A 70-year-old male patient with a history of pulmonary hypertension and smoking has been admitted to the neurocritical care unit because of a Hunt and Hess Grade 4 subarachnoid hemorrhage (SAH) caused by a ruptured aneurysm of the anterior communicating artery (ACA). Successful endovascular clot retrieval was performed on day 1. On day 4, his hypoxemia worsened, reaching a ratio of PaO2 to inspired oxygen (FiO2 ) of less than 200 mm Hg at a FiO2 of 0.6. The chest x-ray shows bilateral diffuse infiltrates suggestive of pulmonary edema.
Which among the following is the best test to identify the cause of pulmonary edema?
A. Transpulmonary thermodilutionCorrect Answer: A
Neurogenic pulmonary edema typically occurs within 72 hours after the onset of neurologic injury, but can occur later as well. It results in a combination of cardiogenic and noncardiogenic pulmonary edema and occurs as a result of a large sympathetic stimulus causing hydrostatic as well as permeability pulmonary edema. In this patient, identifying the degree of contribution to lung edema from hydrostatic versus permeability will help guide therapy. Transpulmonary thermodilution technique allows the calculation cardiac index, extravascular lung water index (ELWI), and pulmonary vascular permeability index, which will help differentiate between purely hydrostatic (cardiogenic) pulmonary edema from that occurring due to increased capillary pulmonary permeability.
Although, CT scan might give information on type of lung pathology, it would not differentiate between cardiogenic and noncardiogenic pulmonary edema. Similarly, lung ultrasound will not differentiate between types of pulmonary edema but is most effective in monitoring effect of treatment on pulmonary interstitial fluid. Measuring circulating levels of catecholamines is reasonable as well, but it only allows to identify a specific subset of patients who may benefit of alfa-adrenergic blockade.
Reference: