Pneumonia/Empyema

Epidemiology

  • Inflammatory process of the lungs as a result of bacterial infection. May involve interstitial tissue and pleura but ultimately results in alveolar consolidation
  • Frequency of bacteria as cause of lower infection ranges from 10-50%
  • Risk factors include: numerous siblings, cigarette smoke exposure, preterm delivery, and lower socioeconomic status

Pathophysiology

  • Bacterial invasion via aspiration or hematogenous spread
  • Bacterial infection overwhelms host immune response 
  • Host response may be impaired due to presence of viral infections, foreign body, or ETT/tracheostomy
  • Inflammatory response leads to increased capillary permeability with subsequent alveolar edema and leukocyte accumulation
  • This leads to decreased compliance with intrapulmonary shunt leading to hypoxemia
  • Bacteria can reach the blood via the pulmonary lymphatic tissue leading to sepsis
  • Tachypnea is the most sensitive index of disease severity
Figure 1: Pathophysiology of Pneumonia

Diagnosis

  • Fever, leukocytosis with left shift, respiratory symptoms suggest the diagnosis
  • Lobar consolidation, multilobar consolidation, abscess, pneumatocele all suggestive of bacterial pneumonia
  • May be associated with bacteremia
  • Sputum samples difficult to obtain from most children due to inability to expectorate a sample
  • Tracheal aspirates can be helpful with numerous PMN's and organisms on gram stain being suggestive while numerous epithelial cells or few PMN's suggest a poorly obtained specimen (contaminated with oral flora) or colonization, respectively
  • Pleural fluid may be helpful in identifying an organism (via gram stain and culture)
  • BAL can be considered in severely ill children or those not responding to typical treatment to identify other potential agents (ie fungal infection, PJP, etc.)
  • Typical pathogens vary by age:
    • Group B Strep: Newborn infants
    • Strep Pneumo: Typically children <2 yrs of age (3-5 mo old infants) but can affect all ages
    • H Flu: All ages, often associated with empyema (40%) and bacteremia
    • Staphylococcus (MSSA and MRSA): Often preceded by viral infections such as influenza, often associated with pleural effusion/empyema (up to 80%)
    • Mycoplasma: Most common in school-age children although can occur in young children/infants as well. Can be diagnosed via PCR. Requires atypical antibiotic coverage (ie azithromycin)
    • Pseudomonas: Often seen in those with underlying pulmonary disease or chronic illness. Also seen with artificial airways (ETT/tracheostomy) and along with staphylococcus, is one of the leading causes of ventilator associated pneumonia.

Treatment

  • Antibiotic therapy targeted toward likely organisms, beginning with generally broad coverage
    • In the PICU we typically initiate vancomycin and pipercillin-tazobactam to empirically cover MRSA, resistant strep, as well as gram negative organisms including pseudomonas
    • More typical community acquired inpatient regimens include: Ceftriaxone for broad gram positive and gram negative coverage (lacking MRSA, pseudomonas coverage) and azithromycin for atypical organism coverage
    • Outpatient treatment regimens may include azithromycin as monotherapy, amoxicillin-clavulanic acid, or amoxicillin.
    • If other organisms are suspected (ie PJP with significant hypoxemia and suspicion for immunocompromise), other agents are used (ie Trimethoprim-Sulfamethoxazole + steroids for PJP)
  • Respiratory support as indicated
    • Supplemental oxygen
    • HFNC
    • NIPPV (CPAP/BiPAP)
    • Mechanical ventilation
    • HFOV
    • ECMO

