Pneumonia is an infection of the lower respiratory tract specifically the lungs. You can refer to the introduction of the study unit on SINUSITIS for a detailed discussion of the respiratory system.
This study unit is based on the current Clinical Practice Guideline of the American Thoracic Society and Infectious Diseases Society of America (ATS/IDSA) for the treatment of community acquired pneumonia (CAP), hospital acquired pneumonia (HAP) and ventilator associated pneumonia (VAP).
Infectious organisms can enter the lower respiratory tract in 1 of 3 ways:
- direct inhalation
- aspiration from the throat (oropharyngeal)
- via the blood from another site of infection (hematogenous transfer)
Community Acquired Pneumonia
Community acquired pneumonia (CAP) describes the clinical scenario where signs and symptoms of a lung infection started outside of the hospital OR within 48 hours (2 days) of hospital admission. Within this timeframe, it is likely the patient encountered the bug and it has been incubating prior to being admitted.
Causative Organisms
The most common cause of community acquired pneumonia is a viral infection. Rhinovirus and influenza are the 2 most common viral causes. As a reminder, antibiotics have no effect on viruses. Unnecessary treatment with antibiotics will only increase the potential for developing multidrug resistant bacteria that are hard to treat if they become pathogenic.
Bacterial pathogens often coexist with viruses. There is no current test that can quickly and accurately distinguish viral CAP from bacterial CAP. In the study unit covering community acquired pneumonia, we will talk about “double sickening” where an infection starts off as viral and then transitions to bacterial. The ATS/IDSA guidelines recommend treating empirically for possible bacterial infection or coinfection.
The most common bacterial pathogen in community acquired pneumonia is Streptococcus pneumoniae.
Haemophilus influenzae, Mycoplasma pneumoniae, Staphylococcus aureus, Legionella species, Chlamydia pneumoniae, and Moraxella catarrhalis are the other common bacterial agents.
Hospital Acquired Pneumonia
Hospital acquired pneumonia (HAP) describes the clinical scenario where signs and symptoms of a lung infection started at least 48 hours (2 days) after hospital admission. Within this timeframe, it is likely that the patient contracted the bug from a source in the hospital.
Ventilator Acquired Pneumonia
Ventilator associated pneumonia (VAP) describes the clinical scenario where signs and symptoms of a lung infection started after at least 48 hours after intubation.
Causative Organisms
The common bacterial pathogens are the same for HAP and VAP. They vary by institution and is influenced by antibiotic use practices at the particular site. These bugs include Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, Enterobacter, Acinetobacter, Staphylococcus aureus and Streptococcus.
Why does “WHERE” matter so much?
The antibiotic we use for the treatment of pneumonia is dependent on 3 “where” questions: where the bug was contracted and where the patient will be treated (home versus hospital) and where in the hospital they will be treated.
The setting where infection occurred is used to categorize pneumonia and the associated distinction between CAP/HAP/VAP is an important one. As we will see, it informs the choice of antibiotics and duration of therapy. This is because where it was contracted gives us a best-guess of the likely causative agent. Specifically whether we need to cover potentially resistant bacteria.
Where the patient will be treated (outpatient versus inpatient) will also determine the route of administration.
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Classification of Pneumonia
The clinical presentation of HAP and CAP are fairly similar. This creates the potential to overtreat CAP and breed resistant bugs or undertreat HAP and increase risk of mortality. This is why “WHERE” infection occurred is the first important question you must answer in the treatment of pneumonia.
Multi Drug Resistant Bacteria
Because there is greater, more consistent use of antibiotics within a hospital, there is greater potential for the development of multi drug resistant (MDR) bacteria. These organism like methicillin resistant staphylococcus aureus (MRSA) and pseudomonas aeruginosa (pseudomonas) are associated with higher mortality and require targeted treatment.
We do not want to expose patients who are unlikely to be infected with MDR bacteria with antibiotics used for these bugs. Whenever pathogens are exposed to antibiotics, over time they develop genetic mutations. These mutations allow that bug to circumvent the effect of the drug, thus developing resistance. This process is accelerated as more antibiotics are used in more people.
