In certain circumstances, the bladder site for temperature measurement has been considered to be an accurate reflection and estimation of core body temperature in infants and children where it has not been possible to use a pulmonary artery catheter.
Bladder thermometry requires the use of a specific sterile, disposable indwelling urinary catheter with a temperature sensor running through the catheter. The temperature sensor is usually located 13mm from the catheter tip. Many infants and children in the paediatric critical care unit routinely have a urinary catheter in situ so the use of a catheter with a thermistor probe is no more invasive than a ‘normal’ catheter and if cared for correctly should cause no additional discomfort to the infant or child.
Bladder thermometry is used in paediatric, neonatal and adult intensive care units as well as during some operative procedures, as it is thought to provide a continuous temperature reading or trend without being influenced greatly by changes in ambient temperature. Some earlier studies have suggested that accuracy of bladder temperature monitoring may be influenced by urine flow rate. Whereas, other studies have found that bladder temperature remains reliable with changes in urine flow rate.
The nurse must be aware of the limitations of bladder thermometry if choosing this method of temperature monitoring. For example, urinary catheters with thermistor probes are available in a variety of sizes. However, the smallest catheter available at present is a size 8FG and may be too large for neonates and smaller infants less than 4kg.
Bladder thermometry readings may be unreliable and inaccurate where there are extremes of temperature and thermal flux such as during the cooling and warming phases of cardiopulmonary bypass. In shock states where there is poor perfusion to the lower abdomen and kidneys, or in the presence of fever, a ‘lag’ in bladder temperature reading, compared to other temperature sites (including pulmonary artery) has been reported.
There are documented risks when using bladder thermometry although these are related to the fact that the infant or child has an indwelling catheter. These include urethral trauma (from insertion), urinary tract infection, blockage and haematuria.
If the nurse finds any abnormal temperature measurements using bladder thermometry technique, then first check the catheter is still in situ. If the temperature reading appears accurate then this should be reported and documented. Another method & site of thermometry should also be considered.