A 55-year-old man on ICU with ARDS is receiving lung-protective ventilation. His compliance is 15 mL/cmH2O and the team calculates the functional lung...

Question

A 55-year-old man on ICU with ARDS is receiving lung-protective ventilation. His compliance is 15 mL/cmH2O and the team calculates the functional lung size (baby lung) is approximately 400 mL. If the set tidal volume is 360 mL (6 mL/kg IBW for a 60 kg patient), what is the 'specific tidal volume' (TV normalised to functional lung size) and why does this matter?

Accepted Answer

Specific TV = 360/400 = 0.9 mL/mL - this means each breath inflates the baby lung by 90% of its resting volume, representing enormous strain despite the TV appearing 'protective' at 6 mL/kg IBW; this is why some patients benefit from TV

Answer

Specific TV is irrelevant

Answer

Specific TV = 6 mL/kg - this is always safe

Answer

The calculation is impossible

Answer

Specific TV only matters in paediatrics

uk-fficm MCQ (SBA): ARDS - Specific TV and Strain