A 45-year-old, 73-inch-tall, 200 lb male patient is admitted to ...

[renzo156]

A 45-year-old, 73-inch-tall, 200 lb male patient is admitted to the emergency department with an exacerbation of myasthenia gravis.
 
  The respiratory therapist assesses the patient and finds the patient's maximum inspiratory pres-sure is 15 cm H2O and his vital capacity is 1200 mL. It is decided that the patient requires venti-latory support. The most appropriate ventilator settings for this patient are which of the follow-ing?
  a. Pressure support ventilation (PSV) 5 cm H2O, continuous positive airway pressure (CPAP) 10 cm H2O, FIO2 0.50
  b. Pressure-controlled continuous mandatory ventilation (PC-CMV), f = 16 breaths/min, peak inspiratory pressure (PIP) = 35 cm H2O, positive end-expiratory pressure (PEEP) 3 cm H2O, fractional inspired ox-ygen (FIO2) 0.45
  c. Noninvasive positive pressure ventila-tionbilevel positive airway pressure (NPPVBiPAP), f = 14 breaths/min, in-spiratory positive airway pressure (IPAP) = 28 cm H2O, expiratory positive airway pressure (EPAP) = 5 cm H2O, FIO2 0.30
  d. Volume-controlled intermittent mandatory ventilation (VC-IMV), f = 12 breaths/min, tidal volume (VT) = 725 mL, PSV 5 cm H2O, PEEP 5 cm H2O, FIO2 0.24

Question 2

Patients with acute severe asthma requiring mechanical ventilation are difficult to manage be-cause of which of the following?
 
  a. Diaphragmatic paralysis
  b. Increased lung compliance
  c. Decreased airway resistance
  d. Uneven alveolar hyperexpansion

[akpaschal]

Answer to Question 1

ANS: D
The patient is 73 inches and weighs 200 lb. Thus, ideal body weight (IBW) = 106 + 6(13) = 194 lbs, or 88 kg. The patient's body surface area (BSA) is 2.16 m2. The estimated minute ventilation is 4  2.16 = 8.64 L. Using 7-10 mL/kg the set tidal volume should be between 617 and 880 mL. The positive end-expiratory pressure (PEEP) should be 5 cm H2O and the fractional inspired ox-ygen (FIO2) should be 21 or close to it unless there is hypoxemia. A frequency of 12 with a tid-al volume (VT) of 725 gives a minute volume of 8.7 L. This will give the patient full ventilatory support. Pressure support ventilation (PSV) is not appropriate because the patient appears too weak to breathe spontaneously. Noninvasive positive pressure ventilation (NPPV) is not appro-priate because of the increased risk of aspiration.

Answer to Question 2

ANS: D
Increased airway resistance from bronchospasm, increased secretions, and mucosal edema cause air trapping, which can cause uneven hyperexpansion of various lung units. This can cause rupture or compress other areas of the lungs leading to pneumothorax, pneumomediastinum, subcutane-ous emphysema, and other forms of barotrauma.