emDocs Cases: ED Evaluation of Community-Acquired Pneumonia

Authors: Brit Long, MD (@long_brit, EM Attending Physician at SAUSHEC) and Drew A. Long, BS (@drewlong2232, Vanderbilt University School of Medicine) // Edited by: Alex Koyfman, MD (@EMHighAK, EM Attending Physician, UT Southwestern Medical Center / Parkland Memorial Hospital)

Welcome to emDocs Cases! This will be a case-based discussion of EM topics, ranging from core to cutting edge and controversial. Today, we start with something common in emergency medicine: community-acquired pneumonia (CAP).

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You start your first shift with two patients. One is a 24-year-old male with three days of fever, productive cough, and chills. He has noted decreased appetite, but no nausea, vomiting, or diarrhea. He has no past medical history, takes no medications, and has no allergies.

Exam reveals RR 23/min, HR 112 bpm, Sat 95% on RA, T 38.1C, and BP 128/68. He appears tired though nontoxic, with normal mucosa, HEENT, and abdominal exams. You detect R sided rhonchi on lung exam, but no other abnormalities.

 Your second patient is a 73-year-old female with a history of CAD and DM. She presents with three days of fever, productive cough, and chills. She lives at home with her husband, who has severe dementia. She is the primary caregiver for him. She has not been able to adequately care for him due to her illness. She takes aspirin, metoprolol, hydrochlorothiazide, and metformin.

Exam reveals RR 24/min, HR 92, Sat 90% on RA, T 37.9, and BP 132/75. She has dry mucosa, with rhonchi on the left. She has normal CV and abdominal exams as well, with no skin breakdown.

So these are our two patients. Today we will discuss several aspects of community acquired pneumonia including: 1) disease perspective, 2) history and physical exam, 3) chest radiograph, 4) alternate imaging, 5) ultrasound use, and 6) clinical scores/disposition.

1. Disease perspective: what is community acquired pneumonia?

Pneumonia is an acute infection of the pulmonary alveoli.  Pneumonia is a common infection and the leading cause of infectious deaths. The mortality rate in severe pneumonia is 28%, but it is more commonly under 5%.  The Infectious Diseases Society of America (IDSA) recently redefined pneumonia subtypes, shown here:

Community acquired pneumonia is common, as it is responsible for 60,000 hospitalizations per year.  Causes of pneumonia include bacteria (most common), viruses, and fungi. However, a microbial agent is never identified in over 50% of patients with pneumonia. Typical agents include S. pneumoniae and H. influenza, with S. pneumo being the most common. “Atypical” pathogens include Legionella, Mycoplasma, and Chlamydia. Viral causes include influenza, parainfluenza, coronavirus, and many others.

2. For our patients, what historical and physical examination findings point toward pneumonia?

The common signs and symptoms of pneumonia include cough (79%-91%), fever (up to 80%), increased sputum (up to 65%), pleuritic chest pain (up to 50%), respiratory rate above 24 breaths/minute (45% to 70%), chills (40% to 50%), and dyspnea (approximately 70%).^14-20  However, no combination is diagnostic.  Lung findings like percussion and crackles are most reliable. But, as most of us know, examination varies and is not consistent between providers.^11,14-18,20 

The 24-year-old male clinically appears to have pneumonia. However, the older female does not have a fever. Could this still be pneumonia?

Atypical equals typical in the elderly. Patients who present with nonspecific complaints, such as altered mental status or nausea/vomiting, include elderly, immunocompromised, and debilitated patients.  Other nonspecific symptoms include lightheadedness, malaise, weakness, headache, joint pain, and rash. Older patients often have fewer symptoms, with delirium being more common. Up to 2/3 of elderly patients will not have cough, fever, or shortness of breath, and they are less likely to present with chills. ^21-24 Over half will present with confusion. Respiratory rate is important to assess, as tachypnea is a reliable factor in pneumonia diagnosis. ^21-24  

3. What testing is warranted? Does everyone need a CXR to diagnose pneumonia?

Clinically, the 23-year-old male has pneumonia. You have started 1 L NS, with 1 g ceftriaxone for community acquired pneumonia with 500 mg azithromycin PO. Though he meets sepsis criteria based on SIRS, he appears nontoxic and well. Does he need a CXR? Will it change your management?

 The diagnosis of CAP is typically based on the combination of history, exam, and CXR.^5,6,11,13  In the ED, many patients with respiratory complaints receive a CXR, and if suggestive of pneumonia, antibiotics are often given.^15-19  The prevalence of pneumonia in patients with URI symptoms approaches 5%-7% when vital signs are otherwise normal.

