Air embolism and blunt chest trauma.

To the Editor, I read with interest the case reported in the Journal describing the events surrounding the death of a child from unilateral blunt chest trauma due to coronary and cerebral arterial gas embolism (AGE). The authors used high frequency oscillatory ventilation (HFOV) for oxygenation with a mean airway pressure of 18 cmH2O because the child’s hemoptysis raised concerns regarding airway-vascular connections. Any form of positive pressure ventilation, including HFOV, may contribute to air embolism when pulmonary vessels are damaged. The authors mentioned methods to ensure ‘‘separation of the lungs and the air from the blood’’, and this could have been achieved using a double-lumen endotracheal tube or bronchial blocker (DLT/BB). This and other reported cases suggest strongly that isolation of a lung or lobe is essential if positive pressure ventilation is used in such circumstances. Prompt hyperbaric oxygen treatment (HBOT) is indicated for AGE and may be undertaken with a DLT/BB, but HFOV would be difficult and potentially dangerous in a hyperbaric chamber. At six atmospheres absolute (ATA) pressure, bubble volume decreases immediately to 17% (Boyles Law) with potential for rapid clinical improvement. Despite HFOV with 100% oxygen, sufficient nitrogen likely remained in the patient’s lungs to constitute a substantial portion of the embolizing gas. Oxygen solubility, hemoglobin-binding, and metabolism would result in diffusion out of bubbles, but insoluble inert nitrogen gas may persist for days. Hyperbaric oxygen treatment (using U.S. Navy Decompression Table 6A, perhaps with 50:50 oxyhelium while at six atmospheres absolute [ATA]) to reduce cerebral (seizures) and pulmonary oxygen toxicity while eliminating nitrogen from the inspired gas increases the diffusion gradient for enhanced nitrogen elimination and may help to deliver oxygen to ischemic tissues. Additional benefits may result from HBOT effects on the response to endothelial and systemic inflammatory reactions to the gastissue interface. At three ATA oxygen (three ATA on100% oxygen or six ATA on 50% oxygen), arterial pO2 may exceed 2,000 mmHg with normal lungs. Therefore, even with a 50% shunt and one-lung ventilation, oxygenation inside the chamber is most unlikely to be inadequate. Low pressure continuous positive airway pressure (5 cmH20) to the unventilated lung could be implemented easily if oxygenation were inadequate; even so, it could have a small risk. However, unless vascular entry of inert gas is stopped using DLT/BB, treatment cannot succeed. This profoundly difficult tragic case suggests low airway pressure HFOV is contraindicated when air is entering the pulmonary vessels, and future optimal management for such cases is DLT/BB and prompt HBOT.