Postgrad Med J: first published as 10.1136/pgmj.40.465.404 on 1 July 1964. Downloaded from POSTGRAD. MED. J. (1964), 40, 404 PULMONARY CEDEMA RONALD FINN, M.D., M.R.C.P. Senior Medical Registrar, Royal Southern Hospital, Liverpool, Research Fellow, Department of Medicine, University of Liverpool. OEDEMA of the lungs was defined by TABLE I. Lznnec (1829) as . .. "the infiltration of THE CAUSES OF PULMONARY OEDEMA serum into the substance of this organ, in such A. Heart Disease: degree as to diminish its 1. Hypertension. evidently perme- 2. Aortic and Mitral Valve disease. ability to the air, in respiration." hennec also 3. Myocardial disease. observed that pulmonary cedema was most 4. Pulmonary embolism. commonly caused by disease of the heart, B. Central Nervous System: and could manifest itself as "suffocative 1. Trauma. orthopnoea". James Hope (1832) noted that 2. Haemorrhage and Thrombosis. obstruction of the left heart would lead to 3. Encephalitis. pulmonary congestion associated with severe C. Respiratory System: 1. Pneumonia-(especially influenzal). dyspnoea, and wrote that . "asthma has 2. Drowning and asphyxia. been too much regarded as independent of the 3. Inhalation of irritant gases. heart. Long treatises have even been written 4. Chest trauma. (Traumatic wet lung). by copyright. upon it without ever mentioning disease of D. Allergy: this organ as one of its causes. It is, therefore, 1. Angioneurotic cedema. necessary to dwell a little on this subject, not 2. Serum sickness. only for showing the magnitude of this error, E. Miscellaneous Causes: but of the reader with 1. Distension of cesophagus, stomach, gall making acquainted all bladder. the habitudes and aspects of a complaint, 2. Excessive transfusion. which is perhaps the most distressing in the 3. Overhydration in acute renal failure. whole catalogue of human maladies". 4. Manipulation of stellate ganglion. 5. Overdosage with morphia, heroin, me-http://pmj.bmj.com/ thyl salicylate. Causes of Pulmonary Oedema 6. High altitude pulmonary cedema. Pulmonary cedema may be due to multiple and the resulting pulmonary congestion causes, and extensive aetiological classifications renders the lungs turgid and less distensible, have been given by Cameron (1948), Luisada and the resultant difficulty in expanding and and Cardi (1956) and Visscher, Haddy and retracting the stiffened lung is responsible for Stephens (1956). The more common causes the primary symptom of dyspnoea. If the pul- on September 30, 2021 by guest. Protected are listed in Table 1. monary capillary pressure rises still further and exceeds the osmotic pressure, then true Aetiological Considerations pulmonary cedema occurs. Congestion of the bronchial mucosa and secondary broncho- In the ultimate analysis pulmonary cedema spasm may lead to airway obstruction and must be due to one or more of the following thus further contribute to the sensation of factors; a rise in pulmonary capillary pressure, dyspnoea. a fall in intravascular osmotic pressure, an The classical relationship between cardiac increase in capillary permeability, or a fall in dyspnoea and posture (orthopnoea) is probably tissue pressure. due to increased right ventricular output con- Left Ventricular Failure: sequent on increased right atrial filing in the Failure of the left ventricle is the most horizontal position (McMichael, 1937); and it common cause of pulmonary cedema, and may has been estimated that the lungs contain an be acute or chronic. Left ventricular failure extra 500 ml. of blood in the recumbent pos- leads to damming back of blood in the lungs, ture (McMichael, 1939). The decrease in vital Postgrad Med J: first published as 10.1136/pgmj.40.465.404 on 1 July 1964. Downloaded from July', 1964 FINN: Pulmonary Oedema 405 >Left Ventricular Failure a Tachycardia I~~~~~Raisedcu/n Cap. Pressulre Increased Anoxia and Metabolic RJY Out Acidosis Anx ity Suction Effect Pulmonary Oedema. Ventilation Defect Dyspnoea (foaming})- FIG. 1.-The vicious circle operating in left ventricular failure whereby increasing pulmonary cedema progressively impairs myocardial function, thereby leading to further degrees of pulmonary cedema. This chain reaction is potentially self perpetuating and unless broken at some point may prove fatal. capacity due to upward displacement of the Sampson and Friedman 1962) have demon- diaphragm is a further factor leading to strated very large increases in lymph flow from increased pulmonary congestion in the hori- the lung, and it has therefore been suggested by copyright. zontal position. that reduced lung motion at night decreases pulmonary lymph flow and hence predisposes Paroxysmal nocturnal dyspnoea (cardiac to pulmonary cedema. asthma, acute left ventricular failure) usually Once the attack has