Cardiovascular Insufficiency is a functional state of the Cardiovascular System wherein the circulation of blood does not meet the demand. In the acute state the compensation for this is the development of anaerobic metabolism. In the chronic stages the compensation is fluid retention which manifests itself as the syndrome of Heart Failure.
Acute Cardiovascular Insufficiency is difficult to recognize. It produces a feeling of breathlessness as the cardiovascular system fails to deliver enough oxygen to the tissues. This causes the tissues especially the highly metabolic tissues to develop anaerobic metabolism producing lactic acid. The acidemia that results causes hyperventilation as a respiratory compensation for the metabolic production of lactic acid. The appearance of this functional disturbance mimics respiratory disease. A person cannot perceive or identify the lack of blood flow. One does not say I do not feel enough blood flow and oxygen to the tissues of my body. Instead the lack of oxygen from inadequate perfusion gives the same sensation as in hypoxia from respiratory disease. The individual will complain of shortness of breath and be hyperventilating to compensate for the acidemia.
The term heart failure is strongly associated with the appearance of fluid retention and edema. The point is frequently made that heart failure is a syndrome. It is not defined by measurement of any parameter. It might be said that cardiac function is impaired but that is not the way the syndrome is defigned. Cardiovascular Insufficiency is the concept of insufficient flow weather it can be easily demonstrated or not.
Heart Failure is generally thought of a the result of diseases of the myocardium such as ischemia or other specifically cardiac causes such as valvular heart disease, arrhythmia etc. Cardiovascular Insufficiency is considered an inadequacy of the system more often the result of inappropriate levels of systemic vascular resistance which leads to inadequate perfusion.
In Cardiovascular Insufficiency the emphasis is on supply not meeting demand. In fact the supply may be normal or near normal. The same physiology develops in athletes that exercise strenuously. Such individuals will be breathing heavily and if tests are done will be shown to have acidemia from metabolic acidosis and hyperventilation for respiratory compensation. In any case the system has not failed, just that it has reached its limit of performance.
Inadequate blood flow and oxygen delivery to meet demand is difficult to demonstrate. The flow of blood or cardiac output cannot be measured except by sophisticated technology and or invasive methods. The classic method is a Fick calculation. This requires a closed respiratory system and a pulmonary artery catheter. This is awkward, expensive and invasive. Even an indirect Fick method which utilizes estimates of tissue oxygen consumption and requires a central venous catheter. There are other sophisticated approaches to determining flow such as dynamic MRI and advanced ultrasound techniques. These are not feasible in most situations. Consequently blood flow measurements are generally impractical.
Blood flow is dependent on blood pressure but equally dependent on the resistance to flow in the reverse manner. If resistance were a constant known value we could make a direct correlation. Resistance to flow is variable. The variations are not necessarily predictable. Resistance is often assumed to be normal or constant. This is done for the sake of simplicity but sometimes is wildly inaccurate.
Only the highly metabolic tissues particularly muscle are starved of oxygen when the level of oxygenation is adequate but when flow is low. The skin has low metabolism and therefore oxygen deprivation is not apparent and cyanosis of the skin will not appear. Other metabolic tissues such as liver and kidney are not visible even as they might be starved of oxygen due to low perfusion.
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.