Pulmonary Edema

Introduction: Pulmonary edema in veterinary medicine refers to a non-inflammatory disease in which the blood in the pulmonary capillaries of animals increases abnormally, and the liquid components of the blood leak into the alveoli, bronchi and interstitium. Clinically, it is characterized by extreme dyspnea and foamy nasal discharge. Pulmonary edema progresses rapidly and first aid must be sought immediately. The principle of treatment is to keep the sick dogs and cats quiet, reduce the burden on the heart, improve blood circulation, stop leakage, and relieve dyspnea.

Pulmonary edema is a non-inflammatory disease in which the blood in the pulmonary capillaries increases abnormally and the liquid components of the blood leak into the alveoli, bronchi and interstitium. Clinically, it is characterized by extreme dyspnea and foamy nasal discharge.

Causes of Pulmonary Edema

1. Elevated pulmonary capillary pressure

Seen in left ventricular insufficiency, pulmonary venous embolism disease, blood transfusion and infusion excessive or too fast caused by various reasons.

2. Reduced plasma colloid osmotic pressure

Seen in liver disease, decreased protein synthesis, glomerulonephritis and malabsorption syndrome.

3. Altered alveolar capillary permeability

Seen in poisoning, disseminated intravascular coagulation, immune reaction, anaphylactic shock, in addition to lymphatic system disorders such as tumor infiltration.

The pathogenesis of pulmonary edema

Various physical and chemical factors (such as silver acid, ammonia, etc.), and biological factors (some bacteria, virus infection) stimulate and damage alveolar wall capillary endothelial cells and alveolar epithelial cells, increasing the permeability of the respiratory membrane, causing blood liquid components and even proteins to penetrate into the alveolar cavity and lung tissue space, causing pulmonary edema.

Left ventricular insufficiency, mitral valve stenosis, and other factors can cause obstruction of pulmonary venous return, which can cause pulmonary capillary hydrostatic pressure to increase. When interstitial fluid is greater than the return and exceeds the compensatory limit of lymphatic return, pulmonary edema is prone to occur.

Diagram of breathing membrane

Diagram of breathing membrane

Resource description: The respiratory membrane, also known as the air-blood barrier, is composed of 6 layers. For lung ventilation (gas exchange in the lungs), gases need to cross the breathing membrane. The thickness and permeability of the respiratory membrane have a great influence on gas exchange.
File source: Internet

After the occurrence of pulmonary edema, the edema fluid enters the alveolar septum and alveoli, resulting in an increase in the thickness of the respiratory membrane and a decrease in the gas exchange efficiency in the lungs, causing hypoxia, shortness of breath and dyspnea in animals. When there is a lot of edema fluid, the edema fluid can also enter the bronchioles and small bronchi, resulting in crepitus or moist rales on auscultation of the lungs, and pink or light pink foamy nasal fluid flowing out of the nostrils.

Pathological autopsy of canine pulmonary edema

OLYMPUS DIGITAL CAMERA

Resource description: Dog, antifreeze poisoning, post-mortem examination showed pulmonary edema.
Document source: Gheorghe Solcan

Symptoms of pulmonary edema

1. Clinical examination

Severe pulmonary edema usually presents with sudden onset, progressive and highly mixed dyspnea, exophthalmos, distended veins, cyanosis of mucous membranes, panic, stretched head and neck, dilated nostrils and mouth breathing. A pink foamy nasal fluid flows from the nostrils.

Moist rales were heard on lung auscultation. When the lungs are percussed, the lesion is dull. When the heart function is seriously impaired, the sick dogs show different degrees of shock symptoms.

2. X-ray inspection

On chest X-ray examination, the shadows of the lung field showed sporadic enhancement, the airway was clearly outlined, and the peribronchus was thickened.

If it is pulmonary edema caused by excessive fluid infusion, alveolar shadows increase diffusely, and most blood vessels are almost difficult to find.

Pulmonary edema due to alveolar emphysema, with mottled shadows seen on X-ray examination.

