Thursday, September 26, 2002

This presentation is part of : Posters

The Effect of Urine Flow Rate on Continuous Urinary Bladder Temperature Measurements in Critically Ill Adults

Wendy Marilyn Fallis, RN, BScN, MN, PhC, director of research and evaluation, Department of Research and Evaluation, Department of Research and Evaluation, Victoria General Hospital, Winnipeg, Winnipeg, Manitoba, Canada

Objective: To determine the effect of urine flow rate on the gradient between urinary bladder temperature and pulmonary artery blood temperature measurements in critically ill adults.

Design: Pre-test post-test quasi experimental.

Population, Sample, Setting, Years: Between March and July 2001, 60 patients who had recently undergone cardiac surgery in a tertiary care setting participated in the study. The majority of subjects were male (73%) and ranged in age from 25 to 92 years with a mean age of 63.6 years (SD=15.1). Overall, subjects had a mean height of 174 cm (SD=8.2), mean weight of 85 kg (SD=18.2), mean body surface area of 2.0 meters sq. (SD=0.2), and mean body mass index of 28 kg/meters sq. (SD=5.9). Coronary artery bypass grafting was the primary reason for surgery for 35 (58%) subjects.

Concept or Variables Studies Together or Intervention and Outcome Variable(s): The gradient between urinary bladder temperature (UBT) and pulmonary artery temperature (PAT) was the outcome variable. Urine flow rate was the intervention variable. A single dose of the diuretic Lasix (Furosemide) administered intravenously on the morning following cardiac surgery to selected patients in the sample as part of their usual treatment provided variation in urine flow rate.

Methods: On the morning of postoperative day one, PAT, UBT, and urine flow rate were recorded at 2-minute intervals for 60 minutes prior to and 70 minutes following the intravenous infusion of a diuretic (diuretic group), or the decision not to give a diuretic (non-diuretic group). The first 10 minutes of the post phase were used to allow for the diuretic to take effect (diuretic group) and data from this period were not included in the analysis of either group. PAT served as the reference. Demographic data and ambient temperature (collected at 4 time points) also were recorded. One investigator collected all the data. Catheters were retrieved following removal and tested for accuracy. Bladder and PA temperature data were corrected for instrument error. Descriptive and inferential statistics were used to analyze the data. Level of significance was set at 0.05.

Findings: Analysis of demographic variables revealed that there were no significant differences between the diuretic (n=35) and non-diuretic (n=25) subjects. Ambient temperature ranged from 21.0 to 24.9 degrees Celsius and was not significantly correlated with the UBT - PAT gradient at any of the time points. Urinary bladder temperature was generally higher than PAT. For the non-diuretic group, there was no significant change in either urine flow rate or the UBT-PAT gradient from pre phase to post phase. In contrast, mean urine flow rate for the diuretic group significantly increased from 45 ml/hr prior to the diuretic administration to 428 ml/hr following its administration (p < 0.001). During this same time period, the mean UBT-PAT gradient significantly decreased from 0.32 degrees C in the pre phase to 0.23 degrees Celsius in the post phase. However, this change of less than 0.1 degrees Celsius, although statistically significant (p < 0.001), was not clinically significant. A significant positive correlation (p < .001) between UBT and PAT was noted in both the non-diuretic (r=.910) and the diuretic group (r=.931). Further, a small but significant negative relationship (p < .001) was revealed between urine output and the UBT-PAT gradient for both the non-diuretic (r=- .259) and diuretic group (r=- .320).

Conclusion: It was concluded that for the population under study, urinary bladder temperature measurements, which are convenient for both patients, who already have an indwelling catheter for urinary drainage, and nursing staff, could be relied upon for measurement of body temperature even with varying rates of urine flow. The small change in gradient of less than 0.1 degree Celsius was considered to be clinically insignificant.

Implications: There has been limited research into the role of urine flow rate on continuous bladder temperature measurement in the intensive care setting. The results of this study have implications for direct care providers, managers, and researchers with interests in the critical care population. Temperature- sensing bladder catheters have been reported as a safe, easy, and acceptable method of temperature measurement for patients whose condition necessitates the use of an indwelling urinary catheter. The results of this study support the use of this catheter when urine output varies. It is recommended that additional studies of other critical care populations that would benefit from continuous measurement of temperature, such as neurological trauma patients, be undertaken to investigate this same variable.

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