Synchronized Intermittent Mandatory Ventilation (SIMV) is a commonly used ventilatory mode available in many modern ventilators, frequently applied in intensive care units for patients requiring invasive mechanical ventilation. SIMV delivers a preset tidal volume or pressure at a predetermined respiratory rate and synchronizes with the patient's spontaneous breathing efforts, thereby enhancing patient-ventilator interaction and contributing to rehabilitation.

Mandatory Minute Ventilation (MMV) is a hybrid mode combining features of SIMV and Pressure Support Ventilation (PSV), guaranteeing a preset minute ventilation (tidal volume × respiratory rate). It synchronizes support based on the patient's spontaneous efforts and compensates in cases of insufficient minute ventilation.

Electrical Impedance Tomography (EIT) is a non-invasive, radiation-free imaging technique that enables real-time monitoring of pulmonary ventilation and perfusion by applying alternating electrical currents through surface electrodes. EIT has demonstrated strong correlation with findings from computed tomography, nitrogen washout, PET, and SPECT imaging modalities.

This study aims to evaluate the effectiveness of MMV compared to SIMV in mechanically ventilated, hemodynamically stable adult patients (>18 years old) in the intensive care unit. Patients must not require vasopressors, have a FiO₂ ≤ 60%, PEEP ≤ 8 cmH₂O, or receive neuromuscular blocking agents.

Patients will be monitored under both SIMV and MMV modes, separated by a 12-hour interval. To minimize carry-over effects, a one-hour washout period will be implemented before data collection with EIT. Key parameters including PO₂/FiO₂ ratio, PaCO₂, and EtCO₂ will be assessed. The sequence of ventilatory mode application will follow a crossover study design.

Synchronized Intermittent Mandatory Ventilation (SIMV) and Mandatory Minute Ventilation (MMV) are two established modes of mechanical ventilation commonly used in intensive care settings. SIMV delivers a fixed number of breaths with preset tidal volume or pressure, while allowing the patient to breathe spontaneously between mandatory breaths, enhancing patient-ventilator synchrony. MMV combines features of SIMV and Pressure Support Ventilation (PSV), ensuring a target minute ventilation by supplementing spontaneous efforts when necessary.

Electrical Impedance Tomography (EIT) is a non-invasive, radiation-free imaging modality that provides real-time monitoring of regional lung ventilation and perfusion through surface electrodes. EIT has been validated against conventional imaging and monitoring methods including computed tomography, nitrogen washout, PET, and SPECT. It enables continuous bedside evaluation of ventilation distribution, making it particularly useful for guiding mechanical ventilation strategies in critically ill patients.

This prospective, single-center, crossover study aims to evaluate the effectiveness and physiological impact of MMV compared to SIMV in adult ICU patients who are hemodynamically stable but require mechanical ventilation due to various non-neuromuscular reasons. Inclusion criteria require patients to be over 18 years old, not on vasopressor therapy, with FiO₂ ≤ 60%, and without the need for high PEEP (>8 cmH₂O) or neuromuscular blockade.

Each patient will be ventilated with both SIMV and MMV modes for 12 hours each, with the order of modes randomized using a crossover design. To eliminate carry-over effects, a one-hour washout period will be implemented between mode transitions. During each ventilation mode, EIT will be used to assess real-time regional ventilation distribution. Additionally, gas exchange parameters including PO₂/FiO₂ ratio, PaCO₂, and EtCO₂ will be recorded. The primary objective is to determine whether MMV offers comparable or superior ventilation distribution and gas exchange compared to SIMV in this specific patient population.

Inclusion Criteria:

• Age ≥ 18 years

Intubated and receiving invasive mechanical ventilation

Hemodynamically stable (no vasopressor support)

FiO₂ ≤ 60%

PEEP ≤ 8 cmH₂O

Not receiving neuromuscular blocking agents

Able to tolerate switching between SIMV and MMV modes

Exclusion Criteria:

Pregnant or breastfeeding patients

Patients with neuromuscular diseases affecting respiratory drive

Unstable hemodynamics or ongoing need for vasopressors

Patients requiring high PEEP (>8 cmH₂O)

Patients with DNR (do not resuscitate) status

Participation in another interventional study

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Adult patients (≥18 years) admitted to the intensive care unit who are intubated and receiving invasive mechanical ventilation. All participants are hemodynamically stable and not receiving vasopressors, high levels of PEEP, or neuromuscular blockers at the time of enrollment.

IPD will not be shared due to the limited sample size and the absence of prior consent for data sharing from participants. The collected data is intended solely for internal analysis within the study team.