Anesthesia & Analgesia:
General Articles: Research Report
Predictive Factors of Early Postoperative Urinary Retention in the Postanesthesia Care Unit
Keita, Hawa MD, PhD; Diouf, Elisabeth MD; Tubach, Florence MD; Brouwer, Tammo MD; Dahmani, Souhayl MD; Mantz, Jean MD, PhD; Desmonts, Jean-Marie MD
Department of Anesthesiology and Intensive Care, Hospital Bichat-Claude Bernard, Paris, France
Accepted for publication January 27, 2005.
Address correspondence and reprint requests to Hawa Keita, MD, PhD, Department of Anesthesiology and Intensive Care, Hospital Bichat, 46 rue Henri Huchard, 75018 Paris France. Address e-mail to firstname.lastname@example.org.
Urinary retention is a common postoperative complication associated with bladder overdistension and the risk of permanent detrusor damage. The goal of this study was to determine predictive factors of early postoperative urinary retention in the postanesthesia care unit (PACU). We prospectively collected, in 313 adult patients, variables including age, gender, previous history of urinary tract symptoms, type of surgery and anesthesia, intraoperative administration of anticholinergics, amount of intraoperative fluids, IV morphine titration, and bladder volume on entry to the PACU. For each patient, bladder volume was measured by ultrasound on entry and before discharge from the PACU. Urinary retention was defined as a bladder volume larger than 600 mL with an inability to void within 30 min. Predictive factors were identified by multivariate analysis. The incidence of urinary retention in the PACU was 16%. In the multivariate analysis only the amount of intraoperative fluids (≥750 mL; P = 0.02; odds ratio = 2.3), age (≥50 yr; P = 0.008; odds ratio = 2.4), and bladder volume on entry to PACU (≥270 mL; P = 0.0001; odds ratio = 4.8) were found to independently increase the risk of urinary retention. Considering the clinical impact of undiagnosed postoperative urinary retention, these results suggest systematic evaluation of bladder volume with a portable ultrasound device in the PACU, especially in patients with risk factors.
Retention of urine is a common postoperative problem associated with the risk of overdistension and permanent detrusor damage (1,2). Damage to the detrusor muscle is characterized by motility problems or even atony, especially in the elderly (3). Furthermore, large retention volume is a predisposing factor for prolonged micturition difficulties because of the need to re-catheterize the patients (1). In the past, a diagnosis of urinary retention relied on detection of a palpably distended bladder or a patient experiencing discomfort in the setting of being unable to void after surgery. Diagnosis was confirmed by bladder catheterization. These techniques are crude and yield imprecise results. They have been used in most studies that attempted to determine incidence and factors influencing postoperative urinary retention (POUR). These investigations found rates ranging from 7% to 52% and reported that certain types of anesthesia, surgery, analgesics, anticholinergics, and underlying medical conditions may predispose patients to develop POUR (4–8). Recent refinements of portable ultrasound technology have enabled rapid, noninvasive, and reliable measurements of bladder volume for postoperative monitoring of urinary bladder volume (9–12).
The aim of this study was to identify predictive factors for early POUR in the postanesthesia care unit (PACU) in a large cohort of patients. We studied the effects of age, gender, previous history of urinary tract symptoms, type of surgery, type of anesthesia, intraoperative administration of anticholinergics, amount of intraoperative fluids, IV morphine titration in the PACU and bladder volume on entry to the PACU as possible predictors of POUR.
The study was conducted as a prospective observational study. It was approved by the IRB, who considered that written consent by the patients was not necessary, as the study represents a noninterventionnal analysis of our standard practice. Patients were included consecutively as they presented after a planned surgery. During a 4-mo period, we prospectively collected for each operated patient, using general or spinal anesthesia, demographic, surgical, anesthetic, and postoperative data. Exclusion criterion was intraoperative catheterization (systematically reported by the operating room nurse in the patient’s chart). Patients were scheduled for orthopedic, vascular, thoracic, abdominal, or urologic, nonambulatory, surgery. The specific techniques of anesthesia were at the discretion of the anesthesia care team. For each patient, bladder volume was measured by ultrasound using the BladderScan BVI 3000 (Diagnostic Ultrasound™, Redmond WA) at three different times: on entry to PACU, just before voiding when patients reported the need to void, and before discharge from the PACU. All ultrasound measurements were made by an anesthesiologist trained for the use of the BladderScan BVI 3000.
