The term Flash Pulmonary Edema reflects a common misconception. The typical scenario is the sudden development of severe respiratory distress in someone who has long standing hypertension. The presentation is a patient who arrives by ambulance in the emergency department with severe shortness of breath and breathing rapidly. The blood pressure is greatly elevated which is not thought to be important to the providers. This is taken as a respiratory illness not a cardiovascular illness. Cyanosis is not present and despite the appearance of severe respiratory distress and labored breathing there is a surprising amount of airflow. The blood pressure is impressively elevated to levels that are extreme.
Many such patients have edema of the lower extremities. This is a chronic finding and does not interfere with respiration. The problem is that it is noticeable and deceiving. Often the impression is that dependent edema is important in the function of the respiratory system. A portable plain film CXR is easily done in an Emergency Department. The usual semi upright PA (front to back) image commonly creates or exacerbates the appearance of edema. A standing CXR from back to front is a better technique that is done in non emergency cases but might if possible show little or no edema of the lungs. Edema is visible and noticeable which gives the impression of importance.
Traditions often interfere with critical thinking. For many years this scenario has been treated with IV furosemide. This is considered to be a diuretic which it is, but it also has vascular effects which are much less appreciated. The use of IV furosemide as a vascular agent is forgotten and since the effect is not immediate and dramatic it is generally discounted along with everything else that is discounted if not immediate and dramatic. IV furosemide has a role as a vascular agent but many people pressed into service in the emergency department think of it only as a diuretic. This supports a bias that this scenario is the result of acute edema of the lungs rather than a vascular illness.
It is commonly thought that elevated blood pressure can’t be the
cause of respiratory distress
Elevated blood pressure is an indication that the resistance to blood flow is elevated. Poor circulation of blood flow due to elevated resistance will reduce the delivery of oxygen.
Knowledge is a Toll Road
It is commonly thought that original research is better if the study is recent. Some publications prohibit the citations of research older than 5 to 10 years. This is effectively an ongoing toll on knowledge. We can’t just rely on research already done. It is necessary to fund new research. This certainly benefits universities, grant writers, professional researchers. This also allows us to rewrite history. We can can change the conclusions we don’t like by not asking the same question again.
It has been said that Einstein could give the same test to students a year later. When asked about this he said “The answers have changed”.
In addition to acidemia and breathlessness as the disease progresses edema of the lungs often develops. This gives the mistaken impression that the illness is a respiratory and not a cardiovascular illness. If the edema could somehow be removed we would still have a cardiovascular illness that is the root cause of this disorder. The acidosis would still be present and elevated pulmonary venous pressure that accompanies the edema would still be present.
The plain film CXR is often an easy thing to accomplish. The edema that is seen is much easier to demonstrate than the most significant problem which is the inadequate flow of blood. The clinical picture that is usually referred to as Flash Pulmonary Edema creates confusion because it gives the appearance of a disorder of breathing. The patient is distressed by the lack of oxygen but instead of a lack of oxygen in the blood stream the lack of oxygen is due to a lack of delivery because of limited blood flow. It is not possible to create a proper understanding of the illness with the term Flash Pulmonary Edema. Because of this misnomer, a type of misinformed closure interferes with a critical analysis of the origin and progression of the illness. Some patients with this syndrome are severely distressed but any edema on an X-ray is minimal or sometimes altogether absent. The distress comes primarily from the impaired delivery of oxygen by the cardiovascular system. This will not be obvious as the flow of blood and the delivery of oxygen is essentially impossible to measure. It is commonly assumed that a patient with high blood pressure cannot be in shock (low flow). Patients with severe elevations to blood flow, high peripheral resistance will have the impairment of oxygen delivery. This is perceived as dyspnea. Eventually edema of the lungs may develop and contribute to respiratory distress. Resolving the edema will not resolve the cardiovascular dysfunction. The term pulmonary is misleading because this is a cardiovascular disease not a pulmonary disease. The edema of the lungs is a problem but the edema is not the origin of the distress nor is the major abnormality causing respiratory distress. That the edema is the root of the peoblem is a long held and almost universal misconception. Flash is an appropriate descriptor as the illness flashes or feeds itself similar to the proverbial snowball.
Usually non-invasive is utilized in every severely distressed patient that presents to the emergency department. Little to no thought is given to the origin of the distress before this treatment is instituted. Usually a nurse with call for “bi-pap” and a respiratory therapist will initiate it before a doctor examines the patient. This often gives the doctor the excuses to delay as the impression is given that the therapy has begun which “buys them time”. A patient on Bi-Pap creates a strong visual impression of a respiratory disorder. Most casual observers will have the wrong impression by observing Bi- Pap being used. This has an effect on even the educated and experienced observer. It is often argued that a patient can still communicate with non-invasive ventilation in place. A patient could communicate but often no effort is made to do so. The difficultly of the patient speaking and being understood becomes troublesome to the point that less communication results. The perfunctory yes and no are often communicated typically with a nod. They could verbalize yes and no but typical don’t.
Acute Cardiovascular Insufficiency is not simply a dysfunction of the heart or heart failure but insufficiency of the entire cardiovascular system, the heart and also the blood vessels. Typically there is extremely high resistance to the flow of blood and the delivery of oxygen. Often it is assumed that a person with high blood pressure cannot have low perfusion and therefor be in shock.
It is a common misunderstanding the initiating event is the development of edema in the lungs. The circular reasoning that leads to this conclusion is propagated because of the incorrect naming of this condition as pulmonary edema. It is also erroneously believed that resolving the edema would resolve the illness also. This is also incorrect. Rather it is true that if the illness resolved, the edema would also. The edema is the result of the illness not the cause of it.
The essential facts are
Edema of the lungs is easily observed. The flow of blood is not.
Blood pressure is easily measured. Too much reliance is placed on the observation of blood pressure. Monitoring of the blood pressure continuously or in real time does not solve this problem. In all setting outside the ICU, the insufficiency of blood flow cannot be observed.
The appearance of the most easily obtained image, the plain film chest X-ray is misleading. We need measurements of blood flow which we don’t have and as a practical matter can’t be obtained.
The heart can be imaged. The vascular tree cannot.
The insufficient delivery of oxygen to meet metabolic demand is the cause of shortness of breath not the edema of the lungs.
The importance of oxygen is at the tissue level not in blood of the arteries near the heart. When the flow is low the tissues will be starved of oxygen especially highly metabolic tissue like muscle.
When blood flow is low cyanosis may not be observed as the skin is not a highly metabolic tissue and the requirements for oxygen are not as high as the muscle and internal organs.
The introduction of non-invasive ventilation to treat acute cardiovascular insufficiency known by the colloquialism, flash pulmonary edema has contributed to the misunderstanding of the disease. The insufficiency of the cardiovascular system is the cause of the illness not the edema of the lungs.
The image of a patient severely short of breath with a mask connected to positive pressure paints a picture that is misleading. This is not a respiratory or pulmonary illness as it appears in this situation. Everyone in the room where this treatment is employed gets the wrong impression. It might be that only the doctor that knows that this is a cardiovascular disease. The cause of this illness despite the fact that edema of the lungs is a part of it, is insufficiency of the cardiovascular system. If we removed the edema of the lungs we would still have the inadequate flow, the tissues of the body would still be starved of the flow of blood and oxygen and there would still be the feeling of shortness of breath. The body feels a lack of oxygen at the tissue level. This still occurs if the oxygen in the arterial blood is normal or near normal. Edema of the lungs is the result of the problem not the proximate cause of the illness.