A 63-year-old man with chronic obstructive pulmonary disease is brought to the emergency department due to fever, chills, and shortness of breath for 5 days. His medications include aspirin, inhaled albuterol, and inhaled ipratropium. The patient has smoked a pack of cigarettes daily for 43 years and drinks 3-4 cans of beer daily. His trachea is intubated in the emergency department due to respiratory distress, and intravenous antibiotics and glucocorticoids are initiated. In the intensive care unit, temperature is 38.3 C (100.9 F), blood pressure is 130/80 mm Hg, pulse is 132/min, and respirations are 22/min. Pulse oximetry shows 94% on assist-control mode with a tidal volume of 550 mL, respiratory rate of 22/min, fraction of inspired oxygen of 60%, and positive end-expiratory pressure of 5 mm H₂O. Examination reveals diffuse crackles over the left lung, normal S1 and S2, and clubbing. Laboratory studies are as follows: Chest-x ray shows a left-sided infiltrate and hyperinflated lungs. The ventilator waveforms show air trapping. Which of the following is the most appropriate next step in management of this patient?

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Quizplus · Accepted Answer

11ec193a_9717_3211_853d_c95dd4586039_MD0002_00 In a mechanically ventilated patient, positive end-expiratory pressure (PEEP) can be divided into extrinsic and intrinsic components. The extrinsic component is that provided by the ventilator; the intrinsic component is that caused by air remaining in the lungs due to incomplete expiration. Patients with obstructive lung disease (eg, asthma, chronic obstructive pulmonary disease) are at increased risk of excessive accumulation of intrinsic PEEP (auto-PEEP) as they are unable to complete exhalation before the start of the next inspiratory cycle. As this occurs over repeated breaths, end-expiratory alveolar pressure rises above the extrinsic PEEP and results in auto-PEEP. On ventilatory waveforms, this phenomenon is demonstrated by air flow that does not return to zero before the next breath initiates. Auto-PEEP causes alveolar distension, increasing the risk for ventilator-associated lung injury. Strategies for correcting auto-PEEP include reducing minute ventilation (reduction in tidal volume or respiratory rate), increasing expiratory time, and using bronchodilators and inhaled corticosteroids to relieve airway obstruction. In addition, increasing the extrinsic PEEP can be helpful in treating auto-PEEP by reducing the pressure threshold for initiating a new breath and better distributing inspired air. (Choice A) Decreasing expiratory time would lead to further air-trapping and worsening auto-PEEP. (Choice B) Decreasing inspiratory flow necessitates an increased inspiratory time to achieve the same tidal volume and allows less time for expiration. In contrast, increasing inspiratory flow allows for prolongation of the expiratory phase of the respiratory cycle and may help alleviate auto-PEEP. (Choice D) In COPD patients with acute respiratory failure, fraction of inspired oxygen should be adjusted to the lowest level required to maintain a PaO₂ >60 mm Hg. Higher PaO₂ levels increase the risk of oxygen toxicity without significantly improving tissue oxygenation. (Choice E) Increasing the tidal volume without making other adjustments results in increased minute ventilation and can worsen auto-PEEP. Educational objective: Auto-positive end-expiratory pressure (PEEP) is caused by air remaining in the lungs due to incomplete expiration in mechanically ventilated patients. Strategies for correcting auto-PEEP include reducing minute ventilation, increasing expiratory time, and giving medications to treat airway obstruction. __________ References: Dynamic hyperinflation and auto-positive end-expiratory pressure: lessons learned over 30 years. (http://www.ncbi.nlm.nih.gov/pubmed/21700908) Auto-PEEP in respiratory failure. (http://www.ncbi.nlm.nih.gov/pubmed/21971439)

A 63-Year-Old Man with Chronic Obstructive Pulmonary Disease Is Brought