The two methods for body temperature that will be examined are core temperature measurements with a PA catheter and temperature measurements using the Temp-Traq (measured in Celsius). Paired temperature measurements for both methods will be taken simultaneously every 2 hours for a 6 hour period. This will provide 4 repeated temperature measures per patient. The simultaneous measurements within a given patient should exhibit a high degree of correlation. If .7 is chosen as the lower bound for the correlation between the paired readings (higher correlations would result in an estimate of fewer patient samples thus the choice of .7 is conservative) and if the average standard deviation of the mean of the differences is used as an estimate of the expected variability, then it would be possible to declare measurement equivalence for a difference of ±.19 with a sample size of 40 patients. This assumes the ASTM measurements of instrument variation are representative of the within patient variance. Given the vagaries of patient-to-patient this may be too optimistic an estimate.