COPD exacerbations: Clinical manifestations and evaluation

INTRODUCTION — 

The Global Initiative for Chronic Obstructive Lung Disease (GOLD), a report produced by the National Heart, Lung, and Blood Institute (NHLBI) and the World Health Organization (WHO), defines an exacerbation of chronic obstructive pulmonary disease (COPD) as "an event characterized by dyspnea and/or cough and sputum that worsens over ≤14 days, which may be accompanied by tachypnea and/or tachycardia, and is often associated with increased local and systemic inflammation caused by airway infection, pollution, or other insult to the airways" [1,2]. This generally includes an acute change in one or more of the following cardinal symptoms:

●Cough increases in frequency and severity

●Sputum production increases in volume and/or changes character

●Dyspnea increases

The clinical manifestations and evaluation of patients with exacerbations of COPD are discussed in detail here. A table to assist with emergency management of severe acute exacerbations of COPD is provided (table 1). The diagnosis and treatment of stable COPD and the treatment, risk factors, prognosis, and prevention of exacerbations of COPD are discussed separately.

●(See "Chronic obstructive pulmonary disease: Diagnosis and staging".)

●(See "Stable COPD: Overview of management".)

●(See "COPD exacerbations: Management".)

●(See "COPD exacerbations: Prognosis, discharge planning, and prevention".)

EPIDEMIOLOGY — 

Among patients with COPD, the frequency of exacerbation varies with the severity of disease, and some patients have more frequent exacerbations than others independent of other measures of disease severity [1,3].

●Among almost 100,000 patients with COPD, the number of exacerbations in a baseline year of observation predicted the rate over the subsequent 10 years [4]. Approximately, 25 percent did not have an exacerbation; those with one baseline exacerbation were likely to have another (hazard ratio [HR] 1.71, 95% CI 1.66-1.77); and those with ≥5 events were even more likely to have future events (HR 3.41, 95% CI 3.27-3.56).

●A study of Medicare beneficiaries found a 64 percent readmission rate over one year following a discharge for COPD exacerbation [5].

●In a survey that included over 4000 respondents with COPD, approximately 10 to 25 percent needed an emergency room evaluation for COPD and 5 to 10 percent required hospitalization [6].

●In a separate survey of more than 1000 patients, 21 percent of those who reported a COPD exacerbation required hospitalization [7].

RISK FACTORS AND TRIGGERS

Risk factors — According to observational studies, the risk of developing an exacerbation of COPD correlates with the following features (table 2) [8-19]:

●Advanced age

●Productive cough

●Longer duration of COPD

●History of antibiotic therapy

●COPD-related hospitalization within the previous year

●Chronic mucous hypersecretion

●Peripheral blood eosinophil count >0.34 x 10⁹ cells/L (340 cells/microL)

●Theophylline therapy

●Use of medications leading to sedation or respiratory depression (including opioids, benzodiazepines, non-benzodiazepine hypnotics, and gabapentinoids)

●Presence of one or more comorbidities (eg, ischemic heart disease, heart failure, or diabetes mellitus)

Women are slightly more likely to experience a COPD exacerbation than men [13,20]. In general, worsening airflow limitation (lower forced expiratory volume in one second [FEV₁]) is associated with an increasing risk of COPD exacerbation, although airflow limitation alone does not provide a good assessment of exacerbation risk [1].

Other potential contributors to an increased risk of exacerbations include the following:

●Severity of COPD and history of prior exacerbations – The Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines suggest using primarily history of exacerbations, history of hospitalization or emergency department visits for exacerbation, and symptoms to assess the exacerbation risk [1]. The number of exacerbations in the previous 12 months is stratified: a history of zero or one exacerbation suggests a low future risk of exacerbations, while two or more suggest a high future risk [1]. Having had one hospitalization or emergency room visit due to an exacerbation portends a high risk for future exacerbations [1]. Symptoms (based on instruments such as the COPD Assessment Test [CAT] and the modified Medical Research Council [mMRC] Dyspnea Scale) further divide patients at low-risk into separate categories for more individualized pharmacologic management (algorithm 1).

