Post-Aspiration Balloon Reinjection During Urethral Catheter Removal: A Systematic Review and Meta-Analysis of a Neglected Mechanical Intervention

1. Introduction

Indwelling urethral catheterization is common in hospitals, perioperative care, rehabilitation, and long-term care. Removal may be followed by pain, visible or microscopic hematuria, urinary retention, failed first voiding, and the need for catheter reinsertion. International guidance from the Centers for Disease Control and Prevention, the European Association of Urology, infection-control societies, and nursing reviews focuses on appropriate indication, aseptic insertion, maintenance, infection prevention, duration, clamping, antibiotic prophylaxis, and timely removal [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27]. These sources do not provide evidence-based recommendations on the final mechanical details of balloon deflation and withdrawal. Thus, the questions of when to remove a catheter and how to remove it remain distinct.

The physical act of removal can itself be traumatic. After aspiration, the balloon may not collapse into a smooth cylinder; folds and ridges can form a cuff around the distal catheter. In vitro work and clinical reports indicate that this cuff can increase the effective diameter of the balloon region by approximately 1-5 mm, depending on catheter material and deflation mechanics [28,29,30,31,32]. Passage of an irregular cuff may scrape urethral epithelium, cause bleeding, and stimulate pain-sensitive afferents. Reports of difficult removal provide clinical support for this mechanical pathway, although they do not establish the effect of routine reinjection.

For more than two decades, Chinese nursing teams have used a simple modification: after complete balloon aspiration, 0.2-1.5 mL of sterile water, saline, residual aspirated fluid, or air is reinjected immediately before withdrawal [33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78]. The intended effect is to smooth the cuff and reduce friction. Evidence has remained dispersed across small Chinese studies, with no eligible English-language randomized trial and no previous bilingual synthesis. This regional evidence gap may reflect a nurse-led innovation that developed outside internationally standardized removal protocols and was seldom prospectively registered or reported in English.

This review therefore had three objectives: to quantify effects on pain and removal-related complications; to explore whether reinjection medium, volume, study design, sample size, and clinical population could explain heterogeneity; and to judge whether current certainty is sufficient for clinical or guideline recommendations. The review question was framed by population, intervention, comparator, outcomes, and study design.

This meta-analysis synthesizes scattered domestic clinical evidence of a nurse-led catheter removal intervention, filling the global evidence gap and providing quantitative evidence to support the translation of this low-cost, safe nursing technique into standardized clinical care protocols.

2. Materials and Methods

2.1. Design and Reporting

This systematic review and meta-analysis was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 statement [79,80]. The protocol was registered in the International Prospective Register of Systematic Reviews (CRD420261451421).

2.2. Search Strategy

Searches covered PubMed and MEDLINE, Embase, the Cochrane Library, Google Scholar, China National Knowledge Infrastructure, Wanfang Data, the VIP Chinese Science and Technology Journals Database, and the Chinese Biomedical Literature Database from database inception through 9 July 2026. English concepts included indwelling urinary catheter, Foley catheter, urethral catheter, removal, withdrawal, balloon deflation, cuffing, reinjection, reinflation, pain, hematuria, urinary retention, urethral trauma, and randomized trial; equivalent Chinese subject headings and free-text terms were combined. Controlled vocabulary and free-text terms were linked within four modules covering catheter, reinjection, outcomes, and controlled study design. Reference lists of included reports and relevant systematic reviews were hand-searched. Full line-by-line strategies are specified in Supplementary File S1. The archived materials did not support a reproducible audit of conference abstracts or trial registries; grey-literature coverage was therefore judged uncertain and treated as a potential source of publication bias rather than represented as complete.

2.3. Inclusion and Exclusion Criteria

2.3.1. Population

Adults aged 18 years or older undergoing removal of an ordinary indwelling transurethral balloon catheter. Children, pregnant patients, patients with suprapubic catheters, urethral reconstruction or stricture, traumatic catheterization, or other high-risk difficult-removal conditions were excluded.

2.3.2. Intervention

Complete aspiration of the original balloon contents followed by reinjection of 0.2-1.5 mL sterile water, normal saline, residual aspirated fluid, or air immediately before withdrawal, with no simultaneous pharmacological or mechanical co-intervention.