HAP/VAP and CAP have alot in common in terms of presentation and diagnosis but they will be addressed in different study units. They are distinct infections that have different therapeutic considerations.
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Diagnosing Pneumonia
A diagnosis of pneumonia is based on clinical presentation and radiographic imaging (chest X ray).
How does a patient with pneumonia present?
Signs and symptoms refer to what the patient complains of. For pneumonia this includes fever, chills, shortness of breath, a productive cough and/ or blood in sputum.
The physical exam may show shortness of breath (tachypnea), increased heart rate (tachycardia), diminished breath sounds and/ or crackling when they take a breath (inspiratory crackles).
Their labs can show elevated white blood cells (leukocytosis) which is a classic sign of infection.
Once pneumonia is suspected based on patient presentation the guidelines recommend confirmation of pneumonia via a chest X Ray. Be aware that in most cases imaging does not occur in the outpatient setting for the diagnosis of pneumonia. Most clinics do not have onsite radiography.
The chest X ray will show infiltrates in the lungs.
When we see infiltration in the lungs it means there is something that is more dense than air like pus or blood.
Infiltration with signs and symptoms of infection, as explained above, suggests pneumonia.
The ATS/IDSA guidelines recommend a chest X ray for all adult patients with suspected pneumonia.
Using patient’s sign and symptoms, physical exam, labs and chest X ray we can make a diagnosis of pneumonia.
At this point we know what to treat. Before we can select the appropriate antibiotics we need to answer the second “where”: where to treat. To objectively determine whether a patient would be best treated inpatient or outpatient we clinical prediction tools: CURB 65 and the (Pneumonia Severity Index) PSI scale.
Where to Treat Pneumonia
At this point we know where our patient encountered in the infecting organism. The next step is to determine where our patient needs to be treated: outpatient, inpatient or inpatient ICU.
CAP or HAP is not an indication of disease severity or where they get treated.
A patient with either one of these has the potential to be treated outpatient, inpatient or in critical care.
Where they are treated is based on clinical presentation and risk of mortality.
A patient with VAP will of course be treated in the hospital because they are on a ventilator. A patient with HAP may develop signs and symptoms after recent discharge from the hospital. Whether they need some be treated outpatient or inpatient depends on their clinical presentation (difficulty breathing, low oxygenation, organ failure).
Unnecessary hospital admission for cases that could be treated outpatient results in high costs for both patients and hospitals. It can also place the patient at risk for complications associated with hospital admission including exposure to MDR bacteria, and increased risk if blood clots.
The implications of not admitting a patient who needs additional support is more straight forward, it increases the risk of morbidity and mortality.
The Problem with PSI
The preferred way to asses whether hospital admission is required for pneumonia is the Pneumonia Severity Index (PSI). PSI estimates the mortality of adult patients with CAP. It is complicated to calculate. It requires alot of patient history and labs that are not readily available in the outpatient setting including pH and partial pressure of oxygen.
CURB 65
Instead the CURB 65 score is used to assess risk of mortality and therefore the level of care (inpatient, outpatient) in patients presenting with CAP.
CURB-65 assigns 1 point for each of the 4 assessment points.
The urea level is the blood urea nitrogen (BUN). Normal levels are 5-20mg/dL. Because it requires a lab draw, BUN is not always readily available in many outpatient settings. There is an abbreviated score called CRB-65 that eliminates the urea component.
Respiratory rate >30 breaths per minute is 1 point.
Blood pressure <90/60 mmHg is 1 point
Age > 65 is 1 point
A CURB-65 score of 2 or more suggests a high risk for morbidity and/or mortality therefore the need for hospital admission.
Once we’ve made the decision to treat inpatient we need to decide where in the hospital to treat. Is the patient stable enough for the medical floor or does the patient need the additional support of the intensive care unit. This too will determine the choice of antibiotics. We will delve into this in the individual study units.
After answering those “WHERE” questions we can begin appropriate treatment.
The study units for CAP and HAP/VAP will review the specifics for these disease states including appropriate antibiotics, need for cultures, duration of treatment and much more.
I hope this study unit has set a strong foundation for the assessment of pneumonia. Pneumonia is one of those disease states you will see over and over again. Refer to the diagrams presented here often and it will soon become second nature.
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