ACP MKSAP

The most appropriate tidal volume is 300 mL (Option B), which is 6 mL/kg of the patient's calculated predicted body weight (PBW). PBW (in kg) is calculated in men as follows:

50 + 2.3 kg × (height − 60 inches)

It is calculated in women as follows:

45.5 + 2.3 kg × (height − 60 inches)

Acute respiratory distress syndrome (ARDS) is characterized by diffuse alveolar damage with fluid and protein extravasation into interstitial and alveolar spaces, microatelectasis, increased ventilation/perfusion (V/Q) mismatch, decreased lung compliance, and increases in both shunt and dead-space ventilation. Because areas of noncompliant, diseased lung are often adjacent to more compliant lung, high tidal volumes can lead to overdistention and ventilator-associated lung injury (volutrauma) in the more compliant lung tissue. Therefore, patients with ARDS should receive low tidal volume ventilation (LTVV) with a tidal volume of 4 to 8 mL/kg of PBW, and strategies should minimize plateau pressure (<30 cm H₂O). Survival is improved when patients with ARDS are ventilated with a tidal volume of 6 mL/kg of PBW. In patients who have overweight or edema, using actual body weight will typically result in inappropriately large tidal volumes. In this woman with a PBW of 50 kg (110.2 lb), a tidal volume of 6 mL/kg of PBW calculates to an optimal tidal volume of 300 mL.