Answer to Question 1
ANS: D
With assist-control mode, every breath is supported by the ventilator. Breaths are patient- or time-triggered to inspiration and may be volume or pressure limited. Inspiration may be volume, pressure, or time cycled to the expiratory phase. Assist-control ventilation typically is delivered as volume-controlled (VC) continuous mandatory ventilation. Suggested initial settings for as-sist-control volume ventilation in the care of adults are listed in Box 48-4. Advantages of as-sist-control volume ventilation include the assurance that a minimum, safe level of ventilation is achieved. Every breath is a volume breath, yet the patient can set his or her own breathing rate. In the event of sedation or apnea, a minimum, safe level of ventilation is guaranteed by the selection of an appropriate backup rate, usually approximately 2 to 4 breaths/min below the patient's assist rate, but not less than the rate necessary to provide a minimum safe level of ventilation (e.g., a backup rate of at least 8 to 10 breaths/min, depending on tidal volume set). Because assist-control ventilation usually provides full ventilatory support, it may result in a lower work of breathing than partial support modes.
Answer to Question 2
ANS: A
Ventilation strategies for lung protection in ARDS include a low VT, rapid respiratory rates, and permissive hypercapnia if necessary to avoid overdistention or Pplat greater than 28 cm H2O.
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Relatively simple changes in Hox genes control limb formation in tetrapods.
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Negative Feedback and Temperature Control