Due to pulmonary edema complicated by left ventricular insufficiency, the pulmonary veins are clearer than normal, and the hilum is radial.

French Bulldog - X-ray image of pulmonary edema

French Bulldog - X-ray image of pulmonary edema

Resource description: A 5-year-old French bulldog, ♂, presented to the doctor with severe acute dyspnea. On return from vacation, dyspnea and visible cyanosis of the mucous membranes after a road trip of several hours.
X-ray image analysis: First, we observed a large amount of gas in the stomach, which is a sign of severe respiratory distress (aerosclerosis). Extensive peribronchial opacities (thick donuts) in the lung fields, with some areas showing a small amount of air bronchogram as a sign of the alveolar pattern. Mergers of peribronchial infiltrates form the impression of nodules or miliary opacities. The presence of gas within these small “nodules” ruled out the presence of nodules and confirmed peribronchial infiltration. The outline of the heart showed normal size and shape. The vertebral bodies at T7 and T8 are wedge-shaped and triangular (common pathology in brachycephalic dogs, usually not clinically relevant).
Conclusions: Radiographic signs were consistent with noncardiogenic edema or acute respiratory distress syndrome, most likely due to “heat” in the vehicle. The animal received emergency treatment, including oxygen infusion. Its body temperature was lowered due to the placement of alcohol-solidified swabs on its extremities. It’s not taking any diuretics. The administration of diuretics, although much discussed and controversial in the literature, is not mandatory in noncardiogenic edema. The control group underwent chest X-rays, which revealed no abnormalities.
Document source: https://www.vetpixel.com/en/cas/32-a-case-of-non-cardiogenic-pulmonary-edema-secondary-to-heat-shock-in-a-french-bouledogue

Diagnosis of Pulmonary Edema

According to medical history materials, clinically, sudden dyspnea and pink foamy nasal fluid flowing from both nostrils and X-ray examination results can make a diagnosis.

It should be differentiated from heatstroke, pulmonary hemorrhage, and diffuse bronchitis.

Treatment of pulmonary edema

The disease progresses rapidly and emergency treatment must be given immediately.

The principle of treatment is to keep the sick dogs and cats quiet, reduce the burden on the heart, improve blood circulation, stop leakage, and relieve dyspnea.

1. Sedation

First of all, make the sick dog quiet and avoid using stimulants. In order to reduce animal anxiety, sedatives can be used, such as oral or intramuscular injection of 0.5-1 mg of morphine sulfate per kilogram of body weight, 2-4 mg of pentobarbital sodium per kilogram of body weight, or 5-15 mg of phenobarbital sodium per kilogram of body weight.

2. Correct hypoxic state

When the blood is hypoxic, oxygen should be supplied immediately, and oxygen should be infused through the nasal passages with a fine rubber tube or an oxygen mask at a rate of 5-6 L/min to improve the ventilation function.

3. Asthma

For those with symptoms of bronchospasm, the most effective method is to use bronchodilators, such as intravenous injection of aminophylline 6~10mg per kilogram of body weight.

For pulmonary edema caused by causes other than acute left ventricular insufficiency, powerful bronchodilators such as epinephrine and isoproterenol can be used.

4. Cardiac and diuretic

To strengthen the heart and diuresis, in order to enhance myocardial contractility, digitalis therapy can be used, such as intravenous injection of digoxin, the first dose is 0.044 mg per kg body weight, and the maintenance dose is 0.0055~0.011 mg per kg body weight, administered once every 12 hours. 24~36h after administration, the saturation amount should be calculated. Digigenin can also be used. To facilitate fluid removal, diuretics may be used.

5. Other symptomatic treatment measures

In case of anemia, giving red blood cells can not only increase blood viscosity and reduce the burden on the heart, but also improve the oxygen supply to tissues.

When the osmotic pressure is reduced, the infusion of plasma or dextran solution has a significant diuretic effect. However, isotonic solutions should not be used because they can exacerbate the development of pulmonary edema.

When there are too many secretions in the bronchi, anticholinergic drugs such as atropine sulfate can be applied, which can significantly reduce pulmonary edema.