Effect of Ventilation Mode in the Pupillary Light Reflex: A Crossover Study

Launched by EVANGELISMOS HOSPITAL · Jul 23, 2025

Keywords

ClinConnect Summary

This clinical trial is studying how different types of mechanical breathing support, called ventilation modes, might affect the way the pupils in the eyes respond to light in critically ill patients who do not have brain injuries. The researchers want to see if changing the ventilation method influences how quickly the pupils get smaller when exposed to light, which could show subtle changes in how the brain controls automatic body functions. They will compare three common ventilation settings—volume control, pressure control, and pressure-regulated volume control—by measuring pupil responses while patients are switched between these modes.

Patients who might take part are adults in the ICU who are on a breathing machine but are not yet ready to breathe on their own. They need to be fairly stable, lightly sedated or awake enough to respond, and have a small tube in their artery to monitor blood gases. Patients with brain problems, facial injuries, or who are having trouble syncing with the ventilator won’t be eligible. If enrolled, participants will have their pupils measured with a special device while receiving each ventilation mode for about 15 minutes, under steady lighting and sedation conditions. This study aims to better understand how breathing support may subtly affect brain and nerve function in very sick patients.

Gender

ALL

Eligibility criteria

• • Inclusion Criteria
• • Adult patients (≥18 years old)
• • Receiving positive-pressure mechanical ventilation
• • Under light or no sedation (e.g., RASS score between -2 and 0)
• • Clinically assessed by the treating physician as not yet ready for weaning from mechanical ventilation
• • Hemodynamically stable at the time of measurement
• • Presence of an arterial catheter in place for blood gas analysis
• • Written informed consent obtained from the patient's legal representative Exclusion Criteria
• • Acute or chronic neurological disease affecting brainstem function or pupillary responses
• • Dyssynchrony with the ventilator or need for high ventilatory support adjustments
• • Facial injuries, edema, or conditions precluding accurate pupillometry
• • Use of neuromuscular blocking agents within the prior 6 hours
• • Severe metabolic or acid-base imbalances that may influence autonomic regulation
• • Concurrent participation in another interventional study that could affect neurological or autonomic outcomes