Does early intervention improve outcomes for patients with acute ureteral colic?

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https://doi.org/10.1007/s43678-020-00016-4 ORIGINAL RESEARCH

Does early intervention improve outcomes for patients with acute ureteral colic?

Grant D. Innes¹ · Joel M. H. Teichman² · Frank X. Scheuermeyer³ · Andrew D. McRae¹ · Eric Grafstein³ · James Andruchow¹ · Lucy Cheng⁴ · Michael R. Law⁴

Received: 12 June 2020 / Accepted: 26 August 2020 / Published online: 18 January 2021

Abstract

Objectives Early surgical intervention is increasingly employed for patients with ureteral colic, but guidelines and current practice are variable. We compared 60-day outcomes for matched patients undergoing early intervention vs. spontaneous passage.

Methods This multicentre propensity-matched cohort analysis used administrative data and chart review to study all eligible emergency department (ED) patients with confirmed 2.0–9.9 mm ureteral stones. Those having planned stone intervention within 5 days comprised the intervention cohort. Controls attempting spontaneous passage were matched to intervention patients based on age, sex, stone width, stone location, hydronephrosis, ED site, ambulance arrival and acuity level. The primary outcome was treatment failure, defined as rescue intervention or hospitalization within 60 days, using a time to event analysis. Secondary outcome was ED revisit rate.

Results Among 1154 matched patients, early intervention did not reduce the risk of treatment failure (adjusted hazard ratio 0.94; P = 0.61). By 60 days, 21.8% of patients in both groups experienced the composite primary outcome (difference 0.0%;

95% confidence interval − 4.8 to 4.8%). Intervention patients required more hospitalizations (20.1% vs. 12.8%; difference 7.3%; 95% CI 3.0–11.5%) and ED revisits (36.1% vs. 25.5%; difference 10.6%; 95% CI 5.3–15.9%), but (insignificantly) fewer rescue interventions (18.9% vs. 21.3%; difference − 2.4%; 95% CI − 7.0 to 2.2%).

Conclusions In matched patients with 2.0–9.9 mm ureteral stones, early intervention was associated with similar rates of treatment failure but greater patient morbidity, evidenced by hospitalizations and emergency revisits. Physicians should adopt a selective approach to interventional referral and consider that spontaneous passage probably provides better outcomes for many low-risk patients.

Keywords Renal colic · Ureteral colic · Ureteral calculi · Emergency treatment · Ureteroscopy Résumé

Objectifs L’intervention chirurgicale précoce est de plus en plus utilisée pour les patients atteints de coliques urétérales, mais les lignes directrices et la pratique actuelle sont variables. Nous avons comparé les résultats à 60 jours pour les patients appariés subissant une intervention précoce par rapport au passage spontané.

Les méthodes Cette analyse de cohorte multicentrique par appariement de propension a utilisé des données administratives et l’examen des dossiers pour étudier tous les patients admissibles des services d’urgence (ED) ayant des calculs urétéraux confirmés de 2,0-9,9 mm Ceux qui avaient planifié une intervention de calcul dans les cinq jours constituaient la cohorte d’intervention. Les témoins tentant de passer spontanément ont été appariés aux patients d’intervention en fonction de l’âge, du sexe, de la largeur du calcul, de l’emplacement du calcul, de l’hydronéphrose, du site de l’urgence, de l’arrivée de

Electronic supplementary material The online version of this article (https ://doi.org/10.1007/s4367 8-020-00016 -4) contains supplementary material, which is available to authorized users.

* Grant D. Innes Grant.innes@ahs.ca

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l’ambulance et du niveau d’acuité. Le résultat principal était l’échec de traitement, défini comme l’intervention de sauvetage ou l’hospitalisation dans les 60 jours, utilisant un temps à l’analyse d’événement. Le résultat secondaire était le taux de revisite à l’urgence

Résultats Sur 1154 patients appariés, une intervention précoce n’a pas réduit le risque d’échec du traitement (ratio de risque ajusté = 0,94 ; P = 0,61). Au bout de 60 jours, 21,8 % des patients des deux groupes avaient atteint le résultat primaire composite (différence = 0,0 % ; intervalle de confiance à 95 % -4,8 % à 4,8 %). Les patients d’intervention ont nécessité plus d’hospitalisations (20,1 % contre 12,8 % ; différence = 7,3 % ; IC 95 %, 3,0 à 11,5 %) et de nouvelles visites à l’urgence (36,1

% contre 25,5 % ; différence = 10,6 % ; IC 95 %, 5,3 à 15,9 %), mais (de manière non significative) moins d’interventions de sauvetage (18,9 % contre 21,3 % ; différence = 2,4 % ; IC 95 %, -7,0 à 2,2 %).

