The causes of acute COPD exacerbations (chronic obstructive pulmonary disease) are manifold and they can be infective or non-infective. Again, among the infective causes, there can be viral causes and bacterial causes that can be the reason for an acute COPD exacerbation.
Among all the causes, respiratory tract infection is the leading and most common cause of COPD exacerbations.
Infective COPD exacerbations are seen more during the cold winter months and the non-infective flare-ups are more common during the summer months.
Incidentally, an exacerbation or a flare-up is always acute; there is no such thing as a chronic exacerbation. A COPD exacerbation is an acute deterioration of the chronic respiratory symptoms that worsen and the patient goes into the acute phase of the disease.
The advanced stages of COPD and their severe and frequent exacerbations all point to a poor prognosis and an increased risk of mortality.
Frequent COPD exacerbations cause worsening of the patient’s health and prognosis. The focus, therefore, should be to prevent the causative agents and offer prompt treatment, if and when necessary.
Exacerbations come on very quickly within hours or at the most a few days, depending on the potency of the cause while identifying the cause of the exacerbation can take up to a week or more.
Treatment can’t wait for that long after the onset. Here is where the expertise of the pulmonologist comes into effect to identify and diagnose the probable cause and treat it.
Initial reports suggested that about 50% of COPD exacerbations go unreported, but later reports indicate that it may be as high as 67%. This ignorance on the part of the population is a major reason why COPD is the 3rd largest killer in the world.
In a study of patients with acute COPD exacerbations, infection was the proven cause in only 51% of the patients, heart failure, as comorbidity, accounted for 26% of episodes, and about 30% of exacerbations had no proven etiology.
Causes of COPD exacerbations and their risk factors
The principal identified infective and noninfective causes of COPD exacerbations include
- bacterial and/or viral infections – major cause accounting for 50% of the cases
- air pollution
- cold weather and
- interruption of regular treatment
Published data in the journal, Epidemiology and treatment of chronic bronchitis and its exacerbations by Peter Ball, suggest that 50–70% of exacerbations are because of respiratory infections, 10% due to environmental pollution, and up to 30% are due to unknown causes.
Lung infection: viral and bacterial
As mentioned above, lung infection is the major cause of an acute COPD exacerbation. The infection can be due to bacteria or a virus or an atypical organism. It can occur in the:
- lungs tissue and air sacs leading to pneumonia,
- the larger bronchi causing bronchitis, or
- the smaller bronchioles causing bronchiolitis
Due to infection, the lungs develop swelling and inflammation, which further narrow down and block the airways. This leads to the accumulation of mucus in the airways, which acts as a breeding ground for bacteria.
An exacerbation due to a viral infection, therefore, should always be treated with antibiotics also in anticipation of a secondary bacterial infection.
Bacteria are the cause of at least 50% of exacerbations. An American study demonstrated the presence of H influenza in 87% of bronchial biopsy samples from patients with acute COPD exacerbation.
Among the colonizing organisms, H influenzae (19%), S pneumoniae (13%), and M catarrhalis (9%) are the most common. Other less frequent bacteria include Staphylococcus aureus and P aeruginosa.
Infective causes of acute COPD exacerbations are more frequent in the cold winter months when viral infections are more rampant in the population. Viral infections account for approximately 20% of COPD exacerbations.
A recent American study noted that when the dominant strain of influenza was H1N1, hospital admissions for influenza-related chest infections were low. However, when the more virulent strain H3N2 influenza was prevalent, admissions for chest infections and related deaths were significantly higher.
Again, the Rhinovirus, which causes the common cold, has been detected in 23% of the patients during exacerbations due to a viral infection.
Other atypical organisms that can cause a COPD exacerbation include M pneumonia and C pneumonia.
Can the flu vaccine cause a COPD exacerbation?
There is no evidence that influenza vaccination is associated with acute COPD exacerbation. Studies have shown that there is no change or worsening in the symptoms, exercise capacity, lung function, or exacerbation frequency after taking the influenza vaccine irrespective of the severity of the disease.
Indoor and outdoor pollution
The already damaged lungs of COPD patients are increasingly sensitive to further damage by inhaled irritants in the atmosphere. These can be indoor and outdoor air pollutants. Both these causes of COPD exacerbations play a significant role in worsening the status of the disease.
Epidemiological research has linked worsening of the respiratory symptoms, hospital admissions due to exacerbations, and COPD-associated mortality during periods of increased pollution with air pollutants such as particulate matter, black smoke, sulfur dioxide (SO2), ozone (O3), and nitrogen oxides (O3).
Studies indicate that up to 9% of admissions with acute COPD exacerbations may be due to atmospheric pollution, especially during the summer months.
Patients living less than 100 meters from a busy traffic road are at an increased risk of developing COPD exacerbations. The higher the pollution more severe the symptoms and the worse is the COPD exacerbation.
Symptoms that typically worsen are dyspnea, sputum purulence or sputum amount, nasal discharge or congestion, and wheezing or tight chest.
Indoor or household pollutants
According to World Health Organization (WHO), “Around 3 billion people cook and heat their homes using solid fuels (i.e. wood, charcoal, coal, dung, crop wastes) on open fires or traditional stoves”.
These wrong cooking practices produce high levels of lung-damaging indoor or household air pollutants such as fine particles and carbon monoxide. Exposure is particularly high among women and young children, who spend most of their time at home.
Indoor levels of particulate matter are significantly higher in homes with smokers.
According to the 2014 WHO report, air pollution in 2012 caused the deaths of around 7 million people worldwide. That’s one in eight of total global deaths
Interestingly, low- and middle-income countries suffered the most casualties in 2012. There were a total of 3.3 million deaths due to indoor air pollution and 2.6 million deaths related to outdoor air pollution. That shows the major role of indoor pollution.
COPD patients, especially the elderly and those without inhaled medication are at significantly higher risk of developing an exacerbation during lower mean temperatures.
It is during the cold winter months that respiratory infections are most common. The lower temperatures are ideal for the viruses to run amuck, multiply and infect the population.
In COPD patients suffering from respiratory allergy, any of the allergens can trigger a COPD exacerbation. The common allergens are pollen from trees and grasses, house dust mites, and molds. pets such as cats and dogs.
Interruption of treatment
Stopping the regular COPD treatment makes you a very high-risk patient to develop a COPD exacerbation. This long-term therapy includes inhalable bronchodilators and/or steroids, long-term oxygen therapy, and a pulmonary rehabilitation program. All these must be continued regularly for as long as it takes.
Other causes of acute COPD exacerbations include mostly the comorbidities such as:
- Cardiac dysfunction
- Acute left heart dysfunction
- Congestive heart failure
- Right-sided heart failure (cor pulmonale) precipitated by hypoxia-induced pulmonary hypertension
- Pulmonary embolism
Of these, left-sided heart failure is most common because many COPD patients suffer from coronary artery disease and hypertensive heart disease as COPD complications.
No long-term study has reported a mean exacerbation rate of more than about 3 exacerbations a year. This number, therefore, may represent an upper limit of the frequency of acute COPD exacerbations in all populations.
COPD exacerbations and mortality
According to a study, patients with three or more exacerbations in a year had a survival rate of 30% at 5 years while those with no history of any previous exacerbation had a survival rate of 80%. Patients requiring readmission to the hospital had a 20% survival at 5 years.
However, in-hospital mortality varies between less than 10% and 60%, based on the severity level of the disease. According to another study, respiratory causes of a COPD flare-up accounted for 67% of deaths.