Comparator: Conventional withdrawal immediately after complete balloon aspiration, without reinjection or reinflation.

2.3.3. Outcomes

The primary outcome was pain during removal. Secondary outcomes were any hematuria, macroscopic hematuria, microscopic hematuria, urinary retention, successful spontaneous voiding, and catheter reinsertion.

2.3.4. Study Design

Randomized or quasi-randomized controlled trials with a concurrent conventional-removal group.Exclude non-comparative designs, unavailable full text, duplicate reports without additional data, insufficient extractable data, partial aspiration without reinjection, unclear reinjection technique, suprapubic catheter removal, and combined interventions such as lidocaine gel, analgesics, antibiotics, or bladder clamping.

2.4. Intervention Definition and Planned Effect Modifiers

Post-aspiration balloon reinjection was defined as complete withdrawal of the original balloon contents until no further fluid could be aspirated, followed immediately by a small, measured reinjection before gentle catheter withdrawal. Medium (liquid versus air), volume (0.3-0.5 mL versus more than 0.5 mL), sample size, allocation method (randomized versus quasi-randomized), and clinical specialty were prespecified as potential effect modifiers.

Experimental procedure: After complete aspiration, the specified liquid or air volume was reinjected aseptically and the catheter was withdrawn without force. Reported volumes ranged from 0.2 to 1.5 mL; most liquid protocols used 0.3-0.5 mL and most air protocols used 0.4-0.6 mL.

Control procedure: The balloon was aspirated until no further fluid could be withdrawn, after which the catheter was removed without reinjection. No additional procedural difference was eligible.

Timing and safety: Reinjection was performed immediately before withdrawal using a sterile syringe. Resistance, severe pain, suspected encrustation, urethral reconstruction or stricture, traumatic catheterization, and a history of difficult removal were not regarded as indications for reinjection and require appropriate clinical assessment.

2.5. Outcomes

The primary outcome was pain intensity during catheter removal. Because studies used visual analogue, numeric rating, facial, verbal, ordinal, and locally adapted scales, the primary continuous synthesis used the Hedges g standardized mean difference. Where an outcome was reported as ordered categories, category scores and frequencies were converted to an approximate continuous mean and standard deviation using the prespecified extraction rule; these converted data were examined in sensitivity analysis. A mean difference on a harmonized 0-10 scale was retained for clinical interpretation. Secondary outcomes were urinary retention, successful spontaneous voiding, any hematuria, macroscopic hematuria, microscopic hematuria, and catheter reinsertion.

2.6. Study Selection and Data Extraction

Two reviewers independently screened titles and abstracts, assessed full texts, and extracted data into a piloted form; disagreements were resolved by discussion and, when necessary, a third reviewer. The independent screening decisions were not retained in a form that permitted a defensible retrospective calculation of Cohen kappa and its 95% confidence interval; no agreement coefficient was therefore invented. Extracted items included setting, participants, catheter context and material when reported, dwell time, reinjection medium and volume, allocation method, pain instrument, outcome definitions, group sizes, and numeric results. When a standard deviation was absent, it was derived from a reported standard error, confidence interval, or other algebraically recoverable statistic. No outcome value was imputed without recoverable source data; studies with irretrievable data were excluded from the relevant synthesis. No additional author-supplied dataset was available.

2.7. Risk-of-Bias Assessment

Two reviewers independently applied the Cochrane Risk of Bias 2 framework across randomization, deviations from intended interventions, missing outcome data, outcome measurement, and selection of the reported result. Each domain and the overall judgment were rated low risk, some concerns, or high risk; disagreement was resolved by discussion and third-reviewer arbitration. Quasi-random allocation by admission order, ward, treatment route, or a comparable predictable method was judged high risk in the randomization domain. Operator blinding was infeasible, but blinded outcome assessment was considered possible and was judged from the report.

2.8. Certainty of Evidence

Two reviewers independently assessed certainty for each outcome using the Grading of Recommendations Assessment, Development and Evaluation domains of risk of bias, inconsistency, indirectness, imprecision, and publication bias. Downgrading was prespecified for serious methodological limitations, substantial unexplained heterogeneity, evidence restricted to one country or incompletely applicable populations, confidence intervals compatible with materially different effects, and funnel-plot or regression evidence of small-study effects. Disagreements were resolved by consensus or third-reviewer arbitration.

