How should I evaluate and manage a patient three days after total knee arthroplasty who presents to the emergency department with acute dyspnea?

Approach to Post-Total Knee Replacement Dyspnea (Day 3)

This patient requires immediate assessment for pulmonary embolism (PE) as the primary concern, followed by systematic evaluation for cardiac causes, infection, and volume overload—all while maintaining a low threshold for ICU admission given the high-risk post-operative context.

Immediate Stabilization and Assessment

Primary Survey (First 5 Minutes)

• Position the patient upright (30-45 degrees) to reduce work of breathing and assess vital signs immediately: blood pressure, heart rate, respiratory rate, and oxygen saturation 1, 2
• Administer supplemental oxygen if SpO2 <90%, targeting saturation >90% 3, 4
• Obtain arterial or venous blood gas with pH, PaCO2, PaO2, and lactate to assess for hypoxemia, hypercapnia, and metabolic acidosis 3
• Assess for hemodynamic instability: hypotension, tachycardia, signs of shock, or cardiac arrest 5, 6

Critical Red Flags Requiring Immediate Intervention

• Hypoxemia (SpO2 <90%) despite oxygen therapy warrants consideration of non-invasive ventilation (NIV) 3, 4
• Respiratory rate >25/min with SpO2 <90% indicates need for NIV to reduce intubation risk 3
• Hemodynamic instability (systolic BP <90 mmHg, altered mental status) requires ICU admission 3

Differential Diagnosis Priority

1. Pulmonary Embolism (Highest Priority)

PE is the most critical diagnosis to exclude in post-operative orthopedic patients with acute dyspnea. 7

• Risk stratification: Total knee arthroplasty is a major orthopedic surgery with high VTE risk, and day 3 post-op is peak timing for symptomatic PE 7
• Clinical assessment: Look for tachycardia, tachypnea, pleuritic chest pain, hemoptysis, unilateral leg swelling/pain, or signs of right heart strain 7
• ECG: Obtain immediately to assess for sinus tachycardia, S1Q3T3 pattern, right heart strain, or new atrial fibrillation 7
• D-dimer: May be elevated post-operatively regardless, limiting utility, but a normal value in low-risk patients can help exclude PE 7
• CT pulmonary angiography (CTPA): This is the definitive diagnostic test and should be obtained urgently if PE is suspected 7
• Echocardiography: Consider bedside echo to assess for right ventricular dysfunction, which indicates high-risk PE requiring aggressive management 7

2. Cardiac Causes

• Acute decompensated heart failure: Assess for bilateral leg edema, elevated JVP, pulmonary crackles, S3 gallop, and orthopnea 7, 3
• BNP/NT-proBNP: If >100 pg/mL, heart failure is likely; if <100 pg/mL, heart failure is unlikely 7
• Acute coronary syndrome: Obtain troponin and serial ECGs, especially if chest pain is present 7
• Cardiac tamponade: Assess for hypotension, muffled heart sounds, elevated JVP, and pulsus paradoxus—this requires urgent pericardiocentesis and vasodilators/diuretics are absolutely contraindicated 5

3. Pulmonary Infection

• Pneumonia or atelectasis: Common post-operative complications, assess for fever, productive cough, focal crackles, and obtain chest X-ray 7, 3
• Sepsis: Check for systemic signs (fever, hypotension, tachycardia, altered mental status) and obtain blood cultures, lactate, and procalcitonin 6

4. Volume Overload

• Iatrogenic fluid overload: Review perioperative fluid balance, assess for bilateral crackles, peripheral edema, and elevated JVP 3
• Chest X-ray: Look for pulmonary edema, pleural effusions, or cardiomegaly 7, 3

Diagnostic Work-Up

Immediate Laboratory Tests

• Arterial blood gas: pH, PaCO2, PaO2, lactate 3
• Complete blood count: Assess for anemia (blood loss) or leukocytosis (infection) 6
• Troponin: Rule out myocardial infarction 7
• BNP or NT-proBNP: Differentiate cardiac from non-cardiac dyspnea 7
• D-dimer: If PE suspected and not already anticoagulated 7
• Renal function and electrolytes: Assess for metabolic derangements 3

Immediate Imaging

• ECG: Assess for ischemia, arrhythmias, or right heart strain 7
• Chest X-ray: Evaluate for pneumonia, pulmonary edema, pleural effusion, or pneumothorax 7, 3
• CT pulmonary angiography: If PE is suspected based on clinical assessment 7
• Bedside echocardiography: Assess cardiac function, right ventricular strain, pericardial effusion, or tamponade 7, 5

Management Based on Diagnosis

If Pulmonary Embolism Confirmed

• Anticoagulation: Start therapeutic anticoagulation immediately with low molecular weight heparin or unfractionated heparin unless contraindicated by bleeding risk 7
• Risk stratification: High-risk PE (hemodynamic instability) requires thrombolysis or embolectomy; intermediate-risk PE may benefit from closer monitoring in ICU 7
• Avoid early discharge: PE patients require hospitalization for at least 24-48 hours with close monitoring 7

If Heart Failure Confirmed

• Diuretics: IV furosemide for volume overload, but monitor for electrolyte disturbances and renal function 7, 3
• Vasodilators: High-dose nitrates (3 mg IV isosorbide dinitrate every 5 minutes) may be superior to high-dose diuretics in acute pulmonary edema 7
• NIV (CPAP or BiPAP): For respiratory distress with pH <7.35 or respiratory rate >30, reduces intubation rates 7, 3
• Avoid excessive oxygen: In patients with COPD or hypercapnia, controlled oxygen to avoid worsening CO2 retention 7, 3

If Pneumonia/Sepsis Confirmed

• Antibiotics: Broad-spectrum coverage for hospital-acquired pneumonia (e.g., piperacillin-tazobactam or ceftriaxone + azithromycin) 6
• Fluid resuscitation: If septic shock, but avoid excessive fluids if heart failure coexists 6
• Source control: Assess surgical site for infection 6

ICU Admission Criteria

The following patients require ICU admission: 3

• Persistent significant dyspnea despite initial therapy
• Hemodynamic instability (systolic BP <90 mmHg, shock)
• Respiratory failure requiring NIV or intubation
• High-risk PE with right ventricular dysfunction
• Cardiogenic shock or cardiac tamponade

Common Pitfalls to Avoid

• Delaying PE work-up: Post-operative orthopedic patients have high PE risk; do not attribute dyspnea to "anxiety" or "pain" without excluding PE 7
• Over-oxygenation in COPD patients: Excessive oxygen without ventilatory support can worsen hypercapnia 7, 3
• Using diuretics in tamponade: Cardiac tamponade requires pericardiocentesis, not diuretics, which worsen hemodynamics 5
• Ignoring right heart strain on ECG/echo: This indicates high-risk PE requiring aggressive management 7
• Assuming normal D-dimer excludes PE post-operatively: D-dimer has limited utility in post-surgical patients due to baseline elevation 7