available at: pediatrics.org/cgi/content/full/104/5/e54
- ↵Newman TB, Bernzweig JA, Takayama JI, Finch SA, Wasserman RC, Pantell RH. Urine testing and urinary tract infections in febrile infants seen in office settings: the Pediatric Research in Office Settings' Febrile Infant Study. Arch Pediatr Adolesc Med.2002;156 :44– 54
- Copyright © 2005 by the American Academy of Pediatrics