This study was the first of its kind in that it fills the gap in the scientific data created by the absence of any investigation making a direct comparison between 2D-sonograhpic and true urine volumes. While most hospitals in the developed world now prefer to measure urine volumes with portable bladder scanners and 3D ultrasound devices, none of these technology are widely available in Bangladesh and other developing countries. Nonetheless, hundreds to thousands of ultrasound examinations involving the measurement of maximum cystometric capacity (MCC) and postvoid residue (PVR) of urinary bladder are done with 2D stationary ultrasound every day. Despite our clinical experience that these measurements are quite accurate and reliable, it was deemed essential to establish scientific evidence in its favour.
This observational study was done in the Dept of Radiology & Imaging at Bangabandhu Sheikh Mujib Medical University (BSMMU), Dhaka, Bangladesh, during the period July – December 2014. 384 adult patients who came to BSMMU for ultrasound examinations were enrolled in this study and their true urine volumes were compared against that calculated using 2D B-mode ultrasound. The findings were analysed using two statistical approaches – correlation coefficient and limits of agreement. Calculation of the correlation coefficient was done so that the findings of this study could be compared with other relevant studies, most of which have used the correlation coefficient to assess the accuracy of the ultrasound equipment (3D or portable). However, Bland & Altman’s limits of agreement method is the standard statistical approach to assess agreement between two methods of clinical measurement, as determined by The Statistician, The Lancet and others.
Findings of this study show that bladder urine volumes measured by 2D B-mode ultrasound had high correlation (r = 0.96, 95% CI 0.955 – 0.969, P < 0.0001) and agreement (96.35%, LoA : -7.84 ± 53.05 mL) with true urine volumes. Sonographic urine volumes were accurate in both males and females, of all adult age groups and at all volume ranges including <100 mL.
Table of Contents
Abstract
List of Tables
List of Figures
Acknowledgements
Chapter One : Introduction
1.1 Background
1.2 Rationale of the study
1.3 Hypothesis
1.4 Objectives
1.5 Review of Literature
Chapter Two : Materials and Methods
2.1 Study design
2.2 Study place
2.3 Study period
2.4 Study population
2.5 Sampling technique
2.6 Sample size
2.7 Selection criteria
2.7.1 Inclusion criteria
2.7.2 Exclusion criteria
2.8 Operational definitions
2.9 Equipment used
2.10 Data gathering instruments
2.11 Main outcome variables
2.12 Procedure
2.13 Statistical analyses
2.14 Statistical significance levels
2.15 Quality assurance strategies
2.16 Ethical measures
2.17 Study plan flow chart
2.18 Time table
Chapter Three : Results
Chapter Four : Discussion
Conclusion
References
Abbreviations
Appendix A : Data Collection Sheet
Appendix B : Informed Written Consent
Appendix C : Master Data Table
Abstract
Background : Every day, hundreds of ultrasound examinations are done all around developing countries like Bangladesh involving the measurement of maximum cystometric capacity (MCC) and postvoid residue (PVR) of urinary bladder. While it is our clinical experience that these measurements are quite accurate and reliable, there has been no scientific study to establish this fact. Rather, catheterisation has long been considered the best method, although not 100% accurate or gold standard.
Many studies have been carried out to establish ultrasound as a standard tool for measuring bladder capacities, and derived highly favourable results. However, almost all of these studies have tested dedicated portable bladder scanners and 3D ultrasound equipment, none of which is widely available in a developing country like Bangladesh. Therefore, it was considered essential to determine whether the widely used and available conventional stationary 2D B-mode ultrasound is sufficiently accurate in the measurement of bladder capacities.
Methods : This observational study was done in the Dept of Radiology Imaging at Bangabandhu Sheikh Mujib Medical University (BSMMU), Dhaka, Bangladesh, during the period July – December 2014. 384 adult patients who came to BSMMU for ultrasound examinations were enrolled in this study and their urine volumes were calculated using 2D B-mode ultrasound. The participants were then asked to void into a measuring cylinder (in the privacy of a patient examination screen) and the measured urine volumes were compared against the sonographically calculated volumes. The participants were immediately rescanned after voiding and were excluded from the study if any postvoid residual urine was detected.