In the prospective Evaluation of COPD Longitudinally to Identify Predictive Surrogate Endpoints (ECLIPSE) study, 2138 patients with moderate to severe airflow limitation (forced expiratory volume in one second [FEV₁] <80 percent predicted) were followed for three years [21]. The single best predictor of exacerbations was a history of prior exacerbations, regardless of the severity of airway obstruction [4]. In a separate large cohort study, the best predictors for future exacerbations in those without a recent exacerbation included symptom severity (mMRC, CAT), the presence of chronic bronchitis, severity of airway obstruction (FEV₁ percent predicted), and gastroesophageal reflux disease [22]. In one study, FEV₁/FVC was shown to have similar performance as FEV₁ percent predicted for exacerbation prediction, suggesting utility as an exacerbation predictor in populations where estimated formulas for FEV₁ percent predicted are not available [23].

Worsening airflow obstruction remains associated with an increasing prevalence of exacerbations, hospitalization, and death [24]. It is a component of the BODE index, a prognostic tool that can also assess therapeutic response to medications, pulmonary rehabilitation therapy, and other interventions [25].

Different COPD staging systems and severity assessments are discussed in more detail separately. (See "Chronic obstructive pulmonary disease: Diagnosis and staging", section on 'Assessment of severity'.)

●Gastroesophageal reflux disease – Gastroesophageal reflux disease (GERD) may be an additional risk factor for COPD exacerbations [26,27]. In the ECLIPSE study noted above, the occurrence of two or more exacerbations in a year was associated with a history of GERD or heartburn [21]. Similarly, GERD was one factor associated with a higher likelihood of future exacerbation in a retrospective analysis of 1528 patients from the COPDGENE cohort without prior exacerbations [22]. However, in an observational study of 638 patients with stable COPD, therapy with proton pump inhibitors did not decrease the risk for severe exacerbations [28]. Additional studies are needed to determine whether GERD contributes to the development of COPD exacerbations.

●Left ventricular diastolic dysfunction – Left ventricular diastolic dysfunction at baseline is associated with a higher frequency of hospitalization for COPD exacerbation [29]. Diastolic dysfunction is common in patients with COPD, likely due to both comorbid vascular mechanisms (eg, hypertension, coronary artery disease, systemic inflammation) as well as metabolic and structural consequences of COPD (eg, lung hyperinflation, chronic hypoxia, and hypercapnia) [30,31]. Many of these contributing factors worsen during an exacerbation and may lead to diastolic decompensation, followed by pulmonary congestion and bronchial hyper-reactivity [32]. High heart rates, whether due to breathlessness, anxiety, or atrial arrhythmias, further exacerbate this pathophysiology.

●Pulmonary hypertension – Secondary pulmonary hypertension may be an additional risk factor for COPD exacerbations, possibly as an indicator of disease severity. In a follow-up to the ECLIPSE study, chest computed tomography scans were used to compute the ratio of the diameter of the pulmonary artery to the diameter of the aorta (PA:A ratio) [33]. In the study, a PA:A ratio greater than 1 was an independent risk factor for a future severe exacerbation (OR 3.44, 95% CI 2.78-4.25). Notably, a PA:A ratio >1 suggests the presence of pulmonary hypertension, although it does not clarify the cause of pulmonary hypertension (eg, hypoxemia due to COPD or other lung disease, left heart failure, sleep apnea). The clinical usefulness of this observation in terms of treatment decisions is unclear.

