FIGURE 131.24 Pleural effusion identification using phased array probe Bladder Catheterization Bladder catheterization is commonly performed in the pediatric ED, especially in infants While the catheterization is not technically challenging, it may be uncomfortable for the patient; hence, the importance of avoiding multiple attempts Using ultrasound to identify urine in the bladder may be helpful, especially if the child has recently voided or had a dry bladder on prior catheterization For children who require suprapubic aspiration, it is important to use ultrasound to not only identify that there is urine in the bladder, but also to identify the epigastric vessels prior to the procedure Technique A phased array or curvilinear probe is an appropriate transducer for identifying urine in the bladder prior to urethral catheterizations (Fig 131.25 ) For neonates and smaller infants, a linear probe is also acceptable For suprapubic aspiration, the linear probe is also recommended as it is easier to visualize the needle entering the bladder