The review presented here includes several articles [10,11,12,13] that have been overlooked by other reviews. The search identified 326 articles out of which 121 were subjected to full-text review. Of these, 77 articles [40 reviews and 37 clinical studies (i.e., original research articles)] were found to be eligible for this literature summary (Fig. 1). An overview of the evidence level for the different outcomes and pathologies are shown in Table 1. In general, all the studies included compare hydrophilic catheters (both specified and unspecified) to non-hydrophilic, including both prelubricated and unlubricated catheters that require manual lubrication. Catheterization was through urethra, but a few studies also included some patients with abdominal wall catheterizable channels. We included studies with participants of all ages, pathologies (neurogenic and non-neurogenic) and gender. The articles included cover a wide range from meta and systemic reviews and various types of clinical studies, both RCT’s, but also other studies such as cost effectiveness studies, observational cohort studies, retrospective studies and studies based on self-reported questionnaires. Many studies were of low quality and many of the RCT’s had few participants and high drop-out rates and often they did not meet the calculated sample size. In the 18 RCTs that were included, the study period varied from 1 to 24 months and the number of participants from 25 to more than 200.

Table 1 Overview of the evidence level for a comparison of HCIC and non-HCIC catheters for the different pathologiesSatisfaction

Satisfaction was typically evaluated by questionnaires, some studies using interview-type questions and others using scores based on scales such as the visual analogue scale (VAS). Table 2 gives an overview of the available literature and evidence level pertaining to satisfaction. Overall, 28 articles (19 original articles and 9 reviews) were found covering satisfaction either as the primary or the secondary research parameter. Of these, 21 studies favored HCICs over non-hydrophilic catheters for improvement in satisfaction.

Table 2 Satisfaction evidence levelSpinal cord injury

The corresponding literature (6 studies, Table 2) indicates that, in SCI patients, satisfaction is generally higher with HCICs (such as SpeediCath®, Rüsch®, or LoFric®) than non-HCICs (lubricated polyvinyl chloride [PVC] catheters or undefined). For example, Cardenas [14] found a significantly higher satisfaction rate with HCIC (SpeediCath) than gel-lubricated PVC catheters (Conveen®). Wyndaele [15] evaluated patient satisfaction using VAS scores, and like the Cardenas study, observed increased satisfaction with HCICs. Spinu [12] also observed significantly higher satisfaction with HCICs than non-HCICs. Johansen et al. [16] reported increased general satisfaction with HCICs and that 74% of the patients wanted to continue with their hydrophilic catheters (LoFric). In contrast, Sarica [17], who measured satisfaction using VAS scores, found that gel lubricated catheters scored significantly higher than HCICs, which in turn, scored higher than uncoated catheters in satisfaction. In a review, Salameh et al. [18] concluded that the use of HCICs is an innovative technique that leads to better patient comfort and satisfaction in SCI patients.

Spina bifida

Five studies concerned SB patients, two of which showed higher satisfaction with HCICs (DeFoor [19] and Burki [11]) whereas the others either showed higher satisfaction for PVC (Kiddoo [20], Chick [21]) or revealed difficulties inserting the catheter despite being coated or not (Lindehall [13]).

Multiple sclerosis

No information on satisfaction in MS patients was found.

Benign prostate hypertrophy

Only one article investigated satisfaction among BPH patients, which did not find any difference in satisfaction between HCICs and a lubricated (non-hydrophilic) Mentor catheter (Pachler and Frimodt [22]). However, this article was not part of the literature search analysis as it was published before 2000.

Bladder cancer

Cindolo [23] found that among bladder cancer patients, HCIC users had significantly more comfort than users of non-coated catheters; the analysis was based on VAS scores. Compared to some of the neurogenic disorders, this patient group may, to a higher degree, have full sensation, affecting results on satisfaction.

Mixed population

Nine studies and eight reviews were performed on mixed pathology patient groups. Most studies were in favor of HCICs with regard to satisfaction [1, 6, 10, 24,25,26,27,28,29,30,31,32]. A few studies had ambiguous results [4, 33, 34], and one study did not find any difference; in this study, Yamanishi et al. [35] compared SpeediCath Compact (HCIC) with standard non-coated nelaton catheters in males and found no statistically significant difference in terms of ease of use, convenience, discreetness, and psychological well‐being between the two catheter types. However, there were significant differences in favor of SpeediCath Compact in terms of storage of catheters at home and the response that the “catheter allows me to feel confident when away from home,” although these scores are probably more related to the fact that the HCIC was compact. Stensballe et al. [25] performed a study on healthy males to test withdrawal force, pain, and preference for different types of catheters. SpeediCath exerted significantly lower withdrawal friction force compared to LoFric (also hydrophilic) and gel lubricated PVC catheters; moreover, SpeediCath and LoFric caused less hematuria and pain than the non-hydrophilic PVC catheter. Newman et al. [32, 36] presented an increase in mean Intermittent Self-Catheterization Questionnaire (ISC-Q) score from 58.00 to 67.19 when patients switched to single-use HCICs. This corresponds to a statistically significant change of 9.42 units (p = 0.0101) and a 20% increase in health-related QoL. In a population of female neurogenic patients, comparing hydrophilic catheters (SpeediCath) with uncoated catheters, Yoshida et al. [10] found that the hydrophilic catheter was considered significantly more safe than the uncoated catheter, and satisfaction with the hydrophilic catheter was significantly higher (13/16 vs 3/13, p = 0.003).

