BMI-Adjusted PEEP During One-Lung Ventilation in Thoracic Surgery (SIMPLE-PEEP)

Effect of Body Mass Index-Adjusted Positive End-Expiratory Pressure on Respiratory Mechanics During One-Lung Ventilation in Thoracic Surgery

One-lung ventilation (OLV) is required during many thoracic surgical procedures and is associated with reduced functional residual capacity, atelectasis, ventilation-perfusion mismatch, hypoxemia, and potentially ventilator-induced lung injury. Lung-protective ventilation strategies include low tidal volumes, limitation of airway pressures, and positive end-expiratory pressure (PEEP), but the optimal PEEP level during OLV remains uncertain. Fixed PEEP is simple and reproducible but does not account for individual patient characteristics. Body mass index (BMI) is readily available before anesthesia and is associated with respiratory mechanics, making it a pragmatic candidate for simple PEEP individualization.

SIMPLE-PEEP is a prospective, multicenter, pragmatic, open-label, randomized clinical trial including 150 adults undergoing elective pulmonary resection under general anesthesia requiring OLV. Participants will be randomized to either fixed PEEP of 4 cmH2O or BMI-adjusted PEEP calculated as BMI/3 cmH2O. Other key components of lung-protective ventilation will be standardized between groups.

The primary outcome is driving pressure during the first 20 minutes of OLV, assessed at 5, 10, and 20 minutes after OLV initiation. Secondary outcomes include respiratory system compliance and other respiratory mechanics, estimated mechanical power, oxygenation, intraoperative hypoxemia and rescue maneuvers, hemodynamic safety, vasopressor requirements, and exploratory postoperative respiratory outcomes. No investigational medicinal product, additional invasive procedure, or study-specific advanced monitoring is required.

Study Overview

• Status: Recruiting
• Conditions: General Anesthetic; One Lung Ventillation (OLV); Pulmonary Resection Surgery
• Intervention / Treatment: Procedure: Fixed PEEP; Procedure: BMI-adjusted PEEP

• Study Type: Interventional
• Enrollment (Estimated): 150
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Jesús M Nieves Alonso, MD; Phone Number: +34915202540; Email: jesusmna@gmail.com

Study Locations

• Spain
  • Catalonia
    • Barcelona, Catalonia, Spain, 08036
      • Not yet recruiting
      • Hospital Clinic Barcelona
      • Contact: Manuel L López; Email: LOPEZ10@clinic.cat
    • Barcelona, Catalonia, Spain, 08041
      • Not yet recruiting
      • Hospital de la Santa Creu i Sant Pau
      • Contact: Ana P Parera; Email: AParera@santpau.cat
  • Madrid
    • Madrid, Madrid, Spain, 28006
      • Recruiting
      • Hospital Universitario de La Princesa
      • Contact: Jesús M Nieves Alonso, MD; Phone Number: +34915202540; Email: jesusmna@gmail.com
    • Madrid, Madrid, Spain, 28007
      • Not yet recruiting
      • Hospital General Universitario Geogorio Marañón
      • Contact: Estrela C Caamaño; Email: estrelacaamano@gmail.com

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 18 years and older (Adult, Older Adult)
• Accepts Healthy Volunteers: No
• Genders Eligible for Study: All

Description

Inclusion Criteria:

1. Age 18 years or older.
2. Scheduled thoracic surgery for pulmonary resection requiring general anesthesia and one-lung ventilation.
3. Written informed consent obtained before any study-specific procedure.

Exclusion Criteria:

1. Simultaneous participation in another interventional clinical trial that could interfere with the protocol.
2. Severe hemodynamic instability before the start of the procedure, defined as continuous vasopressor infusion or shock of any etiology.
3. Severe restrictive lung disease, defined as total lung capacity <50% of predicted or forced vital capacity <50% of predicted.
4. Body mass index >45 kg/m2.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Supportive Care
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Active Comparator: Fixed PEEP of 4 cmH2O	Procedure: Fixed PEEP; Fixed PEEP of 4 cmH2O
Experimental: BMI-adjusted PEEP calculated as BMI/3 cmH2O	Procedure: BMI-adjusted PEEP; BMI-adjusted PEEP calculated as BMI/3 cmH2O

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Driving pressure during the primary T2-T4 window	Driving pressure during the primary T2-T4 window, measured at 5, 10, and 20 minutes after initiation of one-lung ventilation and expressed in cmH2O. In conventional volume-controlled ventilation, driving pressure is calculated as plateau pressure minus applied PEEP. In pressure-regulated volume-targeted/volume-guaranteed modes, driving pressure is calculated as total end-inspiratory pressure minus applied PEEP.	20 minutes