Accuracy of sonographic urine volumetry was derived in terms of Pearson’s coefficient of correlation (r) and Bland Altman’s limits of agreement (LoA) between sonographic and true (voided) urine volumes.
Results : Findings of this study show that bladder urine volumes measured by 2D B-mode ultrasound had high correlation (r = 0.96, 95% CI 0.955 – 0.969, P < 0.0001) and agreement (96.35%, LoA : -7.84 ± 53.05 mL) with true urine volumes. Sonographic urine volumes were accurate in both males and females, of all adult age groups and at all volume ranges including <100 mL.
Conclusion : 2D B-mode ultrasound is an accurate and reliable tool for the calculation of bladder urine volumes at all volume ranges and adult age groups, in both males and females. Its accuracy is comparable to the portable bladder scanners and 3D ultrasound equipment that are highly recommended and widely used in developed countries.
List of Tables
Table 1 Sub-group analysis based on age
Table 2 Sub-group analysis of different true urine volume ranges
Table 3 Sub-group analysis based on gender of the study participants
Table 4 Comparison of results with some related studies
Table 5 Master Data Table
List of Figures
Figure 1 Gender distribution of study participants
Figure 2 Age distribution of study participants
Figure 3 Linear scatter-plot of USG volumes against true urine volumes
Figure 4 Bland-Altman plot of differences (D = U – V) against averages [A = (U+V)/2]
Acknowledgements
Praises and thanks be to Allah for making difficult things easy and tough things possible. It is only with the help of Allah that good deeds are accomplished and bad things avoided.
On the auspicious occasion of publishing my research, I would like to express my respect and reverence to Prof Salahuddin Al-Azad, Chairman, Dept of Radiology Imaging, BSMMU, for his thorough, meticulous supervision and active patronage at all stages of my study.
Special thanks are due to Prof Golam Hasan Rabbani, Director of Public Health Informatics and Dr M A Shakoor, Associate Professor of Physical Medicine, both members of the Institutional Review Board of BSMMU, for their keen interest and valuable inputs regarding the statistical and ethical aspects of the study, respectively.
It is also befitting to acknowledge with deep gratitude the inspiring support and uncompromising sacrifices afforded to me by my parents and sisters, without which it would have been a lot more difficult and challenging to complete the work.
I should duly recognise the time and experience sharing by my former room-mate, training-mate and course-mate Dr Shafayat Bin Mollah Mosharraf, whose suggestions helped me to avoid many common mistakes and deficiencies.
Finally, I would like to thank all the patients who agreed to participate in my study.
May Allah reward all with the very best.
Dr Muhammad Shoyab
Dept of Radiology Imaging
BSMMU, Dhaka, Bangladesh
Chapter One : Introduction
1.1 Background
Since its inception, ultrasonographic imaging has made significant contribution by obtaining important diagnostic information from patients in a rapid and noninvasive manner and has benefited from considerable improvements in image quality and visualization clarity. With the rapid advance in the field of imaging technology, ultrasound is now able to offer superior image quality, faster data acquisition, analysis and display, thus providing maximum diagnostic information.
Measurements are an important aspect of ultrasound examinations. Measurements of different organs, parts of organs, tumours, as well as the developing foetus are routine components of ultrasound studies. Linear distance measurements are considered to be sufficiently accurate and reliable. Volumetric measurements, however, are more complex as they often involve irregularly shaped organs such as the urinary or gall bladder or the ovaries (1). Nonetheless, volume measurement is important because it is necessary for the diagnosis, treatment planning and prognosis in many clinical situations and ultrasound is an easy, affordable and widely available way to do so. The most commonly used formula for this calculation is the ellipsoid formula, i.e. length × width × depth × π/6 (2,3). Since π = 3.142, π/6 = 0.52 and so volume = length × width × depth × 0.52.
Every day, hundreds of ultrasound examinations are done all around developing countries like Bangladesh involving the measurement of maximum cystometric capacity (MCC) and postvoid residue (PVR) of urinary bladder. While it is our clinical experience that these measurements are quite accurate and reliable, there has been no scientific study to establish this fact.