How good is CXR for diagnosing pneumonia?

CXR is often considered a standard for diagnosis of pneumonia, but this test lacks specificity and sensitivity. ^15,16,20 The 2007 IDSA guidelines recommend some form of imaging, with clinical symptoms, to diagnose pneumonia (Level III evidence, moderate recommendation).⁶ However, CXR is negative in over 30% of patients with pneumonia, with a sensitivity ranging from 46%-77%.^19,25-28  One study found CXR missed one third of pneumonias, and CT excluded pneumonia in 30% of cases where pneumonia was diagnosed based on CXR.^20,25-28 CXR cannot be relied on for diagnosis, and many other conditions may demonstrate radiograph findings that mimic pneumonia. Immunosuppression, dehydration, and elderly patients more commonly do not demonstrate radiographic findings due to lack of neutrophil migration. ^27-30 These patients may present later with radiographic findings on repeat imaging.  Other patients with influenza, pertussis, asthma, and COPD present similarly to pneumonia with negative radiograph.¹¹  Strep pneumoniae classically presents as lobar infiltrate, Staph aureus as abscess or extensive infiltration, and Klebsiella as lobar pneumoina with bulging minor fissure. These are just several examples of “classic” findings, but these should not be relied on.

 Other findings on CXR include pleural effusions, basilar infiltrates, interstitial infiltrates, or abscesses. Pneumonia can present with varying patterns on CXR, and many patients may not demonstrate the classic radiologic findings, particularly elderly and immunocompromised patients.^11,15

When is chest radiograph not warranted?

We know that history and physical exam are not always reliable. Some form of imaging, usually CXR, is often used to evaluate for pneumonia.^16,23 Patients with abnormal vital signs or signs of sepsis (including tachycardia, respiratory rate > 20 breaths/minute, or fever), age greater than 64 years, and exam findings (focal consolidation, egophony, rales, rhonchi, or wheezes unilaterally) warrant radiograph.^{16,23,36,39-41} Patients younger than 64 years with the absence of abnormal vital signs or physical examination findings may not need CXR, as probability of pneumonia is less than 5%.^16,36,41-44  Despite this, many institutional and provider preferences vary.

You obtain a CXR for both patients, as the younger male meets SIRS criteria with positive findings on exam, and the older patient has an abnormal exam. The CXR in the male is positive for right lower lobe pneumonia, and labs show WBC 12, BUN 22 mg/dL, and normal electrolytes otherwise. His lactate is 1.2. The female has nonspecific findings with negative CXR. Her lactate is 2.8, WBC is 15.2, influenza rapid screen is negative, and BUN 32 mg/dL. You are still suspicious of pneumonia based on her history and exam. What else can help you?

4. How about ultrasound?

US is quick and reliable for the diagnosis of pneumonia.  US demonstrates a sensitivity of 95%, compared to 60% for CXR.^33-35 US findings suggestive of pneumonia include air bronchograms, b-lines, consolidations, pleural line abnormalities, and pleural effusions. Pathognomonic findings include dynamic air bronchograms.^33-35 Positive likelihood ratios (LR) for these findings are 15.6 to 16.8, with negative likelihood ratios of 0.03 to 0.07.^33-35

Please see this video for more: https://www.youtube.com/watch?v=21yJm6IDuRA

You ultrasound the female patient, and on the left side you detect the following imaging:

 You start antibiotics and fluids, as your suspicion on pneumonia has increased. What can you use to further characterize these findings?

5. How about CT?

Chest CT has a sensitivity that approaches 100%.^19,30 In patients with suspected pneumonia, 27% have identifiable infiltrate on CT and nothing on CXR.³⁰ Another study suggests CT reveals pulmonary infiltrates in 33% of patients with no finding on CXR, while excluding CAP in close to 30% of patients with infiltrates on CXR.^19,28,30 CT is more precise and accurate for pneumonia.^19,28,30  Like every test in the ED, the risks and benefits must be weighed, as CT has significant cost and increased radiation compared to CXR, and it can potentially increase the ED length of stay. It should not be used as the standard diagnostic tool.  However, in septic patients with no identifiable source and negative chest radiograph but upper respiratory symptoms suggestive of pneumonia, it should be considered.

CT chest noncontrast demonstrates infiltrate on the left. You continue your management.

 6. Ok, I’ve diagnosed pneumonia, and it seems to be community acquired. Who can go home? Are there scales or systems that can assist in making this decision?

