CLINICAL RESEARCH
Development of an in vitro bladder model Anne Mulhall BSc, PhD, is Deputy Director, Nursing Practice Research Unit, University of Surrey.
Thefirst ofthe three articles in this series (1) expound ed the casefor a broader approach to research design in nursing. In particular, the experimental approach and tlx use of laboratory studies were highlighted as areas that nurses have tended to neglect. This second article explores the development ofan in vitro bladder model for use in experiments examining infections in catheterisedpatients. In vitro studies have been extensively employed to great success within medical research. In parallel, the experimental approach integral to randomised controlled trials has provided a powerful tool by which clinicians can make rational and objective choices about treatment. Many nurse researchers have shied away from traditional laboratory experiments, perhaps per ceiving them as being too biological or based on a ‘medical model’. Departments of nursing which have a strong foundation in the biological sci ences should, however, take advantage of the opportunities this design offers and strive to inte grate it with other approaches to answering research questions. This second article explores the development of an in vitro bladder model for use in experiments examining infections in catheterised patients. Infection in the catheterised patient Catheter associated bacteriuria may be related to patient susceptibility, equipment design and errors in practice (2,3).
In vivo micro-organisms may enter the bladder: • During the catheterisation procedure • By migration between the external catheter surface and the urethral epithelium (the pericatheter route) • Through contamination of the closed drainage system. The existence of the pericatheter route was first demonstrated by Kass and Schneiderman (4) and subsequently by Brehmer and Madsen (5)- How ever, Thornton and Andriole (6) reported prior drainage bag contamination in 20 of the 23 patients they studied. Both routes possibly play a part in the aetiology of bacteriuria.
Investigate the question A survey of the nursing care associated with catheterised patients highlighted a number of potential errors in practice (7). In particular, disconnections occurred in 42 per cent of patients and drainage bags were observed in incorrect positions in 52 per cent of observations. The question of whether these errors in practice affect ed the rate of infection in patients remained. We decided, therefore, to develop a laborato ry model to investigate this question in a con trolled environment. Advantages and disadvantages of models A number of bladder model systems have been developed, usually by microbiologists wishing to
Table 1. Advantages and disadvantages of bladder models
ADVANTAGES:
DISADVANTAGES:
• Controlled input and output
• No bladder or urethral mucosae
• Controlled constituents eg. pH, urea concentration
• Difficulties in maintaining sterility
• Ability to examine different micro-organisms or mixtures of micro-organisms
• No humoral/cellular defence mechanisms • Time consuming
• Possibility of mimicking errors in practice • Low cost • Avoids using laboratory animals
October 14 Volume 7/Number 4/1992 Nursing Standard 35 Downloaded from RCNi.com by ${individualUser.displayName} on Sep 01, 2016. For personal use only. No other uses without permission. Copyright © 2016 RCNi Ltd. All rights reserved.
CLINICAL RESEARCH ,,,,
, (j ■
WARNING oecoNMiCT
Ui&
—
4 A
Fig. 1. The final model, developed in the laboratory.
study the growth of bacteria and their sensitivi ty to antibiotics in a dynamic system (8, 9). The continual replacement and removal of urine in the human bladder will affect both the multi plication of micro-organisms and the concentra
tion of antibiotics available to destroy them. These models therefore have an important role in examining the pathogenesis and treatment of urinary infections. The major advantages and disadvantages of in
36 Nursing Standard October 1-iA'olume 7/Number i '1992 Downloaded from RCNi.com by ${individualUser.displayName} on Sep 01, 2016. For personal use only. No other uses without permission. Copyright © 2016 RCNi Ltd. All rights reserved.
CLINICAL RESEARCH vitro bladder models are summarised in Table 1.
The main advantages are derived from the rig orous control of conditions which is possible in the experimental situation. The design features of catheters and drainage bags may therefore be examined under various precise operating condi tions. Additionally, the relationship between nurs ing practice and patient complications such as infection or catheter blockage can be explored. This is particularly relevant when investigating the effects of potential errors (such as breaking the closed system) which could not, on ethical grounds, be deliberately invoked in patients.
