Summary:Total hip arthroplasty is occasionally accompanied by a syndrome of hypotension, hypoxemia, tachycardia, and rarely cardiac arrest. The etiology of this remains somewhat obscure, although clinical and animal research have strongly implicated embolism of marrow contents to the pulmonary vascular bed as a potential cause for this syndrome. The author and a number of anesthesia and surgical colleagues made a step-wise search to confirm pulmonary fat embolism as a cause for this event. By using an established and by now well-recognized canine model for pulmonary fat embolism, we confirmed that marrow content is capable of causing all of the changes seen in this syndrome in the clinical situation. The vasoactive factors actually responsible for the changes have not yet been identified.