dead space
Summary
Dead space refers to the portion of the respiratory system where gas exchange does not occur. It includes anatomical dead space (conducting airways) and physiological dead space (alveoli that are ventilated but not perfused). Normal dead space is approximately 150 mL or 2.2 mL/kg body weight.
Detail
Dead space represents areas of the respiratory system that contribute to ventilation but not gas exchange. Anatomical dead space consists of the conducting airways from the nose/mouth to the terminal bronchioles, totaling ~150 mL in healthy adults. Physiological dead space includes anatomical dead space plus alveolar dead space (ventilated alveoli that receive little to no blood flow). The dead space-to-tidal volume ratio (Vd/Vt) is normally 0.2-0.35 (20-35%). Pathological increases in dead space occur in conditions like pulmonary embolism, emphysema, or mechanical ventilation with excessive PEEP. Clinical significance includes decreased ventilation efficiency, requiring increased minute ventilation to maintain adequate alveolar ventilation. Dead space can be measured using the Bohr equation or estimated through capnography. Understanding dead space is crucial for ventilator management and interpreting arterial blood gases.
Sources
- West's Respiratory Physiology
- First Aid for the USMLE Step 1
- Ganong's Review of Medical Physiology
- Miller's Anesthesia
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