Conclusions Chez des patients appariés présentant des calculs urétéraux de 2,0 à 9,9 mm, l’intervention précoce a été asso- ciée à des taux similaires d’échec du traitement mais à une morbidité plus importante des patients, comme en témoignent les hospitalisations et les revisites aux urgences. Les médecins devraient adopter une approche sélective de l’orientation interventionnelle et considérer que le passage spontané offre probablement de meilleurs résultats pour de nombreux patients à faible risque

Clinician’s capsule

What is known about this topic?

Early surgical intervention is increasingly employed for ureteral colic, but supporting evidence is sparse and intervention may increase morbidity for some.

What did this study ask?

Does early intervention improve outcomes for patients with 2–9.9 mm ureteral stones?

What did this study find?

Among propensity-matched patients, early intervention had similar treatment failure rates, but more hospitalizations and ED revisits than spontaneous passage.

Why does this study matter to clinicians?

Non-selective referral of ureteral colic patients for early stone intervention may increase patient morbidity.

Research has shown that early stone removal is achievable with relatively few complications [6–8, 18–20]; however, studies supporting emergency intervention lack control comparisons and patient-oriented outcomes [6–8, 18–20]. Fur- thermore, procedural sequelae such as infection, bleeding, stent pain and incomplete stone removal may offset benefit for some patients [7, 8, 18, 19, 21]. Two recent population- level studies found that rising stone intervention rates were associated with increased post-treatment morbidity mani- fested by ED revisits and hospitalizations [15, 16]. No trials have compared early intervention to spontaneous passage for ED patients with acute ureteral colic.

Limited evidence, conflicting guidelines and high practice variability suggest uncertainty regarding the role of early intervention [9–11]. Given this evidence gap, our objective was to compare 60-day treatment failure, defined as the need for rescue intervention or hospitalization, in patients having early intervention compared to propensity-matched controls undergoing trial of spontaneous passage.

Methods

Design and setting

We used administrative data and structured chart review to study all ED patients with acute ureteral colic seen in two Canadian health regions during 2014. The Calgary Health Region has four adult hospitals serving 1.4 million people, while Vancouver Coastal Health (VCH) has five hospitals serving 1.2 million people. The regions have similar demographics, health infrastructure and technology. Both have integrated care systems with regionalized program over- sight, data management and information systems. Urolo- gists and emergency physicians have equivalent training

Introduction

Ureteral colic is a common disorder that compromises quality of life and generates substantial system utilization [1–4].

During acute stone episodes, many patients seek emergency department (ED) care. The technological imperative suggests that what can be done should be done [5], and it is intuitive to many physicians that the best treatment is to remove the offending stone, which should logically reduce patient morbidity, downstream ED visits, hospitalizations and costs [6–8]. Despite guidelines indicating that most patients are appropriate for a trial of spontaneous passage [9–11], and passage success rates of 60–90% [9, 10, 12–14], early intervention rates have doubled during the last decade and practice is highly variable [15–17]. Recent Canadian data showed seven-fold differences in index intervention in two similar health regions [16].

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and competency requirements, and managed patients at their discretion during the study period. Calgary practice favors early intervention while VCH physicians typically initiate a trial of spontaneous passage [16]. This dichotomy provides an opportunity to study comparable patients exposed to different treatments. Regional care integration and health data collection allowed us to conduct a population-based study of consecutive patients with a low likelihood of missing outcome events.

Subjects

We used administrative data to identify all ED patients who had a renal colic diagnosis based on the following ICD-10 codes: [3] calculus of kidney (N200), calculus of ureter (N201), calculus of kidney and ureter (N202), hydronephrosis with renal and ureteral calculus obstruction (N132), unspecified renal colic (N23), and unspecified urinary calculus (N209). Eligible patients required computed tomography (CT) showing a 2.0–9.9 mm ureteral stone, including assessment of stone width, location, and hydronephrosis.

