Mechanical ventilation (MV) is a life-saving supportive therapy and one of the most common interventions implemented in intensive care.

To date, only the inspiratory phase of breathing has been extensively investigated, and new MV methods have been implemented to reduce its harmful effects. Despite this, lung injury still occurs and propagates, causing multiorgan failure and patient deaths. The expiratory phase is considered unharmful and is not monitored or assisted during MV. In animal experiments, we recently showed that the loss of diaphragmatic contraction during expiration can harm the lungs during MV. During mechanical ventilation, the expiratory phase of breathing is completely disregarded. However, in all conditions that promote lung collapse, peripheral airways gradually compress and close throughout the expiration, potentially worsening lung injury.

This cyclical lung collapse and consequent air-trapping may have an impact on the Starling resistor mechanisms that regulate venous return from the brain, potentially affecting cerebral perfusion and intracranial pressure.

This study will investigate the incidence and the consequences of an uncontrolled expiration and expiratory lung collapse in spontaneously breathing critically ill neurosurgical patients during mechanical ventilation.

Electrical impedance tomography measurements , oesophagus and gastric pressure, electrical activity of the diaphragm and intracranial pressure will be acquired in a synchronised manner during controlled mechanical ventilation, on a daily bases during assisted mechanical ventilation.

Neurosurgical patients on mechanical ventilation and with ongoing intracerebral pressure monitoring will be included in the study

Inclusion Criteria:

• Age >18 years;
• MV expected for more than 72 hours;
• Not pregnant;
• Informed consent from patient or next of kin.

Exclusion Criteria:

• Previously demonstrated paralysis of the diaphragm or know pathology of the phrenic nerve or neuromuscular disorder;
• Chest tube;
• Patients with clinical conditions that contraindicate the insertion of esophageal/gastric catheters (e.g., esophagus rupture, esophageal bleeding);
• Pacemaker and/or implantable cardioverter defibrillator, these last being a contraindication for EIT;
• Hemicraniectomy. In case of late hemicraniectomy (after patient inclusion), the patient will drop-out from the study.

Relative contraindication: in case of skull base fracture the patient can be included only if oesophageal/gastric and NAVA catheters can be inserted orally.

Patients recruitment will be kept equally distributed between sexes.

Critically ill adult patients affected by acute brain injury (e.g., subarachnoid hemorrhage, subdural hemorrhage, epidural hemorrhage, traumatic brain injury, intracerebral hemorrhage) admitted to the NICU of Uppsala. Consecutive patients will be prospectively screened for eligibility according to inclusion criteria