The beneficial effects of inhaled nitric oxide in patients with severe traumatic brain injury complicated by acute respiratory distress syndrome: a hypothesis

Inhalational Gases for Neuroprotection in Traumatic Brain Injury

Despite multiple prior pharmacological trials in traumatic brain injury (TBI), the search for an effective, safe, and practical treatment of these patients remains ongoing. Given the ease of delivery and rapid absorption into the systemic circulation, inhalational gases that have neuroprotective properties will be an invaluable resource in the clinical management of TBI patients. In this review, we perform a systematic review of both pre-clinical and clinical reports describing inhalational gas therapy in the setting of TBI. Hyperbaric oxygen, which has been investigated for many years, and some of the newest developments are reviewed. Also, promising new therapies such as hydrogen gas, hydrogen sulfide gas, and nitric oxide are discussed. Moreover, novel therapies such as xenon and argon gases and delivery methods using microbubbles are explored.

Acute respiratory distress syndrome in traumatic brain injury: how do we manage it?

Traumatic brain injury (TBI) is an important cause of morbidity and mortality worldwide. TBI patients frequently suffer from lung complications and acute respiratory distress syndrome (ARDS), which is associated with poor clinical outcomes. Moreover, the association between TBI and ARDS in trauma patients is well recognized. Mechanical ventilation of patients with a concomitance of acute brain injury and lung injury can present significant challenges. Frequently, guidelines recommending management strategies for patients with traumatic brain injuries come into conflict with what is now considered best ventilator practice. In this review, we will explore the strategies of the best practice in the ventilatory management of patients with ARDS and TBI, concentrating on those areas in which a conflict exists. We will discuss the use of ventilator strategies such as protective ventilation, high positive end expiratory pressure (PEEP), prone position, recruitment maneuvers (RMs), as well as techniques which at present are used for 'rescue' in ARDS (including extracorporeal membrane oxygenation) in patients with TBI. Furthermore, general principles of fluid, haemodynamic and hemoglobin management will be discussed. Currently, there are inadequate data addressing the safety or efficacy of ventilator strategies used in ARDS in adult patients with TBI. At present, choice of ventilator rescue strategies is best decided on a case-by-case basis in conjunction with local expertise.

The Pathophysiology of Nitrogen Dioxide During Inhaled Nitric Oxide Therapy

Administration of inhaled nitric oxide (NO) with the existing compressed gas delivery systems is associated with unavoidable codelivery of nitrogen dioxide (NO2), an unwanted toxic contaminant that forms when mixed with oxygen. The NO2 is generated when NO is diluted with O2-enriched air before delivery to the patient. When NO2 is inhaled by the patient, it oxidizes protective antioxidants within the epithelial lining fluid (ELF) and triggers extracellular damage in the airways. The reaction of NO2 within the ELF triggers oxidative stress (OS), possibly leading to edema, bronchoconstriction, and a reduced forced expiratory volume in 1 second. Nitrogen dioxide has been shown to have deleterious effects on the airways of high-risk patients including neonates, patients with respiratory and heart failure, and the elderly. Minimizing co-delivery of NO2 for the next generation delivery systems will be a necessity to fully optimize the pulmonary perfusion of NO because of vasodilation, whereas minimizing the negative ventilatory and histopathological effects of NO2 exposure during inhaled NO therapy.

The role of inhaled nitric oxide beyond ARDS

Patients with traumatic brain injury complicated by acute respiratory distress syndrome (ARDS) are not uncommon in intensive care unit (ICU). The ventilatory management of patients combined with both of these catastrophic conditions is not straightforward. Evidence-based permissive hypercapnia strategy for ARDS could be fatal in patients with intracranial hypertension. Adjunctive use of inhaled nitric oxide (INO) is well-defined as a rescue therapy in severe ARDS, but its specific role in intracranial hypertension is somewhat uncertain. We report a case, which following traumatic brain injury developed both intracranial hypertension and ARDS. INO was given for ARDS, but coincidentally it also improved the raised intracranial pressure (ICP) and patient's neurological outcome. The case report will be followed by literature review on the role of INO in raised ICP.

Ventilatory strategies for patients with acute brain injury

PURPOSE OF REVIEW

The ventilation of patients with acute brain injuries can present significant challenges. Frequently, guidelines recommending management strategies for patients with traumatic brain injuries come into conflict with what is now considered best ventilatory practice. In this review, we will explore many of these areas of conflict.

RECENT FINDINGS

The use of ventilatory strategies to control partial pressure of carbon dioxide in patients with traumatic brain injury is associated with the development of acute lung injury. Analysis of the International Mission for Prognosis And Clinical Trial (IMPACT) database has confirmed the association between hypoxia and poor neurological outcome. Although a recent meta-analysis has suggested a survival benefit for steroids in acute lung injury, the use of steroids has been associated with a worsening of outcome in patients with traumatic brain injuries and their effects on the brain have not been fully elucidated.

SUMMARY

There are unlikely to be randomized controlled trials advising how best to ventilate patients with acute brain injuries because of the heterogeneous nature of such injuries. Hypoxia should be avoided. The more widespread use of multimodal brain monitoring, including brain tissue oxygen and cerebral blood flow monitoring, may allow clinicians to tolerate a higher arterial partial pressure of carbon dioxide than has been traditional, allowing a less injurious ventilatory strategy. Modest positive end-expiratory pressure can be used. In severe respiratory failure, most 'rescue' strategies have been attempted in patients with acute brain injuries. Choice of rescue therapy at present is best decided on a case-by-case basis in conjunction with local expertise.