●Low serum immunoglobulin G (IgG) – Lower levels of serum IgG may be associated with an increased risk for COPD exacerbations and hospitalization [34,35]. In one prospective cohort study, patients in the lowest tertile of serum IgG concentration (less than 1225 mg/dL) had a higher exacerbation risk compared with the rest of the cohort (incidence rate ratio [IRR] 1.28, 95% CI 1.08–1.51), even after accounting for demographics, smoking history, and COPD severity [35]. Among IgG subclasses, IgG1 and IgG2 were associated with an increased risk of severe exacerbation (IRR 1.39, 95% CI 1.06–1.84; and IRR 1.50, 95% CI 1.14–1.97).

Triggers — Evaluation and treatment of potential triggers is a critical component of exacerbation management. Respiratory infections, most commonly viral (eg, rhinovirus) or bacterial, are estimated to trigger approximately 70 percent of COPD exacerbations (table 3) [1,36]; atypical bacteria are a relatively uncommon cause [37,38]. The remaining 30 percent are due to environmental pollution and weather conditions, pulmonary embolism, or an unknown etiology [1,39-41]. (See "Management of infection in exacerbations of chronic obstructive pulmonary disease".)

COPD exacerbations have been associated with exposure to poor indoor and outdoor air quality, such as higher levels of ozone, carbon monoxide, inhalable particulate matter (≤10 microns, aka PM₁₀), and nitrogen dioxide [42-44]. Increased ambient levels of fine particulate matter (≤2.5 microns, aka PM_2.5) are associated with an increase in hospitalization and mortality in COPD [45]. In a trial of 116 patients with COPD and exposure to poor air quality at home (PM_2.5 >10 mcg/m³), use of indoor air filters versus sham air filters resulted in a dose-dependent improvement in respiratory symptoms and risk of moderate exacerbations [46].

Indoor and outdoor temperature have also been linked to COPD exacerbations. Low outdoor temperatures are associated with an increased risk of exacerbations, while high outdoor temperatures are associated with an increased risk of hospitalization for COPD [47,48]. Indoor temperature and humidity can vary based on building type, insulation, socioeconomic factors, and behavioral factors, and have been associated with increased dyspnea and short-acting bronchodilator use [49,50].

COPD exacerbations of unknown etiology may also be triggered or caused by other medical conditions, such as myocardial ischemia, heart failure, aspiration, or pulmonary embolism [1,51].

The relationship between COPD exacerbation and pulmonary embolism is illustrated by a prospective multicenter study of 1580 patients with COPD who were admitted to the hospital with acute worsening of respiratory symptoms [52]. Pulmonary embolism was identified in 266 (17 percent) when all patients were screened with CT of the pulmonary arteries (CTPA); 166 patients (11 percent) had pulmonary embolism involving the main or lobar pulmonary arteries. The presence of new purulent sputum reduced the odds of pulmonary embolism. Although the frequency of pulmonary embolism among patients hospitalized with an exacerbation of COPD varies across studies [53-56], a systematic review prior to this multicenter study showed a similar pooled prevalence of 23 percent when all patients were evaluated by CTPA within 48 hours of hospital admission (seven studies, 999 patients) [57]. An important limitation of these studies is their inability to determine whether the pulmonary embolism is the cause of the COPD exacerbation, a result of the COPD exacerbation, or a mere bystander.

CLINICAL MANIFESTATIONS — 

The clinical manifestations of exacerbations of COPD range from a mild increase in dyspnea, cough that is productive or nonproductive to respiratory failure with acute respiratory acidosis and/or hypoxemia.

Medical history — By definition, patients present with the acute onset or worsening of respiratory symptoms, such as dyspnea, cough, and/or sputum production, over several hours to days [1,58]. These symptoms should be characterized further in terms of the following features:

●Time course of the symptoms

●Comparison to baseline level of symptoms

●Severity of respiratory compromise (eg, dyspnea at rest, dyspnea climbing stairs, dyspnea severity using a visual analog [1-10] scale)

●Delineation of sputum characteristics (eg, amount, color, purulence, blood)

●Use of home oxygen now or in the past

Associated features that might suggest an alternate diagnosis or comorbidity include:

●Constitutional symptoms (eg, fever, chills, night sweats)

●Chest pain, chest pressure, peripheral edema, or palpitations

●Risk factors for coronary disease

●Risk factors for thromboembolic disease

●Upper respiratory symptoms that might suggest a viral respiratory infection or exposure to anyone with influenza

Patients should be asked if they currently smoke cigarettes or use vaping products. The past history of exacerbations should be ascertained: number of prior exacerbations, courses of systemic glucocorticoids, antibiotic therapy in the preceding three months, prior exacerbations requiring hospitalization or ventilatory support, and response to therapy of previous exacerbations.

