This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fluid & Electrolyte, Subject name: Surgery
Generally accepted indications for mechanical ventilatory support include 
Select and explain. 
A. PaO2 of less than 70 kPa and PaCO2 of greater than 50 kPa while breathing room air, B. Alveolar-arterial oxygen tension difference of 150 kPa while breathing 100% O2, C. Vital capacity of 40-60 mL/kg, D. Respiratory rate greater than 35 breaths/min
D: Respiratory rate greater than 35 breaths/min
Answer: D: Respiratory rate greater than 35 breaths/min 
Explanation: Anticipation and early aggressive treatment of pulmonary insufficiency by mechanical ventilatory support are critical in managing the seriously ill patient. Readily measured changes that can be used to determine either the need for intubation or the appropriate time for weaning from mechanical respiratory support include arterial blood gas levels, dead space-tidal volume ratio (VD /VT ), alveolar-arterial oxygen tension difference , vital capacity, and respiratory rate. Indications for mechanical ventilation include a respiratory rate over 35 breaths/min, vital capacity less than 15 mL/kg, greater than 350 kPa after 15 min on 100% oxygen, VD /VT greater than 0.6, PaO2 less than 60 kPa, and PaCO2 greater than 60 kPa.