Cyanosis: Definition and Causes

Cyanosis

• Dusky blue skin discoloration occurs when reduced form (deoxygenated) hemoglobin is ≥ 5 g/dl of Hb.
• In anemia, cyanosis appears only in severe hypoxia, while in polycythemia, it occurs more readily.
• There are two types of cyanosis: central (lips and tongue) and peripheral (fingers).

Causes of Central Cyanosis

• Lung diseases: inadequate O2 exchange (e.g., luminal obstruction, pneumothorax, pneumonia, pulmonary edema) - corrected by increasing inspired O2.
• Cyanotic congenital heart diseases: results in blood admixture, not corrected by increasing inspired O2.
• Rare causes: methemoglobinaemia, congenital or acquired red cell disorders.

Causes of Peripheral Cyanosis

• Peripheral cyanosis can occur in causes of central cyanosis, but also induced by peripheral and cutaneous vascular system changes in persons with normal O2 saturation (e.g., exposure to cold, hypovolemia, and arterial diseases).

Pulmonary Oedema

• Definition: accumulation of fluid into the alveoli.
• It's one of the medical emergencies that requires immediate and aggressive treatment.
• Causes: acute left ventricular failure, acute respiratory distress syndrome, fluid overload, neurogenic, and others.

Pathophysiology (LV Failure)

• Increase in left ventricular diastolic pressure.
• Rising of left atrium, pulmonary veins, and capillaries pressures.
• When hydrostatic pressure of pulmonary capillaries exceeds osmotic pressure of plasma, fluids move into the alveoli.

Pathophysiology (RDS)

• Normal left ventricular diastolic pressure.
• Normal left atrium, pulmonary veins, and capillaries pressures.
• Fluids move into the alveoli due to increased capillary permeability (inflammation).

Exacerbating Factors of Pulmonary Oedema

• Arrhythmias (e.g., atrial fibrillation).
• Infection.
• Pulmonary embolism.
• Increase in blood pressure.
• Anemia.
• Inadequate therapy or poor drug compliance.
• Thyroid disease.
• Drug-induced (e.g., NSAIDS, corticosteroids, and verapamil).

Clinical Features

• Symptoms: sudden onset of dyspnea at rest, orthopnoea, PND, prostration.
• Signs: patient looks distressed, pale, and sweaty, with tachycardia, pulsus alternans, tachypnea, increased JVP, fine basal crackles, gallop/triple rhythm, and wheezing.

Investigations

• Chest x-ray: important for diagnosis, shows cardiomegaly, sings of pulmonary edema.
• ECG: shows signs of predisposing factor or cause.
• Lab tests: electrolytes, cardiac enzymes, arterial blood gas analysis.
• Echocardiography: can be considered.

Treatment

• Begin treatment before investigations.
• Sit the patient in an upright position.
• Oxygen.
• I.V access and monitor the ECG.
• Morphine: 2.5-5 mg slowly I.V.
• Furosemide: 40-80 mg slowly I.V.
• Nitrates: GTN (systolic pressure > 90 mmHg) and I.V infusion of nitrates (systolic pressure > or = 100).
• Consider assisted ventilation if the patient worsens.
• Treat any arrhythmia, e.g., atrial fibrillation.
• If the pressure is below 100 mmHg, treat as cardiogenic shock.

Learn about cyanosis, a condition characterized by dusky blue skin discoloration due to high levels of deoxygenated hemoglobin. Explore its types, causes, and relationship with anemia and polycythemia.