A 56-year-old woman with a history of recently diagnosed acute myeloid leukemia is admitted to the ICU after undergoing induction chemotherapy. She is febrile with temperature of 39°C and has a respiratory rate of 36 breaths per minute with SaO2 84% on 10L per minute oxygen by face mask. Her labs are otherwise notable for an absolute neutrophil count of 125.
Which of the following is the most accurate statement regarding her management?
Correct Answer: C
Immunocompromised patients with ARDS are a unique population with both different epidemiology of infections and different data for management. Specifically, in patients with single-organ failure, the use of noninvasive ventilation has been associated with improved mortality compared with invasive ventilation (answer A is incorrect). Although APRV can increase mean airway pressure and therefore can improve oxygenation, there is no benefit to APRV compared with standard volume control-assist control ventilation and depending on the settings may not represent a volume-controlled mode (ie may be more injurious) (answer B is incorrect). Although diuresis to a goal body balance even over 7 days is associated with more ventilator-free days, it is not associated with decreased mortality (answer D is incorrect). Sedation with benzodiazepines, as compared with sedation with propofol or dexmedetomidine, is associated with longer length of stay and duration of mechanical ventilation (answer C is correct). Some studies also suggest an association between benzodiazepines and worse cognitive outcomes as well as increased short-term mortality. Sedation with nonbenzodiazepinecontaining regimens is therefore preferred.
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A 22-year-old woman with a history of asthma (previously intubated twice) presents to the emergency department with worsening dyspnea over the past week and is found to have influenza. Her chest radiograph demonstrates bilateral patchy opacities and she is intubated for hypoxemic respiratory failure and receives empiric antibiotics, bronchodilators, and steroids. Ventilator settings are:
On arrival to the ICU, she remains paralyzed after rapid sequence intubation, and on the above settings she is getting a TV of 200 mL (4 mL/kg IBW).
Which of the following statements is MOST accurate regarding her ventilator settings and physiology?
Unlike assist control-volume control, in a pressure-control mode of ventilation, the airway opening pressures are the target variables (ie the variable set on the ventilator). This means that her peak inspiratory pressure will be the same as the pressure that the ventilator has set during an inspiratory pause (in this case, 25 cm H2O) and resistance cannot be calculated from these numbers (answer D is incorrect). Compliance can sometimes be calculated from the set change in pressure at the airway opening and the resulting volume delivered but there are important caveats. If flow does not reach zero at the end of inhalation (for example, in a patient with elevated airways resistance such as this patient or with very short inspiratory times) then you cannot reliably calculate a resistance from the set pressure and the delivered volume (answer A is incorrect). In addition, if the patient is making spontaneous effort in sync with the ventilator then the transpulmonary pressure (the distending pressure of the lung parenchyma) can only be calculated with a measurement of her pleural pressure with an esophageal balloon (answer C is correct). The pleural pressure is not necessary to calculate resistance (answer B is incorrect).
An 84-year-old man with severe chronic obstructive pulmonary disease (FEV1 20% predicted, on 4 L/min home O2 ) is admitted with severe hypoxemic respiratory failure due to a Streptococcus pneumoniae infection. He is intubated and placed on:
When the paralytic used for intubation wears off, the patient is noted to be triggering additional spontaneous breaths with a total respiratory rate of 36 breaths per minute, and his exhaled TVs vary from 100 to 800 mL. During an end-expiratory pause, his airway pressure is 18 cm H2O.
Which of the following is the MOST accurate statement regarding his ventilator settings?
Correct Answer: D
This patient is on a volume-control mode of ventilation but is asynchronous with variable exhaled TVs, which indicates “breath stacking,” a type of cycle asynchrony in which patients do not fully exhale before taking their next breath. In this situation, the patient is no longer receiving the lung-protective TV that has been set despite being on a volume control mode (answer A is incorrect). If the ventilator setting were changed to pressure control, his TVs would vary with respiratory effort and therefore he would not be guaranteed to have more lung-protective TVs (answer E is incorrect).
The patient has evidence of intrinsic PEEP with an end-expiratory pressure that is greater than the set PEEP. In order to trigger breaths on the ventilator, or breath spontaneously, a patient needs to decrease their airway opening pressure and (depending on a ventilator trigger mode) create inspiratory flow. When a patient has intrinsic PEEP, they must overcome this PEEP to decrease their airway opening pressure or initiate inspiratory flow; this is the inspiratory threshold load and it increases the work of breathing both in spontaneously breathing and patients who are mechanically breathing and triggering breaths (answer D is correct). Changing the ventilator mode to pressure control will not necessarily decrease intrinsic PEEP (answer C is incorrect). The measurement of endexpiratory airway pressure often underestimates intrinsic PEEP because lung units that are slow emptying may not equilibrate with the airway opening and therefore the sickest lung units with the highest intrinsic PEEP are not fully represented by bedside measurements (answer B is incorrect).
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