Urinary bladder volume is required in several different contexts in the fields of nephrology, urology and in neurologic rehabilitation care, including the bladder stress test for the evaluation of urinary incontinence. Several different measures of bladder volume or capacity are used, each with different levels of importance.
The anatomic bladder capacity, also known as the maximum anaesthetic bladder capacity, is the maximum volume of urine that can be infused into the bladder under anaesthesia. It is essentially the maximum extent to which the detrusor muscle can stretch, and thus reflects the compliance of the bladder wall. It is an essential parameter in patients with interstitial cystitis or other painful conditions of the bladder (4).
The functional bladder capacity is the volume of urine that urges someone to void. It is an estimate of the average or maximal voided volume of a person (4). It is also a strong prognostic indicator of the level of response to desmopressin treatment in children with nocturnal enuresis (5).
Cystometric capacity is the volume of urine that causes a person to experience lower abdominal pain or results in involuntary voiding, i.e. incontinence. It is ideally measured as voided volume plus postvoid residual volume (PVR). Voided volume is measured by visually inspecting the volume of urine expelled while postvoid residual volume can be measured by catheterization, ultrasonography or fluoroscopic imaging. Cystometric capacities above 600 mL are associated with bladder outlet obstruction or poor detrusor contraction, resulting in incomplete bladder emptying or urinary retention. On the other hand, small bladder capacities are associated with detrusor overactivity and low bladder wall compliance (4).
In general, low bladder volumes in association with involuntary contractions of the detrusor are a feature of “spastic bladder” or detrusor-sphincter dyssynergia. On the other hand, high bladder volumes associated with absence or weakness of detrusor contraction are encountered in “flaccid” or neurogenic bladder. Mixed spastic flaccid patterns are seen in several disease conditions like syphilis, diabetes mellitus, brain or spinal cord tumours (6).
Postvoid residual volume (PVR) is defined as the amount of urine remaining in the bladder immediately after the completion of micturition. It can be measured by catheterization or by ultrasonography. Increased PVR indicates impairments such as lower urinary tract obstruction, poor contractility, detrusor hyperactivity with impaired contractility, or a combination of these (7). PVR is important as it provides a quantitative way to measure the efficacy of the voiding technique. PVR upto 50 mL is considered normal (upto 100 mL above 65 years of age) (8). The importance of PVR is reflected in the fact that men with PVR above the normal values have been reported to be three times more likely to develop acute urinary retention within three years (9). In case of women, the upper limit of PVR is 50 mL regardless of age (10).
Furthermore, serial PVR measurements are an important component in neurologic rehabilitation nursing for the monitoring of bladder dysfunction, bladder retraining programs and the effect of drugs administered for this purpose (11). For example, in patients undergoing bladder training to overcome urinary retention, PVR below 150 mL is considered an acceptable progress (12).
Several methods are used for the determination of urinary bladder volume. Among them, the traditional bedside method of palpation, percussion and measurement has been abandoned due to its crudeness and obvious inaccuracy (13).
From the study of the literature, it is seen that catheterisation is considered the most accurate and reliable method for measuring urine volumes, despite ultrasound being the easiest and safest tool. However, catheterisation is not considered 100% accurate or gold standard. Its accuracy in the measurement of urine volume has been questioned in several studies, to the extent that some researchers have concluded that urine volumes are better measured by ultrasound than by catheterisation (11). However, there are other studies that have reported the opposite, and considered ultrasound measurements to be unreliable and inaccurate (11). In addition, catheterisation is also blamed for 80% of hospital-acquired UTIs, which amounts to more than one-third of all hospital-acquired infections (12). It is also associated with patient discomfort, non-compliance and carries the grave risk of urethral trauma (14).
