What is the differential diagnosis for a patient presenting with noisy breathing and respiratory distress, considering potential pre-existing conditions such as asthma or COPD?

Differential Diagnosis for Noisy Breathing and Respiratory Distress

The differential diagnosis for noisy breathing with respiratory distress must first distinguish upper versus lower airway pathology, with immediate assessment of severity to identify life-threatening conditions requiring urgent intervention.

Immediate Assessment and Severity Stratification

• Assess airway, breathing, and circulation (ABC) first, measuring vital signs including respiratory rate, pulse rate, blood pressure, temperature, and oxygen saturation by pulse oximetry in all patients 1, 2
• Patients with respiratory rate >30 breaths/min should be triaged as very urgent 1
• Use a recognized physiological "track and trigger" system such as the National Early Warning Score (NEWS) for initial assessment and monitoring 2
• Document level of alertness, fluid status, presence of cyanosis, respiratory distress, and wheezing, though wheezing can be an unreliable indicator of airway obstruction 3

Upper Airway Causes (Inspiratory Stridor)

Upper airway obstruction presents with dysphonia, inspiratory stridor, and monophonic wheezing loudest over the central airway 3

• Foreign body aspiration - sudden onset, often with choking history 3
• Epiglottitis - acute onset, drooling, toxic appearance 3
• Laryngospasm - sudden onset, may follow airway manipulation or irritation 3
• Vocal cord dysfunction - mimics asthma but with inspiratory stridor and normal PaO₂ 3
• Extrinsic or intrinsic tracheal narrowing - progressive symptoms, may have history of intubation or malignancy 3
• Anaphylaxis - if respiratory difficulty occurs with cutaneous manifestations (hives, lip/eye swelling) or cardiovascular effects (hypotension, shock) 2

Evaluation for Upper Airway Obstruction

• If upper airway obstruction is suspected, evaluate using flow-volume curves and laryngoscopy, either during or after the emergency visit depending on severity 3
• Clues include complete resolution of airflow obstruction with intubation 3

Lower Airway Causes (Expiratory Wheezing)

Obstructive Lung Disease

COPD Exacerbation:

• Presents with worsening breathlessness, increased sputum production, or change in sputum color in patients with known or suspected COPD 2
• Patients >50 years who are long-term smokers with chronic breathlessness on minor exertion should be treated as having suspected COPD and require spirometric assessment 2
• COPD is diagnosed if airway obstruction (FEV₁/FVC ratio <70%) on spirometry is not reversible with bronchodilators 4
• Manifestations range from dyspnea, poor exercise tolerance, chronic cough with or without sputum production, and wheezing to respiratory failure or cor pulmonale 3

Asthma Exacerbation:

• Characterized by paroxysmal dyspnea with shortness of breath, often with dry cough mainly at night, frequently associated with allergies 5
• Asthma is diagnosed if airway obstruction on spirometry is reversible (>12% and >200 mL improvement in FEV₁) with bronchodilators or through observation of bronchoconstriction (reduction in FEV₁ of ≥20%) with methacholine challenge 4
• Assess severity using physical examination findings including level of alertness, ability to speak in full sentences, accessory muscle use, and presence of cyanosis 3

Asthma-COPD Overlap:

• Affects about a quarter of patients with COPD and almost a third of patients who previously had asthma 6
• Generally encompasses persistent airflow limitation in a patient older than 40 years with either a history of asthma or large bronchodilator reversibility 6
• Spirometry shows reversibility after bronchodilators (consistent with asthma) and persistent baseline airflow limitation (characteristic of COPD) 4
• Patients with asthma-COPD overlap have significantly worse respiratory symptoms, poorer quality of life, and increased risk of exacerbations and hospital admissions compared to asthma or COPD alone 6, 7

Other Lower Airway Causes

• Bronchitis - productive cough, may have fever 8
• Pneumonia - fever, productive cough, focal findings on examination 3
• Bronchospasm - may be medication-induced (ipratropium can cause bronchospasm in 2.3-5.4% of patients) 8

Parenchymal and Pleural Causes

• Pneumothorax - sudden onset, unilateral decreased breath sounds, hyperresonance 3
• Pneumomediastinum - subcutaneous emphysema, mediastinal crunch 3
• Post-obstructive pulmonary edema - occurs after forceful inspiratory efforts against obstructed airway, presents with dyspnoea, agitation, cough, pink frothy sputum, and low oxygen saturations 3
• Pulmonary edema (cardiogenic) - orthopnea, paroxysmal nocturnal dyspnea, peripheral edema 1

End-of-Life Respiratory Sounds

• Death rattle - noisy breathing from retained secretions in approximately one-quarter of imminently dying patients 3
• Agonal breathing - slow, irregular, noisy breathing mimicking grunting, hiccupping, or gasping in minutes before death 3

Diagnostic Workup Based on Clinical Presentation

For Suspected COPD Exacerbation:

• Obtain arterial blood gas measurement on arrival, noting inspired oxygen concentration 1
• Order chest radiograph as urgent investigation 1
• Check arterial blood gases within 60 minutes of starting oxygen therapy 1
• Target oxygen saturation of 88-92% using 24% Venturi mask at 2-3 L/min or 28% Venturi mask at 4 L/min to reduce mortality risk 1

For Suspected Asthma Exacerbation:

• Serial measurement of lung function using FEV₁ or PEF at presentation and 30-60 minutes after initial treatment is useful for categorizing severity 3
• In severe or life-threatening exacerbation with obvious airway compromise and cyanosis, objective measurements are not recommended at presentation; initiate treatment promptly 3
• Pulse oximetry is essential for initial assessment 3

For Upper Airway Obstruction:

• Flow-volume curves and laryngoscopy are indicated 3
• Chest radiograph to rule out complications 3

Initial Management Priorities

Oxygen Therapy:

• For patients without risk of hypercapnic respiratory failure, target oxygen saturation is 94-98% 2
• For patients with risk of hypercapnic respiratory failure (COPD, morbid obesity, chest wall deformities, neuromuscular disorders), target oxygen saturation is 88-92% pending blood gas results 1, 2

Bronchodilator Therapy:

• Administer nebulized bronchodilators on arrival and at 4-6 hourly intervals for COPD exacerbation 1
• For patients with COPD and elevated PaCO₂, nebulizers should be driven by compressed air rather than oxygen 1
• Administer inhaled bronchodilators (albuterol/salbutamol) immediately for patients with known asthma or COPD presenting with acute dyspnea and wheezing 2

Additional Therapies:

• Consider oral corticosteroids (usually 30 mg per day for one week) in patients with COPD exacerbation 1, 9
• Consider antibiotics if two or more of the following are present: increased breathlessness, increased sputum volume, or development of purulent sputum 1

Critical Pitfalls to Avoid

• Administering high-flow oxygen (>28%) to COPD patients before blood gas results are available can worsen hypercapnic respiratory failure 1, 2
• Failing to recognize COPD in older smokers with chronic breathlessness 1
• Assuming wheezing always indicates lower airway disease; upper airway obstruction can present with monophonic wheezing 3
• Overlooking cardiac causes of shortness of breath, particularly in women who may present with atypical symptoms 2
• Delaying assessment when oxygen saturation drops suddenly by 3% or more 2
• Assuming normal pulse oximetry rules out serious pathology (falsely normal in carbon monoxide poisoning) 2
• Discontinuing oxygen therapy abruptly when respiratory acidosis is detected 1