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NCT Number: NCT07050719

Can Atelectasis Be Prevented With Oxygen Reserve Index (ORI) Monitoring?

This single-center randomized controlled trial aims to evaluate whether intraoperative monitoring using the Oxygen Reserve Index (ORI) reduces the incidence of postoperative atelectasis, as assessed by lung ultrasound (LUS), in adult patients undergoing elective robotic surgery under general anesthesia.

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Key information

Conditions

Atelectasis Hyperoxia Lung Diseases Lung Ultrasonography Score Pathological Conditions, Signs and Symptoms Pulmonary Atelectasis Respiratory Tract Diseases Signs and Symptoms Signs and Symptoms, Respiratory

Age range

18 year–75 year

Sex eligibility

All sexes

Study type

Interventional

Phase

Not applicable

Primary location

Antalya Training and Research Hospital

Antalya, Muratpasa, 07100, Turkey (Türkiye)

About this study

Postoperative atelectasis is observed in 60-90% of patients undergoing general anesthesia. Factors such as high inspired oxygen concentration, muscle relaxation, and reduced functional residual capacity contribute to its development through mechanisms like absorption atelectasis. The persistence of atelectasis increases the risk of pneumonia, hypoxia, prolonged hospital stay, healthcare costs, and mortality. Despite the well-known pathophysiology, the optimal intraoperative fraction of inspired oxygen (FiO₂) remains unclear.

The Oxygen Reserve Index (ORI) is a non-invasive, continuous parameter that reflects the oxygen reserve within the moderate hyperoxia range (100-200 mmHg). It may facilitate individualized FiO₂ titration to avoid hyperoxia-related atelectasis. Lung ultrasound (LUS) is a reliable, radiation-free bedside tool for detecting atelectasis.

This study hypothesizes that ORI-guided oxygen therapy will reduce the incidence of postoperative atelectasis compared to standard Peripheral Capillary Oxygen Saturation (SpO₂)-guided therapy.

Who can participate

Healthy volunteers accepted: No

Only the study team can determine whether someone qualifies for participation.

Inclusion criteria

  • American Society of Anesthesiologists Physical Status Classification System (ASA) physical status I-III
  • Elective robotic surgery under general anesthesia
  • Surgery duration >2 hours
  • Requires invasive arterial cannulation
  • Signed informed consent

Exclusion criteria

  • ASA IV or higher
  • Room air SpO₂ <92%
  • Chronic pulmonary disease
  • Hemoglobinopathy
  • Pregnancy
  • Refusal to participate

Treatment and study plan

Peripheral Oxygen Saturation (SpO₂) Group

Procedure

FiO₂ adjusted based on pulse oximetry to maintain SpO₂ ≥98%

Peripheral Oxygen Saturation and Oxygen Reserve Index (SpO₂-ORI) Group

Procedure

FiO₂ adjusted using both SpO₂ and ORI to maintain ORI between 0-0.3

Primary outcomes

  1. Postoperative LUS score at 30 min

    Time frame: At 30 minutes following tracheal extubation at the end of surgery

    Lung ultrasound (LUS) measurements will be performed by an anesthesiologist blinded to the study groups, who is experienced in lung ultrasonography with at least 100 prior examinations. LUS will be performed and recorded 30 minutes before surgery while patients are in the supine position, using a linear probe (6-12 MHz). The total LUS score will be calculated as the sum of the scores for the 12 quadrants of each hemithorax (range: 0-36). Higher scores will indicate more severe loss of aeration. Loss of aeration will be scored as follows:

    • 0: Presence of A-lines or fewer than two B-lines
    • 1: Three or more well-defined B-lines
    • 2: Presence of multiple coalescent B-lines
    • 3: Presence of lung consolidation characterized by dynamic air bronchograms

Secondary outcomes

  1. Preoperative LUS score

    Time frame: 30 minutes prior to patient transfer to the operating room

    Lung ultrasound (LUS) measurements will be performed by an anesthesiologist blinded to the study groups, who is experienced in lung ultrasonography with at least 100 prior examinations. LUS will be performed and recorded 30 minutes before surgery while patients are in the supine position, using a linear probe (6-12 MHz). The total LUS score will be calculated as the sum of the scores for the 12 quadrants of each hemithorax (range: 0-36). Higher scores will indicate more severe loss of aeration. Loss of aeration will be scored as follows: • 0: Presence of A-lines or fewer than two B-lines • 1: Three or more well-defined B-lines • 2: Presence of multiple coalescent B-lines • 3: Presence of lung consolidation characterized by dynamic air bronchograms

  2. Intraoperative arterial partial pressure of oxygen (PaO₂)

    Time frame: At baseline (immediately before incision), and at 1st, 2nd, and 3rd hour intraoperatively

    Arterial blood samples will be collected intraoperatively at baseline (immediately before skin incision) and at the 1st, 2nd, and 3rd hour to measure the partial pressure of oxygen (PaO₂).

  3. Intraoperative fraction of inspired oxygen (FiO₂)

    Time frame: At baseline (immediately before incision), and at 1st, 2nd, and 3rd hour intraoperatively

    The fraction of inspired oxygen administered to the patient will be recorded at baseline (immediately before skin incision) and hourly at the 1st, 2nd, and 3rd hour during surgery.

  4. Intraoperative Oxygen Reserve Index (ORI)

    Time frame: At baseline (immediately before incision), and at 1st, 2nd, and 3rd hour intraoperatively

    Continuous monitoring of the Oxygen Reserve Index (ORI) will be performed, and values will be documented at baseline (immediately before skin incision) and at 1st, 2nd, and 3rd hour intraoperatively.Intraoperative Oxygen Reserve Index (ORI) will be measured. ORI is a unitless index ranging from 0.00 to 1.00, with higher values indicating a greater oxygen reserve.

  5. Number of episodes with severe hyperoxia (PaO₂ > 200 mmHg)

    Time frame: At baseline (immediately before incision), and at 1st, 2nd, and 3rd hour intraoperatively

    The number of severe hyperoxia episodes, defined as PaO₂ levels exceeding 200 mmHg, will be recorded at baseline (immediately before skin incision) and at the 1st, 2nd, and 3rd hour during surgery.Each time point will be evaluated independently, and the number of measurements exceeding 200 mmHg will be counted.This is a binary threshold-based event count, not a continuous scale; thus, no scoring system or scale interpretation is applicable.

Sponsors and collaborators

Lead sponsor

Antalya Training and Research Hospital

Other Gov

Registry information

Official study title

Can Atelectasis be Prevented in Robotic Surgery by Monitoring With Oxygen Reserve Index (ORI)? A Randomized Controlled Trial

Important dates

Study start
2025
Primary completion
2025
Study completion
2025
First posted
Jul 3, 2025
Registry last updated
Dec 10, 2025

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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