Permissive hypoxemia

Q: The formula for 'Inspiratory Time' (IT) on the ventilator is the tidal volume divided by? (select one)

A) the inspiratory flow rate
B) the respiratory rate


Answer: A

Inspiratory time is the tidal volume divided by the inspiratory flow rate.

Clinical implication: Increasing IT increases the I; E ratio on the ventilator and induce the lung injury. Many times in the quest to achieve higher oxygenation,  clinicians increase the IT but the overall impact may be deleterious with an alveolar injury. Concept of "permissive hypoxemia" should be entertained in severe situations till hemodynamics are stable and organ functions are not jeopardized.

#ventilators


References:

1. He HW, Liu DW. Permissive hypoxemia/conservative oxygenation strategy: Dr. Jekyll or Mr. Hyde?. J Thorac Dis. 2016;8(5):748–750.

2. Casetti AV, Bartlett RH, Hirschl RB. Increasing inspiratory time exacerbates ventilator-induced lung injury during high-pressure/high-volume mechanical ventilation. Crit Care Med. 2002;30:2295–9.