Physical examination — Physical findings associated with an exacerbation of COPD often include wheezing and tachypnea and may include features of respiratory compromise such as difficulty speaking due to respiratory effort, use of accessory respiratory muscles, and paradoxical chest wall/abdominal movements (asynchrony between chest and abdominal motion with respiration). Tachycardia is also frequently present.

If present, decreased mental status could reflect hypercapnia or hypoxemia and asterixis could indicate hypercapnia.

Other physical findings, such as fever, hypotension, bibasilar fine crackles, and peripheral edema, should also be considered, as they might suggest a comorbidity or alternate diagnosis.

EVALUATION AND DIAGNOSIS — 

The goals of evaluating a suspected exacerbation of COPD are to confirm the diagnosis, identify the cause (when possible), assess the severity of respiratory impairment and contribution from comorbidities, and exclude alternate diagnostic possibilities. A rapid overview for the evaluation and management of severe exacerbations of COPD may be found in the table (table 1).

Initial evaluation — The choice of specific tests is guided by the severity of the exacerbation and the particular associated clinical findings. (See 'Clinical manifestations' above.)

For patients with a mild exacerbation (absence of resting dyspnea or respiratory distress, preserved ability to perform activities of daily living), who do not require emergency department treatment, the evaluation may be limited to clinical assessment and possibly pulse oxygen saturation.

For patients who require emergency department care, the evaluation should generally include the following (table 1):

●Assessment of pulse oxygen saturation

●A chest radiograph to exclude pneumonia, pneumothorax, pulmonary edema, pleural effusion, followed by a chest CT angiogram to exclude pulmonary embolism and other alternative diagnoses in those whose chest radiograph does not reveal an acute process

●Laboratory studies (eg, complete blood count and differential, serum electrolytes and glucose)

●Electrocardiogram to evaluate for arrhythmias and myocardial ischemia

●Arterial blood gas (ABG) analysis is obtained if acute or acute-on-chronic respiratory acidosis is suspected or if ventilatory support is anticipated. Concern about acute-on-chronic hypercapnia might be prompted by a history of prior elevation in arterial tension of carbon dioxide (PaCO₂), elevated serum bicarbonate (perhaps reflecting compensation for chronic hypercapnia), or the presence of severe airflow obstruction (eg, forced expiratory volume in one second [FEV₁] <50 percent of predicted)

We do not use procalcitonin [59] to determine the need for antibiotics in COPD exacerbations, as study results do not clearly and consistently demonstrate that this assay adds value to clinical judgment alone. C-reactive protein evaluation is also of uncertain utility in antibiotic stewardship; however, it may be useful for severity stratification if results are available quickly enough for triage decisions. (See 'Severity of exacerbation' below and "Evaluation for infection in exacerbations of chronic obstructive pulmonary disease", section on 'Procalcitonin and C-reactive protein'.)

Additional testing — Additional tests are largely used to exclude processes in the differential diagnosis and are obtained depending on the degree of diagnostic uncertainty following clinical evaluation and initial testing.

●Cardiac evaluation – Blood cardiac troponins and N-terminal pro-brain natriuretic peptid (NT-proBNP) are used to evaluate potential myocardial infarction and heart failure, respectively. If congestive heart failure remains high on the differential based on clinical features (eg, respiratory crackles, peripheral edema), NT-proBNP, and imaging findings (eg vascular congestion, pleural effusion), an echocardiogram should also be obtained. (See "Initial evaluation and management of suspected acute coronary syndrome (myocardial infarction, unstable angina) in the emergency department" and "Approach to diagnosis and evaluation of acute decompensated heart failure in adults".)

