A voiding trial (Trial of Void, TOV) is a standardized medical procedure assessing a patient’s ability to urinate effectively without assistance. This assessment is necessary after an indwelling urinary catheter has been in place, typically following surgery or an episode of acute urinary retention. The trial confirms that the interaction between the bladder muscle and the urinary sphincter allows for complete and spontaneous bladder emptying. Successful completion confirms the catheter can be removed permanently and safely.
Why a Voiding Trial is Necessary
The primary purpose of a voiding trial is to confirm the bladder and urethra are working in coordination to prevent post-catheterization urinary retention. When a catheter is in place, the bladder muscle (detrusor) becomes accustomed to continuous passive drainage and does not need to contract actively. Testing function before permanent removal safeguards against the bladder retaining urine once the catheter is gone.
Urinary retention, the inability to fully empty the bladder, can lead to serious complications. An overdistended bladder can suffer damage to its muscle fibers, potentially causing long-term dysfunction. Retained urine also provides a breeding ground for bacteria, significantly increasing the risk of a urinary tract infection or urosepsis. The voiding trial is a non-negotiable step to prevent these adverse outcomes in patients recovering from conditions like severe urinary retention, prostatectomy, or gynecological surgery.
Essential Preparation Before the Trial
Preparation for the voiding trial begins with managing the patient’s fluid intake to ensure the bladder can fill to a functional capacity. Clinicians often encourage the patient to consume 1 to 2 liters of fluid over the four to six hours leading up to the trial, or approximately 250 milliliters per hour, unless medically prohibited. This controlled hydration stimulates the natural urge to urinate without causing the bladder to become excessively overstretched.
Before the catheter is physically removed, the medical team prepares equipment for monitoring the patient’s output. This includes specialized measuring containers, often called “urine hats,” placed in the toilet to accurately record the volume of each void. In some protocols, the bladder may be filled with sterile saline (typically 300 milliliters) through the catheter just before removal, a technique known as backfilling. This technique jump-starts the process, providing an immediate volume to prompt the first attempt to void.
Step-by-Step Execution and Monitoring
The voiding trial formally begins immediately after the indwelling catheter is removed. The patient is instructed to notify a nurse when they feel a natural, strong urge to urinate. The patient must attempt to void only when this sensation occurs, as forcing the process can lead to an inaccurate assessment of natural bladder function. Each time the patient voids, the total volume of urine passed is meticulously measured and recorded on a fluid balance chart.
Immediately following the voiding attempt, medical staff must assess the amount of urine remaining in the bladder, known as the Post-Void Residual (PVR) volume. This PVR measurement is typically performed using a non-invasive bladder ultrasound scanner placed over the lower abdomen. For maximum accuracy, the scan must be completed within ten minutes of the patient finishing urination, since the kidneys continuously produce urine.
The trial usually continues for a set period, often spanning four to six hours, or until the patient has attempted to void two or three consecutive times. During this time, the patient is monitored for signs of discomfort, such as lower abdominal pain or a feeling of fullness. These signs could signal an inability to empty the bladder. If a patient is unable to void within six to eight hours of catheter removal, or if they experience significant discomfort, the trial is considered unsuccessful and intervention is required.
Criteria for Successful Bladder Function
The determination of a successful voiding trial hinges on the measured Post-Void Residual (PVR) volume after each voiding attempt. Success is defined as the ability to spontaneously void with a consistently low PVR volume, demonstrating effective bladder emptying. Although specific thresholds vary, a common benchmark for success is a PVR volume of less than 100 to 150 milliliters across two or three consecutive voids.
Achieving a successful trial means the patient has demonstrated the ability to empty their bladder effectively, and the indwelling catheter can be permanently discontinued. If the patient fails to void, or if the PVR volume repeatedly exceeds the acceptable threshold, the trial is considered a failure. In this instance, the patient will require temporary re-catheterization or instruction on intermittent self-catheterization to prevent bladder overdistention and protect the bladder muscle.