Definition of Tidal Volume
Tidal volume is the volume of air moved into or out of the lungs during a single normal breath at rest, typically measured in milliliters (mL) or liters (L).
Physiological Parameters
Normal adult tidal volume ranges from approximately 500-600 mL per breath, which corresponds to about 6-8 mL/kg of predicted body weight 1
The volume is conventionally expressed in units measured at body temperature and pressure, saturated with water vapor (BTPS) 1
Tidal volume is a fundamental component of minute ventilation, which is calculated by multiplying tidal volume by respiratory rate 2
Clinical Context and Measurement
In healthy anesthetized adults with normal perfusion, tidal volumes of 8-10 mL/kg maintain normal oxygenation and CO₂ elimination 1
During cardiac arrest and CPR, lower tidal volumes of approximately 500-600 mL (6-7 mL/kg predicted body weight) are sufficient because cardiac output is reduced to 25-33% of normal, decreasing oxygen uptake and CO₂ delivery to the lungs 1
The ratio of physiologic dead space to tidal volume (VD/VT) represents the proportion of each breath that does not participate in gas exchange and serves as an index of ventilation-perfusion mismatching 1
Important Clinical Considerations
Tidal volume should be calculated using predicted body weight (PBW) based on height, not actual body weight, as lung size correlates better with height than weight 2, 3
This distinction is particularly critical in obese patients, where using actual body weight can lead to dangerously excessive tidal volumes 2, 4
Visible chest rise serves as a practical clinical indicator of adequate tidal volume delivery during rescue breathing 1, 2
Excessive tidal volumes can cause harmful increases in intrathoracic pressure, decreased venous return, diminished cardiac output, and increased mortality 1