Cyanosis

Introduction

Cyanosis is the bluish discoloration of skin, nail beds, and mucous membranes caused by elevated deoxygenated hemoglobin or abnormal hemoglobin derivatives. It is an important bedside sign that reflects hypoxemia, poor perfusion, or hemoglobin abnormalities.

Cyanosis can be classified as:

• Central cyanosis: Due to low arterial oxygen saturation. Seen in tongue, lips, mucous membranes.

• Peripheral cyanosis: Due to reduced peripheral perfusion (vasoconstriction, low cardiac output). Seen in extremities.

• Differential cyanosis: Upper vs lower limb difference (e.g., patent ductus arteriosus with Eisenmenger’s physiology).

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Pathophysiology

• Normal arterial oxygen saturation: 95–100%.

• Cyanosis occurs when deoxygenated Hb >5 g/dL (thus more apparent in polycythemia, less in anemia).

• Central cyanosis: reduced SaO₂ due to hypoventilation, V/Q mismatch, right-to-left shunt.

• Peripheral cyanosis: sluggish blood flow → increased oxygen extraction.

• Abnormal hemoglobins (methemoglobin, sulfhemoglobin) cause pseudocyanosis.

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Causes of Cyanosis

1. Central Cyanosis

• Respiratory:

  • Severe pneumonia, COPD, asthma exacerbation.

  • Pulmonary embolism.

  • Interstitial lung disease.

  • Hypoventilation (CNS depression, neuromuscular disease).

• Cardiac:

  • Congenital heart disease with right-to-left shunt (Tetralogy of Fallot, Eisenmenger’s).

  • Heart failure with pulmonary edema.

  • Severe arrhythmias with poor perfusion.

• High altitude hypoxemia.

2. Peripheral Cyanosis

• Shock (hypovolemic, septic, cardiogenic).

• Cold exposure, peripheral vasoconstriction.

• Peripheral vascular disease.

• Raynaud’s phenomenon.

3. Abnormal Hemoglobins

• Methemoglobinemia: Oxidized hemoglobin (Fe³⁺ cannot bind oxygen).

  • Causes: nitrates, dapsone, benzocaine, sulfonamides.

• Sulfhemoglobinemia: Sulfur-containing drugs.

• Carboxyhemoglobinemia (CO poisoning): Cherry-red lips (not cyanosis, but mimics).

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Clinical Features

• Central cyanosis: Bluish lips, tongue, oral mucosa, conjunctivae. Warm extremities.

• Peripheral cyanosis: Bluish fingers, toes, nail beds; sparing of mucosa; cold extremities.

• Other symptoms:

  • Dyspnoea, tachypnoea (respiratory cause).

  • Chest pain, palpitations (cardiac).

  • Altered consciousness (severe hypoxemia).

  • Clubbing in chronic hypoxemia.

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Diagnostic Approach

1. History

• Onset (sudden vs gradual).

• Dyspnea, cough, chest pain, fever.

• Past history of lung or heart disease.

• Drug history (nitrates, dapsone, local anesthetics).

• Family history (congenital heart disease, hemoglobinopathies).

2. Examination

• Distinguish central vs peripheral cyanosis.

• Check oxygen saturation (pulse oximetry).

• Cardiovascular exam (murmurs, signs of heart failure).

• Respiratory exam (rales, wheezing, reduced breath sounds).

3. Investigations

• Pulse oximetry: Low in central cyanosis; may be normal in methemoglobinemia.

• Arterial blood gases (ABG): PaO₂ and SaO₂ levels.

• Chest X-ray: Pneumonia, edema, mass.

• ECG/Echocardiography: Cardiac causes, congenital shunts.

• Blood tests: Hemoglobin, hematocrit, methemoglobin levels, lactate.

• CT pulmonary angiography: Pulmonary embolism.

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Management and Treatment

Principle: Identify and treat the underlying cause + supportive oxygen therapy.

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A. Immediate Supportive Care

• Ensure airway, breathing, circulation (ABC).

• Oxygen supplementation: Nasal cannula (2–6 L/min), face mask (6–10 L/min), or high-flow/non-invasive ventilation if needed.

• Mechanical ventilation for respiratory failure.

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B. Treat Underlying Cause

1. Respiratory Causes

• COPD exacerbation:

  • Oxygen therapy (target SpO₂ 88–92%).

  • Salbutamol inhaler/nebulizer 2.5–5 mg every 4–6 h PRN.

  • Prednisone 40 mg orally daily × 5–7 days.

  • Antibiotics if infection suspected: Amoxicillin–clavulanate 875/125 mg orally twice daily for 5–7 days.

• Asthma attack:

  • Salbutamol nebulizer 2.5–5 mg every 20 min for 3 doses.

  • Prednisone 40–60 mg orally daily × 5–7 days.

  • Oxygen + IV fluids if severe.

• Pneumonia:

  • Ceftriaxone 1–2 g IV once daily + Azithromycin 500 mg orally/IV once daily.

• Pulmonary embolism:

  • Anticoagulation (Enoxaparin 1 mg/kg SC every 12 h).

2. Cardiac Causes

• Heart failure with pulmonary edema:

  • Furosemide 20–40 mg IV bolus, repeat as needed.

  • Oxygen, nitrates if BP stable, treat underlying cause.

• Congenital cyanotic heart disease:

  • Pediatric cardiology referral.

  • Surgical repair (e.g., TOF correction, shunt closure).

  • Prostaglandin E1 infusion (0.05–0.1 mcg/kg/min IV) to maintain ductus arteriosus in neonates.

3. Abnormal Hemoglobins

• Methemoglobinemia:

  • Oxygen (though ineffective alone).

  • Methylene blue 1–2 mg/kg IV over 5 min (max 50 mg), repeat if needed after 1 hour.

• Sulfhemoglobinemia: Stop offending drug, supportive care.

4. Peripheral Cyanosis

• Warm extremities, treat shock with fluids/vasopressors.

  • IV crystalloids (0.9% saline 1–2 L in adults).

  • If septic shock: Norepinephrine IV infusion starting at 0.05–0.1 mcg/kg/min.

• Manage vascular occlusion (anticoagulants, surgery).

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Complications

• Tissue hypoxia → organ dysfunction.

• Brain: confusion, seizures, coma.

• Heart: arrhythmias, ischemia.

• Limb ischemia in severe peripheral vascular disease.

• Death if untreated.

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Prognosis

• Acute cyanosis: Prognosis depends on rapid recognition and treatment of cause (pneumonia, PE, heart failure).

• Chronic cyanosis (e.g., congenital heart disease): May lead to clubbing, polycythemia, pulmonary hypertension; prognosis depends on corrective surgery.

• Methemoglobinemia: Excellent prognosis if recognized and treated with methylene blue.

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Patient Education

• Recognize early signs: bluish lips, fingers, shortness of breath.

• Avoid smoking and exposure to respiratory toxins.

• Adhere to treatment of chronic heart/lung conditions.

• Prevent infections with vaccination (influenza, pneumococcal).

• Seek urgent care if cyanosis appears suddenly with chest pain, breathing difficulty, or confusion.