started a vicious circle occurs in patients with chronically congested develops (Fig. 1), whereby increasing degrees lungs, and is due to the sudden trapping of an of pulmonary cedema further reduce myocard- extra few hundred millilitres of blood in the ial function. There are several mechanisms by already congested pulmonary circulation. These means of which pulmonary cedema further attacks usually occur at night and various ex- embarrasses the left ventricle. Thus the severe http://pmj.bmj.com/ planations have been offered to account for dyspnoea leads to intense anxiety, and the this phenomenon. The failing heart is more resultant tachycardia and diminished coronary able to meet demands during the night when filling time place severe demands on the failing the requirements are reduced, and thus ventricle. The intense inspiratory efforts tend to balance is temporarily restored. This allows suck more blood into the pulmonary circulation the resorption of postural cedema which has thus collected in the dependent parts of the body tending to further cedema formation. Pullmonary cedema may produce a severe vent- on September 30, 2021 by guest. Protected during the day, leading to a nocturnal increase ilation defect due to obstruction of the airways in blood volume, and the chronically raised by frothy fluid, and the resulting anoxia and pulmonary venous pressure tends to redistri- metabolic acidosis further impairs myocardial bute this cedema fluid in the lungs. The as- function leading to further degrees of failure sumption of the horizontal position during and progressively severe pulmonary cedema. sleep also tends to increase pulmonary conges- This chain mechanism is potentially self tion by increasing right ventricular filling perpetuating and unless broken at some point pressure and decreasing vital capacity. Com- the sequence of increasing pulmonary cedema pensatory mechanisms are delayed because of and sleep, and thus the patient does not wake and diminishing myocardial function may sit up until pulmonary congestion is well prove fatal. advanced. During sleep less fluid is lost by Mitral Valve Obstruction: evaporation from the lung, thus potentiating the Obstruction at the mitral valve is usually due cedematous state. Recent experimental studies to a tight mitral stenosis, but on rare occasions in rabbits in whom cardiac failure has been ball valve thrombi and atrial myxomata may induced by artificial A-V shunts (Uhley, Leeds, be present. Severe obstruction at the mitral Postgrad Med J: first published as 10.1136/pgmj.40.465.404 on 1 July 1964. Downloaded from 406 POSTGRADUATE MEDICAL JOURNAL .July, 1964 valve leads to pulmonary congestion with a strictor potential (Sarnoff, 1952). The resultant raised pulmonary capillary pressure and sub- overloading of the pulmonary circulation pre- sequent pulmonary aedema, which can be acute disposes to pulmonary oedema. The peripheral or chronic. shut down in the systemic circulation impairs Acute pulmonary cedema in mitral stenosis, left ventricular output and thus strains the unlike that in left ventricular failure, usually left ventricle, and there is evidence that neuro- occurs during exercise. The resulting tachy- genic pulmonary oedema usually occurs in as- cardia decreases the diastolic filling period, sociation with hypertension and coronary thus leading to a hold-up of blood in the left artery disease which act as predisposing factors atrium. Tachycardia associated with acute (Paine, Smith & Howard, 1952). The extreme infections and the onset of an abnormal rhythm bradycardia which sometimes occurs in severe such as auricular fibrillation may similarly intracranial damage may also predispose to precipitate an attack of acute pulmonary pulmonary oedema (Campbell, Haddy and cedema. It is also well known that a chest infec- Visscher, 1949). tion may act as a precipitating factor by Acute pulmonary oedema can occur in increasing capillary permeability, and the heroin poisoning, particulary in "main-line" increased blood volume associated with preg- addicts. (Silber and Clerkin, 1959). The patho- nancy may also precipitate an episode of genesis is not clear, but hypoxia due to respir- pulmonary cedema. atory depression may lead to increased capillary permeability (Drinker, 1945). Morphia is also Other Causes: known to increase intracranial pressure (Keats Irritant gases such as phosgene produce lung and Mithofer, 1955) and may stimulate the cedema by a direct action on the pulmonary vasomotor centres (Schmidt and Livingstone, capillaries, and increased capillary permeability 1933) and thus the oedema might be partly cedema associated is responsible for pulmonary neurogenic in origin. Pulmonary cedema by copyright. in with serum sickness and acute angioneurotic salt