These factors have prompted further evaluation of ultrasound as an easier, safer and reliably accurate alternative for the measurement of urine volumes and many studies have been undertaken to that effect. However, almost all of these studies (3,11–29) have tested portable bladder scanners and 3D ultrasound equipment, none of which is widely available in Bangladesh. Moreover, it requires extensive practice and experience to properly maneuver the mouse of the 3D ultrasound system to follow the contours of different sonographic images. Obtaining accurate volume measurements by manipulating the mouse requires fine control of the hand that is possible only by experts (30).
While many studies (3,11–29) have been undertaken to evaluate the usefulness of portable bladder scanners and 3D ultrasound scanners in the measurement of urine volumes, very little is found relating to the use of the traditional stationary 2D ultrasound machine for this purpose, whereas it is the most available equipment in a developing country like Bangladesh. Among the few studies that make a direct comparison between sonographic and true volumes of urine are those conducted by Mainprize et al (31) and Simforoosh et al (32). These studies compared sonographic urine volumes against catheterised volumes in 50 female (31) and 324 male participants (32), respectively, using multiple formulae, but found that “no correlation existed between calculated ultrasound bladder volumes and measured urine volumes for any of the formulas”. However, both of these studies were conducted 20 years ago, with such outdated equipment whose “lower limit of ultrasonographic visualization of urine in the bladder was approximately 42 mL” (31) and “. . . 48 mL” (32) respectively.
Clearly, ultrasound technology has improved significantly since then and the findings of Mainprize et al (31) and Simforoosh et al (32) are no longer applicable. This is further reflected in another study conducted by Schnider et al (11), entitled Bladder Volume Determination: Portable 3-D Versus Stationary 2-D Ultrasound Device. The results of this study showed that 2D ultrasound measurements were more reproducible than 3D, particularly at lower volumes. They also found that both 2D and 3D machines overestimated lower bladder volumes but underestimated higher volumes (11). However, this study was conducted on only 20 participants and was aimed only at comparing 2D with 3D machines rather than making a direct comparison between 2D ultrasound and true volumes.
1.2 Rationale of the study
Although 3D ultrasound and portable bladder scanners have been determined to be highly accurate alternatives of catheterisation for urine volume measurements (3,11–29), none of them are widely available in developing countries like Bangladesh. On the other hand, stationary 2D ultrasound is widely available, affordable and accessible almost everywhere. However, as mentioned above, no strong evidence has been established to regard 2D ultrasound as an accurate tool for measurement of urine volume. The studies of Mainprize et al (31) and Simforoosh et al (32) are outdated and that of Scnider et al (11) had only 20 participants and was aimed only at comparing 2D with 3D machines.
Therefore, it was considered essential to determine the accuracy of sonographic urine volume calculations by making a direct comparison between true urines volumes and 2D ultrasound, which is the most widely available and used modality for this purpose.
1.3 Hypothesis
2D B-mode ultrasound is an accurate tool for urine volume measurement.
1.4 Objectives
a. General
To determine the accuracy of urine volume measurements made by stationary 2D B-mode ultrasound.
b. Specific
1. To calculate the volume of urine in the bladder by 2D B-mode ultrasound, using the ellipsoid formula (length × width × depth × π/6).
2. To measure the true volume of the urine after the patient voids into a laboratory standard graduated measuring cylinder.
3. To calculate Pearson’s coefficient of correlation between sonographic and true urine volumes.
4. To construct the Bland-Altman graph and calculate the limits of agreement between sonographic and true urine volumes.
1.5 Review of Literature
Many studies have been undertaken to evaluate the usefulness of ultrasound scanners in the measurement of bladder capacities and derived highly favourable results. However, almost all of these studies have tested portable bladder scanners and 3D ultrasound equipment, and very little is found relating to the use of the traditional stationary 2D ultrasound machine for this purpose, whereas it is the most widely used and available tool in developing countries like Bangladesh.
2 D Ultrasound vs True Urine Volumes
Among the few studies that make a direct comparison between sonographic and true volumes of urine are those conducted by Mainprize et al (31) and Simforoosh et al (32). The study of Mainprize et al was conducted on 50 women in 1989. The investigators calculated 2D sonographic urine volumes using eight different formulae and measured urine volumes by catheterisation once in supine position and again in standing position. The true urine volumes thus measured were compared against each of the eight sonographic volumes but found that “no correlation existed between calculated ultrasound bladder volumes and measured urine volumes for any of the formulas” (31).