2.9. Statistical Analysis

Continuous outcomes were pooled with inverse-variance methods as Hedges g standardized mean differences when instruments differed and as mean differences when they could be placed on the same 0-10 scale. Binary outcomes were pooled as risk ratios because the relative probability of an event was clinically interpretable across different baseline risks. A 0.5 continuity correction was applied to a zero cell. A random-effects model was prespecified because differences in population, catheter material and size, reinjection medium and volume, clinical specialty, and pain measurement were expected; fixed-effect results were sensitivity analyses. Heterogeneity was assessed with Cochran Q, tau-squared, and I-squared, with I-squared below 50% interpreted as low, 50-75% as moderate, and above 75% as high. Prespecified subgroup hypotheses concerned medium, reinjection volume, sample size, allocation method, and specialty. Leave-one-out analyses, exclusion of high-risk studies when possible, and fixed-effect reanalysis assessed robustness. Funnel plots and Egger regression were restricted to outcomes with at least 10 studies. For multi-arm trials, eligible reinjection arms were combined when they shared one control group so that the control participants were not counted twice.

3. Results

3.1. Study Selection

Database and manual searching identified 4,774 records (4,767 from databases and 7 from reference lists or manual searching). After 4,580 duplicates and 61 other documented pre-screening removals, 133 records underwent title and abstract screening; 47 were excluded. Eighty-six full-text reports were assessed and 40 were excluded: 7 were not randomized or quasi-randomized, 14 used an ineligible reinjection intervention, 15 included analgesic co-intervention during removal, and 4 had insufficient data or duplicated another report. Forty-six Chinese trials involving 6,365 participants entered qualitative and quantitative synthesis (Figure 1).

3.2. Study Characteristics

The 46 studies were published from 2003 to 2025. Sample sizes ranged from 60 to 418 participants, with a median of 115 (interquartile range 89-186). Settings included urology, neurosurgery, orthopedics and trauma, gynecology, abdominal surgery, thoracic surgery, and mixed adult populations. Thirty-six studies used a liquid, nine used air, and one did not clearly specify the medium. Most used 0.3-0.5 mL, although some used 0.6-1.5 mL or adjusted volume by catheter size or dwell time. Ten studies used a visual analogue scale, four used a numeric rating scale, four used facial scales, nineteen used verbal or ordinal scales, and sixteen used another or unclear pain measure; some studies reported more than one pain representation. Age, sex distribution, catheter material, and catheter dwell time were inconsistently reported, so pooled baseline means, sex proportions, and a median dwell time could not be calculated without inventing data. Abbreviated characteristics of included studies(Part) as Table 1. Study-level reporting is listed in Supplementary File S2.

3.3. Risk of Bias

Using the Cochrane Risk of Bias 2 framework, eight studies (17%) were judged low risk in the randomization process, twenty-seven (59%) raised some concerns, and eleven (24%) were high risk because allocation was predictable or otherwise inadequate. Because operator blinding was infeasible and blinded outcome assessment was usually unreported, all studies raised at least some concern for deviations from intended intervention or outcome measurement. Outcome data were complete in the extracted reports and selective outcome reporting was not evident, although protocols were unavailable. Overall, thirty-five studies (76%) raised some concerns and eleven (24%) were high risk; none met low-risk criteria across all domains (Figure 2).

3.4. Primary Outcome: Pain During Catheter Removal

Twenty-six trials involving 3,900 participants reported pain. Reinjection reduced pain compared with conventional removal (standardized mean difference -1.14, 95% confidence interval -1.35 to -0.92; I-squared=89.8%; Figure 3). On the harmonized 0-10 scale, the mean difference was -1.73 points (95% confidence interval -2.11 to -1.35; I-squared=96.2%), a magnitude likely to be clinically noticeable although interpretation depends on the pain instrument and context. Leave-one-out analyses preserved the direction of effect. Funnel-plot asymmetry and Egger regression (p<0.001) indicated small-study effects, publication bias, or heterogeneity.

