CompletedNot Applicable

Correlation of EtCO₂- and P(A-a)O₂-Based Dead Space Calculations in Mechanically Ventilated ICU Patients

Turkey (Türkiye)41 participantsStarted 2025-01-05

Plain-language summary

This study aims to evaluate two different methods for calculating physiological dead space in adult patients undergoing invasive mechanical ventilation in the intensive care unit (ICU). Physiological dead space refers to the portion of air that is ventilated but does not participate in gas exchange due to impaired perfusion or ventilation-perfusion mismatch. Traditionally, dead space is calculated using the end-tidal carbon dioxide (EtCO₂) method, which estimates the difference between arterial and exhaled CO₂ values. However, this method may be influenced by circulatory failure or abnormal CO₂ distribution. An alternative method using the alveolar-arterial oxygen gradient \[P(A-a)O₂\] has been proposed, as it may provide a more stable measurement under critical conditions by relying on oxygenation efficiency rather than CO₂ elimination. In this prospective observational study, patients receiving mechanical ventilation in a tertiary ICU will be monitored. Physiological dead space will be calculated using both the EtCO₂-based method and the P(A-a)O₂-based method. Various respiratory and clinical parameters, including arterial blood gases, ventilator settings, and severity scores, will be recorded. The correlation between the two methods will be assessed, and their relationship with ICU mortality will be analyzed. The results of this study may help determine whether the P(A-a)O₂ method can be used as a reliable alternative for estimating dead space in ICU patients and whether it has prognostic value in predicting patient outcomes.

Who can participate

Age range

18 Years

Sex

ALL

See this in plain English?

AI-rewrites the medical criteria so a patient or caregiver can understand them. Always confirm with the trial site.

Inclusion Criteria: * Age ≥ 18 years * Admission to the intensive care unit (ICU) * Receiving invasive mechanical ventilation * Expected ICU stay ≥ 24 hours * Availability of both arterial blood gas and volumetric capnography measurements * Central venous cathater for central venous blood analyses * Informed consent obtained from legal representative Exclusion Criteria: * Refusal of participation by the patient or legal surrogate * Hemoglobin \< 7 g/dL * PaCO₂ \> 70 mmHg * Lactate \> 4 mmol/L * Capillary refill time \> 3 seconds * Mean arterial pressure (MAP) \< 65 mmHg * Mottling score ≥ 2 * PaCO₂ - PcCO₂ gradient \> 8 mmHg * pH \< 7.20 * Body temperature \> 38°C * BMI \> 40 kg/m² * VCO₂ \> 4 mL/kg/min * Technical limitations preventing accurate capnographic monitoring * Patients who are extubated, transferred, or deceased within the first 24 hours

Questions worth asking your doctor

Bring these to your next appointment. They're a starting point for a shared conversation — not a sign you qualify or a recommendation to enrol.

1Based on my diagnosis and history, is this trial worth exploring for me — or is there a standard treatment we should try first?
2What does this trial's phase tell us about how much is already known about its safety and benefit?
3What would taking part actually involve for me — visits, tests, time, and travel?
4What are the known and possible risks or side effects I should weigh, and how would they be monitored?
5If this trial isn't the right fit, what other options or trials would you suggest I look into?

Generated to help you prepare — always confirm anything about your own eligibility and care with the study team and your doctor.

Questions for the trial coordinator

The trial coordinator is the person who runs the study day to day. These cover the practical side — logistics, costs, and what taking part would actually mean for your life. The study team confirms whether you meet the criteria; these are questions to ask, not a sign you qualify.

1What does taking part actually involve week to week — how many visits, where, and how long does each one take?
2What costs are covered by the study, and what might I have to pay for myself, including travel, parking, or time off work?
3What happens during screening, and what happens if the study team confirms I don't meet the criteria after those tests?
4Who pays for the scans, blood work, and other tests the trial requires — the study, my insurance, or me?
5How will being in the trial affect my regular care, and will my own doctor stay informed and involved?
6Can I leave the trial at any point if I change my mind, and what would happen to my care if I do?

A starting point for the conversation — always confirm anything about your own eligibility, costs, and care with the study team and your doctor.

What they're measuring

Correlation between EtCO₂- and P(A-a)O₂-based dead space calculations

Timeframe: Within the first 72 hours of ICU admission

Trial details

NCT IDNCT06947486

SponsorKaradeniz Technical University

Sponsor typeOTHER

Study typeOBSERVATIONAL

Primary completion2025-04-10

View on ClinicalTrials.gov More Physiological Dead Space trials