Simforoosh et al carried out a similar study on 324 men in 1997. The sonographic urine volumes were calculated by multiplying transverse and sagittal bladder diameters, as well as by calculating the areas from longitudinal and transverse images, using a total of 11 formulae. These values were compared against true volumes obtained by catheterisation. These authors also found no correlation between sonographic and measured urine volumes (32).
Based on their findings, both Mainprize et al and Simforoosh et al concluded that ultrasound could not measure urine volumes accurately “as yet”. However, both of these studies were conducted about two decades ago, with such outdated equipment whose “lower limit of ultrasonographic visualization of urine in the bladder was approximately 42 mL” (31) and “. . . 48 mL” (32) respectively.
Clearly, ultrasound technology has improved significantly since then and the findings of Mainprize et al (31) and Simforoosh et al (32) are no longer applicable. This is further reflected in another study conducted by Schnider et al (11) in the year 2000, which is discussed below.
2D Ulrasound vs 3D Ultrasound
The study sample of Schnider et al (11) was 23 in-patients (12 male, 11 female) with pre-existing urinary catheters undergoing rehabilitation from a variety of diseases (hepatic failure, respiratory failure, heart failure, neurosurgery, urinary incontinence, loss of bladder sensation, cerebral ischaemia, head injury). After draining the patient’s bladder through the catheter, ensuring complete emptying by applying gentle pressure on the patient’s lower abdomen and confirming it by 3D-ultrasound, different fixed amounts of sterile saline were introduced into the bladder through the catheter. The resulting bladder volumes were then measured with 2D and 3D ultrasound equipment, applying a +10 mL correction for the volume of the catheter balloon. The results of this study showed that 2D ultrasound measurements were more reproducible than 3D, particularly at lower volumes. They also found that both 2D and 3D machines overestimated lower bladder volumes but underestimated higher volumes. The investigators concluded that both 2D and portable 3D ultrasound scanners were “sufficiently accurate” for urine volume measurement. They also suggested that ultrasound measurements above 110 mL should be followed by catheterisation to avoid underestimating higher PVR values (11). This study, though quite thoroughly informative and favourable, was conducted on only 23 participants and was aimed only at comparing 2D with 3D machines rather than making a direct comparison between 2D ultrasound and true volumes. The findings of this study had some sharp contrast with those of Marks et al, who concluded that 3D equipment were more accurate than 2D and reported that sonographic urine volumes were, in general, lower than true urine volumes (20).
2D Ultrasound vs Portable Bladder Scanners
In a study designed to compare portable bladder scanners against traditional stationary ultrasound, Huang et al measured the urine volumes of 64 patients (37 male, 27 female) using a portable bladder scanner, a stationary ultrasound machine and by catheterisation. The mean absolute error of the portable bladder scanner was 34.4 mL (69.5%, P < 0.05) versus 21.9 mL (16.6%, P < 0.05) of the stationary ultrasound. The equipment had sensitivities of 80% and 87% and specificities of 90% and 100%, respectively. It was also found that the mean error of the portable bladder scanner reduced with increase in the volume of urine measured, having a percentage error of 66.1±76.2% with volumes below 100 mL, 20.2±18.7% with volumes between 100–300 mL, 16.8±13.9% with volumes from 300-500 mL and 7.7±5.7% with volumes above 500 mL. The authors therefore concluded that portable bladder scanners may not be as accurate as stationary ultrasound, especially with urine volumes below 100 mL (3). It is to be noted that the critical importance of measuring urine volumes is the accurate determination of whether PVR is more than 100 mL (for otherwise healthy patients) or 150 mL (for patients undergoing bladder training). Equipment that are not sufficiently accurate at this volume range may not be very helpful in a clinical setting.
[...]
- Quote paper
- Muhammad Shoyab (Author), 2014, Determining the Accuracy of Urine Volume Calculations made by Stationary 2D B-Mode Ultrasonography, Munich, GRIN Verlag, https://www.grin.com/document/289001
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