Preference

In total, 15 articles were found discussing preference (Table 3). Only one article, Kiddoo et al. [20], found that participants did not favor the use of HCICs. The results of all the other articles were, to varying degrees, positive towards HCICs in terms of patient preference.

Table 3 Preference evidence levelSpinal cord injury

Both articles in this disease category, Pinder [37] and Johansen [16], found a higher preference for HCICs than lubricated PVC catheters in SCI patients.

Spina bifida

In SB patients, DeFoor [19] and Burki [11] both noticed a significantly higher preference for HCICs after the respective trials, whereas Chick [21] noted that adaption to HCICs was difficult; however, those who got it to work, preferred HCICs. Kiddoo [20] found that fewer participants in the HCIC group (57%) answered “Yes” to “Would you continue using the product?” compared to the PVC catheter group (92%); however, the authors also stated that the issue was related to the initial difficulty in handling the hydrophilic catheter by the children due to the slipperiness. Lucas [38] recorded increased preference for HCICs versus uncoated PVC catheters in myelomeningocele patients.

Multiple sclerosis

No studies were found concerning preference for HCICs in MS patients.

Benign prostate hypertrophy

A study by Pachler and Frimodt in 1999 on BPH comparing HCICs (LoFric) with uncoated PVC catheters, which was not part of the analysis, found a slightly higher preference for HCICs (15/32) compared to the uncoated catheters (11/32); however, the difference was not statistically significant.

Mixed pathology

In mixed pathology patients, Vapnek et al. [27] performed a crossover study comparing HCICs (LoFric; single-use) with uncoated PVC catheters (reuse) and found that patients preferred the HCICs because of ease of use. This was also observed by Sutherland [39] (not included in the analysis but found to be relevant) and Stensballe [25] who both studied male subjects, and found that, respectively, 81% and 93% of the subjects preferred HCICs over uncoated catheters. Johansen [16] reported that patients prefer to use HCICs versus non-HCICs and that HCICs should be regarded as the gold standard for intermittent catheterization. Newman et al. [32, 36] found that at the end of their study in which patients using reusable non-hydrophilic catheters switched to single-use HCICs, 83% preferred to continue with the single-use HCICs. Yoshida et al. [10] compared SpeediCath hydrophilic catheters to uncoated catheters in women with neurogenic diseases. The willingness to use a hydrophilic catheter was significantly higher compared to an uncoated catheter (15/16 vs 6/13, p = 0.01). Similar conclusions were found by Leriche et al. [30] and Hedlund et al. [28] and in the review by Shamout et al. [6], the conclusion was the same. Interestingly Boucher et al. [34] came to a different conclusion, finding that after a short trial period, most children preferred their uncoated catheter and would not change to the HCIC. Only 10 patients (33%) would be ready to change their actual catheter for the HC. Of these patients, 1 was a male (by urethra) and 9 were females.

Adverse events

A total of 31 articles, most of them reviews (n = 19), have discussed adverse events (Table 4). The term adverse events cover a wide spectrum from hematuria, bleeding, urethral irritation, inflammation, and damage. Conflicting conclusions exist with at least 21 articles showing reduction in adverse events with HCICs while 8 either show no difference or reduced number of adverse events in the control (non-HCIC) group.

Table 4 Adverse events evidence levelSpinal cord injury

Five clinical studies and five reviews discussed adverse events in SCI patients. In general, the results point in different directions. Spinu [12] found a significantly lower number of post/intra/inter-catheterization bleeding episodes, and Cardenas [14] found a significant reduction in hematuria in the HCIC group (23%) versus the group using uncoated catheters (34%); however, the number of urethral bleeding episodes in the HCIC group was significantly higher than that in the uncoated catheters group (p < 0.05). On the contrary, De Ridder [24] did not observe any difference in hematuria, and Sarica [17] found that gel lubricated catheters reduced urethral microtrauma and pyuria while at the same time reducing hematuria when compared with HCICs. Samal [40] found no difference in urethral trauma between HCICs (SpeediCath) and standard PVC catheters; however, the lesions resulting after using PVC catheters were of greater extent. Most of the studies were affected by high drop-out rates making conclusions difficult. The five available reviews [8, 18, 41,42,43] all favored HCICs over standard catheters with respect to reducing adverse events.