A 2.0–9.9 mm range encompasses patients who, based on current practice, might be offered either spontaneous passage or early intervention [10, 11, 16]. We excluded patients with isolated intraparenchymal renal stones, which require a different management approach; patients referred from the community for direct urology care, who are a selected group already deemed to require surgical involvement; patients who had a prior ED ureteral colic visit within 30 days (to study incident cases and avoid those already failing outpatient management); and patients with out-of-region postal

Cohort definitions

Patients who underwent stone destruction, extraction, stenting or lithotripsy within 5 days of the index ED presentation comprised the early intervention cohort. Those who had no intervention for more than 5 days comprised the spontaneous passage (control) cohort. Because there are no accepted definitions for what constitutes an early intervention or a sufficient trial of spontaneous passage, the 5-day definition was determined by investigator consensus. Patients discharged for a trial of passage who required an ED revisit (outcome event) followed by rescue intervention within 5 days were evaluated in their intended treatment group (spontaneous passage) and their intervention was considered an adverse outcome (Fig. 1). Having already experienced an adverse outcome (ED revisit) during conservative management, these patients could not be considered early intervention patients.

Outcomes

Our primary outcome was treatment failure, defined by the need for intervention or hospitalization after index discharge but within 60 days. Interventions included stent placement, extracorporeal shock wave lithotripsy, and ureteroscopy with stone basketing or laser lithotripsy. We considered post- index hospitalization or surgical intervention to be rescue events reflecting failure of the intended management strat- egy or highlighting patients in severe distress [15, 21, 22].

We chose 60 days, because prior research showed that most outcomes occurred within 30 days, 15% occurred between 30 and 60 days, and few occurred later [16]. Our secondary outcome was 60-day ureteral colic-related ED revisits [15, 16, 21]. Many patients underwent scheduled procedures aris- ing from study-related interventions (i.e. cystoscopy for stent removal). These were not considered rescue procedures or outcome events.

Data

We obtained patient demographics, arrival mode, triage acuity, diagnosis, index disposition, ED revisits, hospitalizations, procedures and patient diagnoses from regional hospital databases. To assure inclusion of all relevant procedures, we searched the VCH regional diagnostic imaging database to identify outpatient lithotripsy procedures as well as inpa- tient or outpatient surgical procedures not coded in hospital discharge abstracts. Urological interventions in Calgary occur at a single site and are reliably captured in administrative data, but we verified these by auditing a 20% sample of electronic patient charts. The Alberta Strategic Data Analyt- ics unit oversees health data capture and management within

Fig. 1 Study flow diagram and cohort definition

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does so for Vancouver sites. Trained research assistants reviewed imaging reports to identify stone characteristics.

To assess data abstraction reliability, 2 research assistants blinded to patient outcomes independently reviewed 100 consecutive imaging reports. We used Cohen’s kappa to describe interobserver agreement.

Analysis

To reduce selection bias, we employed propensity score matching techniques to identify controls who were similar to early intervention patients [23, 24]. Using [early intervention] as the dependent variable in logistic regression models, we incorporated the following potential explanatory variables: patient age, sex, arrival mode, city, triage acuity, triage heart rate and blood pressure, stone width in millimeters, stone location (proximal, middle or distal ureter), degree of hydronephrosis, wait time to physician (a marker of per- ceived priority), and ED length of stay (LOS—a marker of treatment responsiveness). These variables were part of standard data collection at the study sites or were available in diagnostic imaging reports. Based on the predicted propensity of undergoing early intervention, actual intervention

subjects and controls were matched using a nearest neighbor pair match without replacement.

Before and after matching, we used standardized differences to assess covariate balance, with discrepancies > 10%

suggesting significant imbalance [23]. We converted variables dependent upon site-specific performance, such as ED LOS and wait time, to standardized values within-site before aggregating across sites. We then evaluated primary and secondary outcomes in the matched cohorts using a time to event analysis. We plotted events on Kaplan–Meier curves and generated hazard ratios with 95% CI using the control cohort as the reference group. Patients who did not have an outcome event within 60 days were censored at that time.

We used Cox Proportional Hazards models, with explanatory variables including patient and stone characteristics, and standardized EDLOS, to adjust for residual covariate imbalance. Based on previous data showing 30-day event rates of 17% vs. 11% in surgical vs. medical patients [25], we determined that samples of 524 patients per group would provide 80% power to detect a similar difference in this analysis. Statistical analyses were performed using the R statistical package (R Foundation for Statistical Computing; https ://www.R-proje ct.org/).