●Chest CT pulmonary angiogram – A chest CT pulmonary angiogram can help exclude pulmonary embolism as a trigger or alternative diagnosis for respiratory symptoms. The frequency of pulmonary embolism in patients with COPD and acute respiratory symptoms in the hospital setting appears to be between 15 to 25 percent [52,57]. In one multicenter study of nearly 1600 patients hospitalized for COPD exacerbation who were assessed with CT pulmonary angiogram, the rates of pulmonary embolism based on low, moderate, or high probability Wells criteria scores were 7, 38, and 74 percent, respectively [52]. Purulent sputum production decreased the odds of venous thromboembolism by approximately 60 percent. Given this prevalence rate, we suggest obtaining imaging for pulmonary embolism (typically CT pulmonary angiogram) in patients with severe symptoms who do not have evidence of other triggers (eg, infection or heart failure). (See 'Differential diagnosis' below and "Clinical presentation and diagnostic evaluation of the nonpregnant adult with suspected acute pulmonary embolism".)

●Sputum culture – A sputum Gram stain and culture are not obtained for most exacerbations of COPD. However, they can be useful in patients at risk for a poor outcome or increased risk of infection with Pseudomonas (table 4 and table 5). Sputum culture may also be helpful in patients who are strongly suspected of having a bacterial infection but fail to respond to initial antibiotic therapy. (See "Evaluation for infection in exacerbations of chronic obstructive pulmonary disease", section on 'When to obtain sputum studies'.)

●Respiratory viral testing – The majority of COPD exacerbations are caused by viral infections. Testing for influenza or severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is appropriate when these viruses are circulating in the community or in patients with strong suspicion based on clinical features (eg, acute onset of fever, myalgias, coryza) or known sick contacts. Patients who test positive should often receive antiviral therapies. Rapid antigen testing and direct or indirect immunofluorescence antibody staining tests are useful screening tests but have limited sensitivity; polymerase chain reaction (PCR)-based testing is more sensitive and specific. (See "Seasonal influenza in adults: Clinical manifestations and diagnosis" and "COVID-19: Diagnosis".)

While not necessary in most patients, larger PCR diagnostic panels can detect multiple respiratory viruses simultaneously (eg, influenza, adenovirus, parainfluenza virus, respiratory syncytial virus, human metapneumovirus, coronavirus, and rhinovirus). These studies are more frequently obtained in patients with community-acquired pneumonia, and the exact indications for their use in COPD exacerbations are not clear. (See "Evaluation for infection in exacerbations of chronic obstructive pulmonary disease", section on 'Detection of respiratory viruses'.)

Severity of exacerbation — The classification of exacerbation severity proposed by an international commission and adopted by the Global Initiative for Chronic Obstructive Lung Disease (GOLD) is based on symptoms, vital signs, and arterial blood gas (ABG) and c-reactive protein values (if obtained) (figure 1) [1,25]:

●Mild – Dyspnea <5 on a visual analog (1-10) scale (VAS); respiratory rate <24 breaths per minute; heart rate <95 beats per minute; resting SaO2 ≥92 percent breathing ambient air or the patient's usual oxygen prescription and change in saturation ≤3 percent from baseline (if known); CRP<10 mg/L (if obtained). Treatment with short-acting bronchodilators is often sufficient for mild exacerbations.

●Moderate – Three out of five of the following: Dyspnea ≥5 on VAS; respiratory rate ≥24 breaths per minute, heart rate ≥95 beats per minute; resting SaO2 <92 percent breathing ambient air or the patient's usual oxygen prescription and/or change in saturation >3 percent from baseline (if known); CRP ≥10 mg/L (if obtained). Treatment of moderate exacerbations generally includes short-acting bronchodilators plus antibiotics and/or oral glucocorticoids.

