From the Guidelines
In patients with pulmonary embolism (PE), ventilation refers to the movement of air into and out of the lungs, while perfusion is the blood flow through the pulmonary capillaries that allows for gas exchange, with a mismatch between ventilation and perfusion leading to hypoxaemia, as indicated in the 2020 ESC guidelines 1. In physical examination (PE) of the respiratory system, key parameters include:
- Ventilation: the movement of air into and out of the lungs
- Perfusion: the blood flow through the pulmonary capillaries that allows for gas exchange
- Airway resistance: the opposition to airflow in the respiratory tract, with increased resistance occurring in conditions like asthma or COPD
- Compliance: the lungs' elasticity or ability to expand, with decreased compliance seen in pulmonary fibrosis or ARDS
- Minute ventilation: the total volume of air breathed per minute, calculated by multiplying tidal volume by respiratory rate On arterial blood gas (ABG) analysis:
- pCO2 measures carbon dioxide partial pressure (normal 35-45 mmHg), reflecting ventilation adequacy
- pO2 measures oxygen partial pressure (normal 80-100 mmHg), indicating oxygenation status These parameters help assess respiratory function, with abnormal values suggesting specific pathologies, such as elevated pCO2 indicating hypoventilation, decreased pO2 suggesting impaired oxygenation, reduced compliance pointing to restrictive lung disease, and increased airway resistance indicating obstructive disorders, as discussed in the 2008 ESC guidelines 1. The management of PE should prioritize correction of hypoxaemia, with supplemental oxygen indicated in patients with SaO2 <90%, and mechanical ventilation used with caution to avoid adverse haemodynamic effects, as recommended in the 2020 ESC guidelines 1.
From the Research
Definitions and Effects of Pulmonary Embolism on Respiratory Parameters
- Ventilation: The process of exchanging air between the lungs and the environment. In the context of pulmonary embolism (PE), ventilation can be affected due to increased pulmonary vascular resistance and disturbances in matching ventilation and blood flow 2.
- Perfusion: The process of supplying blood to the lungs. PE can lead to decreased perfusion due to occlusion of blood flow in the pulmonary arteries 3.
- Airway Resistance: The resistance to airflow in the airways. PE can cause abnormalities in airway resistance, although the exact mechanisms are not fully understood 2.
- Compliance: The ability of the lungs to expand and fill with air. PE can lead to decreased compliance due to increased pulmonary vascular resistance and other pathophysiologic derangements 2.
- Minute Ventilation: The total amount of air breathed in or out of the lungs per minute. In response to PE, there can be an increase in minute ventilation as the body attempts to compensate for decreased oxygenation and increased carbon dioxide levels 4.
- pCO2 and pO2 on ABG (Arterial Blood Gas):
- pCO2: The partial pressure of carbon dioxide in arterial blood, which can be elevated in PE due to decreased ventilation and increased dead space.
- pO2: The partial pressure of oxygen in arterial blood, which can be decreased in PE due to decreased perfusion and ventilation-perfusion mismatching 2.
Effects of Pulmonary Embolism on Gas Exchange and Blood Pressure
- PE can lead to increased pulmonary blood pressure, which may contribute to pulmonary hypertension and right ventricular dysfunction or failure 4.
- The increase in ventilation and cardiac output in response to PE can improve overall gas exchange, but may also exacerbate cardiorespiratory instability 4, 5.
- Thrombolytic therapy can reverse the hemodynamic derangements of acute PE more rapidly than anticoagulant therapy, and may also improve pulmonary gas exchange and reduce pulmonary vascular resistance 2.