How are tidal volumes and rates determined in mechanical ventilation?

Updated: Apr 11, 2019
  • Author: Christopher D Jackson, MD; Chief Editor: Zab Mosenifar, MD, FACP, FCCP  more...
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Answer

Answer

For a patient without preexisting lung disease, the tidal volume and rate are traditionally selected by using the 12-12 rule. A tidal volume of 12 mL for each kilogram of lean body weight is programmed to be delivered 12 times a minute in the assist-control mode.

For patients with chronic obstructive pulmonary disease (COPD), the tidal volume and rate are slightly reduced to the 10-10 rule to prevent overinflation, hyperventilation, and auto–positive end-expiratory pressure (PEEP). A tidal volume of 10 mL/kg lean body weight is delivered 10 times a minute in the assist-control mode.

In acute respiratory distress syndrome (ARDS), the lungs may function best and volutrauma (see Complications of Mechanical Ventilation) is minimized with low tidal volumes of 6-8 mL/kg. Tidal volumes are preset at 6-8 mL/kg of lean body weight in the assist-control mode. This ventilatory strategy is called lung-protective ventilation. These lowered volumes may lead to slight hypercarbia. An elevated PCO2 is typically recognized and accepted without correction, leading to the term permissive hypercapnia. However, the degree of respiratory acidosis allowable is a pH not less than 7.25. The respiratory rate of the ventilator may need to be adjusted upward to increase the minute ventilation lost by using smaller tidal volumes.


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