●Severe – Meets moderate criteria combined with hypercapnia and acidosis on ABG (PaCO2 >45 mmHg and pH <7.35). Treatment of severe exacerbations includes short-acting bronchodilators, antibiotics, and oral or intravenous glucocorticoids. Severe exacerbations may be associated with respiratory failure and require noninvasive or invasive ventilation.

DIFFERENTIAL DIAGNOSIS — 

Patients with COPD who present to the hospital with acute worsening of dyspnea should be evaluated for potential alternative diagnoses, such as heart failure, cardiac arrhythmia, pneumonia, pulmonary embolism, and pneumothorax [1,60,61]. A chest radiograph will differentiate among several of these possibilities (eg, heart failure, pneumonia, pneumothorax); a clear chest radiograph may be a clue to pulmonary embolism, especially when dyspnea and hypoxemia are more prominent than cough or sputum production.

The importance of considering these alternate diagnoses was illustrated in an autopsy study of 43 patients with COPD who died within 24 hours of admission for a COPD exacerbation [60]. The primary causes of death were heart failure, pneumonia, pulmonary thromboembolism, and COPD in 37, 28, 21, and 14 percent, respectively.

●Heart failure – Acute decompensated heart failure (ADHF) is characterized by the development of acute dyspnea associated with elevated intracardiac filling pressures with or without pulmonary edema. HF may be new or an exacerbation of chronic disease. The diagnosis of ADHF is a clinical diagnosis based upon the presence of a constellation of symptoms and signs of HF. While test results (eg, natriuretic peptide level, chest radiograph, echocardiogram) are often supportive, the diagnosis cannot be based on a single test. (See "Approach to diagnosis and evaluation of acute decompensated heart failure in adults".)

●Cardiac arrhythmias – Cardiac arrhythmias, such as atrial fibrillation, are frequent in patients with COPD, and may be a trigger or consequence of COPD exacerbation [1]. A bedside electrocardiogram can be diagnostic. (See "Atrial fibrillation: Overview and management of new-onset atrial fibrillation".)

●Pneumonia – Pneumonia can present with acute shortness of breath, hypoxemia, and an inconclusive pulmonary examination. Chest radiograph findings may differ, but some cases of bibasilar pneumonia may be similar to HF, although evidence of upper zone redistribution is not present with pneumonia. Fever and leukocytosis may suggest an infectious process. (See "Clinical evaluation and diagnostic testing for community-acquired pneumonia in adults".)

●Pneumothorax – COPD is a risk factor for pneumothorax. Worsening dyspnea can be due to either a COPD exacerbation or pneumothorax, but acute pleuritic chest pain would be more suggestive of pneumothorax while increased volume of sputum and sputum purulence would suggest a COPD exacerbation. A pneumothorax is usually apparent on conventional chest radiograph or thoracic ultrasound, although bullous emphysema can mimic a pneumothorax and necessitate a chest computed tomography (CT) scan for differentiation. (See "Clinical presentation and diagnosis of pneumothorax".)

●Pulmonary embolism – The sudden onset of symptoms such as dyspnea, pleuritic chest pain, tachypnea, and cough may be caused by a pulmonary embolism. The suspicion for pulmonary embolism rises in the absence of purulent sputum production, history of an upper respiratory infection, or pneumothorax [51-57,62,63]. (See 'Triggers' above and 'Additional testing' above.)

Testing may include a blood D-dimer test, lower extremity compression ultrasonography with Doppler, and CT pulmonary angiogram. (See "Clinical presentation and diagnostic evaluation of the nonpregnant adult with suspected acute pulmonary embolism".)

SOCIETY GUIDELINE LINKS — 

Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Chronic obstructive pulmonary disease".)