Most important mechanisms There are limitations to model systems, primarily related to the lack of immunological defence mechanisms, but it is thought that hydrokinetic forces (the removal and renewal of urine in the bladder) are the most important mechanisms whereby infection is prevented from occurring (10, 11). Development of the model 'lire models described to date have simulated normal micturition, but at least 41 per cent of hospital acquired urinary tract infection is catheter associated (12). We decided, therefore, to develop a catheterised blad der model by adapting the design of Greenwood and Tupper (13), incorporating a ‘urethra’, catheter, and drainage bag. Several difficulties were encountered in design ing and running the model, particularly those related to contamination by extraneous micro organisms. Not only did the model have to be assembled aseptically, but sterility needed to be maintained throughout a four to five-day experimental run. Three main factors contributed to these prob References . 1. Mulhall A. Nursing research: exploring the options. Nursing Stan dard. 1992. 7, 3, 35-36. 2. Shapiro M et al. A multivariate analysis of risk factors for acquiring bacteriuria in patients with indwelling urinary catheters for longer than 24 hours. Infection Control. 1984. 5, 525-532. 3. Mulhall A et al. Bacteriuria during indwelling urethral catheterisation. Journal of Hospital Infection. 1988. 1 1, 253-262. 4. Kass EH, Schneiderman L J. Entry of bacteria into the urinary tracts of patients with inlying catheters. The New EnglandJournal of Medicine. 1957. 256, 556-557.
5. Brehmcr B, Madsen P O. Routes and prophylaxis of ascending bladder infection in male patients with indwelling catheters. TheJournal of Urology. 1972. 108, 719-721. 6. Thornton G F, Andriole V T. Bac teriuria during indwelling catheter drainage. Effect of a closed steriledrainage system. Journal of the Ameri can Medical Association. 1970. 214, 339-342. 7. Crow R et al. Indwelling urethral catheterisation and related nursing practice. Journal of Advanced Nursing. 1988. 13,489 -495. 8. O’Grady F, Pennington J H. Bac terial growth in an in vitro system simulating conditions in the urinary bladder. British Journal of Experimental
lems: the complex nature of the model; the length of experiments; and the difficulties in aseptically introducing a catheter. Following pilot experiments using Quickfit apparatus, a more sophisticated model incorpo rating a peristaltic pump, a top filling bladder, and a glass ‘urethra’ was assembled. The choice of liquid medium also required consideration. Pooled human urine has been used by other workers (9, 14), but this option was rejected because of the problems of maintaining a consistent supply and the difficulties in collec tion and storage. Synthetic urine can also be prepared (15), but the extra expense and prepa ration time required was not thought merited. As we were only interested in following the routes of infection, it was decided that 10 per cent Nutrient Broth (Oxoid Ltd, Basingstoke) was an adequate alternative. The final model is illustrated in Figure. 1. The temperature of the bladder was maintained at 37 °C by a water jack et. Flow of sterile ‘urine’ from a 10 litre reservoir was maintained by a peristaltic pump at 1 ml per minute, which is the normal rate of secretion of ureteric urine. The residual volume of urine in the bladder was 20 ml, the excess draining via the catheter into the collecting bag in a direct simulation of the situation in vivo . This model was used to investigate the spread of micro-organisms from artificially contaminat ed drainage bags of different design. The results of these experiments, and their implications for clinical practice, are reported in next week’s con cluding article. Acknowledgment The Nursing Practice Research Unit is funded by the Department of Health. Tire opinions expressed in this article are those of the author
Pathology. 1966.47, 152-157. 9 Andersen J D et al. Role of bacteri al growrh rates in the epidemiology and pathogenesis of urinary infections in women./w/w/ of Clinical Microbi ology. 1979. 10,767-771. 10. Asscher A W. The Challenge of Urinary Tract Infections. London, Academic Press. 1980. 11. Kunin C M. Detection. Pretention and Management of Urinary Tract Infec tion. Philadelphia PA, Lea and Fcbiger. 1987. 12. Meers P D et al. National survey of infection in hospitals, 1980. Part2: results. 3- Urinary tract infection. Journal of Hospital Infection. 1981. 2, suppl, 23-28. 13. Greenwood D, Tupper H. A new October
in vitro device for examining the response of bacteria to changing drug concentrations. In Pc-riti P, Grassi G G (Eds). Current Chemotherapy and Immunotherapy. Washington IX!, American Society for Microbiology. 1982. 14. Stickler D et al. Activity of anti septics against Escherichia coli growing as biofilms on silicone surfaces. Euro pean Journal of Clinical M icrobiology and Infectious Diseases. 1989. 8, 974978. 15. Cox A J et al. An automated tech nique for in vitro assessment of the susceptibility of urinary catheter materials to encrustation. Engineering in Medicine. 1987. 16, 37-41.
k Volume 7/Number 4/1992 Nursing Standard 37
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Development of an in vitro bladder model Anne Mulhall BSc, PhD, is Deputy Director, Nursing Practice Research Unit, University of Surrey.