Patients were encouraged to void when bladder volume was more than 600 mL. We ensured privacy and isolated the patient between 2 screens and let him/her alone for 30 min. Patients were allowed to sit in the bed but not to stand. POUR was defined as an inability to void at bladder volume >600 mL within 30 min. If POUR developed, the bladder was drained with in-and-out catheterization.
For the purpose of statistical analysis, data were categorized as reported in Table 2. In the analysis, all factors have been considered as binary variables. Continuous variables were divided at their median values into dichotomous variables. The following variables were considered as potential predictor factors of urinary retention: age (<50 yr versus ≥50 yr), gender (female versus male), history of urinary tract symptoms (including benign prostatic hypertrophy) (yes versus no), type of surgery as previously classified by Dahmani et al. (13) (major versus intermediate and minor), localization of surgery (hernia, anal, or other localization), duration of surgery (<60 mn versus ≥60 mn), type of anesthesia (general versus spinal), duration of anesthesia (<80 mn versus ≥80 mn), intraoperative administration of atropine or atropine-like drugs (analgesics such as nefopam or tramadol) (yes versus no), amount of intraoperative fluids (<750 mL versus ≥750 mL), IV morphine titration in PACU (yes versus no), and bladder volume on entry in PACU (<270 mL versus ≥270 mL).
The description of the population was done by the use of contingency tables. The incidence of bladder volume more than 600 mL and incidence of POUR were computed. Predictive factors of urinary retention were identified both by univariate analysis (Pearson’s χ2 test) and multivariate analysis (logistic regression with stepwise procedure) to assess the specific effect of each predictor. Factors included in the multivariate model were those that had reached a significance level P < 0.20 in the univariate analysis.
Three-hundred-thirteen patients (128 females, 185 males) were included. The mean patient age was 46 yr (range, 16–88 yr). Half of the patients (n = 160) were scheduled for orthopedic surgery. Hernia repair or anal surgery was performed in 45 patients. Intermediate and minor surgery represented 87% of the surgical procedures. Forty-two patients received spinal anesthesia with bupivacaine 0.5% for the following surgeries: urologic (n = 23), hernia repair (n = 7), anal (n = 5), orthopedic (n = 4), and vascular (n = 3). The main characteristics of the study population are summarized in Table 1. Distribution of bladder volumes measured with BladderScan BVI 3000 on PACU entry and discharge is shown in Figure 1.
Seventy-six patients (24%) had a bladder volume more than 600 mL before discharge. Of these, 53 patients (16% of the entire sample) were unable to void within 30 min and were considered to have POUR. In the univariate analysis, the factors associated with the occurrence of POUR (P < 0.20) were age (≥50 yr), type of surgery (major), duration of surgery (≥60 mn), duration of anesthesia (≥80 mn), amount of intraoperative fluids (≥750 mL), and bladder volume on entry to PACU (≥270 mL). In contrast, there was no link between the occurrence of POUR and sex, history of urinary tract symptoms, localization of surgery, type of anesthesia, intraoperative administration of atropine or atropine-like drugs, or IV morphine titration in PACU (Table 2).
In the multivariate analysis, the independent predictive factors for POUR were age (≥50 yr), amount of intraoperative fluids (≥750 mL), and bladder volume on entry in PACU (≥270 mL) (Table 3).
Using ultrasound monitoring of bladder volume, we found that early POUR occurred in 16% of adult nonambulatory patients. Age (≥50 years), amount of intraoperative fluid (≥750 mL), and bladder volume on entry in PACU (≥270 mL) were identified as predictive factors for this outcome.
POUR is reported with incidences ranging between 7% and 52% in the literature. It is difficult to compare published studies, as various definitions for this complication have been proposed: an inability to void urine for 6 to 12 hours after the surgical procedure (14), a palpably distended bladder, a certain volume of urine drained after catheterization (400 to 600 mL) (6,9,15), or a patient experiencing discomfort in the setting of being unable to void (5,15). The specificity and accuracy of these criteria are questionable. Ultrasound allows a reliable measurement of bladder content (9–12). When a scan-predicted volume of 100 mL or more was used as a cutpoint for clinical importance, the BladderScan BVI exhibited a sensitivity of 97%, a specificity of 91%, and an overall accuracy of 94% (16). Pavlin et al. (17) reported that, in 15 patients, the difference between ultrasound measurement and urine collection was <15 mL. They also pointed out that the diagnosis of bladder distention by nurses agreed with diagnosis by ultrasound device in only 54% of cases (17). Another concern is that painless retention is described in 61% of patients with retention after general surgery operation (14). Recently, it has been reported that bladder stretching was experienced by only half of the patients when bladder volume measured by ultrasound exceeded 500 mL (18). Several studies using ultrasound have considered a volume ranging between 400 and 600 mL to be associated with an inability to void as a reasonable criteria to consider POUR (11,18,19). Such values are relevant, as the recommended maximum bladder urine volume is 400–500 mL in adults (3), although there is a large inter-individual difference in maximum bladder capacity (12). This is important because overdistention must not be allowed to persist for more than a few hours to prevent bladder dysfunction (1,2,20). With a limit of bladder volume measured by ultrasound fixed at 500 mL, Lamonerie et al. (18) reported a prevalence of 23.7% POUR on discharge from the PACU in 177 non-ambulatory surgical patients. In the present study, the prevalence of urinary retention was decreased (16%). One explanation could be that we defined a larger bladder volume (600 mL versus 500 mL) as a criterion for POUR. Other hypotheses are a longer duration of surgery (a mean of 134 minutes versus 78 minutes in our study) and a larger percentage of patients benefited from spinal anesthesia in the Lamonerie et al. study (26% versus 13.5% in the present study). Both of these factors are likely to promote urinary retention (11,18,19).
Numerous factors previously described in the literature as risk factors of postoperative urinary retention were not confirmed in our study. In fact, although we observed a more frequent incidence of POUR for patients with a history of urinary tract symptoms (20%), spinal anesthesia (17.3%), or hernia repair/anal surgery (24.4%), these factors were not been considered to be predictive. Similar observations concern sex, intraoperative administration of atropine or atropine-like drugs, and postoperative morphine titration. Other variables, such as the type and duration of surgery or anesthesia, were associated with POUR in the univariate analysis but did not appear as independent factors. Only age, amount of intraoperative fluids, and bladder volume on entry to PACU were independent predictive factors of early POUR. Several reasons could be suggested to explain why our results are not fully consistent with those of previous studies. First, contrary to numerous earlier studies, urinary retention was defined on an objective and reliable criterion: a bladder volume of more than 600 mL, diagnosed by ultrasound associated with an inability to void. Second, we investigated only the early postoperative period in the PACU and not later periods at the surgical wards. Third, we studied a large cohort of patients undergoing a variety of surgical procedures and not a selected group of patients having specific surgical procedures, demographic characteristics, or anesthetic techniques. Nevertheless, our series of patients probably included too few subjects in subgroups, such as a spinal anesthesia group or patients undergoing hernia repair or anal surgery, to permit definitive conclusions about their association with POUR in the PACU.
Age older than 50 years appears to be a predictive factor of urinary retention. The coordination of bladder filling, urine storage, and voluntary micturition are under the control of supraspinal central, somatic, and visceral neurons in the thoracic, lumbar, and sacral spinal cord (21). Degeneration of this pathway with aging could explain the increased incidence of POUR in older patients. It could also be suggested that this group is at increased risk because it includes males with enlarged prostates.
The amount of intraoperative fluids is an expected factor for POUR. In fact, several studies have highlighted this variable. However, the quantities of fluids administrated in these studies were excessive (over 4 L) (1,22). Petros et al. (5) reported, in 2 studies, a significant increase in POUR in patients who had received more than 1000 mL (6) and 1200 mL of IV perioperative fluid. In our study, we only calculated the intraoperative fluids administered and not the total amount of perioperative fluids. There is a good correlation between the volume of fluid infused intraoperatively and bladder volume at the end of surgery (10). The present study confirms and extends this result, as the amount of intraoperative fluids (≥750 mL) also highly predicts early POUR (odds ratio = 2.3). Nevertheless, good perioperative fluid administration (15–20 mL/kg) has been shown to reduce the frequency of postoperative symptoms, particularly nausea and vomiting (23,24). For the first time, we report that bladder volume on entry to the PACU is predictive of POUR. In fact, patients with more than 270 mL urine on arrival have an increased risk of urinary retention (odds ratio = 4.8). This factor is important because in our study population half of the patients had a bladder volume ≥270 mL, and of these patients 27.6% developed POUR. These results strongly support the need of bladder monitoring for most patients admitted in the PACU.
In conclusion, in the early postoperative period, urinary retention diagnosed with systematic ultrasound monitoring of bladder content occurred with an incidence of 16% in non-ambulatory patients. Considering the clinical impact of undiagnosed POUR, these results suggest the routine evaluation of bladder content in the PACU on entry and before discharge, especially in patients older than 50 years, receiving more than 750 mL intraoperative fluids, or with bladder volume exceeding 270 mL on entry to PACU.
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