Related Experiment Video
Updated: Aug 17, 2026
Expired CO2 Measurement in Intubated or Spontaneously Breathing Patients from the Emergency Department
Published on: January 29, 2011
Initial transcutaneous PCO2 overshoot with ear probe at 42 degrees C
Sohei Kagawa1, Norimasa Otani, Masayuki Kamide
1Department of Anesthesia, Atsugi City Hospital, Atsugi, Kanagawa, Japan. skagawa@pc.highway.ne.jp
Objective:
To investigate an unexpectedly high initial skin CO2 pressure with a new small earlobe probe* heated to 42 degrees C containing both transcutaneous (tcPCO2) and pulse oximeter saturation (SpO2) sensors.
Methods:
The probe was mounted on the ear lobe of six patients during abdominal or thoracic surgery and on several awake volunteers. The probe was mounted on a cheek or forearm in two other volunteers. Patients were artificially ventilated under general anesthesia at constant end-expiratory PCO2.
Results:
In patients, at 8 +/- 3 min after mounting, tcPCO2 peaked 5 mmHg higher than its final value (p = 0.0067, n = 6, paired t-test). After 25 min, tcPCO2 was not different from PaCO2 (arterial). Similar overshoots were recorded with this device when mounted on the arm or cheek and with a standard transcutaneous PCO2 probe set to 42 degrees C, mounted on the ear lobe, arm or chest of awake volunteers. In two volunteers, we found that heating the sensor to 45 degrees C for the first 15 min on the ear, and then decreasing it to 42 degrees C prevented overshoot, and provided valid tcPCO2 data 3 - 5 min after application of the sensor.
Conclusions:
A temperature of 42 degrees C may increase local skin temperature and metabolism before vasodilating more remote arteriolar control of sub-sensor capillary flow. We suggest that transcutaneous PCO2 probes be initially set to 44 - 45 degrees C for 5 - 15 min to induce prompt vasodilation to prevent this overshoot and then reduced to 42 degrees C to avoid skin thermal injury in case of long-term application.
Related Concept Videos
01:17Assessment of Diffusion and Perfusion
The Role of Diffusion in Respiration
Diffusion is the process by which molecules move from an area of higher concentration to an area of lower concentration. In the respiratory system, this principle...
01:24Diagnosing Acidosis and Alkalosis
First, the pH level is assessed to determine whether the blood pH is normal (7.35–7.45), low (acidosis), or high (alkalosis).
Next, the PCO2 and HCO3− values are examined to...
01:14Assessing Body Temperature - Tympanic membrane
Step 1: Begin by practicing good hand hygiene to prevent the transmission of microorganisms.
Step 2: Turn on the thermometer and wait until the ready sign appears on the screen to ensure accurate measurement.
Step 3: Slide the probe cover in place to prevent cross-contamination.
Step 4: Instruct the patient to tilt their head to the side for comfort and check for cerumen...
01:14Temperature Measurement Sites
Oral: When assessing oral temperature, the thermometer tip should be placed under the tongue in the posterior sublingual pocket. It offers accurate readings and can be...
01:19Assessing Body Temperature - Temporal Artery
Step 1: Perform hand hygiene and don a fresh pair of gloves to prevent cross-infection and ensure patient safety.
Step 2: Explain the procedure to the patient to establish trust. Clear communication establishes trust with the patient, ensures they understand what to expect, promotes cooperation, and enhances comfort during the procedure.
Step 3: Assess the patient's forehead...
01:30Acute Respiratory Failure-III