3.5. Secondary Outcomes

Reinjection was associated with improvement across secondary outcomes (Table 2). Urinary retention fell by approximately 78% (risk ratio 0.22, 95% confidence interval 0.14-0.32; I-squared=0.0%). Successful spontaneous voiding increased by 29% in relative terms (risk ratio 1.29, 95% confidence interval 1.21-1.39; I-squared=65.8%). Any hematuria fell by approximately 79% (risk ratio 0.21, 95% confidence interval 0.14-0.32; I-squared=52.5%); macroscopic hematuria fell by approximately 72% (risk ratio 0.28, 95% confidence interval 0.19-0.41; I-squared=21.8%); and microscopic hematuria fell by approximately 66% (risk ratio 0.34, 95% confidence interval 0.22-0.52; I-squared=78.8%). Catheter reinsertion fell by approximately 56% (risk ratio 0.44, 95% confidence interval 0.28-0.69; I-squared=0.0%). Additional forest plots are identified for Supplementary File S3.

3.6. Subgroup, Sensitivity, and Small-Study-Effect Analyses

Subgroup hypotheses for liquid versus air, 0.3-0.5 mL versus larger volumes, allocation method, sample size, and specialty were prespecified. The direction of effect favored reinjection in the available medium strata, but inconsistent arm-level reporting of dose, catheter material, dwell time, allocation method, and specialty prevented reliable estimation of each factor's independent contribution to heterogeneity. These analyses were therefore treated as exploratory rather than causal. Leave-one-out analyses did not reverse any pooled effect, and fixed-effect models produced more precise estimates without resolving clinical heterogeneity; random-effects estimates remained the primary results. Funnel plots were examined only for outcomes with at least 10 studies (Additional funnel plot are identified for Supplementary File S4.). The pain funnel plot was asymmetric and Egger regression was significant (p<0.001), supporting downgrading for suspected publication bias and caution against effect-size overestimation.

4. Discussion

4.1. Principal Findings

This review found a consistent direction of benefit across pain, urinary retention, spontaneous voiding, hematuria, and catheter reinsertion. Relative effects were strongest and heterogeneity lowest for several objective outcomes: any hematuria fell by 79%, urinary retention by 78%, and catheter reinsertion by 56%, whereas the large pain effect showed high heterogeneity. This pattern is compatible with a more consistent effect on mechanical mucosal trauma than on subjective pain, which is also shaped by expectation, sex, anxiety, pain instrument, clinical setting, and operator technique. Nevertheless, low or very low certainty prevents firm causal or guideline-level conclusions.

4.2. Relationship to Existing Evidence

The most recent Cochrane review of short-term catheter removal addressed timing, clamping, and antibiotic prophylaxis but did not identify trials of balloon-deflation and reinjection technique [1]. Infection-prevention and catheter-management guidance similarly emphasizes indication, maintenance, and prompt removal [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]. This review therefore addresses a separate mechanical question: how the final withdrawal step is performed. The absence of eligible English-language randomized trials may reflect the local, nurse-led evolution of the technique, limited prospective registration, inconsistent terminology, and the low visibility of small Chinese nursing trials in international evidence systems. These circumstances explain both the novelty of the synthesis and why its regional evidence base cannot be assumed to transfer unchanged to other countries. This review supplements missing evidence to advance evidence-based urinary nursing and facilitate cross-regional knowledge translation of nursing innovation.

4.3. Mechanistic Insights from Effect-Size Patterns

The findings are compatible with an injury-pain dual-pathway hypothesis. In vitro and clinical reports show that incomplete balloon collapse can create a circumferential cuff and increase the effective withdrawal diameter [28,29,30,31,32] First, an irregular ridge may scrape urethral epithelium and produce visible or microscopic bleeding. Second, tissue stretch and friction may activate urethral pain afferents and trigger guarding or reflex difficulty voiding even without visible injury. A measured small reinjection may redistribute balloon material and blunt the ridge. This mechanism explains why hematuria could respond more consistently than pain, but it remains a hypothesis because the included trials did not directly measure balloon geometry, mucosal force, or neural activation.

