Tidal volume


Tidal volume is the lung volume representing the normal volume of air displaced between normal inhalation and exhalation when extra effort is not applied. In a healthy, young human adult, tidal volume is approximately 500 mL per inspiration or 7 mL/kg of body mass.

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 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 ALI/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:

For patient without preexisting lung disease

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

For 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 peep

Acute respiratory distress syndrome

Protective Lung Ventilation Strategies apply. VT 6 to 8 ml/kg or as low as 5ml/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 same peep levels. Patient should be started on 6 ml/kg and peep increased till plateau pressure is 30 cmH20 in most severe cases.