Chapter 22. Critical Care
What is the most sensitive predictor for successful extubation?
D. Minute ventilation <10 L/min
Answer: C. The rapid shallow breathing index (RSBI) is the ratio of the respiratory frequency (f) and the tidal volume (VT). An RSBI <105 has been shown to be the most sensitive criteria for weaning the patient to extubation.
A 68-year-old female is postoperative day 3 status post-pancreaticoduodenectomy. Her post-extubation arterial blood gas shows pH 7.58, pCO2 30, HCO3 26, O2Sat 94%, and BE 2.2. Based solely on this ABG, what is her underlying acid-base disturbance?
B. Compensated metabolic alkalosis
Answer: D. First, look at the pH; in this case it is alkalotic. You must now distinguish if this is respiratory, mixed, or metabolic. So pay attention to the pCO2 and the HCO3 and note that the HCO3 is normal but the pCO2 is low. The characteristic of respiratory alkalosis is an increase in pH with a decrease in pCO2. In the acute setting, note that HCO3 typically decreases by 2 mEq/L for every 10 mm Hg drop in pCO2. In chronic respiratory alkalosis, HCO3 typically increases by 4 mEq/L of HCO3 for every 10 mm Hg drop in pCO2.
Which is not indicative of ARDS?
C. Wedge pressure <18 mm Hg
Answer: D. The distinction between ALI and ARDS is the degree of hypoxemia defined by the P/F ratio. In ALI the ratio is less than 300 mm Hg, and for ARDS it is 200 mm Hg or less.
Which of the following ventilation modes is more likely to cause increased auto-PEEP?
A. Pressure support ventilation
B. Airway pressure release ventilation
C. Assist-control ventilation