🧑‍⚕️9.18 SU MedSchool: Acute Pulmonary Edema Experiment Setup

This week's experiment focused on acute pulmonary edema. The goal was to learn how to replicate an acute pulmonary edema model and observe its pathological manifestations.

Background

Pulmonary edema is a pathological process where excess fluid accumulates in the lung interstitium and/or alveolar spaces. Initially, fluid accumulates in the lung tissue interstitium, forming interstitial pulmonary edema. If the fluid continues to leak into the alveolar spaces, it results in alveolar pulmonary edema.
There are multiple causes of pulmonary edema. Common ones include left heart failure and mitral stenosis, which increase pulmonary capillary hydrostatic pressure, leading to fluid leakage. Other causes include physical, chemical, or biological factors that damage the endothelial or epithelial layers of pulmonary blood vessels, increasing permeability and causing pulmonary edema.

Experimental Method

Acute pulmonary edema in this experiment was induced by intravenous injection of a toxic dose of epinephrine. Epinephrine, secreted by the adrenal medulla, acts on both α-receptors and β-receptors:

• α-receptor activation: A high dose of epinephrine causes vasoconstriction in areas rich in α-receptors (such as the skin, mucous membranes, and visceral organs), leading to blood pooling in the pulmonary circulation. This increases pulmonary capillary hydrostatic pressure, forcing fluid out of the vessels and resulting in pulmonary edema.

• β-receptor activation: A high dose of epinephrine accelerates the heart rate, shortens the diastolic phase, and raises left ventricular end-diastolic pressure. This increases left atrial pressure, causing pulmonary venous congestion and further raising pulmonary capillary hydrostatic pressure. If fluid formation exceeds reabsorption, pulmonary edema develops.

Experimental Subjects

• Animal model: Rabbits weighing ≥2 kg

Materials & Reagents

• Rabbit surgery table

• 1 mL syringes

• Surgical instruments

• Baby scale, electronic balance

• Stethoscope, gauze

• 0.1% epinephrine solution

• Normal saline

Experimental Procedure & Observations

1. Baseline Measurements

   • Select a rabbit and restrain it.

   • Once calm, record its respiratory rate and heart rate.

   • Use a stethoscope to confirm the absence of abnormal heart sounds.

2. Epinephrine Injection & Observations

   • Inject 1 mL of 0.1% epinephrine into the marginal ear vein.

   • Place the rabbit on the ground and observe changes in respiration, heart rate, activity levels, and mucosal coloration.

   • Monitor for pink frothy fluid from the mouth or nose.

   • A control group receives 1 mL of normal saline, followed by air injection for euthanasia.

3. Reinjection if No Response

   • If no obvious reaction occurs within 15 minutes, administer another 1 mL dose of epinephrine.

4. Post-Mortem Examination

   • Once the animal dies, tie off the trachea below the thyroid cartilage to prevent fluid loss.

   • Open the thoracic cavity, isolate the lungs, and weigh them after removing surface fluid.

   • Calculate the lung weight ratio:

     Lung Weight Ratio=Lung Weight (g)Rabbit Body Weight (kg)Lung Weight Ratio=Rabbit Body Weight (kg)Lung Weight (g)​

     • Normal range: 4–5 g/kg

5. Macroscopic Lung Examination

   • Compare control and experimental rabbits for lung color, texture, and structural changes.

   • Slice open the lungs and observe whether pink, frothy fluid is present.

Discussion Questions We Gave Students:

1. Based on the experimental results, analyze the mechanism of acute pulmonary edema.

2. What types of hypoxia can occur in experimental animals? What are their mechanisms?