Effect of low tidal volume ventilation on cerebral hemodynamics in patients with severe traumatic brain injury

Ventilating acute brain injury patients, with normal lung, using low tidal volume (LTV) ventilation may lead to improved outcomes. Nonetheless, investigations are ongoing to understand its impact on intracranial pressure and cerebral oxygenation. Our study aimed to see the effect of LTV on optic nerve sheath diameter (ONSD) and regional cerebral oxygen saturation (rScO₂) in patients with severe traumatic brain injury (sTBI).

This single-center, prospective, single-blinded, pre-post interventional study included 18 patients with sTBI who were mechanically ventilated with standard high tidal volume (HTV) ventilation (10 ml/kg). After recording outcome variables, ONSD and rScO₂ with HTV, patients were ventilated with LTV (6 ml/kg) for 30 minutes and the outcome variables were recorded.

LTV had no effect on right ONSD (P = 0.94), whereas left ONSD was 0.04 cm less with LTV, but the difference in spite of reaching statistical significance (P = 0.04) was not clinically significant. Mean end-tidal carbon dioxide (EtCO₂) with LTV was 2.5 mm Hg more as compared to HTV. Adjusting for the effect of EtCO₂, ONSD was comparable bilaterally with both tidal volumes (right ONSD; P = 0.52 and left ONSD; P = 0.45). Change in tidal volume had no effect on rScO₂.

Our findings suggest that LTV does not affect ONSD and rScO₂ in sTBI patients. However, ventilator parameters should be guided to control EtCO₂. Larger studies are required to look at the effect of site of injury as a factor affecting ONSD.