Pneumonia explained: What happens inside your lungs when the air sacs fill with fluid?

Pneumonia has been around a long time. So much so that it has been mentioned in descriptions at the time of Hippocrates.

'Pneumon' = lungs 'ia'= condition 

While we associate the term with infection, it more often indicates inflammation. Highlighted by the fact that we have a subtype of chemical pneumonia, seen in people who aspirated their acidic stomach contents or toxic oils used as laxatives or nasal drops; even the crude method of transferring petrol by sucking it out of tanks using pipes can lead to chemical pneumonitis. The usual presentations are prolonged cough, fever, breathlessness and fast breathing (some may have different coloured phlegm).

Pneumonia was initially classified on the basis of the causative pathogen, such as bacterial, viral, atypical bacteria, etc. For example, tuberculosis is actually a pneumonia caused by tubercular bacilli. Recent times have called for an upgrade and now, the classifications are based more on the signs of the patient and severity of the disease. This helps to triage and guides treatment protocols.

That being said, let's delve into the microscopic level changes that happen in pneumonia. Our lungs are made up of 500 million small bubbles like air sacs, called alveoli, behaving like a sponge.

The main purpose of these sacs is the exchange of oxygen. We inspire oxygen into the blood and return carbon dioxide to the atmosphere. These air sacs are also at the receiving end of outside contamination, even though we have defense mechanisms to filter it. The exposure to any toxin or organism starts a cascade of defence mechanisms to fight the infection. These soldier cells arrive and start engulfing the enemy and try to wall off the infection, the initial stage being inflammation followed by breakdown of cells leading to pus formation. When this fills up the alveoli, it is the onset of pneumonia, and depending on the extent of alveoli involved, it determines the severity and radiological presentation.

So what happens next?

As the number of alveoli involved increases, it’s termed differently. When one or isolated lobes are involved, it is called lobar pneumonia. When it involves multiple areas of the lung, it is called bronchopneumonia. And when the extent of involvement is severe and bilateral, we call it acute lung injury (ALI). This eventually leads to acute respiratory distress syndrome (ARDS), as seen in COVID and influenza infections.

As the term indicates, there is respiratory distress leading to respiratory failure. Due to the filling up of the air sacs with fluid or pus, the area available for oxygen exchange decreases, causing oxygen levels to drop; to compensate, there is faster breathing, which further reduces the oxygenation time and thus creates a vicious cycle. For the patient to get better, there needs to be assisted ventilation so that the lungs can recover from the pneumonia with antibiotics and other supportive medicines.

Sepsis means the spread of infection from the source organ to the blood, further affecting other organs. When it shuts down critical organs like the kidney or the heart, it's called septic shock. This is when the patient’s blood pressure falls, and there isn't enough urine produced, and hence the need for dialysis.

Does everyone with pneumonia have it?

With early detection, prevention of pneumonia progression is very easy and helps to avoid triggering the above-said cascade and reduce morbidity and mortality of the disease.

Does that mean anyone with pneumonia can go into sepsis?

Broadly, pneumonia is also classified into Community Acquired Pneumonia (CAP), Hospital Acquired Pneumonia (HAP), Ventilator Associated Pneumonia (VAP) and pneumonia of the immunocompromised (like in patients living with HIV or transplant patients or patients on immunosuppressives).

If vaccinated in a timely manner, CAPs caused by pathogens like Streptococcus, etc. can be contained well. But in current times, with the abuse of over-the-counter antibiotics, these too are becoming resistant to first-line medicines, leading to complications. HAP and VAP are the unfortunate other side of medical care, where any patient with a prolonged stay can get infected with other organisms commonly found in the hospital system, or from tubes and lines inserted. This can be prevented to a certain extent with strict control on visitation and bedside hand hygiene.

These infections usually progress to sepsis and respiratory failure as the patients are usually ICU-bedridden with other comorbidities and issues contributing to weak immunity. The latest nuisance is a rising trend of these organisms causing HAP/VAP in the local community, causing CAP. 

Vaccinate regularly

Vaccinations are not just restricted to children. Flu shots must be taken yearly prior to the local seasonal trends by all age groups. Pneumococcal vaccination is advisable for people above 60 years and those with immunocompromised states, chronic lung disease like asthma, COPD, bronchiectasis. So be aware, stay healthy!

(The author is a consultant in pulmonary medicine, KMC Hospital, Mangalore)

The opinions expressed in this article are those of the author and do not purport to reflect the opinions or views of THE WEEK.