What causes tachypnea (rapid breathing) in pneumonia?

From the Guidelines

Tachypnea in pneumonia is primarily caused by hypoxemia and the body's compensatory mechanisms to maintain adequate oxygenation, as evidenced by the fact that tachypnea is a sensitive indicator of deteriorating respiratory function 1. When pneumonia occurs, the infection causes inflammation and fluid accumulation in the air sacs of the lungs, which impairs gas exchange. This leads to decreased oxygen levels in the blood (hypoxemia), triggering chemoreceptors in the carotid bodies and brain to increase the respiratory rate. Some key factors that contribute to tachypnea in pneumonia include:

• Hypoxemia: decreased oxygen levels in the blood trigger chemoreceptors to increase the respiratory rate 1
• Inflammatory mediators: released during infection, these can directly stimulate the respiratory center in the brain
• Fever: increases metabolic demands and oxygen consumption, further contributing to tachypnea
• Pain from pleural inflammation: may cause shallow breathing, requiring an increased respiratory rate to maintain adequate ventilation
• Metabolic acidosis: from tissue hypoxia, can drive tachypnea as the body attempts to eliminate excess acid through respiratory compensation It is essential to monitor patients with pneumonia using physiological monitoring systems, such as the National Early Warning Score (NEWS), to track and trigger systems that can help identify deteriorating respiratory function early on 1. In patients with severe community-acquired pneumonia, certain risk factors can increase the likelihood of developing tachypnea, including:
• Co-morbidities, such as chronic obstructive pulmonary disease (COPD), renal insufficiency, chronic heart failure, and diabetes mellitus 1
• Age: patients older than 60 years are at increased risk
• Male sex: has been implicated as a risk factor for increased mortality in severe CAP patients 1
• Presence of multilobar consolidation and need for mechanical ventilation or inotropic support: associated with greater disease severity and higher mortality rates 1

From the Research

Causes of Tachypnea in Pneumonia

• Tachypnea, or rapid breathing, is a common symptom of pneumonia, and can be caused by several factors, including:
  • Inflammatory exudate filling alveoli, causing a volume loss at functional residual capacity (FRC) and reducing total lung compliance 2
  • Reduction in surfactant activity, further increasing the work of breathing 2
  • Arterial hypoxemia, which can be caused by persistence of pulmonary artery blood flow to consolidated lung, intrapulmonary oxygen consumption by the lung, and ventilation-perfusion mismatch 2
  • Relative failure of the hypoxic pulmonary vasoconstriction (HPV) mechanism during acute pneumonia, which can be caused by endogenous vasodilator prostaglandins and other mechanisms 2

Clinical Signs of Hypoxia in Pneumonia

• Tachypnea is a significant predictor of hypoxia in children with severe pneumonia, with a sensitivity of 70.2% and specificity of 88.9% 3
• Other clinical signs, such as head nodding, irritability, inability to drink/breastfeed, vomiting, and altered sensorium, are also associated with hypoxia in pneumonia 3
• The combination of age-specific tachypnea, head nodding, and inability to drink/breastfeed has an acceptable sensitivity and specificity for predicting hypoxia in children with severe pneumonia, although no single clinical sign can perform as well as pulse oximetry 3

Treatment of Pneumonia

• Ceftriaxone and azithromycin are commonly used to treat community-acquired pneumonia, and have been shown to be effective in several studies 4, 5, 6
• However, the optimal dosage of ceftriaxone is not well established, and some studies suggest that higher doses may be necessary to treat certain types of pneumonia, such as methicillin-susceptible Staphylococcus aureus (MSSA) 6