Most Accurate Core Temperature Measurement Location
For critically ill patients requiring accurate core temperature measurement, use a bladder catheter thermistor or esophageal thermistor as your first choice, as these provide essentially identical readings to the pulmonary artery gold standard (bias of only -0.04°C for bladder) and are far more practical than pulmonary artery catheters. 1
Hierarchy of Temperature Measurement Methods
Gold Standard (Invasive Central Methods)
Pulmonary artery catheter thermistors remain the reference standard against which all other methods are compared, with excellent accuracy (bias of only -0.15°C with precision of ±0.13°C). 1 However, this method is technically cumbersome, associated with complications including arrhythmias and perforation, and has fallen out of favor for routine use in most noncardiac intensive care situations. 2
Bladder catheter thermistors show essentially identical readings to pulmonary artery thermistors (bias of only -0.04°C) and provide continuous monitoring, making them the most practical and reliable alternative for critically ill patients. 1, 3 In pediatric cardiac surgery patients, bladder temperature demonstrated the greatest agreement with pulmonary artery temperature using intraclass correlation. 3
Esophageal thermistors provide readings comparable to intravascular sites and bladder catheters, with clinically acceptable limits of agreement. 1 In trauma patients, esophageal and nasopharyngeal temperatures were found to be the most accurate when compared to tympanic measurements. 2
Acceptable Peripheral Alternatives
When central monitoring devices are not in place, oral temperature is the most accurate peripheral method with a bias of only -0.15°C compared to pulmonary artery core temperature. 1, 4 This method is safe and convenient for alert, cooperative patients who have not consumed hot or cold fluids for 15-30 minutes and can maintain mouth closure. 1 A study of 102 critically ill orally intubated adults found oral thermometry to be the most accurate and reproducible method when pulmonary artery core measurement was not available, with significantly less variability than tympanic methods. 4
Rectal temperature reads a few tenths of a degree higher than core temperature but has major drawbacks including being perceived as unpleasant/intrusive, having a small risk of trauma/perforation, and showing significant lag behind core temperature (0-150 minutes in pediatric cardiac patients). 1, 3 Rectal values have been shown to lag behind core temperature during cardiopulmonary bypass and are considered an "intermediate" measuring technique. 2
Unreliable Methods to Avoid
Tympanic membrane infrared thermometers show consistently poor agreement with pulmonary artery/esophageal thermistors (bias of -0.38°C with wide variability) and require perfect operator technique. 1 Despite earlier suggestions that tympanic temperature might become a gold standard, recent high-quality evidence fails to support its use in acute care settings. 5
Temporal artery (no-touch) thermometers are unreliable estimates influenced by environmental temperature and sweating, with 25% of measurements showing clinically significant differences (>0.9°F) from core temperature. 1, 6 The Society of Critical Care Medicine and Infectious Diseases Society of America recommend against using no-touch infrared thermometers in critical care settings. 6
Axillary measurements consistently underestimate core temperature by 1.5-1.9°C with variability up to almost 1°C. 2, 6 These measurements are considered insensitive and should not guide clinical decisions. 6
Clinical Decision Algorithm
Step 1: If a pulmonary artery catheter, bladder catheter with thermistor, or esophageal probe is already in place, use these exclusively for temperature measurement. 1
Step 2: If accurate temperature is critical for diagnosis/management (suspected sepsis, hypothermia, hyperthermia) and no central monitoring is present, strongly consider placing a bladder thermistor catheter. 1
Step 3: For alert, cooperative, non-intubated patients without central monitoring, use oral temperature as the most accurate peripheral method. 1, 4
Step 4: If oral measurement is not feasible (altered mental status, inability to cooperate, recent oral intake), consider rectal temperature despite practical limitations, recognizing it reads slightly higher than core. 1
Step 5: If neither central thermometry nor oral/rectal measurements are feasible, any temperature obtained from no-touch infrared or axillary methods is unreliable and should not guide clinical decisions—clinical assessment based on other signs of infection becomes paramount. 6
Critical Pitfalls to Avoid
Missing life-threatening infections due to temperature discrepancies of 1-2 degrees can lead to missed diagnoses of fever or hypothermia with mortality implications. 1, 6 Patients with serious infections may be euthermic or hypothermic, making accurate temperature measurement essential. 6
Over-reliance on convenient but inaccurate methods such as tympanic or temporal artery thermometers can miss critical temperature abnormalities despite their widespread use in clinical practice. 1, 5
Assuming all measurement sites are interchangeable leads to clinical errors—the precision of measurements using nasopharynx, esophagus, and bladder is superior to those obtained in the axilla, forehead, or rectum. 2