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Tidal volume (symbol VT or TV) is the lung volume representing the normal volume of air displaced between[clarification needed] 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.
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 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:
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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.
- Beardsell, I et al: MCEM Part A:MCQs, page 33, Royal Society of Medicine Press, 2009
- Gajic, Ognjen; Saqib Dara; Jose Mendez; Abedola Adensanya; Emir Festic; Sean Caples; Rimki Rana; Jennifer StSauver; James Lymp; Bekele Afessa (2004). "Ventilator-associated lung injury in patients without acute lung injury at the onset of mechanical ventilation". Critical Care Medicine. 32 (9): 1817–1824. doi:10.1097/01.CCM.0000133019.52531.30. PMID 15343007. S2CID 6386675.
- Guay, Joanne; Ochroch, Edward A; Kopp, Sandra (2018-07-09). "Intraoperative use of low volume ventilation to decrease postoperative mortality, mechanical ventilation, lengths of stay and lung injury in adults without acute lung injury". Cochrane Database of Systematic Reviews. 7: CD011151. doi:10.1002/14651858.cd011151.pub3. ISSN 1465-1858. PMC 6513630. PMID 29985541.