Table 1 Characteristics of control and intervention patients in unmatched and matched analyses:

Standardized differences > 10% (bold) suggest significant imbalance

a Patients with moderate or severe hydronephrosis. Stranding refers to perirenal edema seen on CT. Standardized wait time and LOS, expressed as the number of standard deviations from the site mean, adjust for site-based wait time differences

Unmatched patients (N = 3081) Matched patients (N = 1154) Control

N = 1913 (%) Intervention

N = 1168 (%) Standardized

Difference (%) Control

N = 577 (%) Intervention

N = 577 (%) Standardized Difference (%)

Male sex 73.2 67.4 − 12.7 73.0 67.1 − 12.5

EMS arrival 17.0 19.6 6.8 19.1 18.9 − 0.9

Hi-acuity (CTAS 1–2) 42.8 53.9 22.5 50.0 52.0 4.2

Calgary site 42.9 86.8 104.1 79.0 78.0 − 2.1

Proximal stone 19.1 36.3 39.2 26.0 25.0 − 0.8

Middle stone 7.8 13.3 17.7 10.9 10.1 − 4.5

Distal stone 73.1 50.4 − 47.9 63.1 65.0 3.6

Hydronephrosis^a 27.8 48.1 42.9 38.0 38.1 0.3

Stranding 58.7 58.9 0.5 57.7 54.8 − 5.6

Mean Mean Mean Mean

Age in years 49.7 51.9 15.2% 50.9 50.7 − 1.6%

Heart rate 77.1 80.8 24.5% 79.3 80.8 10.2%

Systolic BP (mmHg) 144 144 − 1.5% 144 142 − 7.0%

Stone length (mm) 4.1 6.1 83.6% 5 5 − 3.1%

Stone width (mm) 3.7 5.1 90.1% 4.4 4.4 − 2.7%

Standardized wait − 0.04 − 0.09 − 5.2% − 0.08 − 0.09 − 1.5%

Standardized LOS − 0.11 0.42 50.7% 0 0.09 8.6%

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Fig. 2 Propensity score distributions for unmatched and matched cohorts. Propensity scores reflect the conditional probability, based on all measured covariables, that a patient would undergo early intervention

Table 2 Sixty-day outcomes: unmatched and propensity-matched comparisons

Treatment failure (1° outcome) = hospitalization or rescue intervention within 60-days. Δ = difference between control and intervention groups

a Hospitalizations and rescue procedures are not exclusive; most rescue procedures occurred during an unplanned hospitalization

b Any procedure includes rescue procedures and planned stent removal procedures but does not include early interventions that determined group membership. Bold values are significant

Unmatched analysis (all patients, N = 3081) Propensity matched analysis (N = 1154) Control

(N = 1913) (%) Intervention

(N = 1168) (%) Δ (%) 95% CI Control

(N = 577) (%) Intervention

(N = 577) (%) Δ (%) 95% CI

Treatment failure 16.8 24.4 7.6 4.6, 10.6 21.8 21.8 0.0 − 4.8, 4.8

ED revisit 22.3 34.0 11.7 8.4, 15.0 25.5 36.1 10.6 5.3, 15.9

Rescue intervention 16.2 21.2 5.0 2.2, 8.0 21.3 18.9 −2.4 − 7.0, 2.2

Hospitalization^a 7.5 17.2 9.7 7.3, 12.2 12.8 20.1 7.3 3.0, 11.5

Any procedure^b 16.8 37.2 20.4 17.2, 23.7 21.8 31.5 9.7 4.6, 14.8

Fig. 3 Time to event for primary and secondary outcomes in matched cohorts

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Results

We studied 3081 consecutive eligible patients (Fig. 1). Mean age was 50.6 years and 71% were male. Table 1 summarizes baseline characteristics for control and intervention cohorts before and after propensity matching. Interobserver agreement on stone characteristics was excellent, with kappa values of 0.97 (length), 0.92 (width), 0.95 (location), and 0.90 (hydronephrosis severity). Overall, 1168 patients (37.9%) had early intervention, including 24% with stones < 5 mm wide, 55% with stones from 5.0 to 6.9 mm, and 74% with stones ≥ 7 mm. In the unmatched analysis, intervention patients were older, more often female, had larger and more proximal stones, more severe hydronephrosis, and were more likely to arrive by ambulance. In the propensity-matched analysis, we studied 577 patients in each group. Control and intervention cohorts were balanced on stone size, location and hydronephrosis, as well as all other parameters except sex (73% vs. 67% male). Figure 2 shows that propensity scores were similarly distributed in the matched cohorts.