There are a number of aspects that impact mortality from pneumonia. These are shown below.^{5,6,15,16,20,25}

Scores or scales can assist in patient disposition by stratifying illness severity, including CURB-65 and PSI/PORT.^{5-7,25,31,32,45-48}  CURB-65 was derived and validated in 2003. Based on this score, patients with 0 or 1 point can be discharged with antibiotic therapy. Patients with 2 points can be admitted or observed, while those with greater than 3 points should be admitted. Patients with score 4 or 5 should be admitted to the ICU.^7,25,47,48 The CRB-65 scale may help when labs are difficult or not feasible, and CURB does not incorporate age.^51,52 The table below shows the score, available on MDcalc: https://www.mdcalc.com/curb-65-score-pneumonia-severity

The PSI/PORT score consists of a five-tier risk stratification system.^7,25,31,32 It has been validated several times: one study of 38,000 admitted patients, and another study of 2,287 patients in an inpatient and outpatient setting.^31,32,49-51 The score is based on age, comorbidities, physical exam, and labs, with completion requiring several steps.^{25,31,32,49,50,51} The first step entails evaluating patient age. Patients over 50 years are assigned to classes II – V.^{25,31,32,49-51} A diagram of the PSI/PORT score is shown below. This score can increase the number of patients treated as outpatient, with reduction in mortality and admission rates (by 15%).^25,49-56 See MDCalc: https://www.mdcalc.com/psi-port-score-pneumonia-severity-index-cap. The SOAR score is another option, but we will not discuss this score here.^25,46,57

How do the scores compare?

Several studies have looked at score characteristics. PSI/PORT may have better sensitivity, with CURB-65 demonstrating greater specificity and PPV. Remember, PSI/PORT requires calculation with history, exam, labs, and CXR, while CURB-65 does not have hypoxemia or CXR findings. ROC curves are 0.81 for PSI, 0.73 for CURB, and 0.76 for CURB-65 in one study,^50,51 with 0.736 for PSI and 0.694 for CURB-65 in another.⁵⁸

PSI/PORT can identify more patients as low risk. Keep in mind the scores may be better when used together to predict mortality, though this has not been evaluated. These scores do not assess social status. Homelessness, poor follow up, substance abuse, and PO intolerance are not accounted for in these scores, and they can underestimate severity in younger patients. Clinical gestalt is necessary in association with scores. ^50,51,58-61

 The 24-year-old has a CURB-65 of 0 and PSI/PORT of 24 points (Class 1). The female has a CURB-65 of 2 and PSI/PORT 93 points (Class IV).

Bonus: What about biomarkers other than lactate?

A lot of research has focused on biomarkers. These include WBC, Procalcitonin (PCT), and CRP. Elevated WBC cannot be relied upon, with over ¼ of patients with confirmed pneumonia demonstrating normal WBC. ^21,62-64  The +LR of 1.9-3.7 and poor specificity are also unreliable.^{16,20,25,51,60}

PCT is released in response to bacterial infections, ^65-68 with a meta-analysis finding a pooled sensitivity and specificity of 77% and 79%, respectively.⁶⁶  Sensitivity for bacterial infection in another meta-analysis is 88%, with a specificity of 81%.⁶⁷ Most studies to date have evaluated the use of PCT to determine when to discontinue antibiotics. However, studies including a Cochrane meta-analysis suggest PCT does not affect mortality, relapse rate, or length of stay.^69-71

CRP comes from the liver in response to inflammation and possesses a sensitivity of 70% and specificity of 90% if a threshold of 40 mg/L is used for pneumonia diagnosis, though specificity is 65% in another study.^72,73 

WBC, PCT, and CRP should not be used for routine evaluation of pneumonia, and further study is needed.

The 24-year-old male is looking better, now with normal VS. He wants to leave, and you discharge him with antibiotics. The female also feels improved following your resuscitation, but with her risk stratification score and your clinical gestalt, you discuss her case with the hospitalist, who agrees with you that she should be admitted.

 Summary

– Pneumonia possesses a wide range of presentations.

– One study shows a prevalence of 2.6% for pneumonia in patients with URI symptoms, while other studies suggest this is closer to 7%.

– No combination of history, exam, and testing can improve the diagnostic probability of pneumonia to over 50%.

– Patients younger than 65 years with normal vital signs and normal lung exam may not require a CXR. Patients with URI symptoms, vital sign abnormalities, and abnormal lung findings should have imaging.

– For imaging, US can be beneficial. Patients with high likelihood of pneumonia and negative CXR, such as those with immunosuppression, dehydration, and older age, may need additional imaging such as CT chest.

– Clinical scores can assist in risk stratification and disposition, but they should only be used in association with clinical judgment and gestalt.

– Patient social situation, substance abuse history, and PO tolerance should be taken into consideration.

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