Complications

Empyema

  • Stages of pleural disease
    • 1:  Pre-collection stage - PNA associated with pleuritis
    • 2:  Exudative stage - simple parapneumonic effusion (PPE)
    • 3:  Fibrinopurulent stage - complicated PPE/empyema
      • Light's criteria
        • Effusion protein/serum protein ratio greater than 0.5
        • Effusion lactate dehydrogenase (LDH)/serum LDH ratio greater than 0.6
        • Effusion LDH level greater than two-thirds the upper limit of the laboratory's reference range of serum LDH
      • pH <7.2, LDH >1000, glucose <40, positive GS or culture + loculation/septations on imaging
        • Abx >48hrs before tap lowers culture yield but should not affect biochemistry of fluid
    • 4:  Organizational stage - thick pleural peel --> entrap lung --> restrictive lung disease
  • Optimal imaging modality for pleural disease
    • U/S should be initially used (CT provided no advantage over U/S)
    • CT should be reserved for complicated cases
      • Evaluate for parenchymal abscess
      • U/S is inadequate due to body habitus
  • Methods of intervention for PPE
    • Thoracentesis
    • Chest tube
    • Chest tube w/ chemical debridement
    • Video assisted thoracoscopic surgery (VATS)
  • When to intervene
    • Large effusions (affecting >50% of the thorax on CXR) with or without sxs
    • Moderate effusions (affecting 25-50% of the thorax on CXR) with persistent or worsening sxs
    • Any effusions associated w/ loculations
  • How to drain free flowing simple PPE
    • Consider single thoracentesis
    • First thoracentesis fails to adequately drain --> place chest tube
      • In young children requiring conscious sedation, may be beneficial to just place chest tube first instead of doing thoracentesis to avoid repeat procedures w/ sedation
      • <14F tubes should be used even for loculated effusions
  • How to manage empyema
    • Evidence for below guideline (References 6,7,8)
      • VATS
        • If VATS performed w/in 48hrs of empyema diagnosis --> reduces hospital stay by 4 days
        • If VATS performed >4 days after empyema diagnosis --> longer hospitalization and post-op complications
      • VATS vs. tPA (chemical debridement)
        • No difference in length of hospitalization
        • Failure rate of tPA was ~17% --> eventually got VATS
        • VATS more expensive than tPA
    • Guideline
      1. Diagnose empyema
      2. Give tPA  (0.1 mg/kg up to 4 mg in 40 ml NS with chest tube placement, clamp tube for 1 hour dwell time, q24h x3 days)
      3. If no clinical improvement --> U/S or CT
        • If persistent pleural disease --> VATS
        • If no pleural disease --> continue abx
          • Abx usually for 2-4 wks (minimum of 10 days after resolution of fever)

References

1) Islam S, Calkins CM, Goldin AB, Chen C, Downard CD, Huang EY, Cassidy L, SaitoJ, Blakely ML, Rangel SJ, Arca MJ, Abdullah F, St Peter SD; APSA Outcomes and Clinical Trials Committee, 2011-2012. The diagnosis and management of empyema in children: a comprehensive review from the APSA Outcomes and Clinical Trials Committee. J Pediatr Surg. 2012 Nov;47(11):2101-10.

2) Kurt BA, Winterhalter KM, Connors RH, et al. Therapy of parapneumonic effusions in children: video assisted thoracoscopic surgery versus conventional thoracostomy drainage. Pediatrics
2006;118:e547-53. 

3) Gates RL, Hogan M, Weinstein S, et al. Drainage, fibrinolytics, or surgery: a comparison of treatment options in pediatric empyema.
J Pediatr Surg 2004;39:1638-42.

4) Aziz A, Healey JM, Qureshi F, et al. Comparative analysis of chest tube thoracostomy and video-assisted thoracoscopic surgery in
empyema and parapneumonic effusion associated with pneumonia in children. Surg Infect (Larchmt) 2008;9:317-23.

5) Sonnappa S, Cohen G, Owens CM, et al. Comparison of urokinase and video-assisted thoracoscopic surgery for treatment of childhood
empyema. Am J Respir Crit Care Med 2006;174:221-7.

6) St Peter SD, Tsao K, Spilde TL, et al. Thoracoscopic decortication vs tube thoracostomy with fibrinolysis for empyema in children: a
prospective, randomized trial. J Pediatr Surg 2009;44:106-11.

7) Wells RG, Havens PL. Intrapleural fibrinolysis for parapneumonic effusion and empyema in children. Radiology. 2003 Aug;228(2):370-8.