Dead Space Postscript


1 – an extra piece of information about an event that is added after it has happened

The patient in question did in fact have a massive pulmonary embolus known as a Saddle PE. Because the embolus lodged in the pulmonary artery at the bifurcation between the left and right branch, much of his lung capacity was not actively engaging in gas exchange. He was not able to offload the EtCO2 or fully oxygenate the blood. His altered state was actually a hypoxic event even though his lungs were clear and had perfect tidal volume. The EtCO2 reading was the only finding, other than skin signs and oxygen hunger, that pointed me in the right direction.

Upon turning him over to the MD at the ED I concluded my report with my findings and a differential diagnosis of PE. This bought me a raised eyebrow from the MD as a PE is a very difficult thing to diagnose without the help of a CT. That same MD seemed a little more on board with my findings when the patient flat lined ten minutes later and subsequently three more times before they pushed thrombolytics to dissolve the clot.

Later that night he was moved to the ICU and extubated the next day. He recovered with no lasting deficits yet he remained in the hospital for two more weeks as they continued to administer blood thinners and observe for any reoccurring emboli.

The bifurcation of the cherry tree is a beautiful analog for the inner vasculature of the lungs. Nutrients are carried along the trunk to the blossoms where gas exchange occurs and photosynthesis creates energy that is then carried back along the trunk. When a branch is injured the blossoms die and create a dead space. The cherry tree has the advantage of many bifurcated branches to continue the cycle – we only have one.

Dead Space

A decrease in perfusion relative to ventilation (as occurs in pulmonary embolism, for example) is an example of increased dead space.[3] Dead space is a space at which gas exchange does not take place, such as the trachea. It is ventilation without perfusion.

Saddle Pulmonary Embolus

A large thrombus lodged at an arterial bifurcation, where blood flows from a large-bore vessel to a smaller one. The ‘classic’ saddle embolus—which occurs at the bifurcation of the pulmonary arteries in fatal pulmonary embolism secondary to a centrally migrating venous embolus—is distinctly uncommon.

Segen’s Medical Dictionary. © 2011

Massive pulmonary embolism

As a cause of sudden death, massive pulmonary embolism is second only to sudden cardiac death. Massive pulmonary embolism is defined as presenting with a systolic arterial pressure less than 90 mm Hg. The mortality for patients with massive pulmonary embolism is between 30% and 60%, depending on the study cited. Autopsy studies of patients who died unexpectedly in a hospital setting have shown approximately 80% of these patients died from massive pulmonary embolism.

The majority of deaths from massive pulmonary embolism occur in the first 1-2 hours of care, so it is important for the initial treating physician to have a systemized, aggressive evaluation and treatment plan for patients presenting with pulmonary embolism.



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