An older (pre-2000) retrospective long-term study performed by Waller et al. [44] investigated urethral complications. Urethral damage was found in the study; however, it was induced before catheterization with HCIC (LoFric) was begun, and no urethral trauma was identified during the 5–9 year follow-up period.

Spina bifida

Four clinical studies on adverse events in SB patients were found (DeFoor [19], Burki [11], Kiddoo [20] and Lindehall [13]). None of the studies observed any significant difference between HCICs and non-HCICs with regard to hematuria. All four studies were performed on children, which may affect the outcome when compared with SCI patients, for whom all the studies were on adults.

Multiple sclerosis and benign prostate hypertrophy

No studies on adverse events focusing exclusively on MS or BPH patients were found.

Mixed pathology

Fourteen reviews and guidelines and three studies were on mixed pathologies. Of the three studies, both Stensballe [25] and Vapnek [27] measured significantly less microhematuria with the hydrophilic catheter and Leriche [30] experienced 5 episodes of bleeding with a gel coated catheter compared to no episodes with the hydrophilic catheter. Among the 14 reviews and guidelines, 11 concluded that hydrophilic catheters reduced the risk of microhematuria, urethral irritation, inflammation, and damage [1, 4, 6, 28, 29, 31, 45,46,47,48,49]. Two reported that HCIC may be preferable to standard non-coated catheters, but that uncoated catheters may be just as good [26, 50]; Rognoni et al. [5] reported that a risk reduction for hematuria associated with hydrophilic-coated catheters in general was not demonstrated.

Urinary tract infection

UTI is the most researched field concerning the efficacy of HCICs versus uncoated catheters; yet, it remains the area with the most contradictory findings. In general, the research community is divided into two groups: those that demonstrate reduced UTIs related to the use of HCICs and those who question the benefits of HCICs related to reduced UTI. Another complicating factor is the various UTI definitions and UTI frequency metrics used in the literature.

UTI definition

There is no universally accepted definition of UTI in individuals with neurogenic lower urinary tract dysfunction. Most studies use either (i) a symptomatic definition of UTI (i.e., antibiotic treatment has been prescribed) or (ii) a strict definition of symptomatic UTI [14]:

(a)

Antibiotic treatment has been prescribed.

(b)

Bacteriuria ≥ 102 CFU/mL.

(c)

At least one of seven UTI symptoms based on consensus guidelines (fever, autonomic dysreflexia [sweating, bradycardia, blood pressure elevation], increased spasticity, discomfort or pain over the kidney or bladder or during micturition, onset and/or increase in incontinence episodes, cloudy urine with increased odor, malaise, lethargy, or sense of unease).

(d)

Dipstick test is positive for leukocyte esterase.

However, other studies use either self-reported UTI, bacteriuria, or other definitions, making direct comparisons or meta studies complicated. For this study, we have not defined any exclusion or inclusion criteria regarding UTI definition; however, it could be argued that for catheter-associated UTIs, a higher level of bacteriuria should be accepted like the catheter-associated UTI definition from the 2009 International Clinical Practice Guidelines from the Infectious Diseases Society of America [51]. In general, it must be assumed that UTIs within both neurogenic and non-neurogenic patients suffering from urinary retention are either catheter associated or a result of incomplete bladder emptying.

UTI frequency

The frequency of UTI has been reported differently in the different studies, either as the percent of affected patients within the study period, total number of events in the study period, number of patients with two or more UTIs (i.e., recurrent UTI), or the average number of events/year.

In this review, a total of 20 clinical studies and 32 reviews and guidelines were found that investigated if hydrophilic catheters reduce UTI frequency when compared with uncoated catheters (Table 5). Ten out of the 20 clinical studies included numbers that could be extracted and compared (Table 6), although some presumptions like UTI frequency measures needed to be made. Among these 10 studies, all but two studies found a reduction in UTIs when using HCIC (however, not all findings where significant). The two studies that concluded differently used participants below 18 years of age. In all of the studies [3] that had patients below 18 years, the patients complained that the hydrophilic catheter was too slippery, which indicates that the catheters are touched on the sterile surface before insertion, which may explain the contradictory outcome related to UTI seen in two of these studies.

Table 5 Urinary tract infectionTable 6 Clinical studies with available data for a comparison of urinary tract infection (UTI)Spinal cord injury

For SCI patients, Cardenas et al. [