Thefirst ofthe three articles in this series (1) expound ed the casefor a broader approach to research design in nursing. In particular, the experimental approach and tlx use of laboratory studies were highlighted as areas that nurses have tended to neglect. This second article explores the development ofan in vitro bladder model for use in experiments examining infections in catheterisedpatients. In vitro studies have been extensively employed to great success within medical research. In parallel, the experimental approach integral to randomised controlled trials has provided a powerful tool by which clinicians can make rational and objective choices about treatment. Many nurse researchers have shied away from traditional laboratory experiments, perhaps per ceiving them as being too biological or based on a ‘medical model’. Departments of nursing which have a strong foundation in the biological sci ences should, however, take advantage of the opportunities this design offers and strive to inte grate it with other approaches to answering research questions. This second article explores the development of an in vitro bladder model for use in experiments examining infections in catheterised patients. Infection in the catheterised patient Catheter associated bacteriuria may be related to patient susceptibility, equipment design and errors in practice (2,3).
In vivo micro-organisms may enter the bladder: • During the catheterisation procedure • By migration between the external catheter surface and the urethral epithelium (the pericatheter route) • Through contamination of the closed drainage system. The existence of the pericatheter route was first demonstrated by Kass and Schneiderman (4) and subsequently by Brehmer and Madsen (5)- How ever, Thornton and Andriole (6) reported prior drainage bag contamination in 20 of the 23 patients they studied. Both routes possibly play a part in the aetiology of bacteriuria.
Investigate the question A survey of the nursing care associated with catheterised patients highlighted a number of potential errors in practice (7). In particular, disconnections occurred in 42 per cent of patients and drainage bags were observed in incorrect positions in 52 per cent of observations. The question of whether these errors in practice affect ed the rate of infection in patients remained. We decided, therefore, to develop a laborato ry model to investigate this question in a con trolled environment. Advantages and disadvantages of models A number of bladder model systems have been developed, usually by microbiologists wishing to
Table 1. Advantages and disadvantages of bladder models
ADVANTAGES:
DISADVANTAGES:
• Controlled input and output
• No bladder or urethral mucosae
• Controlled constituents eg. pH, urea concentration
• Difficulties in maintaining sterility
• Ability to examine different micro-organisms or mixtures of micro-organisms
• No humoral/cellular defence mechanisms • Time consuming
• Possibility of mimicking errors in practice • Low cost • Avoids using laboratory animals
October 14 Volume 7/Number 4/1992 Nursing Standard 35 Downloaded from RCNi.com by ${individualUser.displayName} on Sep 01, 2016. For personal use only. No other uses without permission. Copyright © 2016 RCNi Ltd. All rights reserved.
CLINICAL RESEARCH ,,,,
, (j ■
WARNING oecoNMiCT
Ui&
—
4 A
Fig. 1. The final model, developed in the laboratory.
study the growth of bacteria and their sensitivi ty to antibiotics in a dynamic system (8, 9). The continual replacement and removal of urine in the human bladder will affect both the multi plication of micro-organisms and the concentra
tion of antibiotics available to destroy them. These models therefore have an important role in examining the pathogenesis and treatment of urinary infections. The major advantages and disadvantages of in
36 Nursing Standard October 1-iA'olume 7/Number i '1992 Downloaded from RCNi.com by ${individualUser.displayName} on Sep 01, 2016. For personal use only. No other uses without permission. Copyright © 2016 RCNi Ltd. All rights reserved.
CLINICAL RESEARCH vitro bladder models are summarised in Table 1.
The main advantages are derived from the rig orous control of conditions which is possible in the experimental situation. The design features of catheters and drainage bags may therefore be examined under various precise operating condi tions. Additionally, the relationship between nurs ing practice and patient complications such as infection or catheter blockage can be explored. This is particularly relevant when investigating the effects of potential errors (such as breaking the closed system) which could not, on ethical grounds, be deliberately invoked in patients.