4.4. Clinical Implications

Current evidence supports only cautious, conditional consideration in selected adults undergoing routine short-term transurethral catheter removal, particularly when removal pain is anticipated. A provisional protocol based on the most common studies is complete aspiration, aseptic reinjection of 0.3-0.5 mL sterile water, saline, or air, and gentle withdrawal without force, with the volume, medium, catheter type, and adverse events documented. Reinjection should not be used to overcome resistance or in suspected encrustation, urethral reconstruction, known stricture, traumatic catheterization, embedded balloons, or a history of difficult removal; these situations require clinical or urological assessment. Any local use should be standardized, audited, and accompanied by adverse-event monitoring.

For nursing practice, the review highlights that prevention of catheter-related harm should address not only whether and when a catheter is removed but also the mechanics of removal. Domestic clinical pathways may evaluate a standardized, volume-controlled technique under governance and monitoring. International guideline incorporation is premature until multicentre trials outside China reproduce benefit and establish the safest medium and dose.

This synthesized quantitative evidence supports the knowledge translation of balloon reinjection technique in routine urinary catheter care. Hospitals can integrate this standardized low-cost procedure into evidence-based nursing pathways to reduce catheter-related pain and urethral injury risks. Current regional evidence limitation highlights the necessity of international multi-center trials to realize global clinical implementation of this nursing intervention.

4.5. Limitations

Several limitations are important. First, all trials were conducted in China and no eligible English-language randomized trial was found; differences in catheter materials, sizes, balloon designs, nursing workflows, analgesic practice, and patient characteristics limit transferability. Second, most studies were small, single-centre, and not prospectively registered; allocation concealment was unreported, predictable allocation was common, operator blinding was infeasible, and assessor blinding was unclear. Third, pain instruments and converted outcome formats varied, producing high heterogeneity and possible measurement bias. Fourth, catheter material, dwell time, sex-specific anatomy, age, and baseline characteristics were reported too inconsistently for reliable effect-modifier analyses. Fifth, long-term outcomes such as urethral stricture and recurrent urinary infection were not assessed. Sixth, grey-literature, conference-abstract, and non-Chinese/non-English coverage could not be audited from the archived search materials, and screening decisions were not retained for retrospective calculation of inter-reviewer agreement with a 95% confidence interval. Seventh, funnel-plot asymmetry and significant regression suggest that small positive studies may overestimate benefit. These limitations underpin the low or very low certainty ratings.

4.6. Future Research

Priority questions are the optimal reinjection volume and medium, effect modification by catheter material, size, dwell time and sex, objective urethral-injury measurement, long-term safety, and implementation outside China. Future trials should be international, multicentre, prospectively registered, adequately concealed, and reported according to the Consolidated Standards of Reporting Trials. They should use blinded outcome assessment where feasible and monitor difficult removal, catheter reinsertion, urinary infection, and longer-term urethral symptoms.

From a knowledge-translation perspective, this synthesis provides the quantitative evidence base needed to update local nursing protocols for catheter removal. The key translational steps are: 1) incorporating the reinjection technique into nursing skill training; 2) developing a standardized, volume-controlled clinical pathway; 3) monitoring adverse events and patient-reported outcomes during early implementation; and 4) participating in international collaborative research to test its effectiveness in diverse healthcare systems.

5. Conclusions

Small-volume post-aspiration balloon reinjection was associated with less pain, hematuria, urinary retention, and catheter reinsertion and with more successful spontaneous voiding across 46 Chinese trials. The intervention is mechanically plausible, but all evidence came from a single country and was affected by methodological limitations, high heterogeneity for important outcomes, and suspected publication bias; certainty was low or very low and does not support a strong international guideline recommendation.

Under a standardized protocol and adverse-event monitoring, selected domestic centres may evaluate the technique cautiously in routine low-risk catheter removal. International multicentre, adequately concealed, prospectively registered trials are required before wider adoption. Catheter research should address not only when a catheter is removed but also how the mechanical withdrawal step is performed.

This pooled evidence provides actionable evidence for translating improved catheter removal nursing practice into routine ward care, and reminds global nursing researchers to pay more attention to understudied mechanical details of catheter management in evidence-based practice construction.