Lecture on Dead Space

Introduction

Dead Space: Gas in the respiratory system that does not participate in gas exchange.

Anatomic Dead Space:
- Gas in the conducting system (mouth, nose to terminal bronchioles)
- No gas exchange occurs here as there are no capillaries
Alveolar Dead Space:
- Areas where alveoli are ventilated but not perfused
- Increased VQ ratio due to decreased perfusion (Q)
- Results in less oxygenated blood returning to the heart
- Decreased CO2 delivery and exhalation
Physiologic Dead Space:
- Sum of anatomic and alveolar dead spaces
- In healthy individuals, it equals anatomic dead space
- In diseased states, alveolar dead space increases, raising physiologic dead space
Mechanical Dead Space:
- Additional space due to ventilator tubing and devices

Oxygen (O2):
- Diffuses from alveoli into capillaries
- Fully saturates hemoglobin molecules passing through
- Reduced in cases of increased alveolar dead space
Carbon Dioxide (CO2):
- Diffuses from blood into alveoli to be exhaled
- End tidal CO2 measured near the mouth reflects alveolar CO2
- In disease, end tidal CO2 can be markedly lower due to poor perfusion

Pulmonary Embolism (PE): Blocks perfusion regionally
Shock: Decreases right ventricular output, reducing lung perfusion
Positive Pressure Ventilation: Increases intrathoracic pressure, affecting alveolar perfusion

Increased alveolar dead space leads to decreased blood flow and increased physiologic dead space
Decreased end tidal CO2 relative to venous (PV) and arterial (PaCO2) values

Dead space is crucial in understanding respiratory efficiency and gas exchange
Further details on mechanical dead space will be covered in a future ventilator course

Contact: For questions, reach out to Gavin Greenfield via STARS email.