A 20-year-old male patient with no medical history is admitted in the operating room for emergent decompressive craniotomy after a motorbike accident causing a posterior cranial fossa epidural hematoma (diagnosed on CT scan). The neurosurgeon accesses the posterior fossa and relieves an opening pressure of 40 cm H2O. Very quickly, the patient develops severe hypotension with a blood pressure of 50/30 mm Hg, for which high-dose norepinephrine is started. He also develops hypoxemia with an alveolar-arterial gradient of more than 100 mm Hg. In addition, the end-tidal CO2 concentration drops by 10 mm Hg. With a high-dose noradrenaline infusion, the BP returns to normal, but hypoxia remains.
Which among the following is most likely to be present in this patient?a. Ischemic changes in electrocardiogram
Correct Answer: B
The fulminant form of neurogenic pulmonary edema (NPE) develops between 30 and 60 minutes following neurologic injury and has been characterized by hypoxemia with an alveolar-arterial gradient of more than 100 mm Hg, a chest x-ray showing extensive pulmonary edema, the presence of a preserved cardiac output, and the absence of ischemic sign on the electrocardiogram. Typically, these patients have pink frothy fluid on tracheal aspiration or sputum if endotracheal intubation has not been performed yet. Cardiogenic pulmonary edema (CPE) is the main differential diagnosis and may be present at the same time as NPE. In this scenario, though, hypotension occurs specifically at posterior fossa decompression, which can be explained by waning of the Cushing reflex causing a drop in adrenal release of catecholamines. A persisting low end-tidal CO2 concentration would indicate air embolism which typically occurs as a result of air entering a cerebral vein, especially when the patient is in a sitting position. In this case, the pressure of the posterior cranic fossa is positive making this unlikely.