Most important mechanisms There are limitations to model systems, primarily related to the lack of immunological defence mechanisms, but it is thought that hydrokinetic forces (the removal and renewal of urine in the bladder) are the most important mechanisms whereby infection is prevented from occurring (10, 11). Development of the model 'lire models described to date have simulated normal micturition, but at least 41 per cent of hospital acquired urinary tract infection is catheter associated (12). We decided, therefore, to develop a catheterised blad der model by adapting the design of Greenwood and Tupper (13), incorporating a ‘urethra’, catheter, and drainage bag. Several difficulties were encountered in design ing and running the model, particularly those related to contamination by extraneous micro organisms. Not only did the model have to be assembled aseptically, but sterility needed to be maintained throughout a four to five-day experimental run. Three main factors contributed to these prob References . 1. Mulhall A. Nursing research: exploring the options. Nursing Stan dard. 1992. 7, 3, 35-36. 2. Shapiro M et al. A multivariate analysis of risk factors for acquiring bacteriuria in patients with indwelling urinary catheters for longer than 24 hours. Infection Control. 1984. 5, 525-532. 3. Mulhall A et al. Bacteriuria during indwelling urethral catheterisation. Journal of Hospital Infection. 1988. 1 1, 253-262. 4. Kass EH, Schneiderman L J. Entry of bacteria into the urinary tracts of patients with inlying catheters. The New EnglandJournal of Medicine. 1957. 256, 556-557.
5. Brehmcr B, Madsen P O. Routes and prophylaxis of ascending bladder infection in male patients with indwelling catheters. TheJournal of Urology. 1972. 108, 719-721. 6. Thornton G F, Andriole V T. Bac teriuria during indwelling catheter drainage. Effect of a closed steriledrainage system. Journal of the Ameri can Medical Association. 1970. 214, 339-342. 7. Crow R et al. Indwelling urethral catheterisation and related nursing practice. Journal of Advanced Nursing. 1988. 13,489 -495. 8. O’Grady F, Pennington J H. Bac terial growth in an in vitro system simulating conditions in the urinary bladder. British Journal of Experimental
lems: the complex nature of the model; the length of experiments; and the difficulties in aseptically introducing a catheter. Following pilot experiments using Quickfit apparatus, a more sophisticated model incorpo rating a peristaltic pump, a top filling bladder, and a glass ‘urethra’ was assembled. The choice of liquid medium also required consideration. Pooled human urine has been used by other workers (9, 14), but this option was rejected because of the problems of maintaining a consistent supply and the difficulties in collec tion and storage. Synthetic urine can also be prepared (15), but the extra expense and prepa ration time required was not thought merited. As we were only interested in following the routes of infection, it was decided that 10 per cent Nutrient Broth (Oxoid Ltd, Basingstoke) was an adequate alternative. The final model is illustrated in Figure. 1. The temperature of the bladder was maintained at 37 °C by a water jack et. Flow of sterile ‘urine’ from a 10 litre reservoir was maintained by a peristaltic pump at 1 ml per minute, which is the normal rate of secretion of ureteric urine. The residual volume of urine in the bladder was 20 ml, the excess draining via the catheter into the collecting bag in a direct simulation of the situation in vivo . This model was used to investigate the spread of micro-organisms from artificially contaminat ed drainage bags of different design. The results of these experiments, and their implications for clinical practice, are reported in next week’s con cluding article. Acknowledgment The Nursing Practice Research Unit is funded by the Department of Health. Tire opinions expressed in this article are those of the author
Pathology. 1966.47, 152-157. 9 Andersen J D et al. Role of bacteri al growrh rates in the epidemiology and pathogenesis of urinary infections in women./w/w/ of Clinical Microbi ology. 1979. 10,767-771. 10. Asscher A W. The Challenge of Urinary Tract Infections. London, Academic Press. 1980. 11. Kunin C M. Detection. Pretention and Management of Urinary Tract Infec tion. Philadelphia PA, Lea and Fcbiger. 1987. 12. Meers P D et al. National survey of infection in hospitals, 1980. Part2: results. 3- Urinary tract infection. Journal of Hospital Infection. 1981. 2, suppl, 23-28. 13. Greenwood D, Tupper H. A new October
in vitro device for examining the response of bacteria to changing drug concentrations. In Pc-riti P, Grassi G G (Eds). Current Chemotherapy and Immunotherapy. Washington IX!, American Society for Microbiology. 1982. 14. Stickler D et al. Activity of anti septics against Escherichia coli growing as biofilms on silicone surfaces. Euro pean Journal of Clinical M icrobiology and Infectious Diseases. 1989. 8, 974978. 15. Cox A J et al. An automated tech nique for in vitro assessment of the susceptibility of urinary catheter materials to encrustation. Engineering in Medicine. 1987. 16, 37-41.
k Volume 7/Number 4/1992 Nursing Standard 37
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