Evaluation of Respiratory Mechanics in Supine and PARK-bench Positions (SPARK)

The Park-Bench position is a variant of the lateral position used in neurosurgical interventions where lesions of the posterior cranial fossa and ponto-cerebellar angle need to be approached. The patient is placed in a lateral-oblique position with the arm on the side they are lying on extending out of the operating bed and supported by an external support. The head is fixed in flexion and rotation with the Mayfield headrest immobilizing the head, allowing exposure of the surgical region of interest.

In the lateral decubitus position, several factors contribute to changing respiratory mechanics: airway resistance increases and compliance decreases.

Furthermore, the gravitational gradient is altered, which is one of the main factors in the regional distribution of intrapulmonary air volume and tidal volume distribution: the phenomenon of overdistension of the non-dependent lung and collapse of the dependent lung could occur.

Fully understanding these physiological changes could optimize mechanical ventilation settings and thus avoid causing damage to lung parenchyma (Ventilator-Induced Lung Injury).

The primary hypothesis of this physiological study is to evaluate changes in regional distribution of intrapulmonary volume when transitioning from the supine position to the Park-Bench position.

Inclusion criteria

• Age >18
• Patients scheduled for elective neurosurgery in Park-Bench position.

Exclusion criteria

• Age < 18
• BMI > 30 kg/m2
• Obstructive or restrictive lung disease with oxygen supplementation
• Pacemaker
• Pregnancy
• Absence of history of pulmonary embolism, thoracic surgery or chest wall abnormalities, organ transplant, lung metastases
• New York Heart Association >2 or hemodynamic instability (Mean Arterial Pressure<60mHg)