SUMMARY AND RECOMMENDATIONS

●Definition – A COPD exacerbation is an event characterized by dyspnea and/or cough and sputum production that worsens over ≤14 days; it may be accompanied by tachypnea and/or tachycardia and is often associated with increased local and systemic inflammation arising from airway infection, pulmonary embolism, pollution, or other airway insult. (See 'Introduction' above.)

●Risk factors – The single best predictor of exacerbations is a history of prior exacerbations. Other risk factors include advanced age, longer duration of COPD, chronic bronchitis (productive cough, mucus hypersecretion), elevated peripheral eosinophils, more severe dyspnea or symptoms, severe airflow obstruction, use of medications associated with sedation or respiratory depression, and comorbid diseases (especially heart disease, gastroesophageal reflux disease, and pulmonary hypertension) (table 2). (See 'Risk factors and triggers' above and "COPD exacerbations: Prognosis, discharge planning, and prevention", section on 'Prognosis after an exacerbation'.)

●Triggers – Respiratory infections are estimated to trigger approximately 70 percent of COPD exacerbations. Viral and typical bacterial infections are most common; atypical bacterial infection is an uncommon trigger. In general, patients with more advanced COPD and those with a higher number of cardinal symptoms (particularly sputum purulence) are more likely to have bacterial infections. Other potential triggers include myocardial ischemia, heart failure, aspiration, and pulmonary embolism. (See 'Triggers' above.)

●Clinical manifestations

•Symptoms – The three cardinal symptoms of COPD exacerbation are dyspnea, cough, and/or sputum production; they can occur alone or in combination. Exacerbations typically develop over several hours to days. Symptoms such as fever, chills, night sweats, chest pain, or peripheral edema suggest an alternate or comorbid diagnosis. (See 'Clinical manifestations' above.)

•Physical examination findings – Physical findings associated with an exacerbation of COPD often include wheezing and tachypnea. Features of respiratory compromise may be present, such as use of accessory muscles, fragmented speech, orthopnea, and depressed mental status. Fever, hypotension, bibasilar fine crackles, and peripheral edema may suggest systemic infection or heart failure. (See 'Physical examination' above.)

●Diagnosis – COPD exacerbation can often be diagnosed based on clinical history and manifestations; additional evaluation may be needed based on clinical severity and site of care.

Exacerbation severity (mild, moderate, or severe) is established based on the degree of dyspnea, respiratory and heart rates, and oxygenation status (figure 1).

Patients with COPD who present with acute worsening of dyspnea should be evaluated for potential alternative or concomitant conditions, including heart failure, cardiac arrhythmia, pulmonary embolism, pneumonia, and pneumothorax.

●Evaluation – Physical examination and assessment of oxygenation using resting and ambulatory pulse oximetry can establish a likely diagnosis and help triage patients to more urgent settings (for moderate to severe exacerbations). Additional work-up for mild exacerbations also may also include a chest radiograph to assess for pneumonia or heart failure, a sputum culture in patients at increased risk for Pseudomonas infection (algorithm 2), and respiratory viral testing for infectious triggers (eg, influenza, COVID-19, respiratory syncytial virus) based on season and symptoms.

For patients who require emergency department care, additional evaluation should generally include pulse oximetry, chest radiograph, electrocardiogram, complete blood count and differential, and serum electrolytes and glucose (table 1). Arterial blood gases (ABGs) are obtained when acute or acute-on-chronic hypercapnia is suspected due to prior elevation in arterial tension of carbon dioxide (P_aCO₂), elevated serum bicarbonate, or the presence of severe airflow obstruction (eg, FEV₁ <50 percent predicted). (See 'Initial evaluation' above.)

Additional testing to evaluate for noninfectious triggers depends on the degree of diagnostic uncertainty following initial clinical evaluation and testing. (See 'Additional testing' above.)

●Differential diagnosis – The most common processes in the differential diagnosis of a COPD exacerbation are heart failure, cardiac arrhythmias, pulmonary embolism, pneumonia, and pneumothorax. (See 'Differential diagnosis' above.)