Bladder Pressure Measurements and Urinary Tract Infection in Trauma Patients

Patients and Methods

We performed a prospective evaluation of all patients admitted to the surgical trauma ICU (STICU) between January 2006 and December 2009 at our Level 1 trauma center. A dedicated epidemiology nurse collected daily data on the presence of urinary drainage catheters (UDCs), the performance of BPMs, and the diagnosis of UTI [4]. Patients with and without UTIs were compared using demographics, Injury Severity Score (ISS), and outcomes from data obtained from the trauma registry. Comparisons also were performed between patients who had BPM and those who did not.

The BPMs were performed at the discretion of the ICU team when there was a concern about intra-abdominal hypertension. A closed system was used in which the UDC remained connected to the urine collection bag. Forty-five mL of saline was injected through a two-way valved sideport with subsequent measurements through the sideport. Using this technique, the catheter drainage system was never disconnected, ensuring that the closed system was not violated.

Continuous variables were evaluated using the Wilcoxon rank sum test, and nominal variables were evaluated using the Fisher exact test. Logistic regression was used to determine independent predictors of UTI and death. This study was approved by the Virginia Commonwealth University Institutional Review Board.

Results

A total of 1,641 patients were included in the trial. There were 285 patients who never had a UDC placed, and only one of these patients had a UTI (0.35%). Of the remaining patients who had a UDC, 1,292 never had a BPM taken, and 37 had a UTI (2.86%). The remaining 64 patients had a UDC and BPM, and 8 of these had a UTI (12.50%; p<0.0001). As shown in Table 1, the UTI group was sicker, with a greater length of stay (LOS) and more UDC days than the no-UTI group.

Comparisons based on whether a BPM was obtained found that the BPM group had more UDC days (15.6±16.0 BPM vs. 5.4±7.3 no BPM; p<0.0001), yet no differences in UTI rate/1,000 UDC days (5.7 no BPM vs. 8.0 BPM; p=0.5291) compared with those patients who did not have BPM. Subset evaluation of the 64 patients with BPM found that those patients who also had UTIs had more BPM than those with no UTIs (22±16.1 UTI vs. 9.34±8.34 no UTI; p=0.0147). There was no difference in UTI rates in those patients who had elevated values (>20 mm Hg) compared with those with only normal measurements (three in the<20 mm Hg group and four in the >20 mm Hg group, one not documented; p=0.1771). Logistic regression demonstrated only UDC days to be a predictor of UTI, as shown in Table 2. The ISS (1.083; 95% confidence interval [CI] 1.063–1.104; p<0.0001) and age (1.051; 95% CI 1.037–1.065; p<0.0001) were the only predictors of death.

Discussion

In 2002, Foxman noted that there were well over one million cases of catheter-related UTIs, making them the most common nosocomial infection [5]. Consequently, a great deal of time has gone into identifying risk factors associated with UTIs in an effort to decrease these rates. Female patients have consistently been found to be 1.5 times more likely than their male counterparts to suffer a catheter-related UTI [6,7]. Other risk factors include medical ICU versus surgical ICU stays, previous antibiotic exposure, duration of catheter use, and ICU length of stay (LOS) [6–9].

On the basis of these findings, controllable risk factors can be manipulated in an attempt to decrease infection rates. Previous authors have decreased infection rates by better protocol compliance and focusing on early discontinuation of catheters [1,2,10]. These successes have drawn international attention and prompted other authors to look at their rates and interventions. Moreno et al. [11] from Colombia found a crude mortality rate of 10.5% attributable to catheter-related UTI, prompting more aggressive infection control measures in their ICUs. In addition, Talaat et al. [7] recently demonstrated rates of 15.7 catheter-associated UTI/1,000 catheter days in four ICUs in Egypt. They now have tailored intervention strategies to minimize their risks of prolonged catheter times and ICU stays.

We incorporated a number of these interventions but were concerned about the role of BPMs as a risk factor, particularly for our trauma patients. With the greater awareness of intra-abdominal hypertension and the role of BPM in making the diagnosis [12], more of our patients were having their catheters manipulated. Hence, we investigated our open technique and found that it was an independent predictor of UTI [3]. Moreover, it was an independent predictor of death. This finding was somewhat surprising, as UTI alone had not been shown to be an independent risk factor for death [6,8,9,13].

Prior to our publication, there were no studies evaluating the open technique. Only Cheatham et al. [14] addressed the question but used a closed procedure in which the system was not violated. In their retrospective study, they found no difference in UTI rates when the BPMs were performed without breaking the sterile circuit. Given their favorable findings and our problematic results using the open technique, we changed our approach.

Although patients having BPM had more UTIs than patients without BPM, it was not an independent predictor of UTI using the closed system, thereby supporting the hypothesis. The small numbers involved may have resulted in an underpowered evaluation and inability to demonstrate a difference. However, in our previous trial using the open technique, the difference was significant despite similar overall numbers.

This finding remained unchanged regardless of whether the measurements were elevated above 20 mm Hg, suggesting sicker patients. Regardless of BPM or ISS, patients with prolonged UDC use were at higher risk for UTI, which is consistent with the published literature. A more subtle yet important finding was that those patients who had more BPMs had higher UTI rates, although this was not an independent predictor, suggesting a need for thoughtful use of BPM in the diagnosis of intra-abdominal hypertension.

This trial has some limitations, including the lack of data on potential confounders of UTI such as genitourinary injury, immunocompetence status, and documentation of other forms of catheter manipulation in which reflux occurs during patient transfers secondary to catheter bag elevation. In addition, only the anatomic ISS system was used to standardize patients, as data from physiologic scoring systems were not available. Although this study suffers the limitation of a single–institution trial, a benefit is that the same ICU nurses who performed the open technique also performed the closed technique once we changed our protocol. We have little turnover of our ICU staff, supporting the concept that the only meaningful change from the previous trial was the BPM technique.

These findings emphasize the judicious use of BPM using a closed system and the need to evaluate our techniques continually with more patients and experience in an effort to minimize complications. Even though more severely ill patients require catheters longer, we should always look for opportunities to remove these catheters. Hence, patients should be evaluated every day for the need for BPM and UDC, both of which should be discontinued whenever possible.