Which statement about bladder temperature during cardiac surgery is true?

Which statement about bladder temperature during cardiac surgery is true?

• A. It is always lower than pulmonary artery temperature
• B. It equals pulmonary artery temperature when urine flow is high
• C. It is unreliable during cardiopulmonary bypass
• D. It is not used to assess rewarming decisions

Answer: (B)

The main concept is how bladder temperature reflects core temperature during cardiac surgery and how urine flow affects that relationship. When urine flow is high, the urine entering the bladder is produced from the kidneys at body temperature and is continuously refreshed with blood-warmed fluid. The bladder sensor, sitting in contact with this urine, rapidly equilibrates with the core temperature, so bladder temperature essentially matches the pulmonary artery (core) temperature. If urine flow is low, the bladder temperature can lag behind and may be influenced by bladder wall heat, irrigation fluids, or stagnant urine, causing departures from the true core temperature. Therefore, stating that bladder temperature equals pulmonary artery temperature when urine flow is high accurately describes this behavior. Other choices aren’t as accurate: the bladder temperature isn’t always lower than PA, as high urine flow can bring it in line with PA; saying it’s unreliable during cardiopulmonary bypass is too absolute—it can track core under appropriate conditions but is less reliable when urine flow is poor or there's irrigation; and it is used as an adjunct to monitor rewarming, not as a sole determinant, so it’s not true to say it’s not used for rewarming decisions.

The main concept is how bladder temperature reflects core temperature during cardiac surgery and how urine flow affects that relationship. When urine flow is high, the urine entering the bladder is produced from the kidneys at body temperature and is continuously refreshed with blood-warmed fluid. The bladder sensor, sitting in contact with this urine, rapidly equilibrates with the core temperature, so bladder temperature essentially matches the pulmonary artery (core) temperature. If urine flow is low, the bladder temperature can lag behind and may be influenced by bladder wall heat, irrigation fluids, or stagnant urine, causing departures from the true core temperature. Therefore, stating that bladder temperature equals pulmonary artery temperature when urine flow is high accurately describes this behavior.

Other choices aren’t as accurate: the bladder temperature isn’t always lower than PA, as high urine flow can bring it in line with PA; saying it’s unreliable during cardiopulmonary bypass is too absolute—it can track core under appropriate conditions but is less reliable when urine flow is poor or there's irrigation; and it is used as an adjunct to monitor rewarming, not as a sole determinant, so it’s not true to say it’s not used for rewarming decisions.