Impact of optic nerve sheath diameter variations on respiratory mechanics in ventilated traumatic brain injury...

In traumatic brain injury (TBI) patients, elevated intracranial pressure leading to brain-lung interactions is well described. This study aimed to find the association between the optic nerve sheath diameter (ONSD) variations and respiratory mechanics, that is, static lung compliance (Cstat), and driving pressure (DP) in TBI patients. The secondary objectives were to observe the association between ONSD and lung ultrasound score (LUS), arterial partial pressure of oxygen and fraction of inspired oxygen ratio (PaO₂/FiO₂), and clinical pulmonary infection score (CPIS).

The prospective observational study, conducted at a tertiary care centre, recruited patients with moderate to severe TBI admitted to the neuro-intensive care unit within 24 h of injury. From day 1 to 5, once a day, ONSD, Cstat, DP, minute ventilation (MV), and LUS were recorded. The association between the ONSD variations and respiratory mechanics, LUS, PaO₂/FiO₂ ratio, and CPIS was studied using linear mixed-effect models.

A total of 27 patients were included. No significant association was found between ONSD and Cstat [ipsilateral ONSD: model coefficient (β) = 1.13, P = 0.70; contralateral ONSD β = 2.0, P = 0.46] and driving pressure (ipsilateral ONSD: β = 0.18, P = 0.82; contralateral ONSD: β = 0.29, P = 0.7). Higher MV was observed with higher ONSD (ipsilateral ONSD: β = 1.44, P = 0.033; contralateral ONSD: β = 2.23, P = 0.001). ONSD variations were not associated with LUS, PaO₂/FiO₂, or CPIS.

Variations in ONSD did not impact the respiratory mechanics of ventilated acute TBI patients, though patients with higher ONSD were found to have higher MV.