Monitoring bladder temperatures in the OR

AORN Journal,  Sept, 2002  by Wendy M. Fallis

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The purpose of temperature monitoring in any clinical setting, including the OR, is to obtain a measure of core temperature. Temperature can be measured at varying sites, each producing its own range of temperatures, (1) thus true core temperature has been described as a nebulous term (2) lacking definition (3) Nevertheless, this term continues to be used to physically differentiate between the more uniform temperatures in the body core (eg, cranium, thorax, abdominal areas) and the more variable, nonhomogeneous temperatures at peripheral sites. (4)

It has been argued that the hypothalamus should be regarded as the site of true core temperature measurement because central thermal receptors are particularly numerous in this area. (5) A heat loss center is located in the preoptic region and anterior hypothalamus, and a center for heat production and conservation is located in the posterior hypothalamus. (6) Inaccessibility of the hypothalamus, however, has necessitated the use of other sites for temperature measurement. In the OR, conventional sites include the lower esophagus, nasopharynx, pulmonary artery (PA), rectum, bladder, and tympanic membrane. (7) Placement of temperature probes directly on the tympanic membrane is used less frequently because perforation (8) and bleeding (9) are concerns. Urinary bladder temperature measurement has been used in the OR, often as a replacement for temperature measurement at the bacteria-laden rectal site.

This article provides a systematic, integrated review and synthesis of research related to bladder temperature monitoring in the OR. Systematic reviews help keep practitioners abreast of the literature by addressing specific clinical questions. (10) and providing an objective summary of large amounts of data. (11) More importantly, synthesis of research provides a compilation and evaluation of evidence on which practice or change in practice can be based. This review will address the role of bladder temperature monitoring in the OR and assess the validity of temperature measured at the bladder site to represent core temperature both in the steady state and during times of thermally dynamic change.

ARTICLE SELECTION CRITERIA

Before the review was undertaken, criteria were established to narrow the scope of the literature search. Studies were required to be published in English, use adult participants, and compare temperatures at the bladder site with temperatures at sites considered representative of core temperature measurement. These sites include the lower esophagus, (12) nasopharynx, (13) and PA. (14) Databases searched include Medline, CINAHL, Current Contents, and Pro Quest Digital Dissertation Abstracts. Additional sources from the reference sections of relevant articles also were reviewed. Key words used include body temperature, bladder, esophageal, nasopharyngeal, pulmonary artery, operating room, and surgery.

Sources meeting these criteria were reviewed for sample size, demographics, methods, results, and limitations. Of particular importance was the agreement or mean difference and the accompanying variation between temperatures at the urinary bladder site and temperatures at the core. Less emphasis was placed on the degree of association or correlation between bladder and core site temperatures because measurements obtained from the two sites may correlate highly (ie, have similar slope and direction) but have large differences between them such that one measurement could not be used to approximate the other measurement in clinical practice.

Also important was whether the instruments used for temperature measurement were tested for accuracy to validate the data. Ideally, instruments should be tested before and after data collection, particularly if the data collection period is prolonged. With temperature-sensing probes that are inserted sterilely, such as PA and urinary bladder catheters, testing before insertion generally is not feasible. Testing after removal, however, is possible, and if inaccuracy is demonstrated, data should be adjusted accordingly. In studies in which temperature probes were not tested for accuracy or information was not provided regarding the procedure used, this was noted as a limitation. If exact placement of esophageal or nasopharyngeal probes was omitted, this too was noted. When information regarding instrument accuracy or the specifics of probe placement is lacking, the internal validity of study results is compromised.

This article begins with information related to the conventional sites used for temperature measurement in the OR, with key information provided in Table 1. Information relating to the use of the bladder site for temperature measurement precedes a discussion of bladder anatomy and urine production. The detailed review and discussion of articles related to bladder temperature monitoring follows. Bladder temperature tends to behave differently during steady thermal states compared with thermally dynamic states, so the literature was categorized and presented accordingly. Unsteady thermal states exist, for example, during the rapid cooling and rewarming phases of cardiopulmonary bypass (CPB), a procedure frequently used during cardiac surgery to oxygenate, circulate, and control the temperature of blood while bypassing the heart and lungs. Participant demographics and additional information regarding procedures and temperature measurements are presented in Table 2. Unless otherwise stated, means are accompanied by their standard deviations.