Unmatched analysis showed worse outcomes with early intervention, an expected finding because more severe cases were selected for intervention; but these differences dimin- ished after matching (Table 2). In the matched analysis, early intervention patients required more hospitalizations (20.1% vs. 12.8%; difference 7.3%; 95% CI 3.0–11.5%), but had (insignificantly) fewer rescue interventions (18.9% vs.

21.3%; difference − 2.4%; 95% CI − 7.0 to 2.2%). Time to event analysis (Fig. 3) showed that 21.8% in both groups experienced the composite primary outcome of treatment failure (difference 0%; 95% CI − 4.8 to 4.8%), and that intervention patients required more ED revisits (36.1% v. 25.5%;

difference 10.6%; 95% CI 5.3–15.9%).

Cox proportional hazard modeling (supplemental material, Appendix Table 1) demonstrated that, in these matched cohorts, early intervention did not significantly reduce treatment failure. Multivariable models showed that the strongest predictors of treatment failure were increased stone width [adjusted hazard ratio (aHR) = 1.1 per mm], a proximal or middle stone (aHR = 2.3 and 1.8), and prolonged ED length of stay (aHR = 1.1 per standard deviation). Age, sex, acuity level, arrival mode, day, time, and degree of hydronephrosis were not significantly associated with treatment failure.

Discussion

Interpretation

Among matched stone patients with equal probability of spontaneous passage or early intervention, treatment failure rates were similar with both approaches. While we found

no difference in the primary outcome, early intervention was associated with increased morbidity, evidenced by substantially more ED revisits and hospitalizations. Early intervention was also associated with higher system utilization: by definition, 100% of early intervention patients had stone intervention, with 21.8% requiring a rescue procedure or hospitalization within 60 days. In contrast, 21.8%

of matched controls required intervention or hospitalization during their trial of passage.

Acknowledging that intervention benefits patients with refractory symptoms and large or infected stones [10], our findings infer that there are many patients for whom procedure-related morbidity exceeds that related to spontaneous passage. Previous studies confirm that ureteroscopic intervention carries morbidity [7, 18, 19, 21], and our data show that one-third of intervention patients experienced difficulty sufficient to trigger ED revisits, a 10.6% increase relative to controls. Our experience is that they did so because of clot or stent pain, post-op ureteral edema or spasm, incomplete stone removal, infection or, frequently, ongoing pain concerning to patients who expected their symptoms to resolve rapidly after intervention. The fact that intervention patients suffered higher ED revisit and hospitalization rates than matched controls suggests that intervention is being employed not only in patients who benefit, but also in patients who might do well with trial of spontaneous passage.

Other researchers have used matching approaches to compare conservative with interventional management. Hol- lingsworth studied insurance data, finding that intervention was associated with higher costs, similar post-index hospitalization rates and fewer ED visits [26]. Because data were insurance-based, modeling covariates included age, employment, insurance type and region. Important determinants like stone size, location and hydronephrosis were unaccounted for, and it is unlikely these were equally distributed across the medical and surgical groups. Further, this study excluded women and patients who underwent stenting, which is a common cause of morbidity. Dauw used propensity-matching to compare early intervention with medical expulsive therapy, finding that disability and costs were higher for intervention patients, but this study also lacked stone-related covariables, instead matching patients on age, sex, insurance type, region, employment and Charlson score [22].

Clinical implications

Our study is concordant with population-level data showing that ED revisits and readmissions (morbidity markers) increase in parallel with early intervention rates [15, 16]. Based on these findings, physicians can advise patients that surgery is not

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always a better option, despite its intuitive appeal. Although this study indicates that some patients will experience worse outcomes with early intervention, it does not clarify which patients may benefit and which will not. We found that stone size and (proximal) location were the main determinants of treatment failure (supplemental material, Appendix Table 1), therefore, refer readers to Canadian and European guidelines that propose 5 mm and 6 mm treatment thresholds, respec- tively [9, 11]. Adopting this approach would identify 11–21%

of patients as potential early intervention candidates [16]. We also feel that a history of prior successful spontaneous stone passage, favorable response to ED treatment, distal stone location, and patient preference for non-intervention should be considered in emergency management decisions.

Strengths and limitations

We studied a large consecutive sample from nine hospitals in two cities, including all patients who, based on stone size, practice guidelines, and site preferences, might be exposed to either treatment approach. Our findings apply to patients with 2.0–9.9 mm ureteral stones in primary care and emergency settings. They are not relevant to patients who have already failed a trial of spontaneous passage. Although we were able to incorporate the main determinants of stone passage in our analyses, our retrospective design precluded detailed descrip- tion of patient comorbidities. We studied an interventional approach, not a single procedure, and outcomes may differ based on the operator and specific procedure performed.

Notably, we did not isolate the effect of ureteral stenting. Our methods mimic those of Shah et al. [27] who defined passage success by the absence of subsequent intervention, but we did not verify stone passage, nor assess patient experience, quality of life or functional status. We defined adverse events based on ED revisits and hospitalizations, which are markers of patient distress [15, 16], but some patients may have suffered significant morbidity without seeking hospital-based care. Men were over-represented in our sample, because they more often undergo CT imaging [28].

Propensity matching is an effective way to balance control and intervention groups and reduce treatment selection bias, but it falls short of randomization, particularly if there are important unmeasured covariables. Propensity matching also depletes sample size, which is unfortunate but unavoidable, because the treatment groups have many members for whom conditional probability of intervention differs substantially (Fig. 2). Despite sample size shrinkage, our final sample is large relative to most renal colic studies, it exceeded our sample size estimate, and cohorts were well balanced on all important determinants. Finally, this research is subject to the limitations of observational research, and a randomized trial would be helpful to confirm our findings. Such a trial

status, clarify patient subgroups most likely to benefit, and address the importance of other predictors such as previous stone experience, prior interventions and renal comorbidities.

Conclusion

In matched patients with 2.0–9.9 mm ureteral stones, early intervention was associated with similar rates of treatment failure, and greater patient morbidity reflected by hospitalizations and emergency revisits. Physicians should adopt a selective approach to interventional referral and consider that spontaneous passage probably provides better outcomes for many low-risk patients.

Acknowledgements We wish to thank Heidi Boyda, Kevin Lonergan, Dongmei Wang, Lena Cuthbertson, Jennifer Dotchin, Kelsey Innes, Bryce Weber, Kevin Carlson, Eddy Lang, Peter Dickhoff, Kat Koger, David Ward and Brit Sunderani for their valuable contributions. Within the last 3 years, Dr. Teichman has received grants and personal fees from Boston Scientific, grants from Cook Urologic, personal fees from Urigen and non-financial support from Innova Quartz, although none were related to this research. None of the other investigators have any potential conflicts to report.

Funding This study was funded by the MSI Foundation (a non-profit health research funding agency). MRL received salary support through a Canada Research Chair and the Michael Smith Foundation for Health Research.

Compliance with ethical standards

Conflict of interest JA reports grants from MSI Foundation, during the conduct of the study; MHT reports grant from Cook Urologic, from Boston Scientific, from Lumenis, other from Urigen, outside the pre- sent work; the remaining authors have nothing to disclose.

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Affiliations

Grant D. Innes¹ · Joel M. H. Teichman² · Frank X. Scheuermeyer³ · Andrew D. McRae¹ · Eric Grafstein³ · James Andruchow¹ · Lucy Cheng⁴ · Michael R. Law⁴

Joel M. H. Teichman

JTeichman@providencehealth.bc.ca Frank X. Scheuermeyer

frank.scheuermeyer@gmail.com Andrew D. McRae

amcrae@ucalgary.ca Eric Grafstein

egrafstein@providencehealth.bc.ca James Andruchow

James.Andruchow@albertahealthservices.ca Lucy Cheng

lucy.cheng@ubc.ca Michael R. Law michael.law@ubc.ca

1 Department of Emergency Medicine and Department of Community Health Sciences, University of Calgary, Room C231, Foothills Medical Centre, 1403, 29 Street NW, Calgary, AB T2N 2T9, Canada

2 Department of Urologic Sciences, University of British Columbia, Vancouver, BC, Canada

3 Department of Emergency Medicine and Center

for Healthcare Evaluation and Outcome Sciences, St Paul’s Hospital, University of British Columbia, Vancouver, BC, Canada

4 Centre for Health Services and Policy Research, School for Population and Public Health, University of British Columbia, Vancouver, BC, Canada