Transcutaneous capnometry (tPCO₂) is a non-invasive method for continuous monitoring of ventilation status. In pediatric intensive care patients, it may reduce the need for repeated arterial or arterialized blood sampling. However, the accuracy of tPCO₂ may be influenced by factors such as peripheral perfusion, skin temperature, and vasopressor therapy. This prospective observational study compares transcutaneous carbon dioxide measurements with arterialized or arterial blood gas PaCO₂ values in children with respiratory insufficiency, including a subgroup receiving vasopressor support.

This prospective observational study will be conducted in a pediatric intensive care unit to assess agreement between transcutaneous carbon dioxide monitoring and arterialized or arterial blood gas analysis. Consecutive pediatric patients aged 1-18 years with respiratory insufficiency or impaired peripheral perfusion requiring vasopressor support will be included if repeated blood gas sampling is clinically indicated.

Paired measurements of tPCO₂ and PaCO₂ will be analyzed using Bland-Altman methods with correction for repeated measures. Subgroup analyses will evaluate the influence of vasopressor therapy on measurement accuracy. Secondary analyses will compare tPO₂ and PaO₂ values. The study aims to define the clinical applicability and limitations of transcutaneous capnometry in critically ill pediatric patients.

Inclusion Criteria:

• Age 1-18 years
• Diagnosis of respiratory insufficiency or impaired peripheral perfusion
• Expected need for more than one arterialized capillary or arterial blood gas sample
• Admission to PICU

Exclusion Criteria:

• Repeated failure of sensor adhesion
• Hypothermia < 35 °C
• Time difference > ±5 minutes between tPCO₂ and blood sampling
• Large tPCO₂ variability (> ±1 kPa) in 15 minutes preceding blood sampling
• Non-physiological tPCO₂ values incompatible with life

Critically ill pediatric patients admitted to a tertiary PICU with respiratory insufficiency or circulatory compromise.