IAP has gained interest in a wide variety of patient populations since IAH and ACS have been recognized as a major cause of potentially life-threatening end-organ dysfunction. As IAP increases, the physiology of multiple organ systems is affected leading to inadequate organ perfusion and tissue oxygenation, multiple organ failure, and death. IBP monitoring has been recommended by the World Society on Abdominal Compartment Syndrome http://www.wsacs.org
as the method of choice for indirect measurement of IAP due to its accuracy and relative ease of measurement [10
The original method for IBP monitoring was described by Kron and co-workers and required the patient's urinary catheter to be disconnected [18
]. This leads to justified fears for device-related UTI. The modified technique proposed by Cheatham still used sterile saline instillation into the bladder but maintained the patient's urinary catheter as a closed system, which put to rest some of the concerns relating to UTI [19
]. The FoleyManometer is also a closed sterile system but uses freshly produced urine as IAP transmitting medium and measures the height of the fluid/urine column in an especially designed drainage tube with a 35-ml reservoir. After several reports stating that lower instillation volumes can and should be used for IBP measurements in order to avoid overestimation of IAP, a new FoleyManometerLV was designed with less than 10-ml infusion volume [11
]. The re-instillation of the patient's own urine which may have been in the drainage tube for some time raised even more concerns about the risk for UTI than the previous IBP measurement techniques. Our study is, to our knowledge, the first to examine the risk for UTI using urine as a transmitting medium for IBP measurement.
Before this publication, Cheatham et al. published already a study on UTI risk in relation to IBP monitoring using other devices [12
]. They found that IBP monitoring using a closed transducer technique with sterile saline instillations is safe and does not increase the risk of UTI. Ejike et al. found similar results in a prospective observational study in critically ill children, also using a closed technique with sterile saline installations [13
]. On the other hand, Duane et al. demonstrated a greater risk of UTI with bladder pressure measurements using an open technique in which the Foley catheter was compromised through insertion of an 18-gauge needle and disconnection of the Foley catheter to allow instillation of 50 ml of saline into the bladder [14
]. We confirmed that the UTI rate, when adjusted for disease severity, remained unchanged with or without IBP monitoring using different devices, all being closed systems. There was a trend toward higher adjusted UTI rates using the FoleyManometer with larger instillation volumes that was used during period 3, but this was not statistically significant when compared to the other groups. With the newer FoleyManometerLV, the trend toward higher adjusted UTI rates disappeared, and thus, this is a safe technique.
The UTI rates per 1,000 CD reported in this study are higher than those reported by Cheatham who found 10.4 crude and 7.9 adjusted UTI/1,000 CD in the patient population that underwent IAP monitoring versus 6.5 in the control group. We observed 12.7 in our control group, and this could be related to the fact that CD in our study coincided with ICU stay, so it could be possible that some patients kept their Foley catheters after ICU discharge leading to actual longer CD (that were not taken into account) and thus overestimation of UTI risk. In a large study on 2,644 ICU patients, van der Kooi et al. found a UTI incidence of 8% (versus 8.8% in our study) and 9 UTI/1,000 CD (versus 16.1 crude and 12.8 adjusted in our study) [22
]. In another study on 337 adult ICU patients, the crude risk for UTI was 14/1,000 CD, which is close to what we observed [23
One could state that the more UC taken, the greater the chance of identifying a positive UC. But although the total number of UC taken and thus the number of UC per patient increased during our observation, there was no increase in the UTI rates during period 4.
The strong points of our study, although still retrospective and purely observational in nature, are the presence of a historic control group, allowing comparison of subsequent groups versus a 'baseline' UTI rate, and, more importantly, the standardized approach to both IAP monitoring and urine sampling. IAP monitoring is used in all mechanically ventilated patients in our ICU, and cultures are taken at least twice a week or more frequently if clinically indicated.
There are also some important and obvious limitations to our study. First of all, there is the retrospective design leading to missing data on antibiotic use and other infectious foci, among other problems. Secondly, our patient population evolved significantly over the 8-year time period. Disease severity (SAPS-II score), ICU length of stay, number of ventilation days, and ICU mortality increased significantly over the four time periods. To correct for this evolution, crude UTI rates were adjusted for disease severity, but naturally, this does not correct for all possible sources of bias in the study. Third, potential etiological factors for the development of IBP monitoring-associated UTI were not considered. The duration of urinary catheterization could be different in the four groups, although this was determined by the standard ICU procedures as stated in the methods (urine drainage tubing, collection bags, and FoleyManometers were replaced every 7 days). Fourth, due to the epidemiologic and observational nature of the study looking at global incidences, we could not look for individual factors predictive for UTI or outcome by multiple logistic regression analysis.