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Respiratory system compliance	Respiratory system compliance will be calculated at each applicable time point as tidal volume divided by driving pressure and expressed in mL/cmH2O	At 5, 10, and 20 minutes after initiation of one-lung ventilation; at 60 minutes when applicable; and at the end of one-lung ventilation, all during the surgical procedure on Day 1.
Driving pressure at 60 minutes and at the end of one-lung ventilation	Driving pressure will be assessed at 60 minutes after initiation of one-lung ventilation, when this time point is applicable, and at the actual end of one-lung ventilation, to evaluate the persistence of the physiological effect of the assigned PEEP strategy.	At 60 minutes after initiation of one-lung ventilation, when applicable, and at the end of one-lung ventilation.
Estimated mechanical power during one-lung ventilation	Ventilatory mechanical power will be estimated from prospectively recorded ventilatory parameters using a prespecified calculation method appropriate to the ventilation mode and expressed in J/min.	At 5, 10, and 20 minutes after initiation of one-lung ventilation; at 60 minutes when applicable; and at the end of one-lung ventilation, all during the surgical procedure on Day 1.
Incidence of intraoperative hypoxemia during one-lung ventilation	Intraoperative hypoxemia will be defined as SpO2 <90% sustained for at least 60 seconds during one-lung ventilation with baseline FiO2 0.6, or any episode of SpO2 <90% requiring immediate clinical intervention at the discretion of the attending anesthesiologist.	From initiation until completion of one-lung ventilation during the surgical procedure on Day 1 (up to 1 day).
Incidence of major ventilatory rescue	Major ventilatory rescue during the first 20 minutes after initiation of one-lung ventilation will be defined as any intervention that substantially modifies the assigned ventilatory strategy or respiratory mechanics, including modification of PEEP from the assigned value, recruitment maneuver, CPAP to the non-ventilated lung, temporary restoration of two-lung ventilation, or protocol interruption for safety reasons.	During the first 20 minutes after initiation of one-lung ventilation on Day 1.
Incidence of intraoperative hypotension	Intraoperative hypotension will be defined as mean arterial pressure <65 mmHg sustained for more than 1 minute.	Intraoperative/periprocedural period on Day 1, from induction of anesthesia until the end of surgery.
Requirement for intraoperative vasopressor support	Proportion of participants requiring vasopressor administration during the intraoperative period. Vasopressor use will be recorded as a measure of the hemodynamic safety of the assigned PEEP strategy.	Time Frame: Intraoperative/periprocedural period on Day 1, from induction of anesthesia until the end of surgery.
Incidence of postoperative pulmonary complications	Occurrence of at least one prespecified postoperative pulmonary complication, including acute respiratory failure, pneumonia, acute respiratory distress syndrome, atelectasis, pneumothorax, bronchopleural fistula, aspiration pneumonitis, pulmonary embolism, pleural empyema, bronchospasm, pleural effusion, or need for postoperative respiratory support or reintubation for respiratory deterioration. This outcome will be considered exploratory.	From the end of surgery until hospital discharge during the index hospitalization (estimated average duration: 3-10 days).

Collaborators and Investigators

• Sponsor: Jesús Manuel Nieves Alonso

Study record dates

Study Major Dates

• Study Start (Actual): October 7, 2026
• Primary Completion (Estimated): March 1, 2028
• Study Completion (Estimated): March 30, 2028

Study Registration Dates

• First Submitted: September 21, 2026
• First Submitted That Met QC Criteria: September 25, 2026
• First Posted (Actual): October 1, 2026

Study Record Updates

• Last Update Posted (Actual): October 9, 2026
• Last Update Submitted That Met QC Criteria: October 8, 2026
• Last Verified: October 1, 2026

More Information

Terms related to this study

• Keywords: Postoperative pulmonary complications; Respiratory mechanics; One-lung ventilation; Thoracic surgery; Hypoxemia; Lung resection; Driving pressure; Lung-protective ventilation; Respiratory system compliance; Positive end-expiratory pressure; PEEP; Body mass index; BMI
• Additional Relevant MeSH Terms: Signs and Symptoms, Respiratory; Pathological Conditions, Signs and Symptoms; Signs and Symptoms; Hypoxia
• Other Study ID Numbers: SIMPLE-PEEP

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: UNDECIDED

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No