Neurogenic pulmonary edema and other mechanisms of impaired oxygenation after aneurysmal subarachnoid hemorrhage

Introduction: Aneurysmal subarachnoid hemorrhage (SAH) affects 30,000 patients per year, causing neurologic morbidity and mortality. The etiology of hypoxemia and its role in comorbidity are controversial and unknown. Purpose: To identify the incidence and etiologies of oxygenation abnormalities following SAH and to determine its impact on length of hospital stay (LOS). Methods: We retrospectively reviewed 70 consecutive SAH patients' records, including review of computed tomography scans, chest X-rays, arterial blood gases, electrocardiograms, echocardiograms, blood pressure, carbon monoxide, central venous pressure, and pulmonary capillary wedge pressure. Fluid balance and chest X-ray interpretation on admission and at time of worst alveolar-arterial oxygen difference was assessed, as was length of hospital stay. Results: Fifty six (80%) patients had impaired oxygenation (alveolar-arterial oxygen difference >100 mmHg). Of these 56, 50% had normal chest Xrays. Patients were euvolemic and normodynamic with mean central venous pressure 8.8 +/- 4.1 mmHg and had normal cardiac output 6.8 +/- 2.4 L/min. The most frequent etiologies of hypoxemia based on composite data assessment were pneumonia 8/56 (14%), fulminant neurogenic pulmonary edema 9/56 (16%), atelectasis 5/56 (27%), and cryptogenic (57%). The mean length of stay was doubled in the impaired oxygenation group 19.3 days 14.6 compared with 7.1 +/- 4.3 days in the normal oxygenation group (p<0.001; df=36). Likewise, the patients with fulminant neurogenic pulmonary edema had a prolonged length of stay of 13.4 +/- 6.2 (p<0.002; df=27) compared with the normal oxygenation group. Neither the occurrence of vasospasm nor delayed neurologic deficit influenced the incidence of poor oxygenation (p<0.93). Conclusion: Oxygenation abnormalities after SAH occur more frequently than previously suspected. They are frequently the result of noncardiogenic and hydrostatic causes and contribute to an increased length of hospital stay.