Previous research has highlighted the importance of brain-lung interaction in critically unwell individuals. Nonetheless, further investigation is required to know the pathophysiological linkages between the lungs and brain to develop neuroprotective-type ventilatory treatments for people with acute brain injury (ABI), provide advice on conflicting therapies for people with concomitant lung and brain injury, and increase predictive modeling efforts to enhance tracheostomy and extubation decisions.

In a recent editorial published within the journal BMC Pulmonary Medicine, researchers review evidence on the crosstalk between the lung and brain and identified potential areas for further research.

Study: Brain-lung crosstalk: how should we manage the respiration brain? Image Credit: Prapat Aowsakorn / Shutterstock.com

How do the lungs and brain interact?

ABI can precipitate lung injury and modulate pulmonary physiology through several mechanisms, including elevated intracranial pressure (ICP), systemic inflammatory response, hormonal dysregulation, catecholamine surges, and dysregulated central respiration control.

Moreover, arterial blood gas derangements and systemic inflammation can precipitate secondary brain injury. Long-standing cognitive deficits and mood disorders occur incessantly after acute respiratory distress syndrome (ARDS).

One phase II randomized controlled trial (RCT) showed that a method based on continuous brain tissue oxygen (PbtO2) and ICP led to less cerebral hypoxia and fewer deaths amongst individuals affected by severe trauma to the brain. As a driver of blood flow to the brain, the partial pressure of carbon dioxide (PaCO2) is crucial in ABI. Researchers have also investigated different ventilator variables and their associations with ABI results.

ARDS is incessantly reported amongst critically sick ABI patients and may end up in hostile consequences. Nonetheless, ARDS investigations have excluded individuals with neurological illnesses, notably those with increased ICP. The danger of ICP increases attributable to pulmonary protective ventilation, prone position (PP), or increased positive end-expiratory pressure (PEEP) levels amongst individuals with ARDS and ABI.

In line with recent research, protective lung ventilation was used more incessantly in ABI between 2004 and 2016. Nevertheless, only 53% of clinicians utilized 4.0-6.0 ml/kg of predicted body weight (PBW) for ABI patients with a partial pressure of oxygen (PaO2)/fraction of inspired oxygen (FiO2) ratio lower than 150.

One recent RCT reported no significant impact of protective lung ventilation on brain self-regulation and ICP levels in most patients. Nonetheless, 22% required protocol interruptions attributable to prolonged ICP rises.

Several studies assessing the impact of positive end-expiratory pressure on ICP have yielded conflicting results. For instance, some studies have reported that cerebral perfusion pressure (CPP) and ICP are mediated by PEEP-based reductions in average arterial pressure and cardiac output. Comparatively, other studies reported that PEEP-mediated ICP increases are inclined to occur amongst individuals with poor pulmonary conformity.

As well as, the recently published SETPOINT-2 multicenter RCT amongst mixed stroke individuals reported no significant advantages of performing tracheostomy within the initial five days. Notably, 22 individuals who underwent tracheostomy within the later period could wean from mechanical ventilators and didn’t need tracheostomy placements.

Future perspectives on the brain-lung crosstalk

ABI patients comprise 25% of people requiring MV. Nonetheless, there may be scarce evidence to guide ventilatory targets on this population.

Cerebral and pulmonary pathophysiology are intimately connected through complex and sometimes bi-directional pathways that remain unclear. Different arterial blood gas targets could also be needed in some patients to reduce secondary ischemic brain injury, optimize ICP, or enhance cerebral perfusion.

A recent European Society of Intensive Care Medicine (ESICM) consensus statement acknowledges uncertainties and the paucity of evidence regarding ventilator targets and parameters for patients with ABI. Optimal PaO2 and PaCO2 ranges remain to be determined for ABI patients. The potential advantages of targeting therapeutic PaCO2 ranges in specific ABI subpopulations have to be studied.

Given their impaired airway defenses and decreased degree of consciousness, ABI patients incessantly should be mechanically ventilated. Thus, further prognostic clarification is required to tell tracheostomy and extubation decisions.

The recent prospective-design ENIO trial reported a 19% failure rate for extubation inside five days; nevertheless, the low precision of the rating indicates that accurately forecasting extubation success stays a challenge. The indications and optimal timing for tracheostomy placement proceed to be debatable.

Conclusions

The editorial highlights lung-brain interactions and identifies necessary areas for further research. Additional studies are needed to emphasise novel findings on the pathophysiological lung-brain interplay, inform MV techniques in ABI, aid in assessing the lung-brain dispute, and enhance predictive models used to guide tracheostomy and extubation decisions.

Journal reference:

• Wahlster, S., Town, J. A., Battaglini, D. et al. (2023). Brain-lung crosstalk: how should we manage the respiration brain?. BMC Pulmonary Medicine 23(180). doi:10.1186/s12890-023-02484-7