Pulmonary edema is a disease in which fluid seeps into the lungs’ air sacs (alveoli), impairing their ability to transfer oxygen into the blood. This condition has a plethora of causes. When it develops quickly due to an associated pathology in the body’s central nervous system, it is referred to as neurogenic pulmonary edema.
Etymology
Neuro + genic:
Neuro: meaning related to or originating from the nervous system.
Genic: meaning to be generated or produced from something.
Pathophysiology
The mechanism by which neurogenic pulmonary edema develops is not very well understood and has been controversial. A structure found in the brainstem, called the medulla oblongata, is believed to be a critical factor in the development of the disease. The most likely link between a neural insult and alveolar flooding is through a massive increase in the pressure inside the skull (often called the cranium) in response to the nervous system injury associated with a deluge of neurochemicals called catecholamines, which include adrenaline.
These neurochemicals affect the lungs’ blood vessels, causing them to become more permeable to fluids, thus allowing the transfer of water from the blood vessels into the alveoli. They also narrow some of the body’s blood vessels (the systemic circulation), making it more difficult for the heart to pump blood efficiently into them. This tires out the left ventricle of the heart, and blood start to accumulate within it, then within the left atrium above it as well. This consequently causes backup of residual blood into the lungs’ blood vessels, which generally pour their blood into the left atrium. The congested pulmonary vasculature inevitably leaks fluid into the air spaces, causing pulmonary edema.
The hypothesis that these chemicals cause direct injury to the heart has also been proposed. The damaged heart cannot pump blood efficiently, forcing more and more accumulated blood into the pulmonary vascular tree, which seeps into the air sacs.
» Now, Let’s discuss causes, symptoms and treatment of Neurogenic Pulmonary Edema
Causes
The neurological insults that cause neurogenic pulmonary edema are often exceptionally severe. This, unfortunately, means that many potential cases of neurogenic pulmonary edema may be left undiagnosed. These diseases include:
- Epilepsy or seizures, especially the more malevolent form “Status Epilepticus,” which is characterized by prolonged or rapidly recurring convulsions.
- Bleeding inside the head, such as that caused by a stroke.
- Head trauma, including bullet wounds, blunt trauma, or penetrating trauma.
- Brain tumors such as glioma.
- Multiple Sclerosis (MS).
- Injury to the spinal cord.
- Meningitis or encephalitis (infection of the brain).
Symptoms
Like all pulmonary edema types, the most common symptom of neurogenic pulmonary edema is a sudden difficulty in breathing. This is because the fluid filling the lungs’ air sacs impairs their ability to transfer oxygen to the bloodstream. In severe cases, the patient may breathe heavily, even at rest.
Another symptom is coughing, which may produce pinkish, frothy, blood-tinged sputum. Patients may also experience wheezing, which is a high-pitched whistling sound heard while breathing and is caused by narrowing of the person’s airways through which air flows rapidly. Fast breathing and a pounding heart may also be felt. A concurrent fever is often present in cases with concomitant meningitis.
The patient obviously also presents with the neurological insult that predisposed to the pulmonary edema, which sometimes overshadows the lung disease.
Treatment
The three essential resuscitative steps for stabilizing the patient are indispensable.
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- Clearing and securing the airway is often done first. It may require putting a breathing tube inside the patient’s trachea.
- The second step is to administer oxygen through a face mask or using nasal prongs,
- and the third step is injecting medications that make the heart’s job easier, including diuretics, nitroglycerin, dopamine, dobutamine, Angiotensin-Converting Enzyme Inhibitors (ACE inhibitors), and Angiotensin II Receptor Blockers (ARBs).
These are often referred to as the “ABCs”: Airway, Breathing, and Circulation.
The most critical step, however, is to correct the underlying neurological problem. If the neural pathology is treated, the torrent of catecholamines is stopped, and the neurogenic pulmonary edema often resolves on its own within hours. Treatment of the cause is either medical or surgical:
Medical treatment of neurogenic pulmonary edema is not very well documented in the literature but should include alpha-blockers, which prevent catecholamines from acting on the respiratory and cardiovascular systems, thus directly combating the most likely mechanism for the development of neurogenic pulmonary edema.
Patients with intracranial bleeding should be given drugs to cautiously decrease blood pressure, as well as clotting factors to stop the hemorrhage. Seizure patients should receive antiepileptic drugs, and people with bacterial meningitis need antibiotics, bed rest, and antipyretics.
Surgical care is often considered the mainstay of therapy. Examples include surgical decompression, clipping or coiling of the blood vessels that bled into the brain or removing the incriminated brain tumor.