Blast Lung Injury Severity Score

Why Use

Useful in guiding triage decisions in the setting of mass casualties, determining ventilation treatment, and predicting outcomes. BLI severity correlates with the likelihood of developing acute respiratory distress syndrome (ARDS), and can be helpful to delineate patients who will require more aggressive and potentially unconventional respiratory care (e.g. nitric oxide, high-frequency jet ventilation, independent lung ventilation, or extracorporeal membrane oxygenation).

When to Use

Patients with respiratory symptoms after blast injury.

Formula

Pearls / Pitfalls

Primary blast injury (PBI) occurs when a blast wave accelerates and decelerates while traveling through tissues of varying density. Thus, PBI affects organs with greater air-tissue interfaces such as auditory, pulmonary, and gastrointestinal systems. Primary blast lung injury (BLI) is radiological and clinical evidence of acute lung injury occurring after blast injury that is not due to secondary or tertiary blast injury. The pathophysiology is thought to be due to capillary rupture within alveoli leading to hemorrhage and pulmonary edema, which then reduce gas exchange, causing hypoxia and hypercarbia. Clinical suspicion of primary BLI should be high after blast injury within an enclosed space, as the blast wave becomes amplified as it reflects off of the structural walls ( Leibovici 1996 ). Characteristic chest x-ray shows bilateral diffuse opacities in a “butterfly” pattern. Patients present with hypoxemia with associated pneumothoraces, bronchopleural fistulae, or hemoptysis. In the studies, patients diagnosed with BLI were intubated immediately or within 2 hours of presentation due to respiratory decompensation. Thus, patients breathing spontaneously and adequately 2 hours after injury are unlikely to require mechanical ventilation because of BLI alone ( Pizov et al 1999 , Avidan et al 2005 ).

Management

Intubated patients require the following ventilation management: Mild BLI patients will usually require volume-controlled or pressure support ventilation modes. PEEP requirement is ≤5 cm H₂O. Moderate BLI will use conventional ventilator modes, including inverse-ratio ventilation as needed. PEEP requirement is 5-10 cm H₂O. Severe BLI will use conventional ventilator modes and commonly require additional therapies such as nitric oxide, high-frequency jet ventilation, independent lung ventilation, or extracorporeal membrane oxygenation. PEEP requirement is >10 cm H₂O.

Advice

Screening chest x-rays for asymptomatic patients is not recommended ( Matthews et al 2015 ), as patients with blast lung injury (BLI) present either immediately or early with hypoxemia. Contrary to previous belief that the clinical picture of BLI may develop over 24 to 48 hours, studies have shown that patients do not present with a delay in manifestation of lung injury ( Pizov et al 1999 , Avidan et al 2005 ). Similarly, it was previously suggested that tympanic membrane (TM) rupture, the most common primary blast injury, was a marker for increased risk of development of BLI. Studies have shown that TM perforation is in fact poorly correlated with BLI ( Leibovici et al 1999 , Ballivet de Regloix 2017 ). Low inspiratory pressure with avoidance of positive end-expiratory pressure (PEEP) is ideal in BLI in order to avoid secondary barotrauma, arterial air embolism, or pneumothorax. However, patients with blast lung often have injury patterns similar to acute respiratory distress syndrome (ARDS) and require positive pressure ventilation (PPV) and PEEP. Other treatment considerations include avoiding aggressive intravenous hydration after physiology capture, as it can worsen pulmonary edema, and considering the need for a prophylactic thoracostomy tube before air transportation.

More Information

Interpretation: BLI Severity Score Severity ARDS Risk (ARDS 24 hrs post-injury)* BLI-associated mortality* 0 Mild ~0% ~0** 1-4 Moderate 33% ~0% 5 Severe 100% 75% *From Pizov et al 1999 . Note the study was small (n = 10 patients). A more recent study by Avidan et al in 2005 saw 1 mortality out of 29 patients but not primarily due to pulmonary issues. **One patient with mild BLI died from head injury.