Tidal volume

Tidal volume (symbol V_T or TV) is the volume of air inspired and expired with each passive breath. It is typically assumed that the volume of air inhaled is equal to the volume of air exhaled such as in the figure on the right. In a healthy, young human adult, tidal volume is approximately 500 ml per inspiration at rest or 7 ml/kg of body mass.

TLC	Total lung capacity: the volume in the lungs at maximal inflation, the sum of VC and RV.
TV	Tidal volume: that volume of air moved into or out of the lungs in 1 breath (TV indicates a subdivision of the lung; when tidal volume is precisely measured, as in gas exchange calculation, the symbol TV or VT is used.)
RV	Residual volume: the volume of air remaining in the lungs after a maximal exhalation
ERV	Expiratory reserve volume: the maximal volume of air that can be exhaled from the end-expiratory position
IRV	Inspiratory reserve volume: the maximal volume that can be inhaled from the end-inspiratory level
IC	Inspiratory capacity: the sum of IRV and TV
IVC	Inspiratory vital capacity: the maximum volume of air inhaled from the point of maximum expiration
VC	Vital capacity: the volume of air breathed out after the deepest inhalation.
VT	Tidal volume: that volume of air moved into or out of the lungs during quiet breathing (VT indicates a subdivision of the lung; when tidal volume is precisely measured, as in gas exchange calculation, the symbol TV or VT is used.)
FRC	Functional residual capacity: the volume in the lungs at the end-expiratory position
RV/TLC%	Residual volume expressed as percent of TLC
VA	Alveolar gas volume
VL	Actual volume of the lung including the volume of the conducting airway.
FVC	Forced vital capacity: the determination of the vital capacity from a maximally forced expiratory effort
FEVt	Forced expiratory volume (time): a generic term indicating the volume of air exhaled under forced conditions in the first t seconds
FEV1	Volume that has been exhaled at the end of the first second of forced expiration
FEFx	Forced expiratory flow related to some portion of the FVC curve; modifiers refer to amount of FVC already exhaled
FEFmax	The maximum instantaneous flow achieved during a FVC maneuver
FIF	Forced inspiratory flow: (Specific measurement of the forced inspiratory curve is denoted by nomenclature analogous to that for the forced expiratory curve. For example, maximum inspiratory flow is denoted FIFmax. Unless otherwise specified, volume qualifiers indicate the volume inspired from RV at the point of measurement.)
PEF	Peak expiratory flow: The highest forced expiratory flow measured with a peak flow meter
MVV	Maximal voluntary ventilation: volume of air expired in a specified period during repetitive maximal effort

Mechanical ventilation

Tidal volume plays a significant role during mechanical ventilation to ensure adequate ventilation without causing trauma to the lungs. Tidal volume is measured in milliliters and ventilation volumes are estimated based on a patient's ideal body mass. Measurement of tidal volume can be affected (usually overestimated) by leaks in the breathing circuit or the introduction of additional gas, for example during the introduction of nebulized drugs.

Ventilator-induced lung injury such as Acute lung injury (ALI) /Acute Respiratory Distress Syndrome (ARDS) can be caused by ventilation with very large tidal volumes in normal lungs, as well as ventilation with moderate or small volumes in previously injured lungs, and research shows that the incidence of ALI increases with higher tidal volume settings in nonneurologically impaired patients. . Similarly A 2018 systematic review by The Cochrane Collaboration provided evidence that low tidal volume ventilation reduced post operative pneumonia and reduced the requirement for both invasive and non invasive ventilation after surgery

Initial settings of mechanical ventilation:

Patients without pre-existing lung disease

Protective lung ventilation strategies should be applied with V_T 6ml/kg to 8ml/kg with RR = 12 to 20 and an average starting target minute ventilation of 7 L/min.

Patients with chronic obstructive lung disease

Protective lung volumes apply 6ml/kg to 8ml/kg with a rate high enough for proper alveolar ventilation but does not create or aggravate intrinsic Positive End-Expiry Pressure (PEEP).

Acute respiratory distress syndrome

Protective lung ventilation strategies apply. V_T 6 to 8 ml/kg or as low as 5 ml/kg in severe cases. Permissive hypercapnia can be employed in an attempt to minimize aggressive ventilation leading to lung injury. Higher PEEPs are often required however not all ARDS patients require the same PEEP levels. Patient should be started on 6 ml/kg and PEEP increased until plateau pressure is 30 cm H₂0 in most severe cases.

External links

• Ricard JD (May 2003). "Are we really reducing tidal volume—and should we?". American Journal of Respiratory and Critical Care Medicine. 167 (10): 1297–8. doi:10.1164/rccm.2303003. PMID 12738592.