A 54-year-old man with ischemic cardiomyopathy is admitted to ICU for respiratory failure due to decompensated heart failure and cardiogenic pulmonary edema. On the day of admission, he requires intubation and mechanical ventilation, and aggressive diuresis is initiated. On day 3 of his ICU stay, his ventilator is set on:
He is fully awake and breathing comfortably. He is placed on a spontaneous breathing trial with pressure support settings of:
Within minutes, he experiences oxygen desaturation, tachypnea, and respiratory distress.
Which among the following in the MOST LIKELY cause for failure of his spontaneous breathing trial?
Correct Answer: E
The application of PEEP in both noninvasive and invasive positive pressure ventilation serves to decrease cardiac preload, through decreased venous return and decrease cardiac afterload as a result of decreased ventricular volume (and therefore radius) and transmural cardiac wall tension. In patients with baseline cardiac dysfunction, weaning-induced cardiac dysfunction may be observed when the absence of PEEP leads to an acute increase in cardiac preload and afterload (answer E is correct; answers C and D are incorrect).
Atelectrauma is a form of lung injury most common in ARDS, in which loss of surfactant and alveolar flooding result in alveolar instability and cyclic opening and closing of lung units with ventilation. Although atelectrauma can occur in other types of respiratory failure, it is less likely to result in such a rapid decompensation (answer A is incorrect). Mucous plugging can occur on any PEEP and is less likely to explain this increased respiratory distress associated with the reduction in positive pressure (answer B is incorrect).
Reference:
A 75-year-old woman has been intubated for 7 days for communityacquired pneumonia. She is placed on a spontaneous breathing trial on ventilator settings of:
What is the most accurate explanation of how breaths are cycled (initiated or terminated) on this ventilator mode?
Correct Answer: B
Pressure support breaths are cycled from inspiratory to expiratory when the patient’s inspiratory flow reaches a set percentage of the peak inspiratory flow, often 25% of peak inspiratory flow by default (answer B is correct). Pressure assist-control, a form of continuous mandatory ventilation, cycles based on a set inspiratory time (answer A is incorrect). Volume assist-control, a form of continuous mandatory ventilation, cycles when a breath reaches a target TV, the time for which is dictated by an inspiratory flow rate (answer C is incorrect). Neurally assisted ventilation coordinates inspiratory support with diaphragmatic muscular effort (answer D is incorrect). There are no modes that are terminated by reaching a peak inspiratory flow (answer E is incorrect).
A 68-year-old woman with HIV is admitted to the ICU with respiratory failure secondary to pneumocystis pneumonia, requiring intubation and mechanical ventilation. A chest CT scan was performed before intubation and demonstrated cystic changes throughout the lungs, thought to be a sequela of past pneumocystis infection, with superimposed diffuse ground glass opacities. Her ventilator is set on:
On day 2 of her critical illness, her ventilator suddenly alarms for elevated peak pressures. She is observed to be deeply sedated and breathing passively on the ventilator. The peak pressure has risen from 25 cm H2O several hours before 50 cm H2O. The patient has simultaneously experienced oxygen desaturation from 95% to 90%. She is otherwise hemodynamically stable. A chest radiograph is ordered. An inspiratory hold maneuver is performed and her plateau pressure is 20 cm H2O.
Which of the following is the MOST LIKELY explanation for this acute event?
The ventilator mechanics reported here describe an acute increase in peak airway pressure with a normal plateau pressure. This indicates that the peak airway pressure is reflective of an acute increase in resistance within the respiratory system or endotracheal tube. Potential causes of this include biting or other kinking of the endotracheal tube, mucous within the endotracheal tube or airway without complete obstruction, bronchospasm, or airway edema/inflammation (answer B is correct). An increase in peak airway pressure, with a corresponding increase in plateau pressure, represents decrease in respiratory system compliance. This may be secondary to lobar collapse, mainstem intubation, pulmonary edema, pneumonia, ARDS, pleural effusion, pneumothorax, elevated intraabdominal pressure, or elevated chest wall pressure (answers A, C and E are incorrect). Given that the patient is deeply sedated, biting on the endotracheal tube is not a likely explanation for the increase in airway resistance (answer D is incorrect).
A 68-year-old man with chronic obstructive pulmonary disease (FEV1 30% predicted, on 3 L home O2 ) presents to the emergency department with increased dyspnea for the past 3 days requiring a frequent albuterol-ipratropium nebulizer use at home. He is found to have labored breathing and his initial ABG shows pH 7.27 with a PCO2 90 mm Hg. His chest radiograph demonstrates no infiltrate but some increased interstitial markings consistent with volume overload. He is diagnosed with an acute exacerbation of chronic obstructive pulmonary disease and possible cardiogenic pulmonary edema and started on bronchodilators and given a dose of furosemide. On reevaluation, he is somnolent but arousable to sternal rub and is placed on bilevel positive airway pressure ventilation (BiPAP).
Which of the following is most true regarding use of BiPAP in this patient?
Noninvasive positive pressure ventilation may reduce the rates of intubation, reduce the time to clinical improvement, and reduce mortality in patients with an acute exacerbation of chronic obstructive pulmonary disease with hypercarbia (answers A and B are incorrect). In patients with acute cardiogenic pulmonary edema, noninvasive positive pressure ventilation is associated with a decreased rate of intubation and decreased time to improvement in symptoms (answer C is incorrect).
Relative contraindications to BiPAP include significant secretions, altered mental status, and a patient’s inability to protect their airway (answer E is correct). The data for use of BiPAP in patients with asthma are inconclusive and much less robust than data supporting use in chronic obstructive pulmonary disease (answer D is incorrect).
References:
A 48-year-old man with no prior medical history is admitted with community-acquired pneumonia and severe acute respiratory distress syndrome (ARDS). On day 1 of his illness, he is admitted to your ICU on:
volume control-assist control ventilation with a VT of 4 mL/kg IBW
On those settings, he is found to be hypoxemic with a SaO2 of 86% with an ABG that demonstrates:
Which of the following interventions is most likely to improve his survival?
Correct Answer: A
Although prior data were conflicting, a recent large, multicenter randomized controlled study of prone positioning in patients with ARDS within the first 48 hours demonstrated a significant reduction in mortality in the prone position group (answer A is correct). Although ECMO is increasingly employed as a rescue therapy in patients with severe ARDS and refractory hypoxemia, there have been no trials that demonstrate a significant mortality benefit (answer B is incorrect). PEEP titration using an esophageal balloon improves oxygenation and pulmonary mechanics in patients with ARDS but does not improve mortality. High-frequency oscillatory ventilation has been shown to potentially harm patients with ARDS (answer D is incorrect). Although inhaled pulmonary vasodilators improve oxygenation in patients with ARDS, there are